draft-ietf-mmusic-sdp-comedia-10.txt		rfc4145.txt
	MMUSIC Working Group D. Yon
	Internet-Draft Tactical Software, LLC		Network Working Group D. Yon
	Expires: May 27, 2005 G. Camarillo		Request for Comments: 4145 Tactical Software, LLC
			Category: Standards Track G. Camarillo
	Ericsson		Ericsson
	November 26, 2004		September 2005
	TCP-Based Media Transport in the Session Description Protocol (SDP)		TCP-Based Media Transport in the Session Description Protocol (SDP)
	draft-ietf-mmusic-sdp-comedia-10.txt
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is subject to all provisions		This document specifies an Internet standards track protocol for the
	of section 3 of RFC 3667. By submitting this Internet-Draft, each		Internet community, and requests discussion and suggestions for
	author represents that any applicable patent or other IPR claims of		improvements. Please refer to the current edition of the "Internet
	which he or she is aware have been or will be disclosed, and any of		Official Protocol Standards" (STD 1) for the standardization state
	which he or she become aware will be disclosed, in accordance with		and status of this protocol. Distribution of this memo is unlimited.
	RFC 3668.
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	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2004).		Copyright (C) The Internet Society (2005).
	Abstract		Abstract
	This document describes how to express media transport over TCP using		This document describes how to express media transport over TCP using
	the Session Description Protocol (SDP). It defines the SDP 'TCP'		the Session Description Protocol (SDP). It defines the SDP 'TCP'
	protocol identifier, the SDP 'setup' attribute, which describes the		protocol identifier, the SDP 'setup' attribute, which describes the
	connection setup procedure, and the SDP 'connection' attribute, which		connection setup procedure, and the SDP 'connection' attribute, which
	handles connection reestablishment.		handles connection reestablishment.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 3		3. Protocol Identifier . . . . . . . . . . . . . . . . . . . . . 3
	4. Setup Attribute . . . . . . . . . . . . . . . . . . . . . . . 4		4. Setup Attribute . . . . . . . . . . . . . . . . . . . . . . . 4
	4.1 The Setup Attribute in the Offer/answer Model . . . . . . 4		4.1. The Setup Attribute in the Offer/Answer Model. . . . . . 4
	5. The Connection Attribute . . . . . . . . . . . . . . . . . . . 5		5. The Connection Attribute . . . . . . . . . . . . . . . . . . . 5
	5.1 Offerer Behaviour . . . . . . . . . . . . . . . . . . . . 6		5.1. Offerer Behaviour. . . . . . . . . . . . . . . . . . . . 6
	5.2 Answerer Behaviour . . . . . . . . . . . . . . . . . . . . 7		5.2. Answerer Behaviour . . . . . . . . . . . . . . . . . . . 7
	6. Connection Management . . . . . . . . . . . . . . . . . . . . 8		6. Connection Management . . . . . . . . . . . . . . . . . . . . 8
	6.1 Connection Establishment . . . . . . . . . . . . . . . . . 8		6.1. Connection Establishment . . . . . . . . . . . . . . . . 8
	6.2 Connection Reestablishment . . . . . . . . . . . . . . . . 8		6.2. Connection Reestablishment . . . . . . . . . . . . . . . 8
	6.3 Connection Termination . . . . . . . . . . . . . . . . . . 8		6.3. Connection Termination . . . . . . . . . . . . . . . . . 8
	7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 8		7. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
	7.1 Passive/Active . . . . . . . . . . . . . . . . . . . . . . 9		7.1. Passive/Active . . . . . . . . . . . . . . . . . . . . . 9
	7.2 Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9		7.2. Actpass/Passive. . . . . . . . . . . . . . . . . . . . . 9
	7.3 Existing Connection Reuse . . . . . . . . . . . . . . . . 10		7.3. Existing Connection Reuse. . . . . . . . . . . . . . . . 10
	7.4 Existing Connection Refusal . . . . . . . . . . . . . . . 10		7.4. Existing Connection Refusal. . . . . . . . . . . . . . . 10
	8. Other Connection-Oriented Transport Protocols . . . . . . . . 11		8. Other Connection-Oriented Transport Protocols. . . . . . . . . 11
	9. Security Considerations . . . . . . . . . . . . . . . . . . . 12		9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12		10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12		11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
	12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12		12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	12.1 Normative References . . . . . . . . . . . . . . . . . . . . 12		12.1. Normative References . . . . . . . . . . . . . . . . . . 13
	12.2 Informative References . . . . . . . . . . . . . . . . . . . 13		12.2. Informative References . . . . . . . . . . . . . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 14
	Intellectual Property and Copyright Statements . . . . . . . . 15
	1. Introduction		1. Introduction
	The Session Description Protocol [4] provides a general-purpose		The Session Description Protocol [4] 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 [11]) to maximize portability among transports. SDP		subset of UTF-8 [11]) to maximize portability among transports. SDP
	does not define a protocol, but only the syntax to describe a		does not define a protocol; it defines the syntax to describe a
	multimedia session with sufficient information to participate in that		multimedia session with sufficient information to participate in that
	session. Session descriptions may be sent using arbitrary existing		session. Session descriptions may be sent using arbitrary existing
	application protocols for transport (e.g., SAP [9], SIP [10], RTSP		application protocols for transport (e.g., SAP [9], SIP [10], RTSP
	[6], email, HTTP [8], etc.).		[6], email, HTTP [8], etc.).
