draft-ietf-mmusic-sdp-comedia-09.txt		draft-ietf-mmusic-sdp-comedia-10.txt
	MMUSIC Working Group D. Yon		MMUSIC Working Group D. Yon
	Internet-Draft Tactical Software, LLC		Internet-Draft Tactical Software, LLC
	Expires: March 30, 2005 G. Camarillo		Expires: May 27, 2005 G. Camarillo
	Ericsson		Ericsson
	September 29, 2004		November 26, 2004
	Connection-Oriented Media Transport in the Session Description		TCP-Based Media Transport in the Session Description Protocol (SDP)
	Protocol (SDP)		draft-ietf-mmusic-sdp-comedia-10.txt
	draft-ietf-mmusic-sdp-comedia-09.txt
	Status of this Memo		Status of this Memo
	This document is an Internet-Draft and is subject to all provisions		This document is an Internet-Draft and is subject to all provisions
	of section 3 of RFC 3667. By submitting this Internet-Draft, each		of section 3 of RFC 3667. By submitting this Internet-Draft, each
	author represents that any applicable patent or other IPR claims of		author represents that any applicable patent or other IPR claims of
	which he or she is aware have been or will be disclosed, and any of		which he or she is aware have been or will be disclosed, and any of
	which he or she become aware will be disclosed, in accordance with		which he or she become aware will be disclosed, in accordance with
	RFC 3668.		RFC 3668.
	skipping to change at page 1, line 38		skipping to change at page 1, line 36
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
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	http://www.ietf.org/ietf/1id-abstracts.txt.		http://www.ietf.org/ietf/1id-abstracts.txt.
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	This Internet-Draft will expire on March 30, 2005.		This Internet-Draft will expire on May 27, 2005.
	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2004).		Copyright (C) The Internet Society (2004).
	Abstract		Abstract
	This document describes how to express media transport over		This document describes how to express media transport over TCP using
	connection-oriented protocols using the Session Description Protocol		the Session Description Protocol (SDP). It defines the SDP 'TCP'
	(SDP). It defines the SDP TCP protocol identifier, the SDP setup		protocol identifier, the SDP 'setup' attribute, which describes the
	attribute, which describes the connection setup procedure, and the		connection setup procedure, and the SDP 'connection' attribute, which
	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 . . . . . . . . . . . . . . . . . . . . 7		6. Connection Management . . . . . . . . . . . . . . . . . . . . 8
	6.1 Connection Establishment . . . . . . . . . . . . . . . . . 7		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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	7.1 Passive/Active . . . . . . . . . . . . . . . . . . . . . . 8		7.1 Passive/Active . . . . . . . . . . . . . . . . . . . . . . 9
	7.2 Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9		7.2 Actpass/Passive . . . . . . . . . . . . . . . . . . . . . 9
	7.3 Existing Connection Reuse . . . . . . . . . . . . . . . . 9		7.3 Existing Connection Reuse . . . . . . . . . . . . . . . . 10
	7.4 Existing Connection Refusal . . . . . . . . . . . . . . . 10		7.4 Existing Connection Refusal . . . . . . . . . . . . . . . 10
	8. Security Considerations . . . . . . . . . . . . . . . . . . . 11		8. Other Connection-Oriented Transport Protocols . . . . . . . . 11
	9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		9. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12		10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 12
	11. References . . . . . . . . . . . . . . . . . . . . . . . . . 12		11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
	11.1 Normative References . . . . . . . . . . . . . . . . . . . . 12		12. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
	11.2 Informative References . . . . . . . . . . . . . . . . . . . 12		12.1 Normative References . . . . . . . . . . . . . . . . . . . . 12
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 13		12.2 Informative References . . . . . . . . . . . . . . . . . . . 13
	Intellectual Property and Copyright Statements . . . . . . . . 14		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, but only 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 connection-oriented transports, such as TCP,		applications for which TCP is more appropriate. This document
	are more appropriate. This document defines a new protocol		defines a new protocol identifier, 'TCP', to describe TCP connetions
	identifier, TCP, to describe TCP connetions in SDP.		in SDP.
	Connection-oriented protocols introduce two new factor when		TCP introduces two new factors when describing a session: how and
	describing a session: how and when should endpoints perform the		when should endpoints perform the TCP connection setup procedure.
	connection setup procedure. This document defines two new attributes		This document defines two new attributes to describe TCP connection
	to describe 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 indicate requirement levels for
	compliant implementations.		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'.
