One document matched: draft-ietf-sip-location-conveyance-09.txt
Differences from draft-ietf-sip-location-conveyance-08.txt
SIP Working Group James Polk
Internet Draft Cisco Systems
Expiration: May 16th, 2008 Brian Rosen
Intended Status: Standards Track (PS) NeuStar
Location Conveyance for the Session Initiation Protocol
draft-ietf-sip-location-conveyance-09.txt
Nov 16th, 2007
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines an extension to the Session Initiation
Protocol (SIP) to convey geographic location information from one
SIP entity to another SIP entity. The extension covers end to end
conveyance as well as location-based routing, where proxy servers
make routing decisions based on the location of the SIP user agents.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Overview of SIP Location Conveyance . . . . . . . . . . . 4
3.2 The Geolocation Header . . . . . . . . . . . . . . . . . 5
3.3 424 (Bad Location Information) Response Code . . . . . . 8
3.4 The Geolocation-Error Header . . . . . . . . . . . . . . 9
3.5 The Geolocation Option Tag . . . . . . . . . . . . . . . 18
3.6 Using sip/sips/pres as a Dereference Scheme . . . . . . . 19
4. Geolocation Examples . . . . . . . . . . . . . . . . . . . . 20
4.1 Location-by-value (Coordinate Format) . . . . . . . . . . 20
4.2 Location-by-reference . . . . . . . . . . . . . . . . . . 22
5. SIP Element Behavior . . . . . . . . . . . . . . . . . . . . 23
5.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 24
5.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . 26
5.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 29
6. Geopriv Privacy Considerations . . . . . . . . . . . . . . . 32
7. Security Considerations . . . . . . . . . . . . . . . . . . . 33
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 34
8.1 IANA Registration for New SIP Geolocation Header . . . . 34
8.2 IANA Registration for New SIP Geolocation Option Tag . . 35
8.3 IANA Registration for New 424 Response Code . . . . . . . 35
8.4 IANA Registration for New SIP Geolocation-Error Header . 35
8.5 IANA Registration for New SIP Geolocation-Error Codes . . 35
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 37
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 37
10.1 Normative References . . . . . . . . . . . . . . . . . 37
10.2 Informative References . . . . . . . . . . . . . . . . . 38
Author Information . . . . . . . . . . . . . . . . . . . . . 38
Appendix A. Requirements for SIP Location Conveyance . . . . 39
Appendix B. Example of Civic-based PIDF-LO w/ S/MIME . . . . 41
Intellectual Property and Copyright Statements . . . . . . . 42
1. Introduction
This document describes how Location can be "conveyed" (that is,
transmitted over the Internet) from one SIP user agent (UA), or in
some circumstances, a proxy server acting in support of a UA, to
another entity using SIP [RFC3261]. Here "Location" is a
description of the physical geographical area where something
currently exists. The phrase "location conveyance" describes
scenarios in which a SIP user agent client (UAC) is informing a user
agent server (UAS), or intermediate SIP server where the UAC is. A
superset of this can also be true as well, in which one UA(1) is
telling another UA(2) where another Target is, meaning not
necessarily where UA(1) is. The key to this is whether UA(1) has
permission to retransmit that other Target's location. If yes, then
this is valid. If no, then this is breaking a fundamental rule
within this extension.
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Location Conveyance is different from a UAC seeking the location the
UAS. Location conveyance is a 'sending location out in the request'
model, where 'asking that someone else's location be in a response'
is not discussed here.
Geographic location in the IETF is discussed in RFC 3693 (Geopriv
Requirements) [RFC3693]. It defines a "Target" as the entity whose
location is being sought. In this case, this is the UA's
(UA) location. A [RFC3693] "Using Protocol" defines how a "location
Server" transmits a "Location Object" to a "Location Recipient"
while maintaining the contained privacy intentions of the Target
intact. This document describes the extension to SIP for how it
complies with the Using Protocol requirements, where the location
server is a UA or Proxy Server and the Location Recipient is
another UA or Proxy Server.
Location can be transmitted by-value or by-reference. The location
"value" in this SIP extension is in the form of a Presence
Information Data Format - Location Object, or PIDF-LO, as described
in [RFC4119]. A PIDF-LO is an XML Scheme specifically for carrying
geographic location of a Target. Location-by-value refers to a UA
including a PIDF-LO as a body part of a SIP message, sending that
Location Object to another SIP element. Location-by-reference
refers to a UA or proxy server including a URI in a SIP message
header field which can be dereferenced by a Location Recipient for a
Location Object, in the form of a PIDF-LO. Dereferencing can be by
a SIP UA or a SIP server.
As recited in RFC 3693, location often must be kept private. The
Location Object (PIDF-LO) contains rules which provides guidance to
the Location Recipient and controls onward distribution and
retention of the location. This document describes the security and
privacy considerations that must be applied to location conveyed
with SIP.
Another use for location is location-based routing of a
SIP request, where the choice of the next hop (and usually, the
outgoing Request-URI) is determined by the location of the UAC which
is in the message by-value or by-reference. This document describes
how location can be conveyed from the UAC, or a proxy acting on its
behalf, to a routing proxy. How the location is actually used to
determine the next hop or Request-URI is beyond the scope of this
document.
We refer to the "emergency case". This refers to a specific,
important use of SIP location conveyance where the location of the
caller is used to determine which Public Safety Answering Point
(PSAP) is expected to receive an emergency call request for help
(e.g., a call to 1-1-2 or 9-1-1). This is an example of
location-based routing. The location conveyed is also used by the
PSAP to dispatch first responders to the caller's location. There
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are special security considerations, which make the emergency case
unique, compared to a normal location conveyance within SIP.
2. 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].
3. Mechanisms
3.1 Overview of SIP Location Conveyance
This document defines a new SIP header: Geolocation. The
Geolocation header field contains a URI which can either be a "cid:"
URI (Content Identification), per [RFC2392], or a
location-by-reference URI to be dereferenced by a Location Recipient
to retrieve the location of the Target UA.
Where the Geolocation header contains a "cid:", the URI points to a
message body that is in the form of a PIDF [RFC3863], which was
extended in [RFC4119] to include location, as a PIDF-LO. This is
location-by-value, the actual location information in the PIDF-LO is
included in the body of the message.
If the URI in the Geolocation header field is a scheme other than
"cid:", another protocol operation is needed by the SIP message
recipient to obtain the location of the Target (UA). This is
location-by-reference. This document describes how a SIP presence
subscription [RFC3856] can be used as a dereference protocol.
The Geolocation header, either with the PIDF-LO in a body or as a
location-by-reference URI, can be included by a UA in a
SIP message. A SIP proxy server may assert location of the UA by
inserting the header field, which must specify a
location-by-reference URI. Since body parts cannot be inserted by a
SIP proxy server, location-by-value message body cannot be inserted
by a proxy.
The Geolocation header can have parameters that are associated
with a URI in the header field. The "inserted-by" parameter has
values of "endpoint" or "server", indicating which entry added
location to the message. This header parameter MAY be added every
time a new location is added into a message.
Retargeting means the Request-URI of the request has changed to
point at a new destination UAS. This is different than message
routing, that all SIP proxies do. If a SIP request is retargeted
based on the location contained or referenced within that message,
the "used-for-routing" parameter MUST be added as a header parameter
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within the appropriate locationValue.
There is no mechanism by which the veracity of these parameters can
be verified. They are hints to downstream entities on how the
location information in the message was originated and used.
This document creates a new option tag: geolocation, to indicate
support for the this extension by UAs.
A new error message (424 Bad Location Information) is also defined
in this document. Within this response is a new header indicating
location-based errors, call the Geolocation-Error header. This
header has various codes that provide additional information about
the type of location error experienced by a Location Recipient.
Both new headers, the header parameters, the new option-tag, the new
error response, and Geolocation-Error codes are IANA registered by
this document.
3.2 The Geolocation Header
This document defines and IANA registers a new SIP header:
Geolocation. The Geolocation header field MUST contain at least one
of two types of URIs:
o a location-by-reference URI, or
o a content-ID indicating where location is within the message body
of this message
A location-by-reference URI is a pointer to a record on a remote
node containing location of the location Target, typically the
UA in this transaction.
A location-by-value content-ID (cid-url) [RFC2392] indicates which
message body part contains location for this UA.
The Geolocation header has the following BNF syntax:
Geolocation = "Geolocation" HCOLON (locationValue *(COMMA
locationValue))
locationValue = LAQUOT locationURI RAQUOT *(SEMI geoloc-param)
locationURI = sip-URI / sips-URI / pres-URI
/ cid-url ; (from RFC 2392)
/ absoluteURI ; (from RFC 3261)
geoloc-param = "inserted-by" EQUAL geoloc-inserter
/ "used-for-routing"
/ "recipient" EQUAL recipient-type
/ generic-param ; (from RFC 3261)
geoloc-inserter = host-id
/ gen-value ; (from RFC 3261)
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recipient-type = "endpoint" / "routing-entity" / "both"
/ gen-value ; (from RFC 3261)
sip-URI, sips-URI and absoluteURI are defined according to RFC 3261.
