< draft-ietf-ecrit-psap-callback-09.txt		draft-ietf-ecrit-psap-callback-10.txt >
	ECRIT H. Schulzrinne		ECRIT H. Schulzrinne
	Internet-Draft Columbia University		Internet-Draft Columbia University
	Intended status: Standards Track H. Tschofenig		Intended status: Standards Track H. Tschofenig
	Expires: September 20, 2013 Nokia Siemens Networks		Expires: January 14, 2014 Nokia Siemens Networks
	C. Holmberg		C. Holmberg
	Ericsson		Ericsson
	M. Patel		M. Patel
	InterDigital Communications		InterDigital Communications
	March 19, 2013		July 13, 2013
	Public Safety Answering Point (PSAP) Callback		Public Safety Answering Point (PSAP) Callback
	draft-ietf-ecrit-psap-callback-09.txt		draft-ietf-ecrit-psap-callback-10.txt
	Abstract		Abstract
	After an emergency call is completed (either prematurely terminated		After an emergency call is completed (either prematurely terminated
	by the emergency caller or normally by the call taker) it is possible		by the emergency caller or normally by the call taker) it is possible
	that the call taker feels the need for further communication. For		that the call taker feels the need for further communication. For
	example, the call may have been dropped by accident without the call		example, the call may have been dropped by accident without the call
	taker having sufficient information about the current situation of a		taker having sufficient information about the current situation of a
	wounded person. A call taker may trigger a callback towards the		wounded person. A call taker may trigger a callback towards the
	emergency caller using the contact information provided with the		emergency caller using the contact information provided with the
	skipping to change at page 2, line 10 ¶		skipping to change at page 2, line 10 ¶
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on September 20, 2013.		This Internet-Draft will expire on January 14, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2013 IETF Trust and the persons identified as the		Copyright (c) 2013 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
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	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
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	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Callback Scenarios . . . . . . . . . . . . . . . . . . . . . . 6		3. Callback Scenarios . . . . . . . . . . . . . . . . . . . . . 4
	3.1. Routing Asymmetry . . . . . . . . . . . . . . . . . . . . 6		3.1. Routing Asymmetry . . . . . . . . . . . . . . . . . . . . 5
	3.2. Multi-Stage Routing . . . . . . . . . . . . . . . . . . . 7		3.2. Multi-Stage Routing . . . . . . . . . . . . . . . . . . . 6
	3.3. Call Forwarding . . . . . . . . . . . . . . . . . . . . . 8		3.3. Call Forwarding . . . . . . . . . . . . . . . . . . . . . 7
	3.4. Network-based Service URN Resolution . . . . . . . . . . . 10		3.4. Network-based Service URN Resolution . . . . . . . . . . 8
	3.5. PSTN Interworking . . . . . . . . . . . . . . . . . . . . 11		3.5. PSTN Interworking . . . . . . . . . . . . . . . . . . . . 9
	4. SIP PSAP Callback Indicator . . . . . . . . . . . . . . . . . 12		4. SIP PSAP Callback Indicator . . . . . . . . . . . . . . . . . 10
	4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 12		4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10
	4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 12		4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . . 12		4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 11
	4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 12		4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 11
	4.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . . 12		4.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . 11
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 13		5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
	5.1. Security Threat . . . . . . . . . . . . . . . . . . . . . 13		5.1. Security Threat . . . . . . . . . . . . . . . . . . . . . 11
	5.2. Security Requirements . . . . . . . . . . . . . . . . . . 13		5.2. Security Requirements . . . . . . . . . . . . . . . . . . 11
	5.3. Security Solution . . . . . . . . . . . . . . . . . . . . 13		5.3. Security Solution . . . . . . . . . . . . . . . . . . . . 12
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
	7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16		7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17		8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 17		8.1. Normative References . . . . . . . . . . . . . . . . . . 13
	8.2. Informative References . . . . . . . . . . . . . . . . . . 17		8.2. Informative References . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	Summoning police, the fire department or an ambulance in emergencies		Summoning police, the fire department or an ambulance in emergencies
	is one of the fundamental and most-valued functions of the telephone.		is one of the fundamental and most-valued functions of the telephone.
