draft-ietf-mmusic-sdp-comedia-00.txt   draft-ietf-mmusic-sdp-comedia-01.txt 
INTERNET-DRAFT D. Yon INTERNET-DRAFT D. Yon
Document: draft-ietf-mmusic-sdp-comedia-00.txt Dialout.Net Document: draft-ietf-mmusic-sdp-comedia-01.txt Dialout.Net
Expires August 2001 February 2001 Expires April 2002 October 2001
Connection-Oriented Media Transport in SDP Connection-Oriented Media Transport in SDP
<draft-ietf-mmusic-sdp-comedia-00.txt> <draft-ietf-mmusic-sdp-comedia-01.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at line 36 skipping to change at line 36
The list of Internet-Draft Shadow Directories can be accessed at: The list of Internet-Draft Shadow Directories can be accessed at:
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
Abstract Abstract
This document describes how to express media transport over This document describes how to express media transport over
connection-oriented protocols using the Session Description Protocol connection-oriented protocols using the Session Description Protocol
(SDP). It defines three new protocol identifiers: TCP, TLS and (SDP). It defines two new protocol identifiers: TCP and TLS. It
SCTP. It also defines the syntax and semantics for an SDP also defines the syntax and semantics for an SDP "direction"
"direction" attribute that describes the connection setup procedure. attribute that describes the connection setup procedure.
Yon 1 Yon 1
Introduction Introduction
The Session Description Protocol [SDP] provides a general-purpose The Session Description Protocol [SDP] provides a general-purpose
format for describing multimedia sessions in announcements or format for describing multimedia sessions in announcements or
invitations. SDP uses an entirely textual data format (the US-ASCII invitations. SDP uses an entirely textual data format (the US-ASCII
subset of [UTF-8]) to maximize portability among transports. SDP subset of [UTF-8]) to maximize portability among transports. SDP
does not define a protocol, but only the syntax to describe a does not define a protocol, but only the syntax to describe a
multimedia session with sufficient information to discover and multimedia session with sufficient information to discover and
participate in that session. Session descriptions may be sent using participate in that session. Session descriptions may be sent using
any number of existing application protocols for transport (e.g., any number of existing application protocols for transport (e.g.,
SAP, SIP, RTSP, email, HTTP, etc.). SAP, SIP, RTSP, email, HTTP, etc.).
Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [7]
and indicate requirement levels for compliant implementations.
Motivation Motivation
[SDP] describes two protocol identifiers: RTP/AVP and UDP, both of [SDP] describes two protocol identifiers: RTP/AVP and UDP, both of
which are unreliable, connectionless protocols, an appropriate which are unreliable, connectionless protocols, an appropriate
choice for multimedia streams. There are, however, applications for choice for multimedia streams. There are, however, applications for
which the connection-oriented transports such as TCP or SCTP is more which the connection-oriented transports such as TCP are more
appropriate, but [SDP] provides no way to describe a session that appropriate, but [SDP] provides no way to describe a session that
uses protocols other than RTP or UDP. uses protocols other than RTP or UDP.
Connection-oriented protocols introduce a new factor when describing Connection-oriented protocols introduce a new factor when describing
a session: not only must it be possible to express that a protocol a session: not only must it be possible to express that a protocol
will be based on this protocol, but it must also describe the will be based on this protocol, but it must also describe the
connection setup procedure. connection setup procedure.
1 Protocol Identifiers 1 Protocol Identifiers
1.1 TCP 1.1 TCP
The TCP protocol identifier is similar to the UDP protocol The TCP protocol identifier is similar to the UDP protocol
identifier in that it only describes the transport protocol without identifier in that it only describes the transport protocol without
any connotation as to the upper-layer protocol. An m= line that any connotation as to the upper-layer protocol. An m= line that
specifies TCP must further qualify the protocol using a fmt specifies "TCP" MUST further qualify the protocol using a fmt
identifier (see [SDP] Appendix B). identifier (see [SDP] Appendix B).
