XCON Working Group G. Camarillo
Internet-Draft Ericsson
Expires: July 1, 2005 J. Ott
Universitaet Bremen
K. Drage
Lucent Technologies
December 31, 2004
The Binary Floor Control Protocol (BFCP)
draft-ietf-xcon-bfcp-03.txt
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Copyright (C) The Internet Society (2004).
Abstract
Floor control is a means to manage joint or exclusive access to
shared resources in a (multiparty) conferencing environment.
Thereby, floor control complements other functions -- such as
conference and media session setup, conference policy manipulation,
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and media control -- that are realized by other protocols.
This document specifies the Binary Floor Control Protocol (BFCP).
BFCP is used between floor participants and floor control servers,
and between floor chairs (i.e., moderators) and floor control
servers.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1 Floor Creation . . . . . . . . . . . . . . . . . . . . . . 8
3.2 Obtaining Information to Contact a Floor Control Server . 8
3.3 Generating a Shared Secret . . . . . . . . . . . . . . . . 8
3.4 Obtaining Floor-Resource Associations . . . . . . . . . . 8
3.5 Policy Enforcement . . . . . . . . . . . . . . . . . . . . 9
4. Overview of Operation . . . . . . . . . . . . . . . . . . . 9
4.1 Floor Participant to Floor Control Server Interface . . . 10
4.2 Floor Chair to Floor Control Server Interface . . . . . . 13
5. Packet Format . . . . . . . . . . . . . . . . . . . . . . . 14
5.1 FIXED-HEADER Format . . . . . . . . . . . . . . . . . . . 14
5.2 Attribute Format . . . . . . . . . . . . . . . . . . . . . 15
5.2.1 FLOOR-ID . . . . . . . . . . . . . . . . . . . . . . . 17
5.2.2 USER-ID . . . . . . . . . . . . . . . . . . . . . . . 17
5.2.3 BENEFICIARY-ID . . . . . . . . . . . . . . . . . . . . 17
5.2.4 TRANSACTION-ID . . . . . . . . . . . . . . . . . . . . 18
5.2.5 FLOOR-REQUEST-ID . . . . . . . . . . . . . . . . . . . 18
5.2.6 HUMAN-READABLE-INFO . . . . . . . . . . . . . . . . . 18
5.2.7 DIGEST . . . . . . . . . . . . . . . . . . . . . . . . 19
5.2.8 REQUEST-STATUS . . . . . . . . . . . . . . . . . . . . 20
5.2.9 ERROR-CODE . . . . . . . . . . . . . . . . . . . . . . 21
5.2.10 USER-DISPLAY-NAME . . . . . . . . . . . . . . . . . 23
5.2.11 USER-URI . . . . . . . . . . . . . . . . . . . . . . 23
5.2.12 PRIORITY . . . . . . . . . . . . . . . . . . . . . . 23
5.2.13 NONCE . . . . . . . . . . . . . . . . . . . . . . . 23
5.2.14 SUPPORTED-TLVS . . . . . . . . . . . . . . . . . . . 24
5.3 Message Format . . . . . . . . . . . . . . . . . . . . . . 24
5.3.1 FloorRequest . . . . . . . . . . . . . . . . . . . . . 24
5.3.2 FloorRelease . . . . . . . . . . . . . . . . . . . . . 25
5.3.3 FloorRequestInfoWanted . . . . . . . . . . . . . . . . 25
5.3.4 FloorRequestInfo . . . . . . . . . . . . . . . . . . . 26
5.3.5 FloorInfoWanted . . . . . . . . . . . . . . . . . . . 26
5.3.6 FloorInfo . . . . . . . . . . . . . . . . . . . . . . 27
5.3.7 ChairAction . . . . . . . . . . . . . . . . . . . . . 27
5.3.8 ChairActionAck . . . . . . . . . . . . . . . . . . . . 28
5.3.9 Hello . . . . . . . . . . . . . . . . . . . . . . . . 28
5.3.10 HelloAck . . . . . . . . . . . . . . . . . . . . . . 28
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5.3.11 Error . . . . . . . . . . . . . . . . . . . . . . . 29
6. Transport . . . . . . . . . . . . . . . . . . . . . . . . . 29
7. Lower-Layer Security . . . . . . . . . . . . . . . . . . . . 30
8. Protocol Transactions . . . . . . . . . . . . . . . . . . . 30
8.1 Client Behavior . . . . . . . . . . . . . . . . . . . . . 31
8.2 Server Behavior . . . . . . . . . . . . . . . . . . . . . 31
9. Authentication and Authorization . . . . . . . . . . . . . . 31
9.1 Client Behavior . . . . . . . . . . . . . . . . . . . . . 31
9.2 Floor Control Server Behavior . . . . . . . . . . . . . . 32
10. Floor Participant Operations . . . . . . . . . . . . . . . . 33
10.1 Requesting a Floor . . . . . . . . . . . . . . . . . . . 33
10.1.1 Sending a FloorRequest Message . . . . . . . . . . . 33
10.1.2 Receiving a Response . . . . . . . . . . . . . . . . 34
10.2 Cancelling a Floor Request and Releasing a Floor . . . . 35
10.2.1 Sending a FloorRelease Message . . . . . . . . . . . 35
10.2.2 Receiving a Response . . . . . . . . . . . . . . . . 36
11. Chair Operations . . . . . . . . . . . . . . . . . . . . . . 36
11.1 Sending a ChairAction Message . . . . . . . . . . . . . 36
11.2 Receiving a Response . . . . . . . . . . . . . . . . . . 37
12. General Client Operations . . . . . . . . . . . . . . . . . 38
12.1 Requesting Information about Floors . . . . . . . . . . 38
12.1.1 Sending a FloorInfoWanted Message . . . . . . . . . 38
12.1.2 Receiving a Response . . . . . . . . . . . . . . . . 38
12.2 Requesting Information about Floor Requests . . . . . . 39
12.2.1 Sending a FloorRequestInfoWanted Message . . . . . . 40
12.2.2 Receiving a Response . . . . . . . . . . . . . . . . 40
12.3 Obtaining the Capabilities of a Floor Control Server . . 41
12.3.1 Sending a Hello Message . . . . . . . . . . . . . . 41
12.3.2 Receiving Responses . . . . . . . . . . . . . . . . 41
13. Floor Control Server Operations . . . . . . . . . . . . . . 41
13.1 Reception of a FloorRequest Message . . . . . . . . . . 42
13.1.1 Generating the First FloorRequestInfo Message . . . 42
13.1.2 Generation of Subsequent FloorRequestInfo Messages . 43
13.2 Reception of a FloorRequestInfoWanted Message . . . . . 44
13.2.1 Information on a Single Floor Request . . . . . . . 44
13.2.2 Information on the Floor Requests Associated to a
Participant . . . . . . . . . . . . . . . . . . . . 45
13.3 Reception of a FloorRelease Message . . . . . . . . . . 45
13.4 Reception of a FloorInfoWanted Message . . . . . . . . . 46
13.4.1 Generation of the First FloorInfo Message . . . . . 47
13.4.2 Generation of Subsequent FloorInfo Messages . . . . 47
13.5 Reception of a ChairAction Message . . . . . . . . . . . 48
13.6 Reception of a Hello Message . . . . . . . . . . . . . . 49
13.7 Error Message Generation . . . . . . . . . . . . . . . . 49
14. Security Considerations . . . . . . . . . . . . . . . . . . 49
15. IANA Considerations . . . . . . . . . . . . . . . . . . . . 51
15.1 Attribute Subregistry . . . . . . . . . . . . . . . . . 51
15.2 Primitive Subregistry . . . . . . . . . . . . . . . . . 51
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15.3 Request Status Subregistry . . . . . . . . . . . . . . . 52
15.4 Error Code Subregistry . . . . . . . . . . . . . . . . . 53
16. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . 54
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 54
17.1 Normative References . . . . . . . . . . . . . . . . . . . 54
17.2 Informational References . . . . . . . . . . . . . . . . . 55
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 56
Intellectual Property and Copyright Statements . . . . . . . 57
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1. Introduction
Within a conference, some applications need to manage the access to a
set of shared resources, such as the right to send media over a
particular media stream. Floor control enables such applications to
provide users with coordinated (shared or exclusive) access to these
resources.
The Requirements for Floor Control Protocol [11] list a set of
requirements that need to be met by floor control protocols. The
Binary Floor Control Protocol (BFCP), which is specified in this
document, meets these requirements.
In addition, BFCP has been designed so that it can be used in
low-bandwidth environments. The binary encoding used by BFCP
achieves a small message size (when message signatures are not used)
that keeps the time it takes to transmit delay-sensitive BFCP
messages at minimum. Delay-sensitive BFCP messages include
FloorRequest, FloorRelease, FloorRequestInfo, and ChairAction. It is
expected that future extensions to these messages do not increase the
size of these messages in a significant way.
The remainder of this document is organized as follows. Section 2
defines the terminology used throughout this document and Section 3
discusses the scope of BFCP (i.e., which tasks fall within the scope
of BFCP and which ones are performed using different mechanisms).
Section 4 provides a non-normative overview of BFCP operation and
subsequent sections provide the normative specification of BFCP.
2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
described in BCP 14, RFC 2119 [2] and indicate requirement levels for
compliant implementations.
Media Participant: An entity that has access to the media resources
of a conference (e.g., it can receive a media stream). In
floor-controlled conferences, a given media participant is typically
co-located with a floor participant, but does not need to.
Third-party floor requests consist of having a floor participant
request a floor for a media participant when they are not colocated.
The protocol between a floor participant and a media participant
(that are not colocated) is outside the scope of this document.
Client: a floor participant or a floor chair that communicate with a
floor control server using BFCP.
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Conference Policy: The complete set of rules for a particular
conference. It includes the membership policy, the media policy, and
policies related to floors and the use of floor control protocols.
There is an instance of conference policy for each conference.
Floor: A permission to temporarily access or manipulate a specific
shared resource or set of resources.
Floor Chair: A logical entity that manages one floor (grants, denies,
or revokes a floor). An entity that assumes the logical role of a
floor chair for a given transaction may assume a different role
(e.g., floor participant) for a different transaction. The roles of
floor chair and floor participant are defined on a
transaction-by-transaction basis. BFCP transactions are defined in
Section 8.
Floor Control: A mechanism that enables applications or users to gain
safe and mutually exclusive or non-exclusive input access to the
shared object or resource.
Floor Control Server: A logical entity that maintains the state of
the floor(s) including which floors exists, who the floor chairs are,
who holds a floor, etc. Requests to manipulate a floor are directed
at the floor control server. The floor control server of a
conference may perform other logical roles (e.g., floor participant)
in another conference.
