draft-ietf-ecrit-psap-callback-10.txt   draft-ietf-ecrit-psap-callback-11.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: January 14, 2014 Nokia Siemens Networks Expires: March 30, 2014 Nokia Solutions and Networks
C. Holmberg C. Holmberg
Ericsson Ericsson
M. Patel M. Patel
InterDigital Communications InterDigital Communications
July 13, 2013 September 26, 2013
Public Safety Answering Point (PSAP) Callback Public Safety Answering Point (PSAP) Callback
draft-ietf-ecrit-psap-callback-10.txt draft-ietf-ecrit-psap-callback-11.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
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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
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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 January 14, 2014. This Internet-Draft will expire on March 30, 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
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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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Callback Scenarios . . . . . . . . . . . . . . . . . . . . . 4 3. Callback Scenarios . . . . . . . . . . . . . . . . . . . . . 4
3.1. Routing Asymmetry . . . . . . . . . . . . . . . . . . . . 5 3.1. Routing Asymmetry . . . . . . . . . . . . . . . . . . . . 5
3.2. Multi-Stage Routing . . . . . . . . . . . . . . . . . . . 6 3.2. Multi-Stage Routing . . . . . . . . . . . . . . . . . . . 6
3.3. Call Forwarding . . . . . . . . . . . . . . . . . . . . . 7 3.3. Call Forwarding . . . . . . . . . . . . . . . . . . . . . 6
3.4. Network-based Service URN Resolution . . . . . . . . . . 8 3.4. Network-based Service URN Resolution . . . . . . . . . . 8
3.5. PSTN Interworking . . . . . . . . . . . . . . . . . . . . 9 3.5. PSTN Interworking . . . . . . . . . . . . . . . . . . . . 9
4. SIP PSAP Callback Indicator . . . . . . . . . . . . . . . . . 10 4. SIP PSAP Callback Indicator . . . . . . . . . . . . . . . . . 10
4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.1. General . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 11 4.3. Syntax . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 11 4.3.1. General . . . . . . . . . . . . . . . . . . . . . . . 10
4.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . 11 4.3.2. ABNF . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
5.1. Security Threat . . . . . . . . . . . . . . . . . . . . . 11 5.1. Security Threat . . . . . . . . . . . . . . . . . . . . . 10
5.2. Security Requirements . . . . . . . . . . . . . . . . . . 11 5.2. Security Requirements . . . . . . . . . . . . . . . . . . 11
5.3. Security Solution . . . . . . . . . . . . . . . . . . . . 12 5.3. Security Solution . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 14 8.2. Informative References . . . . . . . . . . . . . . . . . 13
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
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insufficient. insufficient.
2. Terminology 2. Terminology
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 outbound emergency call
placed earlier.
NOTE: All FQDNs used in the subsections below are used for NOTE: All FQDNs used in the subsections below are used for
illustrative purposes. They are examples to demonstrate the illustrative purposes. They are examples to demonstrate the
limitations of the technical solution outlined in RFC 6881. 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. Figure outgoing SIP messaging routed through different SIP entities. Figure
1 shows this graphically whereby a VoIP provider uses different SIP 1 shows this graphically whereby a VoIP provider uses different SIP
proxies for inbound and for outbound call handling. Unless the two proxies for inbound and for outbound call handling. Unless the two
devices are synchronized as to state the callback hitting the inbound devices are synchronized, the callback hitting the inbound proxy
proxy would get treated like any other call since the emergency call would get treated like any other call since the emergency call
established state information at the outbound proxy only. established state information at the outbound proxy only.
,-------. ,-------.
,' `. ,' `.
,-------. / Emergency \ ,-------. / Emergency \
,' `. | Services | ,' `. | Services |
/ VoIP \ I | Network | / VoIP \ I | Network |
| Provider | n | | | Provider | n | |
| | t | | | | t | |
| | e | | | | e | |
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+------------+---+ESRP | | +------------+---+ESRP | |
| +------+ | | +------+ |
| | | |
\ / \ /
`. ,' `. ,'
'-------' '-------'
Figure 2: Example for Multi-Stage Routing. Figure 2: Example for Multi-Stage Routing.
3.3. Call Forwarding 3.3. Call Forwarding
Imagine the following case where an emergency call enters an Imagine the following case where an emergency call enters an
emergency network (state.org) via an ESRP but then gets forwarded to emergency network (state.org) via an ESRP but then gets forwarded to
a different emergency services network (in our example to police- a different emergency services network (in our example to police-
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 Similar 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 |
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| 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 leaves the
the same PSTN/VoIP gateway or that the same end point identifier is same PSTN/VoIP gateway or that the same end point identifier is used
used in the forward as well as in the backward direction making it 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 |
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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 We would like to thank the ECRIT working group chairs, Marc Linsner
Linsner and Roger Marshall, for their support. Roger Marshall was and Roger Marshall, for their support. Roger Marshall was the
the document shepherd for this document. document shepherd for this document. Vijay Gurbani provided the
general area review.
8. References 8. References
8.1. Normative References 8.1. Normative References
[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.
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Department of Computer Science Department of Computer Science
450 Computer Science Building 450 Computer Science Building
New York, NY 10027 New York, NY 10027
US US
Phone: +1 212 939 7004 Phone: +1 212 939 7004
EMail: hgs+ecrit@cs.columbia.edu EMail: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu URI: http://www.cs.columbia.edu
Hannes Tschofenig Hannes Tschofenig
Nokia Siemens Networks Nokia Solutions and Networks
Linnoitustie 6 Linnoitustie 6
Espoo 02600 Espoo 02600
Finland Finland
Phone: +358 (50) 4871445 Phone: +358 (50) 4871445
EMail: Hannes.Tschofenig@gmx.net EMail: Hannes.Tschofenig@gmx.net
URI: http://www.tschofenig.priv.at URI: http://www.tschofenig.priv.at
Christer Holmberg Christer Holmberg
Ericsson Ericsson
Hirsalantie 11 Hirsalantie 11
Jorvas 02420 Jorvas 02420
Finland Finland
EMail: christer.holmberg@ericsson.com EMail: christer.holmberg@ericsson.com
Milan Patel Milan Patel
InterDigital Communications InterDigital Communications
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