Internet Engineering Task Force James M. Polk
Internet Draft Cisco Systems
Expiration: April 27th, 2003 Brian Rosen
File: draft-polk-sipping-location-requirements-01.txt Marconi
Session Initiation Protocol Location Conveyance
October 27th, 2003
Status of this Memo
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Abstract
This document presents the framework and requirements for an
extension to the Session Initiation Protocol (SIP) [1] for
conveyance of user location information from a Session Initiation
Protocol (SIP) user agent to another SIP entity. We consider cases
where location information is conveyed from end to end, as well as
cases where message routing by intermediaries is influenced by the
location of the session initiator.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Changes from -00 . . . . . . . . . . . . . . . . . . . . 3
2. In the Body or in a Header . . . . . . . . . . . . . . . . . 3
3. Scope of Location in a Message Body . . . . . . . . . . . . . 4
4. Requirements for UA-to-UA Location Conveyance . . . . . . . . 4
5. Requirements for UA-to-Proxy Server Location Conveyance . . . 5
6. Additional Requirements for Emergency Calls . . . . . . . . . 5
7. Current Known Open issues . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
12. Author Information . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document presents the framework and requirements for an
extension to the Session Initiation Protocol (SIP) [1] for
conveyance of user location information object described by [7] from
a SIP User Agent to another SIP entity.
There are several situations in which it is appropriate for SIP to
be used to convey Location Information (LI) from one SIP entity to
another. This document specifies requirements when a SIP UAC knows
its location by some means not specified herein, and needs to inform
another SIP entity. One example is to reach your nearest pizza
parlor. A chain of pizza parlors may have a single well known uri
(sip:pizzaparlor.com), that is forwarded to the closest franchise by
the pizzaparlor.com proxy server. The receiving franchise UAS uses
the location information of the UAC to schedule your delivery.
Another important example is emergency calling. A call to
sip:sos@example.com is an emergency call as in [3]. The example.com
proxy server must route the call to the correct emergency response
center (ERC) determined by the location of the caller. At the ERC,
the UAS must determine the correct police/fire/ambulance/...
service, which is also based on your location. In many
jurisdictions, accurate location information is a required component
of a call to an emergency center.
A third example is a direction service, which might give you verbal
directions to a venue from your present position. This is a case
where only the destination UAS needs to receive the location
information.
This document does not discuss how the UAC discovers or is
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configured with its location (either coordinate based or civil
based). It also does not discuss the contents of the Location
Object (LO). It does specify the requirements for the "using
protocol" in [7].
1.1 Conventions used in this document
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 [2].
1.2 Changes from -00 Version
This is a list of the changes that have been made from the -00
version of this ID:
- Brian Rosen was brought on as a co-author
- Requirements that a location header were negatively received in
the previous version of this document. AD and chair advice was to
move all location information into a message body (and stay away
from headers)
- Added a section of "emergency call" specific requirements
- Added an Open Issues section to mention what hasn't been resolved
yet in this effort
2. In the Body or in a Header
When one user agent wants to inform another user agent where they
are, it seems reasonable to have this accomplished by placing the
location information (coordinate or civil) in an S/Mime registered
and encoded message body, and sending it as part of a SIP request or
response. No routing of the request based on the location
information is required in this case; therefore no SIP Proxies
between these two UAs need to view the location information
contained in the SIP messages.
Although SIP [1} does not permit a proxy server to modify or delete
a body, there is no restriction on viewing bodies. However, S/MIME
protection implemented on bodies is only specified between UAS and
UAC and if engaged, would render the location object opaque to a
proxy server. This problem is similar to that raised in Session
Policy [8], where an intermediary may need information in a body,
such as IP address of media streams or codec choices to route a call
properly. Requirements in [8] are applicable to routing based on
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location, and are incorporated in these requirements by reference.
It is conceivable to create a new header for location information.
However, [7] prefers S/MIME for security of Location Information,
and indeed S/MIME is preferable in SIP for protecting one part of a
message. Accordingly, these requirements specify location be
carried in a body.
It is the use of S/MIME however, that limits routing based on
location. Therefore, it seems appropriate to require that, where
routing is dependent on location, protection of the location
information object be accomplished by other mechanisms, probably TLS
("sips:" from [1]). It is envisioned that S/MIME SHOULD be used
when location information is not required by proxy servers, and TLS
SHOULD be used when it is.
This document does not address the behavior or configuration of SIP
Proxy Servers in these cases in order to accomplish location-
sensitive routing. That is out of scope, and left for further
(complementary) efforts.
3. Scope of Location in a Message Body
If the location information is to be contained within a message
body, and either another body (SDP for example) is also to be sent
in the message, or the LO is to be protected with S/MIME, the rules
stated in section 7 of [1] regarding multipart MIME bodies MUST be
followed. The format and privacy/security rules of the location
information SHOULD be defined within the Geopriv WG.
4. Requirements for UA-to-UA Location Conveyance
The following are the requirements for UA-to-UA Location Conveyance
situations:
U-U1 - MUST work with dialog-initiating SIP Requests and responses,
as well as the SIP MESSAGE method[4], and SHOULD work with
most SIP messages.
