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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MMUSIC C. Holmberg 3 Internet-Draft Ericsson 4 Intended status: Standards Track R. Shpount 5 Expires: April 10, 2017 TurboBridge 6 S. Loreto 7 G. Camarillo 8 Ericsson 9 October 7, 2016 11 Session Description Protocol (SDP) Offer/Answer Procedures For Stream 12 Control Transmission Protocol (SCTP) over Datagram Transport Layer 13 Security (DTLS) Transport. 14 draft-ietf-mmusic-sctp-sdp-18 16 Abstract 18 The Stream Control Transmission Protocol (SCTP) is a transport 19 protocol used to establish associations between two endpoints. 20 draft-ietf-tsvwg-sctp-dtls-encaps-09 specifies how SCTP can be used 21 on top of the Datagram Transport Layer Security (DTLS) protocol, 22 referred to as SCTP-over-DTLS. 24 This specification defines the following new Session Description 25 Protocol (SDP) protocol identifiers (proto values):'UDP/DTLS/SCTP' 26 and 'TCP/DTLS/SCTP'. This specification also specifies how to use 27 the new proto values with the SDP Offer/Answer mechanism for 28 negotiating SCTP-over-DTLS associations. 30 Status of This Memo 32 This Internet-Draft is submitted in full conformance with the 33 provisions of BCP 78 and BCP 79. 35 Internet-Drafts are working documents of the Internet Engineering 36 Task Force (IETF). Note that other groups may also distribute 37 working documents as Internet-Drafts. The list of current Internet- 38 Drafts is at http://datatracker.ietf.org/drafts/current/. 40 Internet-Drafts are draft documents valid for a maximum of six months 41 and may be updated, replaced, or obsoleted by other documents at any 42 time. It is inappropriate to use Internet-Drafts as reference 43 material or to cite them other than as "work in progress." 45 This Internet-Draft will expire on April 10, 2017. 47 Copyright Notice 49 Copyright (c) 2016 IETF Trust and the persons identified as the 50 document authors. All rights reserved. 52 This document is subject to BCP 78 and the IETF Trust's Legal 53 Provisions Relating to IETF Documents 54 (http://trustee.ietf.org/license-info) in effect on the date of 55 publication of this document. Please review these documents 56 carefully, as they describe your rights and restrictions with respect 57 to this document. Code Components extracted from this document must 58 include Simplified BSD License text as described in Section 4.e of 59 the Trust Legal Provisions and are provided without warranty as 60 described in the Simplified BSD License. 62 Table of Contents 64 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 65 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 66 3. SCTP Terminology . . . . . . . . . . . . . . . . . . . . . . 4 67 4. SDP Media Descriptions . . . . . . . . . . . . . . . . . . . 4 68 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 4 69 4.2. Protocol Identifiers . . . . . . . . . . . . . . . . . . 5 70 4.3. Media Format Management . . . . . . . . . . . . . . . . . 5 71 4.4. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 6 72 4.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 6 73 4.4.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . 6 74 4.5. Example . . . . . . . . . . . . . . . . . . . . . . . . . 6 75 5. SDP 'sctp-port' Attribute . . . . . . . . . . . . . . . . . . 6 76 5.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 6 77 5.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 7 78 5.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 7 79 6. SDP 'max-message-size' Attribute . . . . . . . . . . . . . . 7 80 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 7 81 6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8 82 6.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 8 83 7. UDP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 8 84 8. TCP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 9 85 9. Association And Connection Management . . . . . . . . . . . . 9 86 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 9 87 9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute . . . . 9 88 9.3. SCTP Association . . . . . . . . . . . . . . . . . . . . 9 89 9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) . . . 10 90 9.5. TCP Connection (TCP/DTLS/SCTP) . . . . . . . . . . . . . 11 91 10. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 11 92 10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 11 93 10.2. Generating the Initial SDP Offer . . . . . . . . . . . . 11 94 10.3. Generating the SDP Answer . . . . . . . . . . . . . . . 12 95 10.4. Offerer Processing of the SDP Answer . . . . . . . . . . 13 96 10.5. Modifying the Session . . . . . . . . . . . . . . . . . 13 97 11. Multihoming Considerations . . . . . . . . . . . . . . . . . 14 98 12. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 14 99 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 14 100 12.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 14 101 13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15 102 13.1. Establishment of UDP/DTLS/SCTP association . . . . . . . 15 103 14. Security Considerations . . . . . . . . . . . . . . . . . . . 16 104 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17 105 15.1. New SDP proto values . . . . . . . . . . . . . . . . . . 17 106 15.