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'8' -- Possible downref: Non-RFC (?) normative reference: ref. '9' Summary: 11 errors (**), 0 flaws (~~), 3 warnings (==), 10 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Internet Engineering Task Force A. Ghanwani 3 INTERNET DRAFT J. W. Pace 4 V. Srinivasan 5 IBM 6 April 1997 8 A Framework for Providing Integrated Services 9 Over Shared and Switched LAN Technologies 11 draft-ietf-issll-is802-framework-01.txt 13 Status of This Memo 15 This document is an Internet-Draft. Internet Drafts are working 16 documents of the Internet Engineering Task Force (IETF), its areas, 17 and its working groups. Note that other groups may also distribute 18 working documents as Internet Drafts. 20 Internet Drafts are draft documents valid for a maximum of six 21 months, and may be updated, replaced, or obsoleted by other documents 22 at any time. It is not appropriate to use Internet Drafts as 23 reference material, or to cite them other than as a ``working draft'' 24 or ``work in progress.'' 26 To learn the current status of any Internet-Draft, please check 27 the ``1id-abstracts.txt'' listing contained in the internet-drafts 28 Shadow Directories on ds.internic.net (US East Coast), nic.nordu.net 29 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 30 Rim). 32 Abstract 34 Traditionally, LAN technologies such as ethernet and token ring have 35 been required to handle best effort services only. No standard 36 mechanism exists for providing service guarantees on these media as 37 will be required by emerging and future multimedia applications. The 38 anticipated demand for such applications on the Internet has led 39 to the development of RSVP, a signaling mechanism for performing 40 resource reservation in the Internet. Concurrently, the Integrated 41 Services working group within the IETF has been working on the 42 definition of service classes called Integrated Services which are 43 expected to make use of RSVP. Applications will use these service 44 classes in order to obtain the desired quality of service from the 45 network. LAN technologies such as token ring and ethernet typically 46 constitute the last hop in Internet connections. It is therefore 47 necessary to enhance these technologies so that they are able to 48 support the Integrated Services. This memo describes a framework for 49 providing the functionality to support Integrated Services on shared 50 and switched LAN technologies. 52 1. Introduction 54 The Internet has traditionally provided support for best effort 55 traffic only. However, with the recent advances in link layer 56 technology, and with numerous emerging real-time applications such 57 as video conferencing and Internet telephony, there has been much 58 interest for developing mechanisms which enable real-time services 59 over the Internet. These new requirements have led to the design of 60 the Resource ReSerVation Protocol (RSVP) [3], a signaling mechanism 61 for providing resource reservation on the Internet. The protocol 62 is currently being standardized by the IETF. Simultaneously, the 63 Integrated Services working group of the IETF has been working on 64 the specification of various service classes. Each of these service 65 classes is designed to provide certain Quality of Service (QoS) 66 guarantees to traffic conforming to a specified set of parameters. 67 Applications are expected to use one of these classes depending on 68 their QoS requirements. 70 There is no standard mechanism for providing service guarantees on 71 LAN technologies such as ethernet and token ring. They, however, 72 typically constitute the last hop between users and the Internet 73 backbone. Furthermore, the development of standards for high speed 74 LANs such as gigabit ethernet favors the likelihood that these 75 technologies will eventually be deployed in the backbone of campus 76 networks. It is therefore necessary to enhance these technologies so 77 that they are able to support end-to-end service guarantees such as 78 those defined by the Integrated Services. 80 In order to support real-time services, there must be some mechanism 81 for resource management at the link level. Resource management 82 in this context encompasses the functions of admission control, 83 scheduling, traffic policing, etc. The ISSLL (Integrated Services 84 over Specific Link Layers) working group in the IETF was chartered 85 with the purpose of exploring and standardizing such mechanisms for 86 various link layer technologies. 88 This document is concerned with specifying a framework for providing 89 Integrated Services over shared and switched LAN technologies such 90 as ethernet/802.3, token ring/802.5, FDDI, etc. We begin with a 91 list of definitions in Section 2. Section 3 lists the requirements 92 and goals for a mechanism capable of providing Integrated Services 93 in a subnet. We then discuss a taxonomy of topologies for the LAN 94 technologies under consideration with an emphasis on the capabilities 95 of each which can be leveraged for enabling Integrated Services. The 96 resource management functions outlined in Section 3 are expected 97 to be provided by an entity which, in this document, is referred 98 to as the Bandwidth Manager (BM). The various components of the 99 Bandwidth Manager are discussed in the following section and some 100 examples of the implementation of the Bandwidth Manager are provided. 