Session Description Protocol (SDP) Format for Binary Floor Control Protocol (BFCP) Streams
RFC 8856
| Document | Type |
RFC - Proposed Standard
(January 2021; No errata)
Obsoletes RFC 4583
|
||||
|---|---|---|---|---|---|---|
| Authors | Gonzalo Camarillo , Tom Kristensen , Christer Holmberg | |||||
| Last updated | 2021-01-19 | |||||
| Stream | Internet Engineering Task Force (IETF) | |||||
| Formats | plain text html xml pdf htmlized bibtex | |||||
| Reviews | ||||||
| Additional Resources |
|
|||||
| Stream | WG state | Submitted to IESG for Publication | ||||
| Document shepherd | Mary Barnes | |||||
| Shepherd write-up | Show (last changed 2018-08-29) | |||||
| IESG | IESG state | RFC 8856 (Proposed Standard) | ||||
| Action Holders |
(None)
|
|||||
| Consensus Boilerplate | Yes | |||||
| Telechat date | ||||||
| Responsible AD | Adam Roach | |||||
| Send notices to | (None) | |||||
| IANA | IANA review state | Version Changed - Review Needed | ||||
| IANA action state | RFC-Ed-Ack | |||||
Internet Engineering Task Force (IETF) G. Camarillo
Request for Comments: 8856 Ericsson
Obsoletes: 4583 T. Kristensen
Category: Standards Track Jotron
ISSN: 2070-1721 C. Holmberg
Ericsson
January 2021
Session Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams
Abstract
This document defines the Session Description Protocol (SDP) offer/
answer procedures for negotiating and establishing Binary Floor
Control Protocol (BFCP) streams.
This document obsoletes RFC 4583.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8856.
Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction
2. Conventions
3. Floor Control Roles
4. Fields in the "m=" Line
5. SDP Attributes
5.1. SDP 'floorctrl' Attribute
5.2. SDP 'confid' Attribute
5.3. SDP 'userid' Attribute
5.4. SDP 'floorid' Attribute
5.5. SDP 'bfcpver' Attribute
6. Multiplexing Considerations
7. BFCP Connection Management
7.1. TCP Connection Management
8. TLS/DTLS Considerations
9. ICE Considerations
10. SDP Offer/Answer Procedures
10.1. Generating the Initial SDP Offer
10.2. Generating the SDP Answer
10.3. Offerer Processing of the SDP Answer
10.4. Modifying the Session
11. Examples
12. Security Considerations
13. IANA Considerations
13.1. Registration of SDP 'proto' Values
13.2. Registration of the SDP 'floorctrl' Attribute
13.3. Registration of the SDP 'confid' Attribute
13.4. Registration of the SDP 'userid' Attribute
13.5. Registration of the SDP 'floorid' Attribute
13.6. Registration of the SDP 'bfcpver' Attribute
14. Changes from RFC 4583
15. References
15.1. Normative References
15.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
As discussed in the BFCP (Binary Floor Control Protocol)
specification [RFC8855], a given BFCP client needs a set of data in
order to establish a BFCP connection to a floor control server. This
data includes the transport address of the server, the conference
identifier, and the user identifier.
One way for clients to obtain this information is to use a Session
Description Protocol (SDP) offer/answer exchange [RFC3264]. This
document specifies how to encode this information in the SDP session
descriptions that are part of such an offer/answer exchange.
User agents typically use the offer/answer model to establish a
number of media streams of different types. Following this model, a
BFCP connection is described as any other media stream by using an
SDP "m=" line, possibly followed by a number of SDP lines that also
apply to the BFCP connection.
Section 4 defines how the field values in an "m=" line representing a
BFCP connection are set.
Section 5 defines SDP attributes that are used when negotiating a
BFCP connection.
Section 6 defines multiplexing considerations for a BFCP connection.
Section 7 defines procedures for managing a BFCP connection.
Section 8 defines TLS and DTLS considerations when negotiating a BFCP
connection.