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 17 107 15.2.1. sctp-port . . . . . . . . . . . . . . . . . . . . . 17 108 15.2.2. max-message-size . . . . . . . . . . . . . . . . . . 18 109 15.3. association-usage Name Registry . . . . . . . . . . . . 18 110 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19 111 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 112 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 113 18.1. Normative References . . . . . . . . . . . . . . . . . . 21 114 18.2. Informative References . . . . . . . . . . . . . . . . . 23 115 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 117 1. Introduction 119 SDP (Session Description Protocol) [RFC4566] provides a general- 120 purpose format for describing multimedia sessions in announcements or 121 invitations. TCP-Based Media Transport in the Session Description 122 Protocol (SDP) [RFC4145] specifies a general mechanism for describing 123 and establishing TCP [RFC0793] streams. Connection-Oriented Media 124 Transport over the Transport Layer Security (TLS) Protocol in SDP 125 [RFC4572] extends RFC4145 [RFC4145] for describing TCP-based media 126 streams that are protected using TLS. 128 The Stream Control Transmission Protocol (SCTP) [RFC4960] is a 129 transport protocol used to establish associations between two 130 endpoints. 132 The Stream Control Transmission Protocol (SCTP) [RFC4960] is a 133 transport protocol used to establish associations between two 134 endpoints. [I-D.ietf-tsvwg-sctp-dtls-encaps] specifies how SCTP can 135 be used on top of the Datagram Transport Layer Security (DTLS) 136 protocol, referred to as SCTP-over-DTLS. 138 This specification defines the following new Session Description 139 Protocol (SDP) [RFC4566] protocol identifiers (proto 140 values):'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. This specification also 141 specifies how to use the new proto values with the SDP Offer/Answer 142 mechanism [RFC3264] for negotiating SCTP-over-DTLS associations. 144 NOTE: TLS is designed to run on top of a byte-stream oriented 145 transport protocol providing a reliable, in-sequence delivery like 146 TCP. [RFC6083] presents serious limitations with transporting TLS on 147 top of SCTP. Therefore, defining a mechanism to negotiate media 148 streams transported using TLS on top of SCTP, i.e., 'SCTP/TLS', is 149 outside the scope of this specification. In addition, defining a 150 mechanism to negotiate non-protected SCTP associations is also 151 outside the scope of this specification. 153 2. Conventions 155 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 156 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 157 document are to be interpreted as described in [RFC2119]. 159 3. SCTP Terminology 161 SCTP Association: A protocol relationship between SCTP endpoints, 162 composed of the two SCTP endpoints and protocol state information 163 including Verification Tags and the currently active set of 164 Transmission Sequence Numbers (TSNs), etc. An association can be 165 uniquely identified by the transport addresses used by the endpoints 166 in the association. 168 SCTP Stream: A unidirectional logical channel established from one to 169 another associated SCTP endpoint, within which all user messages are 170 delivered in sequence except for those submitted to the unordered 171 delivery service. 173 SCTP Transport address: A transport address is traditionally defined 174 by a network-layer address, a transport-layer protocol, and a 175 transport-layer port number. In the case of SCTP running over IP, a 176 transport address is defined by the combination of an IP address and 177 an SCTP port number (where SCTP is the transport protocol). 179 SCTP-over-DTLS: SCTP used on top of DTLS, as specified in 180 [I-D.ietf-tsvwg-sctp-dtls-encaps]. 182 4. SDP Media Descriptions 184 4.1. General 186 This section defines the following new SDP Media Description (m- 187 line) protocol identifiers (proto values) for describing an SCTP 188 association: UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. The section also 189 describes how an m- line, associated with the proto values, is 190 created. 192 The following is the format for an 'm' line, as specified in RFC4566 193 [RFC4566]: 195 m= ... 197 The 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are similar to 198 both the 'UDP' and 'TCP' proto values in that they only describe the 199 transport-layer protocol and not the upper-layer protocol. 201 NOTE: When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are 202 used, the underlying transport protocol is respectively UDP and TCP; 203 SCTP is carried on top of DTLS which is on top of those transport- 204 layer protocols. 206 The m- line fmt value, identifying the application-layer protocol, 207 MUST be registered by IANA. 209 4.2. Protocol Identifiers 211 The new proto values are defined as below: 213 o The 'UDP/DTLS/SCTP' proto value describes an SCTP association on 214 top of a DTLS association on top of UDP, as defined in Section 7. 216 o The 'TCP/DTLS/SCTP' proto value describes an SCTP association on 217 top of a DTLS association on top of TCP, as defined in Section 8. 