draft-ietf-avt-srtp-not-mandatory-01.txt		draft-ietf-avt-srtp-not-mandatory-02.txt
	Network Working Group C. Perkins		Network Working Group C. Perkins
	Internet-Draft University of Glasgow		Internet-Draft University of Glasgow
	Intended status: Informational M. Westerlund		Intended status: Informational M. Westerlund
	Expires: May 6, 2009 Ericsson		Expires: September 10, 2009 Ericsson
	November 2, 2008		March 9, 2009
	Why RTP Does Not Mandate a Single Security Mechanism		Why RTP Does Not Mandate a Single Security Mechanism
	draft-ietf-avt-srtp-not-mandatory-01.txt		draft-ietf-avt-srtp-not-mandatory-02.txt
	Status of this Memo		Status of this Memo
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	Abstract		Abstract
	This memo discusses the problem of securing real-time multimedia		This memo discusses the problem of securing real-time multimedia
	sessions, and explains why the Real-time Transport Protocol (RTP)		sessions, and explains why the Real-time Transport Protocol (RTP)
	does not mandate a single media security mechanism.		does not mandate a single media security mechanism.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. RTP Applications and Deployment Scenarios . . . . . . . . . . 3		2. RTP Applications and Deployment Scenarios . . . . . . . . . . 3
	3. Implications for RTP Media Security . . . . . . . . . . . . . 4		3. Implications for RTP Media Security . . . . . . . . . . . . . 4
	4. Implications for Key Management . . . . . . . . . . . . . . . 5		4. Implications for Key Management . . . . . . . . . . . . . . . 5
	5. On the Requirement for Strong Security in IETF protocols . . . 6		5. On the Requirement for Strong Security in IETF protocols . . . 6
	6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7		6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 7
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 7		7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
	9. Informative References . . . . . . . . . . . . . . . . . . . . 7		9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9		10. Informative References . . . . . . . . . . . . . . . . . . . . 8
	Intellectual Property and Copyright Statements . . . . . . . . . . 10		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
	1. Introduction		1. Introduction
	The Real-time Transport Protocol (RTP) [1] is widely used for voice		The Real-time Transport Protocol (RTP) [RFC3550] is widely used for
	over IP, Internet television, video conferencing, and various other		voice over IP, Internet television, video conferencing, and various
	real-time and streaming media applications. Despite this, the base		other real-time and streaming media applications. Despite this, the
	RTP specification provides very limited options for media security,		base RTP specification provides very limited options for media
	and defines no standard key exchange mechanism. Rather, a number of		security, and defines no standard key exchange mechanism. Rather, a
	extensions are defined to provide confidentiality and authentication		number of extensions are defined to provide confidentiality and
	of media streams, and to exchange security keys. This memo outlines		authentication of media streams, and to exchange security keys. This
	why it is appropriate that multiple extension mechanisms are defined,		memo outlines why it is appropriate that multiple extension
	rather than mandating a single media security and keying mechanism.		mechanisms are defined, rather than mandating a single media security
			and keying mechanism.
	This memo provides information for the community; it does not specify		This memo provides information for the community; it does not specify
	a standard of any kind.		a standard of any kind.