1.2 SCTP 1.2 TLS
The SCTP protocol identifier, like TCP above, only describes the
transport protocol without any connotation as to the upper-layer
protocol. An m= line that specifies SCTP indicates that media will
be transports using the SCTP protocol [SCTP], with an upper-layer
protocol specified by the fmt identifier.
1.3 TLS
The TLS protocol identifier specifies that the session will use the The TLS protocol identifier specifies that the session will use the
Transport Layer Security protocol [TLS] with an implied transport Transport Layer Security protocol [TLS] with an implied transport
protocol of TCP. To describe a media session that uses TLS over protocol of TCP. To describe a media session that uses TLS over
TCP, the protocol identifier TLS must be specified in the m= line. TCP, the protocol identifier "TLS" must be specified in the m= line.
An m= line that specifies TLS must further qualify the protocol An m= line that specifies TLS MUST further qualify the protocol
using a fmt identifier. using a fmt identifier.
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2 Direction Attribute 2 Direction Attribute
An important attribute of connection-oriented protocols is the setup An important attribute of connection-oriented protocols is the setup
procedure. One endpoint needs to initiate the connection and the procedure. One endpoint needs to initiate the connection and the
other endpoint needs to accept the connection. The direction other endpoint needs to accept the connection. The direction
attribute is used to describe these roles, and the syntax is as attribute is used to describe these roles, and the syntax is as
follows: follows:
a=direction:<role> <source-port> a=direction:<role> [<source-address>]
The <role> is one of the following: The <role> is one of the following:
passive: The endpoint will accept an incoming connection. passive: The endpoint will accept an incoming connection.
active: The endpoint will initiate an outgoing connection. active: The endpoint will initiate an outgoing connection.
both: The endpoint will both accept an incoming connection both: The endpoint will both accept an incoming connection
and will initiate an outgoing connection. and will initiate an outgoing connection.
The <source-port> is an optional value that may only be specified in reuse: The endpoint will use the connection that has already
the context of direction:active or direction:both. been established with the opposite endpoint.
The <source-address> is a sequence of values that describe the
address and port number from where the connection will originate,
and consists of the following values:
nettype addrtype unicast-address [port]
The <source-address> is an optional value that may be specified with
direction:active, direction:both, or direction:reuse. Within the
<source-address>, the source port number is RECOMMENDED but may be
omitted.
2.1 Semantics of direction:passive 2.1 Semantics of direction:passive
By specifying direction:passive, the endpoint indicates that the By specifying direction:passive, the endpoint indicates that the
port number specified in the m= line is available to accept a port number specified in the m= line is available to accept a
connection from the other endpoint. connection from the other endpoint. The endpoint MUST NOT specify a
<source-address> after direction:passive.
2.2 Semantics of direction:active 2.2 Semantics of direction:active
By specifying direction:active, the endpoint indicates that it will By specifying direction:active, the endpoint indicates that it will
initiate a connection to the port number on the m= line of the other initiate a connection to the port number on the m= line of the other
endpoint. The port number on its own m= line is irrelevant and is endpoint. The port number on its own m= line is irrelevant, and the
to be ignored by the other endpoint. Nevertheless, since the m= opposite endpoint MUST NOT attempt to initiate a connection to the
line must contain a valid port number, the endpoint specifying port number specified there. Nevertheless, since the m= line must
direction:active should specify a port number of 9 (the discard contain a valid port number, the endpoint specifying
port) on its m= line. The endpoint must not specify a port number direction:active SHOULD specify a port number of 9 (the discard
port) on its m= line. The endpoint MUST NOT specify a port number
of zero, as that carries other semantics in [SDP]. of zero, as that carries other semantics in [SDP].
The endpoint may optionally specify the port number from which it Yon INTERNET-DRAFT Expires January 2002 3
will initiate the connection in the <source-port> position on the a= The endpoint SHOULD specify the address and port number from which
line. it will initiate the connection in the <source-address> position on
the a= line.