219 4.3. Media Format Management 221 [RFC4566] defines that specifications defining new proto values must 222 define the rules by which their media format (fmt) namespace is 223 managed. Use of an existing MIME subtype for the format is 224 encouraged. If no MIME subtype exists, it is recommended that a 225 suitable one is registered through the IETF process [RFC6838] 226 [RFC4289] by production of, or reference to, a standards-track RFC 227 that defines the transport protocol for the format. 229 An m- line with a proto value of UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP' 230 always describe a single SCTP association. 232 In addition, such m- line MUST further indicate the application-layer 233 protocol using an 'fmt' identifier. There MUST be exactly one 'fmt' 234 value per m- line associated with the proto values defined in this 235 specification. The "fmt" namespace associated with those proto 236 values describes the generic application usage of the entire SCTP 237 association, including the associated SCTP streams. 239 NOTE: A mechanism on how to describe, and manage, individual SCTP 240 streams within an SCTP association, is outside the scope of this 241 specification. 243 4.4. Syntax 245 4.4.1. General 247 This section defines the ABNF [RFC5234] for the SDP media description 248 when associated with any of the proto values defined in this 249 document. 251 This specification creates an IANA registry for 'association-usage' 252 values. 254 4.4.2. ABNF 256 sctp-m-line = %x6d "=" 257 ("application" SP udp-port SP "UDP/DTLS/SCTP" SP fmt CRLF) / 258 ("application" SP tcp-port SP "TCP/DTLS/SCTP" SP fmt CRLF) 260 udp-port = port 262 tcp-port = port 264 fmt = association-usage 266 association-usage = token 268 token and port as defined in RFC4566 270 4.5. Example 272 m=application 12345 UDP/DTLS/SCTP webrtc-datachannel 273 a=max-message-size: 100000 275 5. SDP 'sctp-port' Attribute 277 5.1. General 279 This section defines a new SDP media-level attribute, 'sctp-port'. 280 The attribute can be associated with an SDP media description (m- 281 line) with a 'UDP/DTLS/SCTP' or a 'TCP/DTLS/SCTP' proto value. In 282 that case the m- line port value indicates the port of the underlying 283 transport layer protocol (UDP or TCP), and the 'sctp-port' value 284 indicates the SCTP port. 286 No default value is defined for the SDP sctp-port attribute. 287 Therefore, if the attribute is not present, the associated m- line 288 MUST be considered invalid. 290 Usage of the SDP 'sctp-port' attribute with other proto values is not 291 specified, and MUST be discarded if received. 293 5.2. Syntax 295 The ABNF for the SDP 'sctp-port' attribute is: 297 sctp-port-attr = "a=sctp-port:" port 298 port = (1*5)DIGIT 300 The SCTP port range is between 0 and 65535 (both included). 301 Leading zeroes MUST NOT be used. 303 5.3. Mux Category 305 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the SDP 306 sctp-port' attribute is SPECIAL. Usage of the attribute is only 307 applicable when associated with 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' 308 proto value m- lines. 310 As the usage of multiple SCTP associations on top of a single DTLS 311 association is outside the scope of this specification, no mux rules 312 are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto 313 values. Future extensions, that define how to negotiate multiplexing 314 of multiple SCTP associations of top of a single DTLS association, 315 need to also define the mux rules for the attribute. 317 6. SDP 'max-message-size' Attribute 319 6.1. General 321 This section defines a new SDP media-level attribute, 'max-message- 322 size'. The attribute can be associated with an m- line to indicate 323 the maximum message size (indicated in bytes) that an SCTP endpoint 324 is willing to receive on the SCTP association associated with the m- 325 line. Different attribute values can be used in each direction. 327 The remote peer MUST assume that larger messages will be rejected by 328 the SCTP endpoint. SCTP endpoints need to decide on appropriate 329 behavior in case a message that exceeds the maximum size needs to be 330 sent. 332 If the SDP 'max-message-size' attribute contains a maximum message 333 size value of zero, it indicates the SCTP endpoint will handle 334 messages of any size, subject to memory capacity etc. 336 If the SDP 'max-message-size' attribute is not present, the default 337 value is 64K. 339 NOTE: This specification only defines the usage of the SDP 'max- 340 message-size' attribute when associated with an m- line containing 341 one of the following proto values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/ 342 SCTP'. Usage of the attribute with other proto values needs to be 343 defined in a separate specification. 345 6.2. Syntax 347 The ABNF for the SDP 'max-message-size' attribute is: 349 max-message-size-attr = "a=max-message-size:" max-message-size 350 max-message-size = 1*40DIGIT 352 Leading zeroes MUST NOT be used. 354 6.3. Mux Category 356 The mux category for the SDP 'max-message-size' attribute is SPECIAL. 357 The mux rules depends on the proto value of the associated m- line. 359 As the usage of multiple SCTP associations on top of a single DTLS 360 association is outside the scope of this specification, no mux rules 361 are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto 362 values. 