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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: September 14, 2017 TurboBridge 6 S. Loreto 7 G. Camarillo 8 Ericsson 9 March 13, 2017 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-25 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 September 14, 2017. 47 Copyright Notice 49 Copyright (c) 2017 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 . . . . . . . . . . . . . . . . . . . . . . . . . 5 72 4.4.1. General . . . . . . . . . . . . . . . . . . . . . . . 6 73 4.4.2. SDP Media Description values . . . . . . . . . . . . 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 . . . . . . . . . . . . . . 8 80 6.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 8 81 6.2. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 8 82 6.3. Mux Category . . . . . . . . . . . . . . . . . . . . . . 9 83 7. UDP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 9 84 8. TCP/DTLS/SCTP Transport Realization . . . . . . . . . . . . . 10 85 9. Association And Connection Management . . . . . . . . . . . . 10 86 9.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10 87 9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute . . . . 10 88 9.3. SCTP Association . . . . . . . . . . . . . . . . . . . . 10 89 9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) . . . 11 90 9.5. TCP Connection (TCP/DTLS/SCTP) . . . . . . . . . . . . . 12 91 10. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 12 92 10.1. General . . . . . . . . . . . . . . . . . . . . . . . . 12 93 10.2. Generating the Initial SDP Offer . . . . . . . . . . . . 13 94 10.3. Generating the SDP Answer . . . . . . . . . . . . . . . 13 95 10.4. Offerer Processing of the SDP Answer . . . . . . . . . . 14 96 10.5. Modifying the Session . . . . . . . . . . . . . . . . . 15 97 11. Multihoming Considerations . . . . . . . . . . . . . . . . . 16 98 12. NAT Considerations . . . . . . . . . . . . . . . . . . . . . 16 99 12.1. General . . . . . . . . . . . . . . . . . . . . . . . . 16 100 12.2. ICE Considerations . . . . . . . . . . . . . . . . . . . 16 101 13. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17 102 13.1. Establishment of UDP/DTLS/SCTP association . . . . . . . 17 103 14. Security Considerations . . . . . . . . . . . . . . . . . . . 18 104 15. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 105 15.1. New SDP proto values . . . . . . . . . . . . . . . . . . 19 106 15.2. New SDP Attributes . . . . . . . . . . . . . . . . . . . 19 107 15.2.1. sctp-port . . . . . . . . . . . . . . . . . . . . . 19 108 15.2.2. max-message-size . . . . . . . . . . . . . . . . . . 19 109 15.3. association-usage Name Registry . . . . . . . . . . . . 19 110 16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 20 111 17. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 112 18. References . . . . . . . . . . . . . . . . . . . . . . . . . 23 113 18.1. Normative References . . . . . . . . . . . . . . . . . . 23 114 18.2. Informative References . . . . . . . . . . . . . . . . . 25 115 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25 117 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 [I-D.ietf-mmusic-4572-update] extends RFC4145 [RFC4145] for 126 describing TCP-based media streams that are protected using TLS. 128 The Stream Control Transmission Protocol (SCTP) [RFC4960] is a 129 reliable transport protocol used to transport data between two 130 endpoints using SCTP associations. 132 [I-D.ietf-tsvwg-sctp-dtls-encaps] specifies how SCTP can be used on 133 top of the Datagram Transport Layer Security (DTLS) protocol, 134 referred to as SCTP-over-DTLS. 136 This specification defines the following new Session Description 137 Protocol (SDP) [RFC4566] protocol identifiers (proto 138 values):'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. This specification also 139 specifies how to use the new proto values with the SDP Offer/Answer 140 mechanism [RFC3264] for negotiating SCTP-over-DTLS associations. 142 NOTE: Due to the characteristics of TCP, while multiple SCTP streams 143 can still be used, usage of 'TCP/DTLS/SCTP' will always force ordered 144 and reliable delivery of the SCTP packets, which limits the usage of 145 the SCTP options. Therefore, it is RECOMMENDED that TCP is only used 146 in situations where UDP traffic is blocked. 148 2. Conventions 150 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 151 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 152 document are to be interpreted as described in [RFC2119]. 154 3. SCTP Terminology 156 SCTP Association: A protocol relationship between SCTP endpoints, 157 composed of the two SCTP endpoints and protocol state information 158 including Verification Tags and the currently active set of 159 Transmission Sequence Numbers (TSNs), etc. An association can be 160 uniquely identified by the transport addresses used by the endpoints 161 in the association. 163 SCTP Stream: A unidirectional logical channel established from one to 164 another associated SCTP endpoint, within which all user messages are 165 delivered in sequence except for those submitted to the unordered 166 delivery service. 168 SCTP-over-DTLS: SCTP used on top of DTLS, as specified in 169 [I-D.ietf-tsvwg-sctp-dtls-encaps]. 