101 Some issues with respect to link layer support for Integrated 102 Services are examined in Section 6. In the development of this 103 framework, no assumptions have been made about the technology or 104 topology at the link layer. The framework is intended to be as 105 exhaustive as possible; this means that it is possible that all the 106 functions discussed may not be supportable by a particular topology 107 or technology, but this should not preclude the usage of this model 108 for it. 110 2. Definitions 112 The following is a list of the terms used in this document. 114 - End Station: A device (e.g. router, host) which runs the 115 application program or higher layer protocol which needs to make 116 reservations. 118 - Link Layer/Layer 2: The data link layer. This memo is concerned 119 with link layer technologies such as ethernet, token ring, and 120 FDDI. 122 - Link Layer Domain: A an interconnection of segments and 123 bridges/switches between two end stations. 125 - Segment: A link which is shared by one or more senders. 127 - Traffic Class: A category of flows which are given similar 128 service within a bridge/switch. 130 3. Supporting Integrated Services Within a Subnet: Requirements and 131 Goals 133 This section discusses the requirements and goals which should drive 134 the design of an architecture for supporting Integrated Services over 135 LAN technologies. The requirements refer to functions and features 136 which must be supported, while goals refer to functions and features 137 which are desirable, but are not an absolute necessity. Many of the 138 requirements and goals are driven by the functionality supported by 139 RSVP. 141 3.1. Requirements 143 - Resource Reservation: The mechanism must be capable of reserving 144 resources on a single segment or multiple segments and at 145 bridges/switches connecting them. It must be able to provide 146 reservations for both unicast and multicast sessions. It should 147 be possible to change the level of reservation while the session 148 is in progress. 150 - Admission Control: The mechanism must be able to estimate 151 the level of resources necessary to meet the QoS requested by 152 the session in order to decide whether or not the session can 153 be admitted. For the purpose of management, it is useful to 154 provide the ability to respond to queries about availability of 155 resources. It must be able to make admission control decisions 156 for different types of QoS such as guaranteed delay, guaranteed 157 bandwidth, etc. 159 - Flow Separation and Scheduling: It is necessary to provide a 160 mechanism for traffic flow separation so that real-time flows can 161 be given preferential treatment over best effort flows. Packets 162 of real-time flows can then be isolated and scheduled according 163 to their service requirements. Scheduling algorithms can range 164 from simple static priority queueing to more complex algorithms 165 such as weighted fair queueing and its variants. 167 - Policing: Traffic policing must be performed in order to ensure 168 that sources adhere to their negotiated traffic specifications. 169 Policing must be implemented at the sources and must ensure 170 that violating traffic is either dropped or transmitted as best 171 effort. Policing may optionally be implemented in the bridges 172 and switches. Alternatively, traffic may be shaped to insure 173 conformance to the negotiated parameters. 175 - Soft State: The mechanism must maintain soft state information 176 about the reservations. This means that state information must 177 be periodically refreshed if the reservation is to be maintained; 178 otherwise the state information and reservation will expire after 179 some pre-specified interval. 181 - Centralized or Distributed Implementation: In the case of a 182 centralized implementation, a single entity manages the resources 183 of the entire subnet. This approach has the advantage of being 184 easier to deploy since bridges and switches may not need to be 185 upgraded with additional functionality. However, this approach 186 scales poorly with geographical size of the subnet and the number 187 of hosts attached. In a fully distributed implementation, each 188 segment will have a local entity managing its resources. This 189 approach has better scalability than the former. However, it 190 requires that all bridges and switches in the network support 191 new mechanisms. It is also possible to have a semi-distributed 192 implementation where there is most than one entity, each managing 193 the resources of a subset of segments and bridges/switches 194 within the subnet. Ideally, implementation should be flexible; 195 i.e. a centralized approach may be used for small subnets and a 196 distributed approach can be used for larger subnets. Examples 197 of centralized and distributed implementations are discussed in 198 Section 4. 