2.3 Semantics of direction:both 2.3 Semantics of direction:both
By specifying direction:both, the endpoint indicates that it will By specifying direction:both, the endpoint indicates that it will
both accept a TCP connection on the port number of its own m= line, both accept a TCP connection on the port number of its own m= line,
and that it will also initiate a connection to the port number on and that it will also initiate a connection to the port number on
the m= line of the other endpoint. As with direction:active, the the m= line of the other endpoint.
endpoint may optionally specify the port number from which it will
initiate the connection in the <source-port> position on the a= As with direction:active, the endpoint SHOULD specify the address
line. and port number from which it will initiate the connection in the
<source-address> position on the a= line.
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Since this attribute describes behavior that is similar to Since this attribute describes behavior that is similar to
connectionless media descriptions in [SDP], it is the default value connectionless media descriptions in [SDP], it is the default value
for the direction attribute and is therefore optional. for the direction attribute and is therefore optional.
Endpoints may choose to specify direction:both for one or more of Endpoints may choose to specify direction:both for one or more of
the following reasons: the following reasons:
1) The endpoint has no preference as to whether it accepts or 1) The endpoint has no preference as to whether it accepts or
initiates the connection, and therefore is offering the remote initiates the connection, and therefore is offering the remote
endpoint a choice of connection setup procedures. endpoint a choice of connection setup procedures.
skipping to change at line 174 skipping to change at line 187
prevent either endpoint from initiating or accepting the prevent either endpoint from initiating or accepting the
connection. Therefore both endpoints will attempt to initiate connection. Therefore both endpoints will attempt to initiate
a connection in hopes that at least one will succeed. a connection in hopes that at least one will succeed.
3) The endpoints intend to use two connections to transport the 3) The endpoints intend to use two connections to transport the
media, and one must be initiated by the remote endpoint and media, and one must be initiated by the remote endpoint and
the other must be initiated by the local endpoint. the other must be initiated by the local endpoint.
If one endpoint specifies either direction:active or If one endpoint specifies either direction:active or
direction:passive and the other specifies direction:both, both direction:passive and the other specifies direction:both, both
endpoints must behave as if the latter had specified the inverse endpoints MUST behave as if the latter had specified the inverse
direction of the former. For example, specifying direction:both direction of the former. For example, specifying direction:both
when the other endpoint specifies direction:active should cause both when the other endpoint specifies direction:active SHALL cause both
endpoints to behave as if the former had specified endpoints to behave as if the former had specified
direction:passive. Conversely, specifying direction:both when the direction:passive. Conversely, specifying direction:both when the
other endpoint specifies direction:passive should cause both other endpoint specifies direction:passive SHALL cause both
endpoints to behave as if the former had specified direction:active. endpoints to behave as if the former had specified direction:active.
If both endpoints specify direction:both then each endpoint must If both endpoints specify direction:both then each endpoint MUST
initiate a connection to the port number specified on the m= line of initiate a connection to the port number specified on the m= line of
the opposite endpoint. If only one connection succeeds, then that the opposite endpoint. If a single connection is needed (case #1 or
connection will be used to carry the media. If both connections #2 above), there is one exception to this requirement: if an
succeed but only one was needed (case #2 above), the following rules endpoint receives the incoming connection from the opposite endpoint
shall apply: prior to initiating its own outbound connection, then that endpoint
MAY use that connection rather than attempt to make an outbound
connection to the opposite endpoint.
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If only one connection succeeds, then that connection will be used
to carry the media. Once it has transmitted data on this
connection, the initiating endpoint MUST NOT perform another
connection attempt to the accepting endpoint. This allows the
accepting endpoint to release or recycle the listening port for
another session once it has received data from the initiating
endpoint.
If both connections succeed but only one was needed (case #2 above),
the following rules SHALL apply:
a) Each endpoint MUST accept data from either connection. a) Each endpoint MUST accept data from either connection.
b) Once an endpoint has transmitted data to one of the b) Once an endpoint has transmitted data to one of the
connections, it MUST use that connection exclusively for connections, it MUST use that connection exclusively for
transmission. transmission.
c) Once an endpoint has transmitted AND received data, if one of c) Once an endpoint has transmitted AND received data, if one of
the connections is determined to be idle, the endpoint MAY the connections is determined to be idle, the endpoint MAY
close the idle connection. close the idle connection.
