Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams
draft-ietf-bfcpbis-rfc4583bis-23
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8856.
|
|
|---|---|---|---|
| Authors | Gonzalo Camarillo , Tom Kristensen , Christer Holmberg | ||
| Last updated | 2018-05-21 (Latest revision 2018-04-10) | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART Last Call review
(of
-26)
by Pete Resnick
Ready w/issues
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Consensus: Waiting for Write-Up | |
| Document shepherd | Mary Barnes | ||
| IESG | IESG state | Became RFC 8856 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-bfcpbis-rfc4583bis-23
13. SDP Offer/Answer Procedures
This section defines the SDP offer/answer [4] procedures for
negotiating and establishing a BFCP stream. Generic procedures for
DTLS are defined in [18]. Generic procedures for TLS are defined in
[8].
This section only defines the BFCP-specific procedures. Unless
explicitly stated otherwise, the procedures apply to an 'm' line
describing a BFCP stream. If an offer or answer contains multiple
'm' lines describing BFCP streams, the procedures are applied
independently to each stream.
Within this document, 'initial offer' refers to the first offer,
within an SDP session (e.g. a SIP dialog when the Session Initiation
Protocol (SIP) [3] is used to carry SDP), in which the offerer
indicates that it wants to negotiate the establishment of a BFCP
stream.
If the 'm' line 'proto' value is 'TCP/TLS/BFCP', 'TCP/DTLS/BFCP' or
'UDP/TLS/BFCP', the offerer and answerer follow the generic
procedures defined in [8].
If the 'm' line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP', 'TCP/DTLS/
TCP' or 'UDP/TLS/BFCP', the offerer and answerer use the SDP 'setup'
attribute according to the procedures in [6].
If the 'm' line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP' or
'TCP/DTLS/BFCP', the offerer and anwerer use the SDP 'connection'
attribute according to the procedures in [6].
Note: The use of source-specific SDP parameters [19] is not
defined to BFCP streams.
13.1. Generating the Initial SDP Offer
When the offerer creates an initial offer, the offerer MUST associate
an SDP 'floorctrl' attribute (Section 5) and an SDP 'bfcpver'
attribute (Section 8) with the 'm' line.
In addition, if the offerer includes an SDP 'floorctrl' attribute
with 's-only' or 'c-s' attribute values in the offer, the offerer:
o MUST associate an SDP 'confid' attribute (Section 6) with the 'm'
line; and
o MUST associate an SDP 'userid' attribute (Section 6) with the 'm'
line; and
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o MUST associate an SDP 'floorid' attribute (Section 7) with the 'm'
line; and
o MUST associate an SDP 'label' attribute (Section 7) with the 'm'
line of each BFCP-controlled media stream.
Note: If the offerer includes an SDP 'floorctrl' attribute with a
'c-s' attribute value, or both a 'c-only' and a 's-only' attribute
value, in the offer, the attribute values above will only be used
if it is determined (Section 5) that the offerer will act as floor
control server. If it is determined that the offerer will act as
both floor control server and floor control client, the attribute
values will be used for the BFCP-controlled media streams where
the offerer acts as floor control server.
13.2. Generating the SDP Answer
When the answerer receives an offer, which contains an 'm' line
describing a BFCP stream, the answerer MUST check whether it supports
one or more of the BFCP versions supported by the offerer
(Section 8). If the answerer does not support any of the BFCP
versions, it MUST NOT accept the 'm' line. Otherwise, if the
answerer accepts the 'm' line, it:
o MUST insert a corresponding 'm' line in the answer, with an
identical 'm' line proto value [4]; and
o MUST associate a 'bfcpver' attribute with the 'm' line. The
answerer only indicates support of BFCP versions also supported by
the offerer; and
o MUST, if the offer contained an SDP 'floorctrl' attribute,
associate a 'floorctrl' attribute with the 'm' line.
In addition, if the answerer includes an SDP 'floorctrl' attribute
with 's-only' or 'c-s' attribute values in the answer, the answerer:
o MUST associate an SDP 'confid' attribute with the 'm' line; and
o MUST associate an SDP 'userid' attribute with the 'm' line; and
o MUST associate an SDP 'floorid' attribute with the 'm' line; and
o MUST associate an SDP 'label' attribute with the 'm' line of each
BFCP-controlled media stream.
Note: If the answerer includes an SDP 'floorctrl' attribute with
an 'c-s' attribute value in the answer, the attribute values will
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be used for the BFCP-controlled media streams where the answerer
acts as floor control server.
