wdiff draft-ietf-sipcore-location-conveyance-00.txt draft-ietf-sipcore-location-conveyance-01.txt

SIP
SIPCORE Working Group James Polk
Internet Draft Cisco Systems
Expires: December 18, January 13, 2009 Brian Rosen
Intended Status: Standards Track (PS) NeuStar
June 18,
July 13, 2009

Location Conveyance for the Session Initiation Protocol
draft-ietf-sipcore-location-conveyance-00.txt
draft-ietf-sipcore-location-conveyance-01.txt

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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 end-to-end
conveyance as well as location-based routing, where SIP servers
make routing decisions based on the location of the user agent
clients.
client.

Table of Contents

1. Conventions and Terminology used in this document . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 4
3. Overview of SIP Location Conveyance . . . . . . . . . . . . . 4
4. SIP Modifications for Geolocation Conveyance . . . . . . . . 7
4.1 The Geolocation Header . . . . . . . . . . . . . . . . . 7
4.2 424 (Bad Location Information) Response Code . . . . . . 10
4.3 The Geolocation-Error Header . . . . . . . . . . . . . . 11
4.4 The 'geolocation' Option Tag . . . . . . . . . . . . . . 19 20
4.5 Using sip/sips/pres as a Dereference Scheme . . . . . . . 19 20
5. Geolocation Examples . . . . . . . . . . . . . . . . . . . . 21 22
5.1 Location-by-value (Coordinate Format) . . . . . . . . . . 21 22
5.2 Location-by-reference . . . . . . . . . . . . . . . . . . 23 24
6. SIP Element Behavior . . . . . . . . . . . . . . . . . . . . 23 24
6.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 24 25
6.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . 27 29
6.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 32 34
7. Geopriv Privacy Considerations . . . . . . . . . . . . . . . 36 38
8. Security Considerations . . . . . . . . . . . . . . . . . . . 37 39
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 38 40
9.1 IANA Registration for New SIP Geolocation Header . . . . 38 41
9.2 IANA Registration for New SIP 'geolocation' Option Tag . 39 41
9.3 IANA Registration for New 424 Response Code . . . . . . . 39 41
9.4 IANA Registration for New SIP Geolocation-Error Header . 39 41
9.5 IANA Registration for New SIP Geolocation-Error Codes . . 39 42
9.6 IANA Registration of LbyR Schemes . . . . . . . . . . . 40 43
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40 43
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 41 43
11.1 Normative References . . . . . . . . . . . . . . . . . 41 43
11.2 Informative References . . . . . . . . . . . . . . . . . 42 45
Author Information . . . . . . . . . . . . . . . . . . . . . 42 45
Appendix A. Requirements for SIP Location Conveyance . . . . 43 45

1. Conventions and Terminology 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].

The following terms and acronyms used throughout this document are
defined here:

LbyR = Location-by-Reference

LbyV = Location-by-Value

Location Generator (LG): The entity that initially determines or
gathers the location of the Target and creates Location
Objects describing the location of the Target [RFC3693].

Location Information Server (LIS) - Inserter: a logical server role created in this document describing the
entity that stores
geolocation records of Targets, which correspond to LbyR URIs. included location in a SIP request, either by-value
or by-reference (i.e., including a location URI).

Location Object (LO): An object conveying location information
(and possibly privacy rules) to which Geopriv security
mechanisms and privacy rules are to be applied [RFC3693].

Location Recipient (LR): The entity that receives location
information. It may have asked for this location explicitly
(by sending a query to a location server), or it may receive
this location asynchronously [RFC3693].

Location Server (LS): The entity to which a LG publishes location
objects, the recipient of queries from location receivers, and
the entity that applies rules designed by the rule maker
[RFC3693].

A Location Server is also an entity that retains Target Location
Objects that are dereferenced by Location Recipients via SIP
SUB/NOT transactions.

Target: A person or other entity whose location is communicated by
a Geopriv Location Object [RFC3693].

Using Protocol: A protocol that carries a Location Object [RFC3693].