200 - Fault Tolerance and Recovery: The mechanism must be able to 201 function in the presence of failures; i.e. there should not 202 be a single point of failure. For instance, in a centralized 203 implementation, some mechanism must be specified for back-up and 204 recovery in the event of failure. 206 - Network Management: The MIBs supported must be specified. 208 - Interaction with Existing Resource Management Controls: The 209 interaction with existing infrastructure for resource management 210 needs to be specified. For example, FDDI has a resource 211 management mechanism called the "Synchronous Bandwidth Manager". 212 The mechanism must be designed so that it takes advantage of, 213 and specifies the interaction with, existing controls where 214 available. 216 3.2. Goals 218 - Independence from higher layer protocols: The mechanism should, 219 as far as possible, be independent of higher layer protocols 220 such as RSVP and IP. Independence from RSVP is desirable so that 221 it can interwork with other reservation protocols such as STII. 222 Independence from IP is desirable so that it can interwork with 223 network layer protocols such as IPX, NetBIOS, etc. 225 - Receiver heterogeneity: Receiver heterogeneity refers to 226 multicast communication where different receivers request 227 different levels of service. For example, in a multicast 228 group with many receivers, it is possible that one of the 229 receivers desires a lower delay bound than the others. A 230 better delay bound may be provided by increasing the amount 231 of resources reserved along the path to that receiver while 232 leaving the reservations for the other receivers unchanged. 233 In its most complex form, receiver heterogeneity implies the 234 ability to simultaneously provide various levels of service as 235 requested by different receivers. In its simplest form, receiver 236 heterogeneity will allow a scenario where some of the receivers 237 use best effort service and those requiring service guarantees 238 make a reservation. Receiver heterogeneity, especially for the 239 reserved/best effort scenario, is a very desirable function. 241 More details on supporting receiver heterogeneity are provided in 242 Section 6. 244 - Support for different filter styles: It is desirable to provide 245 support for the different filter styles defined by RSVP such as 246 fixed filter, shared explicit and shared wildcard. Some of the 247 issues with respect to supporting such filter styles in the link 248 layer domain are examined in Section 6. 250 - Scalability: The mechanism and protocols should have a low 251 overhead and should scale to the largest receiver groups likely 252 to occur within a single link layer domain. 254 - Path Selection: In source routed LAN technologies such as token 255 ring/802.5, it may be useful for the mechanism to incorporate the 256 function of path selection. Using an appropriate path selection 257 mechanism will optimize utilization of network resources. 259 4. LAN Topologies and Their Features 261 As stated earlier, this memo is concerned with specifying a framework 262 for supporting Integrated Services in LAN technologies such as 263 ethernet/IEEE 802.3, token ring/IEEE 802.5, and FDDI. The extent 264 to which service guarantees can be provided by a network depend to 265 a large degree on the ability to provide the key functions of flow 266 identification and scheduling in addition to admission control and 267 policing. This section discusses some of the capabilities of these 268 LAN technologies and provides a taxonomy of possible topologies 269 emphasizing the capabilities of each with regard to supporting the 270 above functions. 272 For the technologies considered here, the basic topology of a LAN 273 may be shared, switched half duplex or switched full duplex. In the 274 shared topology, multiple senders share a single segment. Contention 275 for media access is resolved using protocols such as CSMA/CD in 276 ethernet and token passing in token ring and FDDI. Switched half 277 duplex, is essentially a shared topology with the restriction that 278 there are only two transmitters contending for resources on any 279 segment. This topology is fast becoming popular with the need for 280 increased bandwidth. Finally, in a switched full duplex topology, a 281 full bandwidth path is available to the transmitter at each end of 282 the link at all times. Therefore, in this topology, there is no need 283 for any access control mechanism such as CSMA/CD or token passing as 284 there is no contention between the transmitters. 