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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) ** Obsolete normative reference: RFC 4566 (Obsoleted by RFC 8866) Summary: 1 error (**), 0 flaws (~~), 1 warning (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group R. Abhishek 2 Internet-Draft Tencent 3 Intended status: Standards Track October 20, 2020 4 Expires: April 23, 2021 6 SDP Overlay Grouping framework for immersive telepresence media streams 7 draft-overlay-grouping-00 9 Abstract 11 This document defines semantics that allow for signalling a new SDP 12 group "OL" for overlays in an immersive telepresence session. The 13 "OL" attribute can be used by the application to relate all the 14 overlay media streams enabling them to be added as overlay on top of 15 the immersive video. The overlay grouping semantics is required, if 16 the media data is seperate and transported via different protocols. 18 Status of This Memo 20 This Internet-Draft is submitted in full conformance with the 21 provisions of BCP 78 and BCP 79. 23 Internet-Drafts are working documents of the Internet Engineering 24 Task Force (IETF). Note that other groups may also distribute 25 working documents as Internet-Drafts. The list of current Internet- 26 Drafts is at https://datatracker.ietf.org/drafts/current/. 28 Internet-Drafts are draft documents valid for a maximum of six months 29 and may be updated, replaced, or obsoleted by other documents at any 30 time. It is inappropriate to use Internet-Drafts as reference 31 material or to cite them other than as "work in progress." 33 This Internet-Draft will expire on April 23, 2021. 35 Copyright Notice 37 Copyright (c) 2020 IETF Trust and the persons identified as the 38 document authors. All rights reserved. 40 This document is subject to BCP 78 and the IETF Trust's Legal 41 Provisions Relating to IETF Documents 42 (https://trustee.ietf.org/license-info) in effect on the date of 43 publication of this document. Please review these documents 44 carefully, as they describe your rights and restrictions with respect 45 to this document. Code Components extracted from this document must 46 include Simplified BSD License text as described in Section 4.e of 47 the Trust Legal Provisions and are provided without warranty as 48 described in the Simplified BSD License. 50 Table of Contents 52 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 53 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 3 55 4. Overlay Stream Group Identification Attribute . . . . . . . . 4 56 5. Use of group and mid . . . . . . . . . . . . . . . . . . . . 4 57 6. Example of OL . . . . . . . . . . . . . . . . . . . . . . . . 4 58 7. Security Considerations . . . . . . . . . . . . . . . . . . . 5 59 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 60 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 61 9.1. Normative References . . . . . . . . . . . . . . . . . . 6 62 9.2. Informative References . . . . . . . . . . . . . . . . . 7 63 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 65 1. Introduction 67 Telepresence [RFC7205] can be described as a technology that allows a 68 person the experience of "being present" at a remote location for 69 video as well as audio telepresence sessions, so as to enable the 70 users sense of realism and presence [TS26.223] . SDP [RFC4566] is 71 being predominantly used for describing the format for multimedia 72 communication session for telepresence conferencing. These use open 73 standards such as RTP [RFC3550] and SIP [RFC3261] . 75 An SDP session may contain more than one media lines with each media 76 line identified by "m"=line. Each line denotes a single media 77 stream. If multiple media lines are present in a session, a receiver 78 needs to identify relationship between those media lines. 80 Overlay media stream can be defined as a piece of visual media which 81 can be rendered over an immersive video or image or over a viewport 82 [ISO23090] . When an overlay is transmitted, its media stream needs 83 to be uniquely identified across multiple SDP descriptions exchanged 84 with different receivers so that the streams can be identified in 85 terms of its role in the session irrespective of its media type and 86 transport protocol. 88 In an immersive telepresence session, one media is streamed as an 89 immersive stream whereas other media streams are overlaid on top of 90 the immersive video/image. An end user can stream more than one 91 overlay, subject to its decoding capacity. When multiple overlay 92 streams are transmitted within a session, the end application upon 93 receiving, needs to be able to relate the media streams to each 94 other. This can be achieved by SDP grouping framework by using the 95 "group" attribute that groups different "m" lines in a session. 