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2 nwcrg I. Swett
3 Internet-Draft Google
4 Intended status: Informational M-J. Montpetit
5 Expires: December 23, 2018 Triangle Video
6 V. Roca
7 INRIA
8 June 21, 2018
10 Coding for QUIC
11 draft-swett-nwcrg-coding-for-quic-01
13 Abstract
15 This document focusses on the integration of FEC coding in the QUIC
16 transport protocol, in order to recover from packet losses. This
17 document does not specify any FEC code but defines mechanisms to
18 negotiate and integrate FEC Schemes in QUIC. By using proactive loss
19 recovery, it is expected to improve QUIC performance in sessions
20 impacted by packet losses. More precisely it is expected to improve
21 QUIC performance with real-time sessions (since FEC coding makes
22 packet loss recovery insensitive to the round trip time), with
23 multicast sessions (since the same repair packet can recover several
24 different losses at several receivers), and with multipath sessions
25 (since repair packets add diversity).
27 Status of This Memo
29 This Internet-Draft is submitted in full conformance with the
30 provisions of BCP 78 and BCP 79.
32 Internet-Drafts are working documents of the Internet Engineering
33 Task Force (IETF). Note that other groups may also distribute
34 working documents as Internet-Drafts. The list of current Internet-
35 Drafts is at https://datatracker.ietf.org/drafts/current/.
37 Internet-Drafts are draft documents valid for a maximum of six months
38 and may be updated, replaced, or obsoleted by other documents at any
39 time. It is inappropriate to use Internet-Drafts as reference
40 material or to cite them other than as "work in progress."
42 This Internet-Draft will expire on December 23, 2018.
44 Copyright Notice
46 Copyright (c) 2018 IETF Trust and the persons identified as the
47 document authors. All rights reserved.
49 This document is subject to BCP 78 and the IETF Trust's Legal
50 Provisions Relating to IETF Documents
51 (https://trustee.ietf.org/license-info) in effect on the date of
52 publication of this document. Please review these documents
53 carefully, as they describe your rights and restrictions with respect
54 to this document. Code Components extracted from this document must
55 include Simplified BSD License text as described in Section 4.e of
56 the Trust Legal Provisions and are provided without warranty as
57 described in the Simplified BSD License.
59 Table of Contents
61 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
62 2. Definitions and Abbreviations . . . . . . . . . . . . . . . . 3
63 3. General Design Considerations . . . . . . . . . . . . . . . . 4
64 3.1. FEC Code versus FEC Scheme, Block Codes versus Sliding
65 Window Codes . . . . . . . . . . . . . . . . . . . . . . 4
66 3.2. FEC Scheme Negotiation . . . . . . . . . . . . . . . . . 4
67 3.3. FEC Protection Within an Encrypted Channel . . . . . . . 5
68 3.4. About Middleboxes . . . . . . . . . . . . . . . . . . . . 5
69 3.5. FEC Protection at the Stream Level . . . . . . . . . . . 5
70 3.6. About Gaps in the Set of Source Symbols Considered During
71 Encoding . . . . . . . . . . . . . . . . . . . . . . . . 5
72 4. FEC Scheme Negotiation in QUIC . . . . . . . . . . . . . . . 6
73 4.1. FEC Scheme Selection Process . . . . . . . . . . . . . . 7
74 4.2. FEC Scheme Configuration Information . . . . . . . . . . 7
75 5. Procedures when Protecting a Single QUIC Stream . . . . . . . 8
76 5.1. Application data, STREAM Frame data and Source Symbols . 8
77 5.2. Signaling Considerations within STREAM and REPAIR Frames 9
78 5.3. Management of Silent Periods and End of Stream . . . . . 10
79 6. Procedures when Protecting Several QUIC Streams . . . . . . . 11
80 6.1. Application data, STREAM Frame data and Source Symbols . 11
81 6.2. Block or Encoding Window Management . . . . . . . . . . . 11
82 6.3. Signaling Considerations within STREAM and REPAIR Frames 12
83 7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
84 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
85 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
86 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
87 10.1. Normative References . . . . . . . . . . . . . . . . . . 13
88 10.2. Informative References . . . . . . . . . . . . . . . . . 14
89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
91 1. Introduction
93 QUIC is a new transport that aims at improving network performance by
94 enabling out of order delivery, partial reliability, and methods of
95 recovery besides retransmission, while also improving security. This
96 document specifies a framework to enable FEC codes to be used to
97 recover from lost packets within a single QUIC stream or across
98 several QUIC streams.