171 4. SDP Media Descriptions 173 4.1. General 175 This section defines the following new SDP Media Description (m- 176 line) protocol identifiers (proto values) for describing an SCTP 177 association: 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP'. The section also 178 describes how an m- line, associated with the proto values, is 179 created. 181 The following is the format for an m- line, as specified in RFC4566 182 [RFC4566]: 184 m= ... 186 The 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are similar to 187 both the 'UDP' and 'TCP' proto values in that they only describe the 188 transport-layer protocol and not the upper-layer protocol. 190 NOTE: When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values are 191 used, the underlying transport protocol is respectively UDP and TCP; 192 SCTP is carried on top of DTLS which is on top of those transport- 193 layer protocols. 195 4.2. Protocol Identifiers 197 The new proto values are defined as below: 199 o The 'UDP/DTLS/SCTP' proto value describes an SCTP association on 200 top of a DTLS association on top of UDP, as defined in Section 7. 202 o The 'TCP/DTLS/SCTP' proto value describes an SCTP association on 203 top of a DTLS association on top of TCP, as defined in Section 8. 205 4.3. Media Format Management 207 [RFC4566] defines that specifications defining new proto values must 208 define the rules by which their media format (fmt) namespace is 209 managed. 211 An m- line with a proto value of 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP' 212 always describes a single SCTP association. 214 In addition, such m- line MUST further indicate the application-layer 215 protocol using an 'fmt' identifier. There MUST be exactly one fmt 216 value per m- line associated with the proto values defined in this 217 specification. The 'fmt' namespace associated with those proto 218 values describes the generic application usage of the entire SCTP 219 association, including the associated SCTP streams. 221 When the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto values, the m- 222 line fmt value, identifying the application-layer protocol, MUST be 223 registered by IANA. Section 15.3 defines the IANA registry for the 224 media format namespace. 226 NOTE: A mechanism on how to describe, and manage, individual SCTP 227 streams within an SCTP association, is outside the scope of this 228 specification. [I-D.ietf-mmusic-data-channel-sdpneg] defines a 229 mechanism for negotiating individual SCTP streams used to realize 230 WebRTC data channels [I-D.ietf-rtcweb-data-channel]. 232 4.4. Syntax 233 4.4.1. General 235 This section defines the values that can be used within an SDP media 236 description ("m=" line) associated with an SCTP-over-DTLS 237 association. 239 This specification creates an IANA registry for 'association-usage' 240 values. 242 4.4.2. SDP Media Description values 244 m= line parameter parameter value(s) 245 ------------------------------------------------------------------ 246 : 'application' 247 : 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP' 248 : UDP port number (for 'UDP/DTLS/SCTP') 249 TCP port number (for 'TCP/DTLS/SCTP') 250 : a string denoting the association-usage, 251 limited to the syntax of a 'token' as 252 defined in RFC4566. 254 4.5. Example 256 m=application 12345 UDP/DTLS/SCTP webrtc-datachannel 257 a=sctp-port:5000 258 a=max-message-size:100000 260 NOTE: 'webrtc-datachannel' indicates the WebRTC Data Channel 261 Establishment Protocol defined in [I-D.ietf-rtcweb-data-protocol]. 263 5. SDP 'sctp-port' Attribute 265 5.1. General 267 This section defines a new SDP media-level attribute, 'sctp-port'. 268 The attribute can be associated with an SDP media description (m- 269 line) with a 'UDP/DTLS/SCTP' or a 'TCP/DTLS/SCTP' proto value. In 270 that case the m- line port value indicates the port of the underlying 271 transport layer protocol (UDP or TCP), and the 'sctp-port' value 272 indicates the SCTP port. 274 No default value is defined for the SDP sctp-port attribute. 275 Therefore, if the attribute is not present, the associated m- line 276 MUST be considered invalid. 278 NOTE: This specification only defines the usage of the SDP 'sctp- 279 port' attribute when associated with an m- line containing one of the 280 following proto values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/SCTP'. Usage of 281 the attribute with other proto values needs to be defined in a 282 separate specification. 284 5.2. Syntax 286 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 287 document.] 289 The definition of the SDP 'sctp-port' attribute is: 291 Attribute name: sctp-port 292 Type of attribute: media 293 Mux category: CAUTION 294 Subject to charset: No 295 Purpose: Indicate the SCTP port value associated with 296 the SDP Media Description. 297 Appropriate values: Integer 298 Contact name: Christer Holmberg 299 Contact e-mail: christer.holmberg@ericsson.com 300 Reference: RFCXXXX 302 Syntax: 304 sctp-port-value = 1*5 306 The SCTP port range is between 0 and 65535 (both included). 307 Leading zeroes MUST NOT be used. 309 Example: 311 a=sctp-port:5000 313 5.3. Mux Category 315 The mux category [I-D.ietf-mmusic-sdp-mux-attributes] for the SDP 316 'sctp-port' attribute is CAUTION. 318 As the usage of multiple SCTP associations on top of a single DTLS 319 association is outside the scope of this specification, no mux rules 320 are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto 321 values. Future extensions, that define how to negotiate multiplexing 322 of multiple SCTP associations of top of a single DTLS association, 323 need to also define the mux rules for the attribute. 