SIP Working Group James M. Polk
Internet Draft Cisco Systems
Expiration: Sept 6th, 2006 Brian Rosen
NeuStar
Session Initiation Protocol Location Conveyance
draft-ietf-sip-location-conveyance-02.txt
Mar 6th, 2006
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Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines how the Session Initiation Protocol (SIP)
conveys, or pushes, user location information from one SIP entity
to another SIP entity. SIP Location Conveyance is always end to
end, but sometimes the embedded location information can be acted
upon by SIP Servers to direct where the message goes, based on where
the user agent client is.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1 Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
1.2 Changes from Prior Versions . . . . . . . . . . . . . . . 4
2. Location In the Body or in a Header . . . . . . . . . . . . . 8
3. Requirements for SIP Location Conveyance . . . . . . . . . . 9
4. Location Conveyance Using SIP . . . . . . . . . . . . . . . . 12
4.1 New Option Tags and a Location Header Created . . . . . . 13
4.2 424 (Bad Location Information) Response Code . . . . . . 16
4.3 Example PIDF-LO in Geo Format . . . . . . . . . . . . . . 16
4.3 Example PIDF-LO in Civic Format . . . . . . . . . . . . . 17
5. SIP Element Behavior When Conveying Location . . . . . . . . 18
5.1 Location Conveyance Using the INVITE Method . . . . . . . 19
5.2 Location Conveyance Using the MESSAGE Method . . . . . . 21
5.3 Location Conveyance Using the UPDATE Method . . . . . . . 22
5.4 Location Conveyance Using the REGISTER Method . . . . . . 27
6. Special Considerations for Emergency Calls . . . . . . . . . 29
7. Meeting RFC 3693 Requirements . . . . . . . . . . . . . . . . 29
8. Open issues . . . . . . . . . . . . . . . . . . . . . . . . . 30
9. Security Considerations . . . . . . . . . . . . . . . . . . . 30
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . 31
10.1 IANA Registration for the SIP Location Header . . . . . 31
10.2 IANA Registration of the Location Option Tags. . . . . . 31
10.3 IANA Registration for Response Code 424 . . . . . . . . 31
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 31
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
12.1 Normative References . . . . . . . . . . . . . . . . . 31
12.2 Informative References . . . . . . . . . . . . . . . . . 32
Author Information . . . . . . . . . . . . . . . . . . . . . 32
Intellectual Property and Copyright Statements . . . . . . . 33
1. Introduction
There are several situations in which it is desired or necessary for
a Session Initiation Protocol (SIP) [RFC3261] user agent to convey,
or push Location Information (LI) from one SIP entity to another.
This document discusses the scenarios for such conveyance, and
includes the requirements to be met when a SIP UAC wants or needs to
convey its location to another SIP entity. A concept of inheritance
exists in which the conveyance of the location of a user agent means
conveying the location of a user of that user agent. This is not an
absolute in SIP, but applies for the pushing of location using SIP.
The privacy concerns of this topic are also discussed, and need to
meet the requirements laid out in RFC 3693 [RFC3693]. This document
does not discuss the pulling of location information from a user
agent. This is left for a future effort.
Why would a SIP user agent (UA) push its location to another SIP UA?
There are 3 reasonable scenarios why location can be, or needs to be
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conveyed to a remote SIP element:
1) to include location in a request message seeking the nearest
instance of destination, where there could be more than one
choice; (hey, here I am, I want to talk to the nearest instance
of you? i.e. where's the nearest Pizza Hut relative to where I
am).
2) to push the user's location to a server that can deal with all
the inquiries, leaving the UA to do other tasks; (Presence
Server)
3) to inform the user of another UA where the sending user is;
(dude, he is where I am) or (I need help, here I am)
Scenario #1 revolves around the idea of a user wanting to find the
nearest instances of something else. For example, where is the
nearest pizza parlor. A chain of pizza parlors may be contacted
through a single well known URI (sip:pizzaparlor.example.com). This
by itself does not solve enough to the sending UA. The server at
this well known URI needs to know where the nearest one is to the
requester. In SIP, this could be accomplished in the initial
message by including the location of the UAC in the Request message.
This allows the SIP message to be forwarded to the closest physical
site by the pizzaparlor.com proxy server. Additionally, the
receiving site's UAS uses the UAC's location to determine the
location your delivery. A more immediate example may be: where's
the nearest (car) garage repair shop, because the user of the UAC
has a flat tire.
Scenario #2 revolves around pushing the user's location information
to an external server to deal with all location requests in the
future. This leaves a buffer layer between the user and the seeker
of the user's location. This server would typically handle all
security checks and challenges of those seeking the user's location,
as well as handling all the processing of the location target's
profile rules entered into that server. This external server
c/would be a Presence server. This scenario will not be addressed
in this document because of the prevailing Presence solutions for
conveying location information.
Scenario #3 actually has a part A and a part B to it. Both involve
the UAC including its location in the request to the UAS within a
SIP transaction. Part A simply has the user, Alice, informing
another user, Bob, where she is. This could be for the loan purpose
for this SIP message, or it could be part of another transaction -
in which location were merely included, such as within a call set-
up.
Part B of this scenario has a user, Alice calling for help and
including location to inform who she's calling where she is. This
is where the called party needs to come bring help to. Within this
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scenario, the UAC will need to know this is an emergency SIP request
message, and to include the UAC's location in this message.
While scenarios 1, 2 and 3A should use some form of SIP security,
typically at the wishes of the user, scenario 3B may or may not
involve SIP security measures. This is because including any
security measures may cause the SIP request to fail, and that is
likely not a good result. It is also conceivable that a first
attempt with the user's security measures enabled is tried, and if
there are any failures, the subsequent attempt or attempts do not
involve security measures. Most believe that completing the
emergency call is more important than protecting the information in
the SIP message. Obviously this is up to local and jurisdictional
policies, but is mentioned here as a hint of a rationale of a later
section of this document.
This document does not discuss how the UAC discovers or is
configured with its location, however will specify how this spec
meets the requirements for SIP qualifying as a "using protocol" as
defined in [RFC3693], in section 7.
Section 3 lists the requirements for SIP location conveyance.
Section 4 defines how SIP conveys location. Section 5 illustrates
specifics about location conveyance in certain SIP request messages.
