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2 Internet Engineering Task Force E. Grossman, Ed.
3 Internet-Draft DOLBY
4 Intended status: Informational C. Gunther
5 Expires: August 19, 2016 HARMAN
6 P. Thubert
7 P. Wetterwald
8 CISCO
9 J. Raymond
10 HYDRO-QUEBEC
11 J. Korhonen
12 BROADCOM
13 Y. Kaneko
14 Toshiba
15 S. Das
16 Applied Communication Sciences
17 Y. Zha
18 HUAWEI
19 B. Varga
20 J. Farkas
21 Ericsson
22 F. Goetz
23 J. Schmitt
24 Siemens
25 February 16, 2016
27 Deterministic Networking Use Cases
28 draft-ietf-detnet-use-cases-03
30 Abstract
32 This draft documents requirements in several diverse industries to
33 establish multi-hop paths for characterized flows with deterministic
34 properties. In this context deterministic implies that streams can
35 be established which provide guaranteed bandwidth and latency which
36 can be established from either a Layer 2 or Layer 3 (IP) interface,
37 and which can co-exist on an IP network with best-effort traffic.
39 Additional requirements include optional redundant paths, very high
40 reliability paths, time synchronization, and clock distribution.
41 Industries considered include wireless for industrial applications,
42 professional audio, electrical utilities, building automation
43 systems, radio/mobile access networks, automotive, and gaming.
45 For each case, this document will identify the application, identify
46 representative solutions used today, and what new uses an IETF DetNet
47 solution may enable.
49 Status of This Memo
51 This Internet-Draft is submitted in full conformance with the
52 provisions of BCP 78 and BCP 79.
54 Internet-Drafts are working documents of the Internet Engineering
55 Task Force (IETF). Note that other groups may also distribute
56 working documents as Internet-Drafts. The list of current Internet-
57 Drafts is at http://datatracker.ietf.org/drafts/current/.
59 Internet-Drafts are draft documents valid for a maximum of six months
60 and may be updated, replaced, or obsoleted by other documents at any
61 time. It is inappropriate to use Internet-Drafts as reference
62 material or to cite them other than as "work in progress."
64 This Internet-Draft will expire on August 19, 2016.
66 Copyright Notice
68 Copyright (c) 2016 IETF Trust and the persons identified as the
69 document authors. All rights reserved.
71 This document is subject to BCP 78 and the IETF Trust's Legal
72 Provisions Relating to IETF Documents
73 (http://trustee.ietf.org/license-info) in effect on the date of
74 publication of this document. Please review these documents
75 carefully, as they describe your rights and restrictions with respect
76 to this document. Code Components extracted from this document must
77 include Simplified BSD License text as described in Section 4.e of
78 the Trust Legal Provisions and are provided without warranty as
79 described in the Simplified BSD License.
81 Table of Contents
83 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
84 2. Pro Audio Use Cases . . . . . . . . . . . . . . . . . . . . . 5
85 2.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 5
86 2.2. Fundamental Stream Requirements . . . . . . . . . . . . . 6
87 2.2.1. Guaranteed Bandwidth . . . . . . . . . . . . . . . . 6
88 2.2.2. Bounded and Consistent Latency . . . . . . . . . . . 7
89 2.2.2.1. Optimizations . . . . . . . . . . . . . . . . . . 8
90 2.3. Additional Stream Requirements . . . . . . . . . . . . . 9
91 2.3.1. Deterministic Time to Establish Streaming . . . . . . 9
92 2.3.2. Use of Unused Reservations by Best-Effort Traffic . . 9
93 2.3.3. Layer 3 Interconnecting Layer 2 Islands . . . . . . . 10
94 2.3.4. Secure Transmission . . . . . . . . . . . . . . . . . 10
95 2.3.5. Redundant Paths . . . . . . . . . . . . . . . . . . . 10
96 2.3.6. Link Aggregation . . . . . . . . . . . . . . . . . . 10
97 2.3.7. Traffic Segregation . . . . . . . . . . . . . . . . . 11
98 2.3.7.1. Packet Forwarding Rules, VLANs and Subnets . . . 11
99 2.3.7.2. Multicast Addressing (IPv4 and IPv6) . . . . . . 11
100 2.4. Integration of Reserved Streams into IT Networks . . . . 12
101 2.5. Security Considerations . . . . . . . . . . . . . . . . . 12
102 2.5.1. Denial of Service . . . . . . . . . . . . . . . . . . 12
103 2.5.2. Control Protocols . . . . . . . . . . . . . . . . . . 12
104 2.6. A State-of-the-Art Broadcast Installation Hits Technology
105 Limits . . . . . . . . . . . . . . . . . . . . . . . . . 13
106 3. Utility Telecom Use Cases . . . . . . . . . . . . . . . . . . 13
107 3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 13
108 3.2. Telecommunications Trends and General telecommunications
109 Requirements . . . . . . . . . . . . . . . . . . . . . . 14
110 3.2.1. General Telecommunications Requirements . . . . . . . 14
111 3.2.1.1. Migration to Packet-Switched Network . . . . . . 15
112 3.2.2. Applications, Use cases and traffic patterns . . . . 16
113 3.2.2.1. Transmission use cases . . . . . . . . . . . . . 16
114 3.2.2.2. Distribution use case . . . . . . . . . . . . . . 26
115 3.2.2.3. Generation use case . . . . . . . . . . . . . . . 29
116 3.2.3. Specific Network topologies of Smart Grid
117 Applications . . . . . . . . . . . . . . . . . . . . 30
118 3.2.4. Precision Time Protocol . . . . . . . . . . . . . . . 31
119 3.3. IANA Considerations . . . . . . . . . . . . . . . . . . . 32
120 3.4. Security Considerations . . . . . . . . . . . . . . . . . 32
121 3.4.1. Current Practices and Their Limitations . . . . . . . 32
122 3.4.2. Security Trends in Utility Networks . . . . . . . . . 34
123 4. Building Automation Systems . . . . . . . . . . . . . . . . . 35
124 4.1. Use Case Description . . . . . . . . . . . . . . . . . . 35
125 4.2. Building Automation Systems Today . . . . . . . . . . . . 36
126 4.2.1. BAS Architecture . . . . . . . . . . . . . . . . . . 36
127 4.2.2. BAS Deployment Model . . . . . . . . . . . . . . . . 37
128 4.2.3. Use Cases for Field Networks . . . . . . . . . . . . 39
129 4.2.3.1. Environmental Monitoring . . . . . . . . . . . . 39
130 4.2.3.2. Fire Detection . . . . . . . . . . . . . . . . . 39
131 4.2.3.3. Feedback Control . . . . . . . . . . . . . . . . 40
132 4.2.4. Security Considerations . . . . . . . . . . . . . . . 40
133 4.3. BAS Future . . . . . . . . . . . . . . . . . . . . . . . 40
134 4.4. BAS Asks . . . . . . . . . . . . . . . . . . . . . . . . 41
135 5. Wireless for Industrial Use Cases . . . . . . . . . . . . . . 41
136 5.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 41
137 5.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 42
138 5.3. 6TiSCH Overview . . . . . . . . . . . . . . . . . . . . . 43
139 5.3.1. TSCH and 6top . . . . . . . . . . . . . . . . . . . . 46
140 5.3.2. SlotFrames and Priorities . . . . . . . . . . . . . . 46
141 5.3.3. Schedule Management by a PCE . . . . . . . . . . . . 46
142 5.3.4. Track Forwarding . . . . . . . . . . . . . . . . . . 47
143 5.3.4.1. Transport Mode . . . . . . . . . . . . . . . . . 49
144 5.3.4.2. Tunnel Mode . . . . . . . . . . . . . . . . . . . 50
145 5.3.4.3. Tunnel Metadata . . . . . . . . . . . . . . . . . 51
146 5.4. Operations of Interest for DetNet and PCE . . . . . . . . 51
147 5.4.1. Packet Marking and Handling . . . . . . . . . . . . . 52
148 5.4.1.1. Tagging Packets for Flow Identification . . . . . 52
149 5.4.1.2. Replication, Retries and Elimination . . . . . . 52
150 5.4.1.3. Differentiated Services Per-Hop-Behavior . . . . 53
151 5.4.2. Topology and capabilities . . . . . . . . . . . . . . 53
152 5.5. Security Considerations . . . . . . . . . . . . . . . . . 54
153 6. Cellular Radio Use Cases . . . . . . . . . . . . . . . . . . 54
154 6.1. Use Case Description . . . . . . . . . . . . . . . . . . 54
155 6.1.1. Network Architecture . . . . . . . . . . . . . . . . 54
156 6.1.2. Time Synchronization Requirements . . . . . . . . . . 55
157 6.1.3. Time-Sensitive Stream Requirements . . . . . . . . . 57
158 6.1.4. Security Considerations . . . . . . . . . . . . . . . 57
159 6.2. Cellular Radio Networks Today . . . . . . . . . . . . . . 58
160 6.3. Cellular Radio Networks Future . . . . . . . . . . . . . 58
161 6.4. Cellular Radio Networks Asks . . . . . . . . . . . . . . 60
162 7. Industrial M2M . . . . . . . . . . . . . . . . . . . . . . . 60
163 7.1. Use Case Description . . . . . . . . . . . . . . . . . . 60
164 7.2. Industrial M2M Communication Today . . . . . . . . . . . 62
165 7.2.1. Transport Parameters . . . . . . . . . . . . . . . . 62
166 7.2.2. Stream Creation and Destruction . . . . . . . . . . . 63
167 7.3. Industrial M2M Future . . . . . . . . . . . . . . . . . . 63
168 7.4. Industrial M2M Asks . . . . . . . . . . . . . . . . . . . 63
169 8. Other Use Cases . . . . . . . . . . . . . . . . . . . . . . . 64
170 8.1. Introduction . . . . . . . . . . . . . . . . . . . . . . 64
171 8.2. Critical Delay Requirements . . . . . . . . . . . . . . . 65
172 8.3. Coordinated multipoint processing (CoMP) . . . . . . . . 65
173 8.3.1. CoMP Architecture . . . . . . . . . . . . . . . . . . 65
174 8.3.2. Delay Sensitivity in CoMP . . . . . . . . . . . . . . 66
175 8.4. Industrial Automation . . . . . . . . . . . . . . . . . . 67
176 8.5. Vehicle to Vehicle . . . . . . . . . . . . . . . . . . . 67
177 8.6. Gaming, Media and Virtual Reality . . . . . . . . . . . . 68
178 9. Use Case Common Elements . . . . . . . . . . . . . . . . . . 68
179 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 69
180 10.1. Pro Audio . . . . . . . . . . . . . . . . . . . . . . . 69
181 10.2. Utility Telecom . . . . . . . . . . . . . . . . . . . . 69
182 10.3. Building Automation Systems . . . . . . . . . . . . . . 70
183 10.4. Wireless for Industrial . . . . . . . . . . . . . . . . 70
184 10.5. Cellular Radio . . . . . . . . . . . . . . . . . . . . . 70
185 10.6. Industrial M2M . . . . . . . . . . . . . . . . . . . . . 70
186 10.7. Other . . . . . . . . . . . . . . . . . . . . . . . . . 70
187 11. Informative References . . . . . . . . . . . . . . . . . . . 71
188 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 79
190 1. Introduction
192 This draft presents use cases from diverse industries which have in
193 common a need for deterministic streams, but which also differ
194 notably in their network topologies and specific desired behavior.
195 Together, they provide broad industry context for DetNet and a
196 yardstick against which proposed DetNet designs can be measured (to
197 what extent does a proposed design satisfy these various use cases?)
199 For DetNet, use cases explicitly do not define requirements; The
200 DetNet WG will consider the use cases, decide which elements are in
201 scope for DetNet, and the results will be incorporated into future
202 drafts. Similarly, the DetNet use case draft explicitly does not
203 suggest any specific design, architecture or protocols, which will be
204 topics of future drafts.
206 We present for each use case the answers to the following questions:
208 o What is the use case?
210 o How is it addressed today?
212 o How would you like it to be addressed in the future?
214 o What do you want the IETF to deliver?
216 The level of detail in each use case should be sufficient to express
217 the relevant elements of the use case, but not more.
219 At the end we consider the use cases collectively, and examine the
220 most significant goals they have in common.
222 2. Pro Audio Use Cases
224 2.1. Introduction
226 The professional audio and video industry includes music and film
227 content creation, broadcast, cinema, and live exposition as well as
228 public address, media and emergency systems at large venues
229 (airports, stadiums, churches, theme parks). These industries have
230 already gone through the transition of audio and video signals from
231 analog to digital, however the interconnect systems remain primarily
232 point-to-point with a single (or small number of) signals per link,
233 interconnected with purpose-built hardware.
235 These industries are now attempting to transition to packet based
236 infrastructure for distributing audio and video in order to reduce
237 cost, increase routing flexibility, and integrate with existing IT
238 infrastructure.
240 However, there are several requirements for making a network the
241 primary infrastructure for audio and video which are not met by
242 todays networks and these are our concern in this draft.
244 The principal requirement is that pro audio and video applications
245 become able to establish streams that provide guaranteed (bounded)
246 bandwidth and latency from the Layer 3 (IP) interface. Such streams
247 can be created today within standards-based layer 2 islands however
248 these are not sufficient to enable effective distribution over wider
249 areas (for example broadcast events that span wide geographical
250 areas).
252 Some proprietary systems have been created which enable deterministic
253 streams at layer 3 however they are engineered networks in that they
254 require careful configuration to operate, often require that the
255 system be over designed, and it is implied that all devices on the
256 network voluntarily play by the rules of that network. To enable
257 these industries to successfully transition to an interoperable
258 multi-vendor packet-based infrastructure requires effective open
259 standards, and we believe that establishing relevant IETF standards
260 is a crucial factor.
262 It would be highly desirable if such streams could be routed over the
263 open Internet, however even intermediate solutions with more limited
264 scope (such as enterprise networks) can provide a substantial
265 improvement over todays networks, and a solution that only provides
266 for the enterprise network scenario is an acceptable first step.
268 We also present more fine grained requirements of the audio and video
269 industries such as safety and security, redundant paths, devices with
270 limited computing resources on the network, and that reserved stream
271 bandwidth is available for use by other best-effort traffic when that
272 stream is not currently in use.
274 2.2. Fundamental Stream Requirements
276 The fundamental stream properties are guaranteed bandwidth and
277 deterministic latency as described in this section. Additional
278 stream requirements are described in a subsequent section.
280 2.2.1. Guaranteed Bandwidth
282 Transmitting audio and video streams is unlike common file transfer
283 activities because guaranteed delivery cannot be achieved by re-
284 trying the transmission; by the time the missing or corrupt packet
285 has been identified it is too late to execute a re-try operation and
286 stream playback is interrupted, which is unacceptable in for example
287 a live concert. In some contexts large amounts of buffering can be
288 used to provide enough delay to allow time for one or more retries,
289 however this is not an effective solution when live interaction is
290 involved, and is not considered an acceptable general solution for
291 pro audio and video. (Have you ever tried speaking into a microphone
292 through a sound system that has an echo coming back at you? It makes
293 it almost impossible to speak clearly).
295 Providing a way to reserve a specific amount of bandwidth for a given
296 stream is a key requirement.
298 2.2.2. Bounded and Consistent Latency
300 Latency in this context means the amount of time that passes between
301 when a signal is sent over a stream and when it is received, for
302 example the amount of time delay between when you speak into a
303 microphone and when your voice emerges from the speaker. Any delay
304 longer than about 10-15 milliseconds is noticeable by most live
305 performers, and greater latency makes the system unusable because it
306 prevents them from playing in time with the other players (see slide
307 6 of [SRP_LATENCY]).
309 The 15ms latency bound is made even more challenging because it is
310 often the case in network based music production with live electric
311 instruments that multiple stages of signal processing are used,
312 connected in series (i.e. from one to the other for example from
313 guitar through a series of digital effects processors) in which case
314 the latencies add, so the latencies of each individual stage must all
315 together remain less than 15ms.
317 In some situations it is acceptable at the local location for content
318 from the live remote site to be delayed to allow for a statistically
319 acceptable amount of latency in order to reduce jitter. However,
320 once the content begins playing in the local location any audio
321 artifacts caused by the local network are unacceptable, especially in
322 those situations where a live local performer is mixed into the feed
323 from the remote location.
325 In addition to being bounded to within some predictable and
326 acceptable amount of time (which may be 15 milliseconds or more or
327 less depending on the application) the latency also has to be
328 consistent. For example when playing a film consisting of a video
329 stream and audio stream over a network, those two streams must be
330 synchronized so that the voice and the picture match up. A common
331 tolerance for audio/video sync is one NTSC video frame (about 33ms)
332 and to maintain the audience perception of correct lip sync the
333 latency needs to be consistent within some reasonable tolerance, for
334 example 10%.
336 A common architecture for synchronizing multiple streams that have
337 different paths through the network (and thus potentially different
338 latencies) is to enable measurement of the latency of each path, and
339 have the data sinks (for example speakers) buffer (delay) all packets
340 on all but the slowest path. Each packet of each stream is assigned
341 a presentation time which is based on the longest required delay.
342 This implies that all sinks must maintain a common time reference of
343 sufficient accuracy, which can be achieved by any of various
344 techniques.
346 This type of architecture is commonly implemented using a central
347 controller that determines path delays and arbitrates buffering
348 delays.
350 2.2.2.1. Optimizations
352 The controller might also perform optimizations based on the
353 individual path delays, for example sinks that are closer to the
354 source can inform the controller that they can accept greater latency
355 since they will be buffering packets to match presentation times of
356 farther away sinks. The controller might then move a stream
357 reservation on a short path to a longer path in order to free up
358 bandwidth for other critical streams on that short path. See slides
359 3-5 of [SRP_LATENCY].
361 Additional optimization can be achieved in cases where sinks have
362 differing latency requirements, for example in a live outdoor concert
363 the speaker sinks have stricter latency requirements than the
364 recording hardware sinks. See slide 7 of [SRP_LATENCY].
366 Device cost can be reduced in a system with guaranteed reservations
367 with a small bounded latency due to the reduced requirements for
368 buffering (i.e. memory) on sink devices. For example, a theme park
369 might broadcast a live event across the globe via a layer 3 protocol;
370 in such cases the size of the buffers required is proportional to the
371 latency bounds and jitter caused by delivery, which depends on the
372 worst case segment of the end-to-end network path. For example on
373 todays open internet the latency is typically unacceptable for audio
374 and video streaming without many seconds of buffering. In such
375 scenarios a single gateway device at the local network that receives
376 the feed from the remote site would provide the expensive buffering
377 required to mask the latency and jitter issues associated with long
378 distance delivery. Sink devices in the local location would have no
379 additional buffering requirements, and thus no additional costs,
380 beyond those required for delivery of local content. The sink device
381 would be receiving the identical packets as those sent by the source
382 and would be unaware that there were any latency or jitter issues
383 along the path.
385 2.3. Additional Stream Requirements
387 The requirements in this section are more specific yet are common to
388 multiple audio and video industry applications.
390 2.3.1. Deterministic Time to Establish Streaming
392 Some audio systems installed in public environments (airports,
393 hospitals) have unique requirements with regards to health, safety
394 and fire concerns. One such requirement is a maximum of 3 seconds
395 for a system to respond to an emergency detection and begin sending
396 appropriate warning signals and alarms without human intervention.
397 For this requirement to be met, the system must support a bounded and
398 acceptable time from a notification signal to specific stream
399 establishment. For further details see [ISO7240-16].
401 Similar requirements apply when the system is restarted after a power
402 cycle, cable re-connection, or system reconfiguration.
