draft-ietf-dccp-rtp-00.txt		draft-ietf-dccp-rtp-01.txt
	Network Working Group C. Perkins		Network Working Group C. Perkins
	Internet-Draft University of Glasgow		Internet-Draft University of Glasgow
	Expires: January 18, 2007 July 17, 2006		Intended status: Standards Track October 22, 2006
			Expires: April 25, 2007
	RTP and the Datagram Congestion Control Protocol (DCCP)		RTP and the Datagram Congestion Control Protocol (DCCP)
	draft-ietf-dccp-rtp-00.txt		draft-ietf-dccp-rtp-01.txt
	Status of this Memo		Status of this Memo
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	skipping to change at page 1, line 33 ¶		skipping to change at page 1, line 34 ¶
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	Copyright Notice		Copyright Notice
	Copyright (C) The Internet Society (2006).		Copyright (C) The Internet Society (2006).
	Abstract		Abstract
	The Real-time Transport Protocol (RTP) is a widely used transport for		The Real-time Transport Protocol (RTP) is a widely used transport for
	real-time media on IP networks. The Datagram Congestion Control		real-time multimedia on IP networks. The Datagram Congestion Control
	Protocol (DCCP) is a newly defined transport protocol that provides		Protocol (DCCP) is a newly defined transport protocol that provides
	desirable services for real-time applications. This memo specifies a		desirable services for real-time applications. This memo specifies a
	mapping of RTP onto DCCP, along with associated signalling, such that		mapping of RTP onto DCCP, along with associated signalling, such that
	real-time applications can make use of the services provided by DCCP.		real-time applications can make use of the services provided by DCCP.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Conventions Used in this Memo . . . . . . . . . . . . . . . . 4		3. Conventions Used in this Memo . . . . . . . . . . . . . . . . 4
	4. RTP over DCCP: Framing . . . . . . . . . . . . . . . . . . . . 4		4. RTP over DCCP: Framing . . . . . . . . . . . . . . . . . . . . 4
	4.1. RTP Data Packets . . . . . . . . . . . . . . . . . . . . . 4		4.1. RTP Data Packets . . . . . . . . . . . . . . . . . . . . . 4
	4.2. RTP Control Packets . . . . . . . . . . . . . . . . . . . 5		4.2. RTP Control Packets . . . . . . . . . . . . . . . . . . . 5
	4.3. Multiplexing Data and Control . . . . . . . . . . . . . . 6		4.3. Multiplexing Data and Control . . . . . . . . . . . . . . 6
	4.4. RTP Sessions and DCCP Connections . . . . . . . . . . . . 7		4.4. RTP Sessions and DCCP Connections . . . . . . . . . . . . 7
	4.5. RTP Profiles . . . . . . . . . . . . . . . . . . . . . . . 8		4.5. RTP Profiles . . . . . . . . . . . . . . . . . . . . . . . 7
	5. RTP over DCCP: Signalling using SDP . . . . . . . . . . . . . 8		5. RTP over DCCP: Signalling using SDP . . . . . . . . . . . . . 8
	5.1. Protocol Identification . . . . . . . . . . . . . . . . . 8		5.1. Protocol Identification . . . . . . . . . . . . . . . . . 8
	5.2. Service Codes . . . . . . . . . . . . . . . . . . . . . . 9		5.2. Service Codes . . . . . . . . . . . . . . . . . . . . . . 9
	5.3. Connection Management . . . . . . . . . . . . . . . . . . 10		5.3. Connection Management . . . . . . . . . . . . . . . . . . 10
	5.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 10		5.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 11
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 11		6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
	8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12		8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 12		9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
	9.2. Informative References . . . . . . . . . . . . . . . . . . 13		9.2. Informative References . . . . . . . . . . . . . . . . . . 14
	Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15		Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
	Intellectual Property and Copyright Statements . . . . . . . . . . 16		Intellectual Property and Copyright Statements . . . . . . . . . . 16
	1. Introduction		1. Introduction
	The Real-time Transport Protocol (RTP) [1] is widely used in video		The Real-time Transport Protocol (RTP) [1] is widely used in video
	streaming, telephony, and other real-time networked applications.		streaming, telephony, and other real-time networked applications.
	RTP can run over a range of lower-layer transport protocols, and the		RTP can run over a range of lower-layer transport protocols, and the
	performance of an application using RTP is heavily influenced by the		performance of an application using RTP is heavily influenced by the
	choice of lower-layer transport. The Datagram Congestion Control		choice of lower-layer transport. The Datagram Congestion Control
	skipping to change at page 3, line 23 ¶		skipping to change at page 3, line 23 ¶
	provides desirable properties for real-time applications running on		provides desirable properties for real-time applications running on
	unmanaged best-effort IP networks. This memo describes how RTP can		unmanaged best-effort IP networks. This memo describes how RTP can
	be framed for transport using DCCP, and discusses some of the		be framed for transport using DCCP, and discusses some of the
	implications of such a framing. It also describes how the Session		implications of such a framing. It also describes how the Session
	Description Protocol (SDP) [3] can be used to signal such sessions.		Description Protocol (SDP) [3] can be used to signal such sessions.
	The remainder of this memo is structured as follows: we begin with a		The remainder of this memo is structured as follows: we begin with a
	rationale for the work in Section 2, describing why a mapping of RTP		rationale for the work in Section 2, describing why a mapping of RTP
	onto DCCP is needed. Following a description of the conventions used		onto DCCP is needed. Following a description of the conventions used
	in this memo in Section 3, the specification begins in Section 4 with		in this memo in Section 3, the specification begins in Section 4 with
	the definition of how RTP packets are framed within DCCP; associated		the definition of how RTP packets are framed within DCCP. Associated
	signalling is described in Section 5. We conclude with a discussion		signalling is described in Section 5. We conclude with a discussion
	of security considerations in Section 6, and IANA considerations in		of security considerations in Section 6, and IANA considerations in
	Section 7.		Section 7.