Section 6 briefly discusses pertinent behaviors with respect to the
unique nature of emergency calling. Section 9 provides the security
considerations and Section 10 IANA registers one new SIP header, two
new option tags and one new 4XX Response codes.
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 [RFC2119].
1.2 Changes from Prior Versions
[NOTE TO RFC-EDITOR: If this document is to be published as an RFC,
this section 1.2 is to be removed prior to that event.]
This is a list of the changes that have been made from the SIP WG
version -01 to this version -02:
- streamlined the doc by removing text (ultimately removing 42 pages
of text).
- Limited the scope of this document to SIP conveyance, meaning only
how SIP can push location information.
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- reduced emergency calling text to just a few paragraphs now that
the ECRIT WG is taking most of that topic on.
- greatly reduced the number of requirements in this version.
- changed the requirements groups from "UA-to-UA", "UA-to-Proxy",
etc to "UAC Reqs", "UAS-Reqs" and "Proxy-Reqs" to focus on what is
being asked of each SIP element.
- Removed the full SIP message examples.
- completed the ABNF for the Location header, including a cid-url to
point at a message body part to help in parsing for location.
- Deleted the call for a new 425 (Retry Location) response code, as
it appears this can easily be used to spoof a UA into providing
where it is inadvertently, even if the intent is legitimate by the
UAC.
This is a list of the changes that have been made from the SIP WG
version -00 to this version -01:
- cleaned up a lot of loose ends in the text
- created a new Location header to convey many means (location is in
the body - even if not viewable, which location format is present,
which format is requested in a query, how to request more than one
location format in a query, whether the UAC understands location
at all, if the UA knows its location, how to push location from
one UA to through a second to a third UA, etc).
- added the ability to convey location by-reference, but only under
certain conditions.
- Added support for the OPTIONS Request to query a server for the
UAC's location, through the use of the new Location header.
- moved both new Response code sections forward in the document for
their meaning to be clearer, earlier for necessary discussion.
- Changed the message flows to only have the pertinent message
headers shown for brevity.
- Added text to the SUB/NOT section showing how and why the location
of a UA can be refreshed or updated with an interval, or by a
trigger.
This is a list of the changes that have been made from the SIPPING
WG version -02 to this SIP WG item document version -00:
- Changed which WG this document is in from SIPPING to SIP due to
the extension of the protocol with new Response codes (424 and
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425) for when there is an error involving the LO message body.
- Moved most of the well formed SIP messages out of the main body of
this document and into separate appendixes. This should clean up
the document from a readability point of view, yet still provide
the intended decode examples to readers of this document who wish
that level of detail per flow. The first few flows still have the
decoded SIP messages (unencrypted and encrypted).
- Removed some flow examples which no longer made sense
- Changed all references of "ERC" (Emergency Response Center) to
"PSAP" (Public Safety Answering Point) as a result of discussion
within the new ECRIT WG to define a single term
This is a list of the changes that have been made from the sipping-
01 working group version of this effort to the sipping-02 version:
- added requirements for 2 new 4XX error responses (Bad Location
Information) and (Retry Location Body)
- added "Bad Location Information" as section 8.6
- added "Retry Location Body " as section 9.3
- added support for session mode to cover packet sizes larger than
the single packet limit of 1300 bytes in the message body
- added requirement for a SIP entity to SUBSCRIBE to another for
location information
- added SUBSCRIBE and NOTIFY as section 8.5
- added requirement to have user turn off any tracking created by
subscription
- removed doubt about which method to use for updating location
after a INVITE is sent (update)
- cleaned up which method is to be used if there is no dialog
existing (message)
- removed use of reINVITE to convey location
- clarified that UAs include <provided-by> element of PIDF-LO when
placing an emergency call (to inform PSAP who supplied Location
information)
- updated list of open issues
- added to IANA Considerations section for the two new 4XX level
error responses requested in the last meeting
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This is a list of the changes that have been made from the sipping-
00 working group version of this ID to the sipping-01 version:
- Added the offered solution in detail (with message flows,
appropriate SIP Methods for location conveyance, and
- Synchronized the requirements here with those from the Geopriv
Working Group's (attempting to eliminate overlap)
- Took on the task of making this effort the SIP "using protocol"
specification from Geopriv's POV
- Refined the Open Issues section to reflect the progress we've made
here, and to indicate what we have discovered needs addressing,
but has not been to date.
This is a list of the changes that have been made from the -01
individual submission version to the sipping-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
This is a list of the changes that have been made from the
individual submission version -00 to the -01 version
- 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 PSAP,
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
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cases).
- 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. Location In the Body or in a Header
In determining where "location" is placed in a SIP message,
consideration is taken as to where the trust model is based on the
architecture involved.
If the user agent has the location stored within it, and this user
agent wants to inform another user agent where it is, it seems
reasonable to have this accomplished by placing the location
information (coordinate or civic) 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. The UAC should know messages will be
routed based on location when creating a message. This is location
by-value.
SIP currently does not permit SIP intermediaries to modify
or delete a message body [RFC3261]. There is, however, no
restriction on intermediaries viewing message bodies. S/MIME
protected message bodies, implemented on bodies for end-to-end
communications only (i.e. between user agents), would render the
location object opaque to a proxy server from any viewing of the
message body. This problem is similar to that raised in Session
Policy [ID-Sess-Pol], 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 [ID-Sess-Pol] are applicable
to routing based on location, and are incorporated in these
requirements by reference.
The location format is defined in [RFC4119] as a "Presence
Information Data Format - Location Object", or PIDF-LO. The amount
of information that is necessary to appropriately transmit location
information in a format that is understandable is larger than a SIP
header could realistically include. However, there must be a means
for both a UAC to include a reference point to where location can be
retrieved from a remote server, and in some cases, a SIP server
wants or needs to add location to a SIP message as it is processed
by that server. This must be in a compact form in a SIP header. A
URI satisfies this description. This is location-by-reference.
Location-by-Reference allows a UA to place its location on a remote
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node, to be retrieved by who has this URI. This allows the server
to use its processing power to handle all policy rule operations the
user wants performed per request, and all security challenges done
as well.
[RFC3693] prefers S/MIME for security of Location Information, and
indeed S/MIME is preferable in SIP [RFC3261] for protecting a
message body. Accordingly, these requirements specify location be
carried in a body when it is known to/stored in a user agent.