325 6. SDP 'max-message-size' Attribute 327 6.1. General 329 This section defines a new SDP media-level attribute, 'max-message- 330 size'. The attribute can be associated with an m- line to indicate 331 the maximum SCTP user message size (indicated in bytes) that an SCTP 332 endpoint is willing to receive on the SCTP association associated 333 with the m- line. Different attribute values can be used in each 334 direction. 336 An SCTP endpoint MUST NOT send a SCTP user message with a message 337 size that is larger than the maximum size indicated by the peer, as 338 it cannot be assumed that the peer would accept such message. 340 If the SDP 'max-message-size' attribute contains a maximum message 341 size value of zero, it indicates the SCTP endpoint will handle 342 messages of any size, subject to memory capacity etc. 344 If the SDP 'max-message-size' attribute is not present, the default 345 value is 64K. 347 NOTE: This specification only defines the usage of the SDP 'max- 348 message-size' attribute when associated with an m- line containing 349 one of the following proto values: 'UDP/DTLS/SCTP' or 'TCP/DTLS/ 350 SCTP'. Usage of the attribute with other proto values needs to be 351 defined in a separate specification. 353 6.2. Syntax 355 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 356 document.] 358 The definition of the SDP 'max-message-size' attribute is: 360 Attribute name: max-message-size 361 Type of attribute: media 362 Mux category: CAUTION 363 Subject to charset: No 364 Purpose: Indicate the maximum message size 365 (indicated in bytes) that an SCTP 366 endpoint is willing to receive on the 367 SCTP association associated with the SDP 368 Media Description. 369 Appropriate values: Integer 370 Contact name: Christer Holmberg 371 Contact e-mail: christer.holmberg@ericsson.com 372 Reference: RFCXXXX 374 Syntax: 376 max-message-size-value = 1* 378 Leading zeroes MUST NOT be used. 380 Example: 382 a=max-message-size:100000 384 6.3. Mux Category 386 The mux category for the SDP 'max-message-size' attribute is CAUTION. 388 As the usage of multiple SCTP associations on top of a single DTLS 389 association is outside the scope of this specification, no mux rules 390 are specified for the 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' proto 391 values. 393 7. UDP/DTLS/SCTP Transport Realization 395 The UDP/DTLS/SCTP transport is realized as described below: 397 o SCTP on top of DTLS is realized according to the procedures 398 defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and 400 o DTLS on top of UDP is realized according to the procedures in 401 defined in [RFC6347]. 403 NOTE: While [I-D.ietf-tsvwg-sctp-dtls-encaps] allows multiple SCTP 404 associations on top of a single DTLS association, the procedures in 405 this specification only support the negotiation of a single SCTP 406 association on top of any given DTLS association. 408 8. TCP/DTLS/SCTP Transport Realization 410 The TCP/DTLS/SCTP transport is realized as described below: 412 o SCTP on top of DTLS is realized according to the procedures 413 defined in [I-D.ietf-tsvwg-sctp-dtls-encaps]; and 415 o DTLS on top of TCP is realized using the framing method defined in 416 [RFC4571], with DTLS packets being sent and received instead of 417 RTP/RTCP packets using the shim defined in [RFC4571], so that 418 length field defined in [RFC4571] precedes each DTLS message, and 419 SDP signaling according to the procedures defined in this 420 specification. 422 NOTE: TLS on top of TCP, without using the framing method defined in 423 [RFC4571] is outside the scope of this specification. A separate 424 proto value would need to be registered for such transport 425 realization. 427 9. Association And Connection Management 429 9.1. General 431 This section describes how to manage an SCTP association, DTLS 432 association and TCP connection using SDP attributes. 434 The SCTP association, the DTLS association and the TCP connection are 435 managed independently from each other. Each can be established and 436 closed without impacting others. 438 The detailed SDP Offer/Answer [RFC3264] procedures for the SDP 439 attributes are described in Section 10. 441 9.2. SDP sendrecv/sendonly/recvonly/inactive Attribute 443 This specification does not define semantics for the SDP direction 444 attributes [RFC4566]. Unless semantics of these attributes for an 445 SCTP association usage have been defined, SDP direction attributes 446 MUST be ignored if present. 448 9.3. SCTP Association 450 When an SCTP association is established, both SCTP endpoints MUST 451 initiate the SCTP association (i.e. both SCTP endpoints take the 452 'active' role), and MUST use the same SCTP port as client port and 453 server port (in order to prevent two separate SCTP associations from 454 being established). 456 As both SCTP endpoints take the 'active' role, the SDP 'setup' 457 attribute [RFC4145] does not apply to SCTP association establishment. 458 However the 'setup' attribute does apply to establishment of the 459 underlying DTLS association and TCP connection. 461 NOTE: The procedure above is different from TCP, where one endpoint 462 takes the 'active' role, the other endpoint takes the 'passive' role, 463 and only the 'active' endpoint initiates the TCP connection 464 [RFC4145]. 