	2. Rationale		2. Rationale
	With the widespread adoption of RTP have come concerns that many real		With the widespread adoption of RTP have come concerns that many real
	time applications do not implement congestion control, leading to the		time applications do not implement congestion control, leading to the
	potential for congestion collapse of the network [14]. The designers		potential for congestion collapse of the network [16]. The designers
	of RTP recognised this issue, stating that [4]:		of RTP recognised this issue, stating that [4]:
	If best-effort service is being used, RTP receivers SHOULD monitor		If best-effort service is being used, RTP receivers SHOULD monitor
	packet loss to ensure that the packet loss rate is within		packet loss to ensure that the packet loss rate is within
	acceptable parameters. Packet loss is considered acceptable if a		acceptable parameters. Packet loss is considered acceptable if a
	TCP flow across the same network path and experiencing the same		TCP flow across the same network path and experiencing the same
	network conditions would achieve an average throughput, measured		network conditions would achieve an average throughput, measured
	on a reasonable time-scale, that is not less than the RTP flow is		on a reasonable time-scale, that is not less than the RTP flow is
	achieving. This condition can be satisfied by implementing		achieving. This condition can be satisfied by implementing
	congestion control mechanisms to adapt the transmission rate (or		congestion control mechanisms to adapt the transmission rate (or
	skipping to change at page 4, line 9 ¶		skipping to change at page 4, line 9 ¶
	While the goals are clear, the development of TCP friendly congestion		While the goals are clear, the development of TCP friendly congestion
	control that can be used with RTP and real-time media applications is		control that can be used with RTP and real-time media applications is
	an open research question with many proposals for new algorithms, but		an open research question with many proposals for new algorithms, but
	little deployment experience.		little deployment experience.
	Two approaches have been used to provide congestion control for RTP:		Two approaches have been used to provide congestion control for RTP:
	1) develop new RTP profiles that incorporate congestion control; and		1) develop new RTP profiles that incorporate congestion control; and
	2) provide mechanisms for running RTP over congestion controlled		2) provide mechanisms for running RTP over congestion controlled
	transport protocols. The RTP Profile for TCP Friendly Rate Control		transport protocols. The RTP Profile for TCP Friendly Rate Control
	[15] is an example of the first approach, extending the RTP packet		[17] is an example of the first approach, extending the RTP packet
	formats to incorporate feedback information such that TFRC congestion		formats to incorporate feedback information such that TFRC congestion
	control [16] can be implemented at the application level. This		control [18] can be implemented at the application level. This will
	approach has the advantage that congestion control can be added to		allow congestion control to be added to existing applications without
	existing applications, without needing operating system or network		operating system or network support, and it offers the flexibility to
	support, and offers flexibility to experiment with new congestion		experiment with new congestion control algorithms as they are
	control algorithms as they are developed. Unfortunately, there is		developed. Unfortunately, it also passes the complexity of
	also the consequent disadvantage that the complexity of implementing		implementing congestion control onto application authors, a burden
	congestion control is passed onto the application author, a burden
	which many would prefer to avoid.		which many would prefer to avoid.
	The other approach is to run RTP on a lower-layer transport protocol		The other approach is to run RTP on a lower-layer transport protocol
	that provides congestion control. One possibility is to run RTP over		that provides congestion control. One possibility is to run RTP over
	TCP, as defined in [5], but the reliable nature of TCP and the		TCP, as defined in [5], but the reliable nature of TCP and the
	dynamics of its congestion control algorithm make this inappropriate		dynamics of its congestion control algorithm make this inappropriate
	for most interactive real time applications (SCTP is inappropriate		for most interactive real time applications (the Stream Control
	for similar reasons). A better fit for such applications may be to		Transmission Protocol (SCTP) is inappropriate for similar reasons).
	run RTP over DCCP, since DCCP offers unreliable packet delivery and a		A better fit for such applications may be to run RTP over DCCP, since
	choice of congestion control. This gives applications the ability to		DCCP offers unreliable packet delivery and a choice of congestion
	tailor the transport to their needs, taking advantage of better		control. This gives applications the ability to tailor the transport
	congestion control algorithms as they come available, while passing		to their needs, taking advantage of better congestion control
	complexity of implementation to the operating system. If DCCP should		algorithms as they come available, while passing complexity of
	come to be widely available, it is believed these will be compelling		implementation to the operating system. If DCCP should come to be
	advantages. Accordingly, this memo defines a mapping of RTP onto		widely available, it is believed these will be compelling advantages.
	DCCP.		Accordingly, this memo defines a mapping of RTP onto DCCP.
	3. Conventions Used in this Memo		3. Conventions Used in this Memo
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in RFC 2119 [6].		document are to be interpreted as described in RFC 2119 [6].
	4. RTP over DCCP: Framing		4. RTP over DCCP: Framing
	The following section defines how RTP and RTCP packets can be framed		The following section defines how RTP and RTCP packets can be framed
	skipping to change at page 5, line 15 ¶		skipping to change at page 5, line 13 ¶
	Fields in the RTP header MUST be interpreted according to the RTP		Fields in the RTP header MUST be interpreted according to the RTP
	specification, and any applicable RTP Profile and Payload Format.		specification, and any applicable RTP Profile and Payload Format.
	Header processing is not affected by DCCP framing (in particular,		Header processing is not affected by DCCP framing (in particular,
	note that the semantics of the RTP sequence number and the DCCP		note that the semantics of the RTP sequence number and the DCCP
	sequence number are not compatible, and the value of one cannot be		sequence number are not compatible, and the value of one cannot be
	inferred from the other).		inferred from the other).
