Internet DRAFT - draft-ietf-bfcpbis-rfc4583bis
draft-ietf-bfcpbis-rfc4583bis
BFCPbis Working Group G. Camarillo
Internet-Draft Ericsson
Obsoletes: 4583 (if approved) T. Kristensen
Intended status: Standards Track Cisco
Expires: June 11, 2019 C. Holmberg
Ericsson
December 8, 2018
Session Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams
draft-ietf-bfcpbis-rfc4583bis-27
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. Changes from RFC 4583 are
summarized in Section 14.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 11, 2019.
Copyright Notice
Copyright (c) 2018 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Floor Control Roles . . . . . . . . . . . . . . . . . . . . . 4
4. Fields in the 'm' Line . . . . . . . . . . . . . . . . . . . 4
5. SDP Attributes . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. SDP 'floorctrl' Attribute . . . . . . . . . . . . . . . . 5
5.2. SDP 'confid' Attribute . . . . . . . . . . . . . . . . . 7
5.3. SDP 'userid' Attribute . . . . . . . . . . . . . . . . . 8
5.4. SDP 'floorid' Attribute . . . . . . . . . . . . . . . . . 9
5.5. SDP 'bfcpver' Attribute . . . . . . . . . . . . . . . . . 10
6. Multiplexing Considerations . . . . . . . . . . . . . . . . . 11
7. BFCP Connection Management . . . . . . . . . . . . . . . . . 12
7.1. TCP Connection Management . . . . . . . . . . . . . . . . 12
8. TLS/DTLS Considerations . . . . . . . . . . . . . . . . . . . 13
9. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 13
10. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 14
10.1. Generating the Initial SDP Offer . . . . . . . . . . . . 15
10.2. Generating the SDP Answer . . . . . . . . . . . . . . . 15
10.3. Offerer Processing of the SDP Answer . . . . . . . . . . 16
10.4. Modifying the Session . . . . . . . . . . . . . . . . . 17
11. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 17
12. Security Considerations . . . . . . . . . . . . . . . . . . . 19
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
13.1. Registration of SDP 'proto' Values . . . . . . . . . . . 20
13.2. Registration of the SDP 'floorctrl' Attribute . . . . . 20
13.3. Registration of the SDP 'confid' Attribute . . . . . . . 20
13.4. Registration of the SDP 'userid' Attribute . . . . . . . 20
13.5. Registration of the SDP 'floorid' Attribute . . . . . . 21
13.6. Registration of the SDP 'bfcpver' Attribute . . . . . . 21
14. Changes from RFC 4583 . . . . . . . . . . . . . . . . . . . . 21
15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 22
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
16.1. Normative References . . . . . . . . . . . . . . . . . . 22
16.2. Informational References . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
As discussed in the BFCP (Binary Floor Control Protocol)
specification [I-D.ietf-bfcpbis-rfc4582bis], 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 an SDP
offer/answer [RFC3264] exchange. 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 '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 the Interactive Connectivity Establishment (ICE)
[RFC8445] considerations when negotiating a BFCP connection.
Section 10 defines the SDP offer/answer procedures for negotiating a
BFCP connection.
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.
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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 [RFC4566], the 'm' line format is
the following:
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".
The port field is set depending on the value of the proto field, 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 (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 value are used as described below:
'TCP/BFCP' is used for TCP transport of BFCP without TLS
encryption, and is backward compatible with RFC 4583 compliant
endpoints.
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'TCP/TLS/BFCP' is used for TCP transport of BFCP with TLS
encryption, and is backward compatible with RFC 4583 compliant
endpoints that 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 RFC 4583 compliant endpoints 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/RTCP packets using the shim defined in RFC 4571 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 RFC 4583
compliant endpoints 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 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.
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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 floor control client.
s-only: The endpoint is willing to act as 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 floor control
client and 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 client or server (equivalent to
"c-only s-only"). An implementation compliant to this specification
MUST NOT include the "c-s" floorctl 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 to this specification is only
allowed to include one role, either 'c-only' or 's-conly', 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.