2. Introduction

This document describes how Location geolocation can be "conveyed" in a SIP
request from one SIP entity unsolicited to another entity using SIP
[RFC3261]. Here, "Location" is a description of the physical
geographical area where something currently exists. Note that this
information is not solicited by the entity that receives it. The phrase "location conveyance"
describes scenarios
mechanism in which a this document does not allow one SIP user agent client (UAC) is
informing a user agent server (UAS) or intermediate SIP server
without being previously asked where the UAC is.

Location Conveyance is different from a UAC, Alice, seeking to request
the location the UAS, Bob. Location conveyance, using SIP, never asks
for of another entity's location SIP user to be returned in a response. Asking for someone
else's location is not discussed in this document.

Geographic location in the IETF is discussed in RFC 3693 (Geopriv
Requirements) [RFC3693]. It defines a "Target" as the entity whose
location is being transmitted over IP. A [RFC3693] defined [RFC3693]-defined "Using
Protocol" describes 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 a
SIP extension to SIP for carry a Location Object and 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. requirements in RFC 3693.

Common terms are in Section 1. Section 3 provides an overview of SIP
location conveyance. Section 4 details the modifications extensions to SIP
necessary to accomplish location conveyance. Section 5 gives decode
examples of geolocation within SIP requests, both LbyV and LbyR.
Section 6 articulates the SIP element type behaviors for location
conveyance. Section 7 discusses Geopriv privacy considerations.
Section 8 discusses security considerations. Section 9 IANA
registers the modifications made to SIP by this document from in section
4.

3. Overview of SIP Location Conveyance

The concept of conveying location in SIP is fairly straightforward.
Location is conveyed directly or indirectly from a transmitting SIP
entity to a receiving SIP entity. If When location is conveyed
directly, then it is conveyed as a value contained within the SIP
request, see as in Figure 1., 1.

Alice Bob LIS
| | |
| Request w/ Location | |
|------------------------>| |
| | |
| Response | |
|<------------------------| |
| | |

Figure 1. Location Conveyed by Value

When location is conveyed indirectly, analogous to Content
Indirection [RFC4483], this is a case where Bob receives (from Alice) an LbyR a location URI that requires and
must make an additional transaction request - here called a dereference - to
learn Alice's location by requesting that actual location from a LIS, see Location Server (LS)
identified in the location URI, as in Figure 2., 2.

Alice Bob LIS LS
| | |
| Request w/ Location URI | |
|------------------------>| |
| | Fetch Dereference Request |
| |---------------------->|
| | |
| | Fetch Dereference Response |
| |<----------------------|
| Response | (includes location) |
|<------------------------| |
| | |

Figure 2. Location Conveyed by Reference

Many protocols can be used for this fetch dereference transaction, but
this is usually bounded determined by the scheme of the location URI in the
SIP request. In other works, words, if the location URI is a SIPS: URI,
then SIPS would be used to contact the LIS LS to make the dereference.

The location "value" in this SIP extension is in the form of a
Presence
"Presence Information Data Format - Location Object, Object", or PIDF-LO, as
described in [RFC4119]. A PIDF-LO is an XML scheme specifically for
carrying the geographic location of a Target. LbyV refers to a UA
including a PIDF-LO as a message body part of a SIP request, sending
that Location Object to another SIP element. LbyR refers to a UA
including a location URI in a SIP request header field which can be
dereferenced by a Location Recipient to receive retrieve Alice's Location
Object, in the form of a PIDF-LO. Dereferencing is done by a
Location Recipient.

To accomplish location conveyance in SIP, a new SIP header, header field,
Geolocation, is created and described in this document. The
Geolocation header field contains a URI that points to the where the
location is for that the location target, either in the body of the SIP
request itself (LbyV), or on an external server a Location Server (LbyR). A location
URI that points to a message body is always a "cid:" URI (Content
Identification), as defined in [RFC2392].

If the URI in the Geolocation header field is a scheme other than
"cid:", a fetch dereference transaction (see Figure 2) is necessary. This
document describes how a SIP presence subscription [RFC3856] can be
used as a dereference protocol.