286 Another important element in the discussion of topologies is the 287 support for multiple traffic classes. Traffic classes provide a 288 coarse method for isolation between flows and allows the possibility 289 to easily support scheduling algorithms in order to meet service 290 requirements. Native ethernet/802.3 does not support multiple 291 traffic classes. Token ring/802.5 and FDDI on the other hand 292 provides support for traffic classes. Three bits of the Frame 293 Control field are used to indicate the Frame Priority which may be 294 mapped to a traffic class as appropriate. Equally important in 295 token ring networks are the notions of Reserved Priority and Access 296 Priority. Reserved Priority relates to the value of priority which 297 a station uses to reserve the token for the next transmission on 298 the ring. When a free token is circulating, only a station having 299 an Access Priority greater than or equal to the Reserved Priority 300 in the token will be allowed to seize the token for transmission. 301 More recently, the IEEE 802 Standards Committee has been working on 302 the a 802.1p, a standard for expedited traffic classes and dynamic 303 multicast filtering in bridges and switches [1]. The proposed 304 standard requires a new frame format for ethernet in which three 305 bits are used for indicating the User Priority which may be mapped 306 to an appropriate traffic class. Up to eight traffic classes may 307 be supported. The actual number of traffic classes supported is 308 an implementation option. Further, the emerging standard does not 309 specify scheduling algorithms between traffic classes. 311 Depending on the basic topology used and the ability to support 312 traffic classes, there are six possible scenarios as follows: 314 1. Shared topology without traffic classes: This category includes 315 pure shared media such as ethernet/802.3 networks which are 316 multi-access technologies with no support for priority signaling 317 and traffic classes. Shared topology without traffic classes 318 offers little capability for isolation between reserved and 319 unreserved flows. No service guarantees can be provided in 320 this scenario without modification to the basic transmission 321 mechanisms. 323 2. Shared topology with traffic classes: This category includes 324 ethernet/802.3 networks which implement the emerging IEEE 325 802.1p standard, as well as token ring/802.5 and FDDI networks. 326 Even with support for traffic classes, shared ethernet can at 327 best offer loose statistical service guarantees because of the 328 non-deterministic nature of the CSMA/CD protocol. On the other 329 hand, better guarantees can be provided on token ring media if 330 the Frame Priority, Reserved Priority and Access Priority are 331 used in conjunction with appropriate controls. 333 3. Switched half duplex topology without traffic classes: This 334 scenario is a special case of shared topology without traffic 335 classes where there are only two senders contending for resources 336 on any segment (a host and a switch or two switches). This 337 topology provides higher bandwidth per station and fewer 338 collisions. Due to the use of the CSMA/CD protocol and the lack 339 of traffic classes, little can be done to isolate flows and 340 provide scheduling. 342 4. Switched half duplex topology with traffic classes: This 343 scenario is a special case of shared topology with priority 344 but there are now only two senders contending for resources 345 on any segment. This reduces the contention for resources. 346 Ethernet/802.3 networks with this topology will likely be 347 able to support better statistical service guarantees than 348 the corresponding shared topology. Better guarantees will be 349 possible for token ring/802.5 media with this topology. 351 5. Switched full duplex topology without traffic classes: This 352 scenario includes switched ethernet/802.3 and token ring/802.5 353 where the access control protocol is no longer used since a full 354 bandwidth path is available to each transmitter. However, since 355 traffic classes are not available, it is not possible to isolate 356 flows for scheduling. 358 6. Switched full duplex topology with traffic classes: This 359 category is similar to the above, but traffic classes are 360 also available. This topology is the most capable in terms of 361 link layer functions that can be exploited for supporting the 362 functions of flow separation and scheduling. 364 There is also the possibility of hybrid topologies where two or more 365 of the above coexist. For instance, it is possible that within a 366 single subnet, there are some bridges/switches which support traffic 367 classes and some which do not. If the flow in question traverses 368 both kinds of bridges/switches in the network, the least common 369 denominator will prevail. In other words, as far as that flow is 370 concerned, the network is of the type corresponding to the least 371 capable topology that is traversed. 373 Note that even within the different switched topologies categorized 374 above, there are likely to be switches having varied capabilities 375 with respect to providing functions such as receiver heterogeneity 376 and the ability to dedicate resources such as buffering and 377 scheduling algorithms for supporting the various Integrated Services. 378 Future work on service mappings in the ISSLL working group will 379 elaborate on these issues. 