	The structure of this memo is as follows: we begin, in Section 2 by		The structure of this memo is as follows: we begin, in Section 2 by
	describing the scenarios in which RTP is deployed. Following this,		describing the scenarios in which RTP is deployed. Following this,
	Section 3 outlines the implications of this range of scenarios for		Section 3 outlines the implications of this range of scenarios for
	media confidentially and authentication, and Section 4 outlines the		media confidentially and authentication, and Section 4 outlines the
	implications for key exchange. Section 5 outlines how the RTP		implications for key exchange. Section 5 outlines how the RTP
	framework meets the requirement of BCP 61. Section 6 then concludes		framework meets the requirement of BCP 61. Section 6 then concludes
	skipping to change at page 3, line 47		skipping to change at page 3, line 48
	o Centralised group video conferencing with a multipoint conference		o Centralised group video conferencing with a multipoint conference
	unit (MCU)		unit (MCU)
	o Any Source Multicast video conferencing (light-weight sessions;		o Any Source Multicast video conferencing (light-weight sessions;
	Mbone conferencing)		Mbone conferencing)
	o Point-to-point streaming audio and/or video		o Point-to-point streaming audio and/or video
	o Single Source Multicast streaming to large group (IPTV and MBMS		o Single Source Multicast streaming to large group (IPTV and MBMS
	[2])		[MBMS])
	o Replicated unicast streaming to a group		o Replicated unicast streaming to a group
	o Interconnecting components in music production studios and video		o Interconnecting components in music production studios and video
	editing suites		editing suites
	o Interconnecting components of distributed simulation systems		o Interconnecting components of distributed simulation systems
	o Streaming real-time sensor data		o Streaming real-time sensor data
	As can be seen, these scenarios vary from point-to-point to very		As can be seen, these scenarios vary from point-to-point to very
	large multicast groups, from interactive to non-interactive, and from		large multicast groups, from interactive to non-interactive, and from
	low bandwidth (kilobits per second) to very high bandwidth (multiple		low bandwidth (kilobits per second) to very high bandwidth (multiple
	gigabits per second). While most of these applications run over UDP,		gigabits per second). While most of these applications run over UDP
	some use TCP or DCCP as their underlying transport. Some run on		[RFC0768], some use TCP [RFC0793], [RFC4614] or DCCP [RFC4340] as
	highly reliable optical networks, others use low rate unreliable		their underlying transport. Some run on highly reliable optical
	wireless networks. Some applications of RTP operate entirely within		networks, others use low rate unreliable wireless networks. Some
	a single trust domain, others are inter-domain, with untrusted (and		applications of RTP operate entirely within a single trust domain,
	potentially unknown) users. The range of scenarios is wide, and		others are inter-domain, with untrusted (and potentially unknown)
	growing both in number and in heterogeneity.		users. The range of scenarios is wide, and growing both in number
			and in heterogeneity.
	3. Implications for RTP Media Security		3. Implications for RTP Media Security
	The wide range of application scenarios where RTP is used has led to		The wide range of application scenarios where RTP is used has led to
	the development of multiple solutions for media security, considering		the development of multiple solutions for media security, considering
	different requirements. Perhaps the most widely applicable of these		different requirements. Perhaps the most widely applicable of these
	solutions is the Secure RTP (SRTP) framework [3]. This is an		solutions is the Secure RTP (SRTP) framework [RFC3711]. This is an
	application-level media security solution, encrypting the media		application-level media security solution, encrypting the media
	payload data (but not the RTP headers) to provide some degree of		payload data (but not the RTP headers) to provide some degree of
	confidentiality, and providing optional source origin authentication.		confidentiality, and providing optional source origin authentication.
	It was carefully designed to be both low overhead, and to support the		It was carefully designed to be both low overhead, and to support the
	group communication features of RTP, across a range of networks.		group communication features of RTP, across a range of networks.
	SRTP is not the only media security solution in use, however, and		SRTP is not the only media security solution in use, however, and
	alternatives are more appropriate for some scenarios. For example,		alternatives are more appropriate for some scenarios. For example,
	many client-server streaming media applications run over a single TCP		many client-server streaming media applications can run over a single
	connection, multiplexing media data with control information on that		TCP connection, multiplexing media data with control information on
	connection (for example, on an RTSP connection). The natural way to		that connection (RTSP [I-D.ietf-mmusic-rfc2326bis] is a widely used
	provide media security for such client-server media applications is		example of such a protocol). The natural way to provide media
	to use TLS to protect the TCP connection, sending the RTP media data		security for such client-server media applications is to use TLS
			[RFC5246] to protect the TCP connection, sending the RTP media data
	over the TLS connection. Using the SRTP framework in addition to TLS		over the TLS connection. Using the SRTP framework in addition to TLS
	is unncessary, and would result in double encryption of the media,		is unncessary, and would result in double encryption of the media,
	and SRTP cannot be used instead of TLS since it is RTP-specific, and		and SRTP cannot be used instead of TLS since it is RTP-specific, and
	so cannot protect the control traffic.		so cannot protect the control traffic.
	Other RTP use cases work over networks which provide security at the		Other RTP use cases work over networks which provide security at the
	network layer, using IPsec. For example, certain 3GPP networks need		network layer, using IPsec. For example, certain 3GPP networks need
	IPsec security associations for other purposes, and can reuse those		IPsec security associations for other purposes, and can reuse those
	to secure the RTP session [4]. SRTP is, again, unnecessary in such		to secure the RTP session [3GPP.33.210]. SRTP is, again, unnecessary
	environments, and its use would only introduce overhead for no gain.		in such environments, and its use would only introduce overhead for
			no gain.