	SDP [4] defines two protocol identifiers: RTP/AVP and UDP, both of		SDP [4] defines two protocol identifiers: RTP/AVP and UDP, both of
	which represent unreliable connectionless protocols. While these		which represent unreliable, connectionless protocols. While these
	transports are appropriate choices for multimedia streams, there are		transports are appropriate choices for multimedia streams, there are
	applications for which TCP is more appropriate. This document		applications for which TCP is more appropriate. This document
	defines a new protocol identifier, 'TCP', to describe TCP connetions		defines a new protocol identifier, 'TCP', to describe TCP connections
	in SDP.		in SDP.
	TCP introduces two new factors when describing a session: how and		TCP introduces two new factors when describing a session: how and
	when should endpoints perform the TCP connection setup procedure.		when should endpoints perform the TCP connection setup procedure.
	This document defines two new attributes to describe TCP connection		This document defines two new attributes to describe TCP connection
	setups: 'setup' and 'connection'.		setups: 'setup' and 'connection'.
	2. Terminology		2. Terminology
	In this document, the key words "MUST", "MUST NOT", "REQUIRED",		In this document, the key words "MUST", "MUST NOT", "REQUIRED",
	"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT		"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT
	RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as		RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as
	described in BCP 14, RFC 2119 [3] and indicate requirement levels for		described in BCP 14, RFC 2119 [3], and they indicate requirement
	compliant implementations.		levels for compliant implementations.
	3. Protocol Identifier		3. Protocol Identifier
	The following is the ABNF for an 'm' line, as specified by RFC 2327		The following is the ABNF for an 'm' line, as specified by RFC 2327
	[4].		[4].
	media-field = "m=" media space port ["/" integer]		media-field = "m=" media space port ["/" integer]
	space proto 1*(space fmt) CRLF		space proto 1*(space fmt) CRLF
	This document defines a new value for the proto field: 'TCP'.		This document defines a new value for the proto field: 'TCP'.
	skipping to change at page 4, line 28		skipping to change at page 4, line 30
	'active': The endpoint will initiate an outgoing connection.		'active': The endpoint will initiate an outgoing connection.
	'passive': The endpoint will accept an incoming connection.		'passive': The endpoint will accept an incoming connection.
	'actpass': The endpoint is willing to accept an incoming		'actpass': The endpoint is willing to accept an incoming
	connection or to initiate an outgoing connection.		connection or to initiate an outgoing connection.
	'holdconn': The endpoint does not want the connection to be		'holdconn': The endpoint does not want the connection to be
	established for the time being.		established for the time being.
	4.1 The Setup Attribute in the Offer/answer Model		4.1. The Setup Attribute in the Offer/Answer Model
	The offer/answer model, defined in RFC 3264 [5], provides endpoints		The offer/answer model, defined in RFC 3264 [5], provides endpoints
	with a means to obtain shared view of a session. Some session		with a means to obtain shared view of a session. Some session
	parameters are negotiated (e.g., codecs to use), while others are		parameters are negotiated (e.g., codecs to use), while others are
	simply communicated from one endpoint to the other (e.g., IP		simply communicated from one endpoint to the other (e.g., IP
	addresses). The value of the 'setup' attribute falls into the first		addresses). The value of the 'setup' attribute falls into the first
	category. That is, both endpoints negotiate its value using the		category. That is, both endpoints negotiate its value using the
	offer/answer model.		offer/answer model.
	The negotiation of the value of the 'setup' attribute takes places as		The negotiation of the value of the 'setup' attribute takes places as
	follows. The offerer states which role or roles it is willing to		follows. The offerer states which role or roles it is willing to
	perform and the answerer, taking the offerer's willingness into		perform; and the answerer, taking the offerer's willingness into
	consideration, chooses which roles both endpoints will actually		consideration, chooses which roles both endpoints will actually
	perform during connection establishment. The following are the		perform during connection establishment. The following are the
	values that the 'setup' attribute can take in an offer/answer		values that the 'setup' attribute can take in an offer/answer
	exchange:		exchange:
	Offer Answer		Offer Answer
	________________		________________
	active passive / holdconn		active passive / holdconn
	passive active / holdconn		passive active / holdconn
	actpass active / passive / holdconn		actpass active / passive / holdconn
	holdconn holdconn		holdconn holdconn
	The active endpoint SHOULD initiate a connection to the port number		The active endpoint SHOULD initiate a connection to the port number
	on the 'm' line of the other endpoint. The port number on its own		on the 'm' line of the other endpoint. The port number on its own
	'm' line is irrelevant, and the opposite endpoint MUST NOT attempt to		'm' line is irrelevant, and the opposite endpoint MUST NOT attempt to
	initiate a connection to the port number specified there.		initiate a connection to the port number specified there.