364 7. UDP/DTLS/SCTP Transport Realization 366 The UDP/DTLS/SCTP transport is realized as described below: 368 o SCTP on top of DTLS is realized according to the procedures 369 defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and 371 o DTLS on top of UDP is realized according to the procedures in 372 defined in [RFC6347]. 374 NOTE: While [I-D.ietf-tsvwg-sctp-dtls-encaps] allows multiple SCTP 375 associations on top of a single DTLS association, the procedures in 376 this specification only supports the negotiation of a single SCTP 377 association on top of any given DTLS association. 379 8. TCP/DTLS/SCTP Transport Realization 381 The TCP/DTLS/SCTP transport is realized as described below: 383 o SCTP on top of DTLS is realized according to the procedures 384 defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and 386 o DTLS on top of TCP is realized using the framing method defined in 387 [RFC4571], with DTLS packets being sent instead of RTP/RTCP 388 packets, and SDP signaling according to the procedures defined in 389 this specification. 391 NOTE: DTLS on top of TCP, without using the framing method defined in 392 [RFC4571] is outside the scope of this specification. A separate 393 proto value would need to be registered for such transport 394 realization. 396 9. Association And Connection Management 398 9.1. General 400 This section describes how to mange an SCTP association, DTLS 401 association and TCP connection using SDP attributes. 403 In case of UDP/DTLS/SCTP and TCP/DTLS/SCTP the SCTP association, DTLS 404 association and TCP connection are managed independently for each 405 other. An association/connection can be re-established without 406 impacting other associations/connections. 408 The detailed SDP Offer/Answer [RFC3264] procedures for the SDP 409 attributes are described in (Section 10). 411 9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute 413 This specification does not define semantics for the SDP direction 414 attributes [RFC4566]. Unless semantics of these attributes for an 415 SCTP association usage have been defined, SDP direction attributes 416 MUST be discarded if present. 418 9.3. SCTP Association 420 When an SCTP association is established/re-established, both SCTP 421 endpoints MUST initiate the SCTP association (i.e. both SCTP 422 endpoints take the 'active' role), and MUST use the same SCTP port as 423 client port and server port (in order to prevent two separate SCTP 424 associations from being established). 426 As both SCTP endpoints take the 'active' role, this specification 427 does not define usage of the SDP 'setup' attribute [RFC4145] for 428 SCTP. 430 NOTE: The procedure above is different from TCP, where one endpoint 431 takes the 'active' role, the other endpoint takes the 'passive' role, 432 and only the 'active' endpoint initiates the TCP connection 433 [RFC4145]. 435 NOTE: In case of SCTP-over-DTLS, when the SCTP association is 436 established it is assumed that any NAT traversal procedures for the 437 underlying transport protocol (UDP or TCP) has successfully been 438 performed. 440 Usage of the SDP 'connection' attribute [RFC4145] is not defined for 441 SCTP. In order to trigger the closure and re-establishment of an 442 SCTP association, the SDP 'sctp-port' attribute (Section 5) is used 443 to indicate a new (different than the ones currently used) SCTP port. 445 Alternatively, an SCTP association can be closed using the SDP 'sctp- 446 port' attribute with a zero attribute value. Later, the SCTP 447 association can be re-established using the procedures in this 448 section for establishing an SCTP association. 450 SCTP associations might be closed without SDP signalling, e.g, in 451 case of a failure. When such SCTP association is re-established the 452 SCTP endpoints MUST use the procedures in this section for 453 establishing an SCTP association. New (different than the ones 454 currently used) SCTP ports MUST be used. 456 NOTE: Closing and re-establishing the SCTP association using the SDP 457 'sctp-port' attribute will not impact the underlying DTLS 458 association. 460 9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) 462 An DTLS association is managed according to the procedures in 463 [I-D.ietf-mmusic-dtls-sdp]. Hence, the SDP 'setup' attribute is used 464 to negotiate the (D)TLS roles ('client' and 'server') [RFC4572]. 466 NOTE: The SDP 'setup' attribute is used both to negotiate both the 467 DTLS roles and the TCP roles (Section 9.5). 469 NOTE: As described in [RFC5245], if the Interactive Connectivity 470 Establishment (ICE) mechanism [RFC5245] is used, all ICE candidates 471 associated with an DTLS association as considered part of the same 472 DTLS association. Thus, a switch from one candidate pair to another 473 candidate pair will not trigger the establishment of a new DTLS 474 association. 476 9.5. TCP Connection (TCP/DTLS/SCTP) 478 The TCP connection is managed according to the procedures in 479 [RFC4145]. Hence, the SDP 'setup' attribute is used to negotiate the 480 TCP roles ('active' and 'passive'), and the SDP 'connection' 481 attribute is used to indicate whether to use an existing TCP 482 connection, or create a new one. The SDP 'setup' attribute 483 'holdconn' value MUST NOT be used. 485 NOTE: A change of the TCP roles will also trigger a re-establishment 486 of the DTLS association, according to the procedures in 487 [I-D.ietf-mmusic-dtls-sdp]. 