404 In many cases such re-establishment of streaming state must be
405 achieved by the peer devices themselves, i.e. without a central
406 controller (since such a controller may only be present during
407 initial network configuration).
409 Video systems introduce related requirements, for example when
410 transitioning from one camera feed to another. Such systems
411 currently use purpose-built hardware to switch feeds smoothly,
412 however there is a current initiative in the broadcast industry to
413 switch to a packet-based infrastructure (see [STUDIO_IP] and the ESPN
414 DC2 use case described below).
416 2.3.2. Use of Unused Reservations by Best-Effort Traffic
418 In cases where stream bandwidth is reserved but not currently used
419 (or is under-utilized) that bandwidth must be available to best-
420 effort (i.e. non-time-sensitive) traffic. For example a single
421 stream may be nailed up (reserved) for specific media content that
422 needs to be presented at different times of the day, ensuring timely
423 delivery of that content, yet in between those times the full
424 bandwidth of the network can be utilized for best-effort tasks such
425 as file transfers.
427 This also addresses a concern of IT network administrators that are
428 considering adding reserved bandwidth traffic to their networks that
429 users will just reserve a ton of bandwidth and then never un-reserve
430 it even though they are not using it, and soon they will have no
431 bandwidth left.
433 2.3.3. Layer 3 Interconnecting Layer 2 Islands
435 As an intermediate step (short of providing guaranteed bandwidth
436 across the open internet) it would be valuable to provide a way to
437 connect multiple Layer 2 networks. For example layer 2 techniques
438 could be used to create a LAN for a single broadcast studio, and
439 several such studios could be interconnected via layer 3 links.
441 2.3.4. Secure Transmission
443 Digital Rights Management (DRM) is very important to the audio and
444 video industries. Any time protected content is introduced into a
445 network there are DRM concerns that must be maintained (see
446 [CONTENT_PROTECTION]). Many aspects of DRM are outside the scope of
447 network technology, however there are cases when a secure link
448 supporting authentication and encryption is required by content
449 owners to carry their audio or video content when it is outside their
450 own secure environment (for example see [DCI]).
452 As an example, two techniques are Digital Transmission Content
453 Protection (DTCP) and High-Bandwidth Digital Content Protection
454 (HDCP). HDCP content is not approved for retransmission within any
455 other type of DRM, while DTCP may be retransmitted under HDCP.
456 Therefore if the source of a stream is outside of the network and it
457 uses HDCP protection it is only allowed to be placed on the network
458 with that same HDCP protection.
460 2.3.5. Redundant Paths
462 On-air and other live media streams must be backed up with redundant
463 links that seamlessly act to deliver the content when the primary
464 link fails for any reason. In point-to-point systems this is
465 provided by an additional point-to-point link; the analogous
466 requirement in a packet-based system is to provide an alternate path
467 through the network such that no individual link can bring down the
468 system.
470 2.3.6. Link Aggregation
472 For transmitting streams that require more bandwidth than a single
473 link in the target network can support, link aggregation is a
474 technique for combining (aggregating) the bandwidth available on
475 multiple physical links to create a single logical link of the
476 required bandwidth. However, if aggregation is to be used, the
477 network controller (or equivalent) must be able to determine the
478 maximum latency of any path through the aggregate link (see Bounded
479 and Consistent Latency section above).
481 2.3.7. Traffic Segregation
483 Sink devices may be low cost devices with limited processing power.
484 In order to not overwhelm the CPUs in these devices it is important
485 to limit the amount of traffic that these devices must process.
487 As an example, consider the use of individual seat speakers in a
488 cinema. These speakers are typically required to be cost reduced
489 since the quantities in a single theater can reach hundreds of seats.
490 Discovery protocols alone in a one thousand seat theater can generate
491 enough broadcast traffic to overwhelm a low powered CPU. Thus an
492 installation like this will benefit greatly from some type of traffic
493 segregation that can define groups of seats to reduce traffic within
494 each group. All seats in the theater must still be able to
495 communicate with a central controller.
497 There are many techniques that can be used to support this
498 requirement including (but not limited to) the following examples.
500 2.3.7.1. Packet Forwarding Rules, VLANs and Subnets
502 Packet forwarding rules can be used to eliminate some extraneous
503 streaming traffic from reaching potentially low powered sink devices,
504 however there may be other types of broadcast traffic that should be
505 eliminated using other means for example VLANs or IP subnets.
507 2.3.7.2. Multicast Addressing (IPv4 and IPv6)
509 Multicast addressing is commonly used to keep bandwidth utilization
510 of shared links to a minimum.
512 Because of the MAC Address forwarding nature of Layer 2 bridges it is
513 important that a multicast MAC address is only associated with one
514 stream. This will prevent reservations from forwarding packets from
515 one stream down a path that has no interested sinks simply because
516 there is another stream on that same path that shares the same
517 multicast MAC address.
519 Since each multicast MAC Address can represent 32 different IPv4
520 multicast addresses there must be a process put in place to make sure
521 this does not occur. Requiring use of IPv6 address can achieve this,
522 however due to their continued prevalence, solutions that are
523 effective for IPv4 installations are also required.
525 2.4. Integration of Reserved Streams into IT Networks
527 A commonly cited goal of moving to a packet based media
528 infrastructure is that costs can be reduced by using off the shelf,
529 commodity network hardware. In addition, economy of scale can be
530 realized by combining media infrastructure with IT infrastructure.
531 In keeping with these goals, stream reservation technology should be
532 compatible with existing protocols, and not compromise use of the
533 network for best effort (non-time-sensitive) traffic.
535 2.5. Security Considerations
537 Many industries that are moving from the point-to-point world to the
538 digital network world have little understanding of the pitfalls that
539 they can create for themselves with improperly implemented network
540 infrastructure. DetNet should consider ways to provide security
541 against DoS attacks in solutions directed at these markets. Some
542 considerations are given here as examples of ways that we can help
543 new users avoid common pitfalls.
545 2.5.1. Denial of Service
547 One security pitfall that this author is aware of involves the use of
548 technology that allows a presenter to throw the content from their
549 tablet or smart phone onto the A/V system that is then viewed by all
550 those in attendance. The facility introducing this technology was
551 quite excited to allow such modern flexibility to those who came to
552 speak. One thing they hadn't realized was that since no security was
553 put in place around this technology it left a hole in the system that
554 allowed other attendees to "throw" their own content onto the A/V
555 system.
557 2.5.2. Control Protocols
559 Professional audio systems can include amplifiers that are capable of
560 generating hundreds or thousands of watts of audio power which if
561 used incorrectly can cause hearing damage to those in the vicinity.
562 Apart from the usual care required by the systems operators to
563 prevent such incidents, the network traffic that controls these
564 devices must be secured (as with any sensitive application traffic).
565 In addition, it would be desirable if the configuration protocols
566 that are used to create the network paths used by the professional
567 audio traffic could be designed to protect devices that are not meant
568 to receive high-amplitude content from having such potentially
569 damaging signals routed to them.
571 2.6. A State-of-the-Art Broadcast Installation Hits Technology Limits
573 ESPN recently constructed a state-of-the-art 194,000 sq ft, $125
574 million broadcast studio called DC2. The DC2 network is capable of
575 handling 46 Tbps of throughput with 60,000 simultaneous signals.
576 Inside the facility are 1,100 miles of fiber feeding four audio
577 control rooms. (See details at [ESPN_DC2] ).
579 In designing DC2 they replaced as much point-to-point technology as
580 they possibly could with packet-based technology. They constructed
581 seven individual studios using layer 2 LANS (using IEEE 802.1 AVB)
582 that were entirely effective at routing audio within the LANs, and
583 they were very happy with the results, however to interconnect these
584 layer 2 LAN islands together they ended up using dedicated links
585 because there is no standards-based routing solution available.
587 This is the kind of motivation we have to develop these standards
588 because customers are ready and able to use them.
590 3. Utility Telecom Use Cases
592 3.1. Overview
594 [I-D.finn-detnet-problem-statement] defines the characteristics of a
595 deterministic flow as a data communication flow with a bounded
596 latency, extraordinarily low frame loss, and a very narrow jitter.
597 This document intends to define the utility requirements for
598 deterministic networking.
600 Utility Telecom Networks
602 The business and technology trends that are sweeping the utility
603 industry will drastically transform the utility business from the way
604 it has been for many decades. At the core of many of these changes
605 is a drive to modernize the electrical grid with an integrated
606 telecommunications infrastructure. However, interoperability,
607 concerns, legacy networks, disparate tools, and stringent security
608 requirements all add complexity to the grid transformation. Given
609 the range and diversity of the requirements that should be addressed
610 by the next generation telecommunications infrastructure, utilities
611 need to adopt a holistic architectural approach to integrate the
612 electrical grid with digital telecommunications across the entire
613 power delivery chain.
615 Many utilities still rely on complex environments formed of multiple
616 application-specific, proprietary networks. Information is siloed
617 between operational areas. This prevents utility operations from
618 realizing the operational efficiency benefits, visibility, and
619 functional integration of operational information across grid
620 applications and data networks. The key to modernizing grid
621 telecommunications is to provide a common, adaptable, multi-service
622 network infrastructure for the entire utility organization. Such a
623 network serves as the platform for current capabilities while
624 enabling future expansion of the network to accommodate new
625 applications and services.
627 To meet this diverse set of requirements, both today and in the
628 future, the next generation utility telecommunnications network will
629 be based on open-standards-based IP architecture. An end-to-end IP
630 architecture takes advantage of nearly three decades of IP technology
631 development, facilitating interoperability across disparate networks
632 and devices, as it has been already demonstrated in many mission-
633 critical and highly secure networks.
635 IEC (International Electrotechnical Commission) and different
636 National Committees have mandated a specific adhoc group (AHG8) to
637 define the migration strategy to IPv6 for all the IEC TC57 power
638 automation standards. IPv6 is seen as the obvious future
639 telecommunications technology for the Smart Grid. The Adhoc Group
640 has disclosed, to the IEC coordination group, their conclusions at
641 the end of 2014.
643 It is imperative that utilities participate in standards development
644 bodies to influence the development of future solutions and to
645 benefit from shared experiences of other utilities and vendors.
647 3.2. Telecommunications Trends and General telecommunications
648 Requirements
650 These general telecommunications requirements are over and above the
651 specific requirements of the use cases that have been addressed so
652 far. These include both current and future telecommunications
653 related requirements that should be factored into the network
654 architecture and design.
656 3.2.1. General Telecommunications Requirements
658 o IP Connectivity everywhere
660 o Monitoring services everywhere and from different remote centers
662 o Move services to a virtual data center
664 o Unify access to applications / information from the corporate
665 network
667 o Unify services
669 o Unified Communications Solutions
671 o Mix of fiber and microwave technologies - obsolescence of SONET/
672 SDH or TDM
674 o Standardize grid telecommunications protocol to opened standard to
675 ensure interoperability
677 o Reliable Telecommunications for Transmission and Distribution
678 Substations
680 o IEEE 1588 time synchronization Client / Server Capabilities
682 o Integration of Multicast Design
684 o QoS Requirements Mapping
686 o Enable Future Network Expansion
688 o Substation Network Resilience
690 o Fast Convergence Design
692 o Scalable Headend Design
694 o Define Service Level Agreements (SLA) and Enable SLA Monitoring
696 o Integration of 3G/4G Technologies and future technologies
698 o Ethernet Connectivity for Station Bus Architecture
700 o Ethernet Connectivity for Process Bus Architecture
702 o Protection, teleprotection and PMU (Phaser Measurement Unit) on IP
704 3.2.1.1. Migration to Packet-Switched Network
706 Throughout the world, utilities are increasingly planning for a
707 future based on smart grid applications requiring advanced
708 telecommunications systems. Many of these applications utilize
709 packet connectivity for communicating information and control signals
710 across the utility's Wide Area Network (WAN), made possible by
711 technologies such as multiprotocol label switching (MPLS). The data
712 that traverses the utility WAN includes:
714 o Grid monitoring, control, and protection data
715 o Non-control grid data (e.g. asset data for condition-based
716 monitoring)
718 o Physical safety and security data (e.g. voice and video)
720 o Remote worker access to corporate applications (voice, maps,
721 schematics, etc.)
723 o Field area network backhaul for smart metering, and distribution
724 grid management
726 o Enterprise traffic (email, collaboration tools, business
727 applications)
729 WANs support this wide variety of traffic to and from substations,
730 the transmission and distribution grid, generation sites, between
731 control centers, and between work locations and data centers. To
732 maintain this rapidly expanding set of applications, many utilities
733 are taking steps to evolve present time-division multiplexing (TDM)
734 based and frame relay infrastructures to packet systems. Packet-
735 based networks are designed to provide greater functionalities and
736 higher levels of service for applications, while continuing to
737 deliver reliability and deterministic (real-time) traffic support.
739 3.2.2. Applications, Use cases and traffic patterns
741 Among the numerous applications and use cases that a utility deploys
742 today, many rely on high availability and deterministic behaviour of
743 the telecommunications networks. Protection use cases and generation
744 control are the most demanding and can't rely on a best effort
745 approach.
747 3.2.2.1. Transmission use cases
749 Protection means not only the protection of the human operator but
750 also the protection of the electric equipments and the preservation
751 of the stability and frequency of the grid. If a default occurs on
752 the transmission or the distribution of the electricity, important
753 damages could occured to the human operator but also to very costly
754 electrical equipments and perturb the grid leading to blackouts. The
755 time and reliability requirements are very strong to avoid dramatic
756 impacts to the electrical infrastructure.
758 3.2.2.1.1. Tele Protection
760 The key criteria for measuring Teleprotection performance are command
761 transmission time, dependability and security. These criteria are
762 defined by the IEC standard 60834 as follows:
764 o Transmission time (Speed): The time between the moment where state
765 changes at the transmitter input and the moment of the
766 corresponding change at the receiver output, including propagation
767 delay. Overall operating time for a Teleprotection system
768 includes the time for initiating the command at the transmitting
769 end, the propagation delay over the network (including equipments)
770 and the selection and decision time at the receiving end,
771 including any additional delay due to a noisy environment.
773 o Dependability: The ability to issue and receive valid commands in
774 the presence of interference and/or noise, by minimizing the
775 probability of missing command (PMC). Dependability targets are
776 typically set for a specific bit error rate (BER) level.
778 o Security: The ability to prevent false tripping due to a noisy
779 environment, by minimizing the probability of unwanted commands
780 (PUC). Security targets are also set for a specific bit error
781 rate (BER) level.
783 Additional key elements that may impact Teleprotection performance
784 include bandwidth rate of the Teleprotection system and its
785 resiliency or failure recovery capacity. Transmission time,
786 bandwidth utilization and resiliency are directly linked to the
787 telecommunications equipments and the connections that are used to
788 transfer the commands between relays.
790 3.2.2.1.1.1. Latency Budget Consideration
792 Delay requirements for utility networks may vary depending upon a
793 number of parameters, such as the specific protection equipments
794 used. Most power line equipment can tolerate short circuits or
795 faults for up to approximately five power cycles before sustaining
796 irreversible damage or affecting other segments in the network. This
797 translates to total fault clearance time of 100ms. As a safety
798 precaution, however, actual operation time of protection systems is
799 limited to 70- 80 percent of this period, including fault recognition
800 time, command transmission time and line breaker switching time.
801 Some system components, such as large electromechanical switches,
802 require particularly long time to operate and take up the majority of
803 the total clearance time, leaving only a 10ms window for the
804 telecommunications part of the protection scheme, independent of the
805 distance to travel. Given the sensitivity of the issue, new networks
806 impose requirements that are even more stringent: IEC standard 61850
807 limits the transfer time for protection messages to 1/4 - 1/2 cycle
808 or 4 - 8ms (for 60Hz lines) for the most critical messages.
810 3.2.2.1.1.2. Asymetric delay
812 In addition to minimal transmission delay, a differential protection
813 telecommunications channel must be synchronous, i.e., experiencing
814 symmetrical channel delay in transmit and receive paths. This
815 requires special attention in jitter-prone packet networks. While
816 optimally Teleprotection systems should support zero asymmetric
817 delay, typical legacy relays can tolerate discrepancies of up to
818 750us.
820 The main tools available for lowering delay variation below this
821 threshold are:
823 o A jitter buffer at the multiplexers on each end of the line can be
824 used to offset delay variation by queuing sent and received
825 packets. The length of the queues must balance the need to
826 regulate the rate of transmission with the need to limit overall
827 delay, as larger buffers result in increased latency. This is the
828 old TDM traditional way to fulfill this requirement.
830 o Traffic management tools ensure that the Teleprotection signals
831 receive the highest transmission priority and minimize the number
832 of jitter addition during the path. This is one way to meet the
833 requirement in IP networks.
835 o Standard Packet-Based synchronization technologies, such as
836 1588-2008 Precision Time Protocol (PTP) and Synchronous Ethernet
837 (Sync-E), can help maintain stable networks by keeping a highly
838 accurate clock source on the different network devices involved.
840 3.2.2.1.1.2.1. Other traffic characteristics
842 o Redundancy: The existence in a system of more than one means of
843 accomplishing a given function.
845 o Recovery time : The duration of time within which a business
846 process must be restored after any type of disruption in order to
847 avoid unacceptable consequences associated with a break in
848 business continuity.
850 o performance management : In networking, a management function
851 defined for controlling and analyzing different parameters/metrics
852 such as the throughput, error rate.
854 o packet loss : One or more packets of data travelling across
855 network fail to reach their destination.
857 3.2.2.1.1.2.2. Teleprotection network requirements
859 The following table captures the main network requirements (this is
860 based on IEC 61850 standard)
862 +-----------------------------+-------------------------------------+
863 | Teleprotection Requirement | Attribute |
864 +-----------------------------+-------------------------------------+
865 | One way maximum delay | 4-10 ms |
866 | Asymetric delay required | Yes |
867 | Maximum jitter | less than 250 us (750 us for legacy |
868 | | IED) |
869 | Topology | Point to point, point to Multi- |
870 | | point |
871 | Availability | 99.9999 |
872 | precise timing required | Yes |
873 | Recovery time on node | less than 50ms - hitless |
874 | failure | |
875 | performance management | Yes, Mandatory |
876 | Redundancy | Yes |
877 | Packet loss | 0.1% to 1% |
878 +-----------------------------+-------------------------------------+
880 Table 1: Teleprotection network requirements
882 3.2.2.1.2. Inter-Trip Protection scheme
884 Inter-tripping is the controlled tripping of a circuit breaker to
885 complete the isolation of a circuit or piece of apparatus in concert
886 with the tripping of other circuit breakers. The main use of such
887 schemes is to ensure that protection at both ends of a faulted
888 circuit will operate to isolate the equipment concerned. Inter-
889 tripping schemes use signaling to convey a trip command to remote
890 circuit breakers to isolate circuits.