Note: An offerer compliant with [14] might not include 'floorctrl'
and 'bfcpver' attributes in offers, in which cases the default
values apply.
Once the answerer has sent the answer, the answerer:
o MUST, if the answerer is the 'active' endpoint, and if a TCP
connection associated with the 'm' line is to be established (or
re-established), initiate the establishing of the TCP connection;
and
o MUST, if the answerer is the 'active' endpoint, and if an TLS/DTLS
connection associated with the 'm' line is to be established (or
re-established), initiate the establishing of the TLS/DTLS
connection (by sending a ClientHello message).
If the answerer does not accept the 'm' line in the offer, it MUST
assign a zero port value to the corresponding 'm' line in the answer.
In addition, the answerer MUST NOT establish a TCP connection or a
TLS/DTLS connection associated with the 'm' line.
13.3. Offerer Processing of the SDP Answer
When the offerer receives an answer, which contains an 'm' line with
a non-zero port value, describing a BFCP stream, the offerer:
o MUST, if the offerer is the 'active' endpoint, and if a TCP
connection associated with the 'm' line is to be established (or
re-established), initiate the establishing of the TCP connection;
and
o MUST, if the offerer is the 'active' endpoint, and if an TLS/DTLS
connection associated with the 'm' line is to be established (or
re-established), initiate the establishing of the TLS/DTLS
connection (by sending a ClientHello message).
Note: An answerer compliant with [14] might not include
'floorctrl' and 'bfcpver' attributes in answers, in which cases
the default values apply.
If the 'm' line in the answer contains a zero port value, or if the
offerer for some other reason does not accept the answer (e.g., if
the answerer only indicates support of BFCP versions not supported by
the offerer), the offerer MUST NOT establish a TCP connection or a
TLS/DTLS connection associated with the 'm' line.
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13.4. Modifying the Session
When an offerer sends an updated offer, in order to modify a
previously established BFCP stream, it follows the procedures in
Section 13.1, with the following exceptions:
o If the BFCP stream is carried on top of TCP, and if the offerer
does not want to re-establish an existing TCP connection, the
offerer MUST associate an SDP connection attribute with an
'existing' value, with the 'm' line; and
o If the offerer wants to disable a previously established BFCP
stream, it MUST assign a zero port value to the 'm' line
associated with the BFCP connection, following the procedures in
[4].
14. Examples
For the purpose of brevity, the main portion of the session
description is omitted in the examples, which only show 'm' lines and
their attributes.
The following is an example of an offer sent by a conference server
to a client.
m=application 50000 TCP/TLS/BFCP *
a=setup:actpass
a=connection:new
a=fingerprint:sha-256 \
19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \
BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2
a=floorctrl:c-only s-only
a=confid:4321
a=userid:1234
a=floorid:1 mstrm:10
a=floorid:2 mstrm:11
a=bfcpver:1 2
m=audio 50002 RTP/AVP 0
a=label:10
m=video 50004 RTP/AVP 31
a=label:11
Note that due to RFC formatting conventions, this document splits SDP
across lines whose content would exceed 72 characters. A backslash
character marks where this line folding has taken place. This
backslash and its trailing CRLF and whitespace would not appear in
actual SDP content.
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The following is the answer returned by the client.
m=application 9 TCP/TLS/BFCP *
a=setup:active
a=connection:new
a=fingerprint:sha-256 \
6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \
DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08
a=floorctrl:c-only
a=bfcpver:1
m=audio 55000 RTP/AVP 0
m=video 55002 RTP/AVP 31
A similar example using unreliable transport and DTLS is shown below,
where the offer is sent from a client.
m=application 50000 UDP/TLS/BFCP *
a=setup:actpass
a=dtls-id:abc3dl
a=fingerprint:sha-256 \
19:E2:1C:3B:4B:9F:81:E6:B8:5C:F4:A5:A8:D8:73:04: \
BB:05:2F:70:9F:04:A9:0E:05:E9:26:33:E8:70:88:A2
a=floorctrl:c-only s-only
a=confid:4321
a=userid:1234
a=floorid:1 mstrm:10
a=floorid:2 mstrm:11
a=bfcpver:1 2
m=audio 50002 RTP/AVP 0
a=label:10
m=video 50004 RTP/AVP 31
a=label:11
The following is the answer returned by the server.