3 Source-Port Considerations 2.4 Semantics of direction:reuse
In the cases where the endpoint is initiating the connection, a By specifying direction:reuse, the endpoint indicates that it is
source port number may optionally be specified on the a= line by changing the parameter(s) of an existing session on a previously
that endpoint. In most environments, the source port number can be established connection with the opposite endpoint. Therefore no new
connections are to be created. This is intended for cases where
media types are added, removed, or changed during a session. For
example, an endpoint adding a video stream to an existing audio
session may elect to multiplex the new stream over the same
connection that is currently transporting the audio stream.
Yon INTERNET-DRAFT Expires August 2001 4 2.5 Bidirectional versus Unidirectional Media
determined by binding the socket before initiating the connect, as
shown in the sample C code below: In traditional SDP transport types the flow is unidirectional. If
the intent is for media to flow in both directions, both endpoints
must specify SDP that describes where to deliver the media and what
media type(s) to use. For example, if only Endpoint A presents SDP
then media can only flow towards Endpoint A, as Endpoint B has not
specified where and how to send media to it.
Because most connection-oriented media is inherently bi-directional,
endpoints may encounter a situation where only one side presented
SDP yet there is now a network path that can carry media in either
direction. In keeping with traditional SDP semantics, an endpoint
MUST NOT send data to the other endpoint unless it has specified SDP
information describing the type of media it can accept.
It is, however, perfectly acceptable for an endpoint to transmit
data on the same connection it is using to receive data, so long as
the other endpoint has advertised its willingness to accept data.
Likewise, it is perfectly acceptable for an endpoint to receive data
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on the same connection it is using to transmit data to the
corresponding remote endpoint. In other words, for a bi-directional
application-level session, a connection may be used to send data in
both directions (contingent to rules outlined in Section 2.3) as
long as one side of the connection is attached to either of the
advertised SDP transport addresses.
3 Source-Address Considerations
In the cases where the endpoint is initiating the connection, it is
RECOMMENDED that a source address be specified on the a= line by
that endpoint. It is also RECOMMENDED that the source port be
included in the source address. In most environments, the source
port number can be determined by binding the socket before
initiating the connect, as shown in the sample C code below:
{ {
SOCKET s_id SOCKET s_id
SOCKADDR_IN cli_sin; SOCKADDR_IN cli_sin;
int namelen; int namelen;
// Create the socket // Create the socket
s_id = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP); s_id = socket(AF_INET,SOCK_STREAM,IPPROTO_TCP);
// Bind the socket to any IP address and port // Bind the socket to any IP address and port
skipping to change at line 232 skipping to change at line 298
bind(s_id,(SOCKADDR *)&cli_sin,sizeof(cli_sin)); bind(s_id,(SOCKADDR *)&cli_sin,sizeof(cli_sin));
// Find the port number that was bound // Find the port number that was bound
namelen = sizeof(cli_sin); namelen = sizeof(cli_sin);
getsockname(s_id,(SOCKADDR *)&cli_sin,&namelen); getsockname(s_id,(SOCKADDR *)&cli_sin,&namelen);
// Print the port number // Print the port number
printf("Source Port = %d\n",ntohs(cli_sin.sin_port)); printf("Source Port = %d\n",ntohs(cli_sin.sin_port));
} }
The motivation for specifying the source port is to allow topologies If the source address is omitted, the receiver of the SDP packet
where one or more endpoints use a single, fixed TCP port for MUST NOT make any assumptions in regards to the address or port from
incoming connections. Non-RTP protocols transported over TCP where the connection will originate. In particular, the receiver
commonly use this technique. By specifying the source port, an MUST NOT assume that the address information listed on the c= line
endpoint avoids a potential ambiguity when more than one session is has any implication as to where the media connection originates.
set up between two endpoints.