	As telephone functionality moves from circuit-switched telephony to		As telephone functionality moves from circuit-switched telephony to
	Internet telephony, its users rightfully expect that this core		Internet telephony, its users rightfully expect that this core
	functionality will continue to work at least as well as it has for		functionality will continue to work at least as well as it has for
	the legacy technology. New devices and services are being made		the legacy technology. New devices and services are being made
	available that could be used to make a request for help, which are		available that could be used to make a request for help, which are
	skipping to change at page 5, line 7 ¶		skipping to change at page 4, line 41 ¶
	This approach mimics a stateful packet filtering firewall and is		This approach mimics a stateful packet filtering firewall and is
	indeed helpful in a number of cases. It is also relatively simple to		indeed helpful in a number of cases. It is also relatively simple to
	implement even though it requires call state to be maintained by the		implement even though it requires call state to be maintained by the
	user agent as well as by SIP intermediaries. Unfortunately, the		user agent as well as by SIP intermediaries. Unfortunately, the
	solution does not work in all deployment scenarios. In Section 3 we		solution does not work in all deployment scenarios. In Section 3 we
	describe cases where the currently standardized approach is		describe cases where the currently standardized approach is
	insufficient.		insufficient.
	2. Terminology		2. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].
	Emergency services related terminology is borrowed from [RFC5012].		Emergency services related terminology is borrowed from [RFC5012].
	This includes terminology like emergency caller, user equipment, call		This includes terminology like emergency caller, user equipment, call
	taker, Emergency Service Routing Proxy (ESRP), and Public Safety		taker, Emergency Service Routing Proxy (ESRP), and Public Safety
	Answering Point (PSAP).		Answering Point (PSAP).
	3. Callback Scenarios		3. Callback Scenarios
	This section illustrates a number of scenarios where the currently		This section illustrates a number of scenarios where the currently
	specified solution, as specified in [RFC6881], for preferential		specified solution, as specified in [RFC6881], for preferential
	treatment of callbacks fails. As explained in Section 1 a SIP entity		treatment of callbacks fails. As explained in Section 1 a SIP entity
	examines an incoming PSAP callback by comparing the domain of the		examines an incoming PSAP callback by comparing the domain of the
	PSAP with the destination domain of the emergency call.		PSAP with the destination domain of the emergency call.
			NOTE: All FQDNs used in the subsections below are used for
			illustrative purposes. They are examples to demonstrate the
			limitations of the technical solution outlined in RFC 6881.
	3.1. Routing Asymmetry		3.1. Routing Asymmetry
	In some deployment environments it is common to have incoming and		In some deployment environments it is common to have incoming and
	outgoing SIP messaging routed through different SIP entities.		outgoing SIP messaging routed through different SIP entities. Figure
	Figure 1 shows this graphically whereby a VoIP provider uses		1 shows this graphically whereby a VoIP provider uses different SIP
	different SIP proxies for inbound and for outbound call handling.		proxies for inbound and for outbound call handling. Unless the two
	Unless the two devices are synchronized as to state the callback		devices are synchronized as to state the callback hitting the inbound
	hitting the inbound proxy would get treated like any other call since		proxy would get treated like any other call since the emergency call
	the emergency call established state information at the outbound		established state information at the outbound proxy only.
	proxy only.
	,-------.		,-------.
	,' `.		,' `.
	,-------. / Emergency \		,-------. / Emergency \
	,' `. | Services |		,' `. | Services |
	/ VoIP \ I | Network |		/ VoIP \ I | Network |
	| Provider | n | |		| Provider | n | |
	| | t | |		| | t | |
	| | e | |		| | e | |
	| +-------+ | r | |		| +-------+ | r | |
	skipping to change at page 9, line 5 ¶		skipping to change at page 7, line 45 ¶
	town.org, fire-town.org or medic-town.org). The same considerations		town.org, fire-town.org or medic-town.org). The same considerations
	apply when the police, fire and ambulance networks are part of the		apply when the police, fire and ambulance networks are part of the
	state.org sub-domains (e.g., police.state.org).		state.org sub-domains (e.g., police.state.org).