The pres-URI is defined in RFC 3859 [RFC3859].
The cid-url is defined in [RFC2392] to locate message body
parts. This URI type MUST be present in a SIP message if location
is by-value in that same message.
Other protocols used in the Location URI MUST be reviewed against
the RFC 3693 criteria for a Using Protocol.
The Geolocation header MAY have one or more locationValues. SIP
servers inserting a locationValue MUST add the new value to the end
of the header value, such that the last locationValue in the header
is the most recent one added to the message.
A locationValue has the following independent header parameters,
o the "inserted-by=" parameter provides the host-id
(alice.example.com -- which is the same as the "sent-by"
parameter in a Via header) of the SIP entity that inserted this
locationValue into the request. This is used to map to any
Geolocation-Error message to determine which location, if there
is more than one in a request, the error corresponds to. If an
entity receives an Geolocation-Error with a host-id not of this
entity, the Geolocation-Error SHOULD be ignored.
o the "used-for-routing" parameter to inform recipients that the
location in this locationValue was used to route the message
towards the ultimate destination UAS. This can occur more than
once along the request's path. Because locationValues are
inserted as last inserted is last in the header, the last
locationValue is the most recent one added to the message. This
also gives the "used-for-routing" header parameter added
integrity - as the receiving SIP entity knows which locationURI
the message was routed upon.
o the "recipient=" parameter to allow recipients to infer what SIP
element type this locationValue was intended to be for. The
types are
o "endpoint" - meaning the ultimate destination UAS;
o "routing-entity" - meaning SIP servers that route messages
based on the location contents of requests; and
o "both" - meaning this locationValue is to be viewed by both
types of SIP entities.
Not all SIP entities have to read the locationValue within a
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Geolocation header, therefore a parameter value of "both" does
not mean "every" SIP element receiving this request, it means all
that care to pay attention to a locationValue. The default
behavior of SIP entities reading the locationValue is that if
this header parameter is NOT present, the intended recipient is
the destination UAS.
Each locationValue MUST contain exactly one "inserted-by" parameter,
indicating which SIP entity added the locationValue to the SIP
request.
Each of the three types of header parameters listed here MAY appear
in any locationValue once. There MUST NOT be more than one
"inserted-by=" parameter or one "used-for-routing" parameter or one
"recipient=" parameter in the same locationValue. However, there
can be more than one locationValue in the same Geolocation header.
This document defines the Geolocation header as valid in the
following SIP requests:
INVITE [RFC3261], REGISTER [RFC3261],
OPTIONS [RFC3261], BYE [RFC3261],
UPDATE [RFC3311], INFO [RFC2976],
MESSAGE [RFC3428], REFER [RFC3515],
SUBSCRIBE [RFC3265], NOTIFY [RFC3265],
PUBLISH [RFC3903] and PRACK [RFC3262]
Discussing location using the PUBLISH Request Method is out of scope
for this document, but the Table 1 shows PUBLISH is to support
Location Conveyance via this extension.
The following table extends the values in Table 2&3 of RFC 3261
[RFC3261].
Header field where proxy INV ACK CAN BYE REG OPT PRA
----------------------------------------------------------------
Geolocation R ar o - - o o o o
Header field where proxy SUB NOT UPD MSG REF INF PUB
----------------------------------------------------------------
Geolocation R ar o o o o o o o
Table 1: Summary of the Geolocation Header
The Geolocation header field MAY be included in any one of the above
requests by a UAC. A proxy MAY add the Geolocation header, but MUST
NOT modify any pre-existing locationValue, including its associated
header parameters of within an existing Geolocation header value,
unless one of the existing locationValues is used to retarget the
request towards a new destination UAS. This is discussed in section
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5.3.
[RFC3261] states message bodies cannot be added by proxies.
Therefore, any Geolocation header field added by a proxy MUST be in
the form of a location-by-reference URI, in its own locationValue
header value.
Adding a new locationValue to an existing Geolocation header SHOULD
NOT occur without appropriate caution to the fact that Location
Recipients might not understand how to process more than one
location, given this document's limited guidance as to what a
Location Recipient should do when receiving more than one location
(i.e., currently no priority instructions are given for which
locationValue to use if there are more than one). A Location
Recipient can easily be confused by too much location information,
producing undesirable results. The <tuple id> element in the
PIDF-LO XML indicates whose location is contained in the PIDF-LO.
Location Recipients receiving a location object, received directly
or as the result of a dereference, MUST honor the usage element
rules within that XML document, per RFC 4119. Such entities MUST
NOT alter the rule set.
3.3 424 (Bad Location Information) Response Code
If a UAS or SIP intermediary detects an error in a request message
specific to the location information supplied by-value or
by-reference. The new 4XX level error is created here to indicate a
problem with the location in the request message. This document
creates and IANA registers the new error code:
424 (Bad Location Information)
The 424 (Bad Location Information) response code is a rejection of
the request, due to its location contents, indicating the location
information was malformed or not satisfactory for the recipient's
purpose, or could not be dereferenced.
Section 3.4 creates the Geolocation-Error header to provide more
detail about what was wrong with the location information in the
request. This header MUST be in the 424 response, containing a
locationErrorValue for each invalid locationValue in the request
(i.e., and one-for-one matching if all locationValues in the request
were bad).
If more than one location is present in a request (by-value or
by-reference), and any of the locationValues is good for the
Location Recipient to process, a 424 MUST NOT be sent. The 424 is
only appropriate when the Location Recipient needs a locationValue
and there are no locationValues included in a SIP request that are
usable by a recipient.
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A 424 (Bad Location Information) response is a final response within
a transaction, and does not terminate a dialog.
The UAC can use whatever means it knows of to verify/refresh its
location information before attempting a new request that includes
location. There is no cross-transaction awareness expected by either
the UAS or SIP intermediary as a result of this error message.
The new 424 (Bad Location Information) error code is IANA registered
in Section 8 of this document. An initial set of location error of
IANA registered Geolocation-Error codes are in Section 3.4 of this
document.
3.4 The Geolocation-Error Header Providing Error Granularity
As discussed in Section 3.3, more granular error notifications,
specific to location errors within a received request, are required
if the UAC is to know what was wrong within the original request.
The Geolocation-Error header is created here for this purpose.
Geolocation-Error header is used to convey location specific errors
within a response. Additions to this IANA registered header require
an RFC be published.
Geolocation-Error = "Geolocation-Error" HCOLON
[locationErrorValue
*(COMMA locationErrorValue)]
locationErrorValue = location-error-code *(SEMI
location-error-params)
location-error-code = 1*3DIGIT
location-error-params = location-error-node-id
/ DQOUTE location-error-host-id DQOUTE
/ CAtype *(SEMI CAtype)
/ DQOUTE location-error-code-text DQOUTE
/ generic-param ; from RFC3261
location-error-node-id = "node" EQUAL hostname; from RFC3261
location-error-host-id = "inserter" EQUAL hostname ; from RFC3261
CAtype = "CAtype" EQUAL civic-code *(SEMI "CAtype"
EQUAL civic-code)
location-error-code-text = "code" EQUAL quoted-string ; from RFC3261
civic-code = IANA registered CAtypes; from
[IANA-civic]
The Geolocation-Error header MUST contain at least one
locationErrorValue to indicate what was wrong with the original
locationValue in the corresponding request. If a Location Recipient
experienced more than one error in the locationValue of the
corresponding SIP request, there can be one locationErrorValue per
problem with the locationValue in the request (the except to this is
involving CAtypes, which will be covered later here). If there was
something wrong with more than one locationValue in a request, a
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corresponding locationErrorValue would be sent, one per error, in
the response. Each locationErrorValue contains a 3-digit error code
(defined in subsections to this section of this doc) indicating what
was wrong with the location(s) in the request. Each error type has
a corresponding quoted error text string that is human
understandable.
Also within the locationErrorValue is the Location Recipient
identifier (the "node=") who experienced the location error, as well
as an identifier of which SIP entity (the "inserter=") the Location
Recipient is told (in the locationValue) added the locationValue to
this request. The "node=" and "inserter=" are domain identifier of
a SIP entity, the same as is entered in the "sent-by" parameter of
the Via header for that entity [RFC3261]. As stated in section 18
of RFC 3261, the usage of FQDN is RECOMMENDED. Here are examples of
both
node=bob.example.com
inserter=alice.example.com
Both "node=" and "inserter=" parameters MUST be present in all
locationErrorValues in a response, unless the "inserted-by="
parameter was not in the request. The "inserter=" parameter is
copied from the "inserted-by=" parameter within the locationValue of
the request.