466 NOTE: When the SCTP association is established it is assumed that any 467 NAT traversal procedures for the underlying transport protocol (UDP 468 or TCP) have successfully been performed. 470 The SDP 'connection' attribute [RFC4145] does not apply to the SCTP 471 association. In order to trigger the closure of an existing SCTP 472 association, and establishment of a new SCTP association, the SDP 473 'sctp-port' attribute [Section 5] is used to indicate a new 474 (different than the ones currently used) SCTP port. The existing 475 SCTP association is closed, and the new SCTP association is 476 established, if one or both endpoints signal a new SCTP port. The 477 'connection' attribute does apply to establishment of underlying TCP 478 connections. 480 Alternatively, an SCTP association can be closed using the SDP 'sctp- 481 port' attribute with a zero attribute value. Later, a new SCTP 482 association can be established using the procedures in this section 483 for establishing an SCTP association. 485 SCTP associations might be closed without SDP signalling, e.g, in 486 case of a failure. The procedures in this section MUST be followed 487 to establish a new SCTP association. This requires a new SDP Offer/ 488 Answer exchange. New (different than the ones currently used) SCTP 489 ports MUST be used by both endpoints. 491 NOTE: Closing and establishing a new SCTP association using the SDP 492 'sctp-port' attribute will not affect the state of the underlying 493 DTLS association. 495 9.4. DTLS Association (UDP/DTLS/SCTP And TCP/DTLS/SCTP) 497 A DTLS association is managed according to the procedures in 498 [I-D.ietf-mmusic-dtls-sdp]. Hence, the SDP 'setup' attribute is used 499 to negotiate the (D)TLS roles ('client' and 'server') 500 [I-D.ietf-mmusic-4572-update]. 502 NOTE: The SDP 'setup' attribute is used to negotiate both the DTLS 503 roles and the TCP roles (Section 9.5). 505 NOTE: As described in [RFC5245], if the Interactive Connectivity 506 Establishment (ICE) mechanism [RFC5245] is used, all ICE candidates 507 associated with a DTLS association are considered part of the same 508 DTLS association. Thus, a switch from one candidate pair to another 509 candidate pair will not trigger the establishment of a new DTLS 510 association. 512 9.5. TCP Connection (TCP/DTLS/SCTP) 514 The TCP connection is managed according to the procedures in 515 [RFC4145]. Hence, the SDP 'setup' attribute is used to negotiate the 516 TCP roles ('active' and 'passive'), and the SDP 'connection' 517 attribute is used to indicate whether to use an existing TCP 518 connection, or create a new one. The SDP 'setup' attribute 519 'holdconn' value MUST NOT be used. 521 NOTE: A change of the TCP roles will also trigger a closure of the 522 DTLS association, and establishment of a new DTLS association, 523 according to the procedures in [I-D.ietf-mmusic-dtls-sdp]. 525 NOTE: As specified in [I-D.ietf-mmusic-dtls-sdp], usage of the SDP 526 'setup' attribute 'holdconn' value is not allowed. Therefore this 527 specification also forbids usage of the attribute value for TCP, as 528 DTLS is transported on top of TCP. 530 10. SDP Offer/Answer Procedures 532 10.1. General 534 This section defines the SDP Offer/Answer [RFC3264] procedures for 535 negotiating and establishing an SCTP-over-DTLS association. Unless 536 explicitly stated, the procedures apply to both the 'UDP/DTLS/SCTP' 537 and 'TCP/DTLS/SCTP' m- line proto values. 539 Each endpoint MUST associate one or more certificate fingerprints, 540 using the SDP 'fingerprint' attribute with the m- line, following the 541 procedures in [I-D.ietf-mmusic-4572-update]. 543 The authentication certificates are interpreted and validated as 544 defined in [I-D.ietf-mmusic-4572-update]. Self-signed certificates 545 can be used securely, provided that the integrity of the SDP 546 description is assured as defined in [I-D.ietf-mmusic-4572-update]. 548 Each endpoint MUST associate an SDP 'dtls-id' attribute with the m- 549 line, following the procedures in [I-D.ietf-mmusic-dtls-sdp]. 551 10.2. Generating the Initial SDP Offer 553 When the offerer creates an initial offer, the offerer: 555 o MUST associate an SDP setup attribute with the m- line; 557 o MUST associate an SDP 'sctp-port' attribute with the m- line; 559 o MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection' 560 attribute, with a 'new' attribute value, with the m- line; and 562 o MAY associate an SDP 'max-message-size' attribute [Section 6] with 563 the m- line. 565 10.3. Generating the SDP Answer 567 When the answerer receives an offer, which contains an m- line 568 describing an SCTP-over-DTLS association, if the answerer accepts the 569 association, the answerer: 571 o MUST insert a corresponding m- line in the answer, with an m- line 572 proto value [RFC3264] identical to the value in the offer; 574 o MUST associate an SDP 'setup' attribute with the m- line; 576 o MUST associate an SDP 'sctp-port' attribute with the m- line. If 577 the offer contained a new (different than the one currently used) 578 SCTP port value the answerer MUST also associate a new SCTP port 579 value. If the offer contained a zero SCTP port value, or if the 580 answerer does not accept the SCTP association, the answerer MUST 581 also associate a zero SCTP port value; and 583 o MAY associate an SDP 'max-message-size' attribute [Section 6] with 584 the m- line. The attribute value in the answer is independent 585 from the value (if present) in the corresponding m- line of the 586 offer. 