381 5. Architecture for Supporting Integrated Services in LANs 383 The functional requirements described in Section 3 will be performed 384 by an entity which we refer to as the Bandwidth Manager (BM). The BM 385 is responsible for providing mechanisms for an application or higher 386 layer protocol to request QoS from the network. For architectural 387 purposes, the BM consists of the following components. 389 5.1. Components of the Bandwidth Manager 391 5.1.1. Requester Module 393 The Requester Module (RM) resides in every end station in the subnet. 394 One of its functions is to provide an interface between applications 395 or higher layer protocols such as RSVP, STII, SNMP, etc. and the BM. 396 An application can invoke the various functions of the BM by using 397 the primitives for communication with the RM and providing it with 398 the appropriate parameters. To initiate a reservation, in the link 399 layer domain, the following parameters must be passed to the RM: the 400 service desired (Guaranteed Service or Controlled Load), the traffic 401 descriptors contained in the TSpec, and an RSpec specifying the 402 amount of resources to be reserved [8]. More information on these 403 parameters may be found in the relevant Integrated Services documents 404 [8,9]. When RSVP is used for signaling at the network layer, this 405 information is available and needs to be extracted from the RSVP PATH 406 and RSVP RESV messages (See [7] for details). In addition to these 407 parameters, the network layer addresses of the end points must be 408 specified. The RM must then translate the network layer addresses 409 to link layer addresses and convert the request into an appropriate 410 format which is understood by other components of the BM responsible 411 admission control. The RM is also responsible for returning the 412 status of requests processed by the BM to the invoking application or 413 higher layer protocol. 415 5.1.2. Bandwidth Allocator 417 The Bandwidth Allocator (BA) is responsible for performing admission 418 control and maintaining state about the allocation of resources 419 in the subnet. An end station can request various services, e.g. 420 bandwidth reservation, modification of an existing reservation, 421 queries about resource availability, etc. These requests are 422 processed by the BA. The communication between the end station and 423 the BA takes place through the RM. The location of the BA will 424 depend largely on the implementation method. In a centralized 425 implementation, the BA may reside on a single station in the 426 subnet. In a distributed implementation, the functions of the BA 427 may be distributed in all the end stations and bridges/switches as 428 necessary. The BA is also responsible for deciding how to label 429 flows, e.g. based on the admission control decision, the BA may 430 indicate to the RM that packets belonging to a particular flow be 431 tagged with some priority value which maps to the appropriate traffic 432 class. 434 5.1.3. Communication Protocols and Primitives 436 The protocols and primitives for communication between the various 437 components of the BM must be specified. These include the following: 439 - Communication between the higher layer protocols and the RM: 440 The BM must define primitives for the application to initiate 441 reservations, query the BA about available resources, and 442 change or delete reservations, etc. These primitives could be 443 implemented as an API for an application to invoke functions of 444 the BM via the RM. 446 - Communication between the RM and the BA: A signaling mechanism 447 must be defined for the communication between the RM and the BA. 448 This protocol will specify the messages which must be exchanged 449 between the RM and the BA in order to service various requests by 450 the higher layer entity. 452 - Communication between peer BAs: If there is more than one BA in 453 the subnet, a means must be specified for inter-BA communication. 454 Specifically, the BAs must be able to decide among themselves 455 about which BA would be responsible for which segments and 456 bridges or switches. Further, if a request is made for resource 457 reservation along the domain of multiple BAs, the BAs must be 458 able to handle such a scenario correctly. Inter-BA communication 459 will also be responsible for back-up and recovery in the event of 460 failure. 462 5.2. Implementation Scenarios 464 Example scenarios are provided showing the location of the the 465 components of the bandwidth manager in centralized and fully 466 distributed implementations. Note that in either case, the RM must 467 be present in all end stations which desire to make reservations. 468 Essentially, centralized or distributed refers to the implementation 469 of the BA, the component responsible for resource reservation 470 and admission control. In the figures below, "App" refers to 471 the application making use of the BM. It could either be a user 472 application, or a higher layer protocol process such as RSVP. 474 +---------+ 475 .-->| BA |<--. 476 / +---------+ \ 477 / .-->| Layer 2 |<--. \ 478 / / +---------+ \ \ 479 / / \ \ 480 / / \ \ 481 +---------+ / / \ \ +---------+ 482 | App |<----- /-/---------------------------\-\----->| App | 483 +---------+ / / \ \ +---------+ 484 | RM |<----. / \ .