	Similarly to the previous scenario the problem here is with the wrong		Similarly to the previous scenario the problem here is with the wrong
	state information being established during the emergency call setup		state information being established during the emergency call setup
	procedure. A callback would originate in the police-town.org, fire-		procedure. A callback would originate in the police-town.org, fire-
	town.org or medic-town.org domain whereas the emergency caller's SIP		town.org or medic-town.org domain whereas the emergency caller's SIP
	UA or the VoIP outbound proxy has stored state.org.		UA or the VoIP outbound proxy has stored state.org.
	,-------.		,-------.
	,' `.		,' `.
	/ Emergency \		/ Emergency \
	| Services |		| Services |
	| Network |		| Network |
	| (state.org) |		| (state.org) |
	| |		| |
	| |		| |
	| +------+ |		| +------+ |
	| |PSAP +--+ |		| |PSAP +--+ |
	| +--+---+ | |		| +--+---+ | |
	| | | |		| | | |
	| | | |		| | | |
	| | | |		| | | |
	| | | |		| | | |
	| | | |		| | | |
	| +--+---+ | |		| +--+---+ | |
	------------------+---+ESRP | | |		------------------+---+ESRP | | |
	esrp-a@state.org | +------+ | |		esrp-a@state.org | +------+ | |
	| | |		| | |
	| Call Fwd | |		| Call Fwd | |
	| +-+-+---+ |		| +-+-+---+ |
	\ | | | /		\ | | | /
	`. | | | ,'		`. | | | ,'
	'-|-|-|-' ,-------.		'-|-|-|-' ,-------.
	Police | | | Fire ,' `.		Police | | | Fire ,' `.
	+------------+ | +----+ / Emergency \		+------------+ | +----+ / Emergency \
	,-------. | | | | Services |		,-------. | | | | Services |
	,' `. | | | | Network |		,' `. | | | | Network |
	/ Emergency \ | Ambulance | | fire-town.org |		/ Emergency \ | Ambulance | | fire-town.org |
	| Services | | | | | |		| Services | | | | | |
	| Network | | +----+ | | +------+ |		| Network | | +----+ | | +------+ |
	|police-town.org| | ,-------. | +----+---+PSAP | |		|police-town.org| | ,-------. | +----+---+PSAP | |
	| | | ,' `. | | +------+ |		| | | ,' `. | | +------+ |
	| +------+ | | / Emergency \ | | |		| +------+ | | / Emergency \ | | |
	| |PSAP +----+--+ | Services | | | ,		| |PSAP +----+--+ | Services | | | ,
	| +------+ | | Network | | `~~~~~~~~~~~~~~~		| +------+ | | Network | | `~~~~~~~~~~~~~~~
	| | |medic-town.org | |		| | |medic-town.org | |
	| , | | |		| , | | |
	`~~~~~~~~~~~~~~~ | +------+ | |		`~~~~~~~~~~~~~~~ | +------+ | |
	| |PSAP +----+ +		| |PSAP +----+ +
	| +------+ |		| +------+ |
	| |		| |
	| ,		| ,
	`~~~~~~~~~~~~~~~		`~~~~~~~~~~~~~~~
	Figure 3: Example for Call Forwarding.		Figure 3: Example for Call Forwarding.
	3.4. Network-based Service URN Resolution		3.4. Network-based Service URN Resolution
	The IETF emergency services architecture also considers cases where		The IETF emergency services architecture also considers cases where
	the resolution from the Service URN to the PSAP URI does not only		the resolution from the Service URN to the PSAP URI does not only
	happen at the SIP UA itself but at intermediate SIP entities, such as		happen at the SIP UA itself but at intermediate SIP entities, such as
	the user's VoIP provider.		the user's VoIP provider.
	Figure 4 shows this message exchange of the outgoing emergency call		Figure 4 shows this message exchange of the outgoing emergency call
	and the incoming PSAP graphically. While the state information		and the incoming PSAP graphically. While the state information
	stored at the VoIP provider is correct the state allocated at the SIP		stored at the VoIP provider is correct the state allocated at the SIP
	UA is not.		UA is not.