892 +--------------------------------+----------------------------------+
893 | Inter-Trip protection | Attribute |
894 | Requirement | |
895 +--------------------------------+----------------------------------+
896 | One way maximum delay | 5 ms |
897 | Asymetric delay required | No |
898 | Maximum jitter | Not critical |
899 | Topology | Point to point, point to Multi- |
900 | | point |
901 | Bandwidth | 64 Kbps |
902 | Availability | 99.9999 |
903 | precise timing required | Yes |
904 | Recovery time on node failure | less than 50ms - hitless |
905 | performance management | Yes, Mandatory |
906 | Redundancy | Yes |
907 | Packet loss | 0.1% |
908 +--------------------------------+----------------------------------+
910 Table 2: Inter-Trip protection network requirements
912 3.2.2.1.3. Current Differential Protection Scheme
914 Current differential protection is commonly used for line protection,
915 and is typical for protecting parallel circuits. A main advantage
916 for differential protection is that, compared to overcurrent
917 protection, it allows only the faulted circuit to be de-energized in
918 case of a fault. At both end of the lines, the current is measured
919 by the differential relays, and based on Kirchhoff's law, both relays
920 will trip the circuit breaker if the current going into the line does
921 not equal the current going out of the line. This type of protection
922 scheme assumes some form of communications being present between the
923 relays at both end of the line, to allow both relays to compare
924 measured current values. A fault in line 1 will cause overcurrent to
925 be flowing in both lines, but because the current in line 2 is a
926 through following current, this current is measured equal at both
927 ends of the line, therefore the differential relays on line 2 will
928 not trip line 2. Line 1 will be tripped, as the relays will not
929 measure the same currents at both ends of the line. Line
930 differential protection schemes assume a very low telecommunications
931 delay between both relays, often as low as 5ms. Moreover, as those
932 systems are often not time-synchronized, they also assume symmetric
933 telecommunications paths with constant delay, which allows comparing
934 current measurement values taken at the exact same time.
936 +----------------------------------+--------------------------------+
937 | Current Differential protection | Attribute |
938 | Requirement | |
939 +----------------------------------+--------------------------------+
940 | One way maximum delay | 5 ms |
941 | Asymetric delay Required | Yes |
942 | Maximum jitter | less than 250 us (750us for |
943 | | legacy IED) |
944 | Topology | Point to point, point to |
945 | | Multi-point |
946 | Bandwidth | 64 Kbps |
947 | Availability | 99.9999 |
948 | precise timing required | Yes |
949 | Recovery time on node failure | less than 50ms - hitless |
950 | performance management | Yes, Mandatory |
951 | Redundancy | Yes |
952 | Packet loss | 0.1% |
953 +----------------------------------+--------------------------------+
955 Table 3: Current Differential Protection requirements
957 3.2.2.1.4. Distance Protection Scheme
959 Distance (Impedance Relay) protection scheme is based on voltage and
960 current measurements. A fault on a circuit will generally create a
961 sag in the voltage level. If the ratio of voltage to current
962 measured at the protection relay terminals, which equates to an
963 impedance element, falls within a set threshold the circuit breaker
964 will operate. The operating characteristics of this protection are
965 based on the line characteristics. This means that when a fault
966 appears on the line, the impedance setting in the relay is compared
967 to the apparent impedance of the line from the relay terminals to the
968 fault. If the relay setting is determined to be below the apparent
969 impedance it is determined that the fault is within the zone of
970 protection. When the transmission line length is under a minimum
971 length, distance protection becomes more difficult to coordinate. In
972 these instances the best choice of protection is current differential
973 protection.
975 +-------------------------------+-----------------------------------+
976 | Distance protection | Attribute |
977 | Requirement | |
978 +-------------------------------+-----------------------------------+
979 | One way maximum delay | 5 ms |
980 | Asymetric delay Required | No |
981 | Maximum jitter | Not critical |
982 | Topology | Point to point, point to Multi- |
983 | | point |
984 | Bandwidth | 64 Kbps |
985 | Availability | 99.9999 |
986 | precise timing required | Yes |
987 | Recovery time on node failure | less than 50ms - hitless |
988 | performance management | Yes, Mandatory |
989 | Redundancy | Yes |
990 | Packet loss | 0.1% |
991 +-------------------------------+-----------------------------------+
993 Table 4: Distance Protection requirements
995 3.2.2.1.5. Inter-Substation Protection Signaling
997 This use case describes the exchange of Sampled Value and/or GOOSE
998 (Generic Object Oriented Substation Events) message between
999 Intelligent Electronic Devices (IED) in two substations for
1000 protection and tripping coordination. The two IEDs are in a master-
1001 slave mode.
1003 The Current Transformer or Voltage Transformer (CT/VT) in one
1004 substation sends the sampled analog voltage or current value to the
1005 Merging Unit (MU) over hard wire. The merging unit sends the time-
1006 synchronized 61850-9-2 sampled values to the slave IED. The slave
1007 IED forwards the information to the Master IED in the other
1008 substation. The master IED makes the determination (for example
1009 based on sampled value differentials) to send a trip command to the
1010 originating IED. Once the slave IED/Relay receives the GOOSE trip
1011 for breaker tripping, it opens the breaker. It then sends a
1012 confirmation message back to the master. All data exchanges between
1013 IEDs are either through Sampled Value and/or GOOSE messages.
1015 +----------------------------------+--------------------------------+
1016 | Inter-Substation protection | Attribute |
1017 | Requirement | |
1018 +----------------------------------+--------------------------------+
1019 | One way maximum delay | 5 ms |
1020 | Asymetric delay Required | No |
1021 | Maximum jitter | Not critical |
1022 | Topology | Point to point, point to |
1023 | | Multi-point |
1024 | Bandwidth | 64 Kbps |
1025 | Availability | 99.9999 |
1026 | precise timing required | Yes |
1027 | Recovery time on node failure | less than 50ms - hitless |
1028 | performance management | Yes, Mandatory |
1029 | Redundancy | Yes |
1030 | Packet loss | 1% |
1031 +----------------------------------+--------------------------------+
1033 Table 5: Inter-Substation Protection requirements
1035 3.2.2.1.6. Intra-Substation Process Bus Communications
1037 This use case describes the data flow from the CT/VT to the IEDs in
1038 the substation via the merging unit (MU). The CT/VT in the
1039 substation send the sampled value (analog voltage or current) to the
1040 Merging Unit (MU) over hard wire. The merging unit sends the time-
1041 synchronized 61850-9-2 sampled values to the IEDs in the substation
1042 in GOOSE message format. The GPS Master Clock can send 1PPS or
1043 IRIG-B format to MU through serial port, or IEEE 1588 protocol via
1044 network. Process bus communication using 61850 simplifies
1045 connectivity within the substation and removes the requirement for
1046 multiple serial connections and removes the slow serial bus
1047 architectures that are typically used. This also ensures increased
1048 flexibility and increased speed with the use of multicast messaging
1049 between multiple devices.
1051 +----------------------------------+--------------------------------+
1052 | Intra-Substation protection | Attribute |
1053 | Requirement | |
1054 +----------------------------------+--------------------------------+
1055 | One way maximum delay | 5 ms |
1056 | Asymetric delay Required | No |
1057 | Maximum jitter | Not critical |
1058 | Topology | Point to point, point to |
1059 | | Multi-point |
1060 | Bandwidth | 64 Kbps |
1061 | Availability | 99.9999 |
1062 | precise timing required | Yes |
1063 | Recovery time on Node failure | less than 50ms - hitless |
1064 | performance management | Yes, Mandatory |
1065 | Redundancy | Yes - No |
1066 | Packet loss | 0.1% |
1067 +----------------------------------+--------------------------------+
1069 Table 6: Intra-Substation Protection requirements
1071 3.2.2.1.7. Wide Area Monitoring and Control Systems
1073 The application of synchrophasor measurement data from Phasor
1074 Measurement Units (PMU) to Wide Area Monitoring and Control Systems
1075 promises to provide important new capabilities for improving system
1076 stability. Access to PMU data enables more timely situational
1077 awareness over larger portions of the grid than what has been
1078 possible historically with normal SCADA (Supervisory Control and Data
1079 Acquisition) data. Handling the volume and real-time nature of
1080 synchrophasor data presents unique challenges for existing
1081 application architectures. Wide Area management System (WAMS) makes
1082 it possible for the condition of the bulk power system to be observed
1083 and understood in real-time so that protective, preventative, or
1084 corrective action can be taken. Because of the very high sampling
1085 rate of measurements and the strict requirement for time
1086 synchronization of the samples, WAMS has stringent telecommunications
1087 requirements in an IP network that are captured in the following
1088 table:
1090 +----------------------+--------------------------------------------+
1091 | WAMS Requirement | Attribute |
1092 +----------------------+--------------------------------------------+
1093 | One way maximum | 50 ms |
1094 | delay | |
1095 | Asymetric delay | No |
1096 | Required | |
1097 | Maximum jitter | Not critical |
1098 | Topology | Point to point, point to Multi-point, |
1099 | | Multi-point to Multi-point |
1100 | Bandwidth | 100 Kbps |
1101 | Availability | 99.9999 |
1102 | precise timing | Yes |
1103 | required | |
1104 | Recovery time on | less than 50ms - hitless |
1105 | Node failure | |
1106 | performance | Yes, Mandatory |
1107 | management | |
1108 | Redundancy | Yes |
1109 | Packet loss | 1% |
1110 +----------------------+--------------------------------------------+
1112 Table 7: WAMS Special Communication Requirements
1114 3.2.2.1.8. IEC 61850 WAN engineering guidelines requirement
1115 classification
1117 The IEC (International Electrotechnical Commission) has recently
1118 published a Technical Report which offers guidelines on how to define
1119 and deploy Wide Area Networks for the interconnections of electric
1120 substations, generation plants and SCADA operation centers. The IEC
1121 61850-90-12 is providing a classification of WAN communication
1122 requirements into 4 classes. You will find herafter the table
1123 summarizing these requirements:
1125 +----------------+------------+------------+------------+-----------+
1126 | WAN | Class WA | Class WB | Class WC | Class WD |
1127 | Requirement | | | | |
1128 +----------------+------------+------------+------------+-----------+
1129 | Application | EHV (Extra | HV (High | MV (Medium | General |
1130 | field | High | Voltage) | Voltage) | purpose |
1131 | | Voltage) | | | |
1132 | Latency | 5 ms | 10 ms | 100 ms | > 100 ms |
1133 | Jitter | 10 us | 100 us | 1 ms | 10 ms |
1134 | Latency | 100 us | 1 ms | 10 ms | 100 ms |
1135 | Asymetry | | | | |
1136 | Time Accuracy | 1 us | 10 us | 100 us | 10 to 100 |
1137 | | | | | ms |
1138 | Bit Error rate | 10-7 to | 10-5 to | 10-3 | |
1139 | | 10-6 | 10-4 | | |
1140 | Unavailability | 10-7 to | 10-5 to | 10-3 | |
1141 | | 10-6 | 10-4 | | |
1142 | Recovery delay | Zero | 50 ms | 5 s | 50 s |
1143 | Cyber security | extremely | High | Medium | Medium |
1144 | | high | | | |
1145 +----------------+------------+------------+------------+-----------+
1147 Table 8: 61850-90-12 Communication Requirements; Courtesy of IEC
1149 3.2.2.2. Distribution use case
1151 3.2.2.2.1. Fault Location Isolation and Service Restoration (FLISR)
1153 As the name implies, Fault Location, Isolation, and Service
1154 Restoration (FLISR) refers to the ability to automatically locate the
1155 fault, isolate the fault, and restore service in the distribution
1156 network. It is a self-healing feature whose purpose is to minimize
1157 the impact of faults by serving portions of the loads on the affected
1158 circuit by switching to other circuits. It reduces the number of
1159 customers that experience a sustained power outage by reconfiguring
1160 distribution circuits. This will likely be the first wide spread
1161 application of distributed intelligence in the grid. Secondary
1162 substations can be connected to multiple primary substations.
1163 Normally, static power switch statuses (open/closed) in the network
1164 dictate the power flow to secondary substations. Reconfiguring the
1165 network in the event of a fault is typically done manually on site to
1166 operate switchgear to energize/de-energize alternate paths.
1167 Automating the operation of substation switchgear allows the utility
1168 to have a more dynamic network where the flow of power can be altered
1169 under fault conditions but also during times of peak load. It allows
1170 the utility to shift peak loads around the network. Or, to be more
1171 precise, alters the configuration of the network to move loads
1172 between different primary substations. The FLISR capability can be
1173 enabled in two modes:
1175 o Managed centrally from DMS (Distribution Management System), or
1177 o Executed locally through distributed control via intelligent
1178 switches and fault sensors.
1180 There are 3 distinct sub-functions that are performed:
1182 1. Fault Location Identification
1184 This sub-function is initiated by SCADA inputs, such as lockouts,
1185 fault indications/location, and, also, by input from the Outage
1186 Management System (OMS), and in the future by inputs from fault-
1187 predicting devices. It determines the specific protective device,
1188 which has cleared the sustained fault, identifies the de-energized
1189 sections, and estimates the probable location of the actual or the
1190 expected fault. It distinguishes faults cleared by controllable
1191 protective devices from those cleared by fuses, and identifies
1192 momentary outages and inrush/cold load pick-up currents. This step
1193 is also referred to as Fault Detection Classification and Location
1194 (FDCL). This step helps to expedite the restoration of faulted
1195 sections through fast fault location identification and improved
1196 diagnostic information available for crew dispatch. Also provides
1197 visualization of fault information to design and implement a
1198 switching plan to isolate the fault.
1200 2. Fault Type Determination
1202 I. Indicates faults cleared by controllable protective devices by
1203 distinguishing between:
1205 a. Faults cleared by fuses
1207 b. Momentary outages
1209 c. Inrush/cold load current
1211 II. Determines the faulted sections based on SCADA fault indications
1212 and protection lockout signals
1214 III. Increases the accuracy of the fault location estimation based
1215 on SCADA fault current measurements and real-time fault analysis
1217 3. Fault Isolation and Service Restoration
1218 Once the location and type of the fault has been pinpointed, the
1219 systems will attempt to isolate the fault and restore the non-faulted
1220 section of the network. This can have three modes of operation:
1222 I. Closed-loop mode : This is initiated by the Fault location sub-
1223 function. It generates a switching order (i.e., sequence of
1224 switching) for the remotely controlled switching devices to isolate
1225 the faulted section, and restore service to the non-faulted sections.
1226 The switching order is automatically executed via SCADA.
1228 II. Advisory mode : This is initiated by the Fault location sub-
1229 function. It generates a switching order for remotely and manually
1230 controlled switching devices to isolate the faulted section, and
1231 restore service to the non-faulted sections. The switching order is
1232 presented to operator for approval and execution.
1234 III. Study mode : the operator initiates this function. It analyzes
1235 a saved case modified by the operator, and generates a switching
1236 order under the operating conditions specified by the operator.
1238 With the increasing volume of data that are collected through fault
1239 sensors, utilities will use Big Data query and analysis tools to
1240 study outage information to anticipate and prevent outages by
1241 detecting failure patterns and their correlation with asset age,
1242 type, load profiles, time of day, weather conditions, and other
1243 conditions to discover conditions that lead to faults and take the
1244 necessary preventive and corrective measures.
1246 +----------------------+--------------------------------------------+
1247 | FLISR Requirement | Attribute |
1248 +----------------------+--------------------------------------------+
1249 | One way maximum | 80 ms |
1250 | delay | |
1251 | Asymetric delay | No |
1252 | Required | |
1253 | Maximum jitter | 40 ms |
1254 | Topology | Point to point, point to Multi-point, |
1255 | | Multi-point to Multi-point |
1256 | Bandwidth | 64 Kbps |
1257 | Availability | 99.9999 |
1258 | precise timing | Yes |
1259 | required | |
1260 | Recovery time on | Depends on customer impact |
1261 | Node failure | |
1262 | performance | Yes, Mandatory |
1263 | management | |
1264 | Redundancy | Yes |
1265 | Packet loss | 0.1% |
1266 +----------------------+--------------------------------------------+
1268 Table 9: FLISR Communication Requirements
1270 3.2.2.3. Generation use case
1272 3.2.2.3.1. Frequency Control / Automatic Generation Control (AGC)
1274 The system frequency should be maintained within a very narrow band.
1275 Deviations from the acceptable frequency range are detected and
1276 forwarded to the Load Frequency Control (LFC) system so that required
1277 up or down generation increase / decrease pulses can be sent to the
1278 power plants for frequency regulation. The trend in system frequency
1279 is a measure of mismatch between demand and generation, and is a
1280 necessary parameter for load control in interconnected systems.
1282 Automatic generation control (AGC) is a system for adjusting the
1283 power output of generators at different power plants, in response to
1284 changes in the load. Since a power grid requires that generation and
1285 load closely balance moment by moment, frequent adjustments to the
1286 output of generators are necessary. The balance can be judged by
1287 measuring the system frequency; if it is increasing, more power is
1288 being generated than used, and all machines in the system are
1289 accelerating. If the system frequency is decreasing, more demand is
1290 on the system than the instantaneous generation can provide, and all
1291 generators are slowing down.
1293 Where the grid has tie lines to adjacent control areas, automatic
1294 generation control helps maintain the power interchanges over the tie
1295 lines at the scheduled levels. The AGC takes into account various
1296 parameters including the most economical units to adjust, the
1297 coordination of thermal, hydroelectric, and other generation types,
1298 and even constraints related to the stability of the system and
1299 capacity of interconnections to other power grids.
1301 For the purpose of AGC we use static frequency measurements and
1302 averaging methods are used to get a more precise measure of system
1303 frequency in steady-state conditions.
1305 During disturbances, more real-time dynamic measurements of system
1306 frequency are taken using PMUs, especially when different areas of
1307 the system exhibit different frequencies. But that is outside the
1308 scope of this use case.
1310 +---------------------------------------------------+---------------+
1311 | FCAG (Frequency Control Automatic Generation) | Attribute |
1312 | Requirement | |
1313 +---------------------------------------------------+---------------+
1314 | One way maximum delay | 500 ms |
1315 | Asymetric delay Required | No |
1316 | Maximum jitter | Not critical |
1317 | Topology | Point to |
1318 | | point |
1319 | Bandwidth | 20 Kbps |
1320 | Availability | 99.999 |
1321 | precise timing required | Yes |
1322 | Recovery time on Node failure | N/A |
1323 | performance management | Yes, |
1324 | | Mandatory |
1325 | Redundancy | Yes |
1326 | Packet loss | 1% |
1327 +---------------------------------------------------+---------------+
1329 Table 10: FCAG Communication Requirements
1331 3.2.3. Specific Network topologies of Smart Grid Applications
1333 Utilities often have very large private telecommunications networks.
1334 It covers an entire territory / country. The main purpose of the
1335 network, until now, has been to support transmission network
1336 monitoring, control, and automation, remote control of generation
1337 sites, and providing FCAPS (Fault. Configuration. Accounting.
1338 Performance. Security) services from centralized network operation
1339 centers.
1341 Going forward, one network will support operation and maintenance of
1342 electrical networks (generation, transmission, and distribution),
1343 voice and data services for ten of thousands of employees and for
1344 exchange with neighboring interconnections, and administrative
1345 services. To meet those requirements, utility may deploy several
1346 physical networks leveraging different technologies across the
1347 country: an optical network and a microwave network for instance.
1348 Each protection and automatism system between two points has two
1349 telecommunications circuits, one on each network. Path diversity
1350 between two substations is key. Regardless of the event type
1351 (hurricane, ice storm, etc.), one path shall stay available so the
1352 SPS can still operate.
1354 In the optical network, signals are transmitted over more than tens
1355 of thousands of circuits using fiber optic links, microwave and
1356 telephone cables. This network is the nervous system of the
1357 utility's power transmission operations. The optical network
1358 represents ten of thousands of km of cable deployed along the power
1359 lines.
1361 Due to vast distances between transmission substations (for example
1362 as far as 280km apart), the fiber signal can be amplified to reach a
1363 distance of 280 km without attenuation.
1365 3.2.4. Precision Time Protocol
1367 Some utilities do not use GPS clocks in generation substations. One
1368 of the main reasons is that some of the generation plants are 30 to
1369 50 meters deep under ground and the GPS signal can be weak and
1370 unreliable. Instead, atomic clocks are used. Clocks are
1371 synchronized amongst each other. Rubidium clocks provide clock and
1372 1ms timestamps for IRIG-B. Some companies plan to transition to the
1373 Precision Time Protocol (IEEE 1588), distributing the synchronization
1374 signal over the IP/MPLS network.