489 NOTE: As specified in [I-D.ietf-mmusic-dtls-sdp], usage of the SDP 490 'setup' attribute 'holdconn' value is not allowed. Therefore this 491 specification also forbids usage of the attribute value for TCP, as 492 DTLS is transported on top of TCP. 494 10. SDP Offer/Answer Procedures 496 10.1. General 498 This section defines the SDP Offer/Answer [RFC3264] procedures for 499 negotiating and establishing an SCTP-over-DTLS association. Unless 500 explicitly stated, the procedures apply to both the 'UDP/DTLS/SCTP' 501 and 'TCP/DTLS/SCTP' m- line proto values. 503 Each endpoint MUST associate one or more certificate fingerprints, 504 using the SDP 'fingerprint' attribute with the m- line, following the 505 procedures in [RFC4572] and [I-D.ietf-mmusic-4572-update]. 507 The authentication certificates are interpreted and validated as 508 defined in [RFC4572]. Self-signed certificates can be used securely, 509 provided that the integrity of the SDP description is assured as 510 defined in [RFC4572]. 512 Each endpoint MUST associate an SDP 'dtls-id' attribute with the m- 513 line, following the procedures in [I-D.ietf-mmusic-dtls-sdp]. 515 10.2. Generating the Initial SDP Offer 517 When the offerer creates an initial offer, the offerer: 519 o MUST associate an SDP setup attribute, with an 'actpass' value, 520 with the m- line; 522 o MUST associate an SDP 'sctp-port' attribute with the m- line; 524 o MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection' 525 attribute, with a 'new' attribute value, with the m- line; and 527 o MAY associate an SDP 'max-message-size' attribute (Section 6) with 528 the m- line. 530 10.3. Generating the SDP Answer 532 When the answerer receives an offer, which contains an m- line 533 describing an SCTP-over-DTLS association, if the answerer accepts the 534 association line it: 536 o MUST insert a corresponding m- line in the answer, with an 537 identical m- line proto value [RFC3264]; 539 o MUST associate an SDP 'setup' attribute, with an 'active' or 540 'passive' value, with the m- line; 542 o MUST associate an SDP 'sctp-port' attribute with the m- line. If 543 the offer contained a new (different than the one currently used) 544 SCTP port value the answerer MUST also associate a new SCTP port 545 value. If the offer contained a zero SCTP port value the answerer 546 MUST also associate a zero SCTP port value; and 548 o MAY associate an SDP 'max-message-size' attribute (Section 6)with 549 the m- line. The attribute value in the answer is independent 550 from the value (if present) in the corresponding m- line of the 551 offer. 553 Once the answerer has sent the answer the answerer MUST, if an SCTP 554 association has yet not been established, or if an existing SCTP 555 association is to be re-established, initiate the establishment of 556 the SCTP association. 558 The answerer follows the procedures in [I-D.ietf-mmusic-dtls-sdp] 559 regarding the establishment/re-establishment of the DTLS association. 561 In the case of TCP/DTLS/SCTP, the answerer follows the procedures in 562 [RFC4145] regarding the establishment/re-establishment of the TCP 563 connection association. 565 If the answerer does not accept the m- line in the offer, it MUST 566 assign a zero port value to the corresponding m- line in the answer, 567 following the procedures in [RFC3264]. In addition, the answerer 568 MUST NOT initiate the establishment of an SCTP association, or a DTLS 569 association, associated with the m- line. 571 10.4. Offerer Processing of the SDP Answer 573 Once the offerer has received the answer, which contains an m- line 574 with a non-zero port value, the offerer MUST, if an SCTP association 575 has yet not been established, or if an existing SCTP association is 576 to be re-established, initiate the establishment of the SCTP 577 association. 579 If the SDP 'sctp-port' attribute in the answer contains a zero 580 attribute value, the offerer MUST NOT establish an SCTP association. 581 If an SCTP association exists, the offerer MUST close it. 583 The offerer follows the procedures in [I-D.ietf-mmusic-dtls-sdp] 584 regarding the establishment/re-establishment of the DTLS association. 586 In the case of TCP/DTLS/SCTP, the offerer follows the procedures in 587 [RFC4145] regarding the establishment/re-establishment of the TCP 588 connection association. 590 If the m- line in the answer contains a zero port value, the offerer 591 MUST NOT establish a TCP connection, an SCTP association, or a DTLS 592 association, associated with the m- line. If an SCTP association, 593 DTLS association and/or TCP connection exists, the offerer MUST close 594 it. 596 10.5. Modifying the Session 598 When an offerer sends an updated offer, in order to modify a 599 previously established SCTP association, it follows the procedures in 600 Section 10.2, with the following exceptions: 602 o If the offerer wants to close and immediately re-establish an 603 existing SCTP association, the offerer MUST associate an SDP 604 'sctp-port' attribute with a new (different than the one currently 605 used) attribute value. This will not impact the underlying DTLS 606 association (and TCP connection in case of TCP/DTLS/SCTP). 608 o If the offerer wants to close, but not re-establish an existing 609 SCTP association, the offerer MUST associate an SDP 'sctp-port' 610 attribute with a zero attribute value. This will not impact the 611 underlying DTLS association (and TCP connection in case of 612 TCP/DTLS/SCTP). 