100 The ability to add FEC coding in QUIC may be beneficial in several
101 situations:
103 o for a robust transmission of latency sensitive traffic, for
104 instance real-time flows, since it enables to recover packet
105 losses independently of the round trip time;
107 o for the transmission of contents to a large set of QUIC reception
108 endpoints, since the same repair frame may help recovering several
109 different packet losses at different receivers;
111 o for multipath communications, since repair traffic adds diversity.
113 This framework does not mandate the use of any specific FEC code
114 (i.e., how to encode and decode) nor FEC Scheme (i.e., that specifies
115 both a FEC code and how to use it, in particular in terms of
116 signaling). Instead it allows to negotiate the FEC Scheme to use at
117 session startup, assuming that more than one solution could
118 potentially be offered concurrently. Without loss of generality, we
119 assume that the encoding operations compute a linear combination of
120 QUIC packets, regardless of whether these codes are of block type (as
121 with Reed-Solomon codes [RFC5510]) or sliding window type (as with
122 RLC codes [RLC]).
124 2. Definitions and Abbreviations
126 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
127 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
128 document are to be interpreted as described in [RFC2119].
130 Terms and definitions that apply to coding are available in
131 [nc-taxonomy]. More specifically, this document uses the following
132 definitions:
134 Packet versus Symbol: a Packet is the unit of data that is exchanged
135 over the network while a Symbol is the unit of data that is
136 manipulated during the encoding and decoding operations
138 Source Symbol: a unit of data originating from the source that is
139 used as input to encoding operations
141 Repair Symbol: a unit of data that is the result of a coding
142 operation
144 This document uses the following abbreviations:
146 E: size of an encoding symbol (i.e., source or repair symbol),
147 assumed fixed (in bytes)
149 3. General Design Considerations
151 This section lists a few general considerations that govern the
152 framework for FEC coding support in QUIC.
154 3.1. FEC Code versus FEC Scheme, Block Codes versus Sliding Window
155 Codes
157 A FEC code specifies the details of encoding and decoding operations.
158 In addition to that, a FEC Scheme defines the additional protocol
159 aspects required to use a particular FEC code [nc-taxonomy]. In
160 particular the FEC Scheme defines signaling (e.g., information
161 contained in Source and Repair Packet header or trailers) needed to
162 synchronize encoders and decoders.
164 Block coding (e.g., Reed-Solomon [RFC5510]) and sliding window coding
165 (e.g., RLC [RLC]) are two broad classes of FEC codes [nc-taxonomy].
166 In the first case, the input flow must be first segmented into a
167 sequence of blocks, FEC encoding and decoding being performed
168 independently on a per-block basis. In the second case rely, a
169 sliding encoding window continuously slides over the input flow. It
170 is envisioned that the two classes of codes could be used to bring
171 FEC protection to QUIC, usually with an advantage for sliding window
172 codes when it comes to low latency communications.
174 3.2. FEC Scheme Negotiation
176 There are multiple FEC Scheme candidates. Therefore a negotiation
177 step is needed to select one or more codes to be used over a QUIC
178 session. This will be implemented using the one step negotiation of
179 the new QUIC negotiation mechanism [QUIC-transport], during the QUIC
180 handshake.
182 Editor's notes:
184 * It is likely that FEC Scheme negotiation requires the use of a
185 new dedicated Extension Frame Type. To Be Clarified and text
186 updated.
188 * It is not clear whether negotiation is meant to select a
189 **single** FEC Scheme or **multiple** FEC Schemes. In the
190 second case (multiple FEC) it is required to have a
191 complementary mechanism to indicate which FEC Scheme is used
192 in a given REPAIR frame (which could be done through as many
193 REPAIR frame type values as potential FEC Scheme negotiated).
194 Is it what we want to achieve? Not sure.
196 * It is not clear whether negotiation is carried out at QUIC
197 level (and therefore for multiple streams) or at a stream
198 level (and therefore multiple streams may use multiple FEC
199 Schemes). The terminology used above should be updated to
200 reflect the choice.
202 3.3. FEC Protection Within an Encrypted Channel
204 FEC encoding is applied before any QUIC encryption and authentication
205 processing. Source symbols, that constitute the data units used by
206 the FEC codec, contain cleartext application data.
208 3.4. About Middleboxes
210 The coding approach described in this document does not allow on path
211 elements (middleboxes) to take part in FEC protection. The traffic
212 being encrypted end-to-end, the middleboxes are not in position to
213 perform FEC decoding, nor to add any redundant traffic.