	A DCCP connection is opened when an end system joins an RTP session,		A DCCP connection is opened when an end system joins an RTP session,
	and it remains open for the duration of the session. To ensure NAT		and it remains open for the duration of the session. To ensure NAT
	bindings are kept open, an end system SHOULD send a zero length DCCP-		bindings are kept open, an end system SHOULD send a zero length DCCP-
	Data packet once every 15 seconds during periods when it has no RTP		Data packet once every 15 seconds during periods when it has no other
	data to send. This removes the need for RTP no-op packets [17], and		data to send. This removes the need for RTP no-op packets [19], and
	similar application level keep-alives, when using RTP over DCCP.		similar application level keep-alives, when using RTP over DCCP.
	RTP data packets MUST obey the dictates of DCCP congestion control.		RTP data packets MUST obey the dictates of DCCP congestion control.
	In some cases, the congestion control will require a sender to send		In some cases, the congestion control will require a sender to send
	at a rate below that which the payload format would otherwise use.		at a rate below that which the payload format would otherwise use.
	To support this, an application should use either a rate adaptive		To support this, an application should use either a rate adaptive
	payload format, or a range of payload formats (allowing it to switch		payload format, or a range of payload formats (allowing it to switch
	to a lower rate format if necessary). Details of the rate adaptation		to a lower rate format if necessary). Details of the rate adaptation
	policy for particular payload formats are outside the scope of this		policy for particular payload formats are outside the scope of this
	memo.		memo (but see [20] and [21] for guidance).
	TODO: provide more guidance on implementation of congestion control
	within an RTP application.
	DCCP allows an application to choose the checksum coverage, using a		DCCP allows an application to choose the checksum coverage, using a
	partial checksum to allow an application to receive packets with		partial checksum to allow an application to receive packets with
	corrupt payloads. Some RTP Payload Formats (e.g. [18]) can make use		corrupt payloads. Some RTP Payload Formats (e.g. [22]) can make use
	of this feature in conjunction with payload-specific mechanisms to		of this feature in conjunction with payload-specific mechanisms to
	improve performance when operating in environments with frequent non-		improve performance when operating in environments with frequent non-
	congestive packet corruption. If such a payload format is used, an		congestive packet corruption. If such a payload format is used, an
	RTP end system MAY enable partial checksums at the DCCP layer, in		RTP end system MAY enable partial checksums at the DCCP layer, in
	which case the checksum MUST cover at least the DCCP and RTP headers		which case the checksum MUST cover at least the DCCP and RTP headers
	to ensure packets are correctly delivered. Partial checksums MUST		to ensure packets are correctly delivered. Partial checksums MUST
	NOT be used unless supported by mechanisms in the RTP payload format.		NOT be used unless supported by mechanisms in the RTP payload format.
	4.2. RTP Control Packets		4.2. RTP Control Packets
	skipping to change at page 6, line 17 ¶		skipping to change at page 6, line 13 ¶
	packet was sent is then used as the basis for calculating the next		packet was sent is then used as the basis for calculating the next
	RTCP transmission time.		RTCP transmission time.
	RTCP packets comprise only a small fraction of the total traffic in		RTCP packets comprise only a small fraction of the total traffic in
	an RTP session. Accordingly, it is expected that delays in their		an RTP session. Accordingly, it is expected that delays in their
	transmission due to congestion control will not be common, provided		transmission due to congestion control will not be common, provided
	the configured nominal "session bandwidth" (see Section 6.2 of [1])		the configured nominal "session bandwidth" (see Section 6.2 of [1])
	is in line with the bandwidth achievable on the DCCP connection. If,		is in line with the bandwidth achievable on the DCCP connection. If,
	however, the capacity of the DCCP connection is significantly below		however, the capacity of the DCCP connection is significantly below
	the nominal session bandwidth, RTCP packets may be delayed enough for		the nominal session bandwidth, RTCP packets may be delayed enough for
	participants to time out due to apparant inactivity. In such cases,		participants to time out due to apparent inactivity. In such cases,
	the session parameters SHOULD be re-negotiated to more closely match		the session parameters SHOULD be re-negotiated to more closely match
	the available capacity, for example by performing a SIP re-invite		the available capacity, for example by performing a SIP re-invite
	with an updated "b=" line.		with an updated "b=" line.
	Since the nominal session bandwidth is chosen based on media codec		Since the nominal session bandwidth is chosen based on media codec
	capabilities, a session where the nominal bandwidth is much larger		capabilities, a session where the nominal bandwidth is much larger
	than the available bandwidth will likely become unusable due to		than the available bandwidth will likely become unusable due to
	constraints on the media channel, and so require negotiation of a		constraints on the media channel, and so require negotiation of a
	lower bandwidth codec, before it becomes unusable due to		lower bandwidth codec, before it becomes unusable due to
	constraints on the RTCP channel.		constraints on the RTCP channel.