It is the use of S/MIME however, that limits message routing based
on the location of the UAC, scenario 3B from above. Therefore, it
seems appropriate to require that, where routing is dependent on
location, protection of the location information object be
accomplished by other mechanisms visible to SIP proxies: here TLS
("sips:" from [RFC3261]). The UAC will need to know the difference
in the call's intent as to which security mechanism to engage for
location conveyance.
It is conceivable that an initial attempt to communicate with
location included may fail due to the security measures used.
Subsequent requests ought to use less security. For example, if an
initial request used S/MIME and failed. A subsequent request could
downgrade the security measures used to that of TLS. This is a
matter for local and jurisdictional policy, and is merely a hint at
implementation possibilities.
3. Requirements for SIP Location Conveyance
The following subsections address the requirements placed on the
user agent client, the user agent server, as well as SIP proxies
when conveying location.
3.1 Requirements for a UAC Conveying Location
The following are the requirements for location conveyance by a user
agent client. There is a motivational statement below each
requirements that is not obvious in intent.
UAC-1 The SIP INVITE Method [RFC3261] MUST support Location
Conveyance.
UAC-2 The SIP MESSAGE method [RFC3428] MUST support Location
Conveyance.
UAC-3 SIP Requests within a dialog SHOULD support Location
Conveyance.
UAC-4 Other SIP Requests MAY support Location Conveyance.
UAC-5 There MUST be one, mandatory to implement means of
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transmitting location confidentially.
Motivation: interoperability
UAC-6 It MUST be possible for a UAC to update location conveyed
prior to dialog establishment.
Motivation: in case a UAC has moved prior to the establishment of a
dialog between UAs, the UAC must be able to send new location
information.
UAC-7 The privacy and security rules established within [RFC3693]
that would categorize SIP as a 'using protocol' MUST be met.
See Section 7 for analysis.
UAC-8 The PIDF-LO [RFC4119] is a mandatory to implement format for
location conveyance within SIP, whether included by-value or
by-reference.
Motivation: interoperability
UAC-9 A UAC MUST be capable of transmitting a SIP request without
protecting the PIDF-LO message body. It is RECOMMENDED this
not be the default configuration of any UA. This requirement
is orthogonal to the use of TLS or IPSec hop-by-hop between
SIP elements.
Motivation: If a SIP request is part of an emergency call,
therefore includes the UAC's location, the UAC may understand
through local policy or configuration that a proxy server
will need to learn the UAC's location to route the message
correctly. Using S/MIME on the PIDF-LO defeats this
capability in proxies.
UAC-10 A UAC MUST allow its user to be able to disable providing
location within any SIP request message. It is RECOMMENDED
this not be the default configuration of any UA.
Motivation: local laws may give this right to all users within a
jurisdiction, even when the request is initiating an
emergency call.
3.2 Requirements for a UAS Receiving Location
The following are the requirements for location conveyance by a user
agent server:
UAS-1 SIP Responses MUST support Location Conveyance.
UAS-2 There MUST be one, mandatory to implement means of
transmitting location confidentially.
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Motivation: interoperability
UAS-3 The PIDF-LO [RFC4119] is a mandatory to implement format for
location conveyance within SIP, whether included by-value or
by-reference.
Motivation: interoperability
UAS-4 There MUST be a unique 4XX error response code informing
the UAC it did not provide applicable location information.
UAS-5 SIP UAs MUST be prepared to receive location without privacy
mechanisms enabled. It is RECOMMENDED this not be the
default configuration of any UA, however, this is possible
based on local laws.
Motivation: Because a SIP request can fail in transit for security
reasons, UACs are allowed to transmit, or retransmit requests
including location without any security mechanisms utilized,
even when this SIP transaction is an emergency call. UAs
must be prepared to receive the messages without confidential
location.
UAS-6 There MUST be a unique 4XX error response code informing the
UAC it did not provide applicable location information.
3.3 Requirements for SIP Proxies and Intermediaries
The following are the requirements for location conveyance by a SIP
proxies and intermediaries:
Proxy-1 Proxy servers MUST NOT modify or remove a location
message body part, and SHOULD NOT modify or remove a
location header or location header value.
Motivation: [RFC3261] forbids the removal of a message body part,
and the proxy may not have all the relevant information as
to why location was included in this message (meaning it
might need to be there), and should not remove this
critical piece of information.
Proxy-2 Proxy servers MUST be capable of adding a Location header
during processing of SIP requests.
Motivation: If the proxy determines a message needs to have the
location of the UAC in the message, and knows the UAC's
location by-reference, it must be able to add this header
and URI to the message during processing. This MUST NOT
violate requirement Proxy-3 below.
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Proxy-3 If a Proxy server detects "location" already exists within
a SIP message, it MUST NOT add another location header or
location body to the message.
Motivation: This may lead to confusion, and should be left for the
UAC to do on purpose.
Proxy-4 There MUST be a unique 4XX error response code informing
the UAC it did not provide applicable location information.
4. Location Conveyance Using SIP
RFC 4119 defines the PIDF-LO location object to be inside a RFC 3693
defined "using protocol" message from one entity to another entity.
For SIP location conveyance, using the PIDF-LO body satisfies the
entire format and message-handling requirements as stated in the
baseline Geopriv Requirements [RFC3693].
Although a PIDF-LO is to be used to indicate location of a UA, the
actual PIDF-LO does not need to be contained in the message itself,
it can be as a by-reference URI in a SIP header or message body
part, pointing to the PIDF-LO of that UA on a remote node.
Section 26 of [RFC3261] defines the security functionality SIPS for
transporting SIP messages with either TLS or IPSec, and S/MIME for
encrypting message bodies from SIP intermediaries that would
otherwise have access to reading the clear-text bodies. SIP
endpoints MUST implement S/MIME to encrypt the PIDF-LO message body
(part) end-to-end. The SIPS-URI from [RFC3261] SHOULD be used for
message protection (message integrity and confidentiality) and MUST
be used when S/MIME is not used (when not violating the requirements
for emergency messaging detailed in section 3 of this document).
The entities sending and receiving location MUST obey the privacy
and security rules in the PIDF-LO to be compliant with this
specification.
Self-signed certificates SHOULD NOT be used for protecting PIDF-LO,
as the sender does not have a secure identity of the recipient.
