BFCPbis Working Group G. Camarillo
Internet-Draft Ericsson
Obsoletes: 4583 (if approved) T. Kristensen
Intended status: Standards Track Cisco
Expires: November 22, 2018 C. Holmberg
Ericsson
May 21, 2018
Session Description Protocol (SDP) Format for Binary Floor Control
Protocol (BFCP) Streams
draft-ietf-bfcpbis-rfc4583bis-23
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 15.
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
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This Internet-Draft will expire on November 22, 2018.
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
(https://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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Fields in the 'm' Line . . . . . . . . . . . . . . . . . . . 3
4. Floor Control Roles . . . . . . . . . . . . . . . . . . . . . 4
5. SDP 'floorctrl' Attribute . . . . . . . . . . . . . . . . . . 5
6. SDP 'confid' and 'userid' Attributes . . . . . . . . . . . . 6
7. SDP 'floorid' Attribute . . . . . . . . . . . . . . . . . . . 7
8. SDP 'bfcpver' Attribute . . . . . . . . . . . . . . . . . . . 8
9. Multiplexing Considerations . . . . . . . . . . . . . . . . . 9
10. BFCP Connection Management . . . . . . . . . . . . . . . . . 9
10.1. TCP Connection Management . . . . . . . . . . . . . . . 9
11. Authentication . . . . . . . . . . . . . . . . . . . . . . . 10
12. ICE Considerations . . . . . . . . . . . . . . . . . . . . . 11
13. SDP Offer/Answer Procedures . . . . . . . . . . . . . . . . . 12
13.1. Generating the Initial SDP Offer . . . . . . . . . . . . 12
13.2. Generating the SDP Answer . . . . . . . . . . . . . . . 13
13.3. Offerer Processing of the SDP Answer . . . . . . . . . . 14
13.4. Modifying the Session . . . . . . . . . . . . . . . . . 15
14. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 15
15. Security Considerations . . . . . . . . . . . . . . . . . . . 17
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
16.1. Registration of SDP 'proto' Values . . . . . . . . . . . 17
16.2. Registration of the SDP 'floorctrl' Attribute . . . . . 18
16.3. Registration of the SDP 'confid' Attribute . . . . . . . 18
16.4. Registration of the SDP 'userid' Attribute . . . . . . . 18
16.5. Registration of the SDP 'floorid' Attribute . . . . . . 18
16.6. Registration of the SDP 'bfcpver' Attribute . . . . . . 18
17. Changes from RFC 4583 . . . . . . . . . . . . . . . . . . . . 19
18. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
19. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
19.1. Normative References . . . . . . . . . . . . . . . . . . 20
19.2. Informational References . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction
As discussed in the BFCP (Binary Floor Control Protocol)
specification [17], a given BFCP client needs a set of data in order
to establish a BFCP connection to a floor control server. This data
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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 [4] 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 attributes encoded in
'a' lines.
2. Terminology
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, RFC 2119 [1] and indicate requirement levels for compliant
implementations.
3. Fields in the 'm' Line
This section describes how to generate an 'm' line for a BFCP stream.
According to the SDP specification [9], the 'm' line format is the
following:
m=<media> <port> <proto> <fmt> ...
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 [6]. Depending on the value of the 'setup' attribute
(discussed in Section 10.1), 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.
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This document defines five values for the proto field: TCP/BFCP,
TCP/DTLS/BFCP, TCP/TLS/BFCP, UDP/BFCP, and UDP/TLS/BFCP.
TCP/BFCP is used when BFCP runs directly on top of TCP. TCP/TLS/BFCP
is used when BFCP runs on top of TLS, which in turn runs on top of
TCP. TCP/DTLS/BFCP is used when running BFCP on top of DTLS [10], as
described in this specification, which in turn runs on top of TCP
using the framing method defined in [11] with DTLS packets being sent
and received instead of RTP/RTCP packets using the shim defined in
RFC4571 such that the length field defined in RFC4571 precedes each
DTLS message.
Similarly, UDP/BFCP is used when BFCP runs directly on top of UDP,
and UDP/TLS/BFCP is used when BFCP runs on top of DTLS, which in turn
runs on top of UDP.