1376 The Precision Time Protocol (PTP) is defined in IEEE standard 1588.
1377 PTP is applicable to distributed systems consisting of one or more
1378 nodes, communicating over a network. Nodes are modeled as containing
1379 a real-time clock that may be used by applications within the node
1380 for various purposes such as generating time-stamps for data or
1381 ordering events managed by the node. The protocol provides a
1382 mechanism for synchronizing the clocks of participating nodes to a
1383 high degree of accuracy and precision.
1385 PTP operates based on the following assumptions :
1387 It is assumed that the network eliminates cyclic forwarding of PTP
1388 messages within each communication path (e.g., by using a spanning
1389 tree protocol). PTP eliminates cyclic forwarding of PTP messages
1390 between communication paths.
1392 PTP is tolerant of an occasional missed message, duplicated
1393 message, or message that arrived out of order. However, PTP
1394 assumes that such impairments are relatively rare.
1396 PTP was designed assuming a multicast communication model. PTP
1397 also supports a unicast communication model as long as the
1398 behavior of the protocol is preserved.
1400 Like all message-based time transfer protocols, PTP time accuracy
1401 is degraded by asymmetry in the paths taken by event messages.
1402 Asymmetry is not detectable by PTP, however, if known, PTP
1403 corrects for asymmetry.
1405 A time-stamp event is generated at the time of transmission and
1406 reception of any event message. The time-stamp event occurs when the
1407 message's timestamp point crosses the boundary between the node and
1408 the network.
1410 IEC 61850 will recommend the use of the IEEE PTP 1588 Utility Profile
1411 (as defined in IEC 62439-3 Annex B) which offers the support of
1412 redundant attachment of clocks to Paralell Redundancy Protcol (PRP)
1413 and High-availability Seamless Redundancy (HSR) networks.
1415 3.3. IANA Considerations
1417 This memo includes no request to IANA.
1419 3.4. Security Considerations
1421 3.4.1. Current Practices and Their Limitations
1423 Grid monitoring and control devices are already targets for cyber
1424 attacks and legacy telecommunications protocols have many intrinsic
1425 network related vulnerabilities. DNP3, Modbus, PROFIBUS/PROFINET,
1426 and other protocols are designed around a common paradigm of request
1427 and respond. Each protocol is designed for a master device such as
1428 an HMI (Human Machine Interface) system to send commands to
1429 subordinate slave devices to retrieve data (reading inputs) or
1430 control (writing to outputs). Because many of these protocols lack
1431 authentication, encryption, or other basic security measures, they
1432 are prone to network-based attacks, allowing a malicious actor or
1433 attacker to utilize the request-and-respond system as a mechanism for
1434 command-and-control like functionality. Specific security concerns
1435 common to most industrial control, including utility
1436 telecommunication protocols include the following:
1438 o Network or transport errors (e.g. malformed packets or excessive
1439 latency) can cause protocol failure.
1441 o Protocol commands may be available that are capable of forcing
1442 slave devices into inoperable states, including powering-off
1443 devices, forcing them into a listen-only state, disabling
1444 alarming.
1446 o Protocol commands may be available that are capable of restarting
1447 communications and otherwise interrupting processes.
1449 o Protocol commands may be available that are capable of clearing,
1450 erasing, or resetting diagnostic information such as counters and
1451 diagnostic registers.
1453 o Protocol commands may be available that are capable of requesting
1454 sensitive information about the controllers, their configurations,
1455 or other need-to-know information.
1457 o Most protocols are application layer protocols transported over
1458 TCP; therefore it is easy to transport commands over non-standard
1459 ports or inject commands into authorized traffic flows.
1461 o Protocol commands may be available that are capable of
1462 broadcasting messages to many devices at once (i.e. a potential
1463 DoS).
1465 o Protocol commands may be available to query the device network to
1466 obtain defined points and their values (i.e. a configuration
1467 scan).
1469 o Protocol commands may be available that will list all available
1470 function codes (i.e. a function scan).
1472 o Bump in the wire (BITW) solutions : A hardware device is added to
1473 provide IPSec services between two routers that are not capable of
1474 IPSec functions. This special IPsec device will intercept then
1475 intercept outgoing datagrams, add IPSec protection to them, and
1476 strip it off incoming datagrams. BITW can all IPSec to legacy
1477 hosts and can retrofit non-IPSec routers to provide security
1478 benefits. The disadvantages are complexity and cost.
1480 These inherent vulnerabilities, along with increasing connectivity
1481 between IT an OT networks, make network-based attacks very feasible.
1482 Simple injection of malicious protocol commands provides control over
1483 the target process. Altering legitimate protocol traffic can also
1484 alter information about a process and disrupt the legitimate controls
1485 that are in place over that process. A man- in-the-middle attack
1486 could provide both control over a process and misrepresentation of
1487 data back to operator consoles.
1489 3.4.2. Security Trends in Utility Networks
1491 Although advanced telecommunications networks can assist in
1492 transforming the energy industry, playing a critical role in
1493 maintaining high levels of reliability, performance, and
1494 manageability, they also introduce the need for an integrated
1495 security infrastructure. Many of the technologies being deployed to
1496 support smart grid projects such as smart meters and sensors can
1497 increase the vulnerability of the grid to attack. Top security
1498 concerns for utilities migrating to an intelligent smart grid
1499 telecommunications platform center on the following trends:
1501 o Integration of distributed energy resources
1503 o Proliferation of digital devices to enable management, automation,
1504 protection, and control
1506 o Regulatory mandates to comply with standards for critical
1507 infrastructure protection
1509 o Migration to new systems for outage management, distribution
1510 automation, condition-based maintenance, load forecasting, and
1511 smart metering
1513 o Demand for new levels of customer service and energy management
1515 This development of a diverse set of networks to support the
1516 integration of microgrids, open-access energy competition, and the
1517 use of network-controlled devices is driving the need for a converged
1518 security infrastructure for all participants in the smart grid,
1519 including utilities, energy service providers, large commercial and
1520 industrial, as well as residential customers. Securing the assets of
1521 electric power delivery systems, from the control center to the
1522 substation, to the feeders and down to customer meters, requires an
1523 end-to-end security infrastructure that protects the myriad of
1524 telecommunications assets used to operate, monitor, and control power
1525 flow and measurement. Cyber security refers to all the security
1526 issues in automation and telecommunications that affect any functions
1527 related to the operation of the electric power systems.
1528 Specifically, it involves the concepts of:
1530 o Integrity : data cannot be altered undetectably
1532 o Authenticity : the telecommunications parties involved must be
1533 validated as genuine
1535 o Authorization : only requests and commands from the authorized
1536 users can be accepted by the system
1538 o Confidentiality : data must not be accessible to any
1539 unauthenticated users
1541 When designing and deploying new smart grid devices and
1542 telecommunications systems, it's imperative to understand the various
1543 impacts of these new components under a variety of attack situations
1544 on the power grid. Consequences of a cyber attack on the grid
1545 telecommunications network can be catastrophic. This is why security
1546 for smart grid is not just an ad hoc feature or product, it's a
1547 complete framework integrating both physical and Cyber security
1548 requirements and covering the entire smart grid networks from
1549 generation to distribution. Security has therefore become one of the
1550 main foundations of the utility telecom network architecture and must
1551 be considered at every layer with a defense-in-depth approach.
1552 Migrating to IP based protocols is key to address these challenges
1553 for two reasons:
1555 1. IP enables a rich set of features and capabilities to enhance the
1556 security posture
1558 2. IP is based on open standards, which allows interoperability
1559 between different vendors and products, driving down the costs
1560 associated with implementing security solutions in OT networks.
1562 Securing OT (Operation technology) telecommunications over packet-
1563 switched IP networks follow the same principles that are foundational
1564 for securing the IT infrastructure, i.e., consideration must be given
1565 to enforcing electronic access control for both person-to-machine and
1566 machine-to-machine communications, and providing the appropriate
1567 levels of data privacy, device and platform integrity, and threat
1568 detection and mitigation.
1570 4. Building Automation Systems
1572 4.1. Use Case Description
1574 A Building Automation System (BAS) manages equipment and sensors in a
1575 building for improving residents' comfort, reducing energy
1576 consumption, and responding to failures and emergencies. For
1577 example, the BAS measures the temperature of a room using sensors and
1578 then controls the HVAC (heating, ventilating, and air conditioning)
1579 to maintain a set temperature and minimize energy consumption.
1581 A BAS primarily performs the following functions:
1583 o Periodically measures states of devices, for example humidity and
1584 illuminance of rooms, open/close state of doors, FAN speed, etc.
1586 o Stores the measured data.
1588 o Provides the measured data to BAS systems and operators.
1590 o Generates alarms for abnormal state of devices.
1592 o Controls devices (e.g. turn off room lights at 10:00 PM).
1594 4.2. Building Automation Systems Today
1596 4.2.1. BAS Architecture
1598 A typical BAS architecture of today is shown in Figure 1.
1600 +----------------------------+
1601 | |
1602 | BMS HMI |
1603 | | | |
1604 | +----------------------+ |
1605 | | Management Network | |
1606 | +----------------------+ |
1607 | | | |
1608 | LC LC |
1609 | | | |
1610 | +----------------------+ |
1611 | | Field Network | |
1612 | +----------------------+ |
1613 | | | | | |
1614 | Dev Dev Dev Dev |
1615 | |
1616 +----------------------------+
1618 BMS := Building Management Server
1619 HMI := Human Machine Interface
1620 LC := Local Controller
1622 Figure 1: BAS architecture
1624 There are typically two layers of network in a BAS. The upper one is
1625 called the Management Network and the lower one is called the Field
1626 Network. In management networks an IP-based communication protocol
1627 is used, while in field networks non-IP based communication protocols
1628 ("field protocols") are mainly used. Field networks have specific
1629 timing requirements, whereas management networks can be best-effort.
1631 A Human Machine Interface (HMI) is typically a desktop PC used by
1632 operators to monitor and display device states, send device control
1633 commands to Local Controllers (LCs), and configure building schedules
1634 (for example "turn off all room lights in the building at 10:00 PM").
1636 A Building Management Server (BMS) performs the following operations.
1638 o Collect and store device states from LCs at regular intervals.
1640 o Send control values to LCs according to a building schedule.
1642 o Send an alarm signal to operators if it detects abnormal devices
1643 states.
1645 The BMS and HMI communicate with LCs via IP-based "management
1646 protocols" (see standards [bacnetip], [knx]).
1648 A LC is typically a Programmable Logic Controller (PLC) which is
1649 connected to several tens or hundreds of devices using "field
1650 protocols". An LC performs the following kinds of operations:
1652 o Measure device states and provide the information to BMS or HMI.
1654 o Send control values to devices, unilaterally or as part of a
1655 feedback control loop.
1657 There are many field protocols used today; some are standards-based
1658 and others are proprietary (see standards [lontalk], [modbus],
1659 [profibus] and [flnet]). The result is that BASs have multiple MAC/
1660 PHY modules and interfaces. This makes BASs more expensive, slower
1661 to develop, and can result in "vendor lock-in" with multiple types of
1662 management applications.
1664 4.2.2. BAS Deployment Model
1666 An example BAS for medium or large buildings is shown in Figure 2.
1667 The physical layout spans multiple floors, and there is a monitoring
1668 room where the BAS management entities are located. Each floor will
1669 have one or more LCs depending upon the number of devices connected
1670 to the field network.
1672 +--------------------------------------------------+
1673 | Floor 3 |
1674 | +----LC~~~~+~~~~~+~~~~~+ |
1675 | | | | | |
1676 | | Dev Dev Dev |
1677 | | |
1678 |--- | ------------------------------------------|
1679 | | Floor 2 |
1680 | +----LC~~~~+~~~~~+~~~~~+ Field Network |
1681 | | | | | |
1682 | | Dev Dev Dev |
1683 | | |
1684 |--- | ------------------------------------------|
1685 | | Floor 1 |
1686 | +----LC~~~~+~~~~~+~~~~~+ +-----------------|
1687 | | | | | | Monitoring Room |
1688 | | Dev Dev Dev | |
1689 | | | BMS HMI |
1690 | | Management Network | | | |
1691 | +--------------------------------+-----+ |
1692 | | |
1693 +--------------------------------------------------+
1695 Figure 2: BAS Deployment model for Medium/Large Buildings
1697 Each LC is connected to the monitoring room via the Management
1698 network, and the management functions are performed within the
1699 building. In most cases, fast Ethernet (e.g. 100BASE-T) is used for
1700 the management network. Since the management network is non-
1701 realtime, use of Ethernet without quality of service is sufficient
1702 for today's deployment.
1704 In the field network a variety of physical interfaces such as RS232C
1705 and RS485 are used, which have specific timing requirements. Thus if
1706 a field network is to be replaced with an Ethernet or wireless
1707 network, such networks must support time-critical deterministic
1708 flows.
1710 In Figure 3, another deployment model is presented in which the
1711 management system is hosted remotely. This is becoming popular for
1712 small office and residential buildings in which a standalone
1713 monitoring system is not cost-effective.
1715 +---------------+
1716 | Remote Center |
1717 | |
1718 | BMS HMI |
1719 +------------------------------------+ | | | |
1720 | Floor 2 | | +---+---+ |
1721 | +----LC~~~~+~~~~~+ Field Network| | | |
1722 | | | | | | Router |
1723 | | Dev Dev | +-------|-------+
1724 | | | |
1725 |--- | ------------------------------| |
1726 | | Floor 1 | |
1727 | +----LC~~~~+~~~~~+ | |
1728 | | | | | |
1729 | | Dev Dev | |
1730 | | | |
1731 | | Management Network | WAN |
1732 | +------------------------Router-------------+
1733 | |
1734 +------------------------------------+
1736 Figure 3: Deployment model for Small Buildings
1738 Some interoperability is possible today in the Management Network,
1739 but not in today's field networks due to their non-IP-based design.
1741 4.2.3. Use Cases for Field Networks
1743 Below are use cases for Environmental Monitoring, Fire Detection, and
1744 Feedback Control, and their implications for field network
1745 performance.
1747 4.2.3.1. Environmental Monitoring
1749 The BMS polls each LC at a maximum measurement interval of 100ms (for
1750 example to draw a historical chart of 1 second granularity with a 10x
1751 sampling interval) and then performs the operations as specified by
1752 the operator. Each LC needs to measure each of its several hundred
1753 sensors once per measurement interval. Latency is not critical in
1754 this scenario as long as all sensor values are completed in the
1755 measurement interval. Availability is expected to be 99.999 %.
1757 4.2.3.2. Fire Detection
1759 On detection of a fire, the BMS must stop the HVAC, close the fire
1760 shutters, turn on the fire sprinklers, send an alarm, etc. There are
1761 typically ~10s of sensors per LC that BMS needs to manage. In this
1762 scenario the measurement interval is 10-50ms, the communication delay
1763 is 10ms, and the availability must be 99.9999 %.
1765 4.2.3.3. Feedback Control
1767 BAS systems utilize feedback control in various ways; the most time-
1768 critial is control of DC motors, which require a short feedback
1769 interval (1-5ms) with low communication delay (10ms) and jitter
1770 (1ms). The feedback interval depends on the characteristics of the
1771 device and a target quality of control value. There are typically
1772 ~10s of such devices per LC.
1774 Communication delay is expected to be less than 10 ms, jitter less
1775 than 1 sec while the availability must be 99.9999% .
1777 4.2.4. Security Considerations
1779 When BAS field networks were developed it was assumed that the field
1780 networks would always be physically isolated from external networks
1781 and therefore security was not a concern. In today's world many BASs
1782 are managed remotely and are thus connected to shared IP networks and
1783 so security is definitely a concern, yet security features are not
1784 available in the majority of BAS field network deployments .
1786 The management network, being an IP-based network, has the protocols
1787 available to enable network security, but in practice many BAS
1788 systems do not implement even the available security features such as
1789 device authentication or encryption for data in transit.
1791 4.3. BAS Future
1793 In the future we expect more fine-grained environmental monitoring
1794 and lower energy consumption, which will require more sensors and
1795 devices, thus requiring larger and more complex building networks.
1797 We expect building networks to be connected to or converged with
1798 other networks (Enterprise network, Home network, and Internet).
1800 Therefore better facilities for network management, control,
1801 reliability and security are critical in order to improve resident
1802 and operator convenience and comfort. For example the ability to
1803 monitor and control building devices via the internet would enable
1804 (for example) control of room lights or HVAC from a resident's
1805 desktop PC or phone application.
1807 4.4. BAS Asks
1809 The community would like to see an interoperable protocol
1810 specification that can satisfy the timing, security, availability and
1811 QoS constraints described above, such that the resulting converged
1812 network can replace the disparate field networks. Ideally this
1813 connectivity could extend to the open Internet.
1815 This would imply an architecture that can guarantee
1817 o Low communication delays (from <10ms to 100ms in a network of
1818 several hundred devices)
1820 o Low jitter (< 1 ms)
1822 o Tight feedback intervals (1ms - 10ms)
1824 o High network availability (up to 99.9999% )
1826 o Availability of network data in disaster scenario
1828 o Authentication between management and field devices (both local
1829 and remote)
1831 o Integrity and data origin authentication of communication data
1832 between field and management devices
1834 o Confidentiality of data when communicated to a remote device
1836 5. Wireless for Industrial Use Cases
1838 (This section was derived from draft-thubert-6tisch-4detnet-01)
1840 5.1. Introduction
1842 The emergence of wireless technology has enabled a variety of new
1843 devices to get interconnected, at a very low marginal cost per
1844 device, at any distance ranging from Near Field to interplanetary,
1845 and in circumstances where wiring may not be practical, for instance
1846 on fast-moving or rotating devices.
1848 At the same time, a new breed of Time Sensitive Networks is being
1849 developed to enable traffic that is highly sensitive to jitter, quite
1850 sensitive to latency, and with a high degree of operational
1851 criticality so that loss should be minimized at all times. Such
1852 traffic is not limited to professional Audio/ Video networks, but is
1853 also found in command and control operations such as industrial
1854 automation and vehicular sensors and actuators.
1856 At IEEE802.1, the Audio/Video Task Group [IEEE802.1TSNTG] Time
1857 Sensitive Networking (TSN) to address Deterministic Ethernet. The
1858 Medium access Control (MAC) of IEEE802.15.4 [IEEE802154] has evolved
1859 with the new TimeSlotted Channel Hopping (TSCH) [RFC7554] mode for
1860 deterministic industrial-type applications. TSCH was introduced with
1861 the IEEE802.15.4e [IEEE802154e] amendment and will be wrapped up in
1862 the next revision of the IEEE802.15.4 standard. For all practical
1863 purpose, this document is expected to be insensitive to the future
1864 versions of the IEEE802.15.4 standard, which is thus referenced
1865 undated.
1867 Though at a different time scale, both TSN and TSCH standards provide
1868 Deterministic capabilities to the point that a packet that pertains
1869 to a certain flow crosses the network from node to node following a
1870 very precise schedule, as a train that leaves intermediate stations
1871 at precise times along its path. With TSCH, time is formatted into
1872 timeSlots, and an individual cell is allocated to unicast or
1873 broadcast communication at the MAC level. The time-slotted operation
1874 reduces collisions, saves energy, and enables to more closely
1875 engineer the network for deterministic properties. The channel
1876 hopping aspect is a simple and efficient technique to combat multi-
1877 path fading and co-channel interferences (for example by Wi-Fi
1878 emitters).