	For some applications it is sufficient to protect the RTP payload		For some applications it is sufficient to protect the RTP payload
	data while leaving RTP, transport, and network layer headers		data while leaving RTP, transport, and network layer headers
	unprotected. An example of this is RTP broadcast over DVB-H [5],		unprotected. An example of this is RTP broadcast over DVB-H
	where one mode of operation uses ISMAcryp to protect the media data		[ETSI.TS.102.474], where one mode of operation uses ISMAcryp
	only.		(http://www.isma.tv) to protect the media data only.
	Finally, the link layer may be secure, and it may be known that the		Finally, the link layer may be secure, and it may be known that the
	RTP media data is constrained to that single link (for example, when		RTP media data is constrained to that single link (for example, when
	operating in a studio environment, with physical link security). An		operating in a studio environment, with physical link security). An
	environment like this is inherently constrained, but might avoid the		environment like this is inherently constrained, but might avoid the
	need for application, transport, or network layer media security.		need for application, transport, or network layer media security.
	All these are application scenarios where RTP has seen commerical		All these are application scenarios where RTP has seen commerical
	deployment. Other use case also exist, with additional requirements.		deployment. Other use case also exist, with additional requirements.
	There is no media security protocol that is appropriate for all these		There is no media security protocol that is appropriate for all these
	skipping to change at page 5, line 34		skipping to change at page 5, line 37
	With such a diverse range of use case come a range of different		With such a diverse range of use case come a range of different
	protocols for RTP session establishment. Mechanisms used to provide		protocols for RTP session establishment. Mechanisms used to provide
	security keying for these different session establishment protocols		security keying for these different session establishment protocols
	can basically be put into two categories: inband and out-of-band in		can basically be put into two categories: inband and out-of-band in
	relation to the session establishment mechanism. The requirements		relation to the session establishment mechanism. The requirements
	for these solutions are highly varying. Thus a wide range of		for these solutions are highly varying. Thus a wide range of
	solutions have been developed in this space:		solutions have been developed in this space:
	o The most common use case for RTP is probably point-to-point voice		o The most common use case for RTP is probably point-to-point voice
	calls or centralised group conferences, negotiated using SIP with		calls or centralised group conferences, negotiated using SIP
	the SDP offer/answer model, operating on a trusted infrastructure.		[RFC3261] with the SDP offer/answer model [RFC3264], operating on
	In such environments, SDP security descriptions [6] or the MIKEY		a trusted infrastructure. In such environments, SDP security
	[7] protocol are appropriate keying mechanisms, piggybacked onto		descriptions [RFC4568] or the MIKEY [RFC4567] protocol are
	the SDP exchange. The infrastructure may be secured by protecting		appropriate keying mechanisms, piggybacked onto the SDP [RFC4566]
	the SIP exchange using SIPS or S/MIME, for example.		exchange. The infrastructure may be secured by protecting the SIP
			exchange using TLS or S/MIME, for example [RFC3261].
	o Point-to-point RTP sessions may be negotiated using SIP with the		o Point-to-point RTP sessions may be negotiated using SIP with the
	offer/answer model, but operating over a network with untrusted		offer/answer model, but operating over a network with untrusted
	infrastructure. In such environments, the key management protocol		infrastructure. In such environments, the key management protocol
	is run on the media path, bypassing the untrusted infrastructure.		is run on the media path, bypassing the untrusted infrastructure.
	Protocols such as DTLS [8] or ZRTP [9] are useful here.		Protocols such as DTLS [I-D.ietf-avt-dtls-srtp] or ZRTP
			[I-D.zimmermann-avt-zrtp] are useful here.
	o For point-to-point client-server streaming of RTP over RTSP [10],		o For point-to-point client-server streaming of RTP over RTSP, a TLS
	a TLS association is appropriate to manage keying material, in		association is appropriate to manage keying material, in much the
	much the same manner as would be used to secure an HTTP session.		same manner as would be used to secure an HTTP session.
	o A session description may be sent by email, secured using X.500 or		o A session description may be sent by email, secured using X.500 or
	PGP, or retrieved from a web page, using HTTP with TLS.		PGP, or retrieved from a web page, using HTTP with TLS.