Floor Participant: A logical entity that requests floors, and
possibly information about them, from a floor control server. An
entity that assumes the logical role of a floor participant for a
given transaction may assume a different role (e.g., a floor chair)
for a different transaction. The roles of floor participant and
floor chair are defined on a transaction-by-transaction basis. BFCP
transactions are defined in Section 8. In floor-controlled
conferences, a given floor participant is typically co-located with a
media participant, but does not need to. Third-party floor requests
consist of having a floor participant request a floor for a media
participant when they are not co-located.
Participant: An entity that acts as a floor participant, as a media
participant, or as both.
3. Scope
As stated earlier, BFCP is a protocol to coordinate access to shared
resources in a conference following the requirements defined in [11].
Floor control complements other functions defined in the conferencing
framework [12]. In particular, it is the conference policy that
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defines which media streams and applications are floor-controlled,
who is/are the respective floor chair(s), and how access to the floor
is managed. Furthermore, it is up to the media policy to define
which (if any) impact on media stream handling (e.g. switching or
mixing) assignment of a floor to a media participant has.
The floor control protocol BFCP defined in this document only
specifies a means to arbitrate access to floors. The rules and
constraints for floor arbitration and the results of floor
assignments are outside the scope of this document and defined by
other protocols [13].
Figure 1 shows the tasks that BFCP can perform.
+---------+
| Floor |
| Chair |
| |
+---------+
^ |
| |
Notification | | Decision
| |
| |
Floor | v
+-------------+ Request +---------+ +-------------+
| Floor |----------->| Floor | Notification | Floor |
| Participant | | Control |------------->| Participant |
| |<-----------| Server | | |
+-------------+ Granted or +---------+ +-------------+
Denied
Figure 1: Functionality provided by BFCP
BFCP provides a means:
o for floor participants to send floor requests to floor control
servers.
o for floor control servers to grant or deny requests to access a
given resource from floor participants.
o for floor chairs to send floor control servers decisions regarding
floor requests.
o for floor control servers to keep floor participants and floor
chairs informed about the status of a given floor or a given floor
request.
Even though tasks that do not belong to the previous list are outside
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the scope of BFCP, some of these out-of-scope tasks relate to floor
control and are essential to create floors and to establish BFCP
connections between different entities. In the following
subsections, we discuss some of these tasks and mechanisms to perform
them.
3.1 Floor Creation
The association of a given floor with a resource or a set of
resources (e.g., media streams) is out of the scope of BFCP as
described in [13]. The conference policy for a particular conference
contains the floors of the conference and the resource or resources
associated with each floor. For example, a conference may have two
floors: one controlling who can talk at a particular time and another
controlling who can write on a shared whiteboard.
Floor creation and termination are also outside the scope of BFCP and
are aspects of the conference policy as well. Consequently, the
floor control server needs to stay up to date on changes on the
conference policy (e.g., when a new floor is created).
3.2 Obtaining Information to Contact a Floor Control Server
A client needs a set of data in order to establish a BFCP connection
to a floor control server. These data include the transport address
of the server, the conference identifier, and the user identifier.
Clients can obtain this information in different ways. One is to use
an offer/answer [10] exchange. How to use an SDP [8] offer/answer
[10] exchange to obtain this information is described in [14].
3.3 Generating a Shared Secret
Authentication in BFCP is based on a shared secret between the client
and the floor control server. So, there is a need for a mechanism to
generate such a shared secret. However, such mechanism is outside
the scope of BFCP.
Shared secrets can also be generated and exchanged using out-of-band
means. For example, when the floor participant or the floor chair
obtains the information needed to contact the BFCP floor control
server over a secure channel (e.g., an offer/answer [10] exchange
using SIP [9] protected using S/MIME), they can get the shared secret
using the same channel.
3.4 Obtaining Floor-Resource Associations
Floors are associated with resources. For example, a floor that
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controls who talks at a given time has a particular audio stream as
its associated resource. Associations between floors and resources
are part of the conference policy.
Floor participants and floor chairs need to know which resources are
associated with which floors. They can obtain this information using
different mechanisms, such as an offer/answer [10] exchange. How to
use an offer/answer exchange to obtain these associations is
described in [14].
Note that floor participants perform offer/answer exchanges with
the SIP focus of the conference. So, the SIP focus needs to
obtain information about associations between floors and resources
in order to be able to provide this information to a floor
participant in an offer/answer exchange.
3.5 Policy Enforcement
A participant whose floor request is granted has the right to use (in
a certain way) the resource or resources associated with the floor
that was requested. For example, the participant may have the right
to send media over a particular audio stream.
Nevertheless, holding a floor does not imply that others will not be
able to use its associated resources at the same time, even if they
do not have the right to do so. According to the definition in
Section 2, the conference policy determines which media participants
can actually use the resources in the conference.
So, if the policy of a conference is to enforce floor control
decisions, every change in the status of any floor needs to be
reflected in the conference policy of the conference. For example,
the mixer only accepts media from the user who holds the floor.
4. Overview of Operation
This section provides a non-normative description of BFCP operations.
Section 4.1 describes the interface between floor participants and
floor control servers and Section 4.2 describes the interface between
floor chairs and floor control servers
BFCP messages, which use a TLV (Type-Length-Value) binary encoding,
consist of a common header followed by a set of TLVs. The common
header contains, among other information, a 32-bit conference
identifier. Floor participants, media participants, and floor chairs
are identified by a 16-bit user identifier, which is carried in a
TLV.
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There are two types of transactions in BFCP: client-initiated
transactions and server-initiated transactions. Client-initiated
transactions consist of a message from a client to the floor control
server and a response from the floor control server to the client.
Both messages can be related because they carry the same
TRANSACTION-ID TLV. Server-initiated transactions consist of a
single message, which has no TRANSACTION-ID TLV, from the floor
control server to a client.
4.1 Floor Participant to Floor Control Server Interface
Floor participants request a floor by sending a FloorRequest message
to the floor control server. BFCP supports third-party floor
requests. That is, the floor participant sending the floor request
need not be co-located with the media participant that will get the
floor once the floor request is granted. FloorRequest messages carry
the identity of the requester in a USER-ID TLV, and the identity of
the beneficiary of the floor, in third party floor requests, in a
BENEFICIARY-ID TLV.
Third party floor requests can be sent, for example, by floor
participants that have a BFCP connection to the floor control
server but that are not media participants (i.e., they do not
handle any media).
FloorRequest messages identify the floor or floors being requested by
carrying their 16-bit floor identifiers in FLOOR-ID TLVs. If a
FloorRequest message carries more than one floor identifier, the
floor control server treats all the floor requests as an atomic
package. That is, the floor control server either grants or denies
all the floors in the FloorRequest message.
Floor control servers respond to FloorRequest messages with
FloorRequestInfo messages, which provide information about the status
of the floor request. The first FloorRequestInfo message is the
response to the FloorRequest message from the client, and therefore
carries the same TRANSACTION-ID TLV as the FloorRequest.
Additionally, the first FloorRequestInfo message carries a
FLOOR-REQUEST-ID TLV. Subsequent FloorRequestInfo messages related
to the same floor request will carry the same FLOOR-REQUEST-ID TLV.
This way, the floor participant can associate them with the
appropriate floor request.
Messages from the floor participant related to a particular floor
request also use the same FLOOR-REQUEST-ID TLV as the first
FloorRequestInfo Message from the floor control server.
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Figure 2 shows how a floor participant requests a floor, obtains it,
and, at a later time, releases it. This figure illustrates the use,
among other TLVs, of the TRANSACTION-ID and the FLOOR-REQUEST-ID
TLVs.
Floor Participant Floor Control
Server
|(1) FloorRequest |
|TRANSACTION-ID: 123 |
|USER-ID: 234 |
|FLOOR-ID: 543 |
|---------------------------------------------->|
|(2) FloorRequestInfo |
|TRANSACTION-ID: 123 |
|USER-ID: 234 |
|FLOOR-REQUEST-ID: 789 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Pending |
|<----------------------------------------------|
|(3) FloorRequestInfo |
|USER-ID: 234 |
|FLOOR-REQUEST-ID: 789 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Accepted (1st in Queue) |
|<----------------------------------------------|
|(4) FloorRequestInfo |
|USER-ID: 234 |
|FLOOR-REQUEST-ID: 789 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Granted |
|<----------------------------------------------|
|(5) FloorRelease |
|TRANSACTION-ID: 154 |
|USER-ID: 234 |
|FLOOR-REQUEST-ID: 789 |
|---------------------------------------------->|
|(6) FloorRequestInfo |
|TRANSACTION-ID: 154 |
|USER-ID: 234 |
|FLOOR-REQUEST-ID: 789 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Released |
|<----------------------------------------------|
Figure 2: Requesting and releasing a floor
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Figure 2 shows how a floor participant requests to be informed on the
status of a floor. The first FloorInfo message from the floor
control server is the response to the FloorInfoWanted message, and as
such, carries the same TRANSACTION-ID TLV as the FloorInfoWanted
message.
Subsequent FloorInfo messages consist of server-initiated
transactions, and therefore carry no TRANSACTION-ID TLV. FloorInfo
message (2) indicates that there are currently two floor requests for
the floor whose Floor ID is 543. FloorInfo message (3) indicates
that the floor requests with Floor Request ID 764 has been granted,
while the floor request with Floor Request ID 635 is the first in the
queue. FloorInfo message (4) indicates that the floor request with
Floor Request ID 635 has been granted.
Floor Participant Floor Control
Server
|(1) FloorInfoWanted |
|TRANSACTION-ID: 257 |
|USER-ID: 234 |
|FLOOR-ID: 543 |
|---------------------------------------------->|
|(2) FloorInfo |
|TRANSACTION-ID: 257 |
|USER-ID: 234 |
|FLOOR-ID:543 |
|FLOOR-REQUEST-ID: 764 |
|FLOOR-ID: 543 |
|BENEFICIARY-ID: 124 |
|REQUEST-STATUS: Accepted (1st in Queue) |
|FLOOR-REQUEST-ID: 635 |
|BENEFICIARY-ID: 154 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Accepted (2nd in Queue) |
|<----------------------------------------------|
|(3) FloorInfo |
|USER-ID: 234 |
|FLOOR-ID:543 |
|FLOOR-REQUEST-ID: 764 |
|FLOOR-ID: 543 |
|BENEFICIARY-ID: 124 |
|REQUEST-STATUS: Granted |
|FLOOR-REQUEST-ID: 635 |
|BENEFICIARY-ID: 154 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Accepted (1st in Queue) |
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|<----------------------------------------------|
|(4) FloorInfo |
|USER-ID: 234 |
|FLOOR-ID:543 |
|FLOOR-REQUEST-ID: 635 |
|BENEFICIARY-ID: 154 |
|FLOOR-ID: 543 |
|REQUEST-STATUS: Granted |
|<----------------------------------------------|
Figure 3: Obtaining status information about a floor
FloorInfo messages contain information about the floor requests they
carry. For example, FloorInfo message (4) indicates that the floor
request with Floor Request ID 635 has as the beneficiary (i.e., the
participant that holds the floor when a particular floor request is
granted) the participant whose User ID is 154. The floor request
applies only to the floor whose Floor ID is 543. That is, this is
not a multi-floor floor request.