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 is ignored.
The following is an example of an 'm' line for a BFCP connection:
m=application 50000 TCP/TLS/BFCP *
4. Floor Control Roles
When two endpoints establish a BFCP stream, they need to determine
which of them acts as floor control client and which acts as floor
control server. Typically, a client that establishes a BFCP stream
with a conference server will act as floor control client, while the
conference server will act as floor control server. However, there
are scenarios where both endpoints would be able to act as floor
control server. For example, in a two-party session that involves an
audio stream and a shared whiteboard, the endpoints need to determine
which party will be act as floor control server.
Furthermore, there are situations where both endpoints act as both
floor control client and floor control server within the same
session. For example, in a two-party session that involves an audio
stream and a shared whiteboard, one endpoint acts as the floor
control server for the audio stream and the other endpoint acts as
the floor control server for the shared whiteboard. However, for a
given BFCP-controlled media stream one endpoint MUST act as floor
control client and one endpoint MUST act as floor control server.
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5. SDP 'floorctrl' Attribute
This section defines the SDP 'floorctrl' media-level attribute. The
attribute is used to determine the floor control role(s) that the
endpoints can take for the BFCP-controlled media streams. As
described in Section 5, an endpoint can take different roles for
different media streams, but for a given media stream an endpoint can
only take one role.
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.
c-s: The endpoint is willing to act as floor control client and
floor control server.
When inserted in an offer, the offerer MAY indicate multiple
attribute values. When inserted in an answer, the answerer MUST
indicate only one attribute value. The offerer indicates which floor
control role(s) that it is willing to take. The answerer indicates
the role taken by the answerer. Based on this, the floor control
role(s) of the offerer is determined, as shown in Table 1.
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+---------+----------+
| Offerer | Answerer |
+---------+----------+
| c-only | s-only |
| s-only | c-only |
| c-s | c-s |
+---------+----------+
Table 1: Roles
Endpoints compliant with [14] might not include the 'floorctrl'
attribute in offers and answerer. If the 'floorctrl' attribute is
not present the offerer will act as floor control client, and the
answerer will act as floor control server, for each BFCP-controlled
media stream.
The SDP Offer/Answer procedures for the 'floorctrl' attribute are
defined in Section 13.
The following is an example of a 'floorctrl' attribute in an offer:
a=floorctrl:c-only s-only c-s
6. SDP 'confid' and 'userid' Attributes
This section defines the SDP 'confid' and the 'userid' media-level
attributes. The attributes are used by a floor control server to
convey the conference ID value and user 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 is defined in [RFC5234]
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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 is defined in [RFC5234]
The SDP Offer/Answer procedures for the 'confid' and 'userid'
attributes are defined in Section 13.
7. SDP 'floorid' Attribute
This section defines the SDP 'floorid' media-level attribute. The
attribute conveys a floor identifier, 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 = "a=floorid:" 1*DIGIT SP "mstrm:" token *(SP token)
;DIGIT is defined in [RFC5234]
;token is defined in [RFC4566]
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 [7] of a media stream.
The SDP Offer/Answer procedures for the 'floorid' attribute are
defined in Section 13.
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Note: In [14] 'm-stream' was erroneously used in Section 14.
Although the example was non-normative, it is implemented by some
vendors and occurs in cases where the endpoint is willing to act
as an server. Therefore, it is RECOMMENDED to support parsing and
interpreting 'm-stream' the same way as 'mstrm' when receiving.
8. SDP 'bfcpver' Attribute
This section defines the SDP 'bfcpver' media-level attribute. The
attribute is used to negotiate the BFCP version.
The Augmented BNF syntax [2] for the attributes is:
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 = "a=bfcpver:" version *(SP version)
version = 1*DIGIT
;DIGIT is defined in [RFC5234]
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
[17]. The BFCP version that will eventually be used will be conveyed
with a BFCP-level Hello/HelloAck.
