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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC S. Loreto 3 Internet-Draft G. Camarillo 4 Intended status: Standards Track Ericsson 5 Expires: January 5, 2012 July 4, 2011 7 Stream Control Transmission Protocol (SCTP)-Based Media Transport in the 8 Session Description Protocol (SDP) 9 draft-ietf-mmusic-sctp-sdp-00 11 Abstract 13 SCTP (Stream Control Transmission Protocol) is a transport protocol 14 used to establish associations between two endpoints. This document 15 describes how to express media transport over SCTP in SDP (Session 16 Description Protocol). This document defines the 'SCTP' and 'SCTP/ 17 DTLS' protocol identifiers for SDP. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on January 5, 2012. 36 Copyright Notice 38 Copyright (c) 2011 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3 55 3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . . 3 56 4. The Setup and Connection Attributes and Association 57 Management . . . . . . . . . . . . . . . . . . . . . . . . . . 4 58 5. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . . 4 59 6. Network Address Translation (NAT) Considerations . . . . . . . 5 60 7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 7.1. Actpass/Passive . . . . . . . . . . . . . . . . . . . . . . 6 62 7.2. Existing Connection Reuse . . . . . . . . . . . . . . . . . 6 63 7.3. SDP description for DTLS Connection . . . . . . . . . . . . 7 64 8. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 65 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 66 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 67 10.1. Normative References . . . . . . . . . . . . . . . . . . . 8 68 10.2. Informative References . . . . . . . . . . . . . . . . . . 9 69 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 71 1. Introduction 73 SDP (Session Description Protocol) [RFC4566] provides a general- 74 purpose format for describing multimedia sessions in announcements or 75 invitations. RFC4145 [RFC4145] specifies a general mechanism for 76 describing and establishing TCP (Transmission Control Protocol) 77 streams. RFC 4572 [RFC4572] extends RFC4145 [RFC4145] for describing 78 TCP-based media streams that are protected using TLS (Transport Layer 79 Security) [RFC5246]. 81 This document defines a new protocol identifier, 'SCTP', to describe 82 SCTP-based [RFC4960] media streams. Additionally, this document 83 specifies the use of the 'setup' and 'connection' SDP attributes to 84 establish SCTP associations. These attributes were defined in 85 RFC4145 [RFC4145] for TCP. This document discusses their use with 86 SCTP. 88 Additionally this document defines a new protocol identifier, 'SCTP/ 89 DTLS', to establish secure SCTP-based media streams over DTLS 90 (Datagram Transport Layer Security) [RFC4347], as specified in 91 [RFC6083], using SDP. The authentication certificates are 92 interpreted and validated as defined in RFC4572 [RFC4572]. Self- 93 signed certificates can be used securely, provided that the integrity 94 of the SDP description is assured as defined in RFC4572 [RFC4572]. 96 TLS is designed to run on top of a byte-stream oriented transport 97 protocol providing a realible, in-sequence delivery like TCP. Since 98 no-one so far has implemented SCTP over TLS, due to some serious 99 limitations described in [RFC6083], this document does not make use 100 of TLS over SCTP as described in RFC3436 [RFC3436]. 102 2. Terminology 104 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 105 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT 106 RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as 107 described in BCP 14, RFC 2119 [RFC2119] and indicate requirement 108 levels for compliant implementations. 110 3. Protocol Identifier 112 The following is the format for an 'm' line, as specified in RFC4566 113 [RFC4566]: 115 m= ... 117 This document defines two new values for the 'proto' field: 'SCTP' 118 and 'SCTP/DTLS'. 120 The 'SCTP' protocol identifier is similar to both the 'UDP' and 'TCP' 121 protocol identifiers in that it only describes the transport protocol 122 and not the upper-layer protocol. Media described using an 'm' line 123 containing the 'SCTP' protocol identifier are carried using SCTP 124 [RFC4960]. 126 The 'SCTP/DTLS' protocol identifier indicates that the media 127 described will use the Datagram Transport Layer Security (DTLS) 128 [RFC4347] over SCTP as specified in [RFC6083]. 130 An 'm' line that specifies 'SCTP' or 'SCTP/DTLS' MUST further qualify 131 the application-layer protocol using an fmt identifier. 133 An 'm' line that specifies 'SCTP/DTLS' MUST further provide a 134 certificate fingerprint. An SDP attribute (an 'a' line) is used to 135 transport and exchange end point certificate. The authentication 136 certificates are interpreted and validated as defined in [RFC4572]. 