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Checking references for intended status: Informational ---------------------------------------------------------------------------- == Outdated reference: A later version (-08) exists of draft-ietf-behave-tcp-04 == Outdated reference: A later version (-19) exists of draft-ietf-mmusic-ice-13 == Outdated reference: A later version (-07) exists of draft-ietf-avt-rtp-and-rtcp-mux-03 == Outdated reference: A later version (-18) exists of draft-ietf-behave-rfc3489bis-05 ** Obsolete normative reference: RFC 4566 (ref. '10') (Obsoleted by RFC 8866) == Outdated reference: A later version (-04) exists of draft-ietf-avt-rtp-no-op-00 Summary: 4 errors (**), 0 flaws (~~), 10 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 BEHAVE Working Group X. Marjou, Ed. 3 Internet-Draft France Telecom 4 Intended status: Informational February 2, 2007 5 Expires: August 6, 2007 7 Application Mechanism for maintaining alive the Network Address 8 Translator (NAT) mappings associated to RTP flows. 9 draft-marjou-behave-app-rtp-keepalive-01 11 Status of this Memo 13 By submitting this Internet-Draft, each author represents that any 14 applicable patent or other IPR claims of which he or she is aware 15 have been or will be disclosed, and any of which he or she becomes 16 aware will be disclosed, in accordance with Section 6 of BCP 79. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as Internet- 21 Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six months 24 and may be updated, replaced, or obsoleted by other documents at any 25 time. It is inappropriate to use Internet-Drafts as reference 26 material or to cite them other than as "work in progress." 28 The list of current Internet-Drafts can be accessed at 29 http://www.ietf.org/ietf/1id-abstracts.txt. 31 The list of Internet-Draft Shadow Directories can be accessed at 32 http://www.ietf.org/shadow.html. 34 This Internet-Draft will expire on August 6, 2007. 36 Copyright Notice 38 Copyright (C) The IETF Trust (2007). 40 Abstract 42 This document defines a mechanism that enables applications using 43 Real Time Protocol (RTP) to maintain their RTP Network Address 44 Translator (NAT) mappings alive. 46 Table of Contents 48 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 49 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 4 50 3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4 51 4. List of Alternatives for Performing RTP Keepalive . . . . . . . 4 52 4.1. UDP Packet of 0-byte . . . . . . . . . . . . . . . . . . . 5 53 4.2. RTCP Packets Multiplexed with RTP Packets . . . . . . . . . 5 54 4.3. STUN Packet . . . . . . . . . . . . . . . . . . . . . . . . 5 55 4.4. RTP Packet with Comfort Noise Payload . . . . . . . . . . . 5 56 4.5. RTP Packet with No-Op Payload . . . . . . . . . . . . . . . 6 57 4.6. RTP Packet with Incorrect Version Number . . . . . . . . . 6 58 4.7. RTP Packet with Unknown Payload Type . . . . . . . . . . . 6 59 5. Recommended Solution . . . . . . . . . . . . . . . . . . . . . 6 60 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 61 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 62 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7 63 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 8 64 Intellectual Property and Copyright Statements . . . . . . . . . . 9 66 1. Introduction 68 [Note: The content of this draft is basically a copy and paste of the 69 current 7.12 section of ICE [5] concerning binding keepalives 70 requirements that apply to a non ICE agent, or that apply to an ICE 71 agent that communicates with a non-ICE agent. It thus makes sense to 72 extract it in a separate document so that non-ICE agents can refer to 73 non-ICE specification.] 75 Documents [2] and [3] describe NAT behaviors and point-out that two 76 key aspects of NAT are mappings (a.k.a. bindings) and their 77 refreshment. This introduces a derived requirement for applications 78 engaged in a multimedia session involving NAT traversal: they need to 79 generate a minimum of flow activity in order to maintain the NAT 80 mappings alive. 82 When applied to applications using RTP [4], the RTP media stream 83 packets themselves normally fulfill this requirement. However, as 84 described in ICE [5], there exist some cases where RTP do not 85 generate a minimum flow activity. 87 The examples are: 88 o Firstly, in some RTP usages, such as SIP, the media streams can be 89 "put on hold". This is accomplished by using the SDP "sendonly" 90 or "inactive" attributes, as defined in RFC 3264 [6]. RFC 3264 91 directs implementations to cease transmission of media in these 92 cases. However, doing so may cause NAT bindings to timeout, and 93 media won't be able to come off hold. 94 o Secondly, some RTP payload formats, such as the payload format for 95 text conversation [7], may send packets so infrequently that the 96 interval exceeds the NAT binding timeouts. 