4.2 Floor Chair to Floor Control Server Interface
Figure 4 shows a floor chair instructing a floor control server to
grant a floor. Note, however, that although the floor control server
needs to take into consideration the instructions received in
ChairAction messages (e.g., granting a floor), it does not
necessarily need to perform them exactly as requested by the floor
chair. The operation that the floor control server performs depends
on the ChairAction message and on the internal state of the floor
control server.
For example, a floor chair may send a ChairAction message granting a
floor which was requested as part of an atomic floor request
operation that involved several floors. Even if the chair
responsible for one of the floors instructs the floor control server
to grant the floor, the floor control server will not grant it until
the chairs responsible for the other floors agree to grant them as
well. In another example, a floor chair may instruct the floor
control server to grant a floor to a participant. The floor control
server needs to revoke the floor from its current holder before
granting it to the new participant.
So, the floor control server is ultimately responsible to keep a
coherent floor state using instructions from floor chairs as input to
this state.
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Floor Chair Floor Control
Server
|(1) ChairAction |
|TRANSACTION-ID: 769 |
|USER-ID: 357 |
|FLOOR-ID: 543 |
|FLOOR-REQUEST-ID: 635 |
|REQUEST-STATUS: Granted |
|---------------------------------------------->|
|(2) ChairActionAck |
|TRANSACTION-ID: 769 |
|USER-ID: 357 |
|<----------------------------------------------|
Figure 4: Chair instructing the floor control server
5. Packet Format
BFCP packets consist of an 8-byte fixed header followed by
attributes. All the protocol values MUST be sent in network byte
order.
5.1 FIXED-HEADER Format
The following is the FIXED-HEADER format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Ver |Reserved | Primitive | Payload Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Conference ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: FIXED-HEADER format
Ver: the 3-bit version field MUST be set to 1 to indicate this
version of BFCP.
Reserved: at this point, the 5 bits in the reserved field SHOULD be
set to zero by the sender of the message and MUST be ignored by the
receiver.
Primitive: this 8-bit field identifies the main purpose of the
message. The following primitive values are defined:
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+-------+------------------------+-----------------------+
| Value | Primitive | Direction |
+-------+------------------------+-----------------------+
| 0 | FloorRequest | P -> S |
| 1 | FloorRelease | P -> S |
| 2 | FloorRequestInfoWanted | P -> S ; Ch -> S |
| 3 | FloorRequestInfo | P <- S ; Ch <- S |
| 4 | FloorInfoWanted | P -> S ; Ch -> S |
| 5 | FloorInfo | P <- S ; Ch <- S |
| 6 | ChairAction | Ch -> S |
| 7 | ChairActionAck | Ch <- S |
| 8 | Hello | P -> S ; Ch -> S |
| 9 | HelloAck | P <- S ; Ch <- S |
| 10 | Error | P <- S ; Ch <- S |
+-------+------------------------+-----------------------+
S: Floor Control Server
P: Floor Participant
Ch: Floor Chair
Table 1: BFCP primitives
Payload Length: this 16-bit field contains length of the message in
4-byte units excluding the fixed header.
Conference ID: this 32-bit identifies the conference the message
belongs to.
5.2 Attribute Format
BFCP attributes are encoded in TLV (Type-Length-Value) format. TLVs
are 32-bit aligned.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type |M| Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
/ Attribute Contents /
/ /
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: TLV format
Type: this 7-bit field contains the type of the attribute. The
following attribute types are defined:
+------+---------------------+
| Type | Attribute |
+------+---------------------+
| 0 | FLOOR-ID |
| 1 | USER-ID |
| 2 | BENEFICIARY-ID |
| 3 | TRANSACTION-ID |
| 4 | FLOOR-REQUEST-ID |
| 5 | HUMAN-READABLE-INFO |
| 6 | DIGEST |
| 7 | REQUEST-STATUS |
| 8 | ERROR-CODE |
| 9 | USER-DISPLAY-NAME |
| 10 | USER-URI |
| 11 | PRIORITY |
| 12 | NONCE |
| 13 | SUPPORTED-TLVS |
+------+---------------------+
Table 2: BFCP attributes
M: the 'M' bit, known as the Mandatory bit, indicates whether support
of the attribute is required. If an unrecognized attribute with the
'M' bit set is received, the message is rejected.
Length: this 8-bit field contains the length of the attribute in
bytes, excluding any padding defined for specific attributes. The
Type, 'M' bit, and Length fields are included.
Attribute Contents: the contents of the different TLVs are defined in
the following sections.
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5.2.1 FLOOR-ID
The following is the format of the FLOOR-ID attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 0|M|0 0 0 0 0 1 0 0| Floor ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: FLOOR-ID format
Floor ID: this field contains a 16-bit value that uniquely identifies
a floor within a conference.
5.2.2 USER-ID
The following is the format of the USER-ID attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 0 1|M|0 0 0 0 0 1 0 0| User ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: USER-ID format
User ID: this field contains a 16-bit value that uniquely identifies
a user within a conference.
5.2.3 BENEFICIARY-ID
The following is the format of the BENEFICIARY-ID attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 0|M|0 0 0 0 0 1 0 0| Beneficiary ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: BENEFICIARY-ID format
Beneficiary ID: this field contains a 16-bit value that uniquely
identifies a user within a conference.
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5.2.4 TRANSACTION-ID
The following is the format of the TRANSACTION-ID attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 0 1 1|M|0 0 0 0 0 1 0 0| Transaction ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: TRANSACTION-ID format
Transaction ID: this field contains a 16-bit value that allows users
to match a given message with its response.
5.2.5 FLOOR-REQUEST-ID
The following is the format of the FLOOR-REQUEST-ID attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 0|M|0 0 0 0 0 1 0 0| Floor Request ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 11: FLOOR-REQUEST-ID format
Floor Request ID: this field contains a 16-bit value that indentifies
a floor request at the floor control server.
5.2.6 HUMAN-READABLE-INFO
The following is the format of the HUMAN-READABLE-INFO attribute.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 0 1|M| Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
/ Text /
/ +-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: HUMAN-READABLE-INFO format
Text: this field contains UTF-8 [7] encoded text.
In some situations, the contents of the Text field may be generated
by an automaton. If such automaton has information about the
preferred language of the receiver of a particular
HUMAN-READABLE-INFO TLV, it MAY use this language to generate the
Text field.
Padding: one, two, or three bytes of padding added so that the
contents of the HUMAN-READABLE-INFO TLV is 32-bit aligned. The
Padding bits SHOULD be set to zero by the sender and MUST be ignored
by the receiver. If the TLV is already 32-bit aligned, no padding is
needed.
5.2.7 DIGEST
The following is the format of the DIGEST attribute.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 1 0|M|0 0 0 1 1 0 0 0| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
+ +
| |
+ HMAC-SHA1 +
| |
+ +
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: DIGEST format
HMAC-SHA1: this 20-byte field contains an HMAC-SHA1 [1] of the BFCP
message. Its calculation is described in Section 9.
Padding: two bytes of padding added so that the contents of the
HMAC-SHA1 TLV is 32-bit aligned. The Padding bits SHOULD be set to
zero by the sender and MUST be ignored by the receiver.
5.2.8 REQUEST-STATUS
The following is the format of the REQUEST-STATUS attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 0 1 1 1|M|0 0 0 0 0 1 0 0|Request Status |Queue Position |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: REQUEST-STATUS format
Request Status: this 8-bit field contains the status of the request,
as described in the following table.
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+-------+-----------+
| Value | Status |
+-------+-----------+
| 0 | Pending |
| 1 | Accepted |
| 2 | Granted |
| 3 | Denied |
| 4 | Cancelled |
| 5 | Released |
| 6 | Revoked |
+-------+-----------+
Table 3: Request Status values
Queue Position: this 8-bit field contains, when applicable, the
position of the floor request in the floor request queue at the
server. If the Request Status value is different from Accepted, the
floor control server does not implement a floor request queue, or the
floor control server does not want to provide the client with this
information, all the bits of this field SHOULD be set to zero.
A floor request is in Pending state if the floor control server needs
to contact a floor chair in order to accept the floor request, but
has not done it yet. Once the floor control chair accepts the floor
request, the floor request is moved to the Accepted state.
5.2.9 ERROR-CODE
The following is the format of the ERROR-CODE attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 0 0 0|M| Length | Error Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Error Specific Details |
/ /
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: ERROR-CODE format
Error Code: this 16-bit field contains an error code from the
following table.
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+---------------------------------+---------------------------------+
| Value | Meaning |
+---------------------------------+---------------------------------+
| 0 | Conference does not Exist |
| 1 | Authentication Failed |
| 2 | Unknown Mandatory TLV |
| 3 | Floor Request ID Does Not Exist |
| 4 | Unauthorized Operation |
| 5 | User does not Exist |
| 6 | Invalid Nonce |
| 7 | DIGEST TLV Required |
| 8 | Invalid Floor ID |
| 9 | You have Already Reached the |
| | Maximum Number of Ongoing Floor |
| | Requests for this Floor |
+---------------------------------+---------------------------------+
Table 4: Error Code meaning
Error Specific Details: Present only for certain Error Codes. In
this document, only for Error Code 2 (Unknown Mandatory TLV). For
Error Code 2, this field contains the Types of the TLVs (which were
present in the message that triggered the Error message) that were
unknown to the receiver, encoded as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unknown TLV Type | Unknown TLV Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Unknown TLV Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Unknown TLV Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Unknown TLVs format
Padding: one, two, or three bytes of padding added so that the
contents of the ERROR-CODE TLV is 32-bit aligned. If the TLV is
already 32-bit aligned, no padding is needed.
The Padding bits SHOULD be set to zero by the sender and MUST be
ignored by the receiver. Note all the Error Codes defined in this
document but Error Code 2, result in a TLV which is already 32-bit
aligned (i.e., no need of padding). Error Code 2 results in a TLV
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that may need 2 bytes of padding.