	o A session description may be distributed to a multicast group		o A session description may be distributed to a multicast group
	using SAP or FLUTE secured with S/MIME.		using SAP or FLUTE secured with S/MIME.
	o A session description may be distributed using OMA's DRM key		o A session description may be distributed using the Open Mobile
	management [11] with pointer for point to point streaming setup		Alliance DRM key management specification [OMA-DRM] when using a
	with RTSP in 3GPP [12].		point-to-point streaming session setup with RTSP in the 3GPP PSS
			environment [PSS].
	o In the 3GPP MBMS system, HTTP and MIKEY are used for key		o In the 3GPP Multimedia Broadcast Multicast Service (MBMS) system,
	management [13].		HTTP and MIKEY are used for key management [MBMS-SEC].
	A more detailed survey of requirements for media security management		A more detailed survey of requirements for media security management
	protocols can be found in [14]. As can be seen, the range of use		protocols can be found in [I-D.ietf-sip-media-security-requirements].
	cases is wide, and there is no single protocol that is appropriate		As can be seen, the range of use cases is wide, and there is no
	for all scenarios. These solutions have be further diversified by		single protocol that is appropriate for all scenarios. These
	the existence of infrastructure elements such as authentication		solutions have been further diversified by the existence of
	solutions that are tied into the key manangement.		infrastructure elements such as authentication solutions that are
			tied into the key manangement.
	5. On the Requirement for Strong Security in IETF protocols		5. On the Requirement for Strong Security in IETF protocols
	BCP 61 [15] puts a requirement on IETF protocols to provide strong,		BCP 61 [RFC3365] puts a requirement on IETF protocols to provide
	mandatory to implement, security solutions. This is actually quite a		strong, mandatory to implement, security solutions. This is actually
	difficult requirement for any type of framework protocol, like RTP,		quite a difficult requirement for any type of framework protocol,
	since one can never know all the deployement scenarios, and if they		like RTP, since one can never know all the deployment scenarios, and
	are covered by the security solution. It would clearly be desirable		if they are covered by the security solution. It would clearly be
	if a single media security solution and a single key management		desirable if a single media security solution and a single key
	solution could be developed, satisfying the range of use cases for		management solution could be developed, satisfying the range of use
	RTP. The authors are not aware of any such solution, however, and it		cases for RTP. The authors are not aware of any such solution,
	is not clear that any single solution can be developed.		however, and it is not clear that any single solution can be
			developed.
	For a framework protocol it appears that the only sensible solution		For a framework protocol it appears that the only sensible solution
	to the requirement of BCP 61 is to develop or use security building		to the requirement of BCP 61 is to develop or use security building
	blocks, like SRTP, SDES, MIKEY, DTLS, or IPsec, to provide the basic		blocks, like SRTP, SDP security descriptions [RFC4568], MIKEY, DTLS,
	security services of authorization, data integrity protocetion and		or IPsec, to provide the basic security services of authorization,
	date confidentiality protection. When new usages of the RTP		data integrity protection and date confidentiality protection. When
	framework arise, one needs to analyze the situation, to determine of		new usages of the RTP framework arise, one needs to analyze the
	the existing building blocks satisfy the requirements. If not, it is		situation, to determine if the existing building blocks satisfy the
	necessary to develop new security building blocks.		requirements. If not, it is necessary to develop new security
			building blocks.
	When it comes to fulfilling the "MUST Implement" strong security for		When it comes to fulfilling the "MUST Implement" strong security for
	a specific application, it will fall on that application to actually		a specific application, it will fall on that application to actually
	consider what building blocks it is required to support. To maximize		consider what building blocks it is required to support. To maximize
	interoperability it is desirable if certain applications, or classes		interoperability it is desirable if certain applications, or classes
	of application with similar requirements, agree on what data security		of application with similar requirements, agree on what data security
	mechanisms and key-management should be used. If such agreement is		mechanisms and key-management should be used. If such agreement is
	not possible, there will be increased cost, either in the lack of		not possible, there will be increased cost, either in the lack of
	interoperability, or in the need to implement more solutions.		interoperability, or in the need to implement more solutions.
	Unfortunately this situation, if not handled reasonably well, can		Unfortunately this situation, if not handled reasonably well, can
	result in a failure to satisfy the requirement of providing the users		result in a failure to satisfy the requirement of providing the users
	with an option of turining on strong security when desired.		with an option of turning on strong security when desired.