96 However, the current SDP signalling framework does not provide such 97 grouping semantics for overlays. 99 This document describes a new SDP group semantics for grouping the 100 overlays when an immersive media stream is transmitted for 101 telepresence conferencing. SDP session description consists of one 102 or multiple media lines know as "m" lines which can be identified by 103 a token carried in a "mid" attribute. The SDP session describes a 104 session-level group level attributes that groups different media 105 lines using a defined group semantics. The semantics defined in this 106 memo is to be used in conjuction with [RFC5888] titled "The Session 107 Description Protocol (SDP) Grouping Framework". 109 2. Terminology 111 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 112 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 113 document are to be interpreted as described in [RFC2119] . 115 3. Overview of Operation 117 A non-normative description of SDP overlay group semantics is 118 described in this section. An immersive stream for a telepresence 119 session may consist of one or more conference rooms with a 360-degree 120 camera and the remote users using head mounted display for streaming. 121 "Participant cameras" are used to capture the conference participants 122 whereas "presentation cameras" or "content cameras" can be used for 123 document display [RFC7205] . The remote participant can stream any 124 of the available immersive video in the session as background whereas 125 other available streams such as the presentation stream or 2D video 126 from any other room or participant can be used as an overlay on top 127 of the immersive video/image. 129 A user with a head mounted display may stream more than one overlay 130 in a single SDP session. These overlay streams are transmitted via 131 "m" line in SDP session description. Each "m" line in the session 132 description is identified by a token carried via the "mid" attribute. 133 When multiple overlay streams are transmitted within a session, the 134 end application upon receiving, needs to be able to relate the media 135 streams to each other. This is achieved by using the SDP grouping 136 framework [RFC5888]. The session descriptions carries session-level 137 "group" attribute for the overlays which groups different "m" lines 138 using overlay(OL) group semantics. 140 4. Overlay Stream Group Identification Attribute 142 The "overlay media stream identification" attribute is used to 143 identify overlay media streams within a session description. In a 144 overlay group, the media lines MAY have different media contents. 145 Its formatting in SDP [RFC4566] is described by the following 146 Augmented Backus-Naur Form (ABNF) [RFC5234] : 148 mid-attribute = "a=mid:" identification-tag 149 identification-tag = token 150 ; token is defined in RFC4566 152 This documents defines a new group semantics "OL" identification 153 media attribute, which is used to identify overlay group media 154 streams within a session description. It is used for grouping the 155 media streams for different overlays together within a session. An 156 application that receives a session description that contains "m" 157 lines grouped together using "OL" semantics MUST overlay the 158 corresponding media streams on top of the immersive media stream. 160 5. Use of group and mid 162 All group and mid attributes MUST follow the rules defined in 163 [RFC5888]. The "mid" attribute should be used for all "m" lines 164 within a session description . If for any "m" lines within a session, 165 no "mid" attribute is identified for a session description, the 166 application MUST NOT perform any media line grouping. If the 167 identification-tags associated with "a=group" lines do not map to any 168 "m" lines, it MUST be ignored. 170 group-attribute ="a=group:" semantics 171 *(SP identification-tag) 172 semantics = "OL" / semantics-extension 173 semantics-extension = token 174 ; token is defined in RFC4566 176 6. Example of OL 178 The following two examples show a session description for overlays in 179 an immersive telepresence conference. The "group" line indicates 180 that the "m" lines with tokens 1 and 2 are grouped for the purpose of 181 overlays and intended to be overlaid on top of the immersive video. 183 In the first example shown below, two overlays are being transmitted. 184 The first media stream (mid:1) carries the video stream, and the 185 second stream (mid:2) contains an audio stream. 187 v=0 188 o=Alice 292742730 29277831 IN IP4 233.252.0.74 189 c=IN IP4 233.252.0.79 190 t=0 0 191 a=group:OL 1 2 192 m=video 30000 RTP/AVP 31 193 a=mid:1 194 m=audio 30002 RTP/AVP 31 195 a=mid:2 197 The second example, below, uses 'content' attribute with the media 198 streams which are transmitted for overlay purpose. 