5.2.10 USER-DISPLAY-NAME
The format of the USER-DISPLAY-NAME attribute is the same as the
HUMAN-READABLE-INFO attribute (still, they have different attribute
types). The Text field in the USER-DISPLAY-NAME attribute contains
the name of the user.
5.2.11 USER-URI
The format of the USER-URI attribute is the same as the
HUMAN-READABLE-INFO attribute (still, they have different attribute
types). The Text field in the USER-URI attribute contains the URI of
the user.
5.2.12 PRIORITY
The following is the format of the PRIORITY attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 0 1 1|M|0 0 0 0 0 1 0 0| Priority | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 17: PRIORITY format
Priority: the higher the 8-bit value, the more priority is requested
for a given floor request.
Reserved: at this point, the 8 bits in the reserved field SHOULD be
set to zero by the sender of the message and MUST be ignored by the
receiver.
5.2.13 NONCE
The following is the format of the NONCE attribute.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 1 0 0|M| Length | Nonce Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 18: NONCE format
Nonce Value: this 16-bit field contains a nonce.
5.2.14 SUPPORTED-TLVS
The following is the format of the SUPPORTED-TLVS attribute.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1 1 0 1|M| Length | Supported TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Supported TLV | Supported TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
/ /
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 19: SUPPORTED-TLVS format
Supported TLV: these fields contain the Types of the TLVs that are
supported by the floor control server.
Padding: two bytes of padding added so that the contents of the
SUPPORTED-TLVS TLV is 32-bit aligned. If the TLV is already 32-bit
aligned, no padding is needed.
The Padding bits SHOULD be set to zero by the sender and MUST be
ignored by the receiver.
5.3 Message Format
This section contains the normative ABNF [3] of the BFCP messages.
5.3.1 FloorRequest
Floor participants request a floor by sending a FloorRequest message
to the floor control server. The following is the format of the
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FloorRequest message:
FloorRequest = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
[BENEFICIARY-ID]
*(FLOOR-ID)
[HUMAN-READABLE-INFO]
[PRIORITY]
[NONCE]
[DIGEST]
Figure 20: FloorRequest format
5.3.2 FloorRelease
Floor participants release a floor by sending a FloorRelease message
to the floor control server. Floor participants also use the
FloorRelease message to cancel pending floor requests. The following
is the format of the FloorRelease message:
FloorRelease = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
(FLOOR-REQUEST-ID)
[NONCE]
[DIGEST]
Figure 21: FloorRelease format
5.3.3 FloorRequestInfoWanted
Floor participants and floor chairs request information about a floor
request by sending a FloorRequestInfoWanted message to the floor
control server. The following is the format of the
FloorRequestInfoWanted message:
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FloorRequestInfoWanted = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
[BENEFICIARY-ID]
[FLOOR-REQUEST-ID]
[NONCE]
[DIGEST]
Figure 22: FloorRequestInfoWanted format
5.3.4 FloorRequestInfo
The floor control server informs floor participants and floor chairs
about the status of their floor requests by sending them
FloorRequestInfo messages. The following is the format of the
FloorRequestInfo message:
FloorRequestInfo = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
[BENEFICIARY-ID]
[USER-DISPLAY-NAME]
[USER-URI]
1*( (FLOOR-REQUEST-ID)
1*(FLOOR-ID)
[HUMAN-READABLE-INFO]
[PRIORITY]
(REQUEST-STATUS) )
[NONCE]
Figure 23: FloorRequestInfo format
5.3.5 FloorInfoWanted
Floor participants and floor chairs request information about a floor
or floors by sending a FloorInfoWanted message to the floor control
server. The following is the format of the FloorRequest message:
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FloorInfoWanted = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
*(FLOOR-ID)
[NONCE]
[DIGEST]
Figure 24: FloorInfoWanted format
5.3.6 FloorInfo
The floor control server informs floor participants and floor chairs
about the status (e.g., the current holder) of a floor by sending
them FloorInfo messages. The following is the format of the
FloorInfo message:
FloorInfo = (FIXED-HEADER)
[TRANSACTION-ID]
(USER-ID)
[FLOOR-ID]
*( (FLOOR-REQUEST-ID)
[BENEFICIARY-ID]
[USER-DISPLAY-NAME]
[USER-URI]
*(FLOOR-ID)
[HUMAN-READABLE-INFO]
[PRIORITY]
(REQUEST-STATUS) )
[NONCE]
Figure 25: FloorInfo format
5.3.7 ChairAction
Floor chairs send instructions to floor control servers by sending
ChairAction messages. The following is the format of the ChairAction
message:
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ChairAction = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
1*(FLOOR-ID)
(FLOOR-REQUEST-ID)
(REQUEST-STATUS)
[HUMAN-READABLE-INFO]
[NONCE]
[DIGEST]
Figure 26: ChairAction format
5.3.8 ChairActionAck
Floor control servers confirm that they have accepted a ChairAction
message by sending a ChairActionAck message. The following is the
format of the ChairActionAck message:
ChairActionAck = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
[NONCE]
Figure 27: ChairActionAck format
5.3.9 Hello
Floor participants and floor chairs check the liveness of floor
control servers by sending a Hello message. The following is the
format of the Hello message:
Hello = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
[NONCE]
[DIGEST]
Figure 28: Hello format
5.3.10 HelloAck
Floor control servers confirm that they are alive on reception of a
Hello message by sending a HelloAck message. The following is the
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format of the HelloAck message:
HelloAck = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
(SUPPORTED-TLVS)
[NONCE]
Figure 29: HelloAck format
5.3.11 Error
Floor control servers inform floor participants and floor chairs
about errors processing requests by sending them Error messages. The
following is the format of the Error message:
Error = (FIXED-HEADER)
(TRANSACTION-ID)
(USER-ID)
(ERROR-CODE)
[NONCE]
[HUMAN-READABLE-INFO]
Figure 30: Error format
6. Transport
BFCP entities exchange BFCP messages using TCP connections. TCP
provides an in-order reliable delivery of a stream of bytes.
Consequently, message framing is implemented in the application
layer. BFCP implements application-layer framing using TLVs.
A client MUST NOT use more than one TCP connection to communicate
with a given floor control server within a conference. Nevertheless,
if the same physical box handles different clients (e.g., a floor
chair and a floor participant), which are identified by different
User IDs, a separate connection per client is allowed.
If a BFCP entity (a client or a floor control server) receives data
from TCP that cannot be parsed the entity MUST close the TCP
connection using a RESET call (send a TCP RST bit) and the connection
SHOULD be reestablished. Similarly, if a TCP connection cannot
deliver a BFCP message and times out, the TCP connection SHOULD be
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reestablished.
The way connection reestablishment is handled depends on how the
client obtains information to contact the floor control server (e.g.,
using an offer/answer exchange [14]). Once the TCP connection is
reestablished, the client MAY resend those message it did not get a
response for from the floor control server.
If a floor control server detects that the TCP connection towards one
of the floor participants is lost, it is up to the local policy of
the floor control server what to do with the pending floor requests
of the floor participant. In any case, it is RECOMMENDED that the
floor control server keeps the floor requests (i.e., does not cancel
them) while the TCP connection is reestablished.
If a client wishes to end its BFCP connection with a floor control
server, the client closes (i.e., a graceful close) the TCP connection
towards the floor control server. If a floor control server wishes
to end its BFCP connection with a client (e.g., the focus of the
conference informs the floor control server that the client has been
kicked out from the conference), the floor control server closes
(i.e., a graceful close) the TCP connection towards the client.
7. Lower-Layer Security
BFCP relies on lower-layer security mechanisms to provide replay and
integrity protection, and confidentiality. BFCP floor control
servers MUST support TLS [4], and BFCP clients (which include both
floor participants and floor chairs) SHOULD support TLS. Any BFCP
entity MAY support other security mechanisms.
BFCP entities that implement TLS MUST support, at a minimum, the TLS
TLS_RSA_WITH_AES_128_CBC_SHA ciphersuite [6].
8. Protocol Transactions
In BFCP, there are two types of transactions: client-initiated
transactions and server-initiated transactions (notifications).
Client-initiated transactions consist of a request from a client to a
floor control server and a response from the floor control server to
the client. The request carries a TRANSACTION-ID TLV which the floor
control server copies into the response. Clients use Transaction ID
values to match responses with previously-issued requests.
Server-initiated transactions consist of a single message from a
floor control server to a client. Since they do not trigger any
response, server-initiated transactions do not have Transaction IDs
associated with them.
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8.1 Client Behavior
A client starting a client-initiated transaction MUST set the
Conference ID in the FIXED-HEADER of the message to the Conference ID
for the conference that the client obtained previously.
The client MUST set the Transaction ID value in the TRANSACTION-ID
TLV to a number which MUST NOT be reused in another message from the
client until a response from the server is received for the
transaction. The client uses the Transaction ID value to match this
message with the response from the floor control server.
8.2 Server Behavior
A floor control server sending a response within a client-initiated
transaction MUST copy the Conference ID, the TRANSACTION-ID TLV, and
the USER-ID TLV from the request received from the client into the
response. Server-initiated transactions MUST NOT contain a
TRANSACTION-ID TLV.
9. Authentication and Authorization
BFCP uses the DIGEST TLV to provide client authentication. The
DIGEST TLV contains an HMAC-SHA1 [1] of the BFCP message. The use of
SHA1 implies that the length of the HMAC is 20 bytes. The text used
as input to HMAC is the BFCP message, including the FIXED-HEADER, up
to and including the TLV preceding the DIGEST TLV. This text is then
padded with zeroes so as to be a multiple of 64 bytes. As a result,
the DIGEST TLV MUST be the last attribute in any BFCP message. The
key used as input to HMAC is the secret shared between the server and
the user identified by the USER-ID TLV in the message.
9.1 Client Behavior
Clients can authenticate floor control servers by checking the floor
control server's certificate when the TLS connection is established
between them.
To achieve client authentication, a client needs to prove to the
floor control server that the client can produce a DIGEST TLV for a
message using their shared secret and that the message is fresh (to
avoid replay attacks). Clients prove the freshness of a message by
including a NONCE TLV in the message. The NONCE TLV is the second to
last TLV in the message (the last one is the DIGEST TLV).
The nonce to be places in the NONCE TLV by the client is typically
provided by the floor control server in an Error response --
typically with Error Code 7 (DIGEST TLV Required) or 6 (Invalid
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Nonce). Additionally, as an optimization, the floor control server
can provide a client with a NONCE to be used in the first message
generated by the client using an out-of-band mechanism (e.g., using
an offer/answer exchange as described in [14]). This way, the client
does not need to generate an initial BFCP message only to have it
rejected by the floor control server with an Error response
containing a nonce.