138 4. The Setup and Connection Attributes and Association Management 140 The use of the 'setup' and 'connection' attributes in the context of 141 an SCTP association is identical to the use of these attributes in 142 the context of a TCP connection. That is, SCTP endpoints MUST follow 143 the rules in Sections 4 and 5 of RFC 4145 [RFC4145] when it comes to 144 the use of the 'setup' and 'connection' attributes in offer/answer 145 [RFC3264] exchanges. 147 The management of an SCTP association is identical to the management 148 of a TCP connection. That is, SCTP endpoints MUST follow the rules 149 in Section 6 of RFC 4145 [RFC4145] to manage SCTP associations. 150 Whether to use the SCTP ordered or unordered delivery service is up 151 to the applications using the SCTP association. 153 5. Multihoming 155 An SCTP endpoint, unlike a TCP endpoint, can be multihomed. An SCTP 156 endpoint is considered to be multihomed if it has more than one IP 157 address. A multihomed SCTP endpoint informs a remote SCTP endpoint 158 about all its IP addresses using the address parameters of the INIT 159 or the INIT-ACK chunk (depending on whether the multihomed endpoint 160 is the one initiating the establishment of the association). 161 Therefore, once the address provided in the 'c' line has been used to 162 establish the SCTP association (i.e., to send the INIT chunk), 163 address management is performed using SCTP. This means that two SCTP 164 endpoints can use addresses that were not listed in the 'c' line but 165 that were negotiated using SCTP mechanisms. 167 During the lifetime of an SCTP association, the endpoints can add and 168 remove new addresses from the association at any point [RFC5061]. If 169 an endpoint removes the IP address listed in its 'c' line from the 170 SCTP association, the endpoint MUST update the 'c' line (e.g., by 171 sending a re-INVITE with a new offer) so that it contains an IP 172 address that is valid within the SCTP association. 174 In some environments, intermediaries performing firewall control use 175 the addresses in offer/answer exchanges to perform media 176 authorization. That is, policy-enforcement network elements do not 177 let media through unless it is sent to the address in the 'c' line. 179 In such network environments, the SCTP endpoints can only exchange 180 media using the IP addresses listed in their 'c' lines. In these 181 environments, an endpoint wishing to use a different address needs to 182 update its 'c' line (e.g., by sending a re-INVITE with a new offer) 183 so that it contains the new IP address. 185 6. Network Address Translation (NAT) Considerations 187 SCTP specific features (not present in UDP/TCP), such as the checksum 188 (CRC32c) value calculated on the whole packet (not just the header) 189 or its multihoming capabilities, present new challenges for NAT 190 traversal. [I-D.ietf-behave-sctpnat] describes an SCTP specific 191 variant of NAT, which provides similar features of Network Address 192 and Port Translation (NAPT). 194 Current NATs do not typically support SCTP. As an alternative to 195 design SCTP specific NATs, Encapsulating SCTP into UDP 196 [I-D.tuexen-sctp-udp-encaps] makes it possible to use SCTP in 197 networks with legacy NAT and firewalls not supporting SCTP. 199 At the time of writing, the work on NAT traversal for SCTP is still 200 work in progress. Additionally, no extension has been defined to 201 integrate ICE (Interactive Connectivity Establishment) [RFC5768] with 202 SCTP and its multihoming capabilities either. Therefore, this 203 specification does not define how to describe SCTP-over-UDP streams 204 in SDP or how to establish and maintain SCTP associations using ICE. 205 Should these features be specified for SCTP in the future, there will 206 be a need to specify how to use them in an SDP environment as well. 208 7. Examples 210 The following examples show the use of the 'setup' and 'connection' 211 SDP attributes. As discussed in Section 4, the use of these 212 attributes with an SCTP association is identical to their use with a 213 TCP connection. For the purpose of brevity, the main portion of the 214 session description is omitted in the examples, which only show 'm' 215 lines and their attributes (including 'c' lines). 217 7.1. Actpass/Passive 219 An offerer at 192.0.2.2 signals its availability for an SCTP 220 association at SCTP port 54111. Additionally, this offerer is also 221 willing to initiate the SCTP association: 223 m=image 54111 SCTP * 224 c=IN IP4 192.0.2.2 225 a=setup:actpass 226 a=connection:new 228 Figure 1 230 The endpoint at 192.0.2.1 responds with the following description: 232 m=image 54321 SCTP * 233 c=IN IP4 192.0.2.1 234 a=setup:passive 235 a=connection:new 237 Figure 2 239 This will cause the offerer (at 192.0.2.2) to initiate an SCTP 240 association to port 54321 at 192.0.2.1. 