--->| RM | 485 +---------+ / +---------+ +---------+ \ +---------+ 486 | Layer 2 |<------>| Layer 2 |<------>| Layer 2 |<------>| Layer 2 | 487 +---------+ +---------+ +---------+ +---------+ 489 RSVP Host/ Intermediate Intermediate RSVP Host/ 490 Router Bridge/Switch Bridge/Switch Router 492 Figure 1: Bandwidth Manager with a centralized Bandwidth Allocator 494 Figure 1 shows a centralized implementation where a single BA is 495 responsible for admission control decisions for the entire subnet. 496 Every end station contains an RM. Intermediate bridges and switches 497 in the network need not have any functions of the BM since they will 498 not be actively participating in admission control. The RM at the 499 end station requesting a reservation initiates communication with 500 its BA. For larger subnets, a single BA may not be able to handle 501 the reservations for the entire subnet. In that case it would be 502 necessary to deploy multiple BAs, each managing the resources of a 503 non-overlapping subset of segments. In a centralized implementation, 504 the BA must be able to access topology information such as link layer 505 spanning tree information in order to be able to reserve resources 506 on appropriate segments. Without this topology information, the BM 507 would have to reserve resources on the entire spanning tree for all 508 flows leading to an inefficient utilization of resources. 510 +---------+ +---------+ 511 | App |<-------------------------------------------->| App | 512 +---------+ +---------+ +---------+ +---------+ 513 | RM/BA |<------>| BA |<------>| BA |<------>| RM/BA | 514 +---------+ +---------+ +---------+ +---------+ 515 | Layer 2 |<------>| Layer 2 |<------>| Layer 2 |<------>| Layer 2 | 516 +---------+ +---------+ +---------+ +---------+ 518 RSVP Host/ Intermediate Intermediate RSVP Host/ 519 Router Bridge/Switch Bridge/Switch Router 521 Figure 2: Bandwidth Manager with a fully distributed Bandwidth 522 Allocator 524 Figure 2 depicts the scenario of a fully distributed bandwidth 525 manager. In this case, all devices in the subnet must have some BM 526 functionality. All the end hosts are still required to have an RM. 527 In addition, all bridges and switches must actively participate in 528 admission control. With this approach, the BA would need only local 529 topology information since each BA is responsible for the resources 530 on segments that are directly connected to it. This local topology 531 information, such as which ports are on the spanning tree and 532 which unicast addresses are reachable from which ports, is readily 533 available in existing bridges/switches. 535 Note that in the figures above, the arrows between peer layers are 536 used to indicate logical connectivity. 538 5.3. Logical Operation of the BM in End Stations and Link Layer Domain 540 The figure below shows the location and logical operation of the 541 BM in end stations and the link layer domain. It is not possible 542 to provide the details of physical flows because of the inherent 543 differences that arise in centralized and distributed implementations 544 as discussed in Section 5.2. 546 +-------------------------+ 547 | +--------+ +------+ | 548 | |Appli- <---> RM | | 549 | | cation | +--^---+ | 550 | +--------+ | | +-------------------------+ 551 | || +--V---+ | | +------+ | 552 | || +------| BA <------------------------> BA | | 553 | || | +------+ | | +----------+ +-^-^|-+ | 554 | || | | | | |Forwarding| | || | 555 | || | | | | |Process <---+ || | 556 | || | | | | +---|------+ || | 557 | || | | | | | +---------+| | 558 | \/ | | | | | | | | 559 | +-----V-+ +--V---+ | | +---V--V+ +----V-+ | 560 | |Class- | |Sched-| | | |Class- | |Sched-| | 561 | | ifier |===>| uler |==========>| ifier |===>| uler |====> 562 | +-------+ +------+ | | +-------+ +------+ | 563 +-------------------------+ +-------------------------+ 565 End Station Link Layer Domain 567 ----> Signaling/Control 568 ====> Data 570 Figure 3: The logical Operation of the BM in end stations and the 571 link layer domain. 573 The application, which may be RSVP or some other higher layer 574 reservation protocol requests resources by passing the relevant 575 parameters to the RM. The RM then starts the process of resource 576 reservation at the link layer by contacting the local BA. In the 577 case of a distributed implementation, The local BA is responsible 578 for admission control on the segment to which the end station is 579 directly attached. If the reservation succeeds, the local BA sets 580 up the classifier and scheduler as required so that the appropriate 581 priority is used for the flow. The request is then propagated 582 to the the "remote" BA controlling the other segments along the 583 forwarding path. In this case, it is possible to set up more complex 584 schedulers as well as policing at the bridges/switches since the 585 BA, which maintains the state, is co-located in every bridge/switch 586 and participates actively in the process of admission control. In 587 a centralized implementation, the BA resides in a server within the 588 subnet. The classifier and scheduler in the bridges/switches along 589 the forwarding path are implicitly set up by the priority carried in 590 the data frames if the reservation is successful. 