Network Working Group R. Abhishek
Internet-Draft Tencent
Intended status: Standards Track October 20, 2020
Expires: April 23, 2021
SDP Overlay Grouping framework for immersive telepresence media streams
draft-overlay-grouping-00
Abstract
This document defines semantics that allow for signalling a new SDP
group "OL" for overlays in an immersive telepresence session. The
"OL" attribute can be used by the application to relate all the
overlay media streams enabling them to be added as overlay on top of
the immersive video. The overlay grouping semantics is required, if
the media data is seperate and transported via different protocols.
Status of This Memo
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This Internet-Draft will expire on April 23, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of Operation . . . . . . . . . . . . . . . . . . . . 3
4. Overlay Stream Group Identification Attribute . . . . . . . . 4
5. Use of group and mid . . . . . . . . . . . . . . . . . . . . 4
6. Example of OL . . . . . . . . . . . . . . . . . . . . . . . . 4
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
Telepresence [RFC7205] can be described as a technology that allows a
person the experience of "being present" at a remote location for
video as well as audio telepresence sessions, so as to enable the
users sense of realism and presence [TS26.223] . SDP [RFC4566] is
being predominantly used for describing the format for multimedia
communication session for telepresence conferencing. These use open
standards such as RTP [RFC3550] and SIP [RFC3261] .
An SDP session may contain more than one media lines with each media
line identified by "m"=line. Each line denotes a single media
stream. If multiple media lines are present in a session, a receiver
needs to identify relationship between those media lines.
Overlay media stream can be defined as a piece of visual media which
can be rendered over an immersive video or image or over a viewport
[ISO23090] . When an overlay is transmitted, its media stream needs
to be uniquely identified across multiple SDP descriptions exchanged
with different receivers so that the streams can be identified in
terms of its role in the session irrespective of its media type and
transport protocol.
In an immersive telepresence session, one media is streamed as an
immersive stream whereas other media streams are overlaid on top of
the immersive video/image. An end user can stream more than one
overlay, subject to its decoding capacity. When multiple overlay
streams are transmitted within a session, the end application upon
receiving, needs to be able to relate the media streams to each
other. This can be achieved by SDP grouping framework by using the
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"group" attribute that groups different "m" lines in a session.
However, the current SDP signalling framework does not provide such
grouping semantics for overlays.
This document describes a new SDP group semantics for grouping the
overlays when an immersive media stream is transmitted for
telepresence conferencing. SDP session description consists of one
or multiple media lines know as "m" lines which can be identified by
a token carried in a "mid" attribute. The SDP session describes a
session-level group level attributes that groups different media
lines using a defined group semantics. The semantics defined in this
memo is to be used in conjuction with [RFC5888] titled "The Session
Description Protocol (SDP) Grouping Framework".
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] .
3. Overview of Operation
A non-normative description of SDP overlay group semantics is
described in this section. An immersive stream for a telepresence
session may consist of one or more conference rooms with a 360-degree
camera and the remote users using head mounted display for streaming.
"Participant cameras" are used to capture the conference participants
whereas "presentation cameras" or "content cameras" can be used for
document display [RFC7205] . The remote participant can stream any
of the available immersive video in the session as background whereas
other available streams such as the presentation stream or 2D video
from any other room or participant can be used as an overlay on top
of the immersive video/image.
A user with a head mounted display may stream more than one overlay
in a single SDP session. These overlay streams are transmitted via
"m" line in SDP session description. Each "m" line in the session
description is identified by a token carried via the "mid" attribute.
When multiple overlay streams are transmitted within a session, the
end application upon receiving, needs to be able to relate the media
streams to each other. This is achieved by using the SDP grouping
framework [RFC5888]. The session descriptions carries session-level
"group" attribute for the overlays which groups different "m" lines
using overlay(OL) group semantics.
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4. Overlay Stream Group Identification Attribute
The "overlay media stream identification" attribute is used to
identify overlay media streams within a session description. In a
overlay group, the media lines MAY have different media contents.
Its formatting in SDP [RFC4566] is described by the following
Augmented Backus-Naur Form (ABNF) [RFC5234] :
mid-attribute = "a=mid:" identification-tag
identification-tag = token
; token is defined in RFC4566
This documents defines a new group semantics "OL" identification
media attribute, which is used to identify overlay group media
streams within a session description. It is used for grouping the
media streams for different overlays together within a session. An
application that receives a session description that contains "m"
lines grouped together using "OL" semantics MUST overlay the
corresponding media streams on top of the immersive media stream.