614 o If the offerer wants to re-establish a previously closed SCTP 615 association, the offerer MUST associate an SDP 'sctp-port' 616 attribute with a new (different than the one currently used) 617 attribute value. If the SCTP association was previously closed 618 using an SDP 'sctp-port' attribute with a zero attribute value, 619 the offerer MAY use the same attribute value that was used prior 620 to the SCTP association was closed. This will not impact the 621 underlying DTLS association (and TCP connection in case of 622 TCP/DTLS/SCTP). 624 o If the offerer wants to close an existing SCTP association, and 625 the underlying DTLS association (and the underlying TCP connection 626 in case of TCP/DTLS/SCTP) it MUST assign a zero port value to the 627 m- line associated with the SCTP and DTLS associations (and TCP 628 connection in case of TCP/DTLS/SCTP), following the procedures in 629 [RFC3264]. 631 o NOTE: This specification does not define a mechanism for 632 explicitly closing an DTLS association while maintaining the 633 overlying SCTP association. However, if a DTLS association is re- 634 established as a result of some other action 635 [I-D.ietf-mmusic-dtls-sdp] the SCTP association is not affected. 637 The offer follows the procedures in [I-D.ietf-mmusic-dtls-sdp] 638 regarding the DTLS association impacts when modifying a session. 640 In the case of TCP/DTLS/SCTP, the offer follows the procedures in 641 [RFC4145] regarding the TCP connection impacts when modifying a 642 session; 644 11. Multihoming Considerations 646 Multihoming is not supported when sending SCTP on top of DTLS, as 647 DTLS does not expose address management of the underlying transport 648 protocols (UDP or TCP) to its upper layer. 650 12. NAT Considerations 652 12.1. General 654 When SCTP-over-DTLS is used in NAT environment, it relies on the NAT 655 traversal procedures for the underlying transport protocol (UDP or 656 TCP). 658 12.2. ICE Considerations 660 When SCTP-over-DTLS is used with UDP based ICE candidates as defined 661 in [RFC5245] procedures for UDP/DTLS/SCTP, as defined in Section 7 662 are used. 664 When SCTP-over-DTLS is used with TCP based ICE candidates as defined 665 in [RFC6544] procedures for TCP/DTLS/SCTP, as defined in Section 8 666 are used. 668 Implementations MUST treat all ICE candidate pairs associated with a 669 an SCTP association on top of a DTLS association as part of the same 670 DTLS association. Thus, there will only be one SCTP handshake and 671 one DTLS handshake even if there are multiple valid candidate pairs, 672 and shifting from one candidate pair to another will not impact the 673 SCTP or DTLS associations. If new candidates are added, they will 674 also be part of the same SCTP and DTLS associations. When 675 transitioning between candidate pairs, different candidate pairs can 676 be currently active in different directions and implementations MUST 677 be ready to receive data on any of the candidates, even if this means 678 sending and receiving data using UDP/DTLS/SCTP and TCP/DTLS/SCTP at 679 the same time in different directions. 681 When an SDP offer or answer is sent, the proto value MUST match the 682 transport protocol associated with the default candidate. Hence, if 683 UDP transport is used for the default candidate the 'UDP/DTLS/SCTP' 684 proto value MUST be used. If TCP transport is used for the default 685 candidate the 'TCP/DTLS/SCTP' proto value MUST be used. However, if 686 an endpoint switch between TCP-based and UDP-based candidates during 687 a session the endpoint is not required to send an SDP offer in order 688 to modify that proto value of the associated m- line. 690 NOTE: The text in the paragraph above only applies when the usage of 691 ICE has been negotiated. If ICE is not used, the proto value MUST 692 always reflect the transport protocol used at any given time. 694 13. Examples 696 13.1. Establishment of UDP/DTLS/SCTP association 697 SDP Offer: 699 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 700 c=IN IP4 192.0.2.1 701 a=dtls-id:abc3dl 702 a=setup:actpass 703 a=sctp-port:5000 704 a=max-message-size:100000 706 - The offerer indicates that the usage of the 707 UDP/DTLS/SCTP association will be as defined 708 for the 'webrtc-datachannel' format value. 709 - The offerer UDP port value is 54111. 710 - The offerer SCTP port value is 5000. 711 - The offerer indicates that it can take either the 712 client or the server DTLS role. 714 SDP Answer: 716 m=application 64300 UDP/DTLS/SCTP webrtc-datachannel 717 c=IN IP4 192.0.2.2 718 a=dtls-id:ggr4rd 719 a=setup:passive 720 a=sctp-port:6000 721 a=max-message-size:100000 723 - The answerer UDP port value is 64300. 724 - The answerer SCTP port value is 6000. 725 - The answerer takes the server DTLS role. 727 14. Security Considerations 729 [RFC4566] defines general SDP security considerations, while 730 [RFC3264], [RFC4145] and [RFC4572] define security considerations 731 when using the SDP offer/answer mechanism to negotiate media streams. 733 [RFC4960] defines general SCTP security considerations and 734 [I-D.ietf-tsvwg-sctp-dtls-encaps] defines security considerations 735 when using SCTP on top of DTLS. 737 This specification does not introduce new security considerations in 738 addition to those defined in the specifications listed above. 