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Montpetit 7 Triangle Video 8 June 21, 2018 10 Sliding Window Random Linear Code (RLC) Forward Erasure Correction (FEC) 11 Schemes for QUIC 12 draft-roca-nwcrg-rlc-fec-scheme-for-quic-00 14 Abstract 16 This document specifies Sliding Window Random Linear Code (RLC) 17 Forward Erasure Correction (FEC) Schemes for the QUIC transport 18 protocol, in order to recover from packet losses. 20 Status of This Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at https://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on December 23, 2018. 37 Copyright Notice 39 Copyright (c) 2018 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (https://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 55 2. Definitions and Abbreviations . . . . . . . . . . . . . . . . 3 56 3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 3 57 3.1. Source Symbols Mapping . . . . . . . . . . . . . . . . . 3 58 3.2. Pseudo-Random Number Generator (PRNG) . . . . . . . . . . 4 59 3.3. Coding Coefficients Generation Function . . . . . . . . . 4 60 4. Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting a 61 Single QUIC Stream . . . . . . . . . . . . . . . . . . . . . 4 62 4.1. Formats and Codes . . . . . . . . . . . . . . . . . . . . 4 63 4.1.1. Configuration Information . . . . . . . . . . . . . . 4 64 4.1.2. REPAIR Frame Format . . . . . . . . . . . . . . . . . 5 65 4.1.3. Additional Procedures . . . . . . . . . . . . . . . . 6 66 4.2. FEC Code Specification . . . . . . . . . . . . . . . . . 6 67 4.2.1. Encoding Side . . . . . . . . . . . . . . . . . . . . 6 68 4.2.2. Decoding Side . . . . . . . . . . . . . . . . . . . . 6 69 5. Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting 70 Several QUIC Streams . . . . . . . . . . . . . . . . . . . . 6 71 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 72 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 73 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7 74 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 75 9.1. Normative References . . . . . . . . . . . . . . . . . . 7 76 9.2. Informative References . . . . . . . . . . . . . . . . . 8 77 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 79 1. Introduction 81 QUIC [QUIC-transport] is a new transport that aims at improving 82 network performance by enabling out of order delivery, partial 83 reliability, and methods of recovery besides retransmission, while 84 also improving security. This document specifies FEC schemes for 85 Sliding Window Random Linear Code (RLC) [RLC] to recover from lost 86 packets within a single QUIC stream or across several QUIC streams, 87 compliant with the FEC coding framework for QUIC [Coding4QUIC]. 89 The ability to add FEC coding in QUIC may be beneficial in several 90 situations: 92 o for a robust transmission of latency sensitive traffic, for 93 instance real-time flows, since it enables to recover packet 94 losses independently of the round trip time; 96 o for the transmission of contents to a large set of QUIC reception 97 endpoints, since the same repair frame may help recovering several 98 different packet losses at different receivers; 100 o for multipath communications, since repair traffic adds diversity. 102 2. Definitions and Abbreviations 104 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 105 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 106 document are to be interpreted as described in [RFC2119]. 108 Terms and definitions that apply to coding are available in 109 [nc-taxonomy]. More specifically, this document uses the following 110 definitions: 112 Packet versus Symbol: a Packet is the unit of data that is exchanged 113 over the network while a Symbol is the unit of data that is 114 manipulated during the encoding and decoding operations 116 Source Symbol: a unit of data originating from the source that is 117 used as input to encoding operations 119 Repair Symbol: a unit of data that is the result of a coding 120 operation 122 This document uses the following abbreviations: 124 E: size of an encoding symbol (i.e., source or repair symbol), 125 assumed fixed (in bytes) 127 3. Procedures 129 This section introduces the procedures that are used by these FEC 130 Schemes. 