A client that obtains a nonce out-of-band SHOULD add a NONCE TLV and
a DIGEST TLV to the first message it sends to the floor control
server. Furthermore, if any client generates a message without a
DIGEST TLV and receives an Error response with Error Code 7 (DIGEST
TLV Required), the client SHOULD re-send the message with a DIGEST
TLV and a NONCE TLV with the nonce received in the Error response.
If after sending a message with a DIGEST TLV, a client receives an
Error response with Error Code 6 (Invalid Nonce), the client SHOULD
re-send the message using the new nonce received in the Error
response. If the Error Code is 1 (Authentication Failed) instead,
the client MUST NOT send further messages to the floor control server
until it has obtained a different (hopefully valid) shared secret
than the one used in the original message.
If a client receives a nonce in a message from the floor control
server, the client SHOULD add a NONCE TLV with this nonce and a
DIGEST TLV to its next message to the floor control server.
9.2 Floor Control Server Behavior
Before accepting any BFCP message, the floor control server SHOULD
authenticate the client. If the floor control server receives a
message without DIGEST TLV from an unauthenticated client, the floor
control server responds with an Error message with Error Code 7
(DIGEST TLV Required). The floor control message MUST include a
NONCE TLV with a nonce value that is unguessable by attackers.
When a floor control server receives a BFCP message with a DIGEST
TLV, it checks whether the NONCE TLV carries a nonce which was
generated by the floor control server for this client and which still
has not expired. If the nonce is not valid, authentication is
considered to have failed, in which case the floor control server
SHOULD return an Error message with Error Code 6 (Invalid Nonce) with
a new nonce in a NONCE TLV.
If the nonce is valid, the floor control server calculates the
HMAC-SHA1 [1] of the message excluding the DIGEST TLV. The key used
as input to HMAC is the secret shared between the server and the user
identified by the USER-ID TLV in the message. If the resulting value
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is the same as the one in the DIGEST TLV, authentication is
considered successful.
If the resulting value is different than the one in the DIGEST TLV,
authentication is considered to have failed, in which case the server
SHOULD return an Error message, as described in Section 13.7, with
Error Code 1 (Authentication Failed). Messages from a client that
cannot be authenticated MUST NOT be processed further.
Floor control servers may include a NONCE TLV in their responses to
provide the nonce to be used in the next message by the client.
However, when TLS is used, floor control servers typically
authenticate only the first message sent over the TLS connection.
After authenticating a BCFP message, the floor control server checks
whether or not the client is authorized to perform the operation it
is requesting. If the client is not authorized to perform the
operation being requested, the floor control server generates an
Error message, as described in Section 13.7, with an Error code with
a value of 4 (Unauthorized Operation). Messages from a client that
cannot be authorized MUST NOT be processed further.
10. Floor Participant Operations
This section specifies how floor participants can perform different
operations, such as requesting a floor, using the protocol elements
described in earlier sections. Section 11 specifies operations that
are specific to floor chairs, such as instructing the floor control
server to grant or revoke a floor, and Section 12 specifies
operations that can be performed by any client (i.e., both floor
participants and floor chairs).
10.1 Requesting a Floor
A floor participant that wishes to request one or more floors does so
by sending a FloorRequest message to the floor control server.
10.1.1 Sending a FloorRequest Message
The ABNF in Section 5.3.1 describes the TLVs that a FloorRequest
message can contain. In addition, the ABNF specifies normatively
which of these TLVs are mandatory, and which ones are optional.
The floor participant sets the Conference ID in the FIXED-HEADER and
the TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the floor participant follows the rules in Section 9.1
which relate to the authentication of the message (i.e., to the
DIGEST TLV).
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The floor participant must insert a USER-ID TLV, which will be used
by the floor control server to authenticate and authorize the
request. If the sender of the FloorRequest message (identified by
the USER-ID TLV) is not the participant that would eventually get the
floor (i.e., a third party floor request), the sender SHOULD add a
BENEFICIARY-ID TLV to the message identifying the beneficiary of the
floor.
Note that the name space for both the User ID and the Beneficiary
ID is the same. That is, a given participant is identified by a
single 16-bit value that can be used in USER-ID and in
BENEFICIARY-ID TLVs.
The floor participant must insert at least one FLOOR-ID TLV in the
FloorRequest message. If the client inserts more than one FLOOR-ID
TLVs, the floor control server will treat all the floor requests as
an atomic package. That is, the floor control server will either
grant or deny all the floors in the FloorRequest message.
The floor participant may use a HUMAN-READABLE-INFO TLV to state the
reason why the floor or floors are being requested. The Text field
in the HUMAN-READABLE-INFO TLV is intended for human consumption.
The floor participant may request the server to handle the floor
request with a certain priority using a PRIORITY TLV.
10.1.2 Receiving a Response
A message from the floor control server is considered to be a
response to the FloorRequest message if the message from the floor
control server has the same Conference ID, Transaction ID, and User
ID as the FloorRequest message, as described in Section 8.1.
The successful processing of a FloorRequest message at the floor
control server involves generating one or several FloorRequestInfo
messages. The floor participant obtains a Floor Request ID in a
FLOOR-REQUEST-ID TLV in the first FloorRequestInfo message from the
floor control server. Subsequent FloorRequestInfo messages from the
floor control server regarding the same floor request will carry the
same Floor Request ID as the initial FloorRequestInfo message. This
way, the floor participant can associate subsequent incoming
FloorRequestInfo messages with the ongoing floor request.
The floor participant obtains information about the status of the
floor request in the REQUEST-STATUS TLV of each of the
FloorRequestInfo messages received from the floor control server. If
the Request Status value is Granted, all the floors that were
requested in the FloorRequest message have been granted. If the
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Request Status value is Denied, all the floors that were requested in
the FloorRequest message have been denied. The HUMAN-READABLE-INFO
TLV, if present, provides extra information which the floor
participant MAY display to the user.
A floor request is considered to be ongoing while it is in the
Pending, Accepted, or Granted states.
If the response is an Error message, the floor control server could
not process the FloorRequest message for some reason, which is
described in the Error message.
10.2 Cancelling a Floor Request and Releasing a Floor
A floor participant that wishes to cancel an ongoing floor request
does so by sending a FloorRelease message to the floor control
server. The FloorRelease message is also used by floor participants
that hold a floor and would like to release it.
10.2.1 Sending a FloorRelease Message
The ABNF in Section 5.3.2 describes the TLVs that a FloorRelease
message can contain. In addition, the ABNF specifies normatively
which of these TLVs are mandatory, and which ones are optional.
The floor participant sets the Conference ID in the FIXED-HEADER and
the TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the floor participant follows the rules in Section 9.1
which relate to the authentication of the message (i.e., to the
DIGEST TLV). The floor participant must insert a USER-ID TLV, which
will be used by the floor control server to authenticate and
authorize the request.
Note that the FloorRelease message is used to release a floor or
floors that were granted and to cancel ongoing floor requests
(from the protocol perspective both are ongoing floor requests).
Using the same message in both situations helps resolve the race
condition that occurs when the FloorRelease message and the
FloorGrant message cross each other on the wire.
The floor participant uses the FLOOR-REQUEST-ID that was received in
the response to the FloorRequest message that the FloorRelease
message is cancelling.
Note that if the floor participant requested several floors as an
atomic operation (i.e., in a single FloorRequest message), all the
floors are released as an atomic operation as well (i.e., all are
released at the same time).
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10.2.2 Receiving a Response
A message from the floor control server is considered to be a
response to the FloorRelease message if the message from the floor
control server has the same Conference ID, Transaction ID, and User
ID as the FloorRequest message, as described in Section 8.1.
If the response is a FloorRequestInfo message, the Request Status
value in the REQUEST-STATUS-TLV will be Cancelled or Released.
If the response is an Error message, the floor control server could
not process the FloorRequest message for some reason, which is
described in the Error message.
It is possible that the FloorRelease message crosses on the wire with
a FloorRequestInfo message from the server with a Request Status
different from Cancelled or Released. In any case, such a
FloorRequestInfo message will not be a response to the FloorRelease
message, because its Transaction ID will not match that of the
FloorRelease.
11. Chair Operations
This section specifies how floor chairs can instruct the floor
control server to grant or revoke a floor using the protocol elements
described in earlier sections.
Floor chairs that wish to send instructions to a floor control server
do so by sending a ChairAction message.
11.1 Sending a ChairAction Message
The ABNF in Section 5.3.7 describes the TLVs that a ChairAction
message can contain. In addition, the ABNF specifies normatively
which of these TLVs are mandatory, and which ones are optional.
The floor chair sets the Conference ID in the FIXED-HEADER and the
TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the floor chair follows the rules in Section 9.1 which
relate to the authentication of the message (i.e., to the DIGEST
TLV). The floor chair must insert a USER-ID TLV, which will be used
by the floor control server to authenticate and authorize the
request.
The ChairAction message contains instructions that apply to one or
more floors within a particular floor request. The floor or floors
are identified by FLOOR-ID TLVs and the floor request is identified
by a FLOOR-REQUEST-ID TLV, which are carried in the ChairAction
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message.
For example, if a floor request consists of two floors that depend
on different floor chairs, each floor chair will grant its floor
within the floor request. Once both chairs have granted their
floor, the floor control server will grant the floor request as a
whole. On the other hand, if one of the floor chairs denies its
floor, the floor control server will deny the floor request as a
whole, regardless of the other floor chair's decision.
The floor chair provides the new status for one or more floors within
the floor request using a REQUEST-STATUS TLV. If the new status of
the floor request is Accepted, the floor chair MAY use the Queue
Position field to provide a queue position for the floor request. If
the floor chair does not wish to provide a queue position, all the
bits of the Queue Position field SHOULD be set to zero. The floor
chair SHOULD use the Status Revoked to revoke a floor that was
granted (i.e., Granted status) and the Status Denied to reject floor
requests in any other status (e.g., Pending and Accepted).
Note that a floor request may involve several floors and that a
ChairAction message may only deal with a subset of these floors
(e.g., if a single floor chair is not authorized to manage all the
floors). In this case, the REQUEST-STATUS that the floor chair
provides in the ChairAction message might not be the actual status
that the floor request gets at the server. The floor control
server will combine the instructions received from the different
floor chairs to come up with the actual status of the floor
request.
The floor chair may use a HUMAN-READABLE-INFO TLV to state the reason
why the floor or floors are being accepted, granted, or revoked. The
Text in the HUMAN-READABLE-INFO TLV is intended for human
consumption.