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+---------+----------+
| 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 answerer. If the 'floorctrl' attribute is
not present, in order to be interoperable with such endpoints, the
offerer will act as floor control client and the answerer will act as
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.
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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 defined in [RFC5234]>
The maximum value of the attribute is determined by the
COMMON-HEADER format [I-D.ietf-bfcpbis-rfc4582bis].
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.
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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 defined in [RFC5234]>
The maximum value of the attribute is determined by the
COMMON-HEADER format [I-D.ietf-bfcpbis-rfc4582bis].
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 conveys a floor identifier, using decimal integer
representation, and optionally pointers to one or more BFCP-
controlled media streams.
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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 defined in [RFC5234]>
token = <token defined in [RFC4566]>
The maximum value of the attribute is determined by the
FLOOR-ID format [I-D.ietf-bfcpbis-rfc4582bis].
The floor identifier value is the integer representation of the Floor
ID 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 [RFC4583] 'm-stream' was erroneously used in Section 11.
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.
The Augmented BNF syntax [RFC5234] for the attributes is:
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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 defined in [RFC5234]>
The maximum value of the attribute is determined by the
COMMON-HEADER format [I-D.ietf-bfcpbis-rfc4582bis].
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" field that would be presented in the BFCP COMMON-HEADER
[I-D.ietf-bfcpbis-rfc4582bis]. 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
field in [I-D.ietf-bfcpbis-rfc4582bis]. If the attribute is not
present, endpoints MUST assume a default value in accordance with
[I-D.ietf-bfcpbis-rfc4582bis]: 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
[I-D.ietf-mmusic-sdp-bundle-negotiation] 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
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BUNDLE group [I-D.ietf-mmusic-sdp-bundle-negotiation]. Note that
BFCP-controlled media streams might be multiplexed with other media
streams.
[I-D.ietf-mmusic-sdp-mux-attributes] 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 a | M | TBD |
| | 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 straight-forward
procedures for connection management as UDP/BFCP 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 [I-D.ietf-bfcpbis-rfc4582bis] 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, that specification 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.
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When the existing TCP connection is closed and re-established
following the rules in [I-D.ietf-bfcpbis-rfc4582bis], 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 [I-D.ietf-mmusic-dtls-sdp] 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 backwards compatibility.
9. ICE Considerations
Generic SDP offer/answer procedures for Interactive Connectivity
Establishment (ICE) are defined in [I-D.ietf-mmusic-ice-sip-sdp].
When BFCP is used with UDP based ICE candidates [RFC8445] then the
procedures for UDP/TLS/BFCP are used.
When BFCP is used with TCP based ICE candidates [RFC6544] then the
procedures for TCP/DTLS/BFCP are used.
Based on the procedures defined in [I-D.ietf-mmusic-dtls-sdp],
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 if BFCP media
is shifted between candidate pairs (including switching between UDP
to TCP candidate pairs) prior to nomination. If new candidates are
added, they will also be part of the same DTLS association.
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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 outside 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 [I-D.ietf-mmusic-dtls-sdp]. 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 SIP dialog when the Session Initiation
Protocol (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 anwerer 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.
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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:
o MUST include an SDP 'confid' attribute (Section 5.2) in the 'm'
section; and
o MUST include an SDP 'userid' attribute (Section 5.3) in the 'm'
section; and
o MUST include an SDP 'floorid' attribute (Section 5.4) in the 'm'
section; and
o 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 a '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
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, it:
o MUST insert a corresponding 'm' section in the answer, with an
identical 'm' line proto value [RFC3264]; and
o 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
o MUST, if the offer contained an SDP 'floorctrl' attribute, include
a 'floorctrl' attribute in the 'm' section.
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In addition, if the answerer includes an SDP 'floorctrl' attribute
with an 's-only' attribute value in the answer, the answerer:
o MUST include an SDP 'confid' attribute in the 'm' section; and
o MUST include an SDP 'userid' attribute in the 'm' section; and
o MUST include an SDP 'floorid' attribute in the 'm' section; and
o 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 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' section 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' section 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' 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 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' section 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' section is to be established
(or re-established), initiate the establishing of the TLS/DTLS
connection (by sending a ClientHello message).