	As noted in Section 17.1 of [2], there is the potential for overlap		As noted in Section 17.1 of [2], there is the potential for overlap
	between information conveyed in RTCP packets and that conveyed in		between information conveyed in RTCP packets and that conveyed in
	DCCP acknowledgement options. In general this is not an issue since		DCCP acknowledgement options. In general this is not an issue since
	RTCP packets contain media-specific data that is not present in DCCP		RTCP packets contain media-specific data that is not present in DCCP
	acknowledgement options, and DCCP options contain network-level data		acknowledgement options, and DCCP options contain network-level data
	that is not present in RTCP. Indeed, there is no overlap between the		that is not present in RTCP. Indeed, there is no overlap between the
	five RTCP packet types defined in the RTP specification [1] and the		five RTCP packet types defined in the RTP specification [1] and the
	standard DCCP options [2]. There are, however, cases where overlap		standard DCCP options [2]. There are, however, cases where overlap
	does occur: most clearly between the optional RTCP Extended Reports		does occur: most clearly between the optional RTCP Extended Reports
	Loss RLE Blocks [19] and the DCCP Ack Vector option. If there is		Loss RLE Blocks [23] and the DCCP Ack Vector option. If there is
	overlap between RTCP report packets and DCCP acknowledgements, an		overlap between RTCP report packets and DCCP acknowledgements, an
	application should use either RTCP feedback or DCCP acknowledgements,		application should use either RTCP feedback or DCCP acknowledgements,
	but not both (use of both types of feedback will waste available		but not both (use of both types of feedback will waste available
	network capacity, but is not otherwise harmful).		network capacity, but is not otherwise harmful).
	4.3. Multiplexing Data and Control		4.3. Multiplexing Data and Control
	The obvious mapping of RTP onto DCCP creates two DCCP connections for		The obvious mapping of RTP onto DCCP creates two DCCP connections for
	each RTP flow: one for RTP data packets, one for RTP control packets.		each RTP flow: one for RTP data packets, one for RTP control packets.
	A frequent criticism of RTP relates to the number of ports it uses,		A frequent criticism of RTP relates to the number of ports it uses,
	since large telephony gateways can support more than 32768 RTP flows		since large telephony gateways can support more than 32768 RTP flows
	between pairs of gateways, and so run out of UDP ports. In addition,		between pairs of gateways, and so run out of UDP ports. In addition,
	use of multiple ports complicates NAT traversal. For these reasons,		use of multiple ports complicates NAT traversal. For these reasons,
	it is RECOMMENDED that RTP and RTCP flows be multiplexed onto a		it is RECOMMENDED that the RTP and RTCP traffic for a single RTP
	single DCCP connection.		session is multiplexed onto a single DCCP connection following the
			guidelines in [7], where possible (it may not be possible in all
	RTP and RTCP packets multiplexed onto a single connection can be		circumstances, for example when translating from an RTP stream over a
	distinguished provided care is taken in assigning RTP payload types.		non-DCCP transport that uses conflicting RTP payload types and RTCP
	The RTP payload type and marker bit(s) occupy the same space in the		packet types).
	packet as does the RTCP packet type field. Provided the RTP payload
	type is chosen such that the payload type, or the payload type plus
	128 (when the marker bit is set), does not clash with any of the used
	RTCP packet types, the two can be demultiplexed. With the RTCP
	packet types registered at the time of this writing, this implies
	that RTP payload types 64-65 and 72-79 must be avoided. None of the
	registered static payload type assignments are in this range, and
	typical practice is to make dynamic assignments in the range 96-127,
	so this restriction is not typically problematic. This multiplexing
	does not otherwise impact the operation of RTP or RTCP.
	There may be circumstances where multiplexing RTP and RTCP is not
	desired, for example when translating from an RTP stream over non-
	DCCP transport that uses conflicting RTP payload types and RTCP
	packet types. As specified in Section 5.1, the "a=rtcp:" SDP
	attribute MAY be used to signal use of non-multiplexed RTCP.
	4.4. RTP Sessions and DCCP Connections		4.4. RTP Sessions and DCCP Connections
	An end system should not assume that it will observe only a single		An end system should not assume that it will observe only a single
	RTP synchronisation source (SSRC) because it is using DCCP framing.		RTP synchronisation source (SSRC) because it is using DCCP framing.
	An RTP session can span any number of transport connections, and can		An RTP session can span any number of transport connections, and can
	include RTP mixers or translators bringing other participants into		include RTP mixers or translators bringing other participants into
	the session. The use of a unicast DCCP connection does not imply		the session. The use of a unicast DCCP connection does not imply
	that the RTP session will have only two participants, and RTP end		that the RTP session will have only two participants, and RTP end
	systems must assume that multiple synchronisation sources may be		systems must assume that multiple synchronisation sources may be
	skipping to change at page 8, line 14 ¶		skipping to change at page 7, line 42 ¶
	second example might be an RTP over DCCP connection that links PSTN		second example might be an RTP over DCCP connection that links PSTN
	gateways. The issues for such an RTP translator are similar to those		gateways. The issues for such an RTP translator are similar to those
	when linking two DCCP connections, except that the congestion control		when linking two DCCP connections, except that the congestion control
	algorithms on either side of the translator may not be compatible.		algorithms on either side of the translator may not be compatible.
	Implementation of effective translators for such an environment is		Implementation of effective translators for such an environment is
	non-trivial.		non-trivial.
	4.5. RTP Profiles		4.5. RTP Profiles
	In general, there is no conflict between new RTP Profiles and DCCP		In general, there is no conflict between new RTP Profiles and DCCP
	framing, and most RTP profiles can be negotiated for use over DCCP.		framing, and most RTP profiles can be negotiated for use over DCCP
	The only potential for conflict occurs if an RTP profile changes the		with the following exceptions:
	RTCP reporting interval or the RTP packet transmission rules, since
	this may conflict with DCCP congestion control. If an RTP profile		o An RTP profile that changes the RTCP reporting interval or the RTP
	conflicts with DCCP congestion control, that profile MUST NOT be used		transmission rules may conflict with DCCP congestion control. For
	with DCCP.		example, the RTP Profile for TFRC [17] conflicts with DCCP by
			changing the RTP packet transmission rules to provide alternate
			congestion control semantics.
			o An RTP profile that is intolerant of packet corruption may
			conflict with the DCCP partial checksum feature. An example of
			this is the integrity protection provided by the RTP/SAVP profile,
			which cannot be used in conjunction with DCCP partial checksums.
			o An RTP profile that mandates a particular non-DCCP lower layer
			transport will conflict with DCCP.