1880 The 6TiSCH Architecture [I-D.ietf-6tisch-architecture] defines a
1881 remote monitoring and scheduling management of a TSCH network by a
1882 Path Computation Element (PCE), which cooperates with an abstract
1883 Network Management Entity (NME) to manage timeSlots and device
1884 resources in a manner that minimizes the interaction with and the
1885 load placed on the constrained devices.
1887 This Architecture applies the concepts of Deterministic Networking on
1888 a TSCH network to enable the switching of timeSlots in a G-MPLS
1889 manner. This document details the dependencies that 6TiSCH has on
1890 PCE [PCE] and DetNet [I-D.finn-detnet-architecture] to provide the
1891 necessary capabilities that may be specific to such networks. In
1892 turn, DetNet is expected to integrate and maintain consistency with
1893 the work that has taken place and is continuing at IEEE802.1TSN and
1894 AVnu.
1896 5.2. Terminology
1898 Readers are expected to be familiar with all the terms and concepts
1899 that are discussed in "Multi-link Subnet Support in IPv6"
1900 [I-D.ietf-ipv6-multilink-subnets].
1902 The draft uses terminology defined or referenced in
1903 [I-D.ietf-6tisch-terminology] and
1904 [I-D.ietf-roll-rpl-industrial-applicability].
1906 The draft also conforms to the terms and models described in
1907 [RFC3444] and uses the vocabulary and the concepts defined in
1908 [RFC4291] for the IPv6 Architecture.
1910 5.3. 6TiSCH Overview
1912 The scope of the present work is a subnet that, in its basic
1913 configuration, is made of a TSCH [RFC7554] MAC Low Power Lossy
1914 Network (LLN).
1916 ---+-------- ............ ------------
1917 | External Network |
1918 | +-----+
1919 +-----+ | NME |
1920 | | LLN Border | |
1921 | | router +-----+
1922 +-----+
1923 o o o
1924 o o o o
1925 o o LLN o o o
1926 o o o o
1927 o
1929 Figure 4: Basic Configuration of a 6TiSCH Network
1931 In the extended configuration, a Backbone Router (6BBR) federates
1932 multiple 6TiSCH in a single subnet over a backbone. 6TiSCH 6BBRs
1933 synchronize with one another over the backbone, so as to ensure that
1934 the multiple LLNs that form the IPv6 subnet stay tightly
1935 synchronized.
1937 ---+-------- ............ ------------
1938 | External Network |
1939 | +-----+
1940 | +-----+ | NME |
1941 +-----+ | +-----+ | |
1942 | | Router | | PCE | +-----+
1943 | | +--| |
1944 +-----+ +-----+
1945 | |
1946 | Subnet Backbone |
1947 +--------------------+------------------+
1948 | | |
1949 +-----+ +-----+ +-----+
1950 | | Backbone | | Backbone | | Backbone
1951 o | | router | | router | | router
1952 +-----+ +-----+ +-----+
1953 o o o o o
1954 o o o o o o o o o o o
1955 o o o LLN o o o o
1956 o o o o o o o o o o o o
1958 Figure 5: Extended Configuration of a 6TiSCH Network
1960 If the Backbone is Deterministic, then the Backbone Router ensures
1961 that the end-to-end deterministic behavior is maintained between the
1962 LLN and the backbone. This SHOULD be done in conformance to the
1963 DetNet Architecture [I-D.finn-detnet-architecture] which studies
1964 Layer-3 aspects of Deterministic Networks, and covers networks that
1965 span multiple Layer-2 domains. One particular requirement is that
1966 the PCE MUST be able to compute a deterministic path and to end
1967 across the TSCH network and an IEEE802.1 TSN Ethernet backbone, and
1968 DetNet MUST enable end-to-end deterministic forwarding.
1970 6TiSCH defines the concept of a Track, which is a complex form of a
1971 uni-directional Circuit ([I-D.ietf-6tisch-terminology]). As opposed
1972 to a simple circuit that is a sequence of nodes and links, a Track is
1973 shaped as a directed acyclic graph towards a destination to support
1974 multi-path forwarding and route around failures. A Track may also
1975 branch off and rejoin, for the purpose of the so-called Packet
1976 Replication and Elimination (PRE), over non congruent branches. PRE
1977 may be used to complement layer-2 Automatic Repeat reQuest (ARQ) to
1978 meet industrial expectations in Packet Delivery Ratio (PDR), in
1979 particular when the Track extends beyond the 6TiSCH network.
1981 +-----+
1982 | IoT |
1983 | G/W |
1984 +-----+
1985 ^ <---- Elimination
1986 | |
1987 Track branch | |
1988 +-------+ +--------+ Subnet Backbone
1989 | |
1990 +--|--+ +--|--+
1991 | | | Backbone | | | Backbone
1992 o | | | router | | | router
1993 +--/--+ +--|--+
1994 o / o o---o----/ o
1995 o o---o--/ o o o o o
1996 o \ / o o LLN o
1997 o v <---- Replication
1998 o
2000 Figure 6: End-to-End deterministic Track
2002 In the example above, a Track is laid out from a field device in a
2003 6TiSCH network to an IoT gateway that is located on a IEEE802.1 TSN
2004 backbone.
2006 The Replication function in the field device sends a copy of each
2007 packet over two different branches, and the PCE schedules each hop of
2008 both branches so that the two copies arrive in due time at the
2009 gateway. In case of a loss on one branch, hopefully the other copy
2010 of the packet still makes it in due time. If two copies make it to
2011 the IoT gateway, the Elimination function in the gateway ignores the
2012 extra packet and presents only one copy to upper layers.
2014 At each 6TiSCH hop along the Track, the PCE may schedule more than
2015 one timeSlot for a packet, so as to support Layer-2 retries (ARQ).
2016 It is also possible that the field device only uses the second branch
2017 if sending over the first branch fails.
2019 In current deployments, a TSCH Track does not necessarily support PRE
2020 but is systematically multi-path. This means that a Track is
2021 scheduled so as to ensure that each hop has at least two forwarding
2022 solutions, and the forwarding decision is to try the preferred one
2023 and use the other in case of Layer-2 transmission failure as detected
2024 by ARQ.
2026 5.3.1. TSCH and 6top
2028 6top is a logical link control sitting between the IP layer and the
2029 TSCH MAC layer, which provides the link abstraction that is required
2030 for IP operations. The 6top operations are specified in
2031 [I-D.wang-6tisch-6top-sublayer].
2033 The 6top data model and management interfaces are further discussed
2034 in [I-D.ietf-6tisch-6top-interface] and [I-D.ietf-6tisch-coap].
2036 The architecture defines "soft" cells and "hard" cells. "Hard" cells
2037 are owned and managed by an separate scheduling entity (e.g. a PCE)
2038 that specifies the slotOffset/channelOffset of the cells to be
2039 added/moved/deleted, in which case 6top can only act as instructed,
2040 and may not move hard cells in the TSCH schedule on its own.
2042 5.3.2. SlotFrames and Priorities
2044 A slotFrame is the base object that the PCE needs to manipulate to
2045 program a schedule into an LLN node. Elaboration on that concept can
2046 be found in section "SlotFrames and Priorities" of the 6TiSCH
2047 architecture [I-D.ietf-6tisch-architecture]. The architecture also
2048 details how the schedule is constructed and how transmission
2049 resources called cells can be allocated to particular transmissions
2050 so as to avoid collisions.
2052 5.3.3. Schedule Management by a PCE
2054 6TiSCH supports a mixed model of centralized routes and distributed
2055 routes. Centralized routes can for example be computed by a entity
2056 such as a PCE. Distributed routes are computed by RPL.
2058 Both methods may inject routes in the Routing Tables of the 6TiSCH
2059 routers. In either case, each route is associated with a 6TiSCH
2060 topology that can be a RPL Instance topology or a track. The 6TiSCH
2061 topology is indexed by a Instance ID, in a format that reuses the
2062 RPLInstanceID as defined in RPL [RFC6550].
2064 Both RPL and PCE rely on shared sources such as policies to define
2065 Global and Local RPLInstanceIDs that can be used by either method.
2066 It is possible for centralized and distributed routing to share a
2067 same topology. Generally they will operate in different slotFrames,
2068 and centralized routes will be used for scheduled traffic and will
2069 have precedence over distributed routes in case of conflict between
2070 the slotFrames.
2072 Section "Schedule Management Mechanisms" of the 6TiSCH architecture
2073 describes 4 paradigms to manage the TSCH schedule of the LLN nodes:
2075 Static Scheduling, neighbor-to-neighbor Scheduling, remote monitoring
2076 and scheduling management, and Hop-by-hop scheduling. The Track
2077 operation for DetNet corresponds to a remote monitoring and
2078 scheduling management by a PCE.
2080 The 6top interface document [I-D.ietf-6tisch-6top-interface]
2081 specifies the generic data model that can be used to monitor and
2082 manage resources of the 6top sublayer. Abstract methods are
2083 suggested for use by a management entity in the device. The data
2084 model also enables remote control operations on the 6top sublayer.
2086 [I-D.ietf-6tisch-coap] defines an mapping of the 6top set of
2087 commands, which is described in [I-D.ietf-6tisch-6top-interface], to
2088 CoAP resources. This allows an entity to interact with the 6top
2089 layer of a node that is multiple hops away in a RESTful fashion.
2091 [I-D.ietf-6tisch-coap] also defines a basic set CoAP resources and
2092 associated RESTful access methods (GET/PUT/POST/DELETE). The payload
2093 (body) of the CoAP messages is encoded using the CBOR format. The
2094 PCE commands are expected to be issued directly as CoAP requests or
2095 to be mapped back and forth into CoAP by a gateway function at the
2096 edge of the 6TiSCH network. For instance, it is possible that a
2097 mapping entity on the backbone transforms a non-CoAP protocol such as
2098 PCEP into the RESTful interfaces that the 6TiSCH devices support.
2099 This architecture will be refined to comply with DetNet
2100 [I-D.finn-detnet-architecture] when the work is formalized.
2102 5.3.4. Track Forwarding
2104 By forwarding, this specification means the per-packet operation that
2105 allows to deliver a packet to a next hop or an upper layer in this
2106 node. Forwarding is based on pre-existing state that was installed
2107 as a result of the routing computation of a Track by a PCE. The
2108 6TiSCH architecture supports three different forwarding model, G-MPLS
2109 Track Forwarding (TF), 6LoWPAN Fragment Forwarding (FF) and IPv6
2110 Forwarding (6F) which is the classical IP operation. The DetNet case
2111 relates to the Track Forwarding operation under the control of a PCE.
2113 A Track is a unidirectional path between a source and a destination.
2114 In a Track cell, the normal operation of IEEE802.15.4 Automatic
2115 Repeat-reQuest (ARQ) usually happens, though the acknowledgment may
2116 be omitted in some cases, for instance if there is no scheduled cell
2117 for a retry.
2119 Track Forwarding is the simplest and fastest. A bundle of cells set
2120 to receive (RX-cells) is uniquely paired to a bundle of cells that
2121 are set to transmit (TX-cells), representing a layer-2 forwarding
2122 state that can be used regardless of the network layer protocol.
2124 This model can effectively be seen as a Generalized Multi-protocol
2125 Label Switching (G-MPLS) operation in that the information used to
2126 switch a frame is not an explicit label, but rather related to other
2127 properties of the way the packet was received, a particular cell in
2128 the case of 6TiSCH. As a result, as long as the TSCH MAC (and
2129 Layer-2 security) accepts a frame, that frame can be switched
2130 regardless of the protocol, whether this is an IPv6 packet, a 6LoWPAN
2131 fragment, or a frame from an alternate protocol such as WirelessHART
2132 or ISA100.11a.
2134 A data frame that is forwarded along a Track normally has a
2135 destination MAC address that is set to broadcast - or a multicast
2136 address depending on MAC support. This way, the MAC layer in the
2137 intermediate nodes accepts the incoming frame and 6top switches it
2138 without incurring a change in the MAC header. In the case of
2139 IEEE802.15.4, this means effectively broadcast, so that along the
2140 Track the short address for the destination of the frame is set to
2141 0xFFFF.
2143 A Track is thus formed end-to-end as a succession of paired bundles,
2144 a receive bundle from the previous hop and a transmit bundle to the
2145 next hop along the Track, and a cell in such a bundle belongs to at
2146 most one Track. For a given iteration of the device schedule, the
2147 effective channel of the cell is obtained by adding a pseudo-random
2148 number to the channelOffset of the cell, which results in a rotation
2149 of the frequency that used for transmission. The bundles may be
2150 computed so as to accommodate both variable rates and
2151 retransmissions, so they might not be fully used at a given iteration
2152 of the schedule. The 6TiSCH architecture provides additional means
2153 to avoid waste of cells as well as overflows in the transmit bundle,
2154 as follows:
2156 In one hand, a TX-cell that is not needed for the current iteration
2157 may be reused opportunistically on a per-hop basis for routed
2158 packets. When all of the frame that were received for a given Track
2159 are effectively transmitted, any available TX-cell for that Track can
2160 be reused for upper layer traffic for which the next-hop router
2161 matches the next hop along the Track. In that case, the cell that is
2162 being used is effectively a TX-cell from the Track, but the short
2163 address for the destination is that of the next-hop router. It
2164 results that a frame that is received in a RX-cell of a Track with a
2165 destination MAC address set to this node as opposed to broadcast must
2166 be extracted from the Track and delivered to the upper layer (a frame
2167 with an unrecognized MAC address is dropped at the lower MAC layer
2168 and thus is not received at the 6top sublayer).
2170 On the other hand, it might happen that there are not enough TX-cells
2171 in the transmit bundle to accommodate the Track traffic, for instance
2172 if more retransmissions are needed than provisioned. In that case,
2173 the frame can be placed for transmission in the bundle that is used
2174 for layer-3 traffic towards the next hop along the track as long as
2175 it can be routed by the upper layer, that is, typically, if the frame
2176 transports an IPv6 packet. The MAC address should be set to the
2177 next-hop MAC address to avoid confusion. It results that a frame
2178 that is received over a layer-3 bundle may be in fact associated to a
2179 Track. In a classical IP link such as an Ethernet, off-track traffic
2180 is typically in excess over reservation to be routed along the non-
2181 reserved path based on its QoS setting. But with 6TiSCH, since the
2182 use of the layer-3 bundle may be due to transmission failures, it
2183 makes sense for the receiver to recognize a frame that should be re-
2184 tracked, and to place it back on the appropriate bundle if possible.
2185 A frame should be re-tracked if the Per-Hop-Behavior group indicated
2186 in the Differentiated Services Field in the IPv6 header is set to
2187 Deterministic Forwarding, as discussed in Section 5.4.1. A frame is
2188 re-tracked by scheduling it for transmission over the transmit bundle
2189 associated to the Track, with the destination MAC address set to
2190 broadcast.
2192 There are 2 modes for a Track, transport mode and tunnel mode.
2194 5.3.4.1. Transport Mode
2196 In transport mode, the Protocol Data Unit (PDU) is associated with
2197 flow-dependant meta-data that refers uniquely to the Track, so the
2198 6top sublayer can place the frame in the appropriate cell without
2199 ambiguity. In the case of IPv6 traffic, this flow identification is
2200 transported in the Flow Label of the IPv6 header. Associated with
2201 the source IPv6 address, the Flow Label forms a globally unique
2202 identifier for that particular Track that is validated at egress
2203 before restoring the destination MAC address (DMAC) and punting to
2204 the upper layer.
2206 | ^
2207 +--------------+ | |
2208 | IPv6 | | |
2209 +--------------+ | |
2210 | 6LoWPAN HC | | |
2211 +--------------+ ingress egress
2212 | 6top | sets +----+ +----+ restores
2213 +--------------+ dmac to | | | | dmac to
2214 | TSCH MAC | brdcst | | | | self
2215 +--------------+ | | | | | |
2216 | LLN PHY | +-------+ +--...-----+ +-------+
2217 +--------------+
2219 Track Forwarding, Transport Mode
2221 5.3.4.2. Tunnel Mode
2223 In tunnel mode, the frames originate from an arbitrary protocol over
2224 a compatible MAC that may or may not be synchronized with the 6TiSCH
2225 network. An example of this would be a router with a dual radio that
2226 is capable of receiving and sending WirelessHART or ISA100.11a frames
2227 with the second radio, by presenting itself as an access Point or a
2228 Backbone Router, respectively.
2230 In that mode, some entity (e.g. PCE) can coordinate with a
2231 WirelessHART Network Manager or an ISA100.11a System Manager to
2232 specify the flows that are to be transported transparently over the
2233 Track.
2235 +--------------+
2236 | IPv6 |
2237 +--------------+
2238 | 6LoWPAN HC |
2239 +--------------+ set restore
2240 | 6top | +dmac+ +dmac+
2241 +--------------+ to|brdcst to|nexthop
2242 | TSCH MAC | | | | |
2243 +--------------+ | | | |
2244 | LLN PHY | +-------+ +--...-----+ +-------+
2245 +--------------+ | ingress egress |
2246 | |
2247 +--------------+ | |
2248 | LLN PHY | | |
2249 +--------------+ | |
2250 | TSCH MAC | | |
2251 +--------------+ | dmac = | dmac =
2252 |ISA100/WiHART | | nexthop v nexthop
2253 +--------------+
2255 Figure 7: Track Forwarding, Tunnel Mode
2257 In that case, the flow information that identifies the Track at the
2258 ingress 6TiSCH router is derived from the RX-cell. The dmac is set
2259 to this node but the flow information indicates that the frame must
2260 be tunneled over a particular Track so the frame is not passed to the
2261 upper layer. Instead, the dmac is forced to broadcast and the frame
2262 is passed to the 6top sublayer for switching.
2264 At the egress 6TiSCH router, the reverse operation occurs. Based on
2265 metadata associated to the Track, the frame is passed to the
2266 appropriate link layer with the destination MAC restored.
2268 5.3.4.3. Tunnel Metadata
2270 Metadata coming with the Track configuration is expected to provide
2271 the destination MAC address of the egress endpoint as well as the
2272 tunnel mode and specific data depending on the mode, for instance a
2273 service access point for frame delivery at egress. If the tunnel
2274 egress point does not have a MAC address that matches the
2275 configuration, the Track installation fails.
2277 In transport mode, if the final layer-3 destination is the tunnel
2278 termination, then it is possible that the IPv6 address of the
2279 destination is compressed at the 6LoWPAN sublayer based on the MAC
2280 address. It is thus mandatory at the ingress point to validate that
2281 the MAC address that was used at the 6LoWPAN sublayer for compression
2282 matches that of the tunnel egress point. For that reason, the node
2283 that injects a packet on a Track checks that the destination is
2284 effectively that of the tunnel egress point before it overwrites it
2285 to broadcast. The 6top sublayer at the tunnel egress point reverts
2286 that operation to the MAC address obtained from the tunnel metadata.
2288 5.4. Operations of Interest for DetNet and PCE
2290 In a classical system, the 6TiSCH device does not place the request
2291 for bandwidth between self and another device in the network.
2292 Rather, an Operation Control System invoked through an Human/Machine
2293 Interface (HMI) indicates the Traffic Specification, in particular in
2294 terms of latency and reliability, and the end nodes. With this, the
2295 PCE must compute a Track between the end nodes and provision the
2296 network with per-flow state that describes the per-hop operation for
2297 a given packet, the corresponding timeSlots, and the flow
2298 identification that enables to recognize when a certain packet
2299 belongs to a certain Track, sort out duplicates, etc...