	Nevertheless, since the 'm' line must contain a valid port number,		Nevertheless, since the 'm' line must contain a valid port number,
	the endpoint specifying using the value active SHOULD specify a port		the endpoint using the value 'active' SHOULD specify a port number of
	number of 9 (the discard port) on its 'm' line. The endpoint MUST		9 (the discard port) on its 'm' line. The endpoint MUST NOT specify
	NOT specify a port number of zero, except to denote an 'm' line that		a port number of zero, except to denote an 'm' line that has been or
	has been or is being refused.		is being refused.
	The passive endpoint SHOULD be ready to accept a connection on the		The passive endpoint SHOULD be ready to accept a connection on the
	port number specified in the 'm' line.		port number specified in the 'm' line.
	A value of 'actpass' indicates that the offerer can either initiate a		A value of 'actpass' indicates that the offerer can either initiate a
	connection to the port number on the 'm' line in the answer or accept		connection to the port number on the 'm' line in the answer, or
	a connection on the port number specified in the 'm' line in the		accept a connection on the port number specified in the 'm' line in
	offer. That is, the offerer has no preference as to whether it		the offer. That is, the offerer has no preference as to whether it
	accepts or initiates the connection and, so, is letting the answerer		accepts or initiates the connection and, so, is letting the answerer
	choose.		choose.
	A value of 'holdconn' indicates that the connection should not be		A value of 'holdconn' indicates that the connection should not be
	established for the time being.		established for the time being.
	The default value of the setup attribute in an offer/answer exchange		The default value of the setup attribute in an offer/answer exchange
	is 'active' in the offer and 'passive' in the answer.		is 'active' in the offer and 'passive' in the answer.
	5. The Connection Attribute		5. The Connection Attribute
	The preceding description of the 'setup' attribute is placed in the		The preceding description of the 'setup' attribute is placed in the
	context of using SDP to initiate a session. Still, SDP may be		context of using SDP to initiate a session. Still, SDP may be
	exchanged between endpoints at various stages of a session to		exchanged between endpoints at various stages of a session to
	accomplish tasks such as terminating a session, redirecting media to		accomplish tasks such as terminating a session, redirecting media to
	a new endpoint, or renegotiating the media parameters for a session.		a new endpoint, or renegotiating the media parameters for a session.
	After the initial session has been established, it may be ambiguous		After the initial session has been established, it may be ambiguous
	as to whether subsequent SDP exchange represents a confirmation that		whether a subsequent SDP exchange represents a confirmation that the
	the endpoint is to continue using the current TCP connection		endpoint is to continue using the current TCP connection unchanged,
	unchanged, or is a request to make a new TCP connection. The		or is a request to make a new TCP connection. The media-level
	media-level 'connection' attribute, which is charset-independent, is		'connection' attribute, which is charset-independent, is used to
	used to disambiguate these two scenarios. The following is the ABNF		disambiguate these two scenarios. The following is the ABNF of the
	of the connection attribute:		connection attribute:
	connection-attr = "a=connection:" conn-value		connection-attr = "a=connection:" conn-value
	conn-value = "new" / "existing"		conn-value = "new" / "existing"
	5.1 Offerer Behaviour		5.1. Offerer Behaviour
	Offerers and answerers use the 'connection' attribute to decide		Offerers and answerers use the 'connection' attribute to decide
	whether a new transport connection needs to be established or, on the		whether a new transport connection needs to be established or, on the
	other hand, the existing TCP connection should still be used. When		other hand, the existing TCP connection should still be used. When
	an offerer generates an 'm' line which uses TCP, it SHOULD provide a		an offerer generates an 'm' line that uses TCP, it SHOULD provide a
	connection attribute for the 'm' line unless the application using		connection attribute for the 'm' line unless the application using
	the 'm' line has other means to deal with connection reestablishment.		the 'm' line has other means to deal with connection reestablishment.
	After the initial offer/answer exchange, any of the endpoints can		After the initial offer/answer exchange, any of the endpoints can
	generate a new offer to change some characteristics of the session		generate a new offer to change some characteristics of the session
	(e.g., the direction attribute). If such an offerer wants to		(e.g., the direction attribute). If such an offerer wants to
	continue using the previously-established transport-layer connection		continue using the previously-established transport-layer connection
	for the 'm' line, the offerer MUST use a connection value of		for the 'm' line, the offerer MUST use a connection value of
	'existing' for the 'm' line. If, on the other hand, the offerer		'existing' for the 'm' line. If, on the other hand, the offerer
	wants to establish a new transport-layer connection for the 'm' line,		wants to establish a new transport-layer connection for the 'm' line,
	it MUST use a connection value of 'new'.		it MUST use a connection value of 'new'.