592 6. Mapping Issues and Link Layer Support for IntServ Traffic Classes 594 As stated earlier, the Integrated Services working group has defined 595 various service classes offering varying degrees of QoS guarantees. 596 Initial effort will concentrate on enabling the Controlled Load 597 and Guaranteed Service classes [4,5]. The Controlled Load service 598 provides a loose guarantee, informally stated as "better than best 599 effort". The Guaranteed Service provides a delay bound which the 600 network guarantees will never be exceeded. The extent to which these 601 services can be supported at the link layer will depend on many 602 factors including the topology and technology used. Some of the 603 mapping issues are dicussed below in light of the emerging link layer 604 standards and the functions supported by higher layer protocols. 605 Considering the limitations of some of the topologies under 606 consideration, it may not be possible to satisfy all the requirements 607 for Integrated Services on a given topology. In such cases, it 608 is useful to consider providing support for an approximation of 609 the service which may suffice in most practical instances. For 610 example, it may not be feasible to provide policing/shaping at each 611 network element (bridge/switch) as required by the Controlled Load 612 specification [4]. But if this task is left to the end stations, a 613 reasonably good approximation to the service can be obtained. 615 6.1. Mapping of Services to Link Level Priority 617 The number of traffic classes supported and access methods of 618 the technology under consideration will determine how many and 619 what services may be supported. Native token ring/802.5, for 620 instance, supports eight priority levels which may be mapped to 621 one or more traffic classes. Ethernet/802.3 has no support for 622 signaling priorities within frames. However, the IEEE 802 standards 623 committee is working on a new standard for bridges/switches related 624 to multimedia traffic expediting and dynamic multicast filtering 625 [1]. These standards allow for eight levels of User Priority on all 626 media. The User Priority is signaled on an end-to-end basis, unless 627 overridden by bridge/switch management. 629 The priority that is used by a flow should depend on the quality of 630 service desired and whether the reservation was successful or not. 631 Therefore, a sender should use the a priority value which maps to 632 the best effort traffic class until told otherwise by the BM. The BM 633 will, upon successful completion of resource reservation, specify 634 the User Priority to be used by the sender for that session's data. 635 Future work in the ISSLL working group will address the issue of 636 mapping User Priority to traffic classes in the bridges/switches. 638 6.2. Supporting Receiver Heterogeneity 640 Receiver heterogeneity means that receivers within a group can each 641 have different QoS requirements; i.e. it is possible that, for a 642 given flow, some receivers make a reservation while others decide 643 to make use of best effort transport. RSVP allows heterogeneous 644 receivers within a group. However, handling the problem at layer 645 2 can be non-trivial. Consider for instance, the scenario in the 646 figure below. 648 +-----+ 649 | R1 | 650 +-----+ 651 | 652 v 653 +-----+ +-----+ +-----+ 654 | R2 |<-----| SW |----->| R3 | 655 +-----+ +-----+ +-----+ 657 Figure 4: An instance of receiver heterogeneity. R1 is the source. 658 R2 is a receiver which makes a reservation, and R3 is a receiver 659 which is satisfied with best effort service. SW is a Layer 2 device 660 (bridge/switch) participating in resource reservation. 662 In the figure above, R1 is the upstream end station and R2 and R3 663 are downstream end stations. R2 would like to make a reservation 664 for the flow while R3 would like to receive the flow using best 665 effort transport. R1 sends RSVP PATH messages which are multicast 666 to both R2 and R3. R2 sends an RSVP RESV message to R1 requesting 667 the reservation of resources. If the reservation is successful at 668 Layer 2, the frames addressed to the group will be categorized in 669 the traffic class corresponding to the service requested by R3. At 670 SW, there must be some mechanism which forwards the packet using 671 providing service corresponding to the reserved traffic class at the 672 interface to R3 while using the best effort traffic class at the 673 interface to R2. This may involve changing the contents of the frame 674 itself, or ignoring the frame priority at the interface to R2. 