2301 For a static configuration that serves a certain purpose for a long
2302 period of time, it is expected that a node will be provisioned in one
2303 shot with a full schedule, which incorporates the aggregation of its
2304 behavior for multiple Tracks. 6TiSCH expects that the programing of
2305 the schedule will be done over COAP as discussed in 6TiSCH Resource
2306 Management and Interaction using CoAP [I-D.ietf-6tisch-coap].
2308 But an Hybrid mode may be required as well whereby a single Track is
2309 added, modified, or removed, for instance if it appears that a Track
2310 does not perform as expected for, say, PDR. For that case, the
2311 expectation is that a protocol that flows along a Track (to be), in a
2312 fashion similar to classical Traffic Engineering (TE) [CCAMP], may be
2313 used to update the state in the devices. 6TiSCH provides means for a
2314 device to negotiate a timeSlot with a neighbor, but in general that
2315 flow was not designed and no protocol was selected and it is expected
2316 that DetNet will determine the appropriate end-to-end protocols to be
2317 used in that case.
2319 Operational System and HMI
2321 -+-+-+-+-+-+-+ Northbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
2323 PCE PCE PCE PCE
2325 -+-+-+-+-+-+-+ Southbound -+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
2327 --- 6TiSCH------6TiSCH------6TiSCH------6TiSCH--
2328 6TiSCH / Device Device Device Device \
2329 Device- - 6TiSCH
2330 \ 6TiSCH 6TiSCH 6TiSCH 6TiSCH / Device
2331 ----Device------Device------Device------Device--
2333 Figure 8: Stream Management Entity
2335 5.4.1. Packet Marking and Handling
2337 Section "Packet Marking and Handling" of
2338 [I-D.ietf-6tisch-architecture] describes the packet tagging and
2339 marking that is expected in 6TiSCH networks.
2341 5.4.1.1. Tagging Packets for Flow Identification
2343 For packets that are routed by a PCE along a Track, the tuple formed
2344 by the IPv6 source address and a local RPLInstanceID is tagged in the
2345 packets to identify uniquely the Track and associated transmit bundle
2346 of timeSlots.
2348 It results that the tagging that is used for a DetNet flow outside
2349 the 6TiSCH LLN MUST be swapped into 6TiSCH formats and back as the
2350 packet enters and then leaves the 6TiSCH network.
2352 Note: The method and format used for encoding the RPLInstanceID at
2353 6lo is generalized to all 6TiSCH topological Instances, which
2354 includes Tracks.
2356 5.4.1.2. Replication, Retries and Elimination
2358 6TiSCH expects elimination and replication of packets along a complex
2359 Track, but has no position about how the sequence numbers would be
2360 tagged in the packet.
2362 As it goes, 6TiSCH expects that timeSlots corresponding to copies of
2363 a same packet along a Track are correlated by configuration, and does
2364 not need to process the sequence numbers.
2366 The semantics of the configuration MUST enable correlated timeSlots
2367 to be grouped for transmit (and respectively receive) with a 'OR'
2368 relations, and then a 'AND' relation MUST be configurable between
2369 groups. The semantics is that if the transmit (and respectively
2370 receive) operation succeeded in one timeSlot in a 'OR' group, then
2371 all the other timeSLots in the group are ignored. Now, if there are
2372 at least two groups, the 'AND' relation between the groups indicates
2373 that one operation must succeed in each of the groups.
2375 On the transmit side, timeSlots provisioned for retries along a same
2376 branch of a Track are placed a same 'OR' group. The 'OR' relation
2377 indicates that if a transmission is acknowledged, then further
2378 transmissions SHOULD NOT be attempted for timeSlots in that group.
2379 There are as many 'OR' groups as there are branches of the Track
2380 departing from this node. Different 'OR' groups are programmed for
2381 the purpose of replication, each group corresponding to one branch of
2382 the Track. The 'AND' relation between the groups indicates that
2383 transmission over any of branches MUST be attempted regardless of
2384 whether a transmission succeeded in another branch. It is also
2385 possible to place cells to different next-hop routers in a same 'OR'
2386 group. This allows to route along multi-path tracks, trying one
2387 next-hop and then another only if sending to the first fails.
2389 On the receive side, all timeSlots are programmed in a same 'OR'
2390 group. Retries of a same copy as well as converging branches for
2391 elimination are converged, meaning that the first successful
2392 reception is enough and that all the other timeSlots can be ignored.
2394 5.4.1.3. Differentiated Services Per-Hop-Behavior
2396 Additionally, an IP packet that is sent along a Track uses the
2397 Differentiated Services Per-Hop-Behavior Group called Deterministic
2398 Forwarding, as described in
2399 [I-D.svshah-tsvwg-deterministic-forwarding].
2401 5.4.2. Topology and capabilities
2403 6TiSCH nodes are usually IoT devices, characterized by very limited
2404 amount of memory, just enough buffers to store one or a few IPv6
2405 packets, and limited bandwidth between peers. It results that a node
2406 will maintain only a small number of peering information, and will
2407 not be able to store many packets waiting to be forwarded. Peers can
2408 be identified through MAC or IPv6 addresses, but a Cryptographically
2409 Generated Address [RFC3972] (CGA) may also be used.
2411 Neighbors can be discovered over the radio using mechanism such as
2412 beacons, but, though the neighbor information is available in the
2413 6TiSCH interface data model, 6TiSCH does not describe a protocol to
2414 pro-actively push the neighborhood information to a PCE. This
2415 protocol should be described and should operate over CoAP. The
2416 protocol should be able to carry multiple metrics, in particular the
2417 same metrics as used for RPL operations [RFC6551]
2419 The energy that the device consumes in sleep, transmit and receive
2420 modes can be evaluated and reported. So can the amount of energy
2421 that is stored in the device and the power that it can be scavenged
2422 from the environment. The PCE SHOULD be able to compute Tracks that
2423 will implement policies on how the energy is consumed, for instance
2424 balance between nodes, ensure that the spent energy does not exceeded
2425 the scavenged energy over a period of time, etc...
2427 5.5. Security Considerations
2429 On top of the classical protection of control signaling that can be
2430 expected to support DetNet, it must be noted that 6TiSCH networks
2431 operate on limited resources that can be depleted rapidly if an
2432 attacker manages to operate a DoS attack on the system, for instance
2433 by placing a rogue device in the network, or by obtaining management
2434 control and to setup extra paths.
2436 6. Cellular Radio Use Cases
2438 6.1. Use Case Description
2440 This use case describes the application of deterministic networking
2441 in the context of cellular telecom transport networks. Important
2442 elements include time synchronization, clock distribution, and ways
2443 of establishing time-sensitive streams for both Layer-2 and Layer-3
2444 user plane traffic.
2446 6.1.1. Network Architecture
2448 Figure 9 illustrates a typical 3GPP-defined cellular network
2449 architecture, which includes "Fronthaul" and "Midhaul" network
2450 segments. The "Fronthaul" is the network connecting base stations
2451 (baseband processing units) to the remote radio heads (antennas).
2452 The "Midhaul" is the network inter-connecting base stations (or small
2453 cell sites).
2455 Y (remote radio heads (antennas))
2456 \
2457 Y__ \.--. .--. +------+
2458 \_( `. +---+ _(Back`. | 3GPP |
2459 Y------( Front )----|eNB|----( Haul )----| core |
2460 ( ` .Haul ) +---+ ( ` . ) ) | netw |
2461 /`--(___.-' \ `--(___.-' +------+
2462 Y_/ / \.--. \
2463 Y_/ _( Mid`. \
2464 ( Haul ) \
2465 ( ` . ) ) \
2466 `--(___.-'\_____+---+ (small cell sites)
2467 \ |SCe|__Y
2468 +---+ +---+
2469 Y__|eNB|__Y
2470 +---+
2471 Y_/ \_Y ("local" radios)
2473 Figure 9: Generic 3GPP-based Cellular Network Architecture
2475 The available processing time for Fronthaul networking overhead is
2476 limited to the available time after the baseband processing of the
2477 radio frame has completed. For example in Long Term Evolution (LTE)
2478 radio, processing of a radio frame is allocated 3ms, but typically
2479 the processing completes much earlier (<400us) allowing the remaining
2480 time to be used by the Fronthaul network. This ultimately determines
2481 the distance the remote radio heads can be located from the base
2482 stations (200us equals roughly 40 km of optical fiber-based
2483 transport, thus round trip time is 2*200us = 400us).
2485 The remainder of the "maximum delay budget" is consumed by all nodes
2486 and buffering between the remote radio head and the baseband
2487 processing, plus the distance-incurred delay.
2489 The baseband processing time and the available "delay budget" for the
2490 fronthaul is likely to change in the forthcoming "5G" due to reduced
2491 radio round trip times and other architectural and service
2492 requirements [NGMN].
2494 6.1.2. Time Synchronization Requirements
2496 Fronthaul time synchronization requirements are given by [TS25104],
2497 [TS36104], [TS36211], and [TS36133]. These can be summarized for the
2498 current 3GPP LTE-based networks as:
2500 Delay Accuracy:
2501 +-8ns (i.e. +-1/32 Tc, where Tc is the UMTS Chip time of 1/3.84
2502 MHz) resulting in a round trip accuracy of +-16ns. The value is
2503 this low to meet the 3GPP Timing Alignment Error (TAE) measurement
2504 requirements.
2506 Packet Delay Variation:
2507 Packet Delay Variation (PDV aka Jitter aka Timing Alignment Error)
2508 is problematic to Fronthaul networks and must be minimized. If
2509 the transport network cannot guarantee low enough PDV then
2510 additional buffering has to be introduced at the edges of the
2511 network to buffer out the jitter. Buffering is not desirable as
2512 it reduces the total available delay budget.
2514 * For multiple input multiple output (MIMO) or TX diversity
2515 transmissions, at each carrier frequency, TAE shall not exceed
2516 65 ns (i.e. 1/4 Tc).
2518 * For intra-band contiguous carrier aggregation, with or without
2519 MIMO or TX diversity, TAE shall not exceed 130 ns (i.e. 1/2
2520 Tc).
2522 * For intra-band non-contiguous carrier aggregation, with or
2523 without MIMO or TX diversity, TAE shall not exceed 260 ns (i.e.
2524 one Tc).
2526 * For inter-band carrier aggregation, with or without MIMO or TX
2527 diversity, TAE shall not exceed 260 ns.
2529 Transport link contribution to radio frequency error:
2530 +-2 PPB. This value is considered to be "available" for the
2531 Fronthaul link out of the total 50 PPB budget reserved for the
2532 radio interface. Note: the reason that the transport link
2533 contributes to radio frequency error is as follows. The current
2534 way of doing Fronthaul is from the radio unit to remote radio head
2535 directly. The remote radio head is essentially a passive device
2536 (without buffering etc.) The transport drives the antenna
2537 directly by feeding it with samples and everything the transport
2538 adds will be introduced to radio as-is. So if the transport
2539 causes additional frequence error that shows immediately on the
2540 radio as well.
2542 The above listed time synchronization requirements are difficult to
2543 meet with point-to-point connected networks, and more difficult when
2544 the network includes multiple hops. It is expected that networks
2545 must include buffering at the ends of the connections as imposed by
2546 the jitter requirements, since trying to meet the jitter requirements
2547 in every intermediate node is likely to be too costly. However,
2548 every measure to reduce jitter and delay on the path makes it easier
2549 to meet the end-to-end requirements.
2551 In order to meet the timing requirements both senders and receivers
2552 must remain time synchronized, demanding very accurate clock
2553 distribution, for example support for IEEE 1588 transparent clocks in
2554 every intermediate node.
2556 In cellular networks from the LTE radio era onward, phase
2557 synchronization is needed in addition to frequency synchronization
2558 ([TS36300], [TS23401]).
2560 6.1.3. Time-Sensitive Stream Requirements
2562 In addition to the time synchronization requirements listed in
2563 Section Section 6.1.2 the Fronthaul networks assume practically
2564 error-free transport. The maximum bit error rate (BER) has been
2565 defined to be 10^-12. When packetized that would imply a packet
2566 error rate (PER) of 2.4*10^-9 (assuming ~300 bytes packets).
2567 Retransmitting lost packets and/or using forward error correction
2568 (FEC) to circumvent bit errors is practically impossible due to the
2569 additional delay incurred. Using redundant streams for better
2570 guarantees for delivery is also practically impossible in many cases
2571 due to high bandwidth requirements of Fronthaul networks. For
2572 instance, current uncompressed CPRI bandwidth expansion ratio is
2573 roughly 20:1 compared to the IP layer user payload it carries.
2574 Protection switching is also a candidate but current technologies for
2575 the path switch are too slow. We do not currently know of a better
2576 solution for this issue.
2578 Fronthaul links are assumed to be symmetric, and all Fronthaul
2579 streams (i.e. those carrying radio data) have equal priority and
2580 cannot delay or pre-empt each other. This implies that the network
2581 must guarantee that each time-sensitive flow meets their schedule.
2583 6.1.4. Security Considerations
2585 Establishing time-sensitive streams in the network entails reserving
2586 networking resources for long periods of time. It is important that
2587 these reservation requests be authenticated to prevent malicious
2588 reservation attempts from hostile nodes (or accidental
2589 misconfiguration). This is particularly important in the case where
2590 the reservation requests span administrative domains. Furthermore,
2591 the reservation information itself should be digitally signed to
2592 reduce the risk of a legitimate node pushing a stale or hostile
2593 configuration into another networking node.
2595 6.2. Cellular Radio Networks Today
2597 Today's Fronthaul networks typically consist of:
2599 o Dedicated point-to-point fiber connection is common
2601 o Proprietary protocols and framings
2603 o Custom equipment and no real networking
2605 Today's Midhaul and Backhaul networks typically consist of:
2607 o Mostly normal IP networks, MPLS-TP, etc.
2609 o Clock distribution and sync using 1588 and SyncE
2611 Telecommunication networks in the cellular domain are already heading
2612 towards transport networks where precise time synchronization support
2613 is one of the basic building blocks. While the transport networks
2614 themselves have practically transitioned to all-IP packet based
2615 networks to meet the bandwidth and cost requirements, highly accurate
2616 clock distribution has become a challenge.
2618 Transport networks in the cellular domain are typically based on Time
2619 Division Multiplexing (TDM-based) and provide frequency
2620 synchronization capabilities as a part of the transport media.
2621 Alternatively other technologies such as Global Positioning System
2622 (GPS) or Synchronous Ethernet (SyncE) are used [SyncE].
2624 Both Ethernet and IP/MPLS [RFC3031] (and PseudoWires (PWE) [RFC3985]
2625 for legacy transport support) have become popular tools to build and
2626 manage new all-IP Radio Access Networks (RAN)
2627 [I-D.kh-spring-ip-ran-use-case]. Although various timing and
2628 synchronization optimizations have already been proposed and
2629 implemented including 1588 PTP enhancements
2630 [I-D.ietf-tictoc-1588overmpls][I-D.mirsky-mpls-residence-time], these
2631 solution are not necessarily sufficient for the forthcoming RAN
2632 architectures or guarantee the higher time-synchronization
2633 requirements [CPRI]. There are also existing solutions for the TDM
2634 over IP [RFC5087] [RFC4553] or Ethernet transports [RFC5086].
2636 6.3. Cellular Radio Networks Future
2638 We would like to see the following in future Cellular Radio networks:
2640 o Unified standards-based transport protocols and standard
2641 networking equipment that can make use of underlying deterministic
2642 link-layer services
2644 o Unified and standards-based network management systems and
2645 protocols in all parts of the network (including Fronthaul)
2647 New radio access network deployment models and architectures may
2648 require time sensitive networking services with strict requirements
2649 on other parts of the network that previously were not considered to
2650 be packetized at all. The time and synchronization support are
2651 already topical for Backhaul and Midhaul packet networks [MEF], and
2652 becoming a real issue for Fronthaul networks. Specifically in the
2653 Fronthaul networks the timing and synchronization requirements can be
2654 extreme for packet based technologies, for example, on the order of
2655 sub +-20 ns packet delay variation (PDV) and frequency accuracy of
2656 +0.002 PPM [Fronthaul].
2658 The actual transport protocols and/or solutions to establish required
2659 transport "circuits" (pinned-down paths) for Fronthaul traffic are
2660 still undefined. Those are likely to include (but are not limited
2661 to) solutions directly over Ethernet, over IP, and MPLS/PseudoWire
2662 transport.
2664 Even the current time-sensitive networking features may not be
2665 sufficient for Fronthaul traffic. Therefore, having specific
2666 profiles that take the requirements of Fronthaul into account is
2667 desirable [IEEE8021CM].
2669 The really interesting and important existing work for time sensitive
2670 networking has been done for Ethernet [TSNTG], which specifies the
2671 use of IEEE 1588 time precision protocol (PTP) [IEEE1588] in the
2672 context of IEEE 802.1D and IEEE 802.1Q. While IEEE 802.1AS
2673 [IEEE8021AS] specifies a Layer-2 time synchronizing service other
2674 specification, such as IEEE 1722 [IEEE1722] specify Ethernet-based
2675 Layer-2 transport for time-sensitive streams. New promising work
2676 seeks to enable the transport of time-sensitive fronthaul streams in
2677 Ethernet bridged networks [IEEE8021CM]. Similarly to IEEE 1722 there
2678 is an ongoing standardization effort to define Layer-2 transport
2679 encapsulation format for transporting radio over Ethernet (RoE) in
2680 IEEE 1904.3 Task Force [IEEE19043].
2682 All-IP RANs and various "haul" networks would benefit from time
2683 synchronization and time-sensitive transport services. Although
2684 Ethernet appears to be the unifying technology for the transport
2685 there is still a disconnect providing Layer-3 services. The protocol
2686 stack typically has a number of layers below the Ethernet Layer-2
2687 that shows up to the Layer-3 IP transport. It is not uncommon that
2688 on top of the lowest layer (optical) transport there is the first
2689 layer of Ethernet followed one or more layers of MPLS, PseudoWires
2690 and/or other tunneling protocols finally carrying the Ethernet layer
2691 visible to the user plane IP traffic. While there are existing
2692 technologies, especially in MPLS/PWE space, to establish circuits
2693 through the routed and switched networks, there is a lack of
2694 signaling the time synchronization and time-sensitive stream
2695 requirements/reservations for Layer-3 flows in a way that the entire
2696 transport stack is addressed and the Ethernet layers that needs to be
2697 configured are addressed.
2699 Furthermore, not all "user plane" traffic will be IP. Therefore, the
2700 same solution also must address the use cases where the user plane
2701 traffic is again another layer or Ethernet frames. There is existing
2702 work describing the problem statement
2703 [I-D.finn-detnet-problem-statement] and the architecture
2704 [I-D.finn-detnet-architecture] for deterministic networking (DetNet)
2705 that targets solutions for time-sensitive (IP/transport) streams with
2706 deterministic properties over Ethernet-based switched networks.
2708 6.4. Cellular Radio Networks Asks
2710 A standard for data plane transport specification which is:
2712 o Unified among all *hauls
2714 o Deployed in a highly deterministic network environment
2716 A standard for data flow information models that are:
2718 o Aware of the time sensitivity and constraints of the target
2719 networking environment
2721 o Aware of underlying deterministic networking services (e.g. on the
2722 Ethernet layer)
2724 Mapping the Fronthaul requirements to IETF DetNet
2725 [I-D.finn-detnet-architecture] Section 3 "Providing the DetNet
2726 Quality of Service", the relevant features are:
2728 o Zero congestion loss.
2730 o Pinned-down paths.
2732 7. Industrial M2M
2734 7.1. Use Case Description
2736 Industrial Automation in general refers to automation of
2737 manufacturing, quality control and material processing. In this
2738 "machine to machine" (M2M) use case we consider machine units in a
2739 plant floor which periodically exchange data with upstream or
2740 downstream machine modules and/or a supervisory controller within a
2741 local area network.