More than one location representation or format MAY be included in
the same message body part, but all MUST point at the same position
on the earth (altitude not withstanding), as this would confuse the
recipient by pointing at more than one position within the same
PIDF-LO. There MAY be a case in which part of one location format
and part of another exist in the same message body part. These all
still MUST point at the same position on the earth, yet are
incomplete within their own format. For example, there maybe be a
latitude and longitude in coordinate format and a civic altitude
value to complete a 3-dimenttional position of a thing (i.e. which
floor of a building the UA is on in a building at a particular
lat/long coordinate pair).
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There MAY be several PIDF-LOs in separate message body parts in the
same message, and each MAY point at different positions on the earth
(altitude not withstanding). If the message length exceeds the
maximum message length of a single packet (1300 bytes), TCP MUST to
be used for proper message fragmentation and reassembly.
Several push-based SIP Request Methods are capable (and applicable)
of carrying location, including:
INVITE,
REGISTER,
UPDATE, and
MESSAGE,
While the authors do not yet see a reason to have location conveyed
in the ACK, PRACK, BYE, REFER and CANCEL Methods, we do not see a
reason to prevent carrying a PIDF-LO within these Method Requests as
long as the SIP message meets the requirements stated within this
document. Discussing Location in the PUBLISH Request Method will be
for another document.
SIP Methods such as SUBSCRIBE and NOTIFY are considered a pull-based
location retrieval mechanism, and are therefore not part of this
document.
A 200 OK to a SIP Request MAY carry the UAS's PIDF-LO back to the
UAC that provided its location in the original request, but this is
not something that can be required due to the timing of the request
to 200 OK messages, with potential local/user policy requiring the
called user to get involved in determining if the caller is someone
they wish to give their location to (and at what precision).
4.1 New Option Tags and a Location Header Created
This document creates and IANA registers two new option tags,
"location" or "unknown-location". User agent clients who support
this specification will indicate that support by including either of
these option-tags in a Supported header.
This document also creates and IANA registers a new Location header.
The Location header, if present, will have one of three header
values defined by this document:
o a Location-by-reference URI
o a Content ID indicating where location is within the message body
o a location based option tag
A location-by-reference URI is a pointer to a record on a remote
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node containing the PIDF-LO of a UA.
If the PIDF-LO of a UA is contained in a SIP message, a Location
header will be present in the message with a content-ID (cid-url)
[RFC2392] indicating where in the message body location is for this
UA. This is to aid a node in not having to parse the whole message
body or body parts looking for this body type.
The Unknown-Location option tag in a Location header indicates a UA
understands the concept of location conveyance, but does not have
its location to provide. This can save error messages from being
generated looking for an answer the UA does not have to give. It
can also allow a processing entity the immediate knowledge it needs
to act as if the UA will not learn location on its own, and perhaps
call on another process to address the location needs for that
message.
The purpose of the Location option-tag is to indicate support for
this document in the Requires, Supported and Unsupported headers.
It gives a UAS the proper means to indicate it does not support the
concept of location in an Unsupported header in a response message
that might otherwise not be clear that the lack of support for
location is the problem with the request message.
The new "Location" header has the following BNF syntax:
Location = "Location" HCOLON Location-value *(COMMA
Location-value)
location-value = (addr-spec / option-tag / token)
addr-spec = cid-url / absoluteURI
option-tag = string
token = token / quoted-string
cid-url = "cid" ":" content-id /
absoluteURI = SIP or SIPS-URI
content-id = url-addr-spec
url-addr-spec = addr-spec ; URL encoding of RFC 822 addr-spec
The Content-ID (cid) is defined in [RFC2392] to locate message body
parts.
The absoluteURI is the SIP or SIPS URI of the location-by-reference,
which points at a PIDF-LO of a UA in a record on a remote node.
The following table extends the values in Table 2/3 of RFC3261
[RFC3261].
Header field where proxy INV ACK CAN BYE REG OPT PRA
----------------------------------------------------------------
Location Rr ar o - - o o o -
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Header field where proxy SUB NOT UPD MSG REF INF PUB
----------------------------------------------------------------
Location Rr ar - - o o o o -
The Location header MAY be added, or read if present in a Request
message listed above. A proxy MAY add the location header in
transit if one is not present. [RFC3261] states message bodies
cannot be added by proxies. A proxy MAY read the location header in
transit if present.
It is RECOMMENDED that only one Location header be in the same
message, but this is not mandatory. That said, there MUST NOT be
more than one cid-url pointing to a location message body (part) in
a SIP message, regardless of how many Location headers there are in
that message. There MUST NOT be more than one location by-reference
URI in any SIP message, regardless of how many Location headers
there are in a message.
Here is an example INVITE that includes the proper Location and
Supported headers (without the PIDF-LO message body part):
INVITE sip:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TCP pc33.atlanta.example.com
;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sip:bob@biloxi.example.com>
From: Alice <sip:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Location: cid:alice123@atlanta.example.com
Supported: location
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sip:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...SDP here
--boundary1
Content-Type: application/pidf+xml
Content-ID: alice123@atlanta.example.com
...PIDF-LO with geo-location coordinates here
--boundary1--
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The location header from the above INVITE:
Location: cid:alice123@atlanta.example.com
indicates the Content-ID location [RFC2392] within the multipart
message body of were location information is.
If the Location header were this instead:
Location: <server5@atlanta.example.com/alice123>
this would indicate location by-reference was included in this
message. It is expected that any node wanting to know where user
alice123 is would fetch the PIDF-LO from the server5 URI.
4.2 424 (Bad Location Information) Response Code
In the case that a UAS or SIP intermediary detects an error
in a Request message specific to the location information supplied
by-value or by-reference, a new 4XX level error is created here to
indicate this is the problem with the request message. This
document creates the new error code:
424 (Bad Location Information)
The 424 (Bad Location Information) Response code is a rejection of
the location contents, whether by-value or by-reference of the
original SIP Request. The server function of the recipient (UAS or
intermediary) has deemed this location by-reference or location by-
value to be bad. No further action by the UAC is required. The UAC
can use whatever means it knows to verify/refresh its location
information before attempting a new request. There is no cross-
transaction awareness expected by either the UAS or SIP intermediary
as a result of this error message.
This new error code will be IANA registered in Section 10.
4.3 Example PIDF-LO in Geo Format
This subsection will show a sample of what just the PIDF-LO can look
like, as defined in [RFC4119]. Having this here will first offer a
look at a location by-value message body, and secondly, give readers
an appreciation for how large a location message body is so that
this document does not have to show a PIDF-LO in every message flow
example. This section shows a coordinate position based PIDF-LO.
