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
publication of this document. Please review these documents publication of this document. Please review these documents
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
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
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

This html diff was produced by rfcdiff 1.41. The latest version is available from http://tools.ietf.org/tools/rfcdiff/