2743 The actors of M2M communication are Programmable Logic Controllers
2744 (PLCs). Communication between PLCs and between PLCs and the
2745 supervisory PLC (S-PLC) is achieved via critical control/data streams
2746 Figure 10.
2748 S (Sensor)
2749 \ +-----+
2750 PLC__ \.--. .--. ---| MES |
2751 \_( `. _( `./ +-----+
2752 A------( Local )-------------( L2 )
2753 ( Net ) ( Net ) +-------+
2754 /`--(___.-' `--(___.-' ----| S-PLC |
2755 S_/ / PLC .--. / +-------+
2756 A_/ \_( `.
2757 (Actuator) ( Local )
2758 ( Net )
2759 /`--(___.-'\
2760 / \ A
2761 S A
2763 Figure 10: Current Generic Industrial M2M Network Architecture
2765 This use case focuses on PLC-related communications; communication to
2766 Manufacturing-Execution-Systems (MESs) are not addressed.
2768 This use case covers only critical control/data streams; non-critical
2769 traffic between industrial automation applications (such as
2770 communication of state, configuration, set-up, and database
2771 communication) are adequately served by currently available
2772 prioritizing techniques. Such traffic can use up to 80% of the total
2773 bandwidth required. There is also a subset of non-time-critical
2774 traffic that must be reliable even though it is not time sensitive.
2776 In this use case the primary need for deterministic networking is to
2777 provide end-to-end delivery of M2M messages within specific timing
2778 constraints, for example in closed loop automation control. Today
2779 this level of determinism is provided by proprietary networking
2780 technologies. In addition, standard networking technologies are used
2781 to connect the local network to remote industrial automation sites,
2782 e.g. over an enterprise or metro network which also carries other
2783 types of traffic. Therefore, flows that should be forwarded with
2784 deterministic guarantees need to be sustained regardless of the
2785 amount of other flows in those networks.
2787 7.2. Industrial M2M Communication Today
2789 Today, proprietary networks fulfill the needed timing and
2790 availability for M2M networks.
2792 The network topologies used today by industrial automation are
2793 similar to those used by telecom networks: Daisy Chain, Ring, Hub and
2794 Spoke, and Comb (a subset of Daisy Chain).
2796 PLC-related control/data streams are transmitted periodically and
2797 carry either a pre-configured payload or a payload configured during
2798 runtime.
2800 Some industrial applications require time synchronization at the end
2801 nodes. For such time-coordinated PLCs, accuracy of 1 microsecond is
2802 required. Even in the case of "non-time-coordinated" PLCs time sync
2803 may be needed e.g. for timestamping of sensor data.
2805 Industrial network scenarios require advanced security solutions.
2806 Many of the current industrial production networks are physically
2807 separated. Preventing critical flows from be leaked outside a domain
2808 is handled today by filtering policies that are typically enforced in
2809 firewalls.
2811 7.2.1. Transport Parameters
2813 The Cycle Time defines the frequency of message(s) between industrial
2814 actors. The Cycle Time is application dependent, in the range of 1ms
2815 - 100ms for critical control/data streams.
2817 Because industrial applications assume deterministic transport for
2818 critical Control-Data-Stream parameters (instead of defining latency
2819 and delay variation parameters) it is sufficient to fulfill the upper
2820 bound of latency (maximum latency). The underlying networking
2821 infrastructure must ensure a maximum end-to-end delivery time of
2822 messages in the range of 100 microseconds to 50 milliseconds
2823 depending on the control loop application.
2825 The bandwidth requirements of control/data streams are usually
2826 calculated directly from the bytes-per-cycle parameter of the control
2827 loop. For PLC-to-PLC communication one can expect 2 - 32 streams
2828 with packet size in the range of 100 - 700 bytes. For S-PLC to PLCs
2829 the number of streams is higher - up to 256 streams. Usually no more
2830 than 20% of available bandwidth is used for critical control/data
2831 streams. In today's networks 1Gbps links are commonly used.
2833 Most PLC control loops are rather tolerant of packet loss, however
2834 critical control/data streams accept no more than 1 packet loss per
2835 consecutive communication cycle (i.e. if a packet gets lost in cycle
2836 "n", then the next cycle ("n+1") must be lossless). After two or
2837 more consecutive packet losses the network may be considered to be
2838 "down" by the Application.
2840 As network downtime may impact the whole production system the
2841 required network availability is rather high (99,999%).
2843 Based on the above parameters we expect that some form of redundancy
2844 will be required for M2M communications, however any individual
2845 solution depends on several parameters including cycle time, delivery
2846 time, etc.
2848 7.2.2. Stream Creation and Destruction
2850 In an industrial environment, critical control/data streams are
2851 created rather infrequently, on the order of ~10 times per day / week
2852 / month. Most of these critical control/data streams get created at
2853 machine startup, however flexibility is also needed during runtime,
2854 for example when adding or removing a machine. Going forward as
2855 production systems become more flexible, we expect a significant
2856 increase in the rate at which streams are created, changed and
2857 destroyed.
2859 7.3. Industrial M2M Future
2861 We would like to see the various proprietary networks replaced with a
2862 converged IP-standards-based network with deterministic properties
2863 that can satisfy the timing, security and reliability constraints
2864 described above.
2866 7.4. Industrial M2M Asks
2868 o Converged IP-based network
2870 o Deterministic behavior (bounded latency and jitter )
2872 o High availability (presumably through redundancy) (99.999 %)
2874 o Low message delivery time (100us - 50ms)
2876 o Low packet loss (burstless, 0.1-1 %)
2878 o Precise time synchronization accuracy (1us)
2880 o Security (e.g. prevent critical flows from being leaked between
2881 physically separated networks)
2883 8. Other Use Cases
2885 8.1. Introduction
2887 The rapid growth of the today's communication system and its access
2888 into almost all aspects of daily life has led to great dependency on
2889 services it provides. The communication network, as it is today, has
2890 applications such as multimedia and peer-to-peer file sharing
2891 distribution that require Quality of Service (QoS) guarantees in
2892 terms of delay and jitter to maintain a certain level of performance.
2893 Meanwhile, mobile wireless communications has become an important
2894 part to support modern sociality with increasing importance over the
2895 last years. A communication network of hard real-time and high
2896 reliability is essential for the next concurrent and next generation
2897 mobile wireless networks as well as its bearer network for E-2-E
2898 performance requirements.
2900 Conventional transport network is IP-based because of the bandwidth
2901 and cost requirements. However the delay and jitter guarantee
2902 becomes a challenge in case of contention since the service here is
2903 not deterministic but best effort. With more and more rigid demand
2904 in latency control in the future network [METIS], deterministic
2905 networking [I-D.finn-detnet-architecture] is a promising solution to
2906 meet the ultra low delay applications and use cases. There are
2907 already typical issues for delay sensitive networking requirements in
2908 midhaul and backhaul network to support LTE and future 5G network
2909 [net5G]. And not only in the telecom industry but also other
2910 vertical industry has increasing demand on delay sensitive
2911 communications as the automation becomes critical recently.
2913 More specifically, CoMP techniques, D-2-D, industrial automation and
2914 gaming/media service all have great dependency on the low delay
2915 communications as well as high reliability to guarantee the service
2916 performance. Note that the deterministic networking is not equal to
2917 low latency as it is more focused on the worst case delay bound of
2918 the duration of certain application or service. It can be argued
2919 that without high certainty and absolute delay guarantee, low delay
2920 provisioning is just relative [rfc3393], which is not sufficient to
2921 some delay critical service since delay violation in an instance
2922 cannot be tolerated. Overall, the requirements from vertical
2923 industries seem to be well aligned with the expected low latency and
2924 high determinist performance of future networks
2926 This document describes several use cases and scenarios with
2927 requirements on deterministic delay guarantee within the scope of the
2928 deterministic network [I-D.finn-detnet-problem-statement].
2930 8.2. Critical Delay Requirements
2932 Delay and jitter requirement has been take into account as a major
2933 component in QoS provisioning since the birth of Internet. The delay
2934 sensitive networking with increasing importance become the root of
2935 mobile wireless communications as well as the applicable areas which
2936 are all greatly relied on low delay communications. Due to the best
2937 effort feature of the IP networking, mitigate contention and
2938 buffering is the main solution to serve the delay sensitive service.
2939 More bandwidth is assigned to keep the link low loaded or in another
2940 word, reduce the probability of congestion. However, not only lack
2941 of determinist but also has limitation to serve the applications in
2942 the future communication system, keeping low loaded cannot provide
2943 deterministic delay guarantee. Take the [METIS] that documents the
2944 fundamental challenges as well as overall technical goal of the 5G
2945 mobile and wireless system as the starting point. It should
2946 supports: -1000 times higher mobile data volume per area, -10 times
2947 to 100 times higher typical user data rate, -10 times to 100 times
2948 higher number of connected devices, -10 times longer battery life for
2949 low power devices, and -5 times reduced End-to-End (E2E) latency, at
2950 similar cost and energy consumption levels as today's system. Taking
2951 part of these requirements related to latency, current LTE networking
2952 system has E2E latency less than 20ms [LTE-Latency] which leads to
2953 around 5ms E2E latency for 5G networks. It has been argued that
2954 fulfill such rigid latency demand with similar cost will be most
2955 challenging as the system also requires 100 times bandwidth as well
2956 as 100 times of connected devices. As a result to that, simply
2957 adding redundant bandwidth provisioning can be no longer an efficient
2958 solution due to the high bandwidth requirements more than ever
2959 before. In addition to the bandwidth provisioning, the critical flow
2960 within its reserved resource should not be affected by other flows no
2961 matter the pressure of the network. Robust defense of critical flow
2962 is also not depended on redundant bandwidth allocation.
2963 Deterministic networking techniques in both layer-2 and layer-3 using
2964 IETF protocol solutions can be promising to serve these scenarios.
2966 8.3. Coordinated multipoint processing (CoMP)
2968 In the wireless communication system, Coordinated multipoint
2969 processing (CoMP) is considered as an effective technique to solve
2970 the inter-cell interference problem to improve the cell-edge user
2971 throughput [CoMP].
2973 8.3.1. CoMP Architecture
2974 +--------------------------+
2975 | CoMP |
2976 +--+--------------------+--+
2977 | |
2978 +----------+ +------------+
2979 | Uplink | | Downlink |
2980 +-----+----+ +--------+---+
2981 | |
2982 ------------------- -----------------------
2983 | | | | | |
2984 +---------+ +----+ +-----+ +------------+ +-----+ +-----+
2985 | Joint | | CS | | DPS | | Joint | | CS/ | | DPS |
2986 |Reception| | | | | |Transmission| | CB | | |
2987 +---------+ +----+ +-----+ +------------+ +-----+ +-----+
2988 | |
2989 |----------- |-------------
2990 | | | |
2991 +------------+ +---------+ +----------+ +------------+
2992 | Joint | | Soft | | Coherent | | Non- |
2993 |Equalization| |Combining| | JT | | Coherent JT|
2994 +------------+ +---------+ +----------+ +------------+
2996 Figure 11: Framework of CoMP Technology
2998 As shown in Figure 11, CoMP reception and transmission is a framework
2999 that multiple geographically distributed antenna nodes cooperate to
3000 improve the performance of the users served in the common cooperation
3001 area. The design principal of CoMP is to extend the current single-
3002 cell to multi-UEs transmission to a multi-cell- to-multi-UEs
3003 transmission by base station cooperation. In contrast to single-cell
3004 scenario, CoMP has critical issues such as: Backhaul latency, CSI
3005 (Channel State Information) reporting and accuracy and Network
3006 complexity. Clearly the first two requirements are very much delay
3007 sensitive and will be discussed in next section.
3009 8.3.2. Delay Sensitivity in CoMP
3011 As the essential feature of CoMP, signaling is exchanged between
3012 eNBs, the backhaul latency is the dominating limitation of the CoMP
3013 performance. Generally, JT and JP may benefit from coordinating the
3014 scheduling (distributed or centralized) of different cells in case
3015 that the signaling exchanging between eNBs is limited to 4-10ms. For
3016 C-RAN the backhaul latency requirement is 250us while for D-RAN it is
3017 4-15ms. And this delay requirement is not only rigid but also
3018 absolute since any uncertainty in delay will down the performance
3019 significantly. Note that, some operator's transport network is not
3020 build to support Layer-3 transfer in aggregation layer. In such
3021 case, the signaling is exchanged through EPC which means delay is
3022 supposed to be larger. CoMP has high requirement on delay and
3023 reliability which is lack by current mobile network systems and may
3024 impact the architecture of the mobile network.
3026 8.4. Industrial Automation
3028 Traditional "industrial automation" terminology usually refers to
3029 automation of manufacturing, quality control and material processing.
3030 "Industrial internet" and "industrial 4.0" [EA12] is becoming a hot
3031 topic based on the Internet of Things. This high flexible and
3032 dynamic engineering and manufacturing will result in a lot of so-
3033 called smart approaches such as Smart Factory, Smart Products, Smart
3034 Mobility, and Smart Home/Buildings. No doubt that ultra high
3035 reliability and robustness is a must in data transmission, especially
3036 in the closed loop automation control application where delay
3037 requirement is below 1ms and packet loss less than 10E-9. All these
3038 critical requirements on both latency and loss cannot be fulfilled by
3039 current 4G communication networks. Moreover, the collaboration of
3040 the industrial automation from remote campus with cellular and fixed
3041 network has to be built on an integrated, cloud-based platform. In
3042 this way, the deterministic flows should be guaranteed regardless of
3043 the amount of other flows in the network. The lack of this mechanism
3044 becomes the main obstacle in deployment on of industrial automation.
3046 8.5. Vehicle to Vehicle
3048 V2V communication has gained more and more attention in the last few
3049 years and will be increasingly growth in the future. Not only
3050 equipped with direct communication system which is short ranged, V2V
3051 communication also requires wireless cellular networks to cover wide
3052 range and more sophisticated services. V2V application in the area
3053 autonomous driving has very stringent requirements of latency and
3054 reliability. It is critical that the timely arrival of information
3055 for safety issues. In addition, due to the limitation of processing
3056 of individual vehicle, passing information to the cloud can provide
3057 more functions such as video processing, audio recognition or
3058 navigation systems. All of those requirements lead to a highly
3059 reliable connectivity to the cloud. On the other hand, it is natural
3060 that the provisioning of low latency communication is one of the main
3061 challenges to be overcome as a result of the high mobility, the high
3062 penetration losses caused by the vehicle itself. As result of that,
3063 the data transmission with latency below 5ms and a high reliability
3064 of PER below 10E-6 are demanded. It can benefit from the deployment
3065 of deterministic networking with high reliability.
3067 8.6. Gaming, Media and Virtual Reality
3069 Online gaming and cloud gaming is dominating the gaming market since
3070 it allow multiple players to play together with more challenging and
3071 competing. Connected via current internet, the latency can be a big
3072 issue to degrade the end users' experience. There different types of
3073 games and FPS (First Person Shooting) gaming has been considered to
3074 be the most latency sensitive online gaming due to the high
3075 requirements of timing precision and computing of moving target.
3076 Virtual reality is also receiving more interests than ever before as
3077 a novel gaming experience. The delay here can be very critical to
3078 the interacting in the virtual world. Disagreement between what is
3079 seeing and what is feeling can cause motion sickness and affect what
3080 happens in the game. Supporting fast, real-time and reliable
3081 communications in both PHY/MAC layer, network layer and application
3082 layer is main bottleneck for such use case. The media content
3083 delivery has been and will become even more important use of
3084 Internet. Not only high bandwidth demand but also critical delay and
3085 jitter requirements have to be taken into account to meet the user
3086 demand. To make the smoothness of the video and audio, delay and
3087 jitter has to be guaranteed to avoid possible interruption which is
3088 the killer of all online media on demand service. Now with 4K and 8K
3089 video in the near future, the delay guarantee become one of the most
3090 challenging issue than ever before. 4K/8K UHD video service requires
3091 6Gbps-100Gbps for uncompressed video and compressed video starting
3092 from 60Mbps. The delay requirement is 100ms while some specific
3093 interactive applications may require 10ms delay [UHD-video].
3095 9. Use Case Common Elements
3097 Looking at the use cases collectively, the following common desires
3098 for the DetNet-based networks of the future emerge:
3100 o Open standards-based network (replace various proprietary
3101 networks, reduce cost, create multi-vendor market)
3103 o Centrally administered (though such administration may be
3104 distributed for scale and resiliency)
3106 o Integrates L2 (bridged) and L3 (routed) environments (independent
3107 of the Link layer, e.g. can be used with Ethernet, 6TiSCH, etc.)
3109 o Carries both deterministic and best-effort traffic (guaranteed
3110 end-to-end delivery of deterministic flows, deterministic flows
3111 isolated from each other and from best-effort traffic congestion,
3112 unused deterministic BW available to best-effort traffic)
3114 o Ability to add or remove systems from the network with minimal,
3115 bounded service interruption (applications include replacement of
3116 failed devices as well as plug and play)
3118 o Uses standardized data flow information models capable of
3119 expressing deterministic properties (models express device
3120 capabilities, flow properties. Protocols for pushing models from
3121 controller to devices, devices to controller)
3123 o Scalable size (long distances (many km) and short distances
3124 (within a single machine), many hops (radio repeaters, microwave
3125 links, fiber links...) and short hops (single machine))
3127 o Scalable timing parameters and accuracy (bounded latency,
3128 guaranteed worst case maximum, minimum. Low latency, e.g. control
3129 loops may be less than 1ms, but larger for wide area networks)
3131 o High availability (99.9999 percent up time requested, but may be
3132 up to twelve 9s)
3134 o Reliability, redundancy (lives at stake)
3136 o Security (from failures, attackers, misbehaving devices -
3137 sensitive to both packet content and arrival time)
3139 10. Acknowledgments
3141 10.1. Pro Audio
3143 This section was derived from draft-gunther-detnet-proaudio-req-01.
3145 The editors would like to acknowledge the help of the following
3146 individuals and the companies they represent:
3148 Jeff Koftinoff, Meyer Sound
3150 Jouni Korhonen, Associate Technical Director, Broadcom
3152 Pascal Thubert, CTAO, Cisco
3154 Kieran Tyrrell, Sienda New Media Technologies GmbH
3156 10.2. Utility Telecom
3158 This section was derived from draft-wetterwald-detnet-utilities-reqs-
3159 02.
3161 Faramarz Maghsoodlou, Ph. D. IoT Connected Industries and Energy
3162 Practice Cisco
3164 Pascal Thubert, CTAO Cisco
3166 10.3. Building Automation Systems
3168 This section was derived from draft-bas-usecase-detnet-00.
3170 10.4. Wireless for Industrial
3172 This section was derived from draft-thubert-6tisch-4detnet-01.
3174 This specification derives from the 6TiSCH architecture, which is the
3175 result of multiple interactions, in particular during the 6TiSCH
3176 (bi)Weekly Interim call, relayed through the 6TiSCH mailing list at
3177 the IETF.
3179 The authors wish to thank: Kris Pister, Thomas Watteyne, Xavier
3180 Vilajosana, Qin Wang, Tom Phinney, Robert Assimiti, Michael
3181 Richardson, Zhuo Chen, Malisa Vucinic, Alfredo Grieco, Martin Turon,
3182 Dominique Barthel, Elvis Vogli, Guillaume Gaillard, Herman Storey,
3183 Maria Rita Palattella, Nicola Accettura, Patrick Wetterwald, Pouria
3184 Zand, Raghuram Sudhaakar, and Shitanshu Shah for their participation
3185 and various contributions.