740 15. IANA Considerations 742 15.1. New SDP proto values 744 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 745 document.] 747 This document updates the "Session Description Protocol (SDP) 748 Parameters" registry, following the procedures in [RFC4566], by 749 adding the following values to the table in the SDP "proto" field 750 registry: 752 +-------+---------------+-----------+ 753 | Type | SDP Name | Reference | 754 +-------+---------------+-----------+ 755 | proto | UDP/DTLS/SCTP | [RFCXXXX] | 756 | proto | TCP/DTLS/SCTP | [RFCXXXX] | 757 +-------+---------------+-----------+ 759 Table 1: SDP "proto" field values 761 15.2. New SDP Attributes 763 15.2.1. sctp-port 765 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 766 document.] 768 This document defines a new SDP media-level attribute,'sctp-port', as 769 follows: 771 Attribute name: sctp-port 772 Type of attribute: media 773 Mux category: SPECIAL 774 Subject to charset: No 775 Purpose: Indicate the SCTP port value associated 776 with the SDP Media Description. 777 Appropriate values: Integer 778 Contact name: Christer Holmberg 779 Contact e-mail: christer.holmberg@ericsson.com 780 Reference: RFCXXXX 782 15.2.2. max-message-size 784 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 785 document.] 787 This document defines a new SDP media-level attribute,'max-message- 788 size', as follows: 790 Attribute name: max-message-size 791 Type of attribute: media 792 Mux category: SPECIAL 793 Subject to charset: No 794 Purpose: Indicate the maximum message size that 795 an SCTP endpoint is willing to receive 796 on the SCTP association associated 797 with the SDP Media Description. 798 Appropriate values: Integer 799 Contact name: Christer Holmberg 800 Contact e-mail: christer.holmberg@ericsson.com 801 Reference: RFCXXXX 803 15.3. association-usage Name Registry 805 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 806 document.] 808 This specification creates a new IANA registry, following the 809 procedures in [RFC5226], for the "fmt" namespace associated with the 810 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' protocol identifiers. Each "fmt" 811 value describes the usage of an entire SCTP association, including 812 all SCTP streams associated with the SCTP association. 814 NOTE: Usage indication of individual SCTP streams is outside the 815 scope of this specification. 817 The "fmt" value, "association-usage", used with these "proto" is 818 required. It is defined in [Section 4]. 820 As part of this registry, IANA maintains the following information: 822 association-usage name: The identifier of the subprotocol, as will 823 be used as the "fmt" value. 825 association-usage reference: A reference to the document in which 826 the association-usage is defined. 828 association-usage names are to be subject to the "First Come First 829 Served" IANA registration policy [RFC5226]. 831 IANA is asked to add initial values to the registry. 833 |----------------------------------------------------------| 834 | name | Reference | 835 |----------------------------------------------------------| 836 | webrtc-datachannel | draft-ietf-rtcweb-data-protocol-xx | 837 |----------------------------------------------------------| 839 [RFC EDITOR NOTE: Please hold the publication of this draft 840 until draft-ietf-rtcweb-data-protocol has been published as an RFC. 841 Then, replace the reference to draft-ietf-rtcweb-data-protocol 842 with the RFC number.] 844 Figure 1 846 16. Acknowledgments 848 The authors wish to thank Harald Alvestrand, Randell Jesup, Paul 849 Kyzivat, Michael Tuexen, Juergen Stoetzer-Bradler, Flemming Andreasen 850 and Ari Keranen for their comments and useful feedback. 852 17. 854 [RFC EDITOR NOTE: Please remove this section when publishing] 856 Changes from draft-ietf-mmusic-sctp-sdp-17 858 o Removal of 'SCTP'. 860 o Document title changed. 862 o Disallow usage of SDP 'setup' attribute 'holdconn' value. 864 o Roman Shpount added as co-editor. 866 Changes from draft-ietf-mmusic-sctp-sdp-15 868 o Chapter about SCTP, DTLS and TCP association/connection management 869 modified. 871 o Removal of SCTP/DTLS. 873 Changes from draft-ietf-mmusic-sctp-sdp-14 874 o Changes based on WGLC comments from Magnus Westerlund. 876 o - ABNF clarification that token and port are defined in RFC4566. 878 o - Specify 40 as maximum digit character length for the SDP max- 879 message-size value. 881 o - Editorial clarification. 883 o Changes based on discussions at IETF#92. 885 o - Specify that all ICE candidate pairs belong to the same DTLS 886 association. 888 Changes from draft-ietf-mmusic-sctp-sdp-13 890 o Changes based on comments from Paul Kyzivat. 892 o - Text preventing usage of well-known ports removed. 894 o - Editorial clarification. 896 Changes from draft-ietf-mmusic-sctp-sdp-12 898 o Mux category rules added for new SDP attributes. 900 o Reference to draft-ietf-mmusic-sdp-mux-attributes added. 902 o Changes based on comments from Roman Shpount: 904 o - Specify that fingerprint or setup roles must not be modified, 905 unless underlying transport protocol is also modified. 907 o Changes based on comments from Ari Keranen: 909 o - Editorial corrections. 