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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) Summary: 2 errors (**), 0 flaws (~~), 1 warning (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 AVT A. Begen 3 Internet-Draft D. Hsu 4 Intended status: Standards Track M. Lague 5 Expires: May 15, 2010 Cisco Systems 6 November 11, 2009 8 Post-Repair Loss RLE Report Block Type for RTCP XR 9 draft-ietf-avt-post-repair-rtcp-xr-07 11 Abstract 13 This document defines a new report block type within the framework of 14 RTP Control Protocol (RTCP) Extended Reports (XR). One of the 15 initial XR report block types is the Loss Run Length Encoding (RLE) 16 Report Block. This report conveys the information regarding the 17 individual Real-time Transport Protocol (RTP) packet receipt and loss 18 events experienced during the RTCP interval preceding the 19 transmission of the report. The new report, which is referred to as 20 the Post-repair Loss RLE Report, carries the information regarding 21 the remaining lost packets after all loss-repair methods are applied. 22 By comparing the RTP packet receipts/losses before and after the loss 23 repair is completed, one can determine the effectiveness of the loss- 24 repair methods in an aggregated fashion. This document also defines 25 the signaling of the Post-repair Loss RLE Report in the Session 26 Description Protocol (SDP). 28 Status of this Memo 30 This Internet-Draft is submitted to IETF in full conformance with the 31 provisions of BCP 78 and BCP 79. 33 Internet-Drafts are working documents of the Internet Engineering 34 Task Force (IETF), its areas, and its working groups. Note that 35 other groups may also distribute working documents as Internet- 36 Drafts. 38 Internet-Drafts are draft documents valid for a maximum of six months 39 and may be updated, replaced, or obsoleted by other documents at any 40 time. It is inappropriate to use Internet-Drafts as reference 41 material or to cite them other than as "work in progress." 43 The list of current Internet-Drafts can be accessed at 44 http://www.ietf.org/ietf/1id-abstracts.txt. 46 The list of Internet-Draft Shadow Directories can be accessed at 47 http://www.ietf.org/shadow.html. 49 This Internet-Draft will expire on May 15, 2010. 51 Copyright Notice 53 Copyright (c) 2009 IETF Trust and the persons identified as the 54 document authors. All rights reserved. 56 This document is subject to BCP 78 and the IETF Trust's Legal 57 Provisions Relating to IETF Documents 58 (http://trustee.ietf.org/license-info) in effect on the date of 59 publication of this document. Please review these documents 60 carefully, as they describe your rights and restrictions with respect 61 to this document. Code Components extracted from this document must 62 include Simplified BSD License text as described in Section 4.e of 63 the Trust Legal Provisions and are provided without warranty as 64 described in the BSD License. 66 This document may contain material from IETF Documents or IETF 67 Contributions published or made publicly available before November 68 10, 2008. The person(s) controlling the copyright in some of this 69 material may not have granted the IETF Trust the right to allow 70 modifications of such material outside the IETF Standards Process. 71 Without obtaining an adequate license from the person(s) controlling 72 the copyright in such materials, this document may not be modified 73 outside the IETF Standards Process, and derivative works of it may 74 not be created outside the IETF Standards Process, except to format 75 it for publication as an RFC or to translate it into languages other 76 than English. 78 Table of Contents 80 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 81 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . . 4 82 3. Post-Repair Loss RLE Report Block . . . . . . . . . . . . . . . 4 83 4. Session Description Protocol Signaling . . . . . . . . . . . . 6 84 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 85 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 86 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8 87 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 88 8.1. Normative References . . . . . . . . . . . . . . . . . . . 8 89 8.2. Informative References . . . . . . . . . . . . . . . . . . 8 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 92 1. Introduction 94 RTP Control Protocol (RTCP) is the out-of-band control protocol for 95 the applications that are using the Real-time Transport Protocol 96 (RTP) for media delivery and communications [RFC3550]. RTCP allows 97 the RTP entities to monitor the data delivery and provides them 98 minimal control functionality via sender and receiver reports as well 99 as other control packets. [RFC3611] expands the RTCP functionality 100 further by introducing the RTCP Extended Reports (XR). 102 One of the initial XR report block types defined in [RFC3611] is the 103 Loss Run Length Encoding (RLE) Report Block. This report conveys the 104 information regarding the individual RTP packet receipt and loss 105 events experienced during the RTCP interval preceding the 106 transmission of the report. However, the Loss RLE in an RTCP XR 107 report is usually collected only on the primary source stream before 108 any loss-repair method is applied. Once one or more loss-repair 109 methods, e.g., Forward Error Correction (FEC) [RFC5109] and/or 110 retransmission [RFC4588], are applied, some or all of the lost 111 packets on the primary source stream may be recovered. However, the 112 pre-repair Loss RLE cannot indicate which source packets were 113 recovered and which are still missing. Thus, the pre-repair Loss RLE 114 cannot specify how well the loss repair performed. 