			RTP profiles which fall under these exceptions SHOULD NOT be used
			with DCCP unless the conflicting features can be disabled.
	Of the profiles currently defined, the RTP Profile for Audio and		Of the profiles currently defined, the RTP Profile for Audio and
	Video Conferences with Minimal Control [4], the Secure Real-time		Video Conferences with Minimal Control [4], the Secure Real-time
	Transport Protocol [7], the Extended RTP Profile for RTCP-based		Transport Protocol [8], the Extended RTP Profile for RTCP-based
	Feedback [8], and the Extended Secure RTP Profile for RTCP-based		Feedback [9], and the Extended Secure RTP Profile for RTCP-based
	Feedback [9] MAY be used with DCCP. The RTP Profile for TFRC [15]		Feedback [10] MAY be used with DCCP (noting the potential conflict
	MUST NOT be used with DCCP, since it conflicts with DCCP congestion		between DCCP partial checksums and the integrity protection provided
	control by providing alternative congestion control semantics.		by the secure RTP variants -- see Section 6). The RTP Profile for
			TFRC [17] MUST NOT be used with DCCP, since it conflicts with DCCP by
			providing alternative congestion control semantics (DCCP CCID 3 [11]
			provides similar congestion control within the DCCP framework).
	5. RTP over DCCP: Signalling using SDP		5. RTP over DCCP: Signalling using SDP
	The Session Description Protocol (SDP) [3] and the offer/answer model		The Session Description Protocol (SDP) [3] and the offer/answer model
	[10] are widely used to negotiate RTP sessions (for example, using		[12] are widely used to negotiate RTP sessions (for example, using
	the Session Initiation Protocol [20]). This section describes how		the Session Initiation Protocol [24]). This section describes how
	SDP is used to signal RTP sessions running over DCCP.		SDP is used to signal RTP sessions running over DCCP.
	5.1. Protocol Identification		5.1. Protocol Identification
	SDP uses a media ("m=") line to convey details of the media format		SDP uses a media ("m=") line to convey details of the media format
	and transport protocol used. The ABNF syntax of a media line is as		and transport protocol used. The ABNF syntax of a media line is as
	follows (from [3]):		follows (from [3]):
	media-field = %x6d "=" media SP port ["/" integer] SP proto		media-field = %x6d "=" media SP port ["/" integer] SP proto
	1*(SP fmt) CRLF		1*(SP fmt) CRLF
	The proto field denotes the transport protocol used for the media,		The proto field denotes the transport protocol used for the media,
	while the port indicates the transport port to which the media is		while the port indicates the transport port to which the media is
	sent. Following [5] and [11] this memo defines the following five		sent. Following [5] and [13] this memo defines the following five
	values of the proto field to indicate media transported using DCCP:		values of the proto field to indicate media transported using DCCP:
	DCCP		DCCP
	DCCP/RTP/AVP		DCCP/RTP/AVP
	DCCP/RTP/SAVP		DCCP/RTP/SAVP
	DCCP/RTP/AVPF		DCCP/RTP/AVPF
	DCCP/RTP/SAVPF		DCCP/RTP/SAVPF
	The "DCCP" protocol identifier is similar to the "UDP" and "TCP"		The "DCCP" protocol identifier is similar to the "UDP" and "TCP"
	protocol identifiers and describes the transport protocol, but not		protocol identifiers and describes the transport protocol, but not
	skipping to change at page 9, line 24 ¶		skipping to change at page 9, line 19 ¶
	protocol MUST further qualify the application layer protocol using a		protocol MUST further qualify the application layer protocol using a
	fmt identifier. A single DCCP port is used, as denoted by the port		fmt identifier. A single DCCP port is used, as denoted by the port
	field in the media line. The "DCCP" protocol identifier MUST NOT be		field in the media line. The "DCCP" protocol identifier MUST NOT be
	used to signal RTP sessions running over DCCP.		used to signal RTP sessions running over DCCP.
	The "DCCP/RTP/AVP" protocol identifier refers to RTP using the RTP		The "DCCP/RTP/AVP" protocol identifier refers to RTP using the RTP
	Profile for Audio and Video Conferences with Minimal Control [4]		Profile for Audio and Video Conferences with Minimal Control [4]
	running over DCCP.		running over DCCP.
	The "DCCP/RTP/SAVP" protocol identifier refers to RTP using the		The "DCCP/RTP/SAVP" protocol identifier refers to RTP using the
	Secure Real-time Transport Protocol [7] running over DCCP.		Secure Real-time Transport Protocol [8] running over DCCP.
	The "DCCP/RTP/AVPF" protocol identifier refers to RTP using the		The "DCCP/RTP/AVPF" protocol identifier refers to RTP using the
	Extended RTP Profile for RTCP-based Feedback [8] running over DCCP.		Extended RTP Profile for RTCP-based Feedback [9] running over DCCP.
	The "DCCP/RTP/SAVPF" protocol identifier refers to RTP using the		The "DCCP/RTP/SAVPF" protocol identifier refers to RTP using the
	Extended Secure RTP Profile for RTCP-based Feedback [9] running over		Extended Secure RTP Profile for RTCP-based Feedback [10] running over
	DCCP.		DCCP.
	By default, a single DCCP connection on the specified port is used		A single DCCP connection can be used to transport multiplexed RTP and
	for both RTP and RTCP packets. The "a=rtcp:" attribute [12] MAY be		RTCP packets. Such multiplexing MUST be signalled using an "a=rtcp:"
	used to specify an alternate DCCP port for RTCP, in which case a		attribute [14] according to the rules in [7]. If multiplexed RTP and
	separate DCCP connection is opened to transport the RTCP data.		RTCP is not to be used, then the "a=rtcp:" attribute MUST NOT be
			present in the SDP offer, and a separate DCCP connection MUST be
			opened to transport the RTCP data on a different DCCP port.