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m=application 55000 UDP/TLS/BFCP *
a=setup:active
a=dtls-id:abc3dl
a=fingerprint:sha-256 \
6B:8B:F0:65:5F:78:E2:51:3B:AC:6F:F3:3F:46:1B:35: \
DC:B8:5F:64:1A:24:C2:43:F0:A1:58:D0:A1:2C:19:08
a=floorctrl:s-only
a=confid:4321
a=userid:1234
a=floorid:1 mstrm:10
a=floorid:2 mstrm:11
a=bfcpver:2
m=audio 55002 RTP/AVP 0
m=video 55004 RTP/AVP 31
15. Security Considerations
The BFCP [17], SDP [9], and offer/answer [4] specifications discuss
security issues related to BFCP, SDP, and offer/answer, respectively.
In addition, [6] and [8] discuss security issues related to the
establishment of TCP and TLS connections using an offer/answer model.
Furthermore, when using DTLS over UDP, considerations for its use
with RTP and RTCP are presented in [18]. The requirements for the
offer/answer exchange, as listed in Section 5 of [18], MUST be
followed.
An initial integrity-protected channel is REQUIRED for BFCP to
exchange self-signed certificates between a client and the floor
control server. For session descriptions carried in SIP [3], S/MIME
[5] is the natural choice to provide such a channel.
16. IANA Considerations
[Editorial note: The changes in Section 16.1 instruct the IANA to
register the three new values TCP/DTLS/BFCP, UDP/BFCP and UDP/TLS/
BFCP for the SDP 'proto' field. The new section Section 8
registers a new SDP "bfcpver" attribute. The rest is unchanged
from [13].]
16.1. Registration of SDP 'proto' Values
The IANA has registered the following values for the SDP 'proto'
field under the Session Description Protocol (SDP) Parameters
registry:
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+---------------+------------+
| Value | Reference |
+---------------+------------+
| TCP/BFCP | [RFC XXXX] |
| TCP/DTLS/BFCP | [RFC XXXX] |
| TCP/TLS/BFCP | [RFC XXXX] |
| UDP/BFCP | [RFC XXXX] |
| UDP/TLS/BFCP | [RFC XXXX] |
+---------------+------------+
Table 3: Values for the SDP 'proto' field
16.2. Registration of the SDP 'floorctrl' Attribute
This document defines the SDP attribute,'floorctrl'. The details of
the attribute are defined in Section 5.
For issues regarding this attribute contact iesg@ietf.org.
16.3. Registration of the SDP 'confid' Attribute
This document defines the SDP attribute,'confid'. The details of the
attribute are defined in Section 6.
For issues regarding this attribute contact iesg@ietf.org.
16.4. Registration of the SDP 'userid' Attribute
This document defines the SDP attribute,'userid'. The details of the
attribute are defined in Section 6.
For issues regarding this attribute contact iesg@ietf.org.
16.5. Registration of the SDP 'floorid' Attribute
This document defines the SDP attribute,'floorid'. The details of
the attribute are defined in Section 7.
For issues regarding this attribute contact iesg@ietf.org.
16.6. Registration of the SDP 'bfcpver' Attribute
This document defines the SDP attribute,'bfcpver'. The details of
the attribute are defined in Section 8.
For issues regarding this attribute contact iesg@ietf.org.
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17. Changes from RFC 4583
Following is the list of technical changes and other fixes from [14].
Main purpose of this work was to add signaling support necessary to
support BFCP over unreliable transport, as described in [17],
resulting in the following changes:
1. Fields in the 'm' line (Section 3):
The section is re-written to remove reference to the exclusivity
of TCP as a transport for BFCP streams. The proto field values
TCP/DTLS/BFCP, UDP/BFCP and UDP/TLS/BFCP added.
2. Authentication (Section 11):
In last paragraph, made clear that a TCP connection was
described.
3. Security Considerations (Section 15):
For the DTLS over UDP case, mention existing considerations and
requirements for the offer/answer exchange in [18].
4. Registration of SDP 'proto' Values (Section 16.1):
Register the three new values TCP/DTLS/BFCP, UDP/BFCP and
UDP/TLS/BFCP in the SDP parameters registry.
5. BFCP Version Negotiation (Section 8):
A new 'bfcpver' SDP media-level attribute is added in order to
signal supported version number.
Clarification and bug fixes:
1. Errata ID: 712 (Section 4 and Section 13):
Language clarification. Don't use terms like an SDP attribute is
"used in an 'm' line", instead make clear that the attribute is a
media-level attribute.
2. Fix typo in example (Section 14):
Do not use 'm-stream' in the SDP example, use the correct 'mstrm'
as specified in Section 14. Recommend interpreting 'm-stream' if
it is received, since it is present in some implementations.