Section 9 defines considerations regarding Interactive Connectivity
Establishment (ICE) [RFC8445] when negotiating a BFCP connection.
Section 10 defines the SDP offer/answer procedures for negotiating a
BFCP connection.
This document obsoletes RFC 4583 [RFC4583]. Section 14 summarizes
the changes from RFC 4583.
2. Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Floor Control Roles
When two endpoints establish a BFCP stream, they need to determine
which of them acts as a floor control client and which acts as a
floor control server.
Once the roles have been determined, the roles will apply to all
BFCP-controlled streams associated with the BFCP stream.
4. Fields in the "m=" Line
According to the SDP specification [RFC8866], the "m=" line format is
as follows:
m=<media> <port> <proto> <fmt> ...
This section describes how to generate an "m=" line of an SDP Media
Description ("m=" section) describing a BFCP stream.
The media field MUST have a value of "application".
Depending on the value of the proto field, the port field is set as
explained below. A port field value of zero has the standard SDP
meaning (i.e., rejection of the media stream), regardless of the
proto field.
* When TCP is used as the transport, the port field is set following
the rules in [RFC4145]. Depending on the value of the 'setup'
attribute (defined in [RFC4145] and discussed in Section 7.1), the
port field contains the port to which the remote endpoint will
direct BFCP messages, or in the case where the endpoint will
initiate the connection towards the remote endpoint, should be set
to a value of 9.
* When UDP is used as the transport, the port field contains the
port to which the remote endpoint will direct BFCP messages,
regardless of the value of the 'setup' attribute.
This document defines five values for the proto field: 'TCP/BFCP',
'TCP/DTLS/BFCP', 'TCP/TLS/BFCP', 'UDP/BFCP', and 'UDP/TLS/BFCP'.
The proto values are used as described below:
* 'TCP/BFCP' is used for TCP transport of BFCP without TLS
encryption and is backward compatible with endpoints that are
compliant with RFC 4583.
* 'TCP/TLS/BFCP' is used for TCP transport of BFCP with TLS
encryption and is backward compatible with endpoints that are
compliant with RFC 4583 and support TLS.
* 'UDP/BFCP' is used for UDP transport of BFCP without DTLS
encryption [RFC6347].
* 'UDP/TLS/BFCP' is used for UDP transport of BFCP with DTLS
encryption. This is one of the options when ICE is used
(Section 9). It can also be used without ICE when backward
compatibility with endpoints compliant with RFC 4583 is not
required.
* 'TCP/DTLS/BFCP' is used for TCP transport of BFCP with DTLS
encryption, running on top of TCP using the framing method defined
in [RFC4571], with DTLS packets being sent and received instead of
RTP / RTP Control Protocol (RTCP) packets, such that the LENGTH
field defined in RFC 4571 precedes each DTLS message. This is one
of the options when ICE is used (Section 9). It can also be used
without ICE when backward compatibility with endpoints compliant
with RFC 4583 is not required.
The fmt (format) list is not applicable to BFCP. The fmt list of
"m=" lines in the case of any proto field value related to BFCP MUST
contain a single "*" character. If the fmt list contains any other
value, it MUST be ignored.
The following is an example of an "m=" line for a BFCP connection:
m=application 50000 TCP/TLS/BFCP *
5. SDP Attributes
5.1. SDP 'floorctrl' Attribute
This section defines the SDP 'floorctrl' media-level attribute. The
attribute is used to determine the floor control roles (client and
server) for the endpoints associated with the BFCP stream.
Attribute Name: floorctrl
Attribute Value: floor-control
Usage Level: media
Charset Dependent: No
Mux Category: TBD
The Augmented BNF syntax [RFC5234] for the attribute is:
floor-control = role *(SP role)
role = "c-only" / "s-only" / "c-s"
An endpoint includes the attribute to indicate the role(s) it would
be willing to perform for the BFCP-controlled media streams:
c-only: The endpoint is willing to act as a floor control client.
s-only: The endpoint is willing to act as a floor control server
only.