Endpoints compliant with [14] might not always include the 'bfcpver'
attribute in offers and answers. If the 'bfcpver' attribute is not
present, the default values are inferred from the transport specified
in the 'm' line (Section 3) associated with the stream. In
accordance with definition of the Version field in [17], 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 SDP Offer/Answer procedures for the 'bfcpver' attribute are
defined in Section 13.
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9. Multiplexing Considerations
[20] 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 [20]. Note that BFCP-
controlled media streams might be multiplexed with other media
streams.
[21] defines the mux categories for the SDP attributes defined in
this specification, excluding the SDP 'bfcpver' attribute. . Table 2
defines the mux category for the 'bfcpver' attribute:
+---------+------------------------+-------+--------------+
| Name | Notes | Level | Mux Category |
+---------+------------------------+-------+--------------+
| bfcpver | Needs further analysis | M | TBD |
+---------+------------------------+-------+--------------+
Table 2: Multiplexing Attribute Analysis
10. 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)
[15], TCP/DTLS/BFCP, and 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.
10.1. TCP Connection Management
The management of the TCP connection used to transport BFCP messages
is performed using the SDP 'setup' and 'connection' attributes [6].
The 'setup' attribute indicates which of the endpoints initiates the
TCP connection. The 'connection' attribute handles TCP connection
re-establishment.
The BFCP specification [17] 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.
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Endpoints using the offer/answer mechanism follow the following
rules.
When the existing TCP connection is closed and re-established
following the rules in [17], 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.
11. Authentication
When a BFCP stream is negotiated using the SDP offer/answer
mechanism, it is assumed that the offerer and the answerer
authenticate each other using some mechanism. TLS/DTLS is the
preferred mechanism. Other mechanisms are possible, but are outside
the scope of this document. Once this mutual authentication takes
place, all the offerer and the answerer need to ensure is that the
entity they are receiving BFCP messages from is the same as the one
that generated the previous offer or answer.
The initial mutual authentication SHOULD take place at the signaling
level. Additionally, signaling can use S/MIME [5] to provide an
integrity-protected channel with optional confidentiality for the
offer/answer exchange. BFCP takes advantage of this integrity-
protected offer/answer exchange to perform authentication. Within
the offer/answer exchange, the offerer and answerer exchange the
fingerprints of their self-signed certificates. These self-signed
certificates are then used to establish the TLS/DTLS connection that
will carry BFCP traffic between the offerer and the answerer.
Endpoints follow the rules in [8] regarding certificate choice and
presentation. Endpoints that use the offer/answer model to establish
BFCP streams MUST support the 'fingerprint' attribute and MUST
include it in their offers and answers.
When TLS is used with TCP, once the underlying connection is
established, the answerer, which can be the floor control client or
the floor control server, acts as the TLS server regardless of its
role (passive or active) in the TCP establishment procedure. If the
TCP connection is lost, the active endpoint is responsible for re-
establishing the TCP connection. Unless a new TLS session is
negotiated, subsequent SDP offers and answers will not impact the
previously negotiated TLS roles.
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When DTLS is used with UDP, the requirements specified in Section 5
of [18] MUST be followed.
Note: How to determine which endpoint initiates the TLS/DTLS
association depends on the selected underlying transport. It was
decided to keep the original semantics in [14] for TCP to retain
backwards compatibility. When using UDP, the procedure defined in
[18] was selected in order to be compatible with other DTLS based
protocol implementations, such as DTLS-SRTP. Furthermore, the
procedure defined in [18] do not overload offer/answer semantics
and works for offerless INVITE in scenarios with B2BUAs.
12. ICE Considerations
Generic SDP offer/answer procedures for Interactive Connectivity
Establishment (ICE) are defined in [16].
When BFCP is used with UDP based ICE candidates [15] then the
procedures for UDP/TLS/BFCP are used.
When BFCP is used with TCP based ICE candidates [12] then the
procedures for TCP/DTLS/BFCP are used.
Based on the procedures defined in [18], 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 BFCF 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.
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.
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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
Camarillo, et al. Expires November 22, 2018 [Page 22]
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Christer Holmberg
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
Email: christer.holmberg@ericsson.com
Camarillo, et al. Expires November 22, 2018 [Page 23]