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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: October 22, 2017 TurboBridge 6 S. Loreto 7 G. Camarillo 8 Ericsson 9 April 20, 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-26 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 October 22, 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 [RFC8122] 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 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') [RFC8122]. 501 NOTE: The SDP 'setup' attribute is used to negotiate both the DTLS 502 roles and the TCP roles (Section 9.5). 504 NOTE: As described in [RFC5245], if the Interactive Connectivity 505 Establishment (ICE) mechanism [RFC5245] is used, all ICE candidates 506 associated with a DTLS association are considered part of the same 507 DTLS association. Thus, a switch from one candidate pair to another 508 candidate pair will not trigger the establishment of a new DTLS 509 association. 511 9.5. TCP Connection (TCP/DTLS/SCTP) 513 The TCP connection is managed according to the procedures in 514 [RFC4145]. Hence, the SDP 'setup' attribute is used to negotiate the 515 TCP roles ('active' and 'passive'), and the SDP 'connection' 516 attribute is used to indicate whether to use an existing TCP 517 connection, or create a new one. The SDP 'setup' attribute 518 'holdconn' value MUST NOT be used. 520 NOTE: A change of the TCP roles will also trigger a closure of the 521 DTLS association, and establishment of a new DTLS association, 522 according to the procedures in [I-D.ietf-mmusic-dtls-sdp]. 524 NOTE: As specified in [I-D.ietf-mmusic-dtls-sdp], usage of the SDP 525 'setup' attribute 'holdconn' value is not allowed. Therefore this 526 specification also forbids usage of the attribute value for TCP, as 527 DTLS is transported on top of TCP. 529 10. SDP Offer/Answer Procedures 531 10.1. General 533 This section defines the SDP Offer/Answer [RFC3264] procedures for 534 negotiating and establishing an SCTP-over-DTLS association. Unless 535 explicitly stated, the procedures apply to both the 'UDP/DTLS/SCTP' 536 and 'TCP/DTLS/SCTP' m- line proto values. 538 Each endpoint MUST associate one or more certificate fingerprints, 539 using the SDP 'fingerprint' attribute with the m- line, following the 540 procedures in [RFC8122]. 542 The authentication certificates are interpreted and validated as 543 defined in [RFC8122]. Self-signed certificates can be used securely, 544 provided that the integrity of the SDP description is assured as 545 defined in [RFC8122]. 547 Each endpoint MUST associate an SDP 'tls-id' attribute with the m- 548 line, following the procedures in [I-D.ietf-mmusic-dtls-sdp]. 550 10.2. Generating the Initial SDP Offer 552 When the offerer creates an initial offer, the offerer: 554 o MUST associate an SDP setup attribute with the m- line; 556 o MUST associate an SDP 'sctp-port' attribute with the m- line; 558 o MUST, in the case of TCP/DTLS/SCTP, associate an SDP 'connection' 559 attribute, with a 'new' attribute value, with the m- line; and 561 o MAY associate an SDP 'max-message-size' attribute [Section 6] with 562 the m- line. 564 10.3. Generating the SDP Answer 566 When the answerer receives an offer, which contains an m- line 567 describing an SCTP-over-DTLS association, if the answerer accepts the 568 association, the answerer: 570 o MUST insert a corresponding m- line in the answer, with an m- line 571 proto value [RFC3264] identical to the value in the offer; 573 o MUST associate an SDP 'setup' attribute with the m- line; 575 o MUST associate an SDP 'sctp-port' attribute with the m- line. If 576 the offer contained a new (different than the one currently used) 577 SCTP port value the answerer MUST also associate a new SCTP port 578 value. If the offer contained a zero SCTP port value, or if the 579 answerer does not accept the SCTP association, the answerer MUST 580 also associate a zero SCTP port value; and 582 o MAY associate an SDP 'max-message-size' attribute [Section 6] with 583 the m- line. The attribute value in the answer is independent 584 from the value (if present) in the corresponding m- line of the 585 offer. 