Section 4.4 shows this same position in a civic address format.
Full example message flows will be left for another document.
Whether this PIDF-LO message body is S/MIME encrypted in the SIP
message or not, the PIDF-LO stays exactly the same. There is no
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change to its format, text or characteristics. Whether TLS or IPSec
is used to encrypt this overall SIP message or not, the PIDF-LO
stays exactly the same. There is no change to its format, text or
characteristics. The examples in section 4.3 (Geo format) taken
from [RFC3825] and 4.4 (Civic format) taken from [ID-CIVIC] are for
the exact same position on the Earth. The differences between the
two formats is within the <gp:location-info> are of the examples.
Other than this portion, of each PIDF-LO, the rest the same for both
location formats.
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gml="urn:opengis:specification:gml:schema-
xsd:feature:v3.0"
entity="pres:alice@atlanta.example.com">
<tuple id="sg89ae">
<timestamp>2006-03-20T14:00:00Z</timestamp>
<status>
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point gml:id="point96" srsName="epsg:4326">
<gml:coordinates>33.001111N
96.68142W</gml:coordinates>
</gml:Point>
</gml:location>
</gp:location-info>
<method>dhcp</method>
<provided-by><nena>www.cisco.com</nena></provided-by/>
<gp:usage-rules>
<gp:retransmission-allowed>no</gp:retransmission-allowed>
<gp:retention-expiry>2006-03-24T18:00:00Z</gp:retention-
expiry>
</gp:usage-rules>
</gp:geopriv>
</status>
</tuple>
</presence>
4.4 Example PIDF-LO in Civic Format
This subsection will show a sample of what just the PIDF-LO can look
like, as defined in [RFC4119]. Having this here will first offer a
look at a location by-value message body, and secondly, give readers
an appreciation for how large a location message body is so that
this document does not have to show a PIDF-LO in every message flow
example. This section shows a civic address based PIDF-LO. Section
4.3 shows this same position in a coordinate format. Full example
message flows will be left for another document.
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Whether this PIDF-LO message body is S/MIME encrypted in the SIP
message or not, the PIDF-LO stays exactly the same. There is no
change to its format, text or characteristics. Whether TLS or IPSec
is used to encrypt this overall SIP message or not, the PIDF-LO
stays exactly the same. There is no change to its format, text or
characteristics. The examples in section 4.3 (Geo format) taken
from [RFC3825] and 4.4 (Civic format) taken from [ID-CIVIC] are for
the exact same position on the Earth. The differences between the
two formats is within the <gp:location-info> are of the examples.
Other than this portion, of each PIDF-LO, the rest the same for both
location formats.
<?xml version="1.0" encoding="UTF-8"?>
<presence xmlns="urn:ietf:params:xml:ns:pidf"
xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
xmlns:gml="urn:opengis:specification:gml:schema-
xsd:feature:v3.0"
entity="pres:alice@atlanta.example.com">
<tuple id="sg89ae">
<timestamp>2006-03-20T14:00:00Z</timestamp>
<status>
<gp:geopriv>
<gp:location-info>
<cl:civilAddress>
<cl:country>US</cl:country>
<cl:A1>Texas</cl:A1>
<cl:A3>Colleyville</cl:A3>
<cl:HNO>3913</cl:HNO>
<cl:A6>Treemont</cl:A6>
<cl:STS>Circle</cl:STS>
<cl:PC>76034</cl:PC>
<cl:LMK>Polk Place</cl:LMK>
<cl:FLR>1</cl:FLR>
<cl:civilAddress>
</gp:location-info>
<method>dhcp</method>
<provided-by><nena>www.cisco.com</nena></provided-by/>
<gp:usage-rules>
<gp:retransmission-allowed>no</gp:retransmission-allowed>
<gp:retention-expiry>2006-03-24T18:00:00Z</gp:retention-
expiry>
</gp:usage-rules>
</gp:geopriv>
</status>
</tuple>
</presence>
5. SIP Element Behavior When Conveying Location
The SIP Request Methods that MUST convey location are the INVITE,
REGISTER, UPDATE and MESSAGE Methods. It is not forbidden by this
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document to convey location with any other SIP method. However, no
other methods are detailed here.
The message flows in this document will be example messages
containing only the key headers to convey the point being made that
do not include all the requisite SIP headers. All well formed SIP
message flows are to be in a separate document for brevity here.
5.1 Location Conveyance Using the INVITE Method
Below is a common SIP session set-up sequence between two user
agents. In this example, Alice will provide Bob with her location
in the INVITE message.
UA Alice UA Bob
| [M1] INVITE |
|---------------------------------------->|
| [M2] 200 OK |
|<----------------------------------------|
| [M3] ACK |
|---------------------------------------->|
| RTP |
|<=======================================>|
| |
Figure 1. Location Conveyance in INVITE Requests
User agent Alice invites user agent Bob to a session [M1 of Figure
1].
INVITE sips:bob@biloxi.example.com SIP/2.0
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=1928301774
Supported: Location
Location: cid:alice123@atlanta.example.com
If the message were S/MIME encrypted, this would be the Content-type
header:
Content-Type: application/pkcs7-mime;
smime-type=enveloped-data; name=smime.p7m
If this INVITE were not S/MIME encrypted, this would be the
Content-Type header:
Content-Type: multipart/mixed; boundary=boundary1
The obvious reason this for a multipart/mixed Content-Type is that
this is an INVITE message and there is an SDP message body part
included. This is not mandatory, but highly likely. The cid-url in
the Location header points a parsing entity that can view the
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message body to where the PIDF-LO is in the message.
Within the non-S/MIME message body is this:
--boundary1
Content-Type: application/sdp
v=0
...
--boundary1
Content-type: application/pidf+xml
PIDF-LO
--boundary1--
In the INVITE, Alice's UAC included the Supported header with the
location option tag, and the Location header with the cid:url
pointing at the by-value PIDF-LO. These two headers MAY be hidden
in the S/MIME encrypted message body next to the topmost
Content-Type header to hide the fact that this message is carrying
location in transit. Bob's UAS, the destination UA of Alice's
message, will read these headers when deciphering the overall
message body.
- If Bob's UA wants to join the call, his UA responses with a 200 OK
[M2]. Bob can include his location in the 200 OK response, but
this shouldn't be expected to due to user timing.