U-U2 - UAC Location information SHOULD remain confidential in route
to the destination UA
U-U3 - The privacy and security rules established within the
Geopriv Working Group that would categorize SIP as a 'using
protocol' MUST be met [7]
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5. Requirements for UA-to-Proxy Server Location Conveyance
The following are the requirements for UA-to-Proxy Server Location
Conveyance situations:
U-PS1 - MUST work with dialog-initiating SIP Requests and
responses, as well as the SIP MESSAGE method[4], and SHOULD
work with most SIP messages.
U-PS2 - UAC location information SHOULD remain confidential in
route to the destination, but MUST be useable by
intermediary proxy servers.
U-PS3 - The privacy and security rules established within the
Geopriv Working Group which would categorize SIP as a
'using protocol' MUST be met [7]
U-PS4 - Modification or removal of the LO by proxy servers MUST NOT
be required
U-PS5 - any mechanism used to prevent unwanted observation of this
Location Header(s) CANNOT fail the SIP Request if not
understood by intermediary SIP entities or the destination
UAS
U-PS6 – It MUST be possible for a proxy server to assert the
validity of the location information provided by the UA.
Alternatively, it is acceptable for there to be a mechanism
for a proxy server to assert a location object itself.
6. Additional Requirements for Emergency Calls
Emergency calls have requirements that are not generally important
to other uses for location in SIP:
Emergency calls presently have between 2 and 8-second call setup
times. There is ample evidence that the longer call setup end of
the range causes an unacceptable number of callers to abandon the
call before it is completed. Two-second call completion time is a
goal of many existing emergency call centers. Allocating 25% of the
call set up for processing privacy concerns seems reasonable; 1
second would be 50% of the goal, which seems unacceptable; less than
0.5 second seems unachievable, therefore:
E-1 - Privacy mechanisms MUST add no more than 0.5 second of call
setup time when implemented in present technology UAs and
Proxy Servers.
It may be acceptable for full privacy mechanisms related to the
location of the UAC (and it's user) to be tried on an initial
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attempt to place a call, as long as the call attempt may be retried
without the mechanism if the first attempt fails. Abandoning
privacy in cases of failure of the privacy mechanism might be
subject to user preference, although such a feature would be within
the domain of a UA implementation and thus not subject to
standardization. It should be noted that some jurisdictions have
laws that explicitly deny any expectation of location privacy when
making an emergency call.
E-2 – Privacy mechanisms MUST NOT be mandatory for successful
conveyance of location during an (sos-type) emergency call.
E-3 – The retention and retransmission policy of the ERC must be
able to be made available to the user, and override the
user's normal policy when local regulation governs such
retention and retransmission. As in E-2 above, requiring the
use of the ERC's retention and/or retransmission policy may
be subject to user preference although in most jurisdictions,
local laws specify such policies and may not be overridden by
user preference.
7. Current Known Open issues
This is a list of open issues that have not yet been addressed to
conclusion:
- Whether self signed S/MIME bodies can work in both directions in
the emergency call scenario (to and from an ERC) as in [9]. It
appears that document covers self-signed certs from the UA to ERC
direction, but it is not clear it solves communications in the
reverse direction.
- If S/MIME is chosen as a SHOULD (in general, vs. TLS), this doc
might consider stipulating a special purpose Proxy (an "emergency
services" proxy) that can process location information (a Geopriv
LO) and route the message directly to the appropriate ERC.
At Issue: plain "vanilla" proxies probably won't have the
capabilities to route based on location information in the
near future, but should that timing be considered here?
8. Security Considerations
Conveyance of geo-location of a UAC is problematic for many reasons.
This document calls for that conveyance to normally be accomplished
through secure message body means (like S/MIME or TLS). In cases
where a session set-up is routed based on the location of the UAC
initiating the session or SIP MESSAGE, securing the location with an
end-to-end mechanism such as S/MIME is problematic.
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9. IANA Considerations
There are no IANA considerations within this document at this time.
10. Acknowledgements
To Dave Oran for helping to shape this idea. To Jon Peterson and
Dean Willis on guidance of the effort.
11. References - Normative
[1] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, E. Schooler, "SIP: Session
Initiation Protocol ", RFC 3261, June 2002
[2] S. Bradner, "Key words for use in RFCs to indicate requirement
levels," RFC 2119, Mar. 1997.
[3] H. Schulzrinne, "draft-schulzrinne-sipping-sos-04.txt", Internet
Draft, Jan 03, Work in progress
[4] B. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema, D.
Gurle, "Session Initiation Protocol (SIP) Extension for Instant
Messaging" , RFC 3428, December 2002
[5] J. Polk, J. Schnizlein, M. Linsner, " draft-ietf-geopriv-dhcp-lci-
option-02.txt", Internet Draft, Aug 2003, Work in progress
[6] H. Schulzrinne, "draft-schulzrinne-geopriv-dhcp-civil-01.txt",
Internet Draft, Feb 03, Work in progress
[7] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk, "draft-
ietf-geopriv-reqs-03.txt", Internet Draft, Mar 03, Work in
progress
[8] J. Rosenberg, "Requirements for Session Policy for the Session
Initiation Protocol”, draft-ietf-sipping-session-policy-req-00",
Internet Draft, "work in progress" June, 2003
[9] C. Jennings, "draft-jennings-sipping-certs-01.txt", Internet
Draft, "work in progress", July 2003
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12. Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
jmpolk@cisco.com
Brian Rosen
Marconi Communications, Inc.
2000 Marconi Drive
Warrendale, PA 15086
Brian.rosen@marconi.com
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