97 o Thirdly, if silence suppression is in use, long periods of silence 98 may cause media transmission to cease sufficiently long for NAT 99 bindings to time out. 101 This document first states the requirements that must be supported to 102 perform RTP keepalives (Section 3). In a second step, several 103 alternatives are laid-out to overcome this problem (Section 4). 104 Finally a single solution is recommended, in order to achieve 105 interoperability (Section 5). 107 The scope of the draft is limited to RTP flows. In particular, this 108 document does not address keepalive activity related to: 109 o Session signaling flows, such as the Session Initiation Protocol 110 (SIP). 111 o RTCP flows. 113 * Recall that [4] recommends a minimum interval of 5 seconds and 114 that "on hold" procedures of [6] do not impact RTCP 115 transmissions. Therefore, when in use, there is always some 116 RTCP flow activity. 117 o Other types of flows, such as the Binary Floor Control Protocol 118 (BFCP) 120 2. Terminology 122 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 123 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 124 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1] 126 3. Requirements 128 This section outlines the key requirements that the solution need to 129 satisfy in order to provide RTP media keepalive. 131 REQ 1. The recommended mechanism MUST generate activity within the 132 RTP media stream 134 REQ 2. The activity is generated periodically for the whole duration 135 of the RTP media stream. 137 REQ 3. Any type of transport (e.g. UDP, TCP) MUST be supported. 139 REQ 4. Any type media of stream (e.g. audio, video, text) MUST be 140 supported. 142 REQ 5. Any type of payload format (e.g. G.711, H.263) MUST be 143 supported. 145 REQ 6: Session signaling protocols SHOULD not be impacted. 147 REQ 7: Session description protocols SHOULD not be impacted. 149 REQ 8: Impacts on existing software SHOULD be minimized. 151 REQ 9: Remote peer SHOULD not be impacted. 153 REQ 10: One single mechanism MUST be recommended. 155 4. List of Alternatives for Performing RTP Keepalive 157 This section lists some alternatives that could be used in order to 158 perform a keepalive message within RTP media streams. 160 A common drawback of most of these alternatives is that they require 161 media packets be sent by the application during "on hold" procedures, 162 which violates the behavior of the inactive and recvonly attributes 163 specified in SDP-NEW [10] and in RFC3264 [6]. Although there can 164 exist some debate whether STUN is a media flow or not, STUN also 165 requires the application to send some packets within the media stream 166 during on-hold procedures. 168 4.1. UDP Packet of 0-byte 170 The application sends an empty UDP packet. 172 Cons: 173 o This alternative is specific to UDP. 174 o There may be some implementations that will not ignore these 175 packets. 177 4.2. RTCP Packets Multiplexed with RTP Packets 179 The application sends RTCP packets in the RTP media stream itself 180 (i.e. same tuples for both RTP and RTCP packets) [8]. RTCP packets 181 therefore maintain the NAT mappings open. 183 Cons: 184 o Multiplexing RTP and RTCP must be supported by the remote peer. 185 o Multiplexing RTP and RTCP must be signalled in SDP offer/answer. 186 o This alternative may significantly impact existing software and 187 specifications. 189 4.3. STUN Packet 191 The application sends a STUN Binding Request packet and receives a 192 STUN Binding Response [9] 194 Cons: 195 o This alternative requires that the remote endpoint support STUN. 197 4.4. RTP Packet with Comfort Noise Payload 199 The application sends a RTP packet with a comfort-noise payload [11]. 201 Cons: 202 o This alternative is limited to voice payload formats only. 203 o For each payload type, the content of the payload needs to be 204 specified. 206 4.5. RTP Packet with No-Op Payload 208 The application sends a RTP No-OP payload [12] . 210 Cons: 211 o This payload type needs to be supported by the remote peer. 212 o This payload type needs to be signalled in SDP offer/answer. 214 4.6. RTP Packet with Incorrect Version Number 216 The application sends a RTP with an incorrect version number. 218 Based on RTP specification [4], the peer should perform a header 219 validity check, and therefore ignore these types of packet. 221 Cons: 222 o Only four version numbers are possible. Using one of them for RTP 223 keepalive would be wasteful. 225 4.7. RTP Packet with Unknown Payload Type 227 The application sends a RTP packet with an unknown payload type. 229 Normally the peer will ignore it, as RTP [4] states that "a receiver 230 MUST ignore packets with payload types that it does not understand". 