588 Once the answerer has sent the answer the answerer: 590 o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not 591 yet been established, or if an existing TCP connection is to be 592 closed and replaced by a new TCP connection, follow the procedures 593 in [RFC4145] for closing and establishing a TCP connection; 595 o MUST, if a DTLS association has not yet been established, or if an 596 existing DTLS association is to be closed and replaced by a new 597 DTLS association, follow the procedures in 599 [I-D.ietf-mmusic-dtls-sdp] for closing the currently used, and 600 establishing a new, DTLS association; and 602 o MUST, if an SCTP association has not yet been established, or if 603 an existing SCTP association is to be closed and replaced by a new 604 SCTP association, initiate the closing of the existing SCTP 605 association (if applicable) and establishment of the SCTP 606 association. 608 If the SDP 'sctp-port' attribute in the answer contains a zero 609 attribute value, the answerer MUST NOT establish an SCTP association. 610 If an SCTP association exists, the offerer MUST close it. 612 If the answerer does not accept the m- line in the offer, it MUST 613 assign a zero port value to the corresponding m- line in the answer, 614 following the procedures in [RFC3264]. In addition, the answerer 615 MUST NOT initiate the establishment of a TCP connection, a DTLS 616 association or a DTLS association associated with the m- line. 618 10.4. Offerer Processing of the SDP Answer 620 Once the offerer has received the answer the offerer: 622 o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not 623 yet been established, or if an existing TCP connection is to be 624 closed and replaced by a new TCP connection, follow the procedures 625 in [RFC4145] for closing and establishing a TCP connection; 627 o MUST, if a DTLS association has not yet been established, or if an 628 existing DTLS association is to be closed and replaced by a new 629 DTLS association, follow the procedures in 630 [I-D.ietf-mmusic-dtls-sdp] for closing and establishing a DTLS 631 association; and 633 o MUST, if an SCTP association has not yet been established, or if 634 an existing SCTP association is to be closed and replaced by a new 635 SCTP association, initiate the closing of the existing SCTP 636 association (if applicable) and establishment of the SCTP 637 association. 639 If the SDP 'sctp-port' attribute in the answer contains a zero 640 attribute value, the offerer MUST NOT establish an SCTP association. 641 If an SCTP association exists in that case, the offerer MUST close 642 it. 644 If the m- line in the answer contains a zero port value, the offerer 645 MUST NOT initiate the establishment a TCP connection, a DTLS 646 association or an SCTP association associated with the m- line. If a 647 TCP connection, or a DTLS association or an SCTP association exists 648 in that case, the offerer MUST close it. 650 10.5. Modifying the Session 652 When an offerer sends an updated offer, in order to modify a 653 previously established SCTP association, it follows the procedures in 654 Section 10.2, with the following exceptions: 656 o If the offerer wants to close an SCTP association, and immediately 657 establish a new SCTP association, the offerer MUST associate an 658 SDP 'sctp-port' attribute with a new (different than the one 659 currently used) attribute value. This will not impact the 660 underlying DTLS association (and TCP connection in case of 661 TCP/DTLS/SCTP). 663 o If the offerer wants to close an SCTP association, without 664 immediately establishing a new SCTP association, the offerer MUST 665 associate an SDP 'sctp-port' attribute with a zero attribute 666 value. This will not impact the underlying DTLS association (and 667 TCP connection in case of TCP/DTLS/SCTP). 669 o If the offerer wants to establish an SCTP association, and another 670 SCTP association was previously closed, the offerer MUST associate 671 an SDP 'sctp-port' attribute with a new attribute value (different 672 than the value associated with the previous SCTP association). If 673 the previous SCTP association was closed successfully following 674 use of an SDP 'sctp-port' attribute with a zero attribute value, 675 the offerer MAY use the same attribute value for the new SCTP 676 association that was used with the previous SCTP association 677 before it was closed. This will not impact the underlying DTLS 678 association (and TCP connection in case of TCP/DTLS/SCTP). 680 o If the offerer wants to close an existing SCTP association, and 681 the underlying DTLS association (and the underlying TCP connection 682 in case of TCP/DTLS/SCTP) it MUST assign a zero port value to the 683 m- line associated with the SCTP and DTLS associations (and TCP 684 connection in case of TCP/DTLS/SCTP), following the procedures in 685 [RFC3264]. 687 o NOTE: This specification does not define a mechanism for 688 explicitly closing a DTLS association while maintaining the 689 overlying SCTP association. However, if a DTLS association is 690 closed and replaced with a new DTLS association, as a result of 691 some other action [I-D.ietf-mmusic-dtls-sdp], the state of the 692 SCTP association is not affected. 694 The offer follows the procedures in [I-D.ietf-mmusic-dtls-sdp] 695 regarding the DTLS association impacts when modifying a session. 