676 Another possibility for supporting heterogeneous receivers would be 677 to have separate groups with distinct addresses, one for each class 678 of service. By default, a receiver would join the "best effort" 679 group where the flow is classified as best effort. If the receiver 680 makes a reservation successfully, it can be transferred to the group 681 for the class of service desired. The dynamic multicast filtering 682 capabilities of bridges and switches implementing the emerging IEEE 683 802.1p standard would be a very useful feature in such a scenario. 684 A given flow would be transmitted only on those segments which are 685 on the path between the sender and the receivers of that flow. The 686 obvious disadvantage of such an approach is that the sender needs to 687 send out multiple copies of the same packet corresponding to each 688 class of service desired. 690 6.3. Support for Different Reservation Styles 692 +-----+ +-----+ +-----+ 693 | R1 | | R2 | | R3 | 694 +-----+ +-----+ +-----+ 695 | | | 696 | v | 697 | +-----+ | 698 +--------->| SW |<---------+ 699 +-----+ 700 | | 701 +----+ +----+ 702 | | 703 v V 704 +-----+ +-----+ 705 | R4 | | R5 | 706 +-----+ +-----+ 708 Figure 5: An illustration of filter styles. R1, R2, R3, R4 and R5 709 are RSVP end stations which are members of the same group. SW is a 710 bridge/switch in the link layer domain. 712 In the figure above, R1-R5 are end stations which are members of a 713 group associated with the same RSVP flow. R1, R2 and R3 are upstream 714 end stations. R4 and R5 are the downstream end stations which 715 receive traffic from all the senders. RSVP allows receivers R4 and 716 R5 to specify reservations which can apply to: (a) one specific 717 sender only (fixed filter); (b) any of two or more explicitly 718 specified senders (shared explicit filter); and (c) any sender in the 719 group (shared wildcard filter). Support for the fixed filter style 720 is straightforward; a separate reservation is made for the traffic 721 from each of the senders. However, support for the the other two 722 filter styles has implications regarding policing; i.e. the merged 723 flow from the different senders must be policed so that they conform 724 to traffic parameters specified in the filter's RSpec. This scenario 725 is further complicated if the services requested by R4 and R5 are 726 different. 728 7. Summary 730 This document has specified a framework for providing Integrated 731 Services over shared and switched LAN technologies. The ability to 732 provide QoS guarantees necessitates some form of admission control 733 and resource management. The requirements and goals of a resource 734 management scheme for subnets have been identified and discussed. 735 We refer to the entire resource management scheme as a Bandwidth 736 Manager. Architectural considerations were discussed and examples 737 were provided to illustrate possible implementations of a Bandwidth 738 Manager. Some of the issues involved in mapping the services from 739 higher layers to the link layer have also been discussed. 741 References 743 [1] IEEE Standards for Local and Metropolitan Area Networks: 744 Draft Standard for Traffic Class and Dynamic Multicast Filtering 745 Services in Bridged Local Area Networks (Draft Supplement to 746 802.1D), P802.1p/D5, February, 1997. 748 [2] IEEE Standards for Local and Metropolitan Area Networks: 749 Draft Standard for Virtual Bridged Local Area Networks, 750 P802.1Q/D5, February, 1997. 752 [3] B. Braden, L. Zhang, S. Berson, S. Herzog and S. Jamin, 753 "Resource Reservation Protocol (RSVP) - Version 1 Functional 754 Specification," Internet Draft, November 1996, 755 757 [4] J. Wroclawski, "Specification of the Controlled Load Network 758 Element Service," Internet Draft, November 1996, 759 761 [5] S. Shenker, C. Partridge and R. Guerin, "Specification of 762 Guaranteed Quality of Service," Internet Draft, August 1996, 763 765 [6] R. Braden, D. Clark and S. Shenker, "Integrated Services in the 766 Internet Architecture: An Overview," RFC 1633, June 1994. 768 [7] J. Wroclawski, "The Use of RSVP with IETF Integrated Services," 769 Internet Draft, October 1996, 771 [8] S. Shenker and J. Wroclawski, "Network Element Service 772 Specification Template", Internet Draft, November 1995, 773 775 [9] S. Shenker and J. Wroclawski, "General Characterization Parameters 776 for Integrated Service Network Elements", Internet Draft, 777 October 1996, 779 Acknowledgements 781 Much of the work presented in this document has benefited greatly 782 from discussion held at the meetings of the Integrated Services over 783 Specific Link Layers (ISSLL) working group. In particular we would 784 like to thank Eric Crawley, Don Hoffman, Mick Seaman, Andrew Smith 785 and Raj Yavatkar who have contributed to this effort via earlier 786 Internet drafts. 788 Authors' Address 790 Anoop Ghanwani 791 IBM Corporation 792 P. O. Box 12195 793 Research Triangle Park, NC 27709 794 Phone: +1-919-254-0260 795 Fax: +1-919-254-5410 796 Email: anoop@raleigh.ibm.com 798 Wayne Pace 799 IBM Corporation 800 P. O. Box 12195 801 Research Triangle Park, NC 27709 802 Phone: +1-919-254-4930 803 Fax: +1-919-254-5410 804 Email: pacew@raleigh.ibm.com 806 Vijay Srinivasan 807 IBM Corporation 808 P. O. Box 12195 809 Research Triangle Park, NC 27709 810 Phone: +1-919-254-2730 811 Fax: +1-919-254-5410 812 Email: vijay@raleigh.ibm.com