	Port 5004 is registered for use by RTP and SHOULD be the default port		Port 5004 is registered for use by RTP and SHOULD be the default port
	chosen by applications. If more than one RTP session is active from		chosen by applications. If more than one RTP session is active from
	a host, ports in the dynamic range SHOULD be used for the other		a host, ports in the dynamic range SHOULD be used for the other
	sessions. If RTCP is to be sent on a separate DCCP connection to		sessions. If RTCP is to be sent on a separate DCCP connection to
	RTP, the RTCP connection SHOULD use port 5005 by default.		RTP, the RTCP connection SHOULD use port 5005 by default.
	5.2. Service Codes		5.2. Service Codes
	In addition to the port number, specified on the SDP "m=" line, a		In addition to the port number, specified on the SDP "m=" line, a
	DCCP connection has an associated service code. A single new SDP		DCCP connection has an associated service code. A single new SDP
	attribute is defined to signal the service code:		attribute is defined to signal the service code:
	dccp-service-attr = %x61 "=dccp-service-code:" service-code		dccp-service-attr = %x61 "=dccp-service-code:" service-code
	service-code = hex-sc / decimal-sc / ascii-sc		service-code = hex-sc / decimal-sc / ascii-sc
	hex-sc = "SC=x" *HEXDIG		hex-sc = %x53 %x43 "=" %x78 *HEXDIG
	decimal-sc = "SC=" *DIGIT		decimal-sc = %x53 %x43 "=" *DIGIT
	ascii-sc = "SC:" *sc-char		ascii-sc = %x53 %x43 ":" *sc-char
	sc-char = %d42-43, %d45-47, %d63-90, %d95, %d97-122		sc-char = %d42-43, %d45-47, %d63-90, %d95, %d97-122
	where DIGIT and HEXDIG are as defined in [13]. The service code		where DIGIT and HEXDIG are as defined in [15]. The service code
	should be interpreted as defined in Section 8.1.2 of [2]. The		should be interpreted as defined in Section 8.1.2 of [2]. The
	following DCCP service codes are registered for use with RTP:		following DCCP service codes are registered for use with RTP:
	o SC:RTPA an RTP session conveying audio data		o SC:RTPA an RTP session conveying audio data and associated RTCP
	o SC:RTPV an RTP session conveying video data		o SC:RTPV an RTP session conveying video data and associated RTCP
	o SC:RTPT an RTP session conveying textual data		o SC:RTPT an RTP session conveying text media and associated RTCP
	o SC:RTPO an RTP session conveying other types of media		o SC:RTPO an RTP session conveying other media and associated RTCP
			o SC:RTCP an RTCP connection, separate from the corresponding RTP
	To ease the job of middleboxes, applications SHOULD use these service		To ease the job of middleboxes, applications SHOULD use these service
	codes to identify RTP sessions running within DCCP.		codes to identify RTP sessions running within DCCP.
	The "a=dccp-service-code:" attribute is a media level attribute which		The "a=dccp-service-code:" attribute is a media level attribute which
	is not subject to the charset attribute.		is not subject to the charset attribute.
	5.3. Connection Management		5.3. Connection Management
	The "a=setup:" attribute indicates which of the end points should		The "a=setup:" attribute indicates which of the end points should
	initiate the DCCP connection establishment (i.e. send the initial		initiate the DCCP connection establishment (i.e. send the initial
	DCCP-Request packet). The "a=setup:" attribute MUST be used in a		DCCP-Request packet). The "a=setup:" attribute MUST be used in a
	manner comparable with [11], except that DCCP connections are being		manner comparable with [13], except that DCCP connections are being
	initiated rather than TCP connections.		initiated rather than TCP connections.
	After the initial offer/answer exchange, the end points may decide to		After the initial offer/answer exchange, the end points may decide to
	re-negotiate various parameters. The "a=connection:" attribute MUST		re-negotiate various parameters. The "a=connection:" attribute MUST
	be used in a manner compatible with [11] to decide whether a new DCCP		be used in a manner compatible with [13] to decide whether a new DCCP
	connection needs to be established as a result of subsequent offer/		connection needs to be established as a result of subsequent offer/
	answer exchanges, or if the existing connection should still be used.		answer exchanges, or if the existing connection should still be used.
	5.4. Example		5.4. Example
	An offerer at 192.0.2.47 signals its availability for an H.261 video		An offerer at 192.0.2.47 signals its availability for an H.261 video
	session, using RTP/AVP over DCCP with service code "RTPV":		session, using RTP/AVP over DCCP with service code "RTPV". RTP and
			RTCP packets are multiplexed onto a single DCCP connection:
	v=0		v=0
	o=alice 1129377363 1 IN IP4 192.0.2.47		o=alice 1129377363 1 IN IP4 192.0.2.47
	s=-		s=-
	c=IN IP4 192.0.2.47		c=IN IP4 192.0.2.47
	t=0 0		t=0 0
	m=video 5004 DCCP/RTP/AVP 99		m=video 5004 DCCP/RTP/AVP 99
			a=rtcp:5004
	a=rtpmap:99 h261/90000		a=rtpmap:99 h261/90000
	a=dccp-service-code:SC=x52545056		a=dccp-service-code:SC=x52545056
	a=setup:passive		a=setup:passive
	a=connection:new		a=connection:new
			SDP offer showing use of RTP/SAVP over DCCP
	An answerer at 192.0.2.128 receives this offer and responds with the		An answerer at 192.0.2.128 receives this offer and responds with the
	following answer:		following answer:
	v=0		v=0
	o=bob 1129377364 1 IN IP4 192.0.2.128		o=bob 1129377364 1 IN IP4 192.0.2.128
	s=-		s=-
	c=IN IP4 192.0.2.128		c=IN IP4 192.0.2.128
	t=0 0		t=0 0
	m=video 9 DCCP/RTP/AVP 99		m=video 9 DCCP/RTP/AVP 99
			a=rtcp:5004
	a=rtpmap:99 h261/90000		a=rtpmap:99 h261/90000
	a=dccp-service-code:SC:RTPV		a=dccp-service-code:SC:RTPV
	a=setup:active		a=setup:active
	a=connection:new		a=connection:new
			SDP answer showing use of RTP/SAVP over DCCP
	The end point at 192.0.2.128 then initiates a DCCP connection to port		The end point at 192.0.2.128 then initiates a DCCP connection to port
	5004 at 192.0.2.47. Note that DCCP port 5004 is used for both the		5004 at 192.0.2.47. Note that DCCP port 5004 is used for both the
	RTP and RTCP data, and port 5005 is unused.		RTP and RTCP data, and port 5005 is unused.