	Note that, according to the rules in this section, an offer that		Note that, according to the rules in this section, an offer that
	changes the transport address (IP address or port number) of an		changes the transport address (IP address or port number) of an
	'm' line will have a connection value of 'new'. The same way, the		'm' line will have a connection value of 'new'. Similarly, the
	'connection' attribute in an initial offer (i.e., no transport		'connection' attribute in an initial offer (i.e., no transport
	connection has been established yet) takes the value of 'new'.		connection has been established yet) takes the value of 'new'.
	The 'connection' value resulting from an offer/answer exchange is the		The 'connection' value resulting from an offer/answer exchange is the
	'connection' value in the answer. If the 'connection' value in the		'connection' value in the answer. If the 'connection' value in the
	answer is 'new', the end-points SHOULD establish a new connection.		answer is 'new', the end-points SHOULD establish a new connection.
	If the connection value in the answer is 'existing', the end-points		If the connection value in the answer is 'existing', the end-points
	SHOULD continue using the exiting connection.		SHOULD continue using the exiting connection.
	Taking into consideration the rules in Section 5.2, the following are		Taking into consideration the rules in Section 5.2, the following are
	the values that the 'connetion' attribute can take in an offer/answer		the values that the 'connection' attribute can take in an
	exchange:		offer/answer exchange:
	Offer Answer		Offer Answer
	________________		________________
	new new		new new
	existing existing / new		existing existing / new
	If the connection value resulting from an offer/answer exchange is		If the connection value resulting from an offer/answer exchange is
	'existing', the end-points continue using the existing connection.		'existing', the end-points continue using the existing connection.
	Consequently, the port numbers, IP addresses, and 'setup' attributes		Consequently, the port numbers, IP addresses, and 'setup' attributes
	negotiated in the offer/answer exchange are ignored because there is		negotiated in the offer/answer exchange are ignored because there is
	no need to establish a new connection.		no need to establish a new connection.
	The previous rule implies that an offerer generating an offer with a		The previous rule implies that an offerer generating an offer with a
	connection value of 'existing' and a setup value of 'passive' needs		connection value of 'existing' and a setup value of 'passive' needs
	to be ready (i.e., needs to allocate resources) to receive a		to be ready (i.e., needs to allocate resources) to receive a
	connection request from the answerer just in case the answerer		connection request from the answerer just in case the answerer
	chooses a connection value of 'new' for the answer. However, if the		chooses a connection value of 'new' for the answer. However, if the
	answerer uses a connection value of 'existing' in the answer, the		answerer uses a connection value of 'existing' in the answer, the
	offerer would need to deallocate the previously allocated resources		offerer would need to deallocate the previously allocated resources
	which were never used because no connection request was received.		that were never used because no connection request was received.
	To avoid allocating resources unnecessary, offerers using a		To avoid allocating resources unnecessarily, offerers using a
	connection value of 'existing' in their offers may choose to use a		connection value of 'existing' in their offers may choose to use a
	setup value of 'holdconn'. Nevertheless, offerers using this		setup value of 'holdconn'. Nevertheless, offerers using this
	strategy should be aware that in the case the answerer chooses a		strategy should be aware that if the answerer chooses a connection
	connection value of 'new', a new offer/answer exchange (typically		value of 'new', a new offer/answer exchange (typically initiated by
	initiated by the previous offerer) with setup value different than		the previous offerer) with setup value different than 'holdconn' will
	'holdconn' will be needed to establish the new connection. This may,		be needed to establish the new connection. This may, of course,
	of course, cause delays in the application using the TCP connection.		cause delays in the application using the TCP connection.
	The default value of the connection attribute in both offers and		The default value of the connection attribute in both offers and
	answers is 'new'.		answers is 'new'.
	5.2 Answerer Behaviour		5.2. Answerer Behaviour
	The connection value for an 'm' line is negotiated using the offer/		The connection value for an 'm' line is negotiated using the offer/
	answer model. The resulting connection value after an offer/answer		answer model. The resulting connection value after an offer/answer
	exchange is the connection value in the answer. If the connection		exchange is the connection value in the answer. If the connection
	value in the offer is 'new', the answerer MUST also use a value of		value in the offer is 'new', the answerer MUST also use a value of
	'new' in the answer. If the connection value in the offer is		'new' in the answer. If the connection value in the offer is
	'existing', the answerer uses a value of 'existing' in the answer if		'existing', the answerer uses a value of 'existing' in the answer if
	it wishes to continue using the existing connection and a value of		it wishes to continue using the existing connection and a value of
	'new' if it wants a new connection to be established.		'new' if it wants a new connection to be established.
	In some scenarios where third party call control [12] is used, an		In some scenarios where third party call control [12] is used, an
	endpoint may receive an initial offer with a connection value of		endpoint may receive an initial offer with a connection value of
	'existing'. Following the previous rules, such an answerer would		'existing'. Following the previous rules, such an answerer would
	use a connection value of 'new' in the answer.		use a connection value of 'new' in the answer.