200 v=0 201 o=Alice 292742730 29277831 IN IP4 233.252.0.74 202 c=IN IP4 233.252.0.79 203 t=0 0 204 a=group:OL 1 2 205 m=video 30000 RTP/AVP 31 206 a= content:slides 207 a=mid:1 208 m=video 30002 RTP/AVP 31 209 a=content:speaker 210 a=mid:2 212 7. Security Considerations 214 All security considerations as defined in [RFC5888] apply: 216 Using the "group" parameter with FID semantics, an entity that 217 managed to modify the session descriptions exchanged between the 218 participants to establish a multimedia session could force the 219 participants to send a copy of the media to any destination of its 220 choosing. 222 Integrity mechanisms provided by protocols used to exchange session 223 descriptions and media encryption can be used to prevent this attack. 224 In SIP, Secure/Multipurpose Internet Mail Extensions (S/MIME) 225 [RFC8550] and Transport Layer Security (TLS) [RFC8446] can be used to 226 protect session description exchanges in an end-to-end and a hop- 227 byhop fashion, respectively. 229 8. IANA Considerations 231 The following contact information shall be used for all registrations 232 included here: 234 Contact: Rohit Abhishek 235 email: rabhishek@rabhishek.com 236 tel : +1-816-585-7500 238 This document defines a new SDP group semantics for overlays for a 239 immersive telepresence session. This attribute can be used by the 240 application to group all the overlays in a session. Semantics values 241 to be used with this framework should be registered by the IANA 242 following the Standards Action policy [RFC8126]. This document adds 243 a new group semantics and follows the registry group defined in 244 [RFC5888]. 246 The following semantics needs to be registered by IANA in Semantics 247 for the "group" SDP Attribute under SDP Parameters. 249 Semantics Token Reference 250 ---------------------------------------------- 251 Overlay OL RFCXXXX 253 The "OL" attribute is used to group different media streams to be 254 rendered as overlays. Its format is defined in Section 4 . 256 The IANA Considerations section of the RFC MUST include the following 257 information, which appears in the IANA registry along with the RFC 258 number of the publication. 260 o A brief description of the semantics. 262 o Token to be used within the "group" attribute. This token may be 263 of any length, but SHOULD be no more than four characters long. 265 o Reference to a standards track RFC. 267 9. References 269 9.1. Normative References 271 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 272 Requirement Levels", BCP 14, RFC 2119, 273 DOI 10.17487/RFC2119, March 1997, 274 . 276 [RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, 277 A., Peterson, J., Sparks, R., Handley, M., and E. 278 Schooler, "SIP: Session Initiation Protocol", RFC 3261, 279 DOI 10.17487/RFC3261, June 2002, 280 . 282 [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. 283 Jacobson, "RTP: A Transport Protocol for Real-Time 284 Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550, 285 July 2003, . 287 [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session 288 Description Protocol", RFC 4566, DOI 10.17487/RFC4566, 289 July 2006, . 291 [RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax 292 Specifications: ABNF", STD 68, RFC 5234, 293 DOI 10.17487/RFC5234, January 2008, 294 . 296 [RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description 297 Protocol (SDP) Grouping Framework", RFC 5888, 298 DOI 10.17487/RFC5888, June 2010, 299 . 301 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 302 Writing an IANA Considerations Section in RFCs", BCP 26, 303 RFC 8126, DOI 10.17487/RFC8126, June 2017, 304 . 306 [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol 307 Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, 308 . 310 [RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ 311 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 312 Certificate Handling", RFC 8550, DOI 10.17487/RFC8550, 313 April 2019, . 315 9.2. Informative References 317 [ISO23090] 318 "Information technology -- Coded representation of 319 immersive media -- Part 2: Omnidirectional MediA Format 320 (OMAF) 2nd Edition", ISO ISO 23090-2:2020(E), February 321 2020. 323 [RFC7205] Romanow, A., Botzko, S., Duckworth, M., and R. Even, Ed., 324 "Use Cases for Telepresence Multistreams", RFC 7205, 325 DOI 10.17487/RFC7205, April 2014, 326 . 328 [TS26.223] 329 "3rd Generation Partnership Project; Technical 330 Specification Group Services and System Aspects; 331 Telepresence using the IP Multimedia Subsystem (IMS); 332 Media Handling and Interaction", 3GPP TS26.223, March 333 2020. 335 Author's Address 337 Rohit Abhishek 338 Tencent 339 2747 Park Blvd 340 Palo Alto 94588 341 USA 343 Email: rabhishek@rabhishek.com