911 o Changes based on comments from Flemming Andreasen: 913 o - Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used, the 914 DTLS association is established before the SCTP association. 916 o - Clarify that max-message-size value is given in bytes, and that 917 different values can be used per direction. 919 o - Section on fmtp attribute removed. 921 o - Editorial corrections. 923 Changes from draft-ietf-mmusic-sctp-sdp-11 925 o Example added. 927 Changes from draft-ietf-mmusic-sctp-sdp-10 929 o SDP max-message-size attribute added to IANA considerations. 931 o Changes based on comments from Paul Kyzivat: 933 o - Text about max message size removed from fmtp attribute section. 935 Changes from draft-ietf-mmusic-sctp-sdp-09 937 o 'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' 939 o Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP 940 transports added. 942 Changes from draft-ietf-mmusic-sctp-sdp-08 944 o Default SCTP port removed: 946 o - Usage of SDP sctp-port attribute mandatory. 948 o SDP max-message-size attribute defined: 950 o - Attribute definition. 952 o - SDP Offer/Answer procedures. 954 o Text about SDP direction attributes added. 956 o Text about TLS role determination added. 958 18. References 960 18.1. Normative References 962 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 963 Requirement Levels", BCP 14, RFC 2119, 964 DOI 10.17487/RFC2119, March 1997, 965 . 967 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 968 with Session Description Protocol (SDP)", RFC 3264, 969 DOI 10.17487/RFC3264, June 2002, 970 . 972 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 973 the Session Description Protocol (SDP)", RFC 4145, 974 DOI 10.17487/RFC4145, September 2005, 975 . 977 [RFC4289] Freed, N. and J. Klensin, "Multipurpose Internet Mail 978 Extensions (MIME) Part Four: Registration Procedures", 979 BCP 13, RFC 4289, DOI 10.17487/RFC4289, December 2005, 980 . 982 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 983 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 984 July 2006, . 986 [RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) 987 and RTP Control Protocol (RTCP) Packets over Connection- 988 Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July 989 2006, . 991 [RFC4572] Lennox, J., "Connection-Oriented Media Transport over the 992 Transport Layer Security (TLS) Protocol in the Session 993 Description Protocol (SDP)", RFC 4572, 994 DOI 10.17487/RFC4572, July 2006, 995 . 997 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 998 RFC 4960, DOI 10.17487/RFC4960, September 2007, 999 . 1001 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1002 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1003 DOI 10.17487/RFC5226, May 2008, 1004 . 1006 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 1007 Specifications: ABNF", STD 68, RFC 5234, 1008 DOI 10.17487/RFC5234, January 2008, 1009 . 1011 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1012 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1013 January 2012, . 1015 [RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type 1016 Specifications and Registration Procedures", BCP 13, 1017 RFC 6838, DOI 10.17487/RFC6838, January 2013, 1018 . 1020 [I-D.ietf-mmusic-4572-update] 1021 Holmberg, C., "SDP Fingerprint Attribute Usage 1022 Clarifications", draft-ietf-mmusic-4572-update-07 (work in 1023 progress), September 2016. 1025 [I-D.ietf-mmusic-dtls-sdp] 1026 Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer 1027 Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-14 (work 1028 in progress), July 2016. 1030 [I-D.ietf-tsvwg-sctp-dtls-encaps] 1031 Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS 1032 Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp- 1033 dtls-encaps-09 (work in progress), January 2015. 1035 [I-D.ietf-mmusic-sdp-mux-attributes] 1036 Nandakumar, S., "A Framework for SDP Attributes when 1037 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-13 1038 (work in progress), June 2016. 1040 18.2. Informative References 1042 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1043 RFC 793, DOI 10.17487/RFC0793, September 1981, 1044 . 1046 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1047 (ICE): A Protocol for Network Address Translator (NAT) 1048 Traversal for Offer/Answer Protocols", RFC 5245, 1049 DOI 10.17487/RFC5245, April 2010, 1050 . 1052 [RFC6083] Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram 1053 Transport Layer Security (DTLS) for Stream Control 1054 Transmission Protocol (SCTP)", RFC 6083, 1055 DOI 10.17487/RFC6083, January 2011, 1056 . 1058 [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach, 1059 "TCP Candidates with Interactive Connectivity 1060 Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, 1061 March 2012, . 1063 Authors' Addresses 1064 Christer Holmberg 1065 Ericsson 1066 Hirsalantie 11 1067 Jorvas 02420 1068 Finland 1070 Email: christer.holmberg@ericsson.com 1072 Roman Shpount 1073 TurboBridge 1074 4905 Del Ray Avenue, Suite 300 1075 Bethesda, MD 20814 1076 USA 1078 Phone: +1 (240) 292-6632 1079 Email: rshpount@turbobridge.com 1081 Salvatore Loreto 1082 Ericsson 1083 Hirsalantie 11 1084 Jorvas 02420 1085 Finland 1087 Email: Salvatore.Loreto@ericsson.com 1089 Gonzalo Camarillo 1090 Ericsson 1091 Hirsalantie 11 1092 Jorvas 02420 1093 Finland 1095 Email: Gonzalo.Camarillo@ericsson.com