Here's why, a Location Recipient that experienced the location
problem with the request needs to tell who added which location into
the original request. Since more than one SIP entity can insert
location into a request, all other SIP elements may be confused by
receiving this error header. So, the header has to identify who it
is for, so that all other SIP entities that read the header know to
ignore it, since it is not for them. This is of particular use if
the original UAC did not include a locationValue in the original SIP
request, but a SIP server along the path did insert a locationValue.
The locationErrorValue would travel to each SIP entity along the
original path and tell both the server that included the
locationValue what was wrong with the location and the UAC who
did not know what the error meant.
A worse case is when both the original UAC and a SIP server along
the path included a locationValue, but there was only something
wrong with one of the locationValues. Without this identification
of which locationValue was in error, both entities would react and
one would do so incorrectly.
Finally, there can be a list of one or more CAtype civic-codes that
are determined to be in error by the Location Recipient. Perhaps
the Location Recipient believes one or more CAtypes are missing, and
required in order to fully process the locationValue in the request,
or perhaps data entered in one or more CAtypes is wrong, according
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to the Location Recipient. The list of CAtypes is taken from those
that are IANA registered at [IANA-civic].
More than one locationErrorValue in a Geolocation-Error header is
separated by a comma.
If more than one locationErrorValue is in a response, and intended
for the same "inserter=", the error codes SHOULD NOT conflict in
meaning. In other words, two error codes (within separate
locationErrorValues of the same response) SHOULD NOT give misleading
or inconsistent indications to the location "inserter=".
Here is an example of a Geolocation-Error header
Geolocation-Error: 106; "node=bob.example.com";
"inserter=alice.example.com";
CAtype=A3; CAtype=STS;
code="incomplete location supplied"
In this example, the Location Recipient (node=Bob) has determined
the location supplied by the "inserter=" (inserter=Alice) was not
enough to determine where (Alice) was. Specifically, Bob has
determined that CAtypes A3 (the city) and STS (the street type
(Street, Road, Avenue, etc)) were not present to form a complete
location of the Alice. A subsequent request by Alice that included
these two additional pieces of location information would tell Bob
where Alice was.
Notice the CAtypes that were in error are (in the above example
Geolocation-Error header), according to the Location Recipient,
listed in the locationErrorValue. The associated CAtype values MUST
NOT be listed in the locationErrorValue. This is for
privacy/security concerns. It is up to the Location Recipient to
determine which CAtypes were in error, and only list those CAtypes
in the response. The "inserter=" entity MUST determine what to do
about correcting each CAtype found in error for subsequent location
conveyance. Usually, this would involve either refreshing its
location information however it learned its location in the first
place, or merely listing what information is lacking/wrong to the
location sender (i.e., the user) or its network management.
The following table extends the values in Table 2&3 of RFC 3261
[RFC3261].
Header field where proxy INV ACK CAN BYE REG OPT PRA
----------------------------------------------------------------
Geolocation-Error r ar o - - o o o o
Header field where proxy SUB NOT UPD MSG REF INF PUB
----------------------------------------------------------------
Geolocation-Error r ar o o o o o o o
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Table 2: Summary of the Geolocation-Error Header
The Geolocation-Error header field MAY be included in any response
to one of the above SIP requests, so long as Geolocation was in the
request part of the transaction. The choice of which SIP requests
are in table 2 above come from which Methods can optionally have the
Geolocation header (see section 3.2).
Here is an example of a transaction that has a location error. In
this case, Bob responds with a 424 (Bad Location Information)
response, including a Geolocation-Error header, is in Figure 1.
Alice Bob
| |
| Request w/ Location |
|--------------------------------------->|
| |
| |
| 424 (Bad Location Information) |
| with Geolocation-Error containing |
| 106 (Incomplete Location Information) |
|<---------------------------------------|
| |
Figure 1. Basic Transaction with 424 and Geolocation-Error Header
The following subsections provide an initial list of location
specific granular codes for any SIP responses, including the new 424
(Bad Location Information) response. If more than one specific
Geolocation-Error code is applicable for a response, each MUST be in
the response. Geolocation-Error Code 100 is the generic 'location
was supplied, but not understood' error. If a more specific code
applies, a code 100 is unnecessary.
3.4.1 Geolocation-Error Code 100 Location Not Understood
Geolocation-Error code 100 "Location Format not supported" means the
location format supplied in the request, by-value or by-reference,
was not supported.
This code means the recipient understood that location was included
in the message, but the format is not supported. Perhaps the format
was a freeform text format or data-URL and the recipient only
understood location in RFC 4119 PIDF-LO format (civic or
x.y(.z) coordinate). This error code applies when a recipient has
difficulty parsing the location supplied in the request.
If the format is understood, but not desired, an error code 101 or
102 MUST be returned in a 424 response, depending on which location
format is desired. The Location Recipient returns an error code 101
or 102 when it only understands one location format (coordinate or
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civic) and did not receive that format.
If a more specific error code is appropriate in a response,
including error code 100 is unnecessary.
error-text-string: Location format not supported
An example usage in a SIP 424 response:
Geolocation-Error: 100; "node=bob.example.com";
"inserter=alice.example.com";
CAtype=A3; CAtype=STS;
code="Location Format not supported"
3.4.2 Geolocation-Error Code 101 Coordinate-location Format Desired
Geolocation-Error code 101 "Coordinate-location Format Desired"
means the location format supplied in the request (probably
formatted in civic), by-value or by-reference, was understood and
supported, but that the recipient, or an application on the
recipient, can or prefers to only process location in the
coordinate-location format.
A typical reaction to receiving this code is to resend the
original message with location formatted in coordinate instead.
error-text-string: Coordinate-location Format Desired
An example usage in a SIP 424 response:
Geolocation-Error: 101; "node=bob.example.com";
"inserter=alice.example.com";
code="Coordinate-location Format Desired"
3.4.3 Geolocation-Error Code 102 Civic-location Format Desired
Geolocation-Error code 102 "Civic-location Format Desired" means the
location format supplied in the request (probably formatted in
coordinate), by-value or by-reference, was understood and supported,
but that the recipient, or an application on the recipient, can or
prefers to only process location in the civic-location format.
A typical reaction to receiving this code is to resend the
original message with location formatted in civic instead.
error-text-string: Civic-location Format Desired
An example usage in a SIP 424 response:
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Geolocation-Error: 102; "node=bob.example.com";
"inserter=alice.example.com";
code="Civic-location Format Desired"
3.4.4 Geolocation-Error Code 103 Cannot Parse Location Supplied
Geolocation-Error code 103 "Cannot parse location supplied" means
the location provided, whether by-value or by-reference, in a
request is not well formed.
error-text-string: Cannot parse location supplied
An example usage in a SIP 424 response:
Geolocation-Error: 103; "node=bob.example.com";
"inserter=alice.example.com";
code="Cannot parse location supplied"
3.4.5 Geolocation-Error Code 104 Cannot Find Location Information
Geolocation-Error code 104 "Cannot find location" means location was
expected in the request, but the recipient cannot find it.
This can be either because the cid: pointed to a message body part
that is not present in the request, there was no location message
body part, or what is dereferenced at the supplied locationURI did
not return a PIDF-LO, or location is encrypted/opaque to the
recipient.
A typical reaction to receiving this code is for the location sender
to verify that it has indeed included location information in the
request in the properly indicated place and then to send the request
again.
error-text-string: Cannot find location
An example usage in a SIP 424 response:
Geolocation-Error: 104; "node=bob.example.com";
"inserter=alice.example.com";
code="Cannot find location"
3.4.6 Geolocation-Error Code 105 Conflicting Locations Supplied
Geolocation-Error code 105 "Conflicting Locations Supplied" means a
Location Recipient received more than one location describing where
the Target is, and is either unsure which whole location is true or
which parts of multiple locations make up where the Target is.
This is generally a case of either too much information, and the
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information is pointing towards at least two different positions,
confusing the recipient.
A possible scenario exists in which at least two locations are in
the request, perhaps one or more were added by proxies along the
path of the request, each pointing to where the UAC is. If these
are pointing at different positions - the UAS does not know which to
trust. This error code unfortunately means the UAS cannot solve for
which location needs to be ignored to make up a complete location,
or how to prioritize one location over all others in the same
request.
A typical reaction to receiving this code is to reduce the number of
different locations supplied in the request, if under control by the
Target, and send another message to the Location Recipient.
error-text-string: Conflicting Locations Supplied
An example usage in a SIP 424 response:
Geolocation-Error: 105; "node=bob.example.com";
"inserter=alice.example.com";
code="Conflicting Locations Supplied"
3.4.7 Geolocation-Error Code 106 Incomplete Location Supplied
Geolocation-Error code 106 "Incomplete Location Supplied" means
there is not enough location information, by-value or retrieved
by-reference, to determine where the location Target is.
Perhaps the coordinate precision is not fine enough, or the civic
address lacks the fields to inform the UAS or proxy where the Target
is. This might be true for request retargeting, or it might be true
for first responder dispatch or pizza delivery (for example, because
the street address is missing).