116 This issue can be addressed by generating an additional report block 117 (within the same or a different RTCP XR report), which reflects the 118 packet receipt/loss events after all loss-repair methods are applied. 119 This report block, which we refer to as the Post-repair Loss RLE, 120 indicates the remaining missing, i.e., unrepairable, source packets. 121 When the pre-repair and post-repair Loss RLEs are compared, the RTP 122 sender or another third party entity can evaluate the effectiveness 123 of the loss-repair methods in an aggregated fashion. To avoid any 124 ambiguity in the evaluation, it is RECOMMENDED that the post-repair 125 Loss RLE is generated for the source packets that have no further 126 chance of being repaired. If the loss-repair method(s) may still 127 recover one or more missing source packets, the post-repair Loss RLE 128 SHOULD NOT be sent until the loss-recovery process has been 129 completed. However, a potential ambiguity may result from sequence 130 number wrapping in the primary source stream. Thus, the post-repair 131 Loss RLE reports may not be delayed arbitrarily. In case of an 132 ambiguity in the incoming reports, it is the sender's or the 133 monitoring entity's responsibility to understand which packets the 134 post-repair Loss RLE report is related to. 136 Similar to the pre-repair Loss RLE, the post-repair Loss RLE conveys 137 the receipt/loss events at the packet level and considers partially 138 repaired packets as unrepaired. Thus, the methods that can partially 139 recover the missing data SHOULD NOT be evaluated based on the 140 information provided by the Post-repair Loss RLE Reports since such 141 information may underestimate the effectiveness of such methods. 143 Note that the idea of using pre-repair and post-repair Loss RLEs can 144 be further extended when multiple sequential loss-repair methods are 145 applied to the primary source stream. Reporting the Loss RLEs before 146 and after each loss-repair method can provide specific information 147 about the individual performances of these methods. However, it can 148 be a difficult task to quantify the specific contribution made by 149 each loss-repair method in hybrid systems, where different methods 150 collectively work together to repair the lost source packets. Thus, 151 in this specification we only consider reporting the Loss RLE after 152 all loss-repair methods are applied. 154 This document registers a new report block type to cover the post- 155 repair Loss RLE within the framework of RTCP XR. Applications that 156 are employing one or more loss-repair methods MAY use Post-repair 157 Loss RLE Reports for every packet they receive or for a set of 158 specific packets they have received. In other words, the coverage of 159 the post-repair Loss RLEs may or may not be contiguous. 161 2. Requirements Notation 163 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 164 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 165 document are to be interpreted as described in [RFC2119]. 167 3. Post-Repair Loss RLE Report Block 169 The Post-repair Loss RLE Report Block is similar to the existing Loss 170 RLE Report Block defined in [RFC3611]. The report format is shown in 171 Figure 1. Using the same structure for reporting both pre-repair and 172 post-repair Loss RLEs allows the implementations to compare the Loss 173 RLEs very efficiently. 175 0 1 2 3 176 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 1 177 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 178 | BT=10 | rsvd. | T | block length | 179 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 180 | SSRC of source | 181 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 182 | begin_seq | end_seq | 183 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 184 | chunk 1 | chunk 2 | 185 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 186 : ... : 187 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 188 | chunk n-1 | chunk n | 189 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 191 Figure 1: Format for the post-repair loss RLE report block 193 o block type (BT): 8 bits 194 A Post-repair Loss RLE Report Block is identified by the constant 195 10. 197 o rsvd.: 4 bits 198 This field is reserved for future definition. In the absence of 199 such definition, the bits in this field MUST be set to zero and 200 MUST be ignored by the receiver. 202 o thinning (T): 4 bits 203 The amount of thinning performed on the sequence number space. 204 Only those packets with sequence numbers 0 mod 2^T are reported on 205 by this block. A value of 0 indicates that there is no thinning, 206 and all packets are reported on. The maximum thinning is one 207 packet in every 32,768 (amounting to two packets within each 16- 208 bit sequence space). 210 If thinning is desired, It is RECOMMENDED to use the same thinning 211 value in the pre-repair and post-repair Loss RLE reports. This 212 will allow easier report processing and correlation. However, 213 based on the specific needs of the application or the monitoring 214 entity, different values of thinning MAY be used for pre-repair 215 and post-repair Loss RLE reports. 217 o block length: 16 bits 218 The length of this report block, including the header, in 32-bit 219 words minus one. 221 o SSRC of source: 32 bits 222 The SSRC of the RTP data packet source being reported upon by this 223 report block. 