	If the connection value for an 'm' line resulting from an offer/		If the connection value for an 'm' line resulting from an offer/
	answer exchange is 'new', the endpoints SHOULD establish a new TCP		answer exchange is 'new', the endpoints SHOULD establish a new TCP
	connection as indicated by the 'setup' attribute. If a previous TCP		connection as indicated by the 'setup' attribute. If a previous TCP
	connection is still up, the endpoints SHOULD close it as soon as the		connection is still up, the endpoints SHOULD close it as soon as the
	offer/answer exchange is completed. It is up to the application to		offer/answer exchange is completed. It is up to the application to
	ensure proper data synchornization between the two TCP connections.		ensure proper data synchronization between the two TCP connections.
	If the connection value for an 'm' line resulting from an offer/		If the connection value for an 'm' line resulting from an offer/
	answer exchange is 'existing', the endpoints SHOULD continue using		answer exchange is 'existing', the endpoints SHOULD continue using
	the existing TCP connection.		the existing TCP connection.
	6. Connection Management		6. Connection Management
	This section addresses connection establishment, connection		This section addresses connection establishment, connection
	reestablishment, and connection termination.		reestablishment, and connection termination.
	6.1 Connection Establishment		6.1. Connection Establishment
	An endpoint that according to an offer/answer exchange is supposed to		An endpoint that according to an offer/answer exchange is supposed to
	initiate a new TCP connection SHOULD initiate it as soon as it is		initiate a new TCP connection SHOULD initiate it as soon as it is
	able to, even if the endpoint does not intend to immediately begin		able to, even if the endpoint does not intend to immediately begin
	sending media to the remote endpoint. This allows media to flow from		sending media to the remote endpoint. This allows media to flow from
	the remote endpoint if needed.		the remote endpoint if needed.
	Note that some endpoints need to wait for some event to happen		Note that some endpoints need to wait for some event to happen
	before being able to establish the connection. For example, a		before being able to establish the connection. For example, a
	wireless terminal may need to set up a radio bearer before being		wireless terminal may need to set up a radio bearer before being
	able to initiate a TCP connection.		able to initiate a TCP connection.
	6.2 Connection Reestablishment		6.2. Connection Reestablishment
	If an endpoint determines that the TCP for an 'm' line has been		If an endpoint determines that the TCP for an 'm' line has been
	closed and it should be reestablished, it SHOULD perform a new offer/		closed and should be reestablished, it SHOULD perform a new offer/
	answer exchange using a connection value of 'new' for this 'm' line.		answer exchange using a connection value of 'new' for this 'm' line.
	Note that the SDP direction attribute (e.g., 'a=sendonly') deals		Note that the SDP direction attribute (e.g., 'a=sendonly') deals
	with the media sent over the TCP connection, but has no impact on		with the media sent over the TCP connection, but has no impact on
	the TCP connection itself.		the TCP connection itself.
	6.3 Connection Termination		6.3. Connection Termination
	Typically, endpoints do not close the TCP connection until the		Typically, endpoints do not close the TCP connection until the
	session has expired, been explicitly terminated, or a new connection		session has expired, been explicitly terminated, or a new connection
	value has been provided for the 'm' line. Additionaly, specific		value has been provided for the 'm' line. Additionally, specific
	applications can describe further scenarios where an end-point may		applications can describe further scenarios where an end-point may
	close a given TCP connection (e.g., whenever a connection is in the		close a given TCP connection (e.g., whenever a connection is in the
	half-close state). As soon as an end-point notices that it needs to		half-close state). As soon as an end-point notices that it needs to
	terminate a TCP connection, it SHOULD do so.		terminate a TCP connection, it SHOULD do so.
	In any case, individual applications may provide further		In any case, individual applications may provide further
	considerations on how to achieve a graceful connection termination.		considerations on how to achieve a graceful connection termination.
	For example, a file application using TCP receiving a FIN from the		For example, a file application using TCP to receive a FIN from the
	remote endpoint may need to finish the ongoing transmission of a file		remote endpoint may need to finish the ongoing transmission of a file
	before sending its own FIN.		before sending its own FIN.
	7. Examples		7. Examples
	The following examples show the most common usage of the 'setup'		The following examples show the most common usage of the 'setup'
	attribute combined with TCP-based media descriptions. For the		attribute combined with TCP-based media descriptions. For the
	purpose of brevity, the main portion of the session description is		purpose of brevity, the main portion of the session description is
	omitted in the examples, which only show 'm' lines and their		omitted in the examples, which only show 'm' lines and their
	attributes (including 'c' lines).		attributes (including 'c' lines).
	7.1 Passive/Active		7.1. Passive/Active
	An offerer at 192.0.2.2 signals its availability for a T.38 fax		An offerer at 192.0.2.2 signals its availability for a T.38 fax
	session at port 54111:		session at port 54111:
	m=image 54111 TCP t38		m=image 54111 TCP t38
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=setup:passive		a=setup:passive
	a=connection:new		a=connection:new
	An answerer at 192.0.2.1 receiving this offer responds with the		An answerer at 192.0.2.1 receiving this offer responds with the
	following answer:		following answer:
	m=image 9 TCP t38		m=image 9 TCP t38
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=setup:active		a=setup:active
	a=connection:new		a=connection:new
	The endpoint at 192.0.2.1 then initiates the TCP connection to port		The endpoint at 192.0.2.1 then initiates the TCP connection to port
	54111 at 192.0.2.2.		54111 at 192.0.2.2.