A typical reaction to receiving this code is for the location sender
to convey more (precise) location information, if doing so is
allowed by local policy.
error-text-string: Incomplete location supplied
An example usage in a SIP 424 response:
Geolocation-Error: 106; "node=bob.example.com";
"inserter=alice.example.com";
code="Incomplete location supplied"
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3.4.8 Geolocation-Error Code 107 Cannot Dereference
Geolocation-Error code 107 "Cannot dereference" means the act of
dereferencing failed to return the Target's location. This
generally means the supplied URI is bad.
error-text-string: Cannot dereference
An example usage in a SIP 424 response:
Geolocation-Error: 107; "node=bob.example.com";
"inserter=alice.example.com";
code="Cannot dereference"
3.4.9 Geolocation-Error Code 108 Dereference Denied
Geolocation-Error code 108 "Dereference Denied" means there was
insufficient authorization to dereference the Target's location.
error-text-string: Dereference Denied
An example usage in a SIP 424 response:
Geolocation-Error: 108; "node=bob.example.com";
"inserter=alice.example.com";
code="Dereference Denied"
3.4.10 Geolocation-Error Code 109 Dereference Timeout
Geolocation-Error code 109 "Dereference Timeout" means the
dereferencing node has not received the Target's location within a
reasonable timeframe.
error-text-string: Dereference Timeout
An example usage in a SIP 424 response:
Geolocation-Error: 109; "node=bob.example.com";
"inserter=alice.example.com";
code="Dereference Timeout"
3.4.11 Geolocation-Error Code 110 Cannot Process Dereference
Geolocation-Error code 110 "Cannot process Dereference" means the
dereference protocol has received an overload condition error,
indicating the location cannot be accessed at this time.
If a SIP or SIPS scheme were used to dereference the Target's
location, and a 503 (Service Unavailable) were the response to the
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dereference query, this Geolocation-Error code 11 would be placed in
the 424 (Bad Location Information) response to the location sender.
error-text-string: Cannot process Dereference
An example usage in a SIP 424 response:
Geolocation-Error: 110; "node=bob.example.com";
"inserter=alice.example.com";
code="Cannot process Dereference"
3.4.12 Geolocation-Error Code 120 Unsupported Scheme - SIP desired
Geolocation-Error code 120 "Unsupported Scheme - SIP desired" means
the location dereferencer cannot dereference using the
location-by-reference URI scheme supplied because it does not
support the necessary protocol to do this.
This code means the Location Recipient can dereference the Target's
location using a SIP-URI scheme. There can be more than one
locationErrorValue in a Geolocation-Error header, indicating in this
context the recipient can dereference using each scheme protocol
included in the Geolocation-Error header.
Note that indicating SIP to be used to dereference location is
requesting the transmission to be in cleartext, which is a security
risk. Therefore, the SIP scheme SHOULD NOT be used to dereference.
An exception can be made for emergency calling, preferably after
SIPS has been attempted, and failed.
A typical reaction to receiving this code would be for the location
sender to send a URI with the sip scheme.
error-text-string: unsupported scheme - SIP desired
An example usage in a SIP 424 response:
Geolocation-Error: 120; "node=bob.example.com";
"inserter=alice.example.com";
code="unsupported scheme - SIP desired"
3.4.13 Geolocation-Error Code 121 Unsupported Scheme - SIPS desired
Geolocation-Error code 121 "Unsupported Scheme - SIPS desired" means
the location dereferencer cannot dereference using the
location-by-reference URI scheme supplied because it does not
support the necessary protocol to do this.
This code means the Location Recipient can dereference the Target's
location using a SIPS-URI scheme. There can be more than one
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locationErrorValue in a Geolocation-Error header, indicating in this
context the recipient can dereference using each scheme protocol
included in the Geolocation-Error header.
error-text-string: unsupported scheme - SIPS desired
An example usage in a SIP 424 response:
Geolocation-Error: 121; "node=bob.example.com";
"inserter=alice.example.com";
code="unsupported scheme - SIPS desired"
3.4.14 Geolocation-Error Code 122 Unsupported Scheme - pres desired
Geolocation-Error code 122 "Unsupported Scheme - pres desired" means
the location dereferencer cannot dereference using the
location-by-reference URI scheme supplied because it does not
support the necessary protocol to do this.
This code means the Location Recipient can dereference the Target's
location using a PRES-URI scheme. There can be more than one
locationErrorValue in a Geolocation-Error header, indicating in this
context the recipient can dereference using each scheme protocol
included in the Geolocation-Error header.
error-text-string: unsupported scheme - pres desired
An example usage in a SIP 424 response:
Geolocation-Error: 122; "node=bob.example.com";
"inserter=alice.example.com";
code="unsupported scheme - pres desired"
3.5 The Geolocation Option Tag
This document creates and IANA registers one new option tag:
"geolocation". This option tag is to be used, per RFC 3261, in the
Require, Supported and Unsupported headers. Whenever a UA wants to
indicate support for this SIP extension, the geolocation option tag
is included in a Supported header of the SIP message.
Including the geolocation option-tag within an Unsupported header of
a 420 (Bad Extension) response is appropriate when a UAS
does not support this Geolocation extension.
A UAC adding this option-tag to a Require header field indicates to
a UAS the UAS MUST support this extension in order to continue
processing the message, or send a 420 response back to the UAC.
Some environments might use a Require header in this way, but it
should be used with caution to prevent unnecessary communications
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problems.
A UAC SHOULD NOT include this option tag in a Proxy-Require header,
since a UAC is not likely to understand the topology of the
infrastructure, and therefore would not understand which proxy will
do the location-based routing function, if any. A potentially bad
scenario would have the first proxy not support this extension, but
a subsequent proxy does. This would result in no communications
past the first proxy, which MUST send the 420 back under these
circumstances.
3.6 Using sip/sips/pres as a Dereference Scheme
If a location-by-reference (LbyR) URI is included in a SIP request,
it MUST be in a locationValue in the Geolocation header and it MUST
be a SIP, SIPS or PRES-URI . When PRES: is used, if the resulting
resolution, per [RFC3856], resolves to a SIP: or SIPS: URI, this
section applies. Use of other protocols for dereferencing of a
PRES: URI is not defined, and such use is subject to review against
RFC 3693 Using Protocol criteria.
Dereferencing a Target's location using SIP or SIPS MUST be
accomplished by treating the URI as a presence URI and generating a
SUBSCRIBE request to a presence server as per [RFC3856] using the
'presence' event package. The resulting NOTIFY will contain a PIDF,
which MUST contain a PIDF-LO. See Figure 2. for a basic message flow
for a dereference.
When used in this manner, SIP is a Using Protocol per [RFC3693] and
elements receiving location MUST honor the 'usage-element' rules as
defined in this extension.
Alice Location Server Bob
| |
| INVITE w/ Location-by-Reference URI |
|-------------------------------------------------------->|
| | |
| 200 (OK) |
|<--------------------------------------------------------|
| | |
| | SUBSCRIBE to LbyR URI |
| |<-----------------------------|
| | 200 (OK) |
| |----------------------------->|
| | |
| | NOTIFY w/ PIDF-LO |
| |----------------------------->|
| | 200 (OK) |
| |<-----------------------------|
| | |
Figure 2. Location-by-Reference and Dereferencing
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In Figure 2., Alice sends Bob her location in a LbyR URI. Bob
receives this LbyR URI in the INVITE and generates a new transaction
(SUBSCRIBE) to retrieve the PIDF-LO of Alice. If accepted, the
PIDF-LO will be in the NOTIFY request from the Location Server.
This is the first instance between Alice and Bob that Alice's
location is in any message, therefore it is sent only once, from the
Location Server to Bob.
A dereference of a location-by-reference URI using SUBSCRIBE is not
violating a PIDF-LO 'retransmission-allowed' element value set to
'no', as the NOTIFY is the only message in this multi-message set
of transactions that contains the Target's location, with the
location recipient being the only SIP element to receive location -
which is the purpose of this extension: to convey location to a
specific destination.
4. Geolocation Examples
This section contains are two examples of messages providing
location. One shows location-by-value with coordinates, the other
shows location-by-reference. The example for (Coordinate format)
is taken from [RFC3825]. A civic format example of the same position
on the earth as is in the coordinate format example is in appendix
B, which is taken from [RFC4776]. The differences between the two
formats are within the <gp:location-info> of the examples. Other
than this portion of each PIDF-LO, the rest is the same for both
location formats.
The key to the provided samples is in the Geolocation header, which
has a different type of URI, based on the different means of
location conveyance. Section 4.1 shows a "cid:" URI, indicating
this SIP request contains a location-by-value message body - which
is in the form of a PIDF-LO. Section 4.2 shows a
location-by-reference URI indicating location is to be acquired via
an indirection dereference mechanism, which is determined by the
scheme of URI supplied.