697 In the case of TCP/DTLS/SCTP, the offerer follows the procedures in 698 [RFC4145] regarding the TCP connection impacts when modifying a 699 session. 701 11. Multihoming Considerations 703 Multihoming is not supported when sending SCTP on top of DTLS, as 704 DTLS does not expose address management of the underlying transport 705 protocols (UDP or TCP) to its upper layer. 707 12. NAT Considerations 709 12.1. General 711 When SCTP-over-DTLS is used in NAT environment, it relies on the NAT 712 traversal procedures for the underlying transport protocol (UDP or 713 TCP). 715 12.2. ICE Considerations 717 When SCTP-over-DTLS is used with UDP based ICE candidates [RFC5245] 718 then the procedures for UDP/DTLS/SCTP [Section 7] are used. 720 When SCTP-over-DTLS is used with TCP based ICE candidates [RFC6544] 721 then the procedures for TCP/DTLS/SCTP [Section 8] are used. 723 In ICE environments, during the nomination process, endpoints go 724 through multiple ICE candidate pairs, until the most preferred 725 candidate pair is found. During the nomination process, data can be 726 sent as soon as the first working candidate pair is found, but the 727 nomination process still continues and selected candidate pairs can 728 still change while data is sent. Furthermore, if endpoints roam 729 between networks, for instance when mobile endpoint switches from 730 mobile connection to WiFi, endpoints will initiate an ICE restart, 731 which will trigger a new nomination process between the new set of 732 candidates and likely result in the new nominated candidate pair. 734 Implementations MUST treat all ICE candidate pairs associated with an 735 SCTP association on top of a DTLS association as part of the same 736 DTLS association. Thus, there will only be one SCTP handshake and 737 one DTLS handshake even if there are multiple valid candidate pairs, 738 and shifting from one candidate pair to another, including switching 739 between UDP to TCP candidate pairs, will not impact the SCTP or DTLS 740 associations. If new candidates are added, they will also be part of 741 the same SCTP and DTLS associations. When transitioning between 742 candidate pairs, different candidate pairs can be currently active in 743 different directions and implementations MUST be ready to receive 744 data on any of the candidates, even if this means sending and 745 receiving data using UDP/DTLS/SCTP and TCP/DTLS/SCTP at the same time 746 in different directions. 748 In order to maximize the likelihood of interoperability between the 749 endpoints, all ICE enabled SCTP-over-DTLS endpoints SHOULD implement 750 support for UDP/DTLS/SCTP. 752 When an SDP offer or answer is sent with multiple ICE candidates 753 during initial connection negotiation or after ICE restart, UDP based 754 candidates SHOULD be included and default candidate SHOULD be chosen 755 from one of those UDP candidates. The proto value MUST match the 756 transport protocol associated with the default candidate. If UDP 757 transport is used for the default candidate, then 'UDP/DTLS/SCTP' 758 proto value MUST be used. If TCP transport is used for the default 759 candidate, then 'TCP/DTLS/SCTP' proto value MUST be used. Note that 760 under normal circumstances the proto value for offers and answers 761 sent during ICE nomination SHOULD be 'UDP/DTLS/SCTP'. 763 When a subsequent SDP offer or answer is sent after ICE nomination is 764 complete, and does not initiate ICE restart, it will contain only the 765 nominated ICE candidate pair. In this case, the proto value MUST 766 match the transport protocol associated with the nominated ICE 767 candidate pair. If UDP transport is used for the nominated pair, 768 then 'UDP/DTLS/SCTP' proto value MUST be used. If TCP transport is 769 used for the nominated pair, then 'TCP/DTLS/SCTP' proto value MUST be 770 used. Please note that if an endpoint switches between TCP-based and 771 UDP-based candidates during the nomination process the endpoint is 772 not required to send an SDP offer for the sole purpose of keeping the 773 proto value of the associated m- line in sync. 775 NOTE: The text in the paragraph above only applies when the usage of 776 ICE has been negotiated. If ICE is not used, the proto value MUST 777 always reflect the transport protocol used at any given time. 779 13. Examples 781 13.1. Establishment of UDP/DTLS/SCTP association 782 SDP Offer: 784 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 785 c=IN IP6 2001:DB8::A8FD 786 a=dtls-id:abc3dl 787 a=setup:actpass 788 a=sctp-port:5000 789 a=max-message-size:100000 791 - The offerer indicates that the usage of the 792 UDP/DTLS/SCTP association will be as defined 793 for the 'webrtc-datachannel' format value. 794 - The offerer UDP port value is 54111. 795 - The offerer SCTP port value is 5000. 796 - The offerer indicates that it can take either the 797 client or the server DTLS role. 799 SDP Answer: 801 m=application 64300 UDP/DTLS/SCTP webrtc-datachannel 802 c=IN IP6 2001:DB8::001D 803 a=dtls-id:ggr4rd 804 a=setup:passive 805 a=sctp-port:6000 806 a=max-message-size:100000 808 - The answerer UDP port value is 64300. 809 - The answerer SCTP port value is 6000. 810 - The answerer takes the server DTLS role. 812 14. Security Considerations 814 [RFC4566] defines general SDP security considerations, while 815 [RFC3264], [RFC4145] and [I-D.ietf-mmusic-4572-update] define 816 security considerations when using the SDP offer/answer mechanism to 817 negotiate media streams. 