132 3.1. Source Symbols Mapping 134 The present FEC Scheme follows the source symbols mapping specified 135 in [Coding4QUIC]. Figure 1 illustrates this mapping. 137 < -E- > < -E- > < -E- > < -E- > 138 +-------+-------+-------+-------+ 139 |< -- Frame 1 -- >< ----- Frame | source symbols 0, 1, 2, 3 140 +-------+-------+-------+-------+ 141 | 2 ----- >< --- Frame 3 -- >< -| source symbols 4, 5, 6, 7 142 +-------+-------+----+--+-------+ 143 | Frame 4 - >< -F5- >| source symbols 8, 9 and 10 144 +-------+-------+----+ (incomplete) 146 Figure 1: Example of source symbol mapping, when the E value is 147 relatively small. 149 3.2. Pseudo-Random Number Generator (PRNG) 151 The RLC FEC Schemes defined in this document rely on the TinyMT32 152 PRNG defined in [RLC]. 154 3.3. Coding Coefficients Generation Function 156 The coding coefficients, used during the encoding process, are 157 generated at the RLC encoder by the generate_coding_coefficients() 158 function each time a new repair symbol needs to be produced. This 159 specification uses the generate_coding_coefficients() defined in 160 [RLC]. 162 4. Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting a Single 163 QUIC Stream 165 This fully-specified FEC Scheme defines the Sliding Window Random 166 Linear Codes (RLC) over GF(2^^8) when protecting a single QUIC 167 stream. 169 4.1. Formats and Codes 171 4.1.1. Configuration Information 173 This section provides the RLC configuration information that needs to 174 be shared during QUIC negotiation between the QUIC sender and 175 receiver endpoints in order to synchronize them. 177 o FEC Encoding ID: the value assigned to this fully specified FEC 178 Scheme MUST be XXXX, as assigned by IANA (Section 7). This FEC 179 Encoding ID is used during the QUIC negotiation to uniquely 180 identify the RLC FEC Scheme for QUIC; 182 o Encoding symbol size, E (in bytes): a non-negative integer that 183 indicates the size of each source and repair symbol, in bytes. 185 This element is required both by the QUIC sender endpoint (RLC 186 encoder) and the QUIC receiver endpoint(s) (RLC decoder). 188 4.1.2. REPAIR Frame Format 190 The RLC FEC Scheme does not use any explicit Source FEC Payload ID, 191 meaning that QUIC STREAM frame format is not modified. 193 On the opposite, the RLC FEC Scheme requires QUIC REPAIR frames to 194 convey enough information. This section specifies the REPAIR frame 195 format specific to the RLC FEC Scheme and a single QUIC stream. Note 196 that the notion of REPAIR frame format is equivalent to the notion of 197 Repair FEC Payload ID in [RLC]. 199 0 1 2 3 200 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 202 | Stream ID (i) ... 203 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 204 | [Offset of First Source Symbol in EW (i)] ... 205 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 206 | [Length (i)] ... 207 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 208 | Repair_Key | DT |NSS (# src symb in ew) | 209 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 210 | Stream Data ... 211 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 Figure 2: REPAIR frame format when protecting a single QUIC stream. 215 More precisely, the REPAIR frame format is composed of the following 216 fields (Figure 2): 218 Stream ID (variable-size field): a variable-length integer 219 indicating the stream ID of the stream. See [QUIC-transport]. 220 The Stream ID for an RLC REPAIR frame MUST be equal to the Stream 221 ID used for the data stream it protects; 223 Offset of First Source Symbol in the Encoding Window (variable-size 224 field): 225 a variable-length integer specifying the byte offset in the stream 226 for the first source symbol of the encoding window. 