4.1 Location-by-value (Coordinate Format)
This example shows an INVITE message with a coordinate, or
coordinate location. In this example, the SIP request uses a
sips-URI [RFC3261], meaning this message is TLS protected on a
hop-by-hop basis all the way to Bob's domain.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
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Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
;inserted-by=alice@atlanta.example.com ;recipient=endpoint
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...SDP goes here
--boundary1
Content-Type: application/pidf+xml
Content-ID: alice123@atlanta.example.com
<?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:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
entity="pres:alice@atlanta.example.com">
<tuple id="sg89ae">
<timestamp>2007-12-02T14:00:00Z</timestamp>
<status>
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>33.001111 -96.68142</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gp:retransmission-allowed>no</gp:retransmission-allowed>
<gp:retention-expiry>2007-12-07T18:00:00Z</gp:retention-
expiry>
</gp:usage-rules>
<gp:method>DHCP</gp:method>
<gp:provided-by>www.example.com</gp:provided-by>
</gp:geopriv>
</status>
</tuple>
</presence>
--boundary1--
The Geolocation header field from the above INVITE...
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Geolocation: <cid:target123@atlanta.example.com>
...indicates the content-ID location [RFC2392] within the multipart
message body of where location information is, with SDP being the
other message body part.
If the Geolocation header field were this instead:
Geolocation: <sips:server5.atlanta.example.com/target123>
...this would indicate location by-reference was included in this
message. It is expected that any node wanting to know where user
target123 is would subscribe to server5 to dereference the sips-URI.
The returning NOTIFY would contain Alice's location in a PIDF-LO, as
if it were included in a message body (part) of the original INVITE
here.
4.2 Location-by-reference
Below is an INVITE request with a location-by-reference URI instead
of a location-by-value PIDF-LO message body part shown in Sections
4.1. It is up to the location recipient to dereference Alice's
location at the Atlanta server containing the location record.
Dereferencing, if done with SIP, is accomplished by the Location
Recipient sending a SUBSCRIBE request to the URI reference for
Alice's location. The received NOTIFY is the first SIP message
containing Alice's UA location, as a PIDF-LO message body. The
NOTIFY, in this case, is the SIP request that is conveying location,
and not the INVITE. There is no retransmission of location in this
usage.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com
;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <sips:3sdefrhy2jj7@lis.atlanta.example.com>
;inserted-by=bigbox3.atlanta.example.com ;recipient=both
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@pc33.atlanta.example.com>
...SDP goes here as the only message body
A Location Recipient would need to dereference the sips-URI in the
Geolocation header field to retrieve Alice's location. If the
atlanta.example.com domain chooses to implement location conveyance
and delivery in this fashion (i.e., location-by-reference), it is
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RECOMMENDED that entities outside this domain be able to reach the
dereference server, otherwise this model of implementation is
only viable within the atlanta.example.com domain.
5. SIP Element Behavior
Because a device's location is generally considered to be sensitive
in nature, privacy of the location information needs to be protected
when transmitting such information. 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 SHOULD implement S/MIME to encrypt
the PIDF-LO message body (part) end-to-end when the Location
Recipient is intended to be another UA. The SIPS-URI from [RFC3261]
MUST be implemented for message protection (message integrity and
confidentiality) and SHOULD be used when S/MIME is not used.
Possession of a dereferenceable location URI can be equivalent to
possession of the location information itself and thus TLS SHOULD be
used when transmitting location-by-reference hop-by-hop along the
path to the Location Recipient.
A PIDF includes identity information. It is possible for the
identity in the PIDF to be anonymous. Implementations of this
extension should consider the appropriateness of including an
anonymous identity in the location information where a real identity
is not required. When using location-by-reference, it is
RECOMMENDED that the URI does not contain any user identifying
information (for example use 3fg5t5yqw@example.com rather than
alice@example.com).
Location Recipients MUST obey the privacy and security rules in the
PIDF-LO as described in RFC 4119 regarding retransmission and
retention.
Self-signed certificates SHOULD NOT be used for protecting a PIDF,
as the sender does not have a secure identity of the recipient.
More than one location format (civic and coordinate) MAY be included
in the same message body part, but all location parts of the same
PIDF-LO MUST point at the same position on the earth. The same
location in multiple formats can allow the recipient to use the most
convenient or preferable format for its use. Multiple PIDF-LOs are
allowed in the same request, with each allowed to point at separate
positions - because each PIDF-LO has a Target identifier in it.
Therefore, there will be no confusion by a Location Recipient
receiving more than one PIDF-LO (in a message body or when
dereferenced, or a combination).
It is RECOMMENDED there is only one "location" in a single SIP
Request for a given Target. This means SIP servers SHOULD NOT add
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another locationValue to a SIP request that already contains
location. This will likely lead to confusion at the ultimate
location recipient because this extension does not provide guidance
on what a recipient is to do with more than one location, nor does
it give any preference regarding which location is better or worse
than another location in the same request.
It is allowed, but NOT RECOMMENDED, for more than one SIP element to
insert location into a request along its path. As described earlier
in this document, each insertion of location into a SIP request is
accompanied by a locationValue in a Geolocation header. Also
described earlier, each locationValue MUST contain an "inserted-by="
value indicated to a Location Recipient which host inserted location
into a particular request.
5.1 UAC Behavior
A UAC can send location in a SIP request, because it is expected
to facilitate location-based routing of the request, or
spontaneously (i.e., a purpose not defined in this document but
known to the UAC).
A UAC conveying location MUST include a locationValue in a
Geolocation header (see section 3.2) with either a location-by-value
indication (a cid-URL), or a location-by-reference indication (a
dereferenceable URI). A location-by-value message body sent without
a Geolocation header field MUST NOT occur. The UAC supporting this
extension MUST include a Supported header with the geolocation
option tag.
The geolocation option-tag is inserted in a Supported header by a
UAC to provide an indication of support for this extension. The
presence of the geolocation option tag in a Supported header without
a Geolocation header field in the same message informs a receiving
SIP element the UAC understands this extension, but it does not know
or wish to convey its location at this time. Certain scenarios
exist (location-based retargeting) in which location is required in
a SIP request in order to retarget the message properly. This
affects how a UAS or SIP server processes to such a request.
The geolocation option tag SHOULD NOT be used in the Proxy-Require
Header, because the UAC often will not know the underlying topology
to know which proxy will do the retargeting, thus increasing the
likelihood of a request failure by the first hop proxy that does not
understand this extension, but is required to by inclusion of the
option-tag in this header.
A UAC inserting a locationValue MUST include an "inserted-by="
parameter to indicate its host-id. This is copied to the
"inserter=" parameter of the Geolocation-Error header in a response
if there is something wrong with the location in the original
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request. Because more than one locationValue can be inserted along
the path of the request, this indication is necessary to show which
locationValue had the problem in the response. For example:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice@atlanta.example.com
The UAC MAY include an intended target of this location parameter by
adding the "recipient=" parameter to the locationValue like this:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice@atlanta.example.com;
recipient=endpoint
See section 3.2 for further details about all the header parameters
of a locationValue.
A UAC MAY SUBSCRIBE to a LbyR URI, using the 'presence' event
package, for its own location. The obvious reason for this is for
the UAC to have its LbyV local to it. This document does not give a
reason why a UAC would want to do this.
5.1.1 UAC Receiving a Location Failure Indication
If a sent request failed based on the location in the original
request, a 424 (Bad Location Information) response is sent back to
the UAC. The 424 MUST have a Geolocation-Error header containing
one or more locationErrorValues in the response message. A
locationErrorValue has a header parameter indicating which entity
inserted the location pertaining to this error, called the
"inserter=" parameter. This "inserter=" parameter is copied from
the "inserted-by=" parameter of the locationValue by the UAS or
proxy sending the error response. A UAC receiving this 424 should
review this "inserter=" parameter in the locationErrorValue to see
if it indicates this UAC. If locationErrorValue does not, the
locationErrorValue should be ignored, and the response SHOULD be
treated as a 4XX response. If locationErrorValue does indicate this
UAC, this UAC MUST process the response, including the
Geolocation-Error code (defined in section 3.4).
In addition to the error code, there MAY be a list of CAtypes in the
locationErrorValue. If there are any, these are what the UAS or
proxy determined was wrong with the location contained in the
original response. The listed CAtypes will not contain the values
sent by the UAC in the request. This is for security/privacy
reasons.
The UAC SHOULD take correct steps to rectify future errors, based on
the received error code and any CAtypes listed, to increase the
probability of successful requests in the future. A UAC MAY
reattempt a new request if it believes it can correct the stated
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failure in the Geolocation-Error header.
Any UAC that inserted location into a request should be prepared to
receive the Geolocation-Error header in any response, looking to
determine if the header is meant for the UAC, and to react
accordingly.
If a UAC includes location in a request, and either the UAS does not
determine errored location was critical to the transaction and
accept the request, or the request failed for another reason than
location, any response MAY contain a Geolocation-Error header
containing a locationErrorValue with the details of the location
error.