587 Once the answerer has sent the answer the answerer: 589 o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not 590 yet been established, or if an existing TCP connection is to be 591 closed and replaced by a new TCP connection, follow the procedures 592 in [RFC4145] for closing and establishing a TCP connection; 594 o MUST, if a DTLS association has not yet been established, or if an 595 existing DTLS association is to be closed and replaced by a new 596 DTLS association, follow the procedures in 598 [I-D.ietf-mmusic-dtls-sdp] for closing the currently used, and 599 establishing a new, DTLS association; and 601 o MUST, if an SCTP association has not yet been established, or if 602 an existing SCTP association is to be closed and replaced by a new 603 SCTP association, initiate the closing of the existing SCTP 604 association (if applicable) and establishment of the SCTP 605 association. 607 If the SDP 'sctp-port' attribute in the answer contains a zero 608 attribute value, the answerer MUST NOT establish an SCTP association. 609 If an SCTP association exists, the offerer MUST close it. 611 If the answerer does not accept the m- line in the offer, it MUST 612 assign a zero port value to the corresponding m- line in the answer, 613 following the procedures in [RFC3264]. In addition, the answerer 614 MUST NOT initiate the establishment of a TCP connection, a DTLS 615 association or a DTLS association associated with the m- line. 617 10.4. Offerer Processing of the SDP Answer 619 Once the offerer has received the answer the offerer: 621 o MUST, in the case of TCP/DTLS/SCTP, if a TCP connection has not 622 yet been established, or if an existing TCP connection is to be 623 closed and replaced by a new TCP connection, follow the procedures 624 in [RFC4145] for closing and establishing a TCP connection; 626 o MUST, if a DTLS association has not yet been established, or if an 627 existing DTLS association is to be closed and replaced by a new 628 DTLS association, follow the procedures in 629 [I-D.ietf-mmusic-dtls-sdp] for closing and establishing a DTLS 630 association; and 632 o MUST, if an SCTP association has not yet been established, or if 633 an existing SCTP association is to be closed and replaced by a new 634 SCTP association, initiate the closing of the existing SCTP 635 association (if applicable) and establishment of the SCTP 636 association. 638 If the SDP 'sctp-port' attribute in the answer contains a zero 639 attribute value, the offerer MUST NOT establish an SCTP association. 640 If an SCTP association exists in that case, the offerer MUST close 641 it. 643 If the m- line in the answer contains a zero port value, the offerer 644 MUST NOT initiate the establishment a TCP connection, a DTLS 645 association or an SCTP association associated with the m- line. If a 646 TCP connection, or a DTLS association or an SCTP association exists 647 in that case, the offerer MUST close it. 649 10.5. Modifying the Session 651 When an offerer sends an updated offer, in order to modify a 652 previously established SCTP association, it follows the procedures in 653 Section 10.2, with the following exceptions: 655 o If the offerer wants to close an SCTP association, and immediately 656 establish a new SCTP association, the offerer MUST associate an 657 SDP 'sctp-port' attribute with a new (different than the one 658 currently used) attribute value. This will not impact the 659 underlying DTLS association (and TCP connection in case of 660 TCP/DTLS/SCTP). 662 o If the offerer wants to close an SCTP association, without 663 immediately establishing a new SCTP association, the offerer MUST 664 associate an SDP 'sctp-port' attribute with a zero attribute 665 value. This will not impact the underlying DTLS association (and 666 TCP connection in case of TCP/DTLS/SCTP). 668 o If the offerer wants to establish an SCTP association, and another 669 SCTP association was previously closed, the offerer MUST associate 670 an SDP 'sctp-port' attribute with a new attribute value (different 671 than the value associated with the previous SCTP association). If 672 the previous SCTP association was closed successfully following 673 use of an SDP 'sctp-port' attribute with a zero attribute value, 674 the offerer MAY use the same attribute value for the new SCTP 675 association that was used with the previous SCTP association 676 before it was closed. This will not impact the underlying DTLS 677 association (and TCP connection in case of TCP/DTLS/SCTP). 