When inserted in an offer, the offerer MAY indicate multiple
attribute values ("c-only" and "s-only"). When inserted in an
answer, the answerer MUST indicate only one attribute value: "c-only"
or "s-only". The answerer indicates the role taken by the answerer.
The offerer will then take the opposite role.
In [RFC4583], there was a third attribute specified, "c-s", which
meant that an endpoint was willing to act as both a floor control
client and a floor control server at the same time for the BFCP
stream, taking different roles for different BFCP-controlled media
streams. The feature was underspecified and implemented in different
ways; in particular, many implementations interpreted "c-s" to mean
that the endpoint is willing to act as either a client or a server
(equivalent to "c-only s-only"). An implementation compliant with
this specification MUST NOT include the "c-s" 'floorctrl' attribute
value in an offer or in an answer but MUST accept the attribute value
in an offer and process it as equivalent to "c-only s-only" (or
"s-only c-only"). Also, as an implementation compliant with this
specification is only allowed to include one role -- either "c-only"
or "s-only" -- in an answer, each endpoint will only take one role,
and as a result the endpoint will take the same role for each BFCP-
controlled media stream associated with the BFCP stream.
Table 1 shows the roles that the answerer is allowed to take, based
on what roles the offerer has indicated that it is willing to take.
+=========+==========+
| Offerer | Answerer |
+=========+==========+
| c-only | s-only |
+---------+----------+
| s-only | c-only |
+---------+----------+
| c-s | c-only |
+---------+----------+
| c-s | s-only |
+---------+----------+
Table 1: Roles
Endpoints compliant with [RFC4583] might not include the 'floorctrl'
attribute in offers and answers. If the 'floorctrl' attribute is not
present, in order to be interoperable with such endpoints, the
offerer will act as a floor control client and the answerer will act
as a floor control server.
The SDP Offer/Answer procedures for the 'floorctrl' attribute are
defined in Section 10.
The following is an example of a 'floorctrl' attribute in an offer:
a=floorctrl:c-only s-only
5.2. SDP 'confid' Attribute
This section defines the SDP 'confid' media-level attribute. The
attribute is used by a floor control server to convey the conference
ID value to the floor control client, using decimal integer
representation.
Attribute Name: confid
Attribute Value: conference-id
Usage Level: media
Charset Dependent: No
Mux Category: TBD
The Augmented BNF syntax [RFC5234] for the attribute is:
conference-id = 1*DIGIT
DIGIT = <DIGIT as defined in [RFC5234]>
The maximum value of the attribute is determined by the COMMON-HEADER
format [RFC8855].
The SDP Offer/Answer procedures for the 'confid' attribute are
defined in Section 10.
5.3. SDP 'userid' Attribute
This section defines the SDP 'userid' media-level attribute. The
attribute is used by a floor control server to convey the user ID
value to the floor control client, using decimal integer
representation.
Attribute Name: userid
Attribute Value: user-id
Usage Level: media
Charset Dependent: No
Mux Category: TBD
The Augmented BNF syntax [RFC5234] for the attribute is:
user-id = 1*DIGIT
DIGIT = <DIGIT as defined in [RFC5234]>
The maximum value of the attribute is determined by the COMMON-HEADER
format [RFC8855].
The SDP Offer/Answer procedures for the 'userid' attribute are
defined in Section 10.
5.4. SDP 'floorid' Attribute
This section defines the SDP 'floorid' media-level attribute. The
attribute is used to convey a floor identifier, using decimal integer
representation, and, optionally, pointers to one or more BFCP-
controlled media streams.
Attribute Name: floorid
Attribute Value: floor-id
Usage Level: media
Charset Dependent: No
Mux Category: TBD
The Augmented BNF syntax [RFC5234] for the attribute is:
floor-id = 1*DIGIT SP "mstrm:" token *(SP token)
DIGIT = <DIGIT as defined in [RFC5234]>
token = <token as defined in [RFC8866]>
The maximum value of the attribute is determined by the FLOOR-ID
format [RFC8855].