	6. Security Considerations		6. Security Considerations
	The security considerations in the RTP specification [1] and any		The security considerations in the RTP specification [1] and any
	applicable RTP profile (e.g. [4], [7], [8], or [9]) or payload format		applicable RTP profile (e.g. [4], [8], [9], or [10]) or payload
	apply when transporting RTP over DCCP.		format apply when transporting RTP over DCCP.
	The security considerations in the DCCP specification [2] apply.		The security considerations in the DCCP specification [2] apply.
	The SDP signalling described in Section 5 is subject to the security		The SDP signalling described in Section 5 is subject to the security
	considerations of [3], [10], [11] and [5].		considerations of [3], [12], [13], [5], [14], and [7].
	It is not believed that any additional security considerations are		The provision of effective congestion control for RTP through use of
	introduced as a result of combining these protocols. Indeed, the		DCCP is expected to help reduce the potential for denial-of-service
	provision of effective congestion control for RTP will alleviate the		present when RTP flows ignore the advice in [1] to monitor packet
	potential for denial-of-service present when RTP flows ignore the		loss and reduce their sending rate in the face of persistent
	advice in [1] to monitor packet loss and reduce their sending rate in		congestion.
	the face of persistent congestion.
			There is a potential conflict between the Secure RTP Profiles [8],
			[10] and the DCCP partial checksum option, since these profiles
			introduce, and recommend the use of, message authentication for RTP
			and RTCP packets. Message authentication codes of the type used by
			these profiles cannot be used with partial checksums, since any bit-
			error in the DCCP packet payload will cause the authentication check
			to fail. Accordingly, DCCP partial checksums SHOULD NOT be used in
			conjunction with SRTP authentication. The confidentiality features
			of the basic RTP specification cannot be used with DCCP partial
			checksums, since bit errors propagate. Also, despite the fact that
			bit errors do not propagate when using AES in counter mode, the
			Secure RTP profiles SHOULD NOT be used with DCCP partial checksums,
			since it requires authentication for security, and authentication is
			incompatible with partial checksums.
	7. IANA Considerations		7. IANA Considerations
	The following SDP "proto" field identifiers are registered: "DCCP",		The following SDP "proto" field identifiers are registered: "DCCP",
	"DCCP/RTP/AVP", "DCCP/RTP/SAVP", "DCCP/RTP/AVPF" and "DCCP/RTP/SAVPF"		"DCCP/RTP/AVP", "DCCP/RTP/SAVP", "DCCP/RTP/AVPF" and "DCCP/RTP/SAVPF"
	(see Section 5.1 of this memo).		(see Section 5.1 of this memo).
	One new SDP attribute ("a=dccp-service-code:") is registered (see		One new SDP attribute ("a=dccp-service-code:") is registered (see
	Section 5.2 of this memo).		Section 5.2 of this memo).
	The following DCCP service codes are registered: SC:RTPA, SC:RTPV,		The following DCCP service codes are registered: SC:RTPA, SC:RTPV,
	SC:RTPT, and SC:RTPO (see Section 5.2 of this memo).		SC:RTPT, SC:RTPO, and SC:RTCP (see Section 5.2 of this memo).
	DCCP ports 5004 ("DCCP RTP") and 5005 ("DCCP RTCP") are registered		DCCP ports 5004 ("DCCP RTP") and 5005 ("DCCP RTCP") are registered
	for use as default RTP/RTCP ports (see Section 5.1 of this memo).		for use as default RTP/RTCP ports (see Section 5.1 of this memo).
	The four services codes listed above are to be associated with these		The four services codes listed above are to be associated with these
	ports.		ports.
	8. Acknowledgements		8. Acknowledgements
	This work was supported in part by the UK Engineering and Physical		This work was supported in part by the UK Engineering and Physical
	Sciences Research Council. Thanks are due to to Philippe Gentric,		Sciences Research Council. Thanks are due to to Philippe Gentric,
	skipping to change at page 13, line 8 ¶		skipping to change at page 13, line 31 ¶
	[4] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video		[4] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video
	Conferences with Minimal Control", STD 65, RFC 3551, July 2003.		Conferences with Minimal Control", STD 65, RFC 3551, July 2003.
	[5] Lazzaro, J., "Framing RTP and RTCP Packets over Connection-		[5] Lazzaro, J., "Framing RTP and RTCP Packets over Connection-
	Oriented Transport", RFC 4571, June 2006.		Oriented Transport", RFC 4571, June 2006.
	[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement		[6] 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.