679 o If the offerer wants to close an existing SCTP association, and 680 the underlying DTLS association (and the underlying TCP connection 681 in case of TCP/DTLS/SCTP) it MUST assign a zero port value to the 682 m- line associated with the SCTP and DTLS associations (and TCP 683 connection in case of TCP/DTLS/SCTP), following the procedures in 684 [RFC3264]. 686 o NOTE: This specification does not define a mechanism for 687 explicitly closing a DTLS association while maintaining the 688 overlying SCTP association. However, if a DTLS association is 689 closed and replaced with a new DTLS association, as a result of 690 some other action [I-D.ietf-mmusic-dtls-sdp], the state of the 691 SCTP association is not affected. 693 The offer follows the procedures in [I-D.ietf-mmusic-dtls-sdp] 694 regarding the DTLS association impacts when modifying a session. 696 In the case of TCP/DTLS/SCTP, the offerer follows the procedures in 697 [RFC4145] regarding the TCP connection impacts when modifying a 698 session. 700 11. Multihoming Considerations 702 Multihoming is not supported when sending SCTP on top of DTLS, as 703 DTLS does not expose address management of the underlying transport 704 protocols (UDP or TCP) to its upper layer. 706 12. NAT Considerations 708 12.1. General 710 When SCTP-over-DTLS is used in NAT environment, it relies on the NAT 711 traversal procedures for the underlying transport protocol (UDP or 712 TCP). 714 12.2. ICE Considerations 716 When SCTP-over-DTLS is used with UDP based ICE candidates [RFC5245] 717 then the procedures for UDP/DTLS/SCTP [Section 7] are used. 719 When SCTP-over-DTLS is used with TCP based ICE candidates [RFC6544] 720 then the procedures for TCP/DTLS/SCTP [Section 8] are used. 722 In ICE environments, during the nomination process, endpoints go 723 through multiple ICE candidate pairs, until the most preferred 724 candidate pair is found. During the nomination process, data can be 725 sent as soon as the first working candidate pair is found, but the 726 nomination process still continues and selected candidate pairs can 727 still change while data is sent. Furthermore, if endpoints roam 728 between networks, for instance when mobile endpoint switches from 729 mobile connection to WiFi, endpoints will initiate an ICE restart, 730 which will trigger a new nomination process between the new set of 731 candidates and likely result in the new nominated candidate pair. 733 Implementations MUST treat all ICE candidate pairs associated with an 734 SCTP association on top of a DTLS association as part of the same 735 DTLS association. Thus, there will only be one SCTP handshake and 736 one DTLS handshake even if there are multiple valid candidate pairs, 737 and shifting from one candidate pair to another, including switching 738 between UDP to TCP candidate pairs, will not impact the SCTP or DTLS 739 associations. If new candidates are added, they will also be part of 740 the same SCTP and DTLS associations. When transitioning between 741 candidate pairs, different candidate pairs can be currently active in 742 different directions and implementations MUST be ready to receive 743 data on any of the candidates, even if this means sending and 744 receiving data using UDP/DTLS/SCTP and TCP/DTLS/SCTP at the same time 745 in different directions. 747 In order to maximize the likelihood of interoperability between the 748 endpoints, all ICE enabled SCTP-over-DTLS endpoints SHOULD implement 749 support for UDP/DTLS/SCTP. 751 When an SDP offer or answer is sent with multiple ICE candidates 752 during initial connection negotiation or after ICE restart, UDP based 753 candidates SHOULD be included and default candidate SHOULD be chosen 754 from one of those UDP candidates. The proto value MUST match the 755 transport protocol associated with the default candidate. If UDP 756 transport is used for the default candidate, then 'UDP/DTLS/SCTP' 757 proto value MUST be used. If TCP transport is used for the default 758 candidate, then 'TCP/DTLS/SCTP' proto value MUST be used. Note that 759 under normal circumstances the proto value for offers and answers 760 sent during ICE nomination SHOULD be 'UDP/DTLS/SCTP'. 