A 424 (Bad Location Information) Response with a Unsupported header
(option tag of 'location') is the proper response if Bob's UA cannot
display this information, but does understand the concept of
location.
[Alternative M2 of Figure 2]
SIP/2.0 424 Bad Location Information
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=1928301774
Unsupported: location
- If Bob's UA accepts with a 200 OK message, Alice's UA replies with
an ACK and the session is set up.
- If Bob's UA does not accept the INVITE for reasons other than
location included, a 488 (Not Acceptable Here) may be the
response.
Figure 1 does not include any Proxies because in it assumed they
would not affect the session set-up with respect to whether or not
Alice's location is in a message body part, and Proxies do not react
to S/MIME encrypted bodies, making their inclusion more or less moot
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and asking for more complex message flows than necessary here.
5.2 Location Conveyance Using the MESSAGE Method
Alice can choose to merely want to communicate her location to Bob
point-to-point, without starting a (voice) conversation, the MESSAGE
Method MAY be used here.
To comply with privacy concerns raised in [RFC3693] and [RFC4119], a
MESSAGE Method Request would be built according to [RFC3428] that
includes a location message body. S/MIME encryption SHOULD be used
on the message body (part), as outlined in [RFC3261]. Figure 2 here
shows a simplistic MESSAGE method message flow.
UA Alice UA Bob
| MESSAGE [M1] |
|---------------------------------------->|
| 200 OK [M2] |
|<----------------------------------------|
| |
Figure 1. Location Conveyance in MESSAGE Requests
Below is a sample, non-well-formed MESSAGE Method message from Alice
to Bob conveying her geo location:
[M1 of Figure 2]
MESSAGE sips:bob@biloxi.example.com SIP/2.0
To: Bob
From: Alice
Supported: location
Location: cid:alice123@atlanta.example.com
If the message were S/MIME encrypted, this would be the Content-type
header:
Content-Type: application/pkcs7-mime;
smime-type=enveloped-data; name=smime.p7m
If this MESSAGE request were not S/MIME encrypted, this would be the
Content-Type header:
Content-Type: multipart/mixed; boundary=boundary1
--boundary1
Content-Type: text/plain
Here's my location, Bob?
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--broundary1
Content-Type: application/pidf+xml
Content-Disposition: render
[Alice's PIDF-LO goes here]
--broundary1--
The Content-type of M1 here is "multipart/mixed" to have a text
message incorporated into the message. Within the PIDF-LO message
body, there is a Content-Disposition of "render" to display this
location information to Bob when his UA receives it. The cautions
about whether or not Bob actually reads this message are outlined in
[RFC3428].
The 200 OK to M1 of Figure 2 is a simple 200 OK.
A 424 (Bad Location Information) Response with a Unsupported header
(option tag of 'location') is the proper response if Bob's UA cannot
display this information, but does understand the concept of
location.
[Alternative M2 of Figure 2]
SIP/2.0 424 Bad Location Information
To: Bob
From: Alice
Unsupported: location
If Bob is declining the M2 MESSAGE Request message, a 488 (Not
Acceptable Here) is the appropriate response. A Supported header
with a location option tag indicates location was not the reason
this message was declined.
[Alternative M2 of Figure 2]
SIP/2.0 488 Not Acceptable Here
To: Bob
From: Alice
Supported: location
5.3 Location Conveyance Using the UPDATE Method
The UPDATE Method [RFC3311] is to be used any time location
information is to be updated between UAs setting up a dialog or
after the dialog has been established, no matter how long that
dialog has been operational. reINVITE is inappropriate here, and
the MESSAGE Method is for non-dialog location conveyance between UAs
only. The same security properties used in the INVITE MUST be
applied in the UPDATE message.
There are 3 conditions UPDATE is to be used to convey location
between UAs:
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1) During dialog establishment, but before the final 200 OK (see
section 5.3.1)
2) After dialog establishment, but no prior location information has
been convey (see section 5.3.2), and
3) After dialog establishment, when a UA has determined it has moved
(see section 5.3.3)
5.3.1 UPDATE Updates Location During Session Establishment
Figure 3a. shows the first example of what the UPDATE Method is
used: during dialog establishment when Alice updates Bob with her
location information [M3]. This might be different location
information than was in message [M1] of Figure 3a. or it could be
the first time Alice conveys location to Bob during the dialog
set-up.
UA Alice UA Bob
| INVITE [M1] |
|---------------------------------------->|
| UPDATE [M2] |
|---------------------------------------->|
| 200 OK (UPDATE) [M3] |
|<----------------------------------------|
| 200 OK (INVITE) [M4] |
|<----------------------------------------|
| ACK (UPDATE) [M5] |
|---------------------------------------->|
| RTP |
|<=======================================>|
| |
Figure 3a. Updating Location During Dialog Establishment
[M2 of Figure 3a]
UPDATE sips:bob@biloxi.example.com SIP/2.0
To: Bob
From: Alice
Supported: location
Location: cid:alice123@atlanta.example.com
Content-Type: multipart/mixed; boundary=boundary1
--boundary1
Content-Type: application/sdp
v=
...
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--broundary1
Content-Type: application/pidf+xml
[Alice's PIDF-LO goes here]
--broundary1--
The above example has Alice also changing something within her
original SDP, but this is not necessary for this update of location
information.
- If Bob agrees with this INVITE and the UPDATE, there his UA
transits 200 OKs for each [M4] and [M5] in Figure 3a.
- Alice, upon receiving the 200 OKs, sends an ACK to establish the
dialog with her modified location.
Bob's UA should send a 424 (Bad Location Information) Response with
a Unsupported header (stating 'location') if his UA does not
understand the concept of location conveyance; meaning to the INVITE
in [M1]. Therefore, a 424 SHOULD NOT be sent to the UPDATE of
location information if the PIDF-LO is well formed and has valid
(not validated!) location fields. If Bob's UA sends a 424 to this
UPDATE without an Unsupported header containing a location option
tag, Alice's UA MUST interpret that to mean the location in the
PIDF-LO was poorly generated. Perhaps it was missing a field.
Perhaps a field was incomplete.
If Bob is declining the M2 UPDATE Request message, a 488 (Not
Acceptable Here) is the appropriate response. A Supported header
with a location option tag indicates location was not the reason
this message was declined.