242 7.2. Existing Connection Reuse 244 Subsequent to the exchange in Section 7.1, another offer/answer 245 exchange is initiated in the opposite direction. The endpoint at 246 192.0.2.1, which now acts as the offerer, wishes to continue using 247 the existing association: 249 m=application 54321 SCTP * 250 c=IN IP4 192.0.2.1 251 a=setup:passive 252 a=connection:new 254 Figure 3 256 The endpoint at 192.0.2.2 also wishes to use the existing SCTP 257 association and responds with the following description: 259 m=application 9 SCTP * 260 c=IN IP4 192.0.2.2 261 a=setup:active 262 a=connection:new 264 Figure 4 266 The existing SCTP association between 192.0.2.2 and 192.0.2.1 will be 267 reused. 269 7.3. SDP description for DTLS Connection 271 An offerer at 192.0.2.2 signals the availability of a T.38 fax 272 session over SCTP/DTLS. 274 m=image 54111 SCTP/DTLS t38 275 c=IN IP4 192.0.2.2 276 a=setup:actpass 277 a=connection:new 278 a=fingerprint:SHA-1 \ 279 4A:AD:B9:B1:3F:82:18:3B:54:02:12:DF:3E:5D:49:6B:19:E5:7C:AB 281 Figure 5 283 8. Security Considerations 285 See RFC 4566 [RFC4566] for security considerations on the use of SDP 286 in general. See RFC 3264 [RFC3264], RFC 4145 [RFC4145] and RFC 4572 287 [RFC4572] for security considerations on establishing media streams 288 using offer/answer exchanges. See RFC 4960 [RFC4960] for security 289 considerations on SCTP in general and [RFC6083] for security 290 consideration using DTLS on top of SCTP. This specification does not 291 introduce any new security consideration in addition to the ones 292 discussed in those specifications. 294 9. IANA Considerations 296 This document defines two new proto values: 'SCTP' and 'SCTP/DTLS'. 297 Their formats are defined in Section 3. These proto values should be 298 registered by the IANA under "Session Description Protocol (SDP) 299 Parameters" under "proto". 301 The SDP specification, [RFC4566], states that specifications defining 302 new proto values, like the SCTP and SCTP/DTLS proto values defined in 303 this RFC, must define the rules by which their media format (fmt) 304 namespace is managed. For the SCTP protocol, new formats SHOULD have 305 an associated MIME registration. Use of an existing MIME subtype for 306 the format is encouraged. If no MIME subtype exists, it is 307 RECOMMENDED that a suitable one is registered through the IETF 308 process [RFC4288] [RFC4289] by production of, or reference to, a 309 standards-track RFC that defines the transport protocol for the 310 format. 312 10. References 314 10.1. Normative References 316 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 317 Requirement Levels", BCP 14, RFC 2119, March 1997. 319 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 320 with Session Description Protocol (SDP)", RFC 3264, 321 June 2002. 323 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 324 the Session Description Protocol (SDP)", RFC 4145, 325 September 2005. 327 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and 328 Registration Procedures", BCP 13, RFC 4288, December 2005. 330 [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail 331 Extensions (MIME) Part Four: Registration Procedures", 332 BCP 13, RFC 4289, December 2005. 334 [RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 335 Security", RFC 4347, April 2006. 337 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 338 Description Protocol", RFC 4566, July 2006. 340 [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the 341 Transport Layer Security (TLS) Protocol in the Session 342 Description Protocol (SDP)", RFC 4572, July 2006. 344 [RFC4960] Stewart, R., "Stream Control Transmission Protocol", 345 RFC 4960, September 2007. 347 [RFC5061] Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M. 348 Kozuka, "Stream Control Transmission Protocol (SCTP) 349 Dynamic Address Reconfiguration", RFC 5061, 350 September 2007. 352 [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security 353 (TLS) Protocol Version 1.2", RFC 5246, August 2008. 355 10.2. Informative References 357 [RFC3436] Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport 358 Layer Security over Stream Control Transmission Protocol", 359 RFC 3436, December 2002. 361 [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram 362 Transport Layer Security (DTLS) for Stream Control 363 Transmission Protocol (SCTP)", RFC 6083, January 2011. 365 [RFC5768] Rosenberg, J., "Indicating Support for Interactive 366 Connectivity Establishment (ICE) in the Session Initiation 367 Protocol (SIP)", RFC 5768, April 2010. 369 [I-D.ietf-behave-sctpnat] 370 Stewart, R., Tuexen, M., and I. Ruengeler, "Stream Control 371 Transmission Protocol (SCTP) Network Address Translation", 372 draft-ietf-behave-sctpnat-04 (work in progress), 373 December 2010. 375 [I-D.tuexen-sctp-udp-encaps] 376 Tuexen, M. and R. Stewart, "UDP Encapsulation of SCTP 377 Packets", draft-tuexen-sctp-udp-encaps-06 (work in 378 progress), January 2011. 380 Authors' Addresses 382 Salvatore Loreto 383 Ericsson 384 Hirsalantie 11 385 Jorvas 02420 386 Finland 388 Email: Salvatore.Loreto@ericsson.com 389 Gonzalo Camarillo 390 Ericsson 391 Hirsalantie 11 392 Jorvas 02420 393 Finland 395 Email: Gonzalo.Camarillo@ericsson.com