	The TCP protocol identifier is similar to the UDP protocol identifier
	in that it only describes the transport protocol, and not the
	upper-layer protocol. An m= line that specifies "TCP" MUST further
	qualify the application-layer protocol using an fmt identifier.
	Media described using an m= lines containing the TCP protocol
	identifier are carried using TCP [1].
	It is RECOMMENDED that documents defining new SDP protocol
	identifiers that involve extra protocol layers between TCP and the
	media itself (e.g., TLS [7] over TCP) start with the string "TCP/"
	(e.g., TCP/TLS).
	The following sections define the setup and the connection		The 'TCP' protocol identifier is similar to the 'UDP' protocol
	attributes. While both attributes are applicable to m= lines that		identifier in that it only describes the transport protocol, and not
	use the TCP protocol identifier, they are not limited to them. These		the upper-layer protocol. An 'm' line that specifies 'TCP' MUST
	attributes MAY be used in conjunction with any m= line which uses a		further qualify the application-layer protocol using an fmt
	connection- oriented transport protocol, even if the protocol		identifier. Media described using an 'm' line containing the 'TCP'
	identifier of the m= line is not TCP.		protocol identifier are carried using TCP [1].
	4. Setup Attribute		4. Setup Attribute
	The setup attribute indicates which of the end points should initiate		The 'setup' attribute indicates which of the end points should
	the connection establishment (e.g., send the initial TCP SYN). The		initiate the TCP connection establishment (i.e., send the initial TCP
	setup attribute is charset-independent and can be a session-level or		SYN). The 'setup' attribute is charset-independent and can be a
	a media-level attribute. The following is the ABNF of the setup		session-level or a media-level attribute. The following is the ABNF
	attribute:		of the 'setup' attribute:
	setup-attr = "a=setup:" role		setup-attr = "a=setup:" role
	role = "active" / "passive" / "actpass"		role = "active" / "passive" / "actpass"
	/ "holdconn"		/ "holdconn"
	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 connection		'actpass': The endpoint is willing to accept an incoming
	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 exchange:		values that the 'setup' attribute can take in an offer/answer
			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 m=		on the 'm' line of the other endpoint. The port number on its own
	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, the		Nevertheless, since the 'm' line must contain a valid port number,
	endpoint specifying using the value active SHOULD specify a port		the endpoint specifying using the value active SHOULD specify a port
	number of 9 (the discard port) on its m= line. The endpoint MUST NOT		number of 9 (the discard port) on its 'm' line. The endpoint MUST
	specify a port number of zero, except to denote an m= line that has		NOT specify a port number of zero, except to denote an 'm' line that
	been or is being refused.		has been or 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 accept
	a connection on the port number specified in the m= line in the		a connection on the port number specified in the 'm' line in the
	offer. That is, the offerer has no preference as to whether it		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 has been 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		as to whether subsequent SDP exchange represents a confirmation that
	the endpoint is to continue using the current media connection		the endpoint is to continue using the current TCP connection
	unchanged, or is a request to make a new media connection. The		unchanged, or is a request to make a new TCP connection. The
	media-level connection attribute, which is charset-independent, is		media-level 'connection' attribute, which is charset-independent, is
	used to disambiguate these two scenarios. The following is the ABNF		used to disambiguate these two scenarios. The following is the ABNF
	of the connection attribute:		of the 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 whether		Offerers and answerers use the 'connection' attribute to decide
	a new transport connection needs to be established or, on the other		whether a new transport connection needs to be established or, on the
	hand, the existing transport connection should still be used. The		other hand, the existing TCP connection should still be used. When
	connection value resulting from an offer/answer exchange is the		an offerer generates an 'm' line which uses TCP, it SHOULD provide a
	connection value in the answer. If the connection value in the		connection attribute for the 'm' line unless the application using
	answer is "new", the end-points SHOULD establish a new connection.		the 'm' line has other means to deal with connection reestablishment.
	If the connection value in the answer is "existing", the end-points
	SHOULD continue using the exiting connection.
	When an offerer generates an m= line which uses a connection-oriented
	transport, it SHOULD provide a connection attribute for the m= line
	unless the application using the m= line has other means to deal with
	connection reestablishment. The connection attribute in an initial
	offer (i.e., no transport connection has been established yet) takes
	the value of "new".