	7.2 Actpass/Passive		7.2. Actpass/Passive
	In another example, an offerer at 192.0.2.2 signals its availability		In another example, an offerer at 192.0.2.2 signals its availability
	for a T.38 fax session at TCP port 54111. Additionally, this offerer		for a T.38 fax session at TCP port 54111. Additionally, this offerer
	is also willing to set up the media stream by initiating the TCP		is also willing to set up the media stream by initiating the TCP
	connection:		connection:
	m=image 54111 TCP t38		m=image 54111 TCP t38
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=setup:actpass		a=setup:actpass
	a=connection:new		a=connection:new
	skipping to change at page 10, line 8		skipping to change at page 10, line 8
	The endpoint at 192.0.2.1 responds with the following description:		The endpoint at 192.0.2.1 responds with the following description:
	m=image 54321 TCP t38		m=image 54321 TCP t38
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=setup:passive		a=setup:passive
	a=connection:new		a=connection:new
	This will cause the offerer (at 192.0.2.2) to initiate a connection		This will cause the offerer (at 192.0.2.2) to initiate a connection
	to port 54321 at 192.0.2.1.		to port 54321 at 192.0.2.1.
	7.3 Existing Connection Reuse		7.3. Existing Connection Reuse
	Subsequent to the exchange in Section 7.2, another offer/answer		Subsequent to the exchange in Section 7.2, another offer/answer
	exchange is initiated in the opposite direction. The endpoint at		exchange is initiated in the opposite direction. The endpoint at
	192.0.2.1 wishes to continue using the existing connection:		192.0.2.1 wishes to continue using the existing connection:
	m=image 54321 TCP t38		m=image 54321 TCP t38
	c=IN IP4 192.0.2.1		c=IN IP4 192.0.2.1
	a=setup:passive		a=setup:passive
	a=connection:existing		a=connection:existing
	skipping to change at page 10, line 33		skipping to change at page 10, line 33
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=setup:active		a=setup:active
	a=connection:existing		a=connection:existing
	The existing connection from 192.0.2.2 to 192.0.2.1 will be reused.		The existing connection from 192.0.2.2 to 192.0.2.1 will be reused.
	Note that the endpoint at 192.0.2.2 uses 'setup:active' in		Note that the endpoint at 192.0.2.2 uses 'setup:active' in
	response to the offer of 'setup:passive', and uses port 9 because		response to the offer of 'setup:passive', and uses port 9 because
	it is active.		it is active.
	7.4 Existing Connection Refusal		7.4. Existing Connection Refusal
	Subsequent to the exchange in Section 7.3, another offer/answer		Subsequent to the exchange in Section 7.3, another offer/answer
	exchange is initiated by the endpoint at 192.0.2.2, again wishing to		exchange is initiated by the endpoint at 192.0.2.2, again wishing to
	reuse the existing connection:		reuse the existing connection:
	m=image 54111 TCP t38		m=image 54111 TCP t38
	c=IN IP4 192.0.2.2		c=IN IP4 192.0.2.2
	a=setup:passive		a=setup:passive
	a=connection:existing		a=connection:existing
	However, this time the answerer is unaware of the old connection and		However, this time the answerer is unaware of the old connection and
	so wishes to establish a new one. (This could be the result of a		thus wishes to establish a new one. (This could be the result of a
	transfer via third-party call control.) It is unable to act in the		transfer via third-party call control.) It is unable to act in the
	'passive' mode so responds as 'active':		'passive' mode and thus responds as 'active':
	m=image 9 TCP t38		m=image 9 TCP t38
	c=IN IP4 192.0.2.3		c=IN IP4 192.0.2.3
	a=setup:active		a=setup:active
	a=connection:new		a=connection:new
	The endpoint at 192.0.2.3 then initiates the TCP connection to port		The endpoint at 192.0.2.3 then initiates the TCP connection to port
	54111 at 192.0.2.2, and the endpoint at 192.0.2.2 closes the old		54111 at 192.0.2.2, and the endpoint at 192.0.2.2 closes the old
	connection.		connection.
	Note that the endpoint at 192.0.2.2, while using a connection		Note that the endpoint at 192.0.2.2, while using a connection
	value of 'existing' has used a setup value of 'passive'. Had it		value of 'existing', has used a setup value of 'passive'. Had it
	not done this and used a setup value of 'holdconn' instead		not done this and instead used a setup value of 'holdconn'
	(probably to avoid allocating resources as described in Section		(probably to avoid allocating resources as described in
	5.1), a new offer/answer exchange would have been needed in order		Section 5.1), a new offer/answer exchange would have been needed
	to establish the new connection.		in order to establish the new connection.