819 [RFC4960] defines general SCTP security considerations and 820 [I-D.ietf-tsvwg-sctp-dtls-encaps] defines security considerations 821 when using SCTP on top of DTLS. 823 This specification does not introduce new security considerations in 824 addition to those defined in the specifications listed above. 826 15. IANA Considerations 828 15.1. New SDP proto values 830 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 831 document.] 833 This document updates the "Session Description Protocol (SDP) 834 Parameters" registry, following the procedures in [RFC4566], by 835 adding the following values to the table in the SDP "proto" field 836 registry: 838 +-------+---------------+-----------+ 839 | Type | SDP Name | Reference | 840 +-------+---------------+-----------+ 841 | proto | UDP/DTLS/SCTP | [RFCXXXX] | 842 | proto | TCP/DTLS/SCTP | [RFCXXXX] | 843 +-------+---------------+-----------+ 845 Table 1: SDP "proto" field values 847 15.2. New SDP Attributes 849 15.2.1. sctp-port 851 This document defines a new SDP media-level attribute,'sctp-port'. 852 The details of the attribute are defined in Section 5.2. 854 15.2.2. max-message-size 856 This document defines a new SDP media-level attribute,'max-message- 857 size'. The details of the attribute are defined in Section 6.2. 859 15.3. association-usage Name Registry 861 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 862 document.] 864 This specification creates a new IANA registry, following the 865 procedures in [RFC5226], for the namespace associated with the 866 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' protocol identifiers. Each fmt 867 value describes the usage of an entire SCTP association, including 868 all SCTP streams associated with the SCTP association. 870 NOTE: Usage indication of individual SCTP streams is outside the 871 scope of this specification. 873 The fmt value, "association-usage", used with these "proto" values is 874 required. It is defined in Section 4. 876 As part of this registry, IANA maintains the following information: 878 association-usage name: The identifier of the subprotocol, as will 879 be used as the fmt value. 881 association-usage reference: A reference to the document in which 882 the association-usage is defined. 884 association-usage names are to be subject to the "First Come First 885 Served" IANA registration policy [RFC5226]. 887 IANA is asked to add initial values to the registry. 889 |----------------------------------------------------------| 890 | name | Reference | 891 |----------------------------------------------------------| 892 | webrtc-datachannel | draft-ietf-rtcweb-data-protocol-xx, | 893 | | RFCXXX | 894 |----------------------------------------------------------| 896 [RFC EDITOR NOTE: Please hold the publication of this draft 897 until draft-ietf-rtcweb-data-protocol has been published as an RFC. 898 Then, replace the reference to draft-ietf-rtcweb-data-protocol 899 with the RFC number.] 901 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number 902 of this document.] 904 Figure 1 906 16. Acknowledgments 908 The authors wish to thank Harald Alvestrand, Randell Jesup, Paul 909 Kyzivat, Michael Tuexen, Juergen Stoetzer-Bradler, Flemming Andreasen 910 and Ari Keranen for their comments and useful feedback. Ben Campbell 911 provided comments as part of his AD review. Brian Carpenter 912 performed the Gen-ART review. 914 17. 916 [RFC EDITOR NOTE: Please remove this section when publishing] 918 Changes from draft-ietf-mmusic-sctp-sdp-24 919 o Minor editorial fix by Roman. 921 Changes from draft-ietf-mmusic-sctp-sdp-23 923 o Changes based on IESG review. 925 o - Proto value clarifications. 927 Changes from draft-ietf-mmusic-sctp-sdp-22 929 o Changes based on Gen-ART review by Brian Carpenter. 931 Changes from draft-ietf-mmusic-sctp-sdp-21 933 o Changes based on AD review by Ben Campbell. 935 Changes from draft-ietf-mmusic-sctp-sdp-20 937 o Informative reference to draft-ietf-rtcweb-data-protocol added. 939 Changes from draft-ietf-mmusic-sctp-sdp-19 941 o Changes based on WG chair comments from Flemming Andreasen. 943 Changes from draft-ietf-mmusic-sctp-sdp-18 945 o Changes based on WGLC comments from Paul Kyzivat. 947 Changes from draft-ietf-mmusic-sctp-sdp-17 949 o Removal of 'SCTP'. 951 o Document title changed. 953 o Disallow usage of SDP 'setup' attribute 'holdconn' value. 955 o Roman Shpount added as co-editor. 957 Changes from draft-ietf-mmusic-sctp-sdp-15 959 o Chapter about SCTP, DTLS and TCP association/connection management 960 modified. 962 o Removal of SCTP/DTLS. 964 Changes from draft-ietf-mmusic-sctp-sdp-14 966 o Changes based on WGLC comments from Magnus Westerlund. 968 o - ABNF clarification that token and port are defined in RFC4566. 970 o - Specify 40 as maximum digit character length for the SDP max- 971 message-size value. 973 o - Editorial clarification. 975 o Changes based on discussions at IETF#92. 977 o - Specify that all ICE candidate pairs belong to the same DTLS 978 association. 980 Changes from draft-ietf-mmusic-sctp-sdp-13 982 o Changes based on comments from Paul Kyzivat. 984 o - Text preventing usage of well-known ports removed. 986 o - Editorial clarification. 988 Changes from draft-ietf-mmusic-sctp-sdp-12 990 o Mux category rules added for new SDP attributes. 