Including location

Location can be inserted in a SIP request is not limited to insertion by a
UA. There are times where a SIP server wants to insert location of a
location target into as well as
by a request from that target towards the
request's destination. UA. This document offers guidance on this practice. This
document also describes how a location recipient can determine which
entity included what a specific location, as it is allowed for more than one location to can
be conveyed in a given SIP request. Section 4 gets into guidance and
limitations of this behavior.

A new error response (424 Bad Location Information) is also defined
in this document. Within this response is a new header field
indicating location-based errors, call called the Geolocation-Error header.
header field. This header field has various codes that provide
additional information about the type of location error experienced
by a Location Recipient. Recipient, separated into actionable categories to be
taken by the UAC.

Because more than one SIP entity can insert location, when
considering SIP as an end-to-end protocol, there needs to be a means
of identifying which location within a message of multiple locations
was considered bad by a location recipient - if that were to occur.
The ability to tell by host-id which entity (identified by host-id) inserted which a
specific location is extremely important. Not only does this allow
each location error to be targeted at a particular inserter of particular location, a
specific location object, but it also allows error recipients to
understand when their inserted the location they inserted was not at fault, and when
that a received error is not meant for them. This optimization is
necessary, otherwise each location error would be a blanket error to
every entity upstream in this the signaling path.

Just as location can be conveyed by more than one entity about the
same target, there can be more than one location recipient along a
message's
request's path. It is possible, and it fact, planned in certain
circumstances possible to have route SIP requests routed based on the
location of the target. target (i.e., source based routing, instead of
normal destination based routing). This means SIP servers can be
location recipients. If this is not desired by a location inserter - the act of including
location into this request, Location Inserter,
then the Location Inserter can also include a separate indication is given in
the Geolocation header it field showing that this usage is allowed.

There is no mechanism by which not desired.

Location Inserters have the veracity of these ability to provide instructional
parameters can
be verified. They about location it has inserted. These are hints to
downstream entities on how the location information in the message
was originated, intended and is to be used.

Transport Layer Security is expected when a request contains a
target's location. Some implementations will choose to have S/MIME
for integrity protection, or to encrypt message bodies from source
to destination. destination(s).

This document creates a new option tag: geolocation, to indicate
support for this extension by UAs.

The new headers, header field, the header parameters, the new option tag, the
new error response, and Geolocation-Error codes, which codes are defined in
Section 4., 4, each of which are IANA registered by this document.

RFC 3693 demands that a transmitted location must be required to maintain
privacy considerations. This document maintains all of the privacy
considerations defined by RFC 3693, plus adds an intended usage
indication within the SIP Geolocation header. header field. This increases
the considerations for recipients not to inspect a target's location
when they are not the intended location recipient.

4. SIP Modifications for Geolocation Conveyance

The following are sections detail the standards track modifications
to SIP for Location Conveyance.

4.1 The Geolocation Header Field

This document defines and IANA registers Geolocation as a new SIP header:
Geolocation, header field
registered by IANA, with the following ABNF [RFC5234]:

Geolocation = "Geolocation" HCOLON (locationValue *(COMMA
locationValue)) (COMMA retrans-param)
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"
/ generic-param ; (from RFC 3261)
geoloc-inserter = DQUOTE hostport DQUOTE
/ gen-value ; (from RFC 3261)
retrans-param = "routing-allowed" EQUAL "yes" / "no"

sip-URI, sips-URI and absoluteURI are defined according to RFC 3261. [RFC3261].

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 is present in a SIP request if where location
is transmitted LbyV only. conveyed as a value.

Other protocols used in the Location location URI MUST be reviewed against
the RFC 3693 criteria for a Using Protocol.

The Geolocation header field MAY have one or more locationValues.
SIP servers inserting a locationValue MUST add the new value as the
last locationValue in the Geolocation header field (i.e., the last
locationValue in the header field is the most recent one added to
the message). Placement of the "routing-allowed" parameter, when
present, MUST be the last header field value in the Geolocation header.
header field.