228 Length (variable-size field): a variable-length integer specifying 229 the length of the Stream Data field in this REPAIR frame. This 230 length MUST be a non zero multiple of the source symbol size, E, 231 since a REPAIR frame contains one or more repair symbols for this 232 stream; 234 Repair_Key (16-bit field): this unsigned integer is used as a seed 235 by the coefficient generation function (Section 3.3) in order to 236 generate the desired number of coding coefficients. When a FEC 237 Repair Packet contains several repair symbols, this repair key 238 value is that of the first repair symbol. The remaining repair 239 keys can be deduced by incrementing by 1 this value, up to a 240 maximum value of 65535 after which it loops back to 0. 242 Density Threshold for the coding coefficients, DT (4-bit field): 243 this unsigned integer carries the Density Threshold (DT) used by 244 the coding coefficient generation function Section 3.3. More 245 precisely, it controls the probability of having a non zero coding 246 coefficient, which equals (DT+1) / 16. When a FEC Repair Packet 247 contains several repair symbols, the DT value applies to all of 248 them; 250 Number of Source Symbols in the encoding window, NSS (12-bit field): 252 this unsigned integer indicates the number of source symbols in 253 the encoding window when this repair symbol was generated. When a 254 FEC Repair Packet contains several repair symbols, this NSS value 255 applies to all of them; 257 Stream Data: data for this repair symbol(s). 259 4.1.3. Additional Procedures 261 4.2. FEC Code Specification 263 This RLC FEC Scheme relies on the FEC code specification defined in 264 [RLC]. 266 4.2.1. Encoding Side 268 [RLC] high level description of a Sliding Window RLC encoder also 269 applies here to this FEC Scheme. 271 4.2.2. Decoding Side 273 [RLC] high level description of a Sliding Window RLC decoder also 274 applies here to this FEC Scheme. 276 5. Sliding Window RLC FEC Scheme over GF(2^^8) when Protecting Several 277 QUIC Streams 279 This section focusses on the general case where FEC protection is 280 globally applied across two or more QUIC streams. 282 TODO 284 6. Security Considerations 286 TBD 288 7. IANA Considerations 290 This document registers two values in the "QUIC FEC Encoding IDs" 291 registry as follows: 293 o XXXX refers to the Sliding Window Random Linear Codes (RLC) over 294 GF(2^^8) FEC Scheme for a Single QUIC Stream, as defined in 295 Section 4 of this document. 297 o YYYY refers to the Sliding Window Random Linear Codes (RLC) over 298 GF(2^^8) FEC Scheme for a Several QUIC Stream, as defined in 299 Section 5 of this document. 301 8. Acknowledgments 303 TBD 305 9. References 307 9.1. Normative References 309 [Coding4QUIC] 310 Swett, I., Montpetit, M-J., and V. Roca, "Coding for 311 QUIC", Work in Progress, NWCRG draft-swett-nwcrg-coding- 312 for-quic (Work in Progress), June 2018, 313 . 316 [QUIC-transport] 317 Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based 318 Multiplexed and Secure Transport", draft-ietf-quic- 319 transport-12 (work in progress), May 2018, 320 . 323 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 324 Requirement Levels", BCP 14, RFC 2119, 325 DOI 10.17487/RFC2119, March 1997, 326 . 328 [RLC] Roca, V., "Sliding Window Random Linear Code (RLC) Forward 329 Erasure Correction (FEC) Scheme for FECFRAME", Work 330 in Progress, Transport Area Working Group (TSVWG) draft- 331 ietf-tsvwg-rlc-fec-scheme (Work in Progress), May 2018, 332 . 335 9.2. Informative References 337 [nc-taxonomy] 338 Roca et al., V., "Taxonomy of Coding Techniques for 339 Efficient Network Communications", draft-irtf-nwcrg- 340 network-coding-taxonomy (Work in Progress) (work in 341 progress), June 2018, . 344 Authors' Addresses 346 Vincent Roca 347 INRIA 348 Univ. Grenoble Alpes 349 France 351 Email: vincent.roca@inria.fr 353 Ian Swett 354 Google 355 Cambridge, MA 356 US 358 Email: ianswett@google.com 360 Marie-Jose Montpetit 361 Triangle Video 362 Boston, MA 363 US 365 Email: marie@mjmontpetit.com