	[7] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.		[7] Perkins, C. and M. Westerlund, "Multiplexing RTP Data and
			Control Packets on a Single Port",
			draft-ietf-avt-rtp-and-rtcp-mux-00 (work in progress),
			October 2006.
			[8] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
	Norrman, "The Secure Real-time Transport Protocol (SRTP)",		Norrman, "The Secure Real-time Transport Protocol (SRTP)",
	RFC 3711, March 2004.		RFC 3711, March 2004.
	[8] Ott, J., Wenger, S., Sato, N., and C. Burmeister, "Extended RTP		[9] Ott, J., Wenger, S., Sato, N., and C. Burmeister, "Extended RTP
	Profile for RTCP-based Feedback(RTP/AVPF)", RFC 4585,		Profile for RTCP-based Feedback(RTP/AVPF)", RFC 4585,
	June 2006.		June 2006.
	[9] Ott, J. and E. Carrara, "Extended Secure RTP Profile for RTCP-		[10] Ott, J. and E. Carrara, "Extended Secure RTP Profile for RTCP-
	based Feedback (RTP/SAVPF)", draft-ietf-avt-profile-savpf-02		based Feedback (RTP/SAVPF)", draft-ietf-avt-profile-savpf-08
	(work in progress), July 2005.		(work in progress), October 2006.
	[10] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with		[11] Floyd, S., Kohler, E., and J. Padhye, "Profile for Datagram
			Congestion Control Protocol (DCCP) Congestion Control ID 3:
			TCP-Friendly Rate Control (TFRC)", RFC 4342, March 2006.
			[12] 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] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the		[13] Yon, D. and G. Camarillo, "TCP-Based Media Transport in the
	Session Description Protocol (SDP)", RFC 4145, September 2005.		Session Description Protocol (SDP)", RFC 4145, September 2005.
	[12] Huitema, C., "Real Time Control Protocol (RTCP) attribute in		[14] Huitema, C., "Real Time Control Protocol (RTCP) attribute in
	Session Description Protocol (SDP)", RFC 3605, October 2003.		Session Description Protocol (SDP)", RFC 3605, October 2003.
	[13] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax		[15] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", RFC 2234, November 1997.		Specifications: ABNF", RFC 2234, November 1997.
	9.2. Informative References		9.2. Informative References
	[14] Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion		[16] Floyd, S. and J. Kempf, "IAB Concerns Regarding Congestion
	Control for Voice Traffic in the Internet", RFC 3714,		Control for Voice Traffic in the Internet", RFC 3714,
	March 2004.		March 2004.
	[15] Gharai, L., "Use of the Extended RTP Profile for RTCP-based		[17] Gharai, L., "RTP Profile for TCP Friendly Rate Control",
	Feedback (RTP/AVPF) to Support TCP-Friendly Rate Control",		draft-ietf-avt-tfrc-profile-06 (work in progress),
	draft-ietf-avt-tfrc-profile-06 (work in progress), June 2006.		September 2007.
	[16] Handley, M., Floyd, S., Padhye, J., and J. Widmer, "TCP		[18] Handley, M., Floyd, S., Padhye, J., and J. Widmer, "TCP
	Friendly Rate Control (TFRC): Protocol Specification",		Friendly Rate Control (TFRC): Protocol Specification",
	RFC 3448, January 2003.		RFC 3448, January 2003.
	[17] Andreasen, F., "A No-Op Payload Format for RTP",		[19] Andreasen, F., "A No-Op Payload Format for RTP",
	draft-wing-avt-rtp-noop-03 (work in progress), May 2005.		draft-wing-avt-rtp-noop-03 (work in progress), May 2005.
	[18] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie, "Real-		[20] Phelan, T., "Strategies for Streaming Media Applications Using
			TCP-Friendly Rate Control", draft-ietf-dccp-tfrc-media-01
			(work in progress), October 2005.
			[21] Phelan, T., "Datagram Congestion Control Protocol (DCCP) User
			Guide", draft-ietf-dccp-user-guide-03 (work in progress),
			April 2005.
			[22] Sjoberg, J., Westerlund, M., Lakaniemi, A., and Q. Xie, "Real-
	Time Transport Protocol (RTP) Payload Format and File Storage		Time Transport Protocol (RTP) Payload Format and File Storage
	Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-		Format for the Adaptive Multi-Rate (AMR) and Adaptive Multi-
	Rate Wideband (AMR-WB) Audio Codecs", RFC 3267, June 2002.		Rate Wideband (AMR-WB) Audio Codecs", RFC 3267, June 2002.
	[19] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol		[23] Friedman, T., Caceres, R., and A. Clark, "RTP Control Protocol
	Extended Reports (RTCP XR)", RFC 3611, November 2003.		Extended Reports (RTCP XR)", RFC 3611, November 2003.
	[20] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A.,		[24] 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.
	Author's Address		Author's Address
	Colin Perkins		Colin Perkins
	University of Glasgow		University of Glasgow
	Department of Computing Science		Department of Computing Science
	17 Lilybank Gardens		17 Lilybank Gardens
	Glasgow G12 8QQ		Glasgow G12 8QQ
	UK		UK
	Email: csp@csperkins.org		Email: csp@csperkins.org
	Intellectual Property Statement		Full Copyright Statement
			Copyright (C) The Internet Society (2006).
			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.
			This document and the information contained herein are provided on an
			"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
			OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
			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
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	skipping to change at page 16, line 29 ¶		skipping to change at page 16, line 45 ¶
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	"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
	OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
	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 (2006). 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		Acknowledgment
	Funding for the RFC Editor function is currently provided by the		Funding for the RFC Editor function is provided by the IETF
	Internet Society.		Administrative Support Activity (IASA).
End of changes. 62 change blocks.
	137 lines changed or deleted		176 lines changed or added
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