11.2 Receiving a Response
A message from the floor control server is considered to be a
response to the ChairAction message if the message from the server
has the same Conference ID, Transaction ID, and User ID as the
ChairAction message, as described in Section 8.1.
A ChairActionAck message from the floor control server confirms that
the floor control server has accepted the ChairAction message. An
Error message indicates that the floor control server could not
process the ChairAction message for some reason, which is described
in the Error message.
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12. General Client Operations
This section specifies operations that can be performed by any
client. That is, they are not specific to floor participants or
floor chairs. They can be performed by both.
12.1 Requesting Information about Floors
A client can obtain information about the status of a floor or floors
in different ways, which include using BFCP and using out-of-band
mechanisms. Clients using BFCP to obtain such information use the
procedures described in this section.
Clients request information about the status of one or several floors
by sending a FloorInfoWanted message to the floor control server.
12.1.1 Sending a FloorInfoWanted Message
The ABNF in Section 5.3.5 describes the TLVs that a FloorInfoWanted
message can contain. In addition, the ABNF specifies normatively
which of these TLVs are mandatory, and which ones are optional.
The client sets the Conference ID in the FIXED-HEADER and the
TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the client follows the rules in Section 9.1 which
relate to the authentication and the protection of the integrity of
the message (i.e., to the DIGEST TLV). The client must insert a
USER-ID TLV, which will be used by the floor control server to
authenticate and authorize the request.
The client inserts in the message all the Floor IDs it wants to
receive information about. The floor control server will send
periodic information about all these floors. If the client does not
want to receive information about a particular floor any longer, it
sends a new FloorInfoWanted message removing the FLOOR-ID of this
floor. If the client does not want to receive information about any
floor any longer, it sends a FloorInfoWanted message with no FLOOR-ID
TLV.
12.1.2 Receiving a Response
A message from the floor control server is considered to be a
response to the FloorInfoWanted message if the message from the floor
control server has the same Conference ID, Transaction ID, and User
ID as the FloorRequest message, as described in Section 8.1.
On reception of the FloorInfoWanted message, the floor control server
will respond with a FloorInfo message or with an Error message. If
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the response is a FloorInfo message, it will contain information
about one of the floors the client requested information about. If
the client did not include any FLOOR-ID TLV in its FloorInfoWanted
message, the FloorInfo message from the floor control server will not
include any either.
FloorInfo messages which carry information about a floor contain a
FLOOR-ID TLV that identifies the floor. After this TLV, FloorInfo
messages contain information about existing (one or more) floor
request that relate to that floor. The information about each
particular floor request consist of a FLOOR-REQUEST-ID TLV that
identifies the floor request followed by a set of TLVs that provide
information about the floor request.
After the first FloorInfo, the floor control server will continue
sending FloorInfo messages periodically informing the client about
changes on the floors the client requested information about.
12.2 Requesting Information about Floor Requests
A client can obtain information about the status of one or several
floor requests in different ways, which include using BFCP and using
out-of-band mechanisms. Clients using BFCP to obtain such
information use the procedures described in this section.
Clients request information about the current status of one or
several floor requests by sending a FloorRequestInfoWanted message to
the floor control server.
Requesting information about a particular floor request is useful
in a number of situations. For example, on reception of a
FloorRequest message, a floor control server may choose to return
FloorRequestInfo messages only when the floor request changes its
state (e.g., from Accepted to Granted), but not when the floor
request advances in its queue. In this situation, if the user
requests it, the floor participant can use a
FloorRequestInfoWanted message to poll the floor control server
for the status of the floor request.
FloorRequestInfoWanted messages can also be used to request
information on all the floor requests associated with a floor
participant. For example, a floor participant, after experiencing
connectivity problems (e.g., its TCP connection with the floor
control server was down for a while and eventually was
re-established), may need to request information about all the
still existing floor requests associated to the floor participant.
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12.2.1 Sending a FloorRequestInfoWanted Message
The ABNF in Section 5.3.3 describes the TLVs that a
FloorRequestInfoWanted message can contain. In addition, the ABNF
specifies normatively which of these TLVs are mandatory, and which
ones are optional.
The client sets the Conference ID in the FIXED-HEADER and the
TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the client follows the rules in Section 9.1 which
relate to the authentication of the message (i.e., to the DIGEST
TLV). The client must insert a USER-ID TLV, which will be used by
the floor control server to authenticate and authorize the request.
If the client wants to request the status of a single floor request,
it MUST insert a FLOOR-REQUEST-ID TLV that identifies the floor
request at the floor control server.
The client can also request information about all the ongoing floor
requests associated with a particular participant. In this case, the
client MUST NOT insert a FLOOR-REQUEST-ID TLV. If the beneficiary of
the floor requests the client is requesting information about is not
the client issuing the FloorRequestInfoWanted message (which is
identified by the USER-ID TLV in the message) the client MUST insert
a BENEFICIARY-ID TLV.
12.2.2 Receiving a Response
A message from the floor control server is considered to be a
response to the FloorRequestInfoWanted message if the message from
the floor control server has the same Conference ID, Transaction ID,a
nd User ID as the FloorRequestInfoWanted message, as described in
Section 8.1.
If the response is a FloorRequestInfo message, the client obtains
information about the status of the FloorRequest the client requested
information about in a REQUEST-STATUS TLVs. If the client requested
information about several floor requests, the FloorRequestInfo
message will carry several FLOOR-REQUEST-ID TLVs. Each
FLOOR-REQUEST-ID TLV will be followed by TLVs (which will include a
REQUEST-STATUS TLV) providing information about the floor request
identified by the FLOOR-REQUEST-ID TLV.
If the response is an Error message, the floor control server could
not process the FloorRequestInfoWanted message for some reason, which
is described in the Error message.
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12.3 Obtaining the Capabilities of a Floor Control Server
A client that wishes to obtain the capabilities of a floor control
server does so by sending a Hello message to the floor control
server.
12.3.1 Sending a Hello Message
The ABNF in Section 5.3.9 describes the TLVs that a Hello message can
contain. In addition, the ABNF specifies normatively which of these
TLVs are mandatory, and which ones are optional.
The client sets the Conference ID in the FIXED-HEADER and the
TRANSACTION-ID TLV following the rules given in Section 8.1.
Additionally, the client follows the rules in Section 9.1 which
relate to the authentication and the protection of the integrity of
the message (i.e., to the DIGEST TLV). The client must insert a
USER-ID TLV, which will be used by the floor control server to
authenticate and authorize the request.
12.3.2 Receiving Responses
A message from the floor control server is considered a response to
the Hello message by the client if the message from the floor control
server has the same Conference ID, Transaction ID, and User ID as the
Hello message, as described in Section 8.1.
If the response is a HelloAck message, the floor control server could
process successfully the Hello message. The SUPPORTED-TLVS TLV
indicates which TLVs are supported by the server.
If the response is an Error message, the floor control server could
not process the Hello message for some reason, which is described in
the Error message.
13. Floor Control Server Operations
This section specifies how floor control servers can perform
different operations, such as granting a floor, using the protocol
elements described in earlier sections.
On reception of a message from a client, the floor control server
MUST check whether or not the value of the Conference ID matched an
existing conference. If it does not, the floor control server SHOULD
send an Error message, as described in Section 13.7, with Error code
0 (Conference does not Exist).
On reception of a message from a client, the floor control server
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follows the rules in Section 9.2, which relate to the authentication
of the message.
On reception of a message from a client, the floor control server
MUST check whether or not it understands all the mandatory ( 'M' bit
set) TLVs in the message. If the floor control server does not
understand all of them, the floor control server SHOULD send an Error
message, as described in Section 13.7, with Error code 2
(Authentication Failed). The Error message SHOULD list the TLVs that
were not understood.
13.1 Reception of a FloorRequest Message
On reception of a FloorRequest message, the floor control server
follows the rules in Section 9.2 which relate to client
authentication and authorization. If while processing the
FloorRequest message, the floor control server encounters an error,
it SHOULD generate an Error response following the procedures
described in Section 13.7
BFCP allows floor participants to have several ongoing floor
requests for the same floor (e.g., the same floor participant can
occupy more than one position in a queue at the same time). A
floor control server that only supports a certain number of
ongoing floor requests per floor participant (e.g., one) can use
Error Code 9 (You have Already Reached the Maximum Number of
Ongoing Floor Requests for this Floor) to inform the floor
participant.
13.1.1 Generating the First FloorRequestInfo Message
The successful processing of a FloorRequest message by a floor
control server involves generating one or several FloorRequestInfo
messages, the first of which SHOULD be generated as soon as possible.
If the floor control server cannot accept, grant, or deny the floor
request right away (e.g., a decision from a chair is needed), it
SHOULD use a Request Status value of Pending in the REQUEST-STATUS
TLV of the first FloorRequestInfo message it generates.
The policy a floor control server follows to grant or deny floors
is outside the scope of this document. A given floor control
server may perform these decisions automatically while another may
contact a human acting as a chair everytime a decision needs to be
made.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the FloorRequest into the
FloorRequestInfo, as described in Section 8.2. Additionally, the
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floor control server copies (if present) the BENEFICIARY-ID TLV from
the FloorRequest into the FloorRequestInfo.
The floor control server MUST assign an identitifier that is unique
within the conference to this floor request, and insert it in a
FLOOR-REQUEST-ID TLV into the FloorRequestInfo message. This
indentifier will be used by the floor participant (or by a chair or
chairs) to refer to this specific floor request in the future.
The floor control server copies the FLOOR-ID TLVs from the
FloorRequest into the FloorRequestInfo. These FLOOR-ID TLVs identify
the floors being requested (i.e., the floors associated with this
particular floor request).
The floor control server also copies (if present) the PRIORITY TLV
from the FloorRequest into the FloorRequestInfo. The Priority value
requested by the floor participant is only a hint, and does not
necessarily need to be taken into consideration to decide whether to
grant or not the floor request.
13.1.2 Generation of Subsequent FloorRequestInfo Messages
A floor request is considered to be ongoing as long as it is not in
the Cancelled, Released, or Revoked states. If the REQUEST-STATUS
TLV of the first FloorRequestInfo message generated by the floor
control server did not indicate any of these states, the floor
control server will need to send subsequent FloorRequestInfo
messages.
When the status of the floor request changes, the floor control floor
control server SHOULD send new FloorRequestInfo messages with the
appropriate Request Status. These FloorRequestInfo messages MUST
contain a FLOOR-REQUEST-ID TLV equal to the one sent in the first
FloorRequestInfo message, but MUST NOT contain any TRANSACTION-ID
TLV. (The Floor Request ID identifies the floor request the
FloorRequestInfo applies to.)