	,-------.		,-------.
	,' `.		,' `.
	/ Emergency \		/ Emergency \
	| Services |		| Services |
	| Network |		| Network |
	|police-town.org|		|police-town.org|
	| |		| |
	| +------+ | Invite to police.example.com		| +------+ | Invite to police.example.com
	| |PSAP +<---+------------------------+		| |PSAP +<---+------------------------+
	| | +----+------------------+ ^		| | +----+------------------+ ^
	| +------+ |Invite from | |		| +------+ |Invite from | |
	| ,police.example.com| |		| ,police.example.com| |
	`~~~~~~~~~~~~~~~ v |		`~~~~~~~~~~~~~~~ v |
	+--------+ ++-----+-+		+--------+ ++-----+-+
	| | query |VoIP |		| | query |VoIP |
	| LoST |<-----------------------|Service |		| LoST |<-----------------------|Service |
	| Server | police.example.com |Provider|		| Server | police.example.com |Provider|
	| |----------------------->| |		| |----------------------->| |
	+--------+ +--------+		+--------+ +--------+
	| ^		| ^
	Invite| | Invite		Invite| | Invite
	from| | to		from| | to
	police.example.com| | urn:service:sos		police.example.com| | urn:service:sos
	V |		V |
	+-------+		+-------+
	| SIP |		| SIP |
	| UA |		| UA |
	| Alice |		| Alice |
	+-------+		+-------+
	Figure 4: Example for Network-based Service URN Resolution.		Figure 4: Example for Network-based Service URN Resolution.
	3.5. PSTN Interworking		3.5. PSTN Interworking
	In case an emergency call enters the PSTN, as shown in Figure 5,		In case an emergency call enters the PSTN, as shown in Figure 5,
	there is no guarantee that the callback some time later does leave		there is no guarantee that the callback some time later does leave
	the same PSTN/VoIP gateway or that the same end point identifier is		the same PSTN/VoIP gateway or that the same end point identifier is
	used in the forward as well as in the backward direction making it		used in the forward as well as in the backward direction making it
	difficult to reliably detect PSAP callbacks.		difficult to reliably detect PSAP callbacks.
	+-----------+		+-----------+
	| PSTN |-------------+		| PSTN |-------------+
	| Calltaker | |		| Calltaker | |
	| Bob |<--------+ |		| Bob |<--------+ |
	+-----------+ | v		+-----------+ | v
	-------------------		-------------------
	//// \\\\ +------------+		//// \\\\ +------------+
	| | |PSTN / VoIP |		| | |PSTN / VoIP |
	| PSTN |---->|Gateway |		| PSTN |---->|Gateway |
	\\\\ //// | |		\\\\ //// | |
	------------------- +----+-------+		------------------- +----+-------+
	^ |		^ |
	| |		| |
	+-------------+ | +--------+		+-------------+ | +--------+
	| | | |VoIP |		| | | |VoIP |
	| PSTN / VoIP | +->|Service |		| PSTN / VoIP | +->|Service |
	| Gateway | |Provider|		| Gateway | |Provider|
	| |<------Invite----| Y |		| |<------Invite----| Y |
	+-------------+ +--------+		+-------------+ +--------+
	| ^		| ^
	| |		| |
	Invite Invite		Invite Invite
	| |		| |
	V |		V |
	+-------+		+-------+
	| SIP |		| SIP |
	| UA |		| UA |
	| Alice |		| Alice |
	+-------+		+-------+
	Figure 5: Example for PSTN Interworking.		Figure 5: Example for PSTN Interworking.
	Note: This scenario is considered outside the scope of this document.		Note: This scenario is considered outside the scope of this document.
	The specified solution does not support this use case.		The specified solution does not support this use case.
	4. SIP PSAP Callback Indicator		4. SIP PSAP Callback Indicator
	4.1. General		4.1. General
	skipping to change at page 12, line 35 ¶		skipping to change at page 11, line 20 ¶
	4.3. Syntax		4.3. Syntax
	4.3.1. General		4.3.1. General
	This section defines the ABNF for the new SIP Priority header field		This section defines the ABNF for the new SIP Priority header field
	value "psap-callback".		value "psap-callback".