A locationValue has the following independent header field
parameters,

o the "inserted-by=" parameter provides the hostport
(alice.example.com -- which is the same as the "sent-by"
parameter in a Via header, header field, with or without a port number)
of the SIP entity that inserted this locationValue into the
request. If a Location Recipient has determined a supplied
location is in error, as there can be more than one location in
any request, the "inserted-by=" parameter is copied into the
locationErrorValue in the response indicating the location error,
and to whom the error is for. Hence, this "inserted-by="
parameter MUST be present in each locationValue. If an entity
receives an Geolocation-Error with a hostport that does not identifying
identify this entity, the Geolocation-Error MUST 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. "used-for-routing" can
occur more than once along the request's path. Because
locationValues are inserted as last inserted is last in the
header,
header field, the last locationValue is the most recent one added
to the message. This also gives the "used-for-routing" header
field parameter added meaning - as the receiving SIP entity knows
which
locationURI location URI the message was routed upon.

Each locationValue MUST contain exactly one "inserted-by" parameter,
indicating which SIP entity added the locationValue to the SIP
request.

There MUST NOT be more than one "inserted-by=" parameter or one
"used-for-routing" parameter in the same locationValue. However,
there can be more than one locationValue in the same Geolocation
header.
header field.

The "routing-allowed" header field parameter is a global parameter
over any (and all/each) locationValues in the Geolocation header. header
field. This is the reason why the placement of the header field
parameter is outside any locationValue, and appears only once, and is
always last in the header field value.

This header field parameter only has the values "=yes" or "=no" only. "=no".
When this parameter is "=yes", any locationValue can be used for
routing decisions along the downstream signaling path by
intermediaries. When this parameter is "=no", this means no
locationValue (inserted by the originating UAC or any (or
subsequent) intermediary(ies) along the signaling path) can be used
by any SIP intermediary to make routing decisions. This behavior
MUST be adhered to. Section 4.3 describes the details on what a
routing intermediary does if it believes it needs to use the
location in the SIP request in order to process the message further.

The practical implication is that when the "routing-allowed"
parameter is set to "no", if an LbyV is present in the SIP request,
intermediaries SHOULD MUST NOT view the location (because it is not
for intermediaries to view), and if an LbyR is present, SHOULD MUST NOT
dereference it. UASs are allowed to view location in the SIP
request even when the "routing-allowed" header field parameter is
set to "no".

The default behavior when this header field parameter is not present
in a message is to treat the SIP request as if the parameter were
present and its value is set to "no".

This document defines the Geolocation header field 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 is out of scope
for this document since it is part of Presence, therefore, for
completeness, Table 1 shows PUBLISH is to support Location
Conveyance via this extension, but is not discussed further.

The following table extends the values in Table 2&3 Tables 2 and 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 Field

The Geolocation header field MAY be included in any one of the above
requests by a UAC. A proxy MAY add the Geolocation header, header field,
but MUST NOT modify any pre-existing locationValue, including any
associated header field parameters within an existing Geolocation
header field value, unless one of the existing locationValues is
used to retarget the request towards a new destination UAS. This is
discussed in section 6.3.

[RFC3261] states message bodies cannot be added by proxies.
Therefore, any Geolocation header field added by a proxy MUST be in
the form of an LbyR location URI, in its own locationValue header field
value.

A SIP proxy MAY add a Geolocation header field if one is not
present, and MAY add the "routing-allowed" parameter if not yet
present in the SIP request. When a "routing-allowed" parameter is
already present in the SIP request, a SIP server MUST NOT change the
value of the parameter (i.e., from 'yes' to 'no', or from 'no' to
'yes'). This would override the policy set by an upstream SIP
entity (i.e., likely the UAC).

Adding a new locationValue to an in-transit request is NOT
RECOMMENDED to occur for at least two reasons,

#1 - SIP Servers are not the best locators geographically of where a
UAC is; meaning the location information is that a SIP server knows may
not necessarily the
greatest. There MAY be exceptions, but this SHOULD be the rule
of thumb. best location information available.