The floor identifier value is the integer representation of the
Floor ID field value [RFC8855] to be used in BFCP. Each media stream
pointer value is associated with an SDP 'label' attribute [RFC4574]
of a media stream.
The SDP Offer/Answer procedures for the 'floorid' attribute are
defined in Section 10.
| Note: In the first SDP example in Section 9 of [RFC4583],
| 'm-stream' was erroneously listed. Although the example was
| non-normative, it is implemented by some vendors and occurs in
| cases where the endpoint is willing to act as a server.
| Therefore, it is RECOMMENDED to support parsing and
| interpreting 'm-stream' the same way as 'mstrm' when receiving.
5.5. SDP 'bfcpver' Attribute
This section defines the SDP 'bfcpver' media-level attribute. The
attribute is used to negotiate the BFCP version, using decimal
integer representation.
Attribute Name: bfcpver
Attribute Value: bfcp-version
Usage Level: media
Charset Dependent: No
Mux Category: TBD
The Augmented BNF syntax [RFC5234] for the attribute is:
bfcp-version = version *(SP version)
version = 1*DIGIT
DIGIT = <DIGIT as defined in [RFC5234]>
The maximum value of the attribute is determined by the COMMON-HEADER
format [RFC8855].
An endpoint uses the 'bfcpver' attribute to convey the version(s) of
BFCP supported by the endpoint, using integer values. For a given
version, the attribute value representing the version MUST match the
version ("Ver") field that would be presented in the BFCP
COMMON-HEADER [RFC8855]. The BFCP version that will eventually be
used will be conveyed with a BFCP-level Hello/HelloAck.
Endpoints compliant with [RFC4583] might not always include the
'bfcpver' attribute in offers and answers. The attribute value, if
present, MUST be in accordance with the definition of the version
("Ver") field in [RFC8855]. If the attribute is not present,
endpoints MUST assume a default value in accordance with [RFC8855]:
when used over a reliable transport, the default attribute value is
"1", and when used over an unreliable transport, the default
attribute value is "2". The value is inferred from the transport
specified in the "m=" line (Section 4) of the "m=" section associated
with the stream.
The SDP Offer/Answer procedures for the 'bfcpver' attribute are
defined in Section 10.
6. Multiplexing Considerations
[RFC8843] defines how multiplexing of multiple media streams can be
negotiated. This specification does not define how BFCP streams can
be multiplexed with other media streams. Therefore, a BFCP stream
MUST NOT be associated with a BUNDLE group [RFC8843]. Note that
BFCP-controlled media streams might be multiplexed with other media
streams.
[RFC8859] defines the mux categories for the SDP attributes defined
in this specification, except for the 'bfcpver' attribute. Table 2
defines the mux category for the 'bfcpver' attribute:
+=========+===========================+=======+==============+
| Name | Notes | Level | Mux Category |
+=========+===========================+=======+==============+
| bfcpver | Needs further analysis in | M | TBD |
| | a separate specification | | |
+---------+---------------------------+-------+--------------+
Table 2: Multiplexing Attribute Analysis
7. BFCP Connection Management
BFCP streams can use TCP or UDP as the underlying transport.
Endpoints exchanging BFCP messages over UDP send the BFCP messages
towards the peer using the connection address and port provided in
the SDP "c=" and "m=" lines. TCP connection management is more
complicated and is described in the following section.
| Note: When using Interactive Connectivity Establishment (ICE)
| [RFC8445], TCP/DTLS/BFCP, or UDP/TLS/BFCP, the straightforward
| procedures for connection management via UDP/BFCP, as described
| above, apply. TCP/TLS/BFCP follows the same procedures as
| TCP/BFCP and is described below.
7.1. TCP Connection Management
The management of the TCP connection used to transport BFCP messages
is performed using the SDP 'setup' and 'connection' attributes
[RFC4145]. The 'setup' attribute indicates which of the endpoints
initiates the TCP connection. The 'connection' attribute handles TCP
connection re-establishment.
The BFCP specification [RFC8855] describes a number of situations
when the TCP connection between a floor control client and the floor
control server needs to be re-established. However, [RFC8855] does
not describe the re-establishment process, because this process
depends on how the connection was established in the first place.