	8. Other Connection-Oriented Transport Protocols		8. Other Connection-Oriented Transport Protocols
	This document specifies how to describe TCP-based media streams using		This document specifies how to describe TCP-based media streams using
	SDP. Still, some of the attributes defined here could possibly be		SDP. Still, some of the attributes defined here could possibly be
	used to describe media streams based on other connection-oriented		used to describe media streams based on other connection-oriented
	transport protocols as well. This section provides advice to authors		transport protocols as well. This section provides advice to authors
	of specifications of SDP extensions which deal with		of specifications of SDP extensions that deal with connection-
	connetion-oriented transport protocols other than TCP.		oriented transport protocols other than TCP.
	It is recommended that documents defining new SDP protocol		It is recommended that documents defining new SDP protocol
	identifiers that involve extra protocol layers between TCP and the		identifiers that involve extra protocol layers between TCP and the
	media itself (e.g., TLS [7] over TCP) start with the string 'TCP/'		media itself (e.g., TLS [7] over TCP) start with the string 'TCP/'
	(e.g., 'TCP/TLS').		(e.g., 'TCP/TLS').
	The 'setup' and the 'connection' attributes are specified in Section		The 'setup' and the 'connection' attributes are specified in
	4 and Section 5 respectively. While both attributes are applicable		Section 4 and Section 5 respectively. While both attributes are
	to 'm' lines that use the 'TCP' protocol identifier, they are general		applicable to 'm' lines that use the 'TCP' protocol identifier, they
	enough to be reused in 'm' lines with other connection-oriented		are general enough to be reused in 'm' lines with other connection-
	transport protocols. Therefore, it is recommended that the 'setup'		oriented transport protocols. Therefore, it is recommended that the
	and 'connection' attributes are reused, as long as it is possible,		'setup' and 'connection' attributes are reused, as long as it is
	for new proto values associated with connection-oriented transport		possible, for new proto values associated with connection-oriented
	protocols.		transport protocols.
	Section 6 deals with TCP connection management. It should be noted		Section 6 deals with TCP connection management. It should be noted
	that while in TCP both end-points need to close a connection, other		that while in TCP both end-points need to close a connection, other
	connection-oriented transport protocols may not have the concept of		connection-oriented transport protocols may not have the concept of
	half-close connections. In such a case, a connection would be		half-close connections. In such a case, a connection would be
	terminated as soon as one of the end-points closed it, making it		terminated as soon as one of the end-points closed it, making it
	unnecessary for the other end-point to perform any further action to		unnecessary for the other end-point to perform any further action to
	terminate the connection. So, specifications dealing with such		terminate the connection. So, specifications dealing with such
	transport protocols may need to specify slightly different procedures		transport protocols may need to specify slightly different procedures
	regarding connection termination.		regarding connection termination.
	9. Security Considerations		9. Security Considerations
	See RFC 2327 [4] for security and other considerations specific to		See RFC 2327 [4] for security and other considerations specific to
	the Session Description Protocol in general.		the Session Description Protocol in general.
	An attacker may attempt to modify the values of the connection and		An attacker may attempt to modify the values of the connection and
	setup attributes to have endpoints reestablish connections		setup attributes in order to have endpoints reestablish connections
	unnecesaryly or to keep them from establishing a connection. So, it		unnecessarily or to keep them from establishing a connection. So, it
	is strongly RECOMMENDED that integrity protection be applied to the		is strongly RECOMMENDED that integrity protection be applied to the
	SDP session descriptions. For session descriptions carried in SIP		SDP session descriptions. For session descriptions carried in SIP
	[10], S/MIME is the natural choice to provide such end-to-end		[10], S/MIME is the natural choice to provide such end-to-end
	integrity protection, as described in RFC 3261 [10]. Other		integrity protection, as described in RFC 3261 [10]. Other
	applications MAY use a different form of integrity protection.		applications MAY use a different form of integrity protection.
	10. IANA Considerations		10. IANA Considerations
	This document defines two session and media level SDP attributes:		This document defines two session- and media-level SDP attributes:
	setup and connection. Their formats are defined in Section 4 and		setup and connection. Their formats are defined in Section 4 and
	Section 5 respectively. These two attributes should be registered by		Section 5, respectively. These two attributes should be registered
	the IANA under "Session Description Protocol (SDP) Parameters" under		by the IANA under "Session Description Protocol (SDP) Parameters"
	"att-field (both session and media level)".		under "att-field (both session and media level)".
	This document defines a proto value: TCP. Its format is defined in		This document defines a proto value: TCP. Its format is defined in
	Section 3. This proto value should be registered by the IANA under		Section 3. This proto value should be registered by the IANA under
	"Session Description Protocol (SDP) Parameters" under "proto".		"Session Description Protocol (SDP) Parameters" under "proto".