3187 10.5. Cellular Radio
3189 This section was derived from draft-korhonen-detnet-telreq-00.
3191 10.6. Industrial M2M
3193 The authors would like to thank Feng Chen and Marcel Kiessling for
3194 their comments and suggestions.
3196 10.7. Other
3198 This section was derived from draft-zha-detnet-use-case-00.
3200 This document has benefited from reviews, suggestions, comments and
3201 proposed text provided by the following members, listed in
3202 alphabetical order: Jing Huang, Junru Lin, Lehong Niu and Oilver
3203 Huang.
3205 11. Informative References
3207 [ACE] IETF, "Authentication and Authorization for Constrained
3208 Environments", .
3211 [bacnetip]
3212 ASHRAE, "Annex J to ANSI/ASHRAE 135-1995 - BACnet/IP",
3213 January 1999.
3215 [CCAMP] IETF, "Common Control and Measurement Plane",
3216 .
3218 [CoMP] NGMN Alliance, "RAN EVOLUTION PROJECT COMP EVALUATION AND
3219 ENHANCEMENT", NGMN Alliance NGMN_RANEV_D3_CoMP_Evaluation_
3220 and_Enhancement_v2.0, March 2015,
3221 .
3224 [CONTENT_PROTECTION]
3225 Olsen, D., "1722a Content Protection", 2012,
3226 .
3229 [CPRI] CPRI Cooperation, "Common Public Radio Interface (CPRI);
3230 Interface Specification", CPRI Specification V6.1, July
3231 2014, .
3234 [DCI] Digital Cinema Initiatives, LLC, "DCI Specification,
3235 Version 1.2", 2012, .
3237 [DICE] IETF, "DTLS In Constrained Environments",
3238 .
3240 [EA12] Evans, P. and M. Annunziata, "Industrial Internet: Pushing
3241 the Boundaries of Minds and Machines", November 2012.
3243 [ESPN_DC2]
3244 Daley, D., "ESPN's DC2 Scales AVB Large", 2014,
3245 .
3248 [flnet] Japan Electrical Manufacturers' Association, "JEMA 1479 -
3249 English Edition", September 2012.
3251 [Fronthaul]
3252 Chen, D. and T. Mustala, "Ethernet Fronthaul
3253 Considerations", IEEE 1904.3, February 2015,
3254 .
3257 [HART] www.hartcomm.org, "Highway Addressable remote Transducer,
3258 a group of specifications for industrial process and
3259 control devices administered by the HART Foundation".
3261 [I-D.finn-detnet-architecture]
3262 Finn, N., Thubert, P., and M. Teener, "Deterministic
3263 Networking Architecture", draft-finn-detnet-
3264 architecture-02 (work in progress), November 2015.
3266 [I-D.finn-detnet-problem-statement]
3267 Finn, N. and P. Thubert, "Deterministic Networking Problem
3268 Statement", draft-finn-detnet-problem-statement-04 (work
3269 in progress), October 2015.
3271 [I-D.ietf-6tisch-6top-interface]
3272 Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
3273 (6top) Interface", draft-ietf-6tisch-6top-interface-04
3274 (work in progress), July 2015.
3276 [I-D.ietf-6tisch-architecture]
3277 Thubert, P., "An Architecture for IPv6 over the TSCH mode
3278 of IEEE 802.15.4", draft-ietf-6tisch-architecture-09 (work
3279 in progress), November 2015.
3281 [I-D.ietf-6tisch-coap]
3282 Sudhaakar, R. and P. Zand, "6TiSCH Resource Management and
3283 Interaction using CoAP", draft-ietf-6tisch-coap-03 (work
3284 in progress), March 2015.
3286 [I-D.ietf-6tisch-terminology]
3287 Palattella, M., Thubert, P., Watteyne, T., and Q. Wang,
3288 "Terminology in IPv6 over the TSCH mode of IEEE
3289 802.15.4e", draft-ietf-6tisch-terminology-06 (work in
3290 progress), November 2015.
3292 [I-D.ietf-ipv6-multilink-subnets]
3293 Thaler, D. and C. Huitema, "Multi-link Subnet Support in
3294 IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
3295 progress), July 2002.
3297 [I-D.ietf-roll-rpl-industrial-applicability]
3298 Phinney, T., Thubert, P., and R. Assimiti, "RPL
3299 applicability in industrial networks", draft-ietf-roll-
3300 rpl-industrial-applicability-02 (work in progress),
3301 October 2013.
3303 [I-D.ietf-tictoc-1588overmpls]
3304 Davari, S., Oren, A., Bhatia, M., Roberts, P., and L.
3305 Montini, "Transporting Timing messages over MPLS
3306 Networks", draft-ietf-tictoc-1588overmpls-07 (work in
3307 progress), October 2015.
3309 [I-D.kh-spring-ip-ran-use-case]
3310 Khasnabish, B., hu, f., and L. Contreras, "Segment Routing
3311 in IP RAN use case", draft-kh-spring-ip-ran-use-case-02
3312 (work in progress), November 2014.
3314 [I-D.mirsky-mpls-residence-time]
3315 Mirsky, G., Ruffini, S., Gray, E., Drake, J., Bryant, S.,
3316 and S. Vainshtein, "Residence Time Measurement in MPLS
3317 network", draft-mirsky-mpls-residence-time-07 (work in
3318 progress), July 2015.
3320 [I-D.svshah-tsvwg-deterministic-forwarding]
3321 Shah, S. and P. Thubert, "Deterministic Forwarding PHB",
3322 draft-svshah-tsvwg-deterministic-forwarding-04 (work in
3323 progress), August 2015.
3325 [I-D.thubert-6lowpan-backbone-router]
3326 Thubert, P., "6LoWPAN Backbone Router", draft-thubert-
3327 6lowpan-backbone-router-03 (work in progress), February
3328 2013.
3330 [I-D.wang-6tisch-6top-sublayer]
3331 Wang, Q. and X. Vilajosana, "6TiSCH Operation Sublayer
3332 (6top)", draft-wang-6tisch-6top-sublayer-04 (work in
3333 progress), November 2015.
3335 [IEC61850-90-12]
3336 TC57 WG10, IEC., "IEC 61850-90-12 TR: Communication
3337 networks and systems for power utility automation - Part
3338 90-12: Wide area network engineering guidelines", 2015.
3340 [IEC62439-3:2012]
3341 TC65, IEC., "IEC 62439-3: Industrial communication
3342 networks - High availability automation networks - Part 3:
3343 Parallel Redundancy Protocol (PRP) and High-availability
3344 Seamless Redundancy (HSR)", 2012.
3346 [IEEE1588]
3347 IEEE, "IEEE Standard for a Precision Clock Synchronization
3348 Protocol for Networked Measurement and Control Systems",
3349 IEEE Std 1588-2008, 2008,
3350 .
3353 [IEEE1722]
3354 IEEE, "1722-2011 - IEEE Standard for Layer 2 Transport
3355 Protocol for Time Sensitive Applications in a Bridged
3356 Local Area Network", IEEE Std 1722-2011, 2011,
3357 .
3360 [IEEE19043]
3361 IEEE Standards Association, "IEEE 1904.3 TF", IEEE 1904.3,
3362 2015, .
3364 [IEEE802.1TSNTG]
3365 IEEE Standards Association, "IEEE 802.1 Time-Sensitive
3366 Networks Task Group", March 2013,
3367 .
3369 [IEEE802154]
3370 IEEE standard for Information Technology, "IEEE std.
3371 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
3372 and Physical Layer (PHY) Specifications for Low-Rate
3373 Wireless Personal Area Networks".
3375 [IEEE802154e]
3376 IEEE standard for Information Technology, "IEEE standard
3377 for Information Technology, IEEE std. 802.15.4, Part.
3378 15.4: Wireless Medium Access Control (MAC) and Physical
3379 Layer (PHY) Specifications for Low-Rate Wireless Personal
3380 Area Networks, June 2011 as amended by IEEE std.
3381 802.15.4e, Part. 15.4: Low-Rate Wireless Personal Area
3382 Networks (LR-WPANs) Amendment 1: MAC sublayer", April
3383 2012.
3385 [IEEE8021AS]
3386 IEEE, "Timing and Synchronizations (IEEE 802.1AS-2011)",
3387 IEEE 802.1AS-2001, 2011,
3388 .
3391 [IEEE8021CM]
3392 Farkas, J., "Time-Sensitive Networking for Fronthaul",
3393 Unapproved PAR, PAR for a New IEEE Standard;
3394 IEEE P802.1CM, April 2015,
3395 .
3398 [IEEE8021TSN]
3399 IEEE 802.1, "The charter of the TG is to provide the
3400 specifications that will allow time-synchronized low
3401 latency streaming services through 802 networks.", 2016,
3402 .
3404 [IETFDetNet]
3405 IETF, "Charter for IETF DetNet Working Group", 2015,
3406 .
3408 [ISA100] ISA/ANSI, "ISA100, Wireless Systems for Automation",
3409 .
3411 [ISA100.11a]
3412 ISA/ANSI, "Wireless Systems for Industrial Automation:
3413 Process Control and Related Applications - ISA100.11a-2011
3414 - IEC 62734", 2011, .
3417 [ISO7240-16]
3418 ISO, "ISO 7240-16:2007 Fire detection and alarm systems --
3419 Part 16: Sound system control and indicating equipment",
3420 2007, .
3423 [knx] KNX Association, "ISO/IEC 14543-3 - KNX", November 2006.
3425 [lontalk] ECHELON, "LonTalk(R) Protocol Specification Version 3.0",
3426 1994.
3428 [LTE-Latency]
3429 Johnston, S., "LTE Latency: How does it compare to other
3430 technologies", March 2014,
3431 .
3434 [MEF] MEF, "Mobile Backhaul Phase 2 Amendment 1 -- Small Cells",
3435 MEF 22.1.1, July 2014,
3436 .
3439 [METIS] METIS, "Scenarios, requirements and KPIs for 5G mobile and
3440 wireless system", ICT-317669-METIS/D1.1 ICT-
3441 317669-METIS/D1.1, April 2013, .
3444 [modbus] Modbus Organization, "MODBUS APPLICATION PROTOCOL
3445 SPECIFICATION V1.1b", December 2006.
3447 [net5G] Ericsson, "5G Radio Access, Challenges for 2020 and
3448 Beyond", Ericsson white paper wp-5g, June 2013,
3449 .
3451 [NGMN] NGMN Alliance, "5G White Paper", NGMN 5G White Paper v1.0,
3452 February 2015, .
3455 [PCE] IETF, "Path Computation Element",
3456 .
3458 [profibus]
3459 IEC, "IEC 61158 Type 3 - Profibus DP", January 2001.
3461 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
3462 Requirement Levels", BCP 14, RFC 2119,
3463 DOI 10.17487/RFC2119, March 1997,
3464 .
3466 [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
3467 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
3468 December 1998, .
3470 [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
3471 "Definition of the Differentiated Services Field (DS
3472 Field) in the IPv4 and IPv6 Headers", RFC 2474,
3473 DOI 10.17487/RFC2474, December 1998,
3474 .
3476 [RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
3477 Label Switching Architecture", RFC 3031,
3478 DOI 10.17487/RFC3031, January 2001,
3479 .
3481 [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
3482 and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
3483 Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
3484 .
3486 [RFC3393] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
3487 Metric for IP Performance Metrics (IPPM)", RFC 3393,
3488 DOI 10.17487/RFC3393, November 2002,
3489 .
3491 [RFC3444] Pras, A. and J. Schoenwaelder, "On the Difference between
3492 Information Models and Data Models", RFC 3444,
3493 DOI 10.17487/RFC3444, January 2003,
3494 .
3496 [RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
3497 RFC 3972, DOI 10.17487/RFC3972, March 2005,
3498 .
3500 [RFC3985] Bryant, S., Ed. and P. Pate, Ed., "Pseudo Wire Emulation
3501 Edge-to-Edge (PWE3) Architecture", RFC 3985,
3502 DOI 10.17487/RFC3985, March 2005,
3503 .
3505 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
3506 Architecture", RFC 4291, DOI 10.17487/RFC4291, February
3507 2006, .
3509 [RFC4553] Vainshtein, A., Ed. and YJ. Stein, Ed., "Structure-
3510 Agnostic Time Division Multiplexing (TDM) over Packet
3511 (SAToP)", RFC 4553, DOI 10.17487/RFC4553, June 2006,
3512 .
3514 [RFC4903] Thaler, D., "Multi-Link Subnet Issues", RFC 4903,
3515 DOI 10.17487/RFC4903, June 2007,
3516 .
3518 [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
3519 over Low-Power Wireless Personal Area Networks (6LoWPANs):
3520 Overview, Assumptions, Problem Statement, and Goals",
3521 RFC 4919, DOI 10.17487/RFC4919, August 2007,
3522 .
3524 [RFC5086] Vainshtein, A., Ed., Sasson, I., Metz, E., Frost, T., and
3525 P. Pate, "Structure-Aware Time Division Multiplexed (TDM)
3526 Circuit Emulation Service over Packet Switched Network
3527 (CESoPSN)", RFC 5086, DOI 10.17487/RFC5086, December 2007,
3528 .
3530 [RFC5087] Stein, Y(J)., Shashoua, R., Insler, R., and M. Anavi,
3531 "Time Division Multiplexing over IP (TDMoIP)", RFC 5087,
3532 DOI 10.17487/RFC5087, December 2007,
3533 .
3535 [RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
3536 Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
3537 DOI 10.17487/RFC6282, September 2011,
3538 .
3540 [RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
3541 Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
3542 JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
3543 Low-Power and Lossy Networks", RFC 6550,
3544 DOI 10.17487/RFC6550, March 2012,
3545 .
3547 [RFC6551] Vasseur, JP., Ed., Kim, M., Ed., Pister, K., Dejean, N.,
3548 and D. Barthel, "Routing Metrics Used for Path Calculation
3549 in Low-Power and Lossy Networks", RFC 6551,
3550 DOI 10.17487/RFC6551, March 2012,
3551 .
3553 [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
3554 Bormann, "Neighbor Discovery Optimization for IPv6 over
3555 Low-Power Wireless Personal Area Networks (6LoWPANs)",
3556 RFC 6775, DOI 10.17487/RFC6775, November 2012,
3557 .
3559 [RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
3560 IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
3561 Internet of Things (IoT): Problem Statement", RFC 7554,
3562 DOI 10.17487/RFC7554, May 2015,
3563 .
3565 [SRP_LATENCY]
3566 Gunther, C., "Specifying SRP Latency", 2014,
3567 .
3570 [STUDIO_IP]
3571 Mace, G., "IP Networked Studio Infrastructure for
3572 Synchronized & Real-Time Multimedia Transmissions", 2007,
3573 .
3576 [SyncE] ITU-T, "G.8261 : Timing and synchronization aspects in
3577 packet networks", Recommendation G.8261, August 2013,
3578 .
3580 [TEAS] IETF, "Traffic Engineering Architecture and Signaling",
3581 .
3583 [TS23401] 3GPP, "General Packet Radio Service (GPRS) enhancements
3584 for Evolved Universal Terrestrial Radio Access Network
3585 (E-UTRAN) access", 3GPP TS 23.401 10.10.0, March 2013.
3587 [TS25104] 3GPP, "Base Station (BS) radio transmission and reception
3588 (FDD)", 3GPP TS 25.104 3.14.0, March 2007.
3590 [TS36104] 3GPP, "Evolved Universal Terrestrial Radio Access
3591 (E-UTRA); Base Station (BS) radio transmission and
3592 reception", 3GPP TS 36.104 10.11.0, July 2013.
3594 [TS36133] 3GPP, "Evolved Universal Terrestrial Radio Access
3595 (E-UTRA); Requirements for support of radio resource
3596 management", 3GPP TS 36.133 12.7.0, April 2015.
3598 [TS36211] 3GPP, "Evolved Universal Terrestrial Radio Access
3599 (E-UTRA); Physical channels and modulation", 3GPP
3600 TS 36.211 10.7.0, March 2013.
3602 [TS36300] 3GPP, "Evolved Universal Terrestrial Radio Access (E-UTRA)
3603 and Evolved Universal Terrestrial Radio Access Network
3604 (E-UTRAN); Overall description; Stage 2", 3GPP TS 36.300
3605 10.11.0, September 2013.
3607 [TSNTG] IEEE Standards Association, "IEEE 802.1 Time-Sensitive
3608 Networks Task Group", 2013,
3609 .
3611 [UHD-video]
3612 Holub, P., "Ultra-High Definition Videos and Their
3613 Applications over the Network", The 7th International
3614 Symposium on VICTORIES Project PetrHolub_presentation,
3615 October 2014, .
3618 [WirelessHART]
3619 www.hartcomm.org, "Industrial Communication Networks -
3620 Wireless Communication Network and Communication Profiles
3621 - WirelessHART - IEC 62591", 2010.
3623 Authors' Addresses
3624 Ethan Grossman (editor)
3625 Dolby Laboratories, Inc.
3626 1275 Market Street
3627 San Francisco, CA 94103
3628 USA
3630 Phone: +1 415 645 4726
3631 Email: ethan.grossman@dolby.com
3632 URI: http://www.dolby.com
3634 Craig Gunther
3635 Harman International
3636 10653 South River Front Parkway
3637 South Jordan, UT 84095
3638 USA
3640 Phone: +1 801 568-7675
3641 Email: craig.gunther@harman.com
3642 URI: http://www.harman.com
3644 Pascal Thubert
3645 Cisco Systems, Inc
3646 Building D
3647 45 Allee des Ormes - BP1200
3648 MOUGINS - Sophia Antipolis 06254
3649 FRANCE
3651 Phone: +33 497 23 26 34
3652 Email: pthubert@cisco.com
3654 Patrick Wetterwald
3655 Cisco Systems
3656 45 Allees des Ormes
3657 Mougins 06250
3658 FRANCE
3660 Phone: +33 4 97 23 26 36
3661 Email: pwetterw@cisco.com
3662 Jean Raymond
3663 Hydro-Quebec
3664 1500 University
3665 Montreal H3A3S7
3666 Canada
3668 Phone: +1 514 840 3000
3669 Email: raymond.jean@hydro.qc.ca
3671 Jouni Korhonen
3672 Broadcom Corporation
3673 3151 Zanker Road
3674 San Jose, CA 95134
3675 USA
3677 Email: jouni.nospam@gmail.com
3679 Yu Kaneko
3680 Toshiba
3681 1 Komukai-Toshiba-cho, Saiwai-ku, Kasasaki-shi
3682 Kanagawa, Japan
3684 Email: yu1.kaneko@toshiba.co.jp
3686 Subir Das
3687 Applied Communication Sciences
3688 150 Mount Airy Road, Basking Ridge
3689 New Jersey, 07920, USA
3691 Email: sdas@appcomsci.com
3693 Yiyong Zha
3694 Huawei Technologies
3696 Email: zhayiyong@huawei.com
3698 Balazs Varga
3699 Ericsson
3700 Konyves Kalman krt. 11/B
3701 Budapest 1097
3702 Hungary
3704 Email: balazs.a.varga@ericsson.com
3705 Janos Farkas
3706 Ericsson
3707 Konyves Kalman krt. 11/B
3708 Budapest 1097
3709 Hungary
3711 Email: janos.farkas@ericsson.com
3713 Franz-Josef Goetz
3714 Siemens
3715 Gleiwitzerstr. 555
3716 Nurnberg 90475
3717 Germany
3719 Email: franz-josef.goetz@siemens.com
3721 Juergen Schmitt
3722 Siemens
3723 Gleiwitzerstr. 555
3724 Nurnberg 90475
3725 Germany
3727 Email: juergen.jues.schmitt@siemens.com