Endpoints using the offer/answer mechanism follow the following
rules.
When the existing TCP connection is closed and re-established
following the rules in [RFC8855], the floor control client MUST send
an offer towards the floor control server in order to re-establish
the connection. If a TCP connection cannot deliver a BFCP message
and times out, the endpoint that attempted to send the message (i.e.,
the one that detected the TCP timeout) MUST send an offer in order to
re-establish the TCP connection.
Endpoints that use the offer/answer mechanism to negotiate TCP
connections MUST support the 'setup' and 'connection' attributes.
8. TLS/DTLS Considerations
When DTLS is used with UDP, the generic procedures defined in
Section 5 of [RFC8842] MUST be followed.
When TLS is used with TCP, once the underlying connection is
established, the answerer always acts as the TLS server. If the TCP
connection is lost, the active endpoint [RFC4583] is responsible for
re-establishing the TCP connection. Unless a new TLS connection is
negotiated, subsequent SDP offers and answers will not impact the
previously negotiated TLS roles.
| Note: For TLS, it was decided to keep the original procedures
| in [RFC4583] to determine which endpoint acts as the TLS
| server, in order to retain backward compatibility.
9. ICE Considerations
Generic SDP offer/answer procedures for ICE are defined in [RFC8839].
When BFCP is used with UDP-based ICE candidates [RFC8445], the
procedures for UDP/TLS/BFCP are used.
When BFCP is used with TCP-based ICE candidates [RFC6544], the
procedures for TCP/DTLS/BFCP are used.
Based on the procedures defined in [RFC8842], endpoints treat all ICE
candidate pairs associated with a BFCP stream on top of a DTLS
association as part of the same DTLS association. Thus, there will
only be one BFCP handshake and one DTLS handshake even if there are
multiple valid candidate pairs, and even if BFCP media is shifted
between candidate pairs (including switching between UDP candidate
pairs and TCP candidate pairs) prior to nomination. If new
candidates are added, they will also be part of the same DTLS
association.
In order to maximize the likelihood of interoperability between the
endpoints, all ICE-enabled BFCP-over-DTLS endpoints SHOULD implement
support for UDP/TLS/BFCP.
When an SDP offer or answer conveys multiple ICE candidates for a
BFCP stream, UDP-based candidates SHOULD be included and the default
candidate SHOULD be chosen from one of those UDP candidates. If UDP
transport is used for the default candidate, then the "m=" line proto
value MUST be 'UDP/TLS/BFCP'. If TCP transport is used for the
default candidate, the "m=" line proto value MUST be 'TCP/DTLS/BFCP'.
| Note: Usage of ICE with protocols other than UDP/TLS/BFCP and
| TCP/DTLS/BFCP is out of scope for this specification.
10. SDP Offer/Answer Procedures
This section defines the SDP offer/answer [RFC3264] procedures for
negotiating and establishing a BFCP stream. Generic procedures for
DTLS are defined in [RFC8842]. Generic procedures for TLS are
defined in [RFC8122].
This section only defines the BFCP-specific procedures. Unless
explicitly stated otherwise, the procedures apply to an "m=" section
describing a BFCP stream. If an offer or answer contains multiple
"m=" sections 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 Session Initiation Protocol (SIP)
dialog when SIP [RFC3261] 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 [RFC8122].
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 [RFC4145].
If the "m=" line proto value is 'TCP/BFCP', 'TCP/TLS/BFCP', or
'TCP/DTLS/BFCP', the offerer and answerer use the SDP 'connection'
attribute according to the procedures in [RFC4145].
| Note: The use of source-specific SDP parameters [RFC5576] is
| not defined for BFCP streams.
10.1. Generating the Initial SDP Offer
When the offerer creates an initial offer, the offerer MUST include
an SDP 'floorctrl' attribute (Section 5.1) and an SDP 'bfcpver'
attribute (Section 5.5) in the "m=" section.