The FIXED-HEADER and the rest of the TLVs (except for the
HUMAN-READABLE-INFO TLV) are the same as in the first
FloorRequestInfo message.
The rate at which the floor control server sends FloorRequestInfo
messages is a matter of local policy. A floor control server may
choose to send a new FloorRequestInfo message every time the floor
request moves in the floor request queue while another may choose
to only send a new FloorRequestInfo message when the floor request
is Granted or Denied.
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The floor control server may add a HUMAN-READABLE-INFO TLV to any of
the FloorRequestInfo messages it generates to provide extra
information about its decisions regarding the floor request (e.g.,
why it was denied).
Floor participants and floor chairs may request to be informed
about the status of a floor following the procedures in Section
12.1. If the processing of a floor request changes the status of
a floor (e.g., the floor request is granted and consequently the
floor has a new holder), the floor control server needs to follow
the procedures in Section 13.4 to inform the clients that have
requested that information
The floor control server can discard the state information about a
particular floor request when this reaches a status of Cancelled,
Released, or Revoked.
13.2 Reception of a FloorRequestInfoWanted Message
On reception of a FloorRequestInfoWanted message, the floor control
server follows the rules in Section 9.2 which relate to client
authentication and authorization. If while processing the
FloorRequestInfoWanted message, the floor control server encounters
an error, it SHOULD generate an Error response following the
procedures described in Section 13.7
The successful processing of a FloorRequestInfoWanted message by a
floor control server involves generating a FloorRequestInfo message,
which SHOULD be generated as soon as possible.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the FloorRequestInfoWanted
message into the FloorRequestInfo message, as described in Section
8.2.
13.2.1 Information on a Single Floor Request
If the FloorRequestInfoWanted message carries a FLOOR-REQUEST-ID, the
sender of the message is requesting information about the floor
request identified by the FLOOR-REQUEST-ID TLV. The floor control
server copies the FLOOR-REQUEST-ID TLV from the
FloorRequestInfoWanted message into the FloorRequestInfo message.
The floor control server adds FLOOR-ID TLVs to the FloorRequestInfo
message identifying the floors being requested (i.e., the floors
associated with the floor request identified by the FLOOR-REQUEST-ID
TLV).
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The floor control server may also add a PRIORITY TLV with the
Priority value requested for the floor request and a
HUMAN-READABLE-INFO TLV with extra information about the floor
request.
The floor control server adds a REQUEST-STATUS TLV with the current
status of the floor request.
13.2.2 Information on the Floor Requests Associated to a Participant
If the FloorRequestInfoWanted message does not carry a
FLOOR-REQUEST-ID TLV, the sender of the message is requesting
information about all the floor requests from a given participant.
This participant is identified by a BENEFICIARY-ID TLV or, in the
absence of a BENEFICIARY-ID TLV, by a USER-ID TLV.
The floor control server copies (if present) the BENEFICIARY-ID TLV
from the FloorRequestInfoWanted message into the FloorRequestInfo
message. Additionally, the floor control server may provide extra
information about the participant by adding a USER-DISPLAY-NAME TLV,
a USER-URI TLV, or both to the FloorRequestInfo message.
The floor control server adds a FLOOR-REQUEST-ID TLV for each floor
request associated to the participant. Each FLOOR-REQUEST-ID TLV is
followed by a number of TLVs which provide information about the
floor request. The floor control server generates the TLVs that
follow each FLOOR-REQUEST-ID following the rules in Section 13.2.1
13.3 Reception of a FloorRelease Message
On reception of a FloorRelease message, the floor control server
follows the rules in Section 9.2 which relate to client
authentication and authorization. If while processing the
FloorRelease message, the floor control server encounters an error,
it SHOULD generate an Error response following the procedures
described in Section 13.7
The successful processing of a FloorRelease message by a floor
control server involves generating a FloorRequestInfo message, which
SHOULD be generated as soon as possible.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the FloorRelease message
into the FloorRequestInfo message, as described in Section 8.2.
The FloorRelease message identifies the floor request it applies to
using a FLOOR-REQUEST-ID. If the beneficiary of the floor request is
not the participant identified by the USER-ID TLV in the FloorRelease
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message, the floor control server adds a BENEFICIARY-ID TLV to the
FloorRequestInfo message identifying the beneficiary of the floor
request. Additionally, the floor control server may provide extra
information about the beneficiary of the floor request by adding a
USER-DISPLAY-NAME TLV, a USER-URI TLV, or both to the
FloorRequestInfo message.
The floor control server copies the FLOOR-REQUEST-ID TLV from the
FloorRelease message into the FloorRequestInfo message.
The floor control server adds FLOOR-ID TLVs to the FloorRequestInfo
message identifying the floors being requested (i.e., the floors
associated with the floor request identified by the FLOOR-REQUEST-ID
TLV).
The floor control server may also add a PRIORITY TLV with the
Priority value requested for the floor request and a
HUMAN-READABLE-INFO TLV with extra information about the floor
request.
The floor control server adds a REQUEST-STATUS TLV to the
FloorRequestInfo message. The Request Status value SHOULD be
Released, if the floor (or floors) had been previously granted, or of
Cancelled, if the floor (or floors) had not been previously granted.
13.4 Reception of a FloorInfoWanted Message
On reception of a FloorInfoWanted message, the floor control server
follows the rules in Section 9.2 which relate to client
authentication. If while processing the FloorRelease message, the
floor control server encounters an error, it SHOULD generate an Error
response following the procedures described in Section 13.7
A floor control server receiving a FloorInfoWanted message from a
client SHOULD keep this client informed about the status of the
floors identified by FLOOR-ID TLVs in the FloorInfoWanted message.
Floor Control Servers keep clients informed by using FloorInfo
messages.
An individual FloorInfo message carries information about a single
floor. So, when a FloorInfoWanted message requests information about
more than one floor, the floor control server needs to send separate
FloorInfo messages for different floors.
The information FloorInfoWanted messages carry may depend on the user
requesting the information. For example, a chair may be able to
receive information about pending requests while a regular user may
not be authorized to do so.
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13.4.1 Generation of the First FloorInfo Message
The successful processing of a FloorInfoWanted message by a floor
control server involves generating one or several FloorInfo messages,
the first of which SHOULD be generated as soon as possible.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the FloorInfoWanted message
into the FloorInfo message, as described in Section 8.2.
If the FloorInfoWanted message did not contain any FLOOR-ID TLV, the
floor control server sends the FloorInfo message without adding any
additional TLV and does not send any subsequent FloorInfo message to
the floor participant.
If the FloorInfoWanted message contained one or more FLOOR-ID TLVs,
the floor control server chooses one among them and adds this
FLOOR-ID TLV to the FloorInfo message. The floor control server adds
a FLOOR-REQUEST-ID TLV for each floor request associated to the
floor. Each FLOOR-REQUEST-ID TLV is followed by a number of TLVs
which provide information about the floor request.
For each FLOOR-REQUEST-ID TLV, the floor control server may add a
BENEFICIARY-ID TLV identifying the requester of the floor and a
USER-DISPLAY-NAME TLV, a USER-URI TLV, or both providing information
about the requester. Additionally, the floor control server adds
FLOOR-ID TLVs to the FloorInfo message identifying the floors being
requested (i.e., the floors associated with the floor request
identified by the FLOOR-REQUEST-ID TLV).
The floor control server may also add a PRIORITY TLV with the
Priority value requested for the floor request and a
HUMAN-READABLE-INFO TLV with extra information about the floor
request.
The floor control server adds a REQUEST-STATUS TLV with the current
status of the floor request.
13.4.2 Generation of Subsequent FloorInfo Messages
If the FloorInfoWanted message carried more than one FLOOR-ID TLV,
the floor control server SHOULD generate a FloorInfo message for each
of them (except for the FLOOR-ID TLV chosen for the first FloorInfo
message) as soon as possible. These FloorInfo messages are generated
following the same rules as for the first FloorInfo message (see
Section 13.4.1, but without adding a TRANSACTION TLV.
After generating these messages, the floor control server sends
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FloorInfo messages periodically keeping the client informed about all
the floors the client requested information about. These messages
MUST NOT carry a TRANSACTION-ID TLV.
The rate at which the floor control server sends FloorInfo
messages is a matter of local policy. A floor control server may
choose to send a new FloorInfo message every time a new floor
request arrives while another may choose to only send a new
FloorInfo message when a new floor request is Granted.
13.5 Reception of a ChairAction Message
On reception of a ChairAction message, the floor control server
follows the rules in Section 9.2 which relate to client
authentication and authorization. If while processing the
ChairAction message, the floor control server encounters an error, it
SHOULD generate an Error response following the procedures described
in Section 13.7
The successful processing of a ChairAction message by a floor control
server involves generating a ChairActionAck message, which SHOULD be
generated as soon as possible.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the ChairAction message
into the ChairActionAck message, as described in Section 8.2.
The floor control server needs to take into consideration the
operation requested in the ChairAction message (e.g., granting a
floor), but does not necessarily need to perform it as requested by
the floor chair. The operation that the floor control server
performs depends on the ChairAction message and on the internal state
of the floor control server.
For example, a floor chair may send a ChairAction message granting a
floor which was requested as part of an atomic floor request
operation that involved several floors. Even if the chair
responsible for one of the floors instructs the floor control server
to grant the floor, the floor control server will not grant it until
the chairs responsible for the other floors agree to grant them as
well.
So, the floor control server is ultimately responsible to keep a
coherent floor state using instructions from floor chairs as input to
this state.
If the new Status in the ChairAction message is Accepted and all the
bits of the Queue Position field are zero, the floor chair is
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requesting the floor control server to assign a queue position (e.g.,
the last in the queue) to the floor request based on the local policy
of the floor control server. (Of course, such a request only applies
in case the floor control server implements a queue.)
13.6 Reception of a Hello Message
On reception of a Hello message, the floor control server follows the
rules in Section 9.2 which relate to client authentication. If while
processing the Hello message, the floor control server encounters an
error, it SHOULD generate an Error response following the procedures
described in Section 13.7
The successful processing of a Hello message by a floor control
server involves generating a HelloAck message, which SHOULD be
generated as soon as possible. The floor control server copies the
Conference ID, the TRANSACTION-ID, and the USER-ID TLVs from the
Hello into the HelloAck, as described in Section 8.2.
The floor control server adds a SUPPORTED-TLVS TLV to the HelloAck
message listing all the TLVs supported by the floor control server.
13.7 Error Message Generation
Error messages are always sent in response to a previous message from
the client as part of a client-initiated transaction. The ABNF in
Section 5.3.11 describes the TLVs that an Error message can contain.