	The SDP specification, RFC2327, states that specifications defining		The SDP specification, RFC2327, states that specifications defining
	new proto values, like the TCP proto value defined in this RFC, must		new proto values, like the TCP proto value defined in this RFC, must
	define the rules by which their media format (fmt) namespace is		define the rules by which their media format (fmt) namespace is
	managed. For the TCP protocol, new formats SHOULD have an associated		managed. For the TCP protocol, new formats SHOULD have an associated
	MIME registration. Use of an existing MIME subtype for the format is		MIME registration. Use of an existing MIME subtype for the format is
	skipping to change at page 12, line 49		skipping to change at page 13, line 7
	protocol for the format.		protocol for the format.
	11. Acknowledgements		11. Acknowledgements
	Jonathan Rosenberg, Rohan Mahy, Anders Kristensen, Joerg Ott, Paul		Jonathan Rosenberg, Rohan Mahy, Anders Kristensen, Joerg Ott, Paul
	Kyzivat, Robert Fairlie-Cuninghame, Colin Perkins, and Christer		Kyzivat, Robert Fairlie-Cuninghame, Colin Perkins, and Christer
	Holmberg provided valuable insights and contributions.		Holmberg provided valuable insights and contributions.
	12. References		12. References
	12.1 Normative References		12.1. Normative References
	[1] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,		[1] Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
	September 1981.		September 1981.
	[2] Freed, N., Klensin, J. and J. Postel, "Multipurpose Internet		[2] Freed, N., Klensin, J., and J. Postel, "Multipurpose Internet
	Mail Extensions (MIME) Part Four: Registration Procedures", BCP		Mail Extensions (MIME) Part Four: Registration Procedures",
	13, RFC 2048, November 1996.		BCP 13, RFC 2048, November 1996.
	[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement		[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
	Levels", BCP 14, RFC 2119, March 1997.		Levels", BCP 14, RFC 2119, March 1997.
	[4] Handley, M. and V. Jacobson, "SDP: Session Description		[4] Handley, M. and V. Jacobson, "SDP: Session Description
	Protocol", RFC 2327, April 1998.		Protocol", RFC 2327, April 1998.
	[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with		[5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with
	Session Description Protocol (SDP)", RFC 3264, June 2002.		Session Description Protocol (SDP)", RFC 3264, June 2002.
	12.2 Informative References		12.2. Informative References
	[6] Schulzrinne, H., Rao, A. and R. Lanphier, "Real Time Streaming		[6] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming
	Protocol (RTSP)", RFC 2326, April 1998.		Protocol (RTSP)", RFC 2326, April 1998.
	[7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0", RFC		[7] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
	2246, January 1999.		RFC 2246, January 1999.
	[8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,		[8] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., Masinter, L.,
	Leach, P. and T. Berners-Lee, "Hypertext Transfer Protocol --		Leach, P., and T. Berners-Lee, "Hypertext Transfer Protocol --
	HTTP/1.1", RFC 2616, June 1999.		HTTP/1.1", RFC 2616, June 1999.
	[9] Handley, M., Perkins, C. and E. Whelan, "Session Announcement		[9] Handley, M., Perkins, C., and E. Whelan, "Session Announcement
	Protocol", RFC 2974, October 2000.		Protocol", RFC 2974, October 2000.
	[10] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,		[10] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,
	Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP:		Peterson, J., Sparks, R., Handley, M., and E. Schooler, "SIP:
	Session Initiation Protocol", RFC 3261, June 2002.		Session Initiation Protocol", RFC 3261, June 2002.
	[11] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD		[11] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
	63, RFC 3629, November 2003.		STD 63, RFC 3629, November 2003.
	[12] Rosenberg, J., Peterson, J., Schulzrinne, H. and G. Camarillo,		[12] Rosenberg, J., Peterson, J., Schulzrinne, H., and G. Camarillo,
	"Best Current Practices for Third Party Call Control (3pcc) in		"Best Current Practices for Third Party Call Control (3pcc) in
	the Session Initiation Protocol (SIP)", BCP 85, RFC 3725, April		the Session Initiation Protocol (SIP)", BCP 85, RFC 3725,
	2004.		April 2004.
	Authors' Addresses		Authors' Addresses
	David Yon		David Yon
	Tactical Software, LLC		Tactical Software, LLC
	670 N Commercial St		1750 Elm St., Suite 803
	Manchester, NH 03101		Manchester, NH 03104
	USA		USA
	EMail: yon-comedia@rfdsoftware.com		EMail: yon-comedia@rfdsoftware.com
	Gonzalo Camarillo		Gonzalo Camarillo
	Ericsson		Ericsson
	Hirsalantie 11		Hirsalantie 11
	Jorvas 02420		Jorvas 02420
	Finland		Finland
	EMail: Gonzalo.Camarillo@ericsson.com		EMail: Gonzalo.Camarillo@ericsson.com
	Intellectual Property Statement		Full Copyright Statement
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			contained in BCP 78, and except as set forth therein, the authors
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			ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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	ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
	INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
	INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
	WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
	Copyright Statement
	Copyright (C) The Internet Society (2004). This document is subject
	to the rights, licenses and restrictions contained in BCP 78, and
	except as set forth therein, the authors retain all their rights.
	Acknowledgment		Acknowledgement
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is currently provided by the
	Internet Society.		Internet Society.
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