In addition, if the offerer includes an SDP 'floorctrl' attribute
with "s-only" or "c-s" attribute values in the offer, the offerer
* MUST include an SDP 'confid' attribute (Section 5.2) in the "m="
section,
* MUST include an SDP 'userid' attribute (Section 5.3) in the "m="
section,
* MUST include an SDP 'floorid' attribute (Section 5.4) in the "m="
section, and
* MUST include an SDP 'label' attribute [RFC4574] with the "m="
section 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 an "s-only"
| attribute value in the offer, the attribute values above will
| only be used if it is determined (Section 5.1) that the offerer
| will act as a floor control server.
10.2. Generating the SDP Answer
When the answerer receives an offer that contains an "m=" section
describing a BFCP stream, the answerer MUST check whether it supports
one or more of the BFCP versions supported by the offerer
(Section 5.5). If the answerer does not support any of the BFCP
versions, it MUST NOT accept the "m=" section. Otherwise, if the
answerer accepts the "m=" section, the answerer
* MUST insert a corresponding "m=" section in the answer, with an
identical "m=" line proto value [RFC8866],
* MUST include a 'bfcpver' attribute in the "m=" section; the
versions indicated by the answer MUST be the same or a subset of
the versions indicated by the offerer in the corresponding offer,
and
* MUST, if the offer contained an SDP 'floorctrl' attribute, include
a 'floorctrl' attribute in the "m=" section.
In addition, if the answerer includes an SDP 'floorctrl' attribute
with an "s-only" attribute value in the answer, the answerer
* MUST include an SDP 'confid' attribute in the "m=" section,
* MUST include an SDP 'userid' attribute in the "m=" section,
* MUST include an SDP 'floorid' attribute in the "m=" section, and
* MUST include an SDP 'label' attribute in the "m=" section of each
BFCP-controlled media stream.
| Note: An offerer compliant with [RFC4583] might not include
| 'floorctrl' and 'bfcpver' attributes in offers, in which case
| the default values apply.
Once the answerer has sent the answer, the answerer
* MUST, if the answerer is the active endpoint and if a TCP
connection associated with the "m=" section is to be established
(or re-established), initiate the establishment of the TCP
connection, and
* MUST, if the answerer is the active endpoint and if a TLS/DTLS
connection associated with the "m=" section is to be established
(or re-established), initiate the establishment of the TLS/DTLS
connection (by sending a ClientHello message).
If the answerer does not accept the "m=" section in the offer, it
MUST assign a zero port value to the "m=" line of the corresponding
"m=" section in the answer. In addition, the answerer MUST NOT
establish a TCP connection or a TLS/DTLS connection associated with
the "m=" section.
10.3. Offerer Processing of the SDP Answer
When the offerer receives an answer that contains an "m=" section
describing a BFCP stream and with a non-zero port value in the "m="
line, the offerer
* MUST, if the offerer is the active endpoint and if a TCP
connection associated with the "m=" section is to be established
(or re-established), initiate the establishment of the TCP
connection, and
* MUST, if the offerer is the active endpoint and if a TLS/DTLS
connection associated with the "m=" section is to be established
(or re-established), initiate the establishment of the TLS/DTLS
connection (by sending a ClientHello message).
| Note: An answerer compliant with [RFC4583] might not include
| 'floorctrl' and 'bfcpver' attributes in answers, in which case
| 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=" section.
10.4. 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 10.1, with the following exceptions:
* 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 include in the "m=" section an SDP 'connection'
attribute with a value of "existing", and
* 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
[RFC3264].
11. Examples
For the purpose of brevity, the main portion of the session
description is omitted in the examples, which only show "m=" sections
and their "m=" lines and 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 the
SDP entries across lines whose content would exceed the maximum line
length. 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.
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 an 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.
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
12. Security Considerations
The BFCP specification [RFC8855], SDP specification [RFC8866], and
offer/answer specification [RFC3264] discuss security issues related
to BFCP, SDP, and offer/answer, respectively. In addition, [RFC4145]
and [RFC8122] discuss security issues related to the establishment of
TCP and TLS connections using an offer/answer model. Furthermore,
when using DTLS over UDP, the generic offer/answer considerations
defined in [RFC8842] MUST be followed.