In addition, the ABNF specifies normatively which of these TLVs are
mandatory, and which ones are optional.
The floor control server copies the Conference ID, the
TRANSACTION-ID, and the USER-ID TLVs from the message from the client
into the Error message, as described in Section 8.2.
The floor control server adds an ERROR-CODE TLV to the Error message.
The ERROR-CODE TLV contains an Error Code from Table 4.
Additionally, the floor control server may add a HUMAN-READABLE-INFO
TLV with extra information about the error.
14. Security Considerations
BFCP uses message signatures to provide client authentication and TLS
to provide floor control server authentication, replay and integrity
protection, and confidentiality. It is RECOMMENDED that TLS with
non-null encryption is always used and that the first message from a
client over a given TLS connection is signed using the DIGEST TLV.
In any case, clients and floor control servers MAY use other security
mechanisms as long as they provide similar security properties.
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The remainder of this Section analyzes some of the threats against
BFCP and how they are addressed.
An attacker may attempt to impersonate a client (a floor participant
or a floor chair) in order to generate forged floor requests or to
grant or deny existing floor requests. Client impersonation is
avoided by having clients sign their messages. A nonce is included
in the signature to ensure the freshness of the message. If the
client is using a TLS connection to communicate with the floor
control server, it is enough that the client signs its first message
over the TLS connection. The floor control server assumes that
attackers cannot hickjack the TLS connection and, therefore, that
subsequent messages over the TLS connection come from the client that
was initially authenticated.
An attacker may attempt to impersonate a floor control server. A
successful attacker would be able to make clients think that they
hold a particular floor so that they would try to access a resource
(e.g., sending media) without having legitimate rights to access it.
Floor control server impersonation is avoided by having floor control
servers present their server certificates at TLS connection
establishment time.
Attackers may attempt to modify messages exchanged by a client and a
floor control server. The integrity protection provided by TLS
connections prevents this attack.
An attacker may attempt to fetch a valid message sent by a client to
a floor control server and replay it at a later point. If the
attacker attempts to replay it over the TLS connection between the
client and the floor control server, TLS mechanisms discard it at the
receiver side. Still, if the message was signed, the attacker may
attempt to establish a new TLS connection with the floor control
server and replay the message over the new connection. Using TLS
confidentiality prevents this attack because the attacker cannot
access the contents of the message in the first place. Additionally,
if the attacker attempts to replay the encrypted message over the new
connection, TLS mechanisms would discard it at the receiver side.
Therefore, it is strongly RECOMMENDED that TLS is used with a
non-null encryption algorithm.
Attackers may attempt to pick messages from the network to get access
to confidential information between the floor control server and a
client (e.g., why a floor request was denied). TLS confidentiality
prevents this attack.
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15. IANA Considerations
This document instructs the IANA to create a new registry for BFCP
parameters called "Binary Floor Control Protocol (BFCP) Parameters".
This new registry has a number of subregistries, which are described
in the following Sections
15.1 Attribute Subregistry
This Section establishes the Attribute subregistry under the BFCP
Parameters registry. As per the terminology in RFC 2434 [5], the
registration policy for BFCP attributes shall be "Specification
Required". For the purposes of this subregistry, the BFCP attributes
for which IANA registration is requested MUST be defined by a
standards-track RFC. Such RFC MUST specify the attribute's type,
name, format, and semantics.
For each BFCP attribute, the IANA registers its type, its name, and
the reference to the RFC where the attribute is defined. The
following table contains the initial values of this subregistry.
+------+---------------------+------------+
| Type | Attribute | Reference |
+------+---------------------+------------+
| 0 | FLOOR-ID | [RFC XXXX] |
| 1 | USER-ID | [RFC XXXX] |
| 2 | BENEFICIARY-ID | [RFC XXXX] |
| 3 | TRANSACTION-ID | [RFC XXXX] |
| 4 | FLOOR-REQUEST-ID | [RFC XXXX] |
| 5 | HUMAN-READABLE-INFO | [RFC XXXX] |
| 6 | DIGEST | [RFC XXXX] |
| 7 | REQUEST-STATUS | [RFC XXXX] |
| 8 | ERROR-CODE | [RFC XXXX] |
| 9 | USER-DISPLAY-NAME | [RFC XXXX] |
| 10 | USER-URI | [RFC XXXX] |
| 11 | PRIORITY | [RFC XXXX] |
| 12 | NONCE | [RFC XXXX] |
| 13 | SUPPORTED-TLVS | [RFC XXXX] |
+------+---------------------+------------+
Table 5: Initial values of the BFCP Attribute subregistry
15.2 Primitive Subregistry
This Section establishes the Primitive subregistry under the BFCP
Parameters registry. As per the terminology in RFC 2434 [5], the
registration policy for BFCP primitives shall be "Specification
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Required". For the purposes of this subregistry, the BFCP primitives
for which IANA registration is requested MUST be defined by a
standards-track RFC. Such RFC MUST specify the primitive's value,
name, format, and semantics.
For each BFCP primitive, the IANA registers its value, its name, and
the reference to the RFC where the primitive is defined. The
following table contains the initial values of this subregistry.
+-------+------------------------+------------+
| Value | Primitive | Reference |
+-------+------------------------+------------+
| 0 | FloorRequest | [RFC XXXX] |
| 1 | FloorRelease | [RFC XXXX] |
| 2 | FloorRequestInfoWanted | [RFC XXXX] |
| 3 | FloorRequestInfo | [RFC XXXX] |
| 4 | FloorInfoWanted | [RFC XXXX] |
| 5 | FloorInfo | [RFC XXXX] |
| 6 | ChairAction | [RFC XXXX] |
| 7 | ChairActionAck | [RFC XXXX] |
| 8 | Hello | [RFC XXXX] |
| 9 | HelloAck | [RFC XXXX] |
| 10 | Error | [RFC XXXX] |
+-------+------------------------+------------+
Table 6: Initial values of the BFCP primitive subregistry
15.3 Request Status Subregistry
This Section establishes the Request Status subregistry under the
BFCP Parameters registry. As per the terminology in RFC 2434 [5],
the registration policy for BFCP request status shall be
"Specification Required". For the purposes of this subregistry, the
BFCP request status for which IANA registration is requested MUST be
defined by a standards-track RFC. Such RFC MUST specify the value
and the semantics of the request status.
For each BFCP request status, the IANA registers its value, its
meaning, and the reference to the RFC where the request status is
defined. The following table contains the initial values of this
subregistry.
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+-------+-----------+------------+
| Value | Status | Reference |
+-------+-----------+------------+
| 0 | Pending | [RFC XXXX] |
| 1 | Accepted | [RFC XXXX] |
| 2 | Granted | [RFC XXXX] |
| 3 | Denied | [RFC XXXX] |
| 4 | Cancelled | [RFC XXXX] |
| 5 | Released | [RFC XXXX] |
| 6 | Revoked | [RFC XXXX] |
+-------+-----------+------------+
Table 7: Initial values of the Request Status subregistry
15.4 Error Code Subregistry
This Section establishes the Error Code subregistry under the BFCP
Parameters registry. As per the terminology in RFC 2434 [5], the
registration policy for BFCP error codes shall be "Specification
Required". For the purposes of this subregistry, the BFCP error
codes for which IANA registration is requested MUST be defined by a
standards-track RFC. Such RFC MUST specify the value and the
semantics of the error code, and any Error Specific Details that
apply to it.
For each BFCP primitive, the IANA registers its value, its meaning,
and the reference to the RFC where the primitive is defined. The
following table contains the initial values of this subregistry.
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+----------------------+----------------------+---------------------+
| Value | Meaning | Reference |
+----------------------+----------------------+---------------------+
| 0 | Conference does not | [RFC XXXX] |
| | Exist | |
| 1 | Authentication | [RFC XXXX] |
| | Failed | |
| 2 | Unknown Mandatory | [RFC XXXX] |
| | TLV | |
| 3 | Floor Request ID | [RFC XXXX] |
| | Does Not Exist | |
| 4 | Unauthorized | [RFC XXXX] |
| | Operation | |
| 5 | User does not Exist | [RFC XXXX] |
| 6 | Invalid Nonce | [RFC XXXX] |
| 7 | DIGEST TLV Required | [RFC XXXX] |
| 8 | Invalid Floor ID | [RFC XXXX] |
| 9 | You have Already | [RFC XXXX] |
| | Reached the Maximum | |
| | Number of Ongoing | |
| | Floor Requests for | |
| | this Floor | |
+----------------------+----------------------+---------------------+
Table 8: Initial Values of the Error Code subregistry
16. Acknowledgments
The XCON WG chairs, Adam Roach and Alan Johnston, provided useful
ideas for this document. Additionally, Xiaotao Wu, Paul Kyzivat,
Jonathan Rosenberg, and Miguel A. Garcia-Martin provided useful
comments.
17. References
17.1 Normative References
[1] Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-Hashing
for Message Authentication", RFC 2104, February 1997.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[3] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
[4] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC
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2246, January 1999.
[5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.
[6] Chown, P., "Advanced Encryption Standard (AES) Ciphersuites for
Transport Layer Security (TLS)", RFC 3268, June 2002.
[7] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD
63, RFC 3629, November 2003.
17.2 Informational References
[8] Handley, M. and V. Jacobson, "SDP: Session Description
Protocol", RFC 2327, April 1998.
[9] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, June 2002.
[10] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
Session Description Protocol (SDP)", RFC 3264, June 2002.
[11] Schulzrinne, H., "Requirements for Floor Control Protocol",
draft-ietf-xcon-floor-control-req-02 (work in progress),
October 2004.
[12] Rosenberg, J., "A Framework for Conferencing with the Session
Initiation Protocol",
draft-ietf-sipping-conferencing-framework-03 (work in
progress), October 2004.
[13] Barnes, M. and C. Boulton, "A Framework for Centralized
Conferencing", draft-barnes-xcon-framework-00 (work in
progress), October 2004.
[14] Camarillo, G., "Session Description Protocol (SDP) Format for
Binary Floor Control Protocol (BFCP) Streams",
draft-camarillo-mmusic-sdp-bfcp-00 (work in progress), April
2005.
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Authors' Addresses
Gonzalo Camarillo
Ericsson
Hirsalantie 11
Jorvas 02420
Finland
EMail: Gonzalo.Camarillo@ericsson.com
Joerg Ott
Universitaet Bremen
MZH 5180
Bibliothekstr. 1
Bremen D-28359
Germany
EMail: jo@tzi.org
Keith Drage
Lucent Technologies
Windmill Hill Business Park
Swindon
Wiltshire SN5 6PP
UK
EMail: drage@lucent.com
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