225 o begin_seq: 16 bits 227 The first sequence number that this block reports on. 229 o end_seq: 16 bits 231 The last sequence number that this block reports on plus one. 233 o chunk i: 16 bits 234 There are three chunk types: run length, bit vector, and 235 terminating null, defined in [RFC3611] (Section 4). If the chunk 236 is all zeroes, then it is a terminating null chunk. Otherwise, 237 the left most bit of the chunk determines its type: 0 for run 238 length and 1 for bit vector. 240 Note that the sequence numbers that are included in the report refer 241 to the primary source stream. 243 When using post-repair Loss RLE reports, the amount of bandwidth 244 consumed by the detailed reports should be considered carefully. The 245 bandwidth usage rules as they are described in [RFC3611] apply to 246 post-repair Loss RLE reports as well. 248 4. Session Description Protocol Signaling 250 A new parameter is defined for the Post-repair Loss RLE Report Block 251 to be used with Session Description Protocol (SDP) [RFC4566] using 252 the Augmented Backus-Naur Form (ABNF) [RFC5234]. It has the 253 following syntax within the "rtcp-xr" attribute [RFC3611]: 255 rtcp-xr-attrib = "a=rtcp-xr:" [xr-format *(SP xr-format)] CRLF 257 xr-format =/ "post-repair-loss-rle" ["=" max-size] 259 max-size = 1*DIGIT ; maximum block size in octets 261 Figure 2 263 Refer to Section 5.1 of [RFC3611] for a detailed description and the 264 full syntax of the "rtcp-xr" attribute. 266 5. Security Considerations 268 The security considerations of [RFC3611] apply in this document as 269 well. Additional security considerations are briefly mentioned 270 below. 272 An attacker who monitors the regular pre-repair Loss RLE reports sent 273 by a group of receivers in the same multicast distribution network 274 may infer the network characteristics (Multicast Inference of Network 275 Characteristics). However, monitoring the post-repair Loss RLE 276 reports will not reveal any further information about the network. 277 Without the regular pre-repair Loss RLE reports, the post-repair ones 278 will not be any use to attackers. Even when used with the regular 279 pre-repair Loss RLE reports, the post-repair Loss RLE reports only 280 reveal the effectiveness of the repair process. However, this does 281 not enable any new attacks nor does it provide information to an 282 attacker that could not be similarly obtained by watching the RTP 283 packets fly by himself, performing the repair algorithms and 284 computing the desired output. 286 An attacker may interfere with the repair process for an RTP stream. 287 In that case, if the attacker is able to see the post-repair Loss 288 RLEs, the attacker may infer whether the attack is effective or not, 289 in which case the attacker may continue attacking or alter the 290 attack. In practice, however, this does not pose a security risk. 292 An attacker may put incorrect information in the regular pre-repair 293 and post-repair Loss RLE reports such that it impacts the proactive 294 decisions made by the sender in the repair process or the reactive 295 decisions when responding to the feedback messages coming from the 296 receiver. A sender application should be aware of such risks and 297 should take the necessary precautions to minimize the chances for (or 298 better eliminate) such attacks. 300 Similar to other RTCP XR reports, the post-repair Loss RLE reports 301 MAY be protected by using SRTP and SRTCP [RFC3711]. 303 6. IANA Considerations 305 New block types for RTCP XR are subject to IANA registration. For 306 general guidelines on IANA considerations for RTCP XR, refer to 307 [RFC3611]. 309 This document assigns the block type value 10 in the RTCP XR Block 310 Type Registry to "Post-repair Loss RLE Report Block." This document 311 also registers the SDP [RFC4566] parameter "post-repair-loss-rle" for 312 the "rtcp-xr" attribute in the RTCP XR SDP Parameters Registry. 314 The contact information for the registrations is: 316 Ali Begen 317 abegen@cisco.com 319 170 West Tasman Drive 320 San Jose, CA 95134 USA 322 7. Acknowledgments 324 The authors would like to thank the members of the VQE Team at Cisco 325 and Colin Perkins for their inputs and suggestions. 327 8. References 329 8.1. Normative References 331 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 332 Requirement Levels", BCP 14, RFC 2119, March 1997. 334 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 335 Jacobson, "RTP: A Transport Protocol for Real-Time 336 Applications", STD 64, RFC 3550, July 2003. 338 [RFC3611] Friedman, T., Caceres, R., and A. Clark, "RTP Control 339 Protocol Extended Reports (RTCP XR)", RFC 3611, 340 November 2003. 342 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 343 Description Protocol", RFC 4566, July 2006. 345 [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax 346 Specifications: ABNF", STD 68, RFC 5234, January 2008. 348 8.2. Informative References 350 [RFC5109] Li, A., "RTP Payload Format for Generic Forward Error 351 Correction", RFC 5109, December 2007. 353 [RFC4588] Rey, J., Leon, D., Miyazaki, A., Varsa, V., and R. 354 Hakenberg, "RTP Retransmission Payload Format", RFC 4588, 355 July 2006. 357 [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 358 Norrman, "The Secure Real-time Transport Protocol (SRTP)", 359 RFC 3711, March 2004. 361 Authors' Addresses 363 Ali Begen 364 Cisco Systems 365 170 West Tasman Drive 366 San Jose, CA 95134 367 USA 369 Email: abegen@cisco.com 371 Dong Hsu 372 Cisco Systems 373 1414 Massachusetts Ave. 374 Boxborough, MA 01719 375 USA 377 Email: dohsu@cisco.com 379 Michael Lague 380 Cisco Systems 381 1414 Massachusetts Ave. 382 Boxborough, MA 01719 383 USA 385 Email: mlague@cisco.com