	6. Conclusions		6. Conclusions
	As discussed earlier it appears that a single solution can't be		As discussed earlier it appears that a single solution can't be
	designed to meet the diverse requirements. In the absense of such a		designed to meet the diverse requirements. In the absence of such a
	solution, it is hoped that this memo explains why SRTP is not		solution, it is hoped that this memo explains why SRTP is not
	mandatory as the media security solution for RTP-based systems, and		mandatory as the media security solution for RTP-based systems, and
	why we can expect multiple key management solutions for systems using		why we can expect multiple key management solutions for systems using
	RTP.		RTP.
	It is important for any RTP-based application to consider how it		It is important for any RTP-based application to consider how it
	meets the security requirements. This will require some analysis to		meets the security requirements. This will require some analysis to
	determine these requirements, followed by a selection of a mandatory		determine these requirements, followed by the selection of a
	to implement solution, or in exceptional scenarios several solutions,		mandatory to implement solution, or in exceptional scenarios several
	including the desired RTP traffic protection and key-management.		solutions, including the desired RTP traffic protection and key-
	SRTP is a preferred solution for the protection of the RTP traffic in		management. SRTP is a preferred solution for the protection of the
	those use cases where it is applicable. It is out of scope for this		RTP traffic in those use cases where it is applicable. It is out of
	memo to recommend a preferred key management solution.		scope for this memo to recommend a preferred key management solution.
	7. Security Considerations		7. Security Considerations
	This entire memo is about security.		This entire memo is about security.
	8. IANA Considerations		8. IANA Considerations
	No IANA actions are required.		No IANA actions are required.
	9. Informative References		9. Acknowledgements
	[1] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson,
	"RTP: A Transport Protocol for Real-Time Applications", STD 64,
	RFC 3550, July 2003.
	[2] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS); Protocols		Thanks to Ralph Blom, Hannes Tschofenig, Dan York, Alfred Hoenes, and
	and codecs TS 26.346".		Martin Ellis for their feedback.
	[3] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.		10. Informative References
	Norrman, "The Secure Real-time Transport Protocol (SRTP)",
	RFC 3711, March 2004.
	[4] 3GPP, "IP network layer security", 3GPP TS 33.210,		[3GPP.33.210]
			3GPP, "IP network layer security", 3GPP TS 33.210,
	September 2008.		September 2008.
	[5] ETSI, "Digital Video Broadcasting (DVB); IP Datacast over		[ETSI.TS.102.474]
			ETSI, "Digital Video Broadcasting (DVB); IP Datacast over
	DVB-H: Service Purchase and Protection", ETSI TS 102 474,		DVB-H: Service Purchase and Protection", ETSI TS 102 474,
	November 2007.		November 2007.
	[6] Andreasen, F., Baugher, M., and D. Wing, "Session Description		[I-D.ietf-avt-dtls-srtp]
	Protocol (SDP) Security Descriptions for Media Streams",		McGrew, D. and E. Rescorla, "Datagram Transport Layer
	RFC 4568, July 2006.		Security (DTLS) Extension to Establish Keys for Secure
			Real-time Transport Protocol (SRTP)",
	[7] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E.		draft-ietf-avt-dtls-srtp-06 (work in progress),
	Carrara, "Key Management Extensions for Session Description		October 2008.
	Protocol (SDP) and Real Time Streaming Protocol (RTSP)",
	RFC 4567, July 2006.
	[8] McGrew, D. and E. Rescorla, "Datagram Transport Layer Security		[I-D.ietf-mmusic-rfc2326bis]
	(DTLS) Extension to Establish Keys for Secure Real-time		Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M.,
	Transport Protocol (SRTP)", draft-ietf-avt-dtls-srtp-06 (work		and M. Stiemerling, "Real Time Streaming Protocol 2.0
	in progress), October 2008.		(RTSP)", draft-ietf-mmusic-rfc2326bis-19 (work in
			progress), November 2008.
	[9] Zimmermann, P., Johnston, A., and J. Callas, "ZRTP: Media Path		[I-D.ietf-sip-media-security-requirements]
	Key Agreement for Secure RTP", draft-zimmermann-avt-zrtp-10		Wing, D., Fries, S., Tschofenig, H., and F. Audet,
			"Requirements and Analysis of Media Security Management
			Protocols", draft-ietf-sip-media-security-requirements-08
	(work in progress), October 2008.		(work in progress), October 2008.