	4.3.2. ABNF		4.3.2. ABNF
	priority-value /= "psap-callback"		priority-value /= "psap-callback"
	Figure 6: ABNF		Figure 6: ABNF
	5. Security Considerations		5. Security Considerations
	5.1. Security Threat		5.1. Security Threat
	The PSAP callback functionality described in this document allows		The PSAP callback functionality described in this document allows
	marked calls to bypass blacklists, ignore call forwarding procedures		marked calls to bypass blacklists, ignore call forwarding procedures
	and other similar features used to raise the attention of emergency		and other similar features used to raise the attention of emergency
	skipping to change at page 14, line 5 ¶		skipping to change at page 12, line 17 ¶
	Figure 7 shows the architecture that utilizes the identity of the		Figure 7 shows the architecture that utilizes the identity of the
	PSAP to decide whether a preferential treatment of callbacks should		PSAP to decide whether a preferential treatment of callbacks should
	be provided. To make this policy decision, the identity of the PSAP		be provided. To make this policy decision, the identity of the PSAP
	is compared with a white list of valid PSAPs available to the SIP		is compared with a white list of valid PSAPs available to the SIP
	entity. The identity assurance in SIP can come in different forms,		entity. The identity assurance in SIP can come in different forms,
	such as SIP Identity [RFC4474] or with P-Asserted-Identity [RFC3325].		such as SIP Identity [RFC4474] or with P-Asserted-Identity [RFC3325].
	The former technique relies on a cryptographic assurance and the		The former technique relies on a cryptographic assurance and the
	latter on a chain of trust. Also the usage of TLS between		latter on a chain of trust. Also the usage of TLS between
	neighboring SIP entities may provide useful identity information.		neighboring SIP entities may provide useful identity information.
	+----------+		+----------+
	| List of |+		| List of |+
	| valid ||		| valid ||
	| PSAPs ||		| PSAPs ||
	+----------+|		+----------+|
	+----------+		+----------+
	*		*
	* white list		* white list
	*		*
	V		V
	Incoming +----------+ Normal		Incoming +----------+ Normal
	SIP Msg | SIP |+ Treatment		SIP Msg | SIP |+ Treatment
	-------------->| Entity ||======================>		-------------->| Entity ||======================>
	+ Identity | ||(if not in white list)		+ Identity | ||(if not in white list)
	Info +----------+|		Info +----------+|
	+----------+		+----------+
	||		||
	||		||
	|| Preferential		|| Preferential
	|| Treatment		|| Treatment
	++========================>		++========================>
	(if successfully verified)		(if successfully verified)
	Figure 7: Identity-based Authorization		Figure 7: Identity-based Authorization
	An important aspect from a security point of view is the relationship		An important aspect from a security point of view is the relationship
	between the emergency services network (containing PSAPs) and the		between the emergency services network (containing PSAPs) and the
	VoIP provider (assuming that the emergency call travels via the VoIP		VoIP provider (assuming that the emergency call travels via the VoIP
	provider and not directly between the SIP UA and the PSAP).		provider and not directly between the SIP UA and the PSAP).
	If there is some form of relationship between the emergency services		If there is some form of relationship between the emergency services
	operator and the VoIP provider then the identification of a PSAP		operator and the VoIP provider then the identification of a PSAP
	skipping to change at page 16, line 15 ¶		skipping to change at page 13, line 32 ¶
	7. Acknowledgements		7. Acknowledgements
	We would like to thank the following persons for their feedback: Paul		We would like to thank the following persons for their feedback: Paul
	Kyzivat, Martin Thomson, Robert Sparks, Keith Drage, Cullen Jennings		Kyzivat, Martin Thomson, Robert Sparks, Keith Drage, Cullen Jennings
	Brian Rosen, Martin Dolly, Bernard Aboba, Andrew Allen, Atle Monrad,		Brian Rosen, Martin Dolly, Bernard Aboba, Andrew Allen, Atle Monrad,
	John-Luc Bakker, John Elwell, Geoff Thompson, Dan Romascanu, James		John-Luc Bakker, John Elwell, Geoff Thompson, Dan Romascanu, James
	Polk, John Medland, Hadriel Kaplan, Kenneth Carlberg, Timothy Dwight,		Polk, John Medland, Hadriel Kaplan, Kenneth Carlberg, Timothy Dwight,
	Janet Gunn		Janet Gunn
	Finally, we would like to thank the ECRIT working group chairs, Marc		Finally, we would like to thank the ECRIT working group chairs, Marc
	Linsner and Roger Marshall, for their support.		Linsner and Roger Marshall, for their support. Roger Marshall was
			the document shepherd for this document.