	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 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 wants		'existing' for the 'm' line. If, on the other hand, the offerer
	to establish a new transport-layer connection for the m= line, it		wants to establish a new transport-layer connection for the 'm' line,
	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 m=		changes the transport address (IP address or port number) of an
	line will have a connection value of "new".		'm' line will have a connection value of 'new'. The same way, the
			'connection' attribute in an initial offer (i.e., no transport
			connection has been established yet) takes the value of 'new'.
	The default value of the connection attribute in an offer/answer		The 'connection' value resulting from an offer/answer exchange is the
	exchange is "new".		'connection' value in the answer. If the 'connection' value in the
			answer is 'new', the end-points SHOULD establish a new connection.
			If the connection value in the answer is 'existing', the end-points
			SHOULD continue using the exiting connection.
			Taking into consideration the rules in Section 5.2, the following are
			the values that the 'connetion' attribute can take in an offer/answer
			exchange:
			Offer Answer
			________________
			new new
			existing existing / new
			If the connection value resulting from an offer/answer exchange is
			'existing', the end-points continue using the existing connection.
			Consequently, the port numbers, IP addresses, and 'setup' attributes
			negotiated in the offer/answer exchange are ignored because there is
			no need to establish a new connection.
			The previous rule implies that an offerer generating an offer with a
			connection value of 'existing' and a setup value of 'passive' needs
			to be ready (i.e., needs to allocate resources) to receive a
			connection request from the answerer just in case the answerer
			chooses a connection value of 'new' for the answer. However, if the
			answerer uses a connection value of 'existing' in the answer, the
			offerer would need to deallocate the previously allocated resources
			which were never used because no connection request was received.
			To avoid allocating resources unnecessary, offerers using a
			connection value of 'existing' in their offers may choose to use a
			setup value of 'holdconn'. Nevertheless, offerers using this
			strategy should be aware that in the case the answerer chooses a
			connection value of 'new', a new offer/answer exchange (typically
			initiated by the previous offerer) with setup value different than
			'holdconn' will be needed to establish the new connection. This may,
			of course, cause delays in the application using the TCP connection.
			The default value of the connection attribute in both offers and
			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/answer		If the connection value for an 'm' line resulting from an offer/
	exchange is "new", the endpoints SHOULD establish a new		answer exchange is 'new', the endpoints SHOULD establish a new TCP
	transport-layer connection as indicated by the setup attribute. If a		connection as indicated by the 'setup' attribute. If a previous TCP
	previous connection is still up, the endpoints SHOULD close it as		connection is still up, the endpoints SHOULD close it as soon as the
	soon as the offer/answer exchange is completed. It is up to the		offer/answer exchange is completed. It is up to the application to
	application to ensure proper data synchornization between the two		ensure proper data synchornization between the two TCP connections.
	connections.
	If the connection value for an m= line resulting from an offer/answer		If the connection value for an 'm' line resulting from an offer/
	exchange is "existing", the endpoints SHOULD continue using the		answer exchange is 'existing', the endpoints SHOULD continue using
	existing 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 connection SHOULD initiate it as soon as it is able		initiate a new TCP connection SHOULD initiate it as soon as it is
	to, even if the endpoint does not intend to immediately begin sending		able to, even if the endpoint does not intend to immediately begin
	media to the remote endpoint. This allows media to flow from the		sending media to the remote endpoint. This allows media to flow from
	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 connection.		able to initiate a TCP connection.
	6.2 Connection Reestablishment		6.2 Connection Reestablishment
	If an endpoint determines that the transport-connection for an m=		If an endpoint determines that the TCP for an 'm' line has been
	line has been closed and it should be reestablished, it SHOULD		closed and it should be reestablished, it SHOULD perform a new offer/
	perform a new offer/answer exchange using a connection value of "new"		answer exchange using a connection value of 'new' for this 'm' line.
	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 transport-connection, but has no		with the media sent over the TCP connection, but has no impact on
	impact on the transport-connection itself.		the TCP connection itself.
	6.3 Connection Termination		6.3 Connection Termination
	Typically, endpoints do not close the connection until the session		Typically, endpoints do not close the TCP connection until the
	has expired, been explicitly terminated, or a new connection value		session has expired, been explicitly terminated, or a new connection
	has been provided for the m= line. Additionaly, specific		value has been provided for the 'm' line. Additionaly, specific
	applications can describe further scenarios where an end-point may		applications can describe further scenarios where an end-point may
	close a given connection. As soon as an end-point notices that it		close a given TCP connection (e.g., whenever a connection is in the
	needs to terminate a connection, it SHOULD do so.		half-close state). As soon as an end-point notices that it needs to
			terminate a TCP connection, it SHOULD do so.