215 3.5. FEC Protection at the Stream Level
217 Streams in QUIC provide a lightweight, ordered byte-stream
218 abstraction. FEC encoding is applied at the stream level, within a
219 single stream or across two or more streams of the same QUIC session.
220 This is motivated by the fact that FEC protection is not necessarily
221 beneficial to all data streams, but only to a subset of them. For
222 instance FEC protection can be highly beneficial to live video
223 streams to which the proactive erasure correction feature of FEC,
224 independent of the RTT, should be highly beneficial. On the
225 opposite, FEC protection is probably less attractive for latency
226 insensitive bulk unicast flows.
228 In order to facilitate experiments, and in order to enable backward
229 compatibility, the STREAM frames that carry application data are kept
230 unmodified. On the opposite, frames that carry one or more repair
231 symbols use a dedicated REPAIR frame type, chosen within the type
232 range dedicated to "Extension Frames".
234 3.6. About Gaps in the Set of Source Symbols Considered During Encoding
236 A given FEC Scheme MAY support or not the presence of gaps in the set
237 of source symbols that constitute a block (for Block codes) or an
238 encoding window (for Sliding Window codes). A potential cause for
239 non contiguous sets of source symbols is the acknowledgment of one of
240 them. When this happens, the QUIC sending endpoint may want to
241 remove this source symbol from further FEC encodings. This is
242 particularly true with Sliding Window codes because of their
243 flexibility during FEC encoding (i.e., the encoding window can change
244 between two consecutive FEC encodings).
246 Supporting gaps can be motivated by the desire to reduce encoding and
247 decoding complexity since there are fewer variables. However this
248 choice has major consequences in terms of signaling. Indeed each
249 repair symbol transmitted MUST be accompanied with enough information
250 for the QUIC decoding endpoint to unambiguously identify the exact
251 composition of the block or encoding window. Without any gap, the
252 identity of the first source symbol plus the number of symbols in the
253 block or encoding window is sufficient. With gaps, a more complex
254 encoding needs to be used, perhaps similar to the encoding used for
255 selective acknowledgments.
257 Whether or not gaps are supported MUST be clarified in each FEC
258 Scheme.
260 4. FEC Scheme Negotiation in QUIC
262 FEC Scheme negotiation has two goals:
264 o Selecting a FEC Scheme (or FEC Schemes) that can be used by the
265 QUIC transmission and reception endpoints. This process requires
266 an exchange between them;
268 o Communicating a certain number of parameters, the "Configuration
269 Information", that are not expected to change over the session
270 lifetime. For instance, this is the case of the symbol size
271 parameter, E (in bytes), that needs either to be agreed between
272 the endpoints, or chosen by the sender and communicated to the
273 receiver(s);
275 Editor's notes:
277 * It is likely that FEC Scheme negotiation requires the use of a
278 new dedicated Extension Frame Type. The details remain TBD.
280 * The Negotiation Frame Type format remains TBD.
282 * How to communicate the parameters remains TBD.
284 * The present document only provides high level principles, the
285 details are of course the responsibility of the FEC Scheme.
287 * In case negotiation is different when protecting a single
288 versus several streams, this section may be moved to the
289 respective sections.
291 * How does it work in case of a multicast session?
293 * Do we negotiate here a FEC Scheme on a per-Stream basis (or
294 group of Streams to be protected jointly)? Or do we negotiate
295 a FEC Scheme on a QUIC session basis, therefore to be used for
296 all the Streams that need FEC protection?
298 4.1. FEC Scheme Selection Process
300 Let us consider the FEC Scheme selection process between the QUIC
301 endpoints. Figure 1 illustrates the principle when a QUIC reception
302 endpoint initiates the exchange.
304 QUIC sender QUIC receiver
305 < - - - - - - - - - - - - - - - - - - - - - -
306 supported_fec_scheme_32b{FS1_Encoding_ID | other}
307 supported_fec_scheme_64b{FS1_Encoding_ID | other}
309 choose FEC Scheme "FS1"
310 - - - - - - - - - - - - - - - - - - - - - - >
311 supported_fec_scheme_32b{FS1_Encoding_ID | other}
313 Figure 1: Example FEC Scheme selection process, during the initial
314 negotiation.
316 The supported_fec_scheme_16b and supported_fec_scheme_32b are two new
317 TransportParameterId to be added to the "Table 7: Initial QUIC
318 Transport Parameters Entries" Section 13.1, of [QUIC-transport]. The
319 supported_fec_scheme_32b contains a 32-bit data field to carry opaque
320 32-bit value, while the supported_fec_scheme_64b contains a 64-bit
321 data field to carry opaque 64-bit value (see Section 4.2).