	8. References		8. References
	8.1. Normative References		8.1. Normative References
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,		[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
	A., Peterson, J., Sparks, R., Handley, M., and E.		A., Peterson, J., Sparks, R., Handley, M., and E.
	Schooler, "SIP: Session Initiation Protocol", RFC 3261,		Schooler, "SIP: Session Initiation Protocol", RFC 3261,
	June 2002.		June 2002.
	[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
	Extensions to the Session Initiation Protocol (SIP) for
	Asserted Identity within Trusted Networks", RFC 3325,
	November 2002.
	[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
	RFC 3966, December 2004.
	[RFC3969] Camarillo, G., "The Internet Assigned Number Authority
	(IANA) Uniform Resource Identifier (URI) Parameter
	Registry for the Session Initiation Protocol (SIP)",
	BCP 99, RFC 3969, December 2004.
	[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
	Authenticated Identity Management in the Session
	Initiation Protocol (SIP)", RFC 4474, August 2006.
	[RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User		[RFC5627] Rosenberg, J., "Obtaining and Using Globally Routable User
	Agent URIs (GRUUs) in the Session Initiation Protocol		Agent URIs (GRUUs) in the Session Initiation Protocol
	(SIP)", RFC 5627, October 2009.		(SIP)", RFC 5627, October 2009.
	[RFC6878] Roach, A., "IANA Registry for the Session Initiation		[RFC6878] Roach, A., "IANA Registry for the Session Initiation
	Protocol (SIP) "Priority" Header Field", RFC 6878,		Protocol (SIP) "Priority" Header Field", RFC 6878, March
	March 2013.		2013.
	8.2. Informative References		8.2. Informative References
	[RFC4484] Peterson, J., Polk, J., Sicker, D., and H. Tschofenig,		[RFC3325] Jennings, C., Peterson, J., and M. Watson, "Private
	"Trait-Based Authorization Requirements for the Session		Extensions to the Session Initiation Protocol (SIP) for
	Initiation Protocol (SIP)", RFC 4484, August 2006.		Asserted Identity within Trusted Networks", RFC 3325,
			November 2002.
			[RFC4474] Peterson, J. and C. Jennings, "Enhancements for
			Authenticated Identity Management in the Session
			Initiation Protocol (SIP)", RFC 4474, August 2006.
	[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for		[RFC5012] Schulzrinne, H. and R. Marshall, "Requirements for
	Emergency Context Resolution with Internet Technologies",		Emergency Context Resolution with Internet Technologies",
	RFC 5012, January 2008.		RFC 5012, January 2008.
	[RFC5031] Schulzrinne, H., "A Uniform Resource Name (URN) for
	Emergency and Other Well-Known Services", RFC 5031,
	January 2008.
	[RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax
	Specifications: ABNF", STD 68, RFC 5234, January 2008.
	[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,		[RFC6443] Rosen, B., Schulzrinne, H., Polk, J., and A. Newton,
	"Framework for Emergency Calling Using Internet		"Framework for Emergency Calling Using Internet
	Multimedia", RFC 6443, December 2011.		Multimedia", RFC 6443, December 2011.
	[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for		[RFC6881] Rosen, B. and J. Polk, "Best Current Practice for
	Communications Services in Support of Emergency Calling",		Communications Services in Support of Emergency Calling",
	BCP 181, RFC 6881, March 2013.		BCP 181, RFC 6881, March 2013.
	Authors' Addresses		Authors' Addresses
End of changes. 20 change blocks.
	198 lines changed or deleted		175 lines changed or added
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