992 o Reference to draft-ietf-mmusic-sdp-mux-attributes added. 994 o Changes based on comments from Roman Shpount: 996 o - Specify that fingerprint or setup roles must not be modified, 997 unless underlying transport protocol is also modified. 999 o Changes based on comments from Ari Keranen: 1001 o - Editorial corrections. 1003 o Changes based on comments from Flemming Andreasen: 1005 o - Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used, the 1006 DTLS association is established before the SCTP association. 1008 o - Clarify that max-message-size value is given in bytes, and that 1009 different values can be used per direction. 1011 o - Section on fmtp attribute removed. 1013 o - Editorial corrections. 1015 Changes from draft-ietf-mmusic-sctp-sdp-11 1016 o Example added. 1018 Changes from draft-ietf-mmusic-sctp-sdp-10 1020 o SDP max-message-size attribute added to IANA considerations. 1022 o Changes based on comments from Paul Kyzivat: 1024 o - Text about max message size removed from fmtp attribute section. 1026 Changes from draft-ietf-mmusic-sctp-sdp-09 1028 o 'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' 1030 o Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP 1031 transports added. 1033 Changes from draft-ietf-mmusic-sctp-sdp-08 1035 o Default SCTP port removed: 1037 o - Usage of SDP sctp-port attribute mandatory. 1039 o SDP max-message-size attribute defined: 1041 o - Attribute definition. 1043 o - SDP Offer/Answer procedures. 1045 o Text about SDP direction attributes added. 1047 o Text about TLS role determination added. 1049 18. References 1051 18.1. Normative References 1053 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1054 RFC 793, DOI 10.17487/RFC0793, September 1981, 1055 . 1057 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1058 Requirement Levels", BCP 14, RFC 2119, 1059 DOI 10.17487/RFC2119, March 1997, 1060 . 1062 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1063 with Session Description Protocol (SDP)", RFC 3264, 1064 DOI 10.17487/RFC3264, June 2002, 1065 . 1067 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 1068 the Session Description Protocol (SDP)", RFC 4145, 1069 DOI 10.17487/RFC4145, September 2005, 1070 . 1072 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1073 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1074 July 2006, . 1076 [RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) 1077 and RTP Control Protocol (RTCP) Packets over Connection- 1078 Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July 1079 2006, . 1081 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1082 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1083 . 1085 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1086 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1087 DOI 10.17487/RFC5226, May 2008, 1088 . 1090 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1091 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1092 January 2012, . 1094 [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach, 1095 "TCP Candidates with Interactive Connectivity 1096 Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, 1097 March 2012, . 1099 [I-D.ietf-mmusic-4572-update] 1100 Lennox, J. and C. Holmberg, "Connection-Oriented Media 1101 Transport over TLS in SDP", draft-ietf-mmusic- 1102 4572-update-13 (work in progress), February 2017. 1104 [I-D.ietf-mmusic-dtls-sdp] 1105 Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer 1106 Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-18 (work 1107 in progress), January 2017. 1109 [I-D.ietf-tsvwg-sctp-dtls-encaps] 1110 Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS 1111 Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp- 1112 dtls-encaps-09 (work in progress), January 2015. 1114 [I-D.ietf-mmusic-sdp-mux-attributes] 1115 Nandakumar, S., "A Framework for SDP Attributes when 1116 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 1117 (work in progress), December 2016. 1119 18.2. Informative References 1121 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1122 (ICE): A Protocol for Network Address Translator (NAT) 1123 Traversal for Offer/Answer Protocols", RFC 5245, 1124 DOI 10.17487/RFC5245, April 2010, 1125 . 1127 [I-D.ietf-rtcweb-data-channel] 1128 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 1129 Channels", draft-ietf-rtcweb-data-channel-13 (work in 1130 progress), January 2015. 1132 [I-D.ietf-mmusic-data-channel-sdpneg] 1133 Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., 1134 and J. Marcon, "SDP-based Data Channel Negotiation", 1135 draft-ietf-mmusic-data-channel-sdpneg-11 (work in 1136 progress), January 2017. 1138 [I-D.ietf-rtcweb-data-protocol] 1139 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 1140 Establishment Protocol", draft-ietf-rtcweb-data- 1141 protocol-09 (work in progress), January 2015. 1143 Authors' Addresses 1145 Christer Holmberg 1146 Ericsson 1147 Hirsalantie 11 1148 Jorvas 02420 1149 Finland 1151 Email: christer.holmberg@ericsson.com 1152 Roman Shpount 1153 TurboBridge 1154 4905 Del Ray Avenue, Suite 300 1155 Bethesda, MD 20814 1156 USA 1158 Phone: +1 (240) 292-6632 1159 Email: rshpount@turbobridge.com 1161 Salvatore Loreto 1162 Ericsson 1163 Hirsalantie 11 1164 Jorvas 02420 1165 Finland 1167 Email: Salvatore.Loreto@ericsson.com 1169 Gonzalo Camarillo 1170 Ericsson 1171 Hirsalantie 11 1172 Jorvas 02420 1173 Finland 1175 Email: Gonzalo.Camarillo@ericsson.com