232 For example, the keepalive RTP packets contain a dynamic payload type 233 that has not been negotiated for the session. 235 [Note: more details on the selection of the payload type are needed 236 here.] 238 Cons: 239 o None 241 5. Recommended Solution 243 An application supporting this specification MUST send keepalive 244 packets under the form of ... [Note: The recommended solution needs 245 to be discussed. However recommending a single method among the 246 alternatives of the previous section is the best in term of 247 interoperability. Proposal is the alternative of Section 4.7] 249 Keepalives packets MUST be sent for each RTP stream regardless of 250 whether the media stream is currently inactive, sendonly, recvonly or 251 sendrecv. 253 Keepalives packets within a particular RTP media stream MUST use the 254 tuple (source IP address, source TCP/UDP ports, target IP address, 255 target TCP/UDP Port) of the regular RTP packets." 257 Keepalive packets MUST be sent every Tr seconds. Tr SHOULD be 258 configurable, and otherwise MUST default to 15 seconds. [Note: same 259 value as in [5].] 261 An application starts sending keepalives packet as soon as the first 262 regular RTP packet of the media stream has been sent. It ceases 263 sending these keepalives packet when the media stream is disabled, or 264 when the communication terminates. 266 6. Security Considerations 268 T.B.D. 270 7. Acknowledgements 272 Jonathan Rosenberg, via the ICE specification, provided the major 273 inputs for this draft. In addition, thanks to the following folks 274 for useful inputs and comments: Dan Wing, and Aurelien Sollaud. 276 8. References 278 [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement 279 Levels", RFC 2119, March 1997. 281 [2] Audet, F. and C. Jennings, "Network Address Translation (NAT) 282 Behavioral Requirements for Unicast UDP", RFC 4787, 283 January 2007. 285 [3] Guha, S., Biswas, K., Ford, B., Francis, P., Sivarkumar, S., 286 and P. Srisuresh, "NAT Behavioral Requirements for TCP", 287 draft-ietf-behave-tcp-04 (work in progress), January 2007. 289 [4] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 290 "RTP: A Transport Protocol for Real-Time Applications", 291 RFC 3550, July 2003. 293 [5] Rosenberg, J., "Interactive Connectivity Establishment (ICE): A 294 Methodology for Network Address Translator (NAT) Traversal for 295 Offer/Answer Protocols", draft-ietf-mmusic-ice-13 (work in 296 progress), January 2007. 298 [6] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 299 the Session Description Protocol (SDP)", RFC 3264, June 2002. 301 [7] Hellstrom, G. and P. Jones, "RTP Payload for Text 302 Conversation", RFC 4103, June 2005. 304 [8] Perkins, C. and M. Magnus, "Multiplexing RTP Data and Control 305 Packets on a Single Port", draft-ietf-avt-rtp-and-rtcp-mux-03 306 (work in progress), December 2006. 308 [9] Rosenberg, J., Huitema, C., Mahy, R., and D. Wing, "Simple 309 Traversal Underneath Network Address Translators (NAT) (STUN)", 310 draft-ietf-behave-rfc3489bis-05 (work in progress), 311 October 2006. 313 [10] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 314 Description Protocol", RFC 4566, July 2006. 316 [11] Robert, R., "Real-time Transport Protocol (RTP) Payload for 317 Comfort Noise (CN)", RFC 3389, September 2002. 319 [12] Andreason, F., Oran, D., and D. Wing, "A No-Op Payload Format 320 for RTP", draft-ietf-avt-rtp-no-op-00 (work in progress), 321 May 2005. 323 Author's Address 325 Xavier Marjou (editor) 326 France Telecom 327 2, hent Pierre Marzin 328 Lannion, Brittany 22307 329 France 331 Email: xavier.marjou@orange-ftgroup.com 333 Full Copyright Statement 335 Copyright (C) The IETF Trust (2007). 337 This document is subject to the rights, licenses and restrictions 338 contained in BCP 78, and except as set forth therein, the authors 339 retain all their rights. 341 This document and the information contained herein are provided on an 342 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 343 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 344 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 345 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 346 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 347 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 349 Intellectual Property 351 The IETF takes no position regarding the validity or scope of any 352 Intellectual Property Rights or other rights that might be claimed to 353 pertain to the implementation or use of the technology described in 354 this document or the extent to which any license under such rights 355 might or might not be available; nor does it represent that it has 356 made any independent effort to identify any such rights. 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