323 4.2. FEC Scheme Configuration Information
325 Let us now focus on the communication of configuration information
326 specific to the selected FEC Scheme. In Figure 1, the
327 supported_fec_scheme_32b{FS1_Encoding_ID} contains a field meant to
328 carry the FEC Encoding ID of the FEC Scheme selected plus addditional
329 configuration information if any. If a 32 bit opaque field is not
330 sufficient, the supported_fec_scheme_64b can be used instead and
331 proposes a 64 bit opaque field.
333 5. Procedures when Protecting a Single QUIC Stream
335 This section focusses on the simple case where FEC protection is
336 applied to a single QUIC stream. We consider a unidirectional data
337 flow between a QUIC sending endpoint and one (or more) QUIC reception
338 endpoints.
340 5.1. Application data, STREAM Frame data and Source Symbols
342 Application data is kept in a transmission buffer at a QUIC sending
343 endpoint, and sent within STREAM frames. Each STREAM frame that
344 carries data contains an Offset field that indicates the offset
345 within the stream of the first byte of the Stream Data field, as well
346 as a Length field that indicates the number of bytes contained in the
347 Stream Data field. Upon receiving a STREAM frame, using the Offset
348 and Length fields, a QUIC reception endpoint can easily store data in
349 its reception buffer. But since a QUIC Packet may be lost during
350 transmission, the reception buffer may have gaps.
352 Figure 2 illustrates how source symbols are mapped to the QUIC
353 transmission or reception buffers (same principle on either side).
354 Since any source (and repair) symbol is of fixed size (E bytes) for a
355 given stream, since QUIC guaranties that the first byte in the stream
356 has an offset of 0, the position of each source symbol is known by
357 both ends.
359 < -E- > < -E- > < -E- > < -E- >
360 +-------+-------+-------+-------+
361 |< -- Frame 1 -- >< ----- Frame | source symbols 0, 1, 2, 3
362 +-------+-------+-------+-------+
363 | 2 ----- >< --- Frame 3 -- >< -| source symbols 4, 5, 6, 7
364 +-------+-------+----+--+-------+
365 | Frame 4 - >< -F5- >| source symbols 8, 9 and 10
366 +-------+-------+----+ (incomplete)
368 Figure 2: Example of source symbol mapping, when the E value is
369 relatively small.
371 Any value for E is possible, from a single byte to several hundreds
372 or thousands of bytes. In general, the source symbols are not
373 aligned with data chunks sent in the STREAM frames. A given STREAM
374 frame may carry all the bytes of a given source symbol. But when a
375 source symbol straddles two or more (e.g., if E is large compared to
376 usual frame size) STREAM frames, a proper reception of these two (or
377 more) STREAM frames is needed for a QUIC reception endpoint to
378 consider that the source symbol is available for FEC decoding
379 operations. The choice of an appropriate value for E may depend on
380 the use case (in particular on the nature of application data). A
381 reasonably small value reduces the probability that a source symbol
382 straddles two or more STREAM frames, a situation that is considered
383 as potentially harmful (the unit of control, the source symbol, and
384 unit of transmission, the frame, are not aligned). However an overly
385 small value also increases processing complexity (FEC encoding and
386 decoding are performed over a larger linear system) so there is an
387 incentive to use a larger value. An appropriate balance should be
388 found, and this choice is considered as out of scope for this
389 document.
391 5.2. Signaling Considerations within STREAM and REPAIR Frames
393 Once the initial negotiation succeeded and an appropriate FEC Scheme
394 has been chosen between the QUIC endpoints, data is exchanged as
395 follows. Source data is transmitted within STREAM frames, as would
396 happen without any FEC based loss recovery mechanism (in particular
397 without considering source symbols boundaries). Repair data,
398 computed during FEC encoding, on the opposite, is sent within a
399 dedicated REPAIR frame type, chosen within the type range dedicated
400 to "Extension Frames". In both cases, the same Stream ID is used
401 since both flows relate to the same stream.