762 When a subsequent SDP offer or answer is sent after ICE nomination is 763 complete, and does not initiate ICE restart, it will contain only the 764 nominated ICE candidate pair. In this case, the proto value MUST 765 match the transport protocol associated with the nominated ICE 766 candidate pair. If UDP transport is used for the nominated pair, 767 then 'UDP/DTLS/SCTP' proto value MUST be used. If TCP transport is 768 used for the nominated pair, then 'TCP/DTLS/SCTP' proto value MUST be 769 used. Please note that if an endpoint switches between TCP-based and 770 UDP-based candidates during the nomination process the endpoint is 771 not required to send an SDP offer for the sole purpose of keeping the 772 proto value of the associated m- line in sync. 774 NOTE: The text in the paragraph above only applies when the usage of 775 ICE has been negotiated. If ICE is not used, the proto value MUST 776 always reflect the transport protocol used at any given time. 778 13. Examples 780 13.1. Establishment of UDP/DTLS/SCTP association 781 SDP Offer: 783 m=application 54111 UDP/DTLS/SCTP webrtc-datachannel 784 c=IN IP6 2001:DB8::A8FD 785 a=tls-id:abc3de65cddef001be82 786 a=setup:actpass 787 a=sctp-port:5000 788 a=max-message-size:100000 790 - The offerer indicates that the usage of the 791 UDP/DTLS/SCTP association will be as defined 792 for the 'webrtc-datachannel' format value. 793 - The offerer UDP port value is 54111. 794 - The offerer SCTP port value is 5000. 795 - The offerer indicates that it can take either the 796 client or the server DTLS role. 798 SDP Answer: 800 m=application 64300 UDP/DTLS/SCTP webrtc-datachannel 801 c=IN IP6 2001:DB8::001D 802 a=tls-id:dbc8de77cddef001be90 803 a=setup:passive 804 a=sctp-port:6000 805 a=max-message-size:100000 807 - The answerer UDP port value is 64300. 808 - The answerer SCTP port value is 6000. 809 - The answerer takes the server DTLS role. 811 14. Security Considerations 813 [RFC4566] defines general SDP security considerations, while 814 [RFC3264], [RFC4145] and [RFC8122] define security considerations 815 when using the SDP offer/answer mechanism to negotiate media streams. 817 [RFC4960] defines general SCTP security considerations and 818 [I-D.ietf-tsvwg-sctp-dtls-encaps] defines security considerations 819 when using SCTP on top of DTLS. 821 This specification does not introduce new security considerations in 822 addition to those defined in the specifications listed above. 824 15. IANA Considerations 826 15.1. New SDP proto values 828 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 829 document.] 831 This document updates the "Session Description Protocol (SDP) 832 Parameters" registry, following the procedures in [RFC4566], by 833 adding the following values to the table in the SDP "proto" field 834 registry: 836 +-------+---------------+-----------+ 837 | Type | SDP Name | Reference | 838 +-------+---------------+-----------+ 839 | proto | UDP/DTLS/SCTP | [RFCXXXX] | 840 | proto | TCP/DTLS/SCTP | [RFCXXXX] | 841 +-------+---------------+-----------+ 843 Table 1: SDP "proto" field values 845 15.2. New SDP Attributes 847 15.2.1. sctp-port 849 This document defines a new SDP media-level attribute,'sctp-port'. 850 The details of the attribute are defined in Section 5.2. 852 15.2.2. max-message-size 854 This document defines a new SDP media-level attribute,'max-message- 855 size'. The details of the attribute are defined in Section 6.2. 857 15.3. association-usage Name Registry 859 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number of this 860 document.] 862 This specification creates a new IANA registry, following the 863 procedures in [RFC5226], for the namespace associated with the 864 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' protocol identifiers. Each fmt 865 value describes the usage of an entire SCTP association, including 866 all SCTP streams associated with the SCTP association. 868 NOTE: Usage indication of individual SCTP streams is outside the 869 scope of this specification. 871 The fmt value, "association-usage", used with these "proto" values is 872 required. It is defined in Section 4. 874 As part of this registry, IANA maintains the following information: 876 association-usage name: The identifier of the subprotocol, as will 877 be used as the fmt value. 879 association-usage reference: A reference to the document in which 880 the association-usage is defined. 