5. Use of group and mid
All group and mid attributes MUST follow the rules defined in
[RFC5888]. The "mid" attribute should be used for all "m" lines
within a session description . If for any "m" lines within a session,
no "mid" attribute is identified for a session description, the
application MUST NOT perform any media line grouping. If the
identification-tags associated with "a=group" lines do not map to any
"m" lines, it MUST be ignored.
group-attribute ="a=group:" semantics
*(SP identification-tag)
semantics = "OL" / semantics-extension
semantics-extension = token
; token is defined in RFC4566
6. Example of OL
The following two examples show a session description for overlays in
an immersive telepresence conference. The "group" line indicates
that the "m" lines with tokens 1 and 2 are grouped for the purpose of
overlays and intended to be overlaid on top of the immersive video.
In the first example shown below, two overlays are being transmitted.
The first media stream (mid:1) carries the video stream, and the
second stream (mid:2) contains an audio stream.
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v=0
o=Alice 292742730 29277831 IN IP4 233.252.0.74
c=IN IP4 233.252.0.79
t=0 0
a=group:OL 1 2
m=video 30000 RTP/AVP 31
a=mid:1
m=audio 30002 RTP/AVP 31
a=mid:2
The second example, below, uses 'content' attribute with the media
streams which are transmitted for overlay purpose.
v=0
o=Alice 292742730 29277831 IN IP4 233.252.0.74
c=IN IP4 233.252.0.79
t=0 0
a=group:OL 1 2
m=video 30000 RTP/AVP 31
a= content:slides
a=mid:1
m=video 30002 RTP/AVP 31
a=content:speaker
a=mid:2
7. Security Considerations
All security considerations as defined in [RFC5888] apply:
Using the "group" parameter with FID semantics, an entity that
managed to modify the session descriptions exchanged between the
participants to establish a multimedia session could force the
participants to send a copy of the media to any destination of its
choosing.
Integrity mechanisms provided by protocols used to exchange session
descriptions and media encryption can be used to prevent this attack.
In SIP, Secure/Multipurpose Internet Mail Extensions (S/MIME)
[RFC8550] and Transport Layer Security (TLS) [RFC8446] can be used to
protect session description exchanges in an end-to-end and a hop-
byhop fashion, respectively.
8. IANA Considerations
The following contact information shall be used for all registrations
included here:
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Contact: Rohit Abhishek
email: rabhishek@rabhishek.com
tel : +1-816-585-7500
This document defines a new SDP group semantics for overlays for a
immersive telepresence session. This attribute can be used by the
application to group all the overlays in a session. Semantics values
to be used with this framework should be registered by the IANA
following the Standards Action policy [RFC8126]. This document adds
a new group semantics and follows the registry group defined in
[RFC5888].
The following semantics needs to be registered by IANA in Semantics
for the "group" SDP Attribute under SDP Parameters.
Semantics Token Reference
----------------------------------------------
Overlay OL RFCXXXX
The "OL" attribute is used to group different media streams to be
rendered as overlays. Its format is defined in Section 4 .
The IANA Considerations section of the RFC MUST include the following
information, which appears in the IANA registry along with the RFC
number of the publication.
o A brief description of the semantics.
o Token to be used within the "group" attribute. This token may be
of any length, but SHOULD be no more than four characters long.
o Reference to a standards track RFC.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
DOI 10.17487/RFC3261, June 2002,
<https://www.rfc-editor.org/info/rfc3261>.
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[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, DOI 10.17487/RFC3550,
July 2003, <https://www.rfc-editor.org/info/rfc3550>.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, DOI 10.17487/RFC4566,
July 2006, <https://www.rfc-editor.org/info/rfc4566>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
[RFC5888] Camarillo, G. and H. Schulzrinne, "The Session Description
Protocol (SDP) Grouping Framework", RFC 5888,
DOI 10.17487/RFC5888, June 2010,
<https://www.rfc-editor.org/info/rfc5888>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC8550] Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Certificate Handling", RFC 8550, DOI 10.17487/RFC8550,
April 2019, <https://www.rfc-editor.org/info/rfc8550>.
9.2. Informative References
[ISO23090]
"Information technology -- Coded representation of
immersive media -- Part 2: Omnidirectional MediA Format
(OMAF) 2nd Edition", ISO ISO 23090-2:2020(E), February
2020.
[RFC7205] Romanow, A., Botzko, S., Duckworth, M., and R. Even, Ed.,
"Use Cases for Telepresence Multistreams", RFC 7205,
DOI 10.17487/RFC7205, April 2014,
<https://www.rfc-editor.org/info/rfc7205>.
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[TS26.223]
"3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects;
Telepresence using the IP Multimedia Subsystem (IMS);
Media Handling and Interaction", 3GPP TS26.223, March
2020.
Author's Address
Rohit Abhishek
Tencent
2747 Park Blvd
Palo Alto 94588
USA
Email: rabhishek@rabhishek.com