The usage of certain proto values in the SDP offer/answer negotiation
will result in a BFCP stream that is not protected by TLS or DTLS.
Operators will need to provide integrity protection and
confidentiality protection of the BFCP stream using other means.
The generic security considerations associated with SDP attributes
are defined in [RFC3264]. While the attributes defined in this
specification do not reveal information about the content of
individual BFCP-controlled media streams, they do reveal which media
streams will be BFCP controlled.
13. IANA Considerations
This document registers three new values in the "proto" subregistry
within the "Session Description Protocol (SDP) Parameters" registry:
'TCP/DTLS/BFCP', 'UDP/BFCP', and 'UDP/TLS/BFCP' (see Section 13.1).
This document also registers a new SDP attribute in the 'attribute-
name (formerly "att-field")' subregistry within the "Session
Description Protocol (SDP) Parameters" registry: 'bfcpver' (see
Section 5.5).
The remaining values are unchanged from [RFC4582], except that the
references have been updated to refer to this document.
13.1. Registration of SDP 'proto' Values
The IANA has registered three new values in the SDP 'proto' field
under the "Session Description Protocol (SDP) Parameters" registry.
+===============+===========+
| Value | Reference |
+===============+===========+
| TCP/BFCP | RFC 8856 |
+---------------+-----------+
| TCP/DTLS/BFCP | RFC 8856 |
+---------------+-----------+
| TCP/TLS/BFCP | RFC 8856 |
+---------------+-----------+
| UDP/BFCP | RFC 8856 |
+---------------+-----------+
| UDP/TLS/BFCP | RFC 8856 |
+---------------+-----------+
Table 3: Values for the
SDP 'proto' Field
13.2. Registration of the SDP 'floorctrl' Attribute
This document defines the SDP 'floorctrl' attribute. Details
regarding this attribute are provided in Section 5.1.
13.3. Registration of the SDP 'confid' Attribute
This document defines the SDP 'confid' attribute. Details regarding
this attribute are provided in Section 5.2.
13.4. Registration of the SDP 'userid' Attribute
This document defines the SDP 'userid' attribute. Details regarding
this attribute are provided in Section 5.3.
13.5. Registration of the SDP 'floorid' Attribute
This document defines the SDP 'floorid' attribute. Details regarding
this attribute are provided in Section 5.4.
13.6. Registration of the SDP 'bfcpver' Attribute
This document defines the SDP 'bfcpver' attribute. Details regarding
this attribute are provided in Section 5.5.
14. Changes from RFC 4583
The technical changes and other fixes from [RFC4583] are listed
below.
The main purpose of this work was to add signaling support necessary
to support BFCP over an unreliable transport, as described in
[RFC8855], resulting in the following changes:
* Fields in the "m=" Line (Section 4):
This section has been rewritten 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' have
been added.
* Security Considerations (Section 12):
For the DTLS-over-UDP case, we direct the reader to existing
considerations and requirements for the offer/answer exchange as
provided in [RFC8842].
* Registration of SDP 'proto' Values (Section 13.1):
This document registers the three new values 'TCP/DTLS/BFCP',
'UDP/BFCP', and 'UDP/TLS/BFCP' in the "Session Description
Protocol (SDP) Parameters" registry.
* SDP 'bfcpver' Attribute (Section 5.5):
A new 'bfcpver' SDP media-level attribute has been added, in order
to signal the supported version number.
In addition to the changes associated with support of BFCP over an
unreliable transport, the possibility that an endpoint can act as
both a floor control client and a floor control server at the same
time has been removed. An endpoint will now take the same role for
all BFCP-controlled streams associated with the BFCP stream.
Clarifications and bug fixes:
* Erratum ID 712 (Sections 3 and 10 of [RFC4583]; see [Err712] for
details):
Do not use language such as 'used in an "m=" line' when discussing
an SDP attribute; instead, make clear that the attribute is a
media-level attribute.