3. Assorted clarifications (Across the document):
Language clarifications as a result of reviews. Also, the
normative language where tightened where appropriate, i.e.
changed from SHOULD strength to MUST in a number of places.
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18. Acknowledgements
Joerg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and
Oscar Novo provided useful ideas for the original [14]. The authors
also acknowledge contributions to the revision of BFCP for use over
an unreliable transport from Geir Arne Sandbakken, Charles Eckel,
Alan Ford, Eoin McLeod and Mark Thompson. Useful and important final
reviews were done by Ali C. Begen, Mary Barnes and Charles Eckel.
In the final stages, Roman Shpount made a considerable effort in
adding proper ICE support and considerations.
19. References
19.1. Normative References
[1] 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>.
[2] 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>.
[3] 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>.
[4] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
DOI 10.17487/RFC3264, June 2002,
<https://www.rfc-editor.org/info/rfc3264>.
[5] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Certificate
Handling", RFC 5750, DOI 10.17487/RFC5750, January 2010,
<https://www.rfc-editor.org/info/rfc5750>.
[6] Yon, D. and G. Camarillo, "TCP-Based Media Transport in
the Session Description Protocol (SDP)", RFC 4145,
DOI 10.17487/RFC4145, September 2005,
<https://www.rfc-editor.org/info/rfc4145>.
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[7] Levin, O. and G. Camarillo, "The Session Description
Protocol (SDP) Label Attribute", RFC 4574,
DOI 10.17487/RFC4574, August 2006,
<https://www.rfc-editor.org/info/rfc4574>.
[8] Lennox, J. and C. Holmberg, "Connection-Oriented Media
Transport over the Transport Layer Security (TLS) Protocol
in the Session Description Protocol (SDP)", RFC 8122,
DOI 10.17487/RFC8122, March 2017,
<https://www.rfc-editor.org/info/rfc8122>.
[9] 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>.
[10] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[11] Lazzaro, J., "Framing Real-time Transport Protocol (RTP)
and RTP Control Protocol (RTCP) Packets over Connection-
Oriented Transport", RFC 4571, DOI 10.17487/RFC4571, July
2006, <https://www.rfc-editor.org/info/rfc4571>.
[12] Rosenberg, J., Keranen, A., Lowekamp, B., and A. Roach,
"TCP Candidates with Interactive Connectivity
Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
March 2012, <https://www.rfc-editor.org/info/rfc6544>.
[13] Camarillo, G., Ott, J., and K. Drage, "The Binary Floor
Control Protocol (BFCP)", RFC 4582, DOI 10.17487/RFC4582,
November 2006, <https://www.rfc-editor.org/info/rfc4582>.
[14] Camarillo, G., "Session Description Protocol (SDP) Format
for Binary Floor Control Protocol (BFCP) Streams",
RFC 4583, DOI 10.17487/RFC4583, November 2006,
<https://www.rfc-editor.org/info/rfc4583>.
[15] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", draft-ietf-ice-
rfc5245bis-20 (work in progress), March 2018.
[16] Petit-Huguenin, M., Nandakumar, S., and A. Keranen,
"Session Description Protocol (SDP) Offer/Answer
procedures for Interactive Connectivity Establishment
(ICE)", draft-ietf-mmusic-ice-sip-sdp-20 (work in
progress), April 2018.
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[17] Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
Eckel, "The Binary Floor Control Protocol (BFCP)", draft-
ietf-bfcpbis-rfc4582bis-16 (work in progress), November
2015.
[18] Holmberg, C. and R. Shpount, "Session Description Protocol
(SDP) Offer/Answer Considerations for Datagram Transport
Layer Security (DTLS) and Transport Layer Security (TLS)",
draft-ietf-mmusic-dtls-sdp-32 (work in progress), October
2017.
19.2. Informational References
[19] Lennox, J., Ott, J., and T. Schierl, "Source-Specific
Media Attributes in the Session Description Protocol
(SDP)", RFC 5576, DOI 10.17487/RFC5576, June 2009,
<https://www.rfc-editor.org/info/rfc5576>.
[20] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-51 (work in progress), May 2018.
[21] Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17
(work in progress), February 2018.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
FI-02420 Jorvas
Finland
Email: Gonzalo.Camarillo@ericsson.com
Tom Kristensen
Cisco
Philip Pedersens vei 1
NO-1366 Lysaker
Norway
Email: tomkrist@cisco.com, tomkri@ifi.uio.no
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Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
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