For example, consider two endpoints with IP addresses of 10.1.1.1 NOTE:
and 10.1.1.2. The endpoint at 10.1.1.1 signals the availability of The motivation for specifying the source address is
a session on TCP port 2393 (passive). Before the endpoint at twofold. First, it aids Application-Level Proxies by
10.1.1.2 has a chance to initiate the connection, events transpire explicitly announcing the source of the outbound
that cause the endpoint at 10.1.1.1 to signal the availability of a connection. This allows, for example, a dynamic
separate session that is also found at TCP port 2393 (passive). firewall pinhole to be created that will allow the
Shortly thereafter, both entities at 10.1.1.2 initiate connections connection to pass.
to 10.1.1.1 on port 2393.
The problem is this: how does the endpoint at 10.1.1.1 differentiate Yon INTERNET-DRAFT Expires January 2002 6
the two connections? To which entity at 10.1.1.2 does each Second, it allows the passive endpoint to correlate
connection correspond? By specifying the source port prior to the incoming connection with the session being
connecting, the entities at 10.1.1.2 can avoid this ambiguity, negotiated. Note that great care must be taken when
because now the endpoint at 10.1.1.1 can simply inspect the port using the source address as a means to identify
number from which the connection originated to determine which incoming connections, as Network Address Translation
entity has initiated the connection. (NAT) can render the source address unreliable. In
addition if the originating endpoint omits the source
port, the source address can be ambiguous if multiple,
logical endpoints share the same network address.
Therefore it is NOT RECOMMENDED that the source
address be used for this purpose unless the SDP occurs
in the context of a controlled network topology that
guarantees that the source address is both correct
(i.e., no NAT, or a NAT with an Application-Level
Proxy that rewrites the SDP) and unambiguous (i.e.,
the source port is specified).
Caution must be exercised when designing systems that rely on this 3.1 Source Address Timing Considerations
feature, as not all environments are able to determine the source
port prior to initiating the connection.
Yon INTERNET-DRAFT Expires August 2001 5 When used in conjunction with a session signaling protocol such as
SIP, there may be cases where an endpoint initiates a connection
prior to the opposite endpoint receiving the SDP that describe the
source address of the initiating endpoint. Therefore, an endpoint
that has advertised an address and port number with direction:both
or direction:passive MUST be ready to accept a connection on that
address and port immediately. If the accepting endpoint requires
the source address to identify the initiating endpoint, it MUST keep
the connection active and allow sufficient time for the source
address to arrive before discarding the connection.
4 Examples 4 Examples
What follows are a number of examples that show the most common What follows are a number of examples that show the most common
usage of the direction attribute combined with TCP-based media usage of the direction attribute combined with TCP-based media
descriptions. For the purpose of brevity, the main portion of the descriptions. For the purpose of brevity, the main portion of the
session description is omitted in the examples and is assumed to be session description is omitted in the examples and is assumed to be
the following: the following:
v=0 v=0
o=Me <me@ietf.org> o=me 2890844526 2890842807 IN IP4 10.1.1.2
e=Me <me@ietf.org>
s=Call me using TCP s=Call me using TCP
t=0 0 t=0 0
4.1 Example: simple passive/active 4.1 Example: simple passive/active
An endpoint at 10.1.1.2 signals the availability of a T.38 fax An endpoint at 10.1.1.2 signals the availability of a T.38 fax
session at port 54111: session at port 54111:
c=IN IP4 10.1.1.2/127 c=IN IP4 10.1.1.2
m=image 54111 TCP t38 m=image 54111 TCP t38
a=direction:passive a=direction:passive
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An endpoint at 10.1.1.1 receiving this description responds with the An endpoint at 10.1.1.1 receiving this description responds with the
following: following:
c=IN IP4 10.1.1.1/127 c=IN IP4 10.1.1.1
m=image 9 TCP t38 m=image 9 TCP t38
a=direction:active a=direction:active
The endpoint at 10.1.1.1 then initiates the TCP connection to port The endpoint at 10.1.1.1 then initiates the TCP connection to port
54111 at 10.1.1.2. Note that the TCP connection may originate from 54111 at 10.1.1.2. Note that the TCP connection may originate from
any port. The endpoint at 10.1.1.1 could have optionally committed any address or port. The endpoint at 10.1.1.1 could have optionally
to a source port with a simple modification: committed to a source address with a simple modification:
c=IN IP4 10.1.1.1/127 c=IN IP4 10.1.1.1
m=image 9 TCP t38 m=image 9 TCP t38
a=direction:active 1892 a=direction:active IN IP4 10.1.1.1 1892
By adding the "1892" to the a= line, the endpoint at 10.1.1.1 must By adding the source address to the a= line, the endpoint at
now use a source port of 1892 when initiating the TCP connection to 10.1.1.1 must now use a source port of 1892 when initiating the TCP
port 54111 at 10.1.1.2. connection to port 54111 at 10.1.1.2.