882 association-usage names are to be subject to the "First Come First 883 Served" IANA registration policy [RFC5226]. 885 IANA is asked to add initial values to the registry. 887 |----------------------------------------------------------| 888 | name | Reference | 889 |----------------------------------------------------------| 890 | webrtc-datachannel | draft-ietf-rtcweb-data-protocol-xx, | 891 | | RFCXXX | 892 |----------------------------------------------------------| 894 [RFC EDITOR NOTE: Please hold the publication of this draft 895 until draft-ietf-rtcweb-data-protocol has been published as an RFC. 896 Then, replace the reference to draft-ietf-rtcweb-data-protocol 897 with the RFC number.] 899 [RFC EDITOR NOTE: Please replace RFCXXXX with the RFC number 900 of this document.] 902 Figure 1 904 16. Acknowledgments 906 The authors wish to thank Harald Alvestrand, Randell Jesup, Paul 907 Kyzivat, Michael Tuexen, Juergen Stoetzer-Bradler, Flemming Andreasen 908 and Ari Keranen for their comments and useful feedback. Ben Campbell 909 provided comments as part of his AD review. Brian Carpenter 910 performed the Gen-ART review. 912 17. 914 [RFC EDITOR NOTE: Please remove this section when publishing] 916 Changes from draft-ietf-mmusic-sctp-sdp-25 917 o SDP 'dtls-id' attribute re-named to 'tls-id'. 919 Changes from draft-ietf-mmusic-sctp-sdp-24 921 o Minor editorial fix by Roman. 923 Changes from draft-ietf-mmusic-sctp-sdp-23 925 o Changes based on IESG review. 927 o - Proto value clarifications. 929 Changes from draft-ietf-mmusic-sctp-sdp-22 931 o Changes based on Gen-ART review by Brian Carpenter. 933 Changes from draft-ietf-mmusic-sctp-sdp-21 935 o Changes based on AD review by Ben Campbell. 937 Changes from draft-ietf-mmusic-sctp-sdp-20 939 o Informative reference to draft-ietf-rtcweb-data-protocol added. 941 Changes from draft-ietf-mmusic-sctp-sdp-19 943 o Changes based on WG chair comments from Flemming Andreasen. 945 Changes from draft-ietf-mmusic-sctp-sdp-18 947 o Changes based on WGLC comments from Paul Kyzivat. 949 Changes from draft-ietf-mmusic-sctp-sdp-17 951 o Removal of 'SCTP'. 953 o Document title changed. 955 o Disallow usage of SDP 'setup' attribute 'holdconn' value. 957 o Roman Shpount added as co-editor. 959 Changes from draft-ietf-mmusic-sctp-sdp-15 961 o Chapter about SCTP, DTLS and TCP association/connection management 962 modified. 964 o Removal of SCTP/DTLS. 966 Changes from draft-ietf-mmusic-sctp-sdp-14 968 o Changes based on WGLC comments from Magnus Westerlund. 970 o - ABNF clarification that token and port are defined in RFC4566. 972 o - Specify 40 as maximum digit character length for the SDP max- 973 message-size value. 975 o - Editorial clarification. 977 o Changes based on discussions at IETF#92. 979 o - Specify that all ICE candidate pairs belong to the same DTLS 980 association. 982 Changes from draft-ietf-mmusic-sctp-sdp-13 984 o Changes based on comments from Paul Kyzivat. 986 o - Text preventing usage of well-known ports removed. 988 o - Editorial clarification. 990 Changes from draft-ietf-mmusic-sctp-sdp-12 992 o Mux category rules added for new SDP attributes. 994 o Reference to draft-ietf-mmusic-sdp-mux-attributes added. 996 o Changes based on comments from Roman Shpount: 998 o - Specify that fingerprint or setup roles must not be modified, 999 unless underlying transport protocol is also modified. 1001 o Changes based on comments from Ari Keranen: 1003 o - Editorial corrections. 1005 o Changes based on comments from Flemming Andreasen: 1007 o - Clarify that, if UDP/DTLS/SCTP or TCP/DTLS/SCTP is used, the 1008 DTLS association is established before the SCTP association. 1010 o - Clarify that max-message-size value is given in bytes, and that 1011 different values can be used per direction. 1013 o - Section on fmtp attribute removed. 1015 o - Editorial corrections. 1017 Changes from draft-ietf-mmusic-sctp-sdp-11 1019 o Example added. 1021 Changes from draft-ietf-mmusic-sctp-sdp-10 1023 o SDP max-message-size attribute added to IANA considerations. 1025 o Changes based on comments from Paul Kyzivat: 1027 o - Text about max message size removed from fmtp attribute section. 1029 Changes from draft-ietf-mmusic-sctp-sdp-09 1031 o 'DTLS/SCTP' split into 'UDP/DTLS/SCTP' and 'TCP/DTLS/SCTP' 1033 o Procedures for realizing UDP/DTLS/SCTP- and TCP/DTLS/SCTP 1034 transports added. 