[Alternative M3 of Figure 3a]
SIP/2.0 488 Not Acceptable Here
To: Bob
From: Alice
Supported: location
5.3.2 UPDATE Updates Location After Session Establishment
Figure 3b. shows the second example of what the UPDATE Method is
used for: if a dialog exists between Alice and Bob without location
having been conveyed previously in either direction, and one of the
UAs wants to convey location to the other. For example, if Alice
invites Bob to a dialog, but does not include her location in that
dialog establishment. Anytime during that dialog that Alice's UA
decides to convey location, she uses the UPDATE Method, not the
INVITE Method (in a reINVITE), to update the location parameters of
that dialog.
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Once a dialog has been established, a UAC MUST NOT use the INVITE
Method as a reINVITE to convey location within a dialog. The UPDATE
Method MUST be used.
Consider the following example message flow in Figure 3b.:
UA Alice UA Bob
| INVITE [M1] |
|---------------------------------------->|
| 200 OK (INVITE) [M2] |
|<----------------------------------------|
| ACK [M3] |
|<----------------------------------------|
| RTP |
|<=======================================>|
| UPDATE [M4] |
|---------------------------------------->|
| 200 OK (UPDATE) [M5] |
|<----------------------------------------|
| |
Figure 3b. Updating Location After Dialog Establishment
For whatever reason, Alice decides to send Bob her location for the
first time. [M4] is an example of the UPDATE message used to
accomplish this.
[M4 of Figure 3b]
UPDATE sips:bob@biloxi.example.com SIP/2.0
To: Bob
From: Alice
Supported: location
Location: cid:alice123@atlanta.example.com
Content-Type: application/pidf+xml
[Alice's PIDF-LO goes here]
A 424 (Bad Location Information) Response with a Unsupported header
(stating Location) is the proper response if Bob's UA does not
understand the concept of location. In this case, the dialog MUST
remain unaffected by this rejection message. Here is a rough idea
of this 424:
[Alternative M5 of Figure 3b]
SIP/2.0 424 Bad Location Information
To: Bob
From: Alice
Unsupported: location
If Bob is declining the M4 UPDATE Request message, a 488 (Not
Acceptable Here) is the appropriate response. A Supported header
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with a location option tag indicates location was not the reason
this message was declined.
[Alternative M5 of figure 3b]
SIP/2.0 488 Not Acceptable Here
To: Bob
From: Alice
Supported: location
5.3.3 UPDATE Updates Location After a UA Moves in a Dialog
Figure 3c. shows the first example of what the UPDATE Method is
used: if one UA that already conveyed location to the other UA, and
has moved since the dialog was originally sent up. How a UA
determines it has moved is out of scope for this document.
However that "movement" trigger occurred, M4 of Figure 3c. is the
result: an UPDATE Method Request indicating new location by Alice,
to keep Bob current with Alice's position.
UA Alice UA Bob
| INVITE [M1] |
|---------------------------------------->|
| 200 OK (INVITE) [M2] |
|<----------------------------------------|
| ACK [M3] |
|<----------------------------------------|
| RTP |
|<=======================================>|
**Alice's UA determines it has moved, and needs to update Bob**
| UPDATE [M4] |
|---------------------------------------->|
| 200 OK (UPDATE) [M5] |
|<----------------------------------------|
| |
Figure 3c. Updating Location During Dialog After Movement
This message flow assumes Alice conveyed location in [M1], and that
Bob's UA supports location conveyance by not rejecting the INVITE
request.
Message M4 of Figure 3c. shows the UPDATE of Alice's location
information to Bob. That message may look like this (non-well-
formed SIP message):
[M4 of Figure 3c]
UPDATE sips:bob@biloxi.example.com SIP/2.0
To: Bob
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From: Alice
Supported: location
Location: cid:alice123@atlanta.example.com
Content-Type: application/pidf+xml
[Alice's PIDF-LO goes here]
There currently is not an indication within the PIDF-LO for Alice to
tell Bob this PIDF-LO is new, replacement location information from
a previous message (here in the M1 INVITE message).
Because of the 200 OK to the INVITE containing location, Alice knows
Bob's UA understands location conveyance. Therefore, if Bob's UA
sends a 424 to this UPDATE, it MUST NOT contain an Unsupported
header containing a location option tag.
If Alice does receive a 424 (with the Unsupported header with a
location option tag), Alice's UA MUST interpret that to mean the
location in the PIDF-LO was poorly generated. Perhaps it was
missing a field. Perhaps a field was incomplete.
If Bob is declining the M4 UPDATE Request message, a 488 (Not
Acceptable Here) is the appropriate response. A Supported header
with a location option tag indicates location was not the reason
this message was declined.
[Alternative M5 of figure 3c]
SIP/2.0 488 Not Acceptable Here
To: Bob
From: Alice
Supported: location
5.4 Location Conveyance Using the REGISTER Method
Alice can choose to merely want to communicate her location to Bob
point-to-point, without starting a (voice) conversation, the
REGISTER Method MAY be used here.
To comply with privacy concerns raised in [RFC3693] and [RFC4119], a
REGISTER Method Request MUST S/MIME encrypt the PIDF-LO, as outlined
in [RFC3261]. A UAC SHOULD use a SIPS-URI, as outlined in
[RFC3261]. Figure 4 here shows a simplistic REGISTER method
message flow.
UA Alice Registrar
| REGISTER [M1] |
|---------------------------------------->|
| 200 OK [M2] |
|<----------------------------------------|
| |
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Figure 4. Location Conveyance in REGISTER Requests
Below is a sample, non-well-formed REGISTER Method message from
Alice to Bob conveying her geo location:
[M1 of Figure 2]
REGISTER sips:registrar1@biloxi.example.com SIP/2.0
To: Alice <sips:alice@atlanta.example.com>;
From: Alice <sips:alice@atlanta.example.com>;tag=1928301774
Supported: location
Location: cid:alice123@atlanta.example.com
Expires: 21600
If the message were S/MIME encrypted, this would be the Content-type
header:
Content-Type: application/pkcs7-mime;
smime-type=enveloped-data; name=smime.p7m
If this REGISTER request were not S/MIME encrypted, this would be
the Content-Type header:
Content-Type: application/pidf+xml
provided there were no other registration event message bodies.
The 200 OK to M1 of Figure 2 is a simple 200 OK.
A 424 (Bad Location Information) Response with a Unsupported header
(option tag of 'location') is the proper response if the Registrar
server does not understand location conveyance.