403 The REPAIR frame format is FEC Scheme dependent. The document
404 specifying a FEC Scheme to be used with QUIC MUST define the REPAIR
405 frame format, among other things. The REPAIR frame MUST carry enough
406 information for a QUIC reception endpoint to understand exactly how
407 this repair symbol(s) has(ve) been generated. It implies that each
408 REPAIR symbol MUST communicate the block (with block codes) or
409 encoding window (with Sliding Window codes) composition. This MAY be
410 achieved by communicating in case there is no gap in the source
411 symbol set (see XXX):
413 o the offset of the first source symbol of the block or encoding
414 window;
416 o the number of source symbols in the block or encoding window,
417 which can be either a number of symbols or a number of bytes since
418 symbols are of fixed size, E.
420 Note that unlike FEC Schemes for FLUTE/ALC, NORM, and FECFRAME, here
421 there is no notion of Encoding Symbol Id (ESI), an identifier managed
422 in a sequential manner to identify source and repair symbols. The
423 use of an offset within the stream, with the guaranty that no
424 wrapping to zero can occur, provides an alternative mechanism to
425 identify any source symbol.
427 As explained above, source data is transmitted without any
428 modification, which provides backward compatibility. This is
429 advantage in situations where the same QUIC stream is delivered to
430 several QUIC reception endpoints (multicast): it may be appropriate
431 to select a given FEC Scheme even if it is known that a subset of the
432 QUIC reception endpoints do not support it.
434 Editor's notes:
436 * This I-D proposes to define a single generic REPAIR frame
437 type, but an alternative could be to have a one-to-one mapping
438 between a REPAIR frame type and a specific FEC Scheme.
440 * The use of frame type within the Extension Frames range for
441 REPAIR frames is meant to facilitate experimentations. If the
442 use of coding in QUIC is recognized as having benefits, a
443 dedicated (or more, see above) frame type could be selected
444 later on.
446 5.3. Management of Silent Periods and End of Stream
448 If an application does not submit fresh data for some time, the last
449 source symbol may not be totally filled. It follows that this last
450 source symbol cannot be considered during FEC encoding and therefore
451 the associated bytes of the application stream are not protected. A
452 similar problem arrives when a stream is finished, the application
453 having no more data to submit to QUIC. Here also, the bytes of the
454 last incomplete source symbol are not protected by FEC encoding.
456 In order to solve this problem, it is RECOMMENDED that a QUIC sending
457 endpoint:
459 o Identifies when such a situation is likely to occur, for instance
460 by waiting no more than a certain time during an application
461 silent period;
463 o Upon time-out, the application falls back to the alternative re-
464 transmission based loss recovery mechanism for the bytes of the
465 last incomplete source symbol;
467 Editor's notes: Clearly, the above mechanism requires more thoughts
468 as well as experimental work. The "end of stream" situation may
469 be addressed through zero padding perhaps easily. However the
470 use of zero padding for transitory silent periods may add a lot
471 of specification and implementation complexity...
473 6. Procedures when Protecting Several QUIC Streams
475 This section focusses on the general case where FEC protection is
476 globally applied across two or more QUIC streams.
478 Editor's notes: It is not clear whether this use-case is needed. It
479 adds specification and implementation complexity that need to be
480 balanced with the expected benefits.
482 * Receiver: A first complexity comes from the requirement to
483 identify to which stream a decoded source symbol belongs to.
484 This is also one of the main difficulty for FECFRAME (both
485 with block and sliding window codes) which required to
486 distinguish an ADU (submitted by the application) from an ADUI
487 (the same ADU plus an additional FlowID among other things).
488 Do we want this level of complexity?
490 * Sender: Another complexity comes from the encoding window
491 management at a sender. With multiple streams, shifting the
492 encoding window to the right needs to be done based on
493 timestamps associated to source symbols of the various
494 streams: the oldest source symbol across all the streams will
495 be removed.
497 * When two largely different streams are protected togethers
498 (e.g., a high definition 4K video flow plus the associated
499 relatively low-rate audio stream), is this extra complexity
500 balanced by significant performance improvements compared to
501 an independent protection on each stream (intuition is yes,
502 the low bitrate flow is better protected iff the encoding
503 window is large enough)? And when the various streams have a
504 comparable bitrate? More work (incl. experimental work) is
505 needed to answer this question.
507 6.1. Application data, STREAM Frame data and Source Symbols
509 Within each stream, the source symbols MUST be defined as in the
510 simple case of a single stream. Figure 2 remains valid.
512 6.2. Block or Encoding Window Management
514 The details of how to create the block or encoding window are
515 specific to the FEC Scheme. A possible approach is the following.
517 When creating the block (block FEC code) or encoding window (sliding
518 window FEC code), the source symbols to consider of each stream are
519 appended. All the relevant source symbols of the first stream are
520 appended, followed by all the source symbols of the second stream,
521 etc. These sequences do not follow any timing consideration in order
522 to simplify signaling.