1036 Changes from draft-ietf-mmusic-sctp-sdp-08 1038 o Default SCTP port removed: 1040 o - Usage of SDP sctp-port attribute mandatory. 1042 o SDP max-message-size attribute defined: 1044 o - Attribute definition. 1046 o - SDP Offer/Answer procedures. 1048 o Text about SDP direction attributes added. 1050 o Text about TLS role determination added. 1052 18. References 1054 18.1. Normative References 1056 [RFC0793] Postel, J., "Transmission Control Protocol", STD 7, 1057 RFC 793, DOI 10.17487/RFC0793, September 1981, 1058 . 1060 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1061 Requirement Levels", BCP 14, RFC 2119, 1062 DOI 10.17487/RFC2119, March 1997, 1063 . 1065 [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model 1066 with Session Description Protocol (SDP)", RFC 3264, 1067 DOI 10.17487/RFC3264, June 2002, 1068 . 1070 [RFC4145] Yon, D. and G. Camarillo, "TCP-Based Media Transport in 1071 the Session Description Protocol (SDP)", RFC 4145, 1072 DOI 10.17487/RFC4145, September 2005, 1073 . 1075 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 1076 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 1077 July 2006, . 1079 [RFC4571] Lazzaro, J., "Framing Real-time Transport Protocol (RTP) 1080 and RTP Control Protocol (RTCP) Packets over Connection- 1081 Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July 1082 2006, . 1084 [RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol", 1085 RFC 4960, DOI 10.17487/RFC4960, September 2007, 1086 . 1088 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1089 IANA Considerations Section in RFCs", BCP 26, RFC 5226, 1090 DOI 10.17487/RFC5226, May 2008, 1091 . 1093 [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer 1094 Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, 1095 January 2012, . 1097 [RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach, 1098 "TCP Candidates with Interactive Connectivity 1099 Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544, 1100 March 2012, . 1102 [RFC8122] Lennox, J. and C. Holmberg, "Connection-Oriented Media 1103 Transport over the Transport Layer Security (TLS) Protocol 1104 in the Session Description Protocol (SDP)", RFC 8122, 1105 DOI 10.17487/RFC8122, March 2017, 1106 . 1108 [I-D.ietf-mmusic-dtls-sdp] 1109 Holmberg, C. and R. Shpount, "Using the SDP Offer/Answer 1110 Mechanism for DTLS", draft-ietf-mmusic-dtls-sdp-24 (work 1111 in progress), April 2017. 1113 [I-D.ietf-tsvwg-sctp-dtls-encaps] 1114 Tuexen, M., Stewart, R., Jesup, R., and S. Loreto, "DTLS 1115 Encapsulation of SCTP Packets", draft-ietf-tsvwg-sctp- 1116 dtls-encaps-09 (work in progress), January 2015. 1118 [I-D.ietf-mmusic-sdp-mux-attributes] 1119 Nandakumar, S., "A Framework for SDP Attributes when 1120 Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-16 1121 (work in progress), December 2016. 1123 18.2. Informative References 1125 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 1126 (ICE): A Protocol for Network Address Translator (NAT) 1127 Traversal for Offer/Answer Protocols", RFC 5245, 1128 DOI 10.17487/RFC5245, April 2010, 1129 . 1131 [I-D.ietf-rtcweb-data-channel] 1132 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data 1133 Channels", draft-ietf-rtcweb-data-channel-13 (work in 1134 progress), January 2015. 1136 [I-D.ietf-mmusic-data-channel-sdpneg] 1137 Drage, K., Makaraju, M., Stoetzer-Bradler, J., Ejzak, R., 1138 and J. Marcon, "SDP-based Data Channel Negotiation", 1139 draft-ietf-mmusic-data-channel-sdpneg-12 (work in 1140 progress), March 2017. 1142 [I-D.ietf-rtcweb-data-protocol] 1143 Jesup, R., Loreto, S., and M. Tuexen, "WebRTC Data Channel 1144 Establishment Protocol", draft-ietf-rtcweb-data- 1145 protocol-09 (work in progress), January 2015. 1147 Authors' Addresses 1149 Christer Holmberg 1150 Ericsson 1151 Hirsalantie 11 1152 Jorvas 02420 1153 Finland 1155 Email: christer.holmberg@ericsson.com 1156 Roman Shpount 1157 TurboBridge 1158 4905 Del Ray Avenue, Suite 300 1159 Bethesda, MD 20814 1160 USA 1162 Phone: +1 (240) 292-6632 1163 Email: rshpount@turbobridge.com 1165 Salvatore Loreto 1166 Ericsson 1167 Hirsalantie 11 1168 Jorvas 02420 1169 Finland 1171 Email: Salvatore.Loreto@ericsson.com 1173 Gonzalo Camarillo 1174 Ericsson 1175 Hirsalantie 11 1176 Jorvas 02420 1177 Finland 1179 Email: Gonzalo.Camarillo@ericsson.com