One document matched: draft-polk-sipping-location-requirements-00.txt
Internet Engineering Task Force James M. Polk
Internet Draft Cisco Systems
Expiration: Dec 23rd, 2003
File: draft-polk-sipping-location-requirements-00.txt
Session Initiation Protocol Location Requirements
June 23rd, 2003
Status of this Memo
This document is an Internet-Draft and is in full conformance
with all provisions of Section 10 of RFC2026.
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Abstract
This document presents the requirements for an extension to the
Session Initiation Protocol (SIP) [1] for conveyance of user
location information from one Session Initiation Protocol (SIP)
User Agent to another SIP User Agent. The idea that in some cases
the UAC's location could affect proper routing of the SIP message
is explored as well.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . . 3
2. In the Body or in a Header . . . . . . . . . . . . . . . . . 3
3. Scope of Location in a Message Body . . . . . . . . . . . . . 4
4. Scope of Location in a Message Header . . . . . . . . . . . . 4
4.1 Location in a Single Header . . . . . . . . . . . . . . . 4
4.2 Location in Separate Message Headers . . . . . . . . . . 5
5. Requirements for UA-to-UA Location Conveyance . . . . . . . . 5
6. Requirements for Proxy-Routed Location Conveyance . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
11. Author Information . . . . . . . . . . . . . . . . . . . . . 8
12. Full Copyright Statement . . . . . . . . . . . . . . . . . . 8
1. Introduction
This document presents the requirements for an extension to the
Session Initiation Protocol (SIP) [1] for conveyance of user
location information from one Session Initiation Protocol (SIP)
User Agent to another SIP User Agent.
While reasonable people will initially lean strongly towards
having any location conveyance in the message body only (where
location confidentiality can be maintained), this document
examines usage cases where intermediaries must act on the
location information in order to determine where the session gets
routed. One such example of this is US e911-type emergency
sessions (voice or instant messaging). With this in mind, both
instances will be looked at here to determine if the requirements
are in fact different enough to necessitate two or more
solutions.
To be clear, the two cases that need to be looked at are the
following:
1. one involving a user of a User Agent wanting to transmit
his/her location to another user of a user agent for
whatever reason (I want to tell you where I am); and
2. a second case involving the UAC including its location in
order to allow an appropriate Emergency Response Center
(ERC) to be contacted, such as a US e911 Public Safety
Answering Point (because that User Agent has signaled for
help);
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This document does not discuss how the UAC discovers or is
configured with its Location (either coordinate based or civil
based). That work is being accomplished in the Geopriv Working
Group.
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].
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.
However, it may be infeasible to place the location information in
the message body of requests where/when message routing is of
particular importance for proper session establishment with the
intended party or parties (i.e. calling an ERC).
SIP message bodies are not viewed by Proxy Servers [per 1] in order
to do proper call routing. The current proposal in front of the
SIPPING WG is to use the mechanism described in [3] to universally
signal for help. This "sos@example.com" URI is proposed to describe
many, if not all ERCs in a region or country - regardless of the
original home domain that UA is from. This poses a particular
problem when a User Agent is signaling via a Proxy that is not
within the civil boundaries of the appropriate PSAP for that user.
For example, a large enterprise has a campus that spans more than
one PSAP jurisdiction, a UA initiates a session containing the To
header "sos@example.com". Where will that Proxy route the SIP
Request to? The problem is compounded if a managed domain only has
Proxies in one location of a multi site infrastructure - including
the possibility of traversing state or country boundaries in cases
in which the UA is mobile.
Routing a session set-up or instant message, such as SIP MESSAGE
from [4], becomes an Achilles Heel for SIP if the user agent is
unaware of the correct ERC routing and expects the correct ERC to be
selected by the SIP proxy routing machinery..
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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, 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. Scope of Location in a Message Header
If the location information of the UAC is to be contained within the
SIP message header (verses a message body as stated above), one
design issue is whether location field(s) are contained within a
single header, or multiple headers. The following 2 subsections
cover both of these choices for discussion.
4.1 Location in a Single Header
Placing location information within a single header of a SIP message
has some big advantages:
- it is easier to specify the semantics when there are missing
fields
- it makes readability much easier when reviewing all the location
fields contained within the SIP message header ordered as if in a
list
- an order of the location fields can be specified within this
single header (ex: Datum, then Latitude, then Longitude, then
Altitude, then... or country, then state/province, then
county/region, then city, then district/borough...)
This might be important if section 7.3.1 of [1] is still true
expedited parsing in Proxies and at the destination.
There exist two documents on Location Configuration Information
within the Geopriv Working Group, one for Coordinate based location
representation (Lat, Long, Alt, Datum, etc) in [5] and one for Civil
based Location representation (country, State/province, city, etc)
in [6]. Each of these documents should be looked to as a basis for
consistency in fields present as well as scope of the fields.
If a field is missing, it probably was left out intentionally by the
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UAC (either because that device didn't know what to populate a
particular field with, or a policy prevented it from being included
within that SIP message).