524 Figure 3 illustrates, in case of a Sliding Window FEC Scheme, an
525 encoding window with source symbols belonging to two streams, of
526 Stream ID 120 and 51 respectively.
528 < ----------- Stream ID 120 ---------- > < --- Stream ID 51 --- >
529 +-------+-------+-------+-------+-------+-------+-------+-------+
530 | | | | | | | | |
531 +-------+-------+-------+-------+-------+-------+-------+-------+
532 ^ < -E- > ^
533 | |
534 offset = 0x42f0, length = 5*E offset = 0x0f24, length = 3*E
536 Figure 3: Example of encoding window of a Sliding Window FEC Scheme
537 and FEC protection across two streams.
539 6.3. Signaling Considerations within STREAM and REPAIR Frames
541 Source data on each stream is transmitted within STREAM frames, as
542 would happen without any FEC based loss recovery mechanism.
544 Repair symbols, generated during FEC encoding as a linear combination
545 of source symbols that belong to one or more of the streams, are
546 transmitted within REPAIR frames. Each REPAIR frame can be
547 associated to any of the input streams it protects, and therefore
548 associated to any of the associated Stream IDs.
550 Editor's notes: Check that indeed, with FEC protection across
551 several streams, assigning a REPAIR frame to any of the streams
552 it protects is meaningful. Should an approach for selecting one
553 stream (and Stream ID) be preferred?
555 The REPAIR frame format is FEC Scheme dependent and MUST be defined
556 by document specifying a FEC Scheme. One of the key information of
557 this REPAIR frame is the composition of the block (with block codes)
558 or encoding window (with sliding window codes) used to perform FEC
559 encoding. Indeed, this is the only manner to convey this information
560 since an application flow is not predictable (e.g., if an application
561 flow is momentarily suspended, the composition of the block or
562 encoding window will be affected). One possibility is to list, in
563 each REPAIR frame header:
565 o the actual number of streams considered (the maximum number is
566 known after the negotiation step, but if one of the streams
567 remains silent for some time, it may not contribute during
568 encoding and therefore be absent from the block or encoding
569 window);
571 o for each stream concerned, its Stream ID, the offset of the first
572 source symbol considered as well as the length, i.e., the number
573 of bytes considered.
575 This approach does not enable to keep track of the source symbol
576 ordering across streams, but enables a non ambiguous description of
577 the encoding window.
579 The FEC Scheme specification MUST also detail how to manage the block
580 or encoding window. For instance, should the oldest source symbol of
581 any stream be removed from the encoding window when this latter is
582 shifted to the right? This would mean that a timestamp is attached
583 to each source symbol in order to identify the oldest one across all
584 streams.
586 7. Security Considerations
588 TBD
590 8. IANA Considerations
592 TBD
594 9. Acknowledgments
596 TBD
598 10. References
600 10.1. Normative References
602 [QUIC-transport]
603 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
604 Multiplexed and Secure Transport", draft-ietf-quic-
605 transport-12 (work in progress), May 2018,
606 .
609 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
610 Requirement Levels", BCP 14, RFC 2119,
611 DOI 10.17487/RFC2119, March 1997,
612 .
614 10.2. Informative References
616 [nc-taxonomy]
617 Roca et al., V., "Taxonomy of Coding Techniques for
618 Efficient Network Communications", draft-irtf-nwcrg-
619 network-coding-taxonomy (Work in Progress) (work in
620 progress), March 2018, .
623 [RFC5510] Lacan, J., Roca, V., Peltotalo, J., and S. Peltotalo,
624 "Reed-Solomon Forward Error Correction (FEC) Schemes",
625 RFC 5510, DOI 10.17487/RFC5510, April 2009,
626 .
628 [RLC] Roca, V., "Sliding Window Random Linear Code (RLC) Forward
629 Erasure Correction (FEC) Scheme for FECFRAME", Work
630 in Progress, Transport Area Working Group (TSVWG) draft-
631 ietf-tsvwg-rlc-fec-scheme (Work in Progress), May 2018,
632 .
635 Authors' Addresses
637 Ian Swett
638 Google
639 Cambridge, MA
640 US
642 Email: ianswett@google.com
644 Marie-Jose Montpetit
645 Triangle Video
646 Boston, MA
647 US
649 Email: marie@mjmontpetit.com
651 Vincent Roca
652 INRIA
653 Univ. Grenoble Alpes
654 France
656 Email: vincent.roca@inria.fr