Internet Engineering Task Force James M. Polk
Internet Draft Cisco Systems
Expiration: Aug 9th, 2004 Brian Rosen
File: draft-ietf-sipping-location-requirements-00.txt Marconi
Requirements for
Session Initiation Protocol Location Conveyance
February 9th, 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 Individual Submission Versions . . . . . . . 3
2. In the Body or in a Header . . . . . . . . . . . . . . . . . 4
3. Scope of Location in a Message Body . . . . . . . . . . . . . 5
4. Requirements for UA-to-UA Location Conveyance . . . . . . . . 5
5. Requirements for UA-to-Proxy Server Location Conveyance . . . 5
6. Additional Requirements for Emergency Calls . . . . . . . . . 6
7. Current Known Open issues . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 8
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12. Author Information . . . . . . . . . . . . . . . . . . . . . 9
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 of the caller in
distress 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 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 Individual Submission Versions
This is a list of the changes that have been made from the -00
individual submission 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
This is a list of the changes that have been made from the
individual submission version -01
- Added the IPR Statement section
- Adjusted a few requirements based on suggestions from the
Minneapolis meeting
- Added requirements that the UAC is to include from where it
learned its location in any transmission of its LI
- Distinguished the facts (known to date) that certain jurisdictions
relieve persons of their right to privacy when they call an ERC,
while other jurisdictions maintain a person's right to privacy,
while still others maintain a person's right to privacy - but only
if they ask that their service be set up that way.
- Made the decision that TLS is the security mechanism for location
conveyance in emergency communications (vs. S/MIME, which is still
the mechanism for UA-to-UA non-emergency location conveyance
cases).
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- Added the Open Issue of whether a Proxy can insert location
information into an emergency SIP INVITE message, and some of the
open questions surrounding the implications of that action
- added a few names to the acknowledgements section
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 for any desired modification if it is not correct or
precise enough from that proxy's point of view (were it to be able
to view it). 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
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: here TLS
("sips:" from [1]). It is envisioned that S/MIME SHOULD be used
when location information is not required by proxy servers, and TLS
MUST be used when it is. The UAC will need to know the difference
in the call's intent as to which security mechanism to engage for LI
conveyance.
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.
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3. Scope of Location in a Message Body
As concluded from the previous section, location information is to
be contained within a message body. If either another body (SDP for
example) is also to be sent in the message, or the LI 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 where routing is not based on the LI of either UA:
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].
U-U4 - The UAC SHOULD indicate in the SIP message that includes
location information where the LI came from (IANA registered
codes for GPS, Cell Tower Triangulation, WiFi, DHCP, manual
entry - as examples).
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 with
respect to entities to which the location information is
not addressed, 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].
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U-PS4 - Modification or removal of the LO by proxy servers MUST NOT
be required (as [1] currently forbids this).
U-PS5 - any mechanism used to prevent unwanted observation of this
Location Information CANNOT fail the SIP Request if not
understood by intermediary SIP entities or the destination
UAS.
U-PS6 - Proxy Servers that do not or cannot understand the Location
Information in the message body for routing purposes MUST
NOT fail the SIP Request.
U-PS7 ¡ 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.
U-PS8 - The UAC SHOULD indicate in the SIP message that includes
location information where the LI came from (IANA
registered codes for GPS, Cell Tower Triangulation, WiFi,
DHCP, manual entry - as examples).
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
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
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making an emergency call, while others grant the user the ability to
remain anonymous even when calling an ERC. So far, this has been
offered in some jurisdictions, but the user within that jurisdiction
must state this preference, as it is not the default configuration.
E-2 ¡ Privacy mechanisms MUST NOT be mandatory for successful
conveyance of location during an (sos-type) emergency call.
E-3 - It MUST be possible to provide a privacy mechanism (that does
not violate the other requirements within this document) to a
user within a jurisdiction that gives that user the right to
choose not to reveal their location even when contacting an
ERC.
E-4 ¡ 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 (but does not violate
requirement E-3). 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.
Location information is considered so important during emergency
calls, that it is to be transmitted even when it is not considered
reliable, or might even be wrong. For example, some application
might know that the DHCP reply with location information was
overwritten recently (or exactly) when a VPN connection was
activated. This could, and likely will, provide any new location
information to the UA from somewhere far away from the UA (perhaps
the user's corporate facility).
E-5 Location information MUST be transmitted, if known to the UAC,
in all calls to an ERC, even in the case it is not considered
reliable.
E-6 The UAC SHOULD be able to inform the ERC that the location
information provided in the SIP message might be wrong.
Requirements U-U4 and U-PS8 stipulate the inclusion of how the UAC
learned its location. This can be especially useful to an ERC
operator attempting to learn all that is possible from this remote
person in distress. With that in mind, it is important to
distinguish the location information learned locally from LI learned
over a VPN; which in itself is useful additional information to that
ERC operator.
E-7 The UA MUST not provide the (overwritten?) location information
provided by a VPN (in lieu of the LI from the local network).
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E-8 The UA SHOULD include within the location conveyance to the ERC
that it is (or recently was) connected to a VPN.
7. Current Known Open issues
This is a list of open issues that have not yet been addressed to
conclusion:
1) Whether SIP Proxies SHOULD be able to insert location information
into an emergency call set-up (the INVITE)?
1a) This has the additional implication of whether or not, or
regardless of the fact the UAC already inserted location into
the sos@localdomain INVITE.
1b) Should the Proxy somehow differentiate its location
information from that provided by the UAC (with each LI
having a SIP entity (type?) originator label?
1c) Should there be any behavior difference with respect to Open
Issue #1b if the Proxy does not know or cannot tell if the
UAC inserted location information (further emphasizing the
need for some form of originator label)?
2) Whether SIP Proxies SHOULD be able to return location information
in a Redirect message to the UAC making the emergency call?
3) 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.
9. IANA Considerations
There are no IANA considerations within this document at this time.
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10. Acknowledgements
To Dave Oran for helping to shape this idea. To Jon Peterson and
Dean Willis on guidance of the effort. To Henning Schulzrinne,
Jonathan Rosenberg, Dick Knight, and Keith Drage for constructive
feedback.
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-03.txt", Internet Draft, Dec 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-04.txt", Internet Draft, Oct 03, Work in
progress
[8] J. Rosenberg, "Requirements for Session Policy for the Session
Initiation Protocolö, draft-ietf-sipping-session-policy-req-00",
Internet Draft, "work in progress" June, 2003
12. Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
jmpolk@cisco.com
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Brian Rosen
Marconi Communications, Inc.
2000 Marconi Drive
Warrendale, PA 15086
Brian.rosen@marconi.com
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