Any location privacy policy of a user agent within a particular
domain should allow the most precise location available be presented
as an S/MIME body in the SIP Request or response message once a
verifiable ERC is determined to be the intended destination of that
session.
4.2 Location in Separate Message Headers
Creating separate SIP headers for each location field type
(latitude, longitude, country, city, etc) does make each header
clean and concise. A grouping of these location headers should occur
for readability when viewing the location headers within a SIP
message header. And since expediting the processing of emergency
calls is important, the header placement considerations of section
7.3.1 of [1] apply to these headers when making emergency calls
Each of the message headers should be unique in name within a
location conveyance type.
In providing location information, the UAC should provide as much
information as possible within a certain type of location field
group (coordinate or civil), and not mix between groups. In other
words, a Latitude header should be used if a coordinate location is
being provided by the UAC, but is not by itself realistically
valuable information if a complete set civil location headers is
also present.
There exist two documents on Location Configuration Information
within the Geopriv Working Group, one for Coordinate based location
representation (Lat, Long, Alt, Datum, etc) in [5] and one for Civil
based Location representation (country, State/province, city, etc)
in [6]. Each of these documents should be looked to as a basis for
consistency in fields present as well as scope of the fields.
If a desire of the SIP working group is to limit the number of
headers that require IANA registration (and coding for), then
fulfilling this requirements document will add as little as 2 to
that process (1 for coordinate location and 1 for civil location),
or as many as 30+ if each location field requires a unique header.
5. Requirements for UA-to-UA Location Conveyance
The following are the requirements for UA-to-UA Location Conveyance
situations:
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REQ UU1 - MUST work with dialog-initiating SIP Requests and
responses, as well as the SIP MESSAGE method[4]
REQ UU2 - the precision of resolution of the location given by the
UAC is determined by the UAC, and SHOULD be based on who
the UAC is sending this location information to (most
likely via local policy)
REQ UU3 - UAC Location information SHOULD remain confidential in
route to the destination UA
REQ UU4 - The privacy and security rules established within the
Geopriv Working Group which would categorize SIP as a
'using protocol' MUST be followed [7]
REQ UU5 - The first sub-field must be what type of location
information it is (coordinate, civil, GPS, other)
6. Requirements for Proxy-Routed Location Conveyance
The following are the requirements for Proxy-Routed Location
Conveyance situations:
REQ PR1 - MUST work with dialog-initiating SIP Requests and
responses, as well as the SIP MESSAGE method[4]
REQ PR2 - a mechanism SHOULD be in place to hide this location
header from unwanted observation while in transit to,
form, and among SIP intermediaries; but MUST NOT be
mandatory for successful conveyance of location (don't
want the SIP Request to fail without this mechanism used
during emergencies)
REQ PR3 - 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
REQ PR4 - There SHOULD be a mechanism for the ERC to request the
UAC's location information (perhaps more precise
location information) after the original SIP Request has
been received without failing the original SIP Request
(which is the most important aspect of this document:
that the session is received by the proper ERC)
It is possible for a Proxy to determine the proper ERC to route
the SIP Request to (based on the included location information
within supplied by the UAC), yet create the situation where the
ERC does not know enough location information for personnel
response to the emergency.
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REQ PR5 - A SIP location Header field (probably the first if there
is an order established to the headers) MUST be what
type of location information type it is (coordinate,
civil, GPS, other)
REQ PR6 - SHOULD have the complete location (coordinate or civil)
contained within a single header
REQ PR7 - the most precise resolution (defined in [5])SHOULD be
given by the UAC when sending its location to an ERC (or
equivalent facility)
REQ PR8 - proxies SHOULD NOT partially remove location
information, but MAY remove it in its entirety when
crossing a trust boundary to preserve privacy
REQ PR9 - proxies MAY add location information unknown to the UAC
if known to the proxy
REQ PR10 - if section 7.3.1 of [1] needs to be followed, the
Location Header SHOULD be near the top of the SIP
message header for rapid parsing purposes
REQ PR11 - mixed or additional location fields CAN be present
providing more precise location information, but MUST be
uniquely identifiable and SHOULD be relevant
An example of this might be using the coordinate location
header and adding an identifiable cube or office number field
at the end of the coordinate header.
7. 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). In cases where a
session set-up is routed based on the location of the UAC initiating
the session or SIP MESSAGE, containing the location in a message
body does no good. At the same time, securing the location in a
header might fail in certain times that is detrimental to that
session (user). These times are those of emergency sessions (like to
a US e911-like service).
Although not advocated, this document therefore requires that
location conveyance in deterministic times of emergency not be bound
to being confidential universally, as that process might fail and
could cost lives.
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8. IANA Considerations
There are no IANA considerations within this document at this
time.
9. Acknowledgements
To Dave Oran for helping to shape this idea
10. 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-01.txt", Internet Draft, June 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
11. Author Information
James M. Polk
Cisco Systems
2200 East President George Bush Turnpike
Richardson, Texas 75082 USA
jmpolk@cisco.com
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12. Full Copyright Statement
"Copyright (C) The Internet Society (February 23rd, 2001).
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The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
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"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
The Expiration date for this Internet Draft is:
Dec 23rd, 2003
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