5.2 UAS Behavior
If the Geolocation header field is present in a received SIP
request, the type of URI contained in the locationValue will
indicate if location has been conveyed by-value in a message body
(part) or by-reference, requiring an additional dereference
transaction. If the by-reference URI is sip:, sips: or pres:, the
UAS MUST initiate a SUBSCRIBE to the URI provided to retrieve the
PIDF-LO being conveyed by the UAC per [RFC3856]. If successful, the
PIDF-LO will be returned in the NOTIFY request from the remote host.
A Require header with the geolocation option tag indicates the
UAC is requiring the UAS understand this extension or else send
an error response. A 420 (Bad Extension) with a geolocation option
tag in an Unsupported header would be the appropriate response in
this case.
It is possible, but undesirable, for a message to arrive with a body
containing a location-by-value, but with no Geolocation header field
value pointing to it (potentially no Geolocation header field at
all). In this case, the recipient MAY still read and use the message
body. Unless stated otherwise by future standards-track
publications, a Location-by-reference URI only has meaning within
the Geolocation header field and MUST NOT appear in any other SIP
header field.
There are 3 Geolocation header parameters,
o "inserted-by="
o "used-for-routing"
o "recipient="
The "inserted-by=" parameter informs a Location Recipient which SIP
element added this locationValue to the SIP request. This parameter
is mandatory for each locationValue in the request. The value in
the "inserted-by=" parameter is copied into the "inserter="
parameter in each locationErrorValue if there is an error in the
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location to be reported back to the location sender. See section
5.2.1.
The "used-for-routing" parameter is included in the locationValue if
a SIP server used the location in the request to determine how to
route or forward the message towards the ultimate destination. If
there are more than one locationValue in the Geolocation header, and
it is possible that different locationValues were used to route the
message at different times of this request's journey. This is
allowed, as it is consistent with the rule that anytime a message is
routed based upon a locationValue, a "used-for-routing" parameter is
added to the applicable locationValue. This parameter should be
present in each locationValue used along the path.
More than one locationValue inserted in a request should be placed
the order it was placed, and not rearranged. This informs a
Location Recipient which was the last locationValue in the message
that was used to route the message. This is for troubleshooting and
management reasons.
The "recipient=" header parameter allow recipients to infer the SIP
entity type this locationValue is intended to be for. The types are
"endpoint", meaning the ultimate destination UAS; "routing-entity",
meaning SIP servers; and "both" meaning this locationValue is to be
viewed by both types of SIP entities.
Individual header parameters in any received locationValue MUST NOT
be modified or deleted in transit to the ultimate destination.
A UAS MUST NOT send location in a response message, as there can be
any number of issues/problems with receiving location, and the UAC
or proxy servers cannot error a response. Therefore, the UAS, if it
wants to send a UAC its location, SHOULD do so in a new request in a
separate transaction. This document gives no guidance which SIP
request to use.
A UAS MAY include a geolocation option-tag in the Supported header
of a response, indicating it does understand this extension, even if
location was not in a request to the UAS.
A UAS wishing to dereference a location-by-reference URI contained
in a received request will use the 'presence' event package in a
SUBSCRIBE request to the URI. If accepted, the PIDF-LO will return
to the UAS in a NOTIFY request. If there are any errors during
dereferencing, or in the PIDF-LO itself, the UAS will error the
original request to the UAC with a locationErrorValue indicating
what the UAS concluded was wrong with the location. This is to
include any dereferencing problems encountered.
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5.2.1 UAS Generating a Location Failure Indication
If a received request conveys location, but the UAS has one or
more problems with a locationValue in the request (to include while
attempting to dereference the UAC's location), the UAS MUST indicate
each problem experienced with the location in the request in a
424 (Bad Location Information) response back to the inserting
entity if the UAS wants to reject the request because of the
location. A Geolocation-Error header is how the UAS informs the UAC
of a location-based error within the request. Section 3.4 lists
these errors, which are all IANA registered.
Because this extension to SIP allows more than one locationValue in
a Geolocation header, each from separate SIP entities, there
needs to be a means of identifying which entity inserted a
particular locationValue for single error response purposes. This
is further complicated because SIP sends a single rejection
response, that in this case, needs to go to more than one entity,
and be ignored by all other entities not identified in such a way as
to not confuse other SIP entities.
Each locationValue has an "inserted-by=" parameter identifying which
SIP entity added this locationValue to the request. This value is
copied to the locationErrorValue "inserter=" parameter if one needs
to be sent, thus identifying the intended target of this
locationErrorValue. This locationErrorValue is ignored by all other
receivers of this SIP response.
Each locationErrorValue can have more than one error code within it.
Each locationErrorValue is destined for one "inserter=" entity.
This gives a UAS one mechanism to tell each inserter what the
Location Recipient concluded was wrong with what the inserter
included (as far as location is concerned). Therefore,
o there MUST be a locationErrorValue for each locationValue that
was considered bad by the UAS to ensure each upstream location
inserter understands which error code(s)is intended for them (and
which to ignore).
o if the PIDF-LO (received by-value or after dereference) contains
civic CAtypes that the Location Recipient considers malformed or
bad, each CAtype SHOULD be listed in the locationErrorValue to
inform the "inserter=" entity what specifically was wrong with
the locationValue, in addition to the error code. Without these
details, the location inserter might not know what part was
malformed or incomplete about the information supplied in the
request.
o the CAtype values MUST NOT be sent along with the CAtype names
listed in the locationErrorValue. This is for privacy/security
reasons.
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o there MUST NOT be more than one locationErrorValue in the
response per locationValue in the request.
o there MUST NOT be more than one locationErrorValue in the
response for the same locationValue in the request.
o there MUST NOT be a locationErrorValue in the response for a
locationValue in the request that was not in error, according to
the Location Recipient.
Here is an example of a Geolocation-Error header
Geolocation-Error: 106; "node=bob.example.com";
"inserter=alice.example.com";
CAtype=A3; CAtype=STS;
code="incomplete location supplied"
See Section 3.4 for further rules about the Geolocation-Error header
and the locationErrorValue.
The Geolocation-Error header is permitted in any response. For
example, Bob can reply to Alice with a 486 because he's not willing
to accept the call at this time, and inform Alice that the location
contained in the request was bad in some way. In this case, the 486
would contain a Geolocation-Error header indicating the specific
location error experienced
If there is more than one locationValue in a request, and any one of
them is valid (i.e., one contains enough information to not generate
a 424 if that was the only location present in the request), all
other locations MAY be ignored, and a 424 MUST NOT be sent because
of these other locations in the request. Another response MAY be
sent, which includes a locationErrorValue. This document says
nothing about what a Location Recipient does with more than one
'good' location in a request (i.e., which to choose to use).
Further, more than one error code is allowed in the
locationErrorValue - each having an "inserter=" parameter. The
error codes destined for the same inserter MUST NOT contradict the
meaning of the problem the UAS had with a particular locationValue.
A Geolocation-Error is permissible in a 200 OK response. This means
everything else in the request was acceptable, but the location was
not for a given error code(s). One exception to this set of rules
is if a geolocation option-tag was in the Require header in the
request. This would necessitate a 424 response.
5.3 Proxy Behavior
[RFC3261] states message bodies cannot be added by proxies.
However, proxies are permitted to add a header to a request. This
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implies that a proxy can add a Geolocation locationValue with
location-by-reference URI, but not location-by-value message body.
However, if location is already in a SIP request, a SIP server
SHOULD NOT add another instance of the UAC's location to the same
request. This will likely cause confusion at the Location Recipient
as to which to use. This document gives no guidance how a UAS is to
deal with more than one location in a SIP request, other than the
intended "recipient=" parameter, which has no integrity protection
in transit. If more than one locationValue states
"recipient=endpoint", this document gives no guidance what the UAS
is to do.
A proxy is permitted to read any locationValue, and the associated
body, if not S/MIME protected, in transit if present, and MUST use
the contents of the header field to make location-based retargeting
decisions, if retargeting requests based on location is a function
of that proxy.
More than one Geolocation locationValue in a message is permitted,
but can cause confusion at the recipient. If a proxy chooses to add
a locationValue to a Geolocation header, which would be a local
policy decision, the new locationValue MUST be added to the end of
the header (after previous locationValue(s)). This is done to
create an order of insertion of locationValues along the path.
Proxies MUST NOT modify the order of locationValues in a geolocation
header.
A proxy wishing to dereference a location-by-reference URI contained
in a received request will use the 'presence' event package in a
SUBSCRIBE request to the URI. If accepted, the PIDF-LO will return
to the proxy in a NOTIFY request. If there are any errors during
dereferencing, or in the PIDF-LO itself, the proxy will error the
original request to the UAC with a locationErrorValue indicating
what the proxy concluded was wrong with the location. This is to
include any dereferencing problems encountered.