* Spelling corrected in the first SDP example in Section 9 of
[RFC4583]:
Do not use 'm-stream' as listed in the first SDP example in
[RFC4583]; instead, use the correct 'mstrm' as specified in
Section 11 of this document. However, we recommend continuing to
interpret 'm-stream', if received, because it is still present in
some implementations.
* Assorted clarifications (throughout the document):
Language clarifications were made as a result of reviews. Also,
normative language was "tightened" where appropriate, i.e.,
changed from "SHOULD" strength to "MUST" in a number of places.
15. References
15.1. 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>.
[RFC3264] 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>.
[RFC4145] 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>.
[RFC4571] 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>.
[RFC4574] 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>.
[RFC4582] 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>.
[RFC4583] 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>.
[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>.
[RFC6347] 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>.
[RFC6544] Rosenberg, J., Keranen, A., Lowekamp, B. B., and A. B.
Roach, "TCP Candidates with Interactive Connectivity
Establishment (ICE)", RFC 6544, DOI 10.17487/RFC6544,
March 2012, <https://www.rfc-editor.org/info/rfc6544>.
[RFC8122] 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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8445] Keranen, A., Holmberg, C., and J. Rosenberg, "Interactive
Connectivity Establishment (ICE): A Protocol for Network
Address Translator (NAT) Traversal", RFC 8445,
DOI 10.17487/RFC8445, July 2018,
<https://www.rfc-editor.org/info/rfc8445>.
[RFC8839] Petit-Huguenin, M., Nandakumar, S., Holmberg, C., Keränen,
A., and R. Shpount, "Session Description Protocol (SDP)
Offer/Answer Procedures for Interactive Connectivity
Establishment (ICE)", RFC 8839, DOI 10.17487/RFC8839,
January 2021, <https://www.rfc-editor.org/info/rfc8839>.
[RFC8842] Holmberg, C. and R. Shpount, "Session Description Protocol
(SDP) Offer/Answer Considerations for Datagram Transport
Layer Security (DTLS) and Transport Layer Security (TLS)",
RFC 8842, DOI 10.17487/RFC8842, January 2021,
<https://www.rfc-editor.org/info/rfc8842>.
[RFC8855] Camarillo, G., Drage, K., Kristensen, T., Ott, J., and C.
Eckel, "The Binary Floor Control Protocol (BFCP)",
RFC 8855, DOI 10.17487/RFC8855, January 2021,
<https://www.rfc-editor.org/info/rfc8855>.
[RFC8859] Nandakumar, S., "A Framework for Session Description
Protocol (SDP) Attributes When Multiplexing", RFC 8859,
DOI 10.17487/RFC8859, January 2021,
<https://www.rfc-editor.org/info/rfc8859>.
[RFC8866] Begen, A., Kyzivat, P., Perkins, C., and M. Handley, "SDP:
Session Description Protocol", RFC 8866,
DOI 10.17487/RFC8866, January 2021,
<https://www.rfc-editor.org/info/rfc8866>.
15.2. Informative References
[Err712] RFC Errata, Erratum ID 712, RFC 4583,
<https://www.rfc-editor.org/errata/eid712>.
[RFC5576] 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>.
[RFC8843] Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", RFC 8843,
DOI 10.17487/RFC8843, January 2021,
<https://www.rfc-editor.org/info/rfc8843>.
Acknowledgements
Jörg Ott, Keith Drage, Alan Johnston, Eric Rescorla, Roni Even, and
Oscar Novo provided useful ideas for the original [RFC4583]. 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.
Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
FI-02420 Jorvas
Finland
Email: Gonzalo.Camarillo@ericsson.com
Tom Kristensen
Jotron AS
Ringdalskogen 8
3270 Larvik
Norway
Email: tom.kristensen@jotron.com, tomkri@ifi.uio.no
Christer Holmberg
Ericsson
Hirsalantie 11
FI-02420 Jorvas
Finland
Email: christer.holmberg@ericsson.com