	[10] Schulzrinne, H., Rao, A., Lanphier, R., Westerlund, M., and M.		[I-D.zimmermann-avt-zrtp]
	Stiemerling, "Real Time Streaming Protocol 2.0 (RTSP)",		Zimmermann, P., Johnston, A., and J. Callas, "ZRTP: Media
	draft-ietf-mmusic-rfc2326bis-18 (work in progress), May 2008.		Path Key Agreement for Secure RTP",
			draft-zimmermann-avt-zrtp-10 (work in progress),
	[11] Open Mobile Alliance, "DRM Specification 2.0".		October 2008.
	[12] 3GPP, "Transparent end-to-end Packet-switched Streaming Service		[MBMS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS);
	(PSS); Protocols and codecs TS 26.234".		Protocols and codecs TS 26.346".
	[13] 3GPP, "Security of Multimedia Broadcast/Multicast Service		[MBMS-SEC]
			3GPP, "Security of Multimedia Broadcast/Multicast Service
	(MBMS) TS 33.246".		(MBMS) TS 33.246".
	[14] Wing, D., Fries, S., Tschofenig, H., and F. Audet,		[OMA-DRM] Open Mobile Alliance, "DRM Specification 2.0".
	"Requirements and Analysis of Media Security Management
	Protocols", draft-ietf-sip-media-security-requirements-08 (work
	in progress), October 2008.
	[15] Schiller, J., "Strong Security Requirements for Internet		[PSS] 3GPP, "Transparent end-to-end Packet-switched Streaming
	Engineering Task Force Standard Protocols", BCP 61, RFC 3365,		Service (PSS); Protocols and codecs TS 26.234".
	August 2002.
			[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
			August 1980.
			[RFC0793] Postel, J., "Transmission Control Protocol", STD 7,
			RFC 793, September 1981.
			[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
			A., Peterson, J., Sparks, R., Handley, M., and E.
			Schooler, "SIP: Session Initiation Protocol", RFC 3261,
			June 2002.
			[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
			with Session Description Protocol (SDP)", RFC 3264,
			June 2002.
			[RFC3365] Schiller, J., "Strong Security Requirements for Internet
			Engineering Task Force Standard Protocols", BCP 61,
			RFC 3365, August 2002.
			[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
			Jacobson, "RTP: A Transport Protocol for Real-Time
			Applications", STD 64, RFC 3550, July 2003.
			[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
			Norrman, "The Secure Real-time Transport Protocol (SRTP)",
			RFC 3711, March 2004.
			[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
			Congestion Control Protocol (DCCP)", RFC 4340, March 2006.
			[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
			Description Protocol", RFC 4566, July 2006.
			[RFC4567] Arkko, J., Lindholm, F., Naslund, M., Norrman, K., and E.
			Carrara, "Key Management Extensions for Session
			Description Protocol (SDP) and Real Time Streaming
			Protocol (RTSP)", RFC 4567, July 2006.
			[RFC4568] Andreasen, F., Baugher, M., and D. Wing, "Session
			Description Protocol (SDP) Security Descriptions for Media
			Streams", RFC 4568, July 2006.
			[RFC4614] Duke, M., Braden, R., Eddy, W., and E. Blanton, "A Roadmap
			for Transmission Control Protocol (TCP) Specification
			Documents", RFC 4614, September 2006.
			[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
			(TLS) Protocol Version 1.2", RFC 5246, August 2008.
	Authors' Addresses		Authors' Addresses
	Colin Perkins		Colin Perkins
	University of Glasgow		University of Glasgow
	Department of Computing Science		Department of Computing Science
	Sir Alwyn Williams Building		Sir Alwyn Williams Building
	Lilybank Gardens		Lilybank Gardens
	Glasgow G12 8QQ		Glasgow G12 8QQ
	UK		UK
	Email: csp@csperkins.org		Email: csp@csperkins.org
	Magnus Westerlund		Magnus Westerlund
	Ericsson		Ericsson
	Torshamgatan 23		Torshamgatan 23
	Stockholm SE-164 80		Stockholm SE-164 80
	Sweden		Sweden
	Email: magnus.westerlund@ericsson.com		Email: magnus.westerlund@ericsson.com
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