5.3.1 Proxy Behavior with Geolocation Header Parameters
SIP servers MUST NOT delete any existing Geolocation locationValue
(URI or header parameter) from a request. A Geolocation
locationValue (URI or header parameter) MAY only be modified to by
adding a "used-for-routing" parameter to an existing locationValue,
if the request was retargeted based on the location within that
locationValue. Further modification of this Geolocation header
field MUST NOT occur. For example, an existing Geolocation
locationValue in a request of:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice123@atlanta.example.com;
can be modified by a proxy to add the "used-for-routing" parameter,
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like this:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice123@atlanta.example.com;
used-for-routing
if this is the locationValue the proxy used to make a retargeting
decision based upon, but make no other modification.
A SIP server MAY add a new Geolocation locationValue to a SIP
request. The proxy SHOULD NOT insert a locationValue of the UAC
unless it is reasonably certain it knows the actual location of the
endpoint, for example, if it thoroughly understands the topology of
the underlying access network and it can identify the device
reliably (in the presence of, for example, NAT).
A server adding a locationValue to an existing Geolocation header
would look like:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice123@atlanta.example.com,
<sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
inserted-by=lis1.atlanta.example.com;
Notice the locationValue added by the proxy is last among
locationValues. This practice MUST be done for all added
locationValues.
If this request was then retargeted by an intermediary using the
locationValue inserted by the server, the intermediary would add a
"used-for-routing" parameter like this:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by=alice123@atlanta.example.com,
<sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
inserted-by=lis1.atlanta.example.com; used-for-routing
It is conceivable that an initial routing decision is made on an
one locationValue, and subsequently another routing decision is
made on a different locationValue. This retargeting decision can be
made on a newly inserted locationValue. While unusual, it can
occur. In such a case, proxies MUST NOT remove any existing
"used-for-routing" header parameter. In this instance, the SIP
server retargeting based on another locationValue MUST add the
"used-for-routing" header parameter to the locationValue used for
retargeting by this server. This will result in a Geolocation
header looking as if it were retargeting more than once, which would
be true - and is the desired outcome.
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5.3.2 Proxy Error Behavior for Sending or Receiving locationErrorValues
For proxies that receive a SIP request that contains a location
error, either in a contained message body or after the proxy does a
dereference of the LbyR URI, all the rules applicable to a UAS apply
here (see Section 5.2.1.), since in this case, the proxy is
considered a Location Recipient. Therefore, there is no reason to
restate them here, and potentially have the two section be
inconsistent. The one thing to add is that a proxy does not need to
examine location contained in a request. Section 5.2.1. only applies
to proxies that are monitoring or policing location within requests
(for whatever reason).
If a proxy inserted a locationValue into a request, it SHOULD be
ready to examine the response to that request, in case there is one
or more location errors in the response. To a great degree, this
scenario has the proxy behaving as a UAC (see section 5.1.1.) that
included a locationValue a request, which then receives an error to
that locationValue.
If there is one or more locationErrorValues in the response, the
proxy SHOULD examine each "inserter=" parameter in each
locationErrorValue - looking for one that identifies the proxy. If
one matches the proxy's "inserted-by" value, that locationErrorValue
is for only that proxy. This locationErrorValue needs to be reviewed
for each error code and CAtype contained in the value. The proxy
SHOULD attempt to correct for the error reported to it for future
insertion of location into requests. This document gives no
guidance what the proxy should do to rectify the bad location
information, but a future document MAY address this.
6. Geopriv Privacy Considerations
Transmitting location information is considered by most to be highly
sensitive information, requiring protection from eavesdropping,
tracking, and altering in transit. [RFC3693] articulates rules to
be followed by any protocol wishing to be considered a Geopriv
"Using Protocol", specifying how a transport protocol meetings
those rules. This section describes how SIP as a Using Protocol
meets those requirements.
Quoting requirement #4 of [RFC3693]:
"The Using Protocol has to obey the privacy and security
instructions coded in the Location Object and in the
corresponding Rules regarding the transmission and storage
of the LO."
This document requires that SIP entities sending or receiving
location MUST obey such instructions.
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Quoting requirement #5 of [RFC3693]:
"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
establishment mechanisms.
Quoting requirement #6 of [RFC3693]:
"(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."
When used for tracking, a simple NOTIFY or UPDATE normally is
relatively small, although the PIDF itself can get large. Normal
RFC 3261 procedures of reverting to TCP when the MTU size is
exceeded would be invoked.
7. Security Considerations
Conveyance of physical location of a UAC raises privacy concerns,
and depending on use, there probably will be authentication and
integrity concerns. This document calls for conveyance to normally
be accomplished through secure mechanisms, like S/MIME protecting
message bodies (but this is not widely deployed) or TLS protecting
the overall signaling. In cases where a session set-up is
retargeted based on the location of the UAC initiating the call or
SIP MESSAGE, securing the by-value location with an end-to-end
mechanism such as S/MIME is problematic, because one or more proxies
on the path need the ability to read the location information to
retarget the message to the appropriate new destination UAS.
Securing the location hop-by-hop, using TLS, protects the message
from eavesdropping and modification, but exposes the information to
all proxies on the path as well as the endpoint. In most cases, the
UAC does not know the identity of the proxy or proxies providing
location-based routing services, so that end-to-middle solutions
might not be appropriate either.
These same issues exist for basic SIP signaling, but SIP normally
does not carry information to physically track a user; making this
extension especially sensitive.
When location is inserted by a UAC, which is RECOMMENDED, it can
decide whether to reveal its location using hop-by-hop methods. UAC
implementations MUST make such capabilities conditional on explicit
user permission, and SHOULD alert a user that location is being
conveyed. Proxies inserting location for location-based routing are
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unable to meet this requirement, and such use is NOT RECOMMENDED.
Proxies conveying location using this extension MUST have the
permission of the Target to do so.
One facet within this extension is such that locations can be placed
on a remote server, accessible with the possession of a URI. The
concept of a location-by-reference URI has its own security
considerations. It is tempting to assume that the dereference would
have authentication, authorization and other security mechanisms
that limit the access to information. Unfortunately, this might not
be true. The access network the UAC is connected to can be the
source of location reference, and it might not have any
credentialing mechanism suitable for controlling access to location.
Consider, specifically, a nomadic user connected to an access
network in a hotel. The UAC has no way to provide a credential
acceptable to the hotel Location Server (LS) to any of its intended
Location Recipients. The recipient of a reference does not know if
a reference has appropriate authorization policies or not. The LS
should provide location to any requestor.
Accordingly, possession of the reference should be considered
equivalent to possession of the value, and the reference should be
treated with the same degree of care as the value. Specifically,
TLS MUST be used to protect the security of the reference. Notice
that this does not constrain the dereference protocol to use TLS.
That specification is left entirely to the dereferencing protocol
Because SIP servers can add location in transit, made more easy of
the server is a Session Border Controller or B2BUA, this might cause
there to be conflicting location information (error-code=6), which
could be purposeful to error the request or just cause operation
problems. This problem might be inadvertent, compounded by the fact
that there will likely be some SIP servers that add location on
every call set-up.
There is no integrity on any locationValue or locationErrorValue
header parameter, so recipients of either header need to implicitly
trust the header contents, and take whatever precautions each entity
deems appropriate give these facts.
8. IANA Considerations
The following are the IANA considerations made by this SIP
extension. Modifications and additions to these registrations
require a standards track RFC (Standards Action).
8.1 IANA Registration for the SIP Geolocation Header
The SIP Geolocation header is created by this document, with its
definition and rules in Section 3.2 of this document, to be added to
the sip-parameters.
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The Geolocation Header has the following header parameters to be
Registered in a new table:
Geolocation Header parameters
Header Parameters Parameter-values Reference
---------------- ---------------- --------------
recipient endpoint RFC XXXX (this document)
recipient routing-entity RFC XXXX (this document)
recipient both RFC XXXX (this document)
8.2 IANA Registration for New SIP Option Tag
The SIP option-tag "geolocation" is created by this document, with
the definition and rule in Section 3.5 of this document, to be added
to sip-parameters within IANA.
8.3 IANA Registration for Response Code 424
Reference: RFC-XXXX (i.e., this document)
Response code: 424 (recommended number to assign)
Default reason phrase: Bad Location Information
This SIP Response code is defined in section 3.3 of this document.
8.4 IANA Registration of New Geolocation-Error Header
The SIP Geolocation-error header is created by this document, with
its definition and rules in Section 3.4 of this document, to be
added to the sip-parameters.
8.5 IANA Registration for the SIP Geolocation-Error Codes
New location specific Geolocation-Error codes are created by this
document, and registered in a new table at sip-parameters within
IANA. Details of these error codes are in Section 3.4 of this
document.
Geolocation-Error codes
-----------------------
Geolocation-Error codes provide reason for the error discovered by
Location Recipients, to place into SIP response messages to inform
the location inserter of the error.
Code Description Reference
---- --------------------------------------------------- ---------
100 Location Format Not Supported: the location format [this doc]
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supplied in the request, by-value or by-reference,
was not supported.