4.2 Example: agnostic both 4.2 Example: agnostic both
An endpoint at 10.1.1.2 signals the availability of a T.38 fax An endpoint at 10.1.1.2 signals the availability of a T.38 fax
session at TCP port 54111, but is also willing to set up the media session at TCP port 54111, but is also willing to set up the media
stream by initiating the TCP connection: stream by initiating the TCP connection:
c=IN IP4 10.1.1.2/127 c=IN IP4 10.1.1.2
m=image 54111 TCP t38 m=image 54111 TCP t38
a=direction:both a=direction:both
The endpoint at 10.1.1.1 has three choices: The endpoint at 10.1.1.1 has three choices:
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1) It can respond with either of the two direction:active 1) It can respond with either of the two direction:active
descriptions listed in the previous example. In this case the descriptions listed in the previous example. In this case the
endpoint at 10.1.1.1 must initiate a connection to port 54111 endpoint at 10.1.1.1 must initiate a connection to port 54111
at 10.1.1.2. at 10.1.1.2.
2) It can respond with a description similar to the following: 2) It can respond with a description similar to the following:
c=IN IP4 10.1.1.1/127 c=IN IP4 10.1.1.1
m=image 54321 TCP t38 m=image 54321 TCP t38
a=direction:passive a=direction:passive
In this case the endpoint at 10.1.1.2 must initiate a In this case the endpoint at 10.1.1.2 must initiate a
connection to port 54321 at 10.1.1.1. connection to port 54321 at 10.1.1.1.
3) It can respond with a description that specifies 3) It can respond with a description that specifies
direction:both, which is covered in the next example. direction:both, which is covered in the next example.
4.3 Example: redundant both 4.3 Example: redundant both
An endpoint at 10.1.1.2 uses the same description as the previous An endpoint at 10.1.1.2 uses the same description as the previous
example: example:
c=IN IP4 10.1.1.2/127 Yon INTERNET-DRAFT Expires January 2002 8
c=IN IP4 10.1.1.2
m=image 54111 TCP t38 m=image 54111 TCP t38
a=direction:both a=direction:both
Unlike the previous example, the endpoint at 10.1.1.1 responds with Unlike the previous example, the endpoint at 10.1.1.1 responds with
the following description: the following description:
c=IN IP4 10.1.1.1/127 c=IN IP4 10.1.1.1
m=image 54321 TCP t38 m=image 54321 TCP t38
a=direction:both a=direction:both
This will cause the endpoint at 10.1.1.2 to initiate a connection to This will cause the endpoint at 10.1.1.2 to initiate a connection to
port 54321 at 10.1.1.1, and the endpoint at 10.1.1.1 to initiate a port 54321 at 10.1.1.1, and the endpoint at 10.1.1.1 to initiate a
connection to port 54111 at 10.1.1.2. Whichever TCP connection connection to port 54111 at 10.1.1.2. Whichever TCP connection
succeeds will be used. If both succeed, one of the connections may succeeds will be used. If both succeed, one of the connections may
be closed as an optimization, using the rules in section 2.3. be closed as an optimization, using the rules in section 2.3.
5 Security Considerations 5 Security Considerations
See [SDP] for security and other considerations specific to the See [SDP] for security and other considerations specific to the
Session Description Protocol in general. There are no new security Session Description Protocol in general. There are no new security
considerations introduced by these protocol identifiers and considerations introduced by these protocol identifiers and
attributes. attributes.