[Alternative M2 of Figure 2]
SIP/2.0 424 Bad Location Information
To: Alice
From: Alice
Unsupported: location
If the Registrar Server is declining the original [M1] REGISTER
Request, a 488 (Not Acceptable Here) is the appropriate response. A
Supported header with a location option tag indicates location was
not the reason this message was declined.
[Alternative M2 of Figure 2]
SIP/2.0 488 Not Acceptable Here
To: Alice
From: Alice
Supported: location
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6. Special Considerations for Emergency Calls
Emergency calling, such as 911, 112 and 999 calling today,
necessitates a UAC to understand the type of call it is about to
generate with an INVITE message to a PSAP. First of all, the
purpose of calling for emergency help is to get someone to respond
to the UAC's location, therefore, location MUST be included in the
INVITE, if known by the UAC.
The emergency services community strongly prefers that message
routing occur in the network with the freshest available Public
Safety Answering Point (PSAP) information. Message routing, in this
context, means choosing which SIP(S)-URI to place in the Request-URI
field of the status line.
If a UAC knows it is generating an emergency request towards a PSAP,
there MAY be unique message handling characteristics that diminish
the level of confidentiality of the location information within the
SIP message(s). This is because emergency call routing requires
proxies to know the location of the message originating UAC in order
to make a decision on where to route the message. This is because
emergency calls are directed to the PSAP local to the caller's
location. A proxy performing this function requires that proxy to
learn the location of the UAC during message processing.
How a message is routed based on the location of the UAC, and if and
by how much the level of confidentiality of location information is
diminished when calling for emergency help are both out of scope of
this document.
Hop-by-hop confidentiality mechanisms, as defined in [RFC3261] MUST
be attempted initially by a UAC that includes location. Local
configuration MAY allow a subsequent retry, after a security related
failure, to be without hop-by-hop confidentiality. SIP elements
MUST obey the rules set forth in [RFC3261] regarding maintaining
hop-by-hop confidentiality when a message using a SIPS-URI.
While many jurisdictions force a user to reveal their location
during an emergency call set-up, there is a small, but real, number
of jurisdictions that allow a user to configure their calling device
to disable providing location, even during emergency calling. This
capability MUST be configurable, but is not RECOMMENDED as the
default configuration of any UA. Local policies will dictate this
ability.
7. Meeting RFC3693 Requirements
Section 7.2 of [RFC3693] details the requirements of a "using
protocol". They are:
Req. 4. The using protocol has to obey the privacy and security
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instructions coded in the Location Object and in the
corresponding Rules regarding the transmission and storage of the
LO.
This document requires, in Section 3, that SIP entities sending or
receiving location MUST obey such instructions.
Req. 5. The using protocol will typically facilitate that the keys
associated with the credentials are transported to the respective
parties, that is, key establishment is the responsibility of the
using protocol.
[RFC3261] and the documents it references define the key establish
mechanisms.
Req. 6. (Single Message Transfer) In particular, for tracking of
small target devices, the design should allow a single
message/packet transmission of location as a complete
transaction.
This document specifies that the LO be contained in the body of a
single message, which may be fragmented via TCP, but is still not a
streaming delivery.
8. Open issues
This is a list of open issues that have not yet been addressed to
conclusion:
none
9. Security Considerations
Conveyance of physical 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, due to
the probability of a proxy from requiring the ability to read that
information to route the message appropriately. This means the use
of S/MIME may not be possible. This leaves location information of
the caller available in each proxy through to the PSAP. This may
not be a perfect solution, but may be a pill we need to swallow to
enable this functionality.
A bad implementation of SIP location conveyance would have a UAC
send location in cleartext, without hop-by-hop confidentiality, or
have any SIP element along the path towards the PSAP alter the
transport of any message carrying location to be without hop-by-hop
confidentiality between elements. The latter would be in clear
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Internet Draft SIP Location Conveyance Mar 6th, 2006
violation of RFC3261 rules surrounding the use of a SIPS-URI.
10. IANA Considerations
This section defines one new SIP header, two new option tags, and
one new 4XX error response code within the sip-parameters section of
IANA. [NOTE: RFC XXXX denotes this document].
10.1 IANA Registration for the SIP Location Header
The Location header is created by this document, with its definition
and rules in Section 4 of this document.
10.2 IANA Registration for Two New SIP Option Tags
Two new SIP option tags are created by this document, "Location" and
"Unknown-location", with the definitions and rules for each in
Section 4 of this document.
10.3 IANA Registration for Response Code 4XX
Reference: RFC-XXXX (i.e. this document)
Response code: 424
Default reason phrase: Bad Location Information
11. 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, Mike Hammer and Keith Drage for
constructive feedback.
To Paul Kyzivat for inspiring some of the recent text addressing
lingering issues the authors could not resolve.
To Jon Peterson for his guidance in this effort.
12. References
12.1 References - Normative
[RFC3261] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, May 2002.
[RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
"Geopriv Requirements", RFC 3693, February 2004
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Internet Draft SIP Location Conveyance Mar 6th, 2006
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
[RFC4119] J. Peterson, "draft-ietf-geopriv-pidf-lo-03", Internet
Draft, Sept 2004, work in progress
[RFC3428] B. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema,
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging" , RFC 3428, December 2002
[RFC2392] E. Levinson, " Content-ID and Message-ID Uniform Resource
Locators", RFC 2393, August 1998
[RFC3311] J. Rosenberg, "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002
12.2 References - Informative
[ID-Sess-Pol] J. Rosenberg, "Requirements for Session Policy for the
Session Initiation Protocol”, draft-ietf-sipping-session-
policy-req-02", Internet Draft, July, 2004, "work in
progress"
[RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004
[ID-CIVIC] H. Schulzrinne, " Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
Information ", draft-ietf-geopriv-dhcp-civil-09, "work in
progress", January 2006
Author Information
James M. Polk
Cisco Systems
3913 Treemont Circle 33.00111N
Colleyville, Texas 76034 96.68142W
Phone: +1-817-271-3552
Email: jmpolk@cisco.com
Brian Rosen
470 Conrad Dr. 40.70497N
Mars, PA 16046 80.01252W
US
Phone: +1 724 382 1051
Email: br@brianrosen.net
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Internet Draft SIP Location Conveyance Mar 6th, 2006
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