101 Coordinate-location Format Desired: the location [this doc]
format supplied in the request was understood
and supported, but that the recipient, or an
application on the recipient, can or prefers to
only process location in the coordinate-location
format.
102 Civic-location Format Desired: the location [this doc]
format supplied in the request was understood
and supported, but that the recipient, or an
application on the recipient, can or prefers to
only process location in the civic-location
format.
103 Cannot Parse Location Supplied: the location [this doc]
provided, whether by-value or by-reference, in a
request is not well formed.
104 Cannot Find Location: the location was expected in [this doc]
the request, but the recipient cannot find it.
105 Conflicting Locations Supplied: a Location Recipient [this doc]
received more than one location describing where the
Target is, and is either unsure which whole location
is true or which parts of multiple locations make up
where the Target is.
106 Incomplete Location Supplied: there is not enough [this doc]
location information in the request to determine
where the location Target is.
107 Cannot Dereference: the act of dereferencing failed [this doc]
to return the Target's location. This generally
means the supplied URI is bad.
108 Dereference Denied: there was insufficient [this doc]
authorization to dereference the Target's location.
109 Dereference Timeout: the dereferencing node has not [this doc]
received the Target's location within a reasonable.
timeframe
110 Cannot Process Dereference: the dereference protocol [this doc]
has received an overload condition error, indicating
the location cannot be accessed at this time.
120 Unsupported Scheme - sip desired: the location [this doc]
dereferencer cannot dereference using the
location-by-reference URI scheme supplied, and
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prefers a sip-uri.
121 Unsupported Scheme - sips desired: the location [this doc]
dereferencer cannot dereference using the
location-by-reference URI scheme supplied, and
prefers a sips-uri.
122 Unsupported Scheme - pres desired: the location [this doc]
dereferencer cannot dereference using the
location-by-reference URI scheme supplied, and
prefers a pres-uri.
9. Acknowledgements
To Dave Oran for helping to shape this idea. To Jon Peterson and
Dean Willis on guidance of the effort. To Allison Mankin, Dick
Knight, Hannes Tschofenig, Henning Schulzrinne, James Winterbottom,
Jeroen van Bemmel, Jean-Francois Mule, Jonathan Rosenberg, Keith
Drage, Marc Linsner, Martin Thomson, Mike Hammer, Paul Kyzivat,
Shida Shubert, Umesh Sharma, Richard Barnes, Ted Hardie and Matt
Lepinski for constructive feedback. A special thanks to Dan Wing
for help with the S/MIME example, and to Robert Sparks for many
helpful comments and the proper building of the Geolocation-Error
header.
10. References
10.1 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.
[RFC4119] J. Peterson, "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
[RFC2392] E. Levinson, " Content-ID and Message-ID Uniform Resource
Locators", RFC 2393, August 1998
[RFC3863] H. Sugano, S. Fujimoto, G. Klyne, A. Bateman, W. Carr, J.
Peterson, "Presence Information Data Format (PIDF)", RFC
3863, August 2004
[RFC3856] J. Rosenberg, " A Presence Event Package for the Session
Initiation Protocol (SIP)", RFC 3856, August 2004
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[RFC3859] J. Peterson, "Common Profile for Presence (CPP)", RFC 3859,
August 2004
[RFC3428] B. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema,
D. Gurle, "Session Initiation Protocol (SIP) Extension for
Instant Messaging" , RFC 3428, December 2002
[RFC3311] J. Rosenberg, "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002
[RFC3265] Roach, A., "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC3262] Rosenberg, J. and H. Schulzrinne, "Reliability of
Provisional Responses in Session Initiation Protocol (SIP)",
RFC 3262, June 2002.
[IANA-civic] http://www.iana.org/assignments/civic-address-types-
registry
10.2 References - Informative
[RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
"Geopriv Requirements", RFC 3693, February 2004
[RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004
[RFC4776] 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 Polk
Cisco Systems
3913 Treemont Circle 33.00111N
Colleyville, Texas 76034 96.68142W
Phone: +1-817-271-3552
Email: jmpolk@cisco.com
Brian Rosen
NeuStar, Inc.
470 Conrad Dr. 40.70497N
Mars, PA 16046 80.01252W
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US
Phone: +1 724 382 1051
Email: br@brianrosen.net
Appendix A. Requirements for SIP Location Conveyance
The following subsections address the requirements placed on the
UAC, the UAS, as well as SIP proxies when conveying location. There
is a motivational statement below each requirements that is not
obvious in intent
A.1 Requirements for a UAC Conveying Location
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
transmitting location confidentially.
Motivation: interoperability
UAC-6 It must be possible for a UAC to update location conveyed
at any time in a dialog, including during 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. In the case of location having been conveyed,
and the UA moves, it needs a means to update the conveyed to
party of this location change.
UAC-7 The privacy and security rules established within [RFC3693]
that would categorize SIP as a 'Using Protocol' must be met.
UAC-8 The PIDF-LO [RFC 4119] is a mandatory to implement format for
location conveyance within SIP, whether included by-value or
by-reference.
Motivation: interoperability with other IETF location protocols and
mechanisms
UAC-9 There must be a mechanism for the UAC to request the UAS send
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its location
UAC-9 has been DEPRECATED by the SIP WG, due to the many
problems this requirement would have caused if implemented.
The solution is for the above UAS to send a new request to
the original UAC with the UAS's location.
UAC-10 There must be a mechanism to differentiate the ability of the
UAC to convey location from the UACs lack of knowledge of its
location
Motivation: Failure to receive location when it is expected can be
because the UAC does not implement this extension, or it can
be that the UAC implements the extension, but does not know
where it is. This may be, for example, due to the failure of
the access network to provide a location acquisition
mechanisms the UAC understands. These cases must be
differentiated.
UAC-11 It must be possible to convey location to proxy servers
along the path.
Motivation: Location-based routing.
A.2 Requirements for a UAS Receiving Location
The following are the requirements for location conveyance by a UAS:
UAS-1 SIP Responses must support location conveyance.
Just as with UAC-9, UAS-1 has been DEPRECATED by the SIP WG,
due to the many problems this requirement would have caused
if implemented. The solution is for the above UAS to send a
new request to the original UAC with the UAS's location.
UAS-2 There must be a unique 4XX response informing the UAC it did
not provide applicable location information.
In addition, requirements UAC-5, 6, 7 and 8 apply to the UAS
A.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 be capable of adding a Location header
field during processing of SIP requests.
Motivation: Provide the capability of network assertion of location
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when UACs are unable to do so, or when network assertion is
more reliable than UAC assertion of location
Note: Because UACs connected to sip signaling networks may have
widely varying access network arrangements, including VPN
tunnels and roaming mechanisms, it may be difficult for a
network to reliably know the location of the endpoint. Proxy
assertion of location is NOT RECOMMENDED unless the sip
signaling network has reliable knowledge of the actual
location of the Targets.
Proxy-2 There must be a unique 4XX response informing the UAC it
did not provide applicable location information.
Appendix B. Example of INVITE with S/MIME encrypted Civic PIDF-LO
This appendix gives an *EXAMPLE* (meaning this might contain errors
based on future review) of a SIP INVITE request that points to the
same position on the earth as the coordinate based example that's in
section 4.1 in the body of this document:
The INVITE request is TLS hop-by-hop encrypted, and the
location-by-value message body is S/MIME encrypted. This example
shows the location message body in its unencrypted form for clarity.
The message body lines below that have the '$' signs are S/MIME
encrypted. In this example, the SDP is not S/MIME encrypted.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com
;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <cid:alice123@atlanta.example.com>
;inserted-by=alice@atlanta.example.com ;recipient=endpoint
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@pc33.atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...SDP goes here
--boundary1
Content-Type: application/pkcs7-mime;
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smime-type=enveloped-data; name=smime.p7m
Content-ID: alice123@atlanta.example.com
$ Content-Type: application/pidf+xml
$
$ <?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:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
$ entity="pres:alice@atlanta.example.com">
$ <tuple id="sg89ae">
$ <timestamp>2007-07-09T14:00:00Z</timestamp>
$ <status>
$ <gp:geopriv>
$ <gp:location-info>
$ <cl:civicAddress>
$ <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:NAM>Haley's Place</cl:NAM>
$ <cl:FLR>1</cl:FLR>
$ <cl:civicAddress>
$ </gp:location-info>
$ <gp:usage-rules>
$ <gp:retransmission-allowed>no</gp:retransmission-allowed>
$ <gp:retention-expiry>2007-07-27T18:00:00Z</gp:retention-
$ expiry>
$ </gp:usage-rules>
$ <gp:method>DHCP</gp:method>
$ <gp:provided-by>www.example.com</gp:provided-by>
$ </gp:geopriv>
$ </status>
$ </tuple>
$ </presence>
--boundary1--
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Internet Draft Location Conveyance in SIP Nov, 2007
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