6 IANA Considerations 6 IANA Considerations
As recommended by [SDP] Appendix B, the direction attribute As recommended by [SDP] Appendix B, the direction attribute
described in this document should be registered with IANA, as should described in this document should be registered with IANA, as should
the TCP, TLS, and SCTP protocol identifiers. the "TCP" and "TLS" protocol identifiers.
Acknowledgements Acknowledgements
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The author would like to thank Jonathan Rosenberg, Anders The author would like to thank Jonathan Rosenberg, Anders
Kristensen, and Robert Fairlie-Cuninghame for their valuable Kristensen, Paul Kyzivat, and Robert Fairlie-Cuninghame for their
insights. valuable insights.
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Appendix A: Direction Attribute Syntax Appendix A: Direction Attribute Syntax
This appendix provides an Augmented BNF [ABNF] grammar for This appendix provides an Augmented BNF [ABNF] grammar for
expressing the direction attribute for connection setup. It is expressing the direction attribute for connection setup. It is
intended as an extension to the grammar for the Session Description intended as an extension to the grammar for the Session Description
Protocol, as defined in [SDP]. Specifically, it describes the Protocol, as defined in [SDP]. Specifically, it describes the
syntax for the new "connection-setup" attribute field, which MAY be syntax for the new "connection-setup" attribute field, which MAY be
either a session-level or media-level attribute. either a session-level or media-level attribute.
connection-setup = "direction" ":" direction-spec connection-setup = "direction" ":" direction-spec
direction-spec = "passive" | qualified-direction direction-spec = "passive" | qualified-direction
qualified-direction = direction-ident | direction-ident port qualified-direction = direction-ident | direction-ident source
direction-ident = "both" | "active" direction-ident = "both" | "active" | "reuse"
source = nettype addrtype unicast-address |
nettype addrtype unicast-address port
References References
[ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax [ABNF] D. Crocker, P. Overell, "Augmented BNF for Syntax
Specifications: ABNF," RFC 2234, November 1997 Specifications: ABNF," RFC 2234, November 1997
[SCTP] Stewart et al, "Stream Control Transmission Protocol,"
RFC 2960, October 2000
[SDP] M. Handley, V. Jacobson, "SDP: Session Description [SDP] M. Handley, V. Jacobson, "SDP: Session Description
Protocol," RFC 2327, April 1998 Protocol," RFC 2327, April 1998
[T38] International Telecommunication Union, "Procedures for [T38] International Telecommunication Union, "Procedures for
Real-Time Group 3 Facsimile Communications over IP Real-Time Group 3 Facsimile Communications over IP
Networks," Recommendation T.38, June 1998 Networks," Recommendation T.38, June 1998
[TLS] T. Dierks, C. Allen, "The TLS Protocol," RFC 2246, [TLS] T. Dierks, C. Allen, "The TLS Protocol," RFC 2246,
January 1999 January 1999
[UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode [UTF-8] F. Yergeau, "UTF-8, a transformation format of Unicode
and ISO 10646," RFC 2044, October 1996 and ISO 10646," RFC 2044, October 1996
Authors Address Authors Address
David Yon David Yon
Dialout.Net, Inc. Dialout.Net, Inc.
402 Amherst St One Indian Head Plaza
Nashua, NH 03063 Nashua, NH 03060
Phone: (603) 577-8708 Phone: (603) 324-4100
EMail: yon@dialout.net EMail: yon@dialout.net
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2001). All Rights Reserved. Copyright (C) The Internet Society (2001). All Rights Reserved.
Yon INTERNET-DRAFT Expires August 2001 9 Yon INTERNET-DRAFT Expires January 2002 10
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for developing Internet standards in which case the procedures for
skipping to change at line 455 skipping to change at line 537
The limited permissions granted above are perpetual and will not be The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE." MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
Yon INTERNET-DRAFT Expires August 2001 10 Yon INTERNET-DRAFT Expires January 2002 11
 End of changes. 

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