	While in TCP both end-points need to close a connection, other
	connection-oriented transport protocols may not have the concept of
	half-close connections. In this case, a connection would be
	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
	terminate the connection.
	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 receiving 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
	skipping to change at page 10, line 18		skipping to change at page 10, line 28
	The endpoint at 192.0.2.2 also wishes to use the existing connection		The endpoint at 192.0.2.2 also wishes to use the existing connection
	and responds with the following description:		and responds with the following description:
	m=image 9 TCP t38		m=image 9 TCP t38
	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 response		Note that the endpoint at 192.0.2.2 uses 'setup:active' in
	to the offer of setup:passive, and uses port 9 because it is		response to the offer of 'setup:passive', and uses port 9 because
	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:actpass		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		so wishes to establish a new one. (This could be the result of a
	transfer via 3pcc.) It is unable to act in the passive mode so		transfer via third-party call control.) It is unable to act in the
	responds as active:		'passive' mode so 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 specifying connection:		Note that the endpoint at 192.0.2.2, while using a connection
	existing has reverted to setup:actpass and its real port number,		value of 'existing' has used a setup value of 'passive'. Had it
	rather than repeating setup:active and port 9 from the previous		not done this and used a setup value of 'holdconn' instead
	cycle. Had it not done this, this negotiation would have failed.		(probably to avoid allocating resources as described in Section
			5.1), a new offer/answer exchange would have been needed in order
			to establish the new connection.
	8. Security Considerations		8. Other Connection-Oriented Transport Protocols
			This document specifies how to describe TCP-based media streams using
			SDP. Still, some of the attributes defined here could possibly be
			used to describe media streams based on other connection-oriented
			transport protocols as well. This section provides advice to authors
			of specifications of SDP extensions which deal with
			connetion-oriented transport protocols other than TCP.
			It is recommended that documents defining new SDP protocol
			identifiers that involve extra protocol layers between TCP and the
			media itself (e.g., TLS [7] over TCP) start with the string 'TCP/'
			(e.g., 'TCP/TLS').
			The 'setup' and the 'connection' attributes are specified in Section
			4 and Section 5 respectively. While both attributes are applicable
			to 'm' lines that use the 'TCP' protocol identifier, they are general
			enough to be reused in 'm' lines with other connection-oriented
			transport protocols. Therefore, it is recommended that the 'setup'
			and 'connection' attributes are reused, as long as it is possible,
			for new proto values associated with connection-oriented transport
			protocols.
			Section 6 deals with TCP connection management. It should be noted
			that while in TCP both end-points need to close a connection, other
			connection-oriented transport protocols may not have the concept of
			half-close connections. In such a case, a connection would be
			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
			terminate the connection. So, specifications dealing with such
			transport protocols may need to specify slightly different procedures
			regarding connection termination.
			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 to have endpoints reestablish connections
	unnecesaryly or to keep them from establishing a connection. So, it		unnecesaryly 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.
	9. 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 by
	the IANA on		the IANA under "Session Description Protocol (SDP) Parameters" under
			"att-field (both session and media level)".
	http://www.iana.org/assignments/sdp-parameters
	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 on		Section 3. This proto value should be registered by the IANA under
			"Session Description Protocol (SDP) Parameters" under "proto".
	http://www.iana.org/assignments/sdp-parameters
	under "proto".
	Specifications defining new proto values, like this one, must define		The SDP specification, RFC2327, states that specifications defining
	the rules by which their media format (fmt) namespace is managed.		new proto values, like the TCP proto value defined in this RFC, must
	For the TCP protocol, new formats SHOULD have an associated MIME		define the rules by which their media format (fmt) namespace is
	registration. Use of an existing MIME subtype for the format is		managed. For the TCP protocol, new formats SHOULD have an associated
			MIME registration. Use of an existing MIME subtype for the format is
	encouraged. If no MIME subtype exists, it is RECOMMENDED that a		encouraged. If no MIME subtype exists, it is RECOMMENDED that a
	suitable one is registered through the IETF process [2] by production		suitable one is registered through the IETF process [2] by production
	of, or reference to, a standards-track RFC that defines the transport		of, or reference to, a standards-track RFC that defines the transport
	protocol for the format.		protocol for the format.
	10. 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.
	11. References		12. References
	11.1 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", BCP
	13, RFC 2048, November 1996.		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.
	11.2 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", RFC
	2246, January 1999.		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.
End of changes.
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