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Note: An answerer compliant with [RFC4583] 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' 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:
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 include an SDP 'connection' attribute with a value of
"existing", in the 'm' section; 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
[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.
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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.
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.
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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 [I-D.ietf-bfcpbis-rfc4582bis], SDP [RFC4566], and offer/
answer [RFC3264] specifications 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 [I-D.ietf-mmusic-dtls-sdp] 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.
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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
[Editorial note: The changes in Section 13.1 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 5.5
registers a new SDP "bfcpver" attribute. The rest is unchanged
from [RFC4582].]
13.1. Registration of SDP 'proto' Values
The IANA is requested to register the following values for the SDP
'proto' field under the Session Description Protocol (SDP) Parameters
registry:
+---------------+------------+
| 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
13.2. Registration of the SDP 'floorctrl' Attribute
This document defines the SDP attribute,'floorctrl'. The details of
the attribute are defined in Section 5.1.
13.3. Registration of the SDP 'confid' Attribute
This document defines the SDP attribute,'confid'. The details of the
attribute are defined in Section 5.2.
13.4. Registration of the SDP 'userid' Attribute
This document defines the SDP attribute,'userid'. The details of the
attribute are defined in Section 5.3.
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13.5. Registration of the SDP 'floorid' Attribute
This document defines the SDP attribute,'floorid'. The details of
the attribute are defined in Section 5.4.
13.6. Registration of the SDP 'bfcpver' Attribute
This document defines the SDP attribute,'bfcpver'. The details of
the attribute are defined in Section 5.5.
14. Changes from RFC 4583
Following is the list of technical changes and other fixes from
[RFC4583].
Main purpose of this work was to add signaling support necessary to
support BFCP over unreliable transport, as described in
[I-D.ietf-bfcpbis-rfc4582bis], resulting in the following changes:
1. Fields in the 'm' line (Section 4):
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. Security Considerations (Section 12):
For the DTLS over UDP case, mention existing considerations and
requirements for the offer/answer exchange in
[I-D.ietf-mmusic-dtls-sdp].
3. Registration of SDP 'proto' Values (Section 13.1):
Register the three new values TCP/DTLS/BFCP, UDP/BFCP and
UDP/TLS/BFCP in the SDP parameters registry.
4. BFCP Version Negotiation (Section 5.5):
A new 'bfcpver' SDP media-level attribute is added in order to
signal supported version number.
In addition to the changes associated with support of BFCP over
unreliable transport, the possibility for an endpoint to act as both
floor control client and 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.
Clarification and bug fixes:
1. Errata ID: 712 (Section 3 and Section 10):
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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 11):
Do not use 'm-stream' in the SDP example, use the correct 'mstrm'
as specified in Section 11. 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.
15. Acknowledgements
Joerg 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.
16. References
16.1. Normative References
[I-D.ietf-bfcpbis-rfc4582bis]
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.
[I-D.ietf-mmusic-dtls-sdp]
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.
[I-D.ietf-mmusic-ice-sip-sdp]
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-24 (work in
progress), November 2018.
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[I-D.ietf-mmusic-sdp-mux-attributes]
Nandakumar, S., "A Framework for SDP Attributes when
Multiplexing", draft-ietf-mmusic-sdp-mux-attributes-17
(work in progress), February 2018.
[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>.
[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>.
[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>.
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[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., 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>.
[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>.
16.2. Informational References
[I-D.ietf-mmusic-sdp-bundle-negotiation]
Holmberg, C., Alvestrand, H., and C. Jennings,
"Negotiating Media Multiplexing Using the Session
Description Protocol (SDP)", draft-ietf-mmusic-sdp-bundle-
negotiation-53 (work in progress), September 2018.
[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>.
Authors' Addresses
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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
Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
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