#2 - without appropriate caution to the fact that Location
Recipients might not understand how to process more than one
location, given this document's document gives limited guidance as to what a Location
Recipient should do when receiving more than one location (i.e., currently no priority (no
instructions are given
for about which locationValue to use if there are when
more than one). A
Location Recipient can easily be confused by too much location
information, producing one is present), so adding a new locationValue may
lead to undesirable results. The <dm:device id>
element [RFC5491] in the PIDF-LO XML indicates whose location
is contained in the PIDF-LO.

Location Recipients receiving a location object, whether received
directly or as the result of a dereference, MUST honor the usage
element rules within that XML document, as defined in [RFC4119].
Such entities MUST NOT alter the rule set.

4.2 424 (Bad Location Information) Response Code

This SIP extension creates a new Location location specific response code,
defined as follows.

424 (Bad Location Information)

The 424 (Bad Location Information) response code is a rejection of
the request, 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 4.3 creates the Geolocation-Error header field to provide
more detail about what was wrong with the location information in
the request. This header field 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 (LbyV or LbyR),
and any of the locationValues is good for the Location Recipient to
process, can process any of the locationValues, 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.

A 424 (Bad Location Information) response is a final response within
a transaction, and does not terminate a usage or a an existing 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 any SIP intermediary as a result of this error message.
The new 424 (Bad Location Information) error code is IANA registered with
IANA in Section 8 of this document. An initial set of location error of
IANA registered
IANA-registered Geolocation-Error codes are in Section 4.3 of this
document.

4.3 The Geolocation-Error Header Field

As discussed in Section 4.2, 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 field is created here used for this purpose.

The Geolocation-Error header field is used to convey location specific
location-specific errors within a response. Additions to this IANA registered header require Additional
IANA-registered values must be defined in an RFC be published. (this is the "RFC
Required" IANA policy defined in [RFC5226]). The Geolocation-Error
header field has the following ABNF [RFC5234]:

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
/ location-error-host-id
/ location-error-code-text
/ generic-param ; from RFC3261
location-error-node-id = "node" EQUAL
DQOUTE hostport DQOUTE ; from RFC3261
location-error-host-id = "inserter" EQUAL
DQOUTE hostport DQOUTE ; from RFC3261
location-error-code-text = "code" EQUAL quoted-string ; from RFC3261

The Geolocation-Error header field MUST contain at least one
locationErrorValue to indicate what was wrong with the original locationValue
in the corresponding request. If a request the Location Recipient
experienced more than one error a particular locationValue of the
corresponding SIP request, there can be one locationErrorValue per
problem with the locationValue in the request. determined was
bad. Each locationErrorValue contains one a 3-digit error code
indicating what was wrong with the location in the request. Each
error type has a corresponding quoted error text string that is
human understandable. If there was something wrong with more than one
locationValue in a request, a corresponding locationErrorValue would
be sent, one per error, in the response.

Each locationErrorValue contains the Location Recipient identifier
(the "node=" parameter) which experienced the location error, as
well as an identifier of which SIP entity (the "inserter="
parameter) the Location Recipient is told (in the locationValue)
added this problematic locationValue to the request. The "node="
and "inserter=" are the domain identifier of a SIP entity, with the
ability to have the same host communicate on different ports - and
have port specific identification. This is the same as is information that
would be entered in the "sent-by" parameter of the Via header field
for that entity [RFC3261]. As stated in section 18 of RFC 3261,
the usage of FQDN is RECOMMENDED. Here are examples of both
locationErrorValue
parameters parameters,

node="bob.example.com"

inserter="alice.example.com"

Both the "node=" and "inserter=" parameters MUST be present in all
locationErrorValues in a response, unless the "inserted-by="
parameter was not in the locationValue of a the
request did not include the "inserted-by=" parameter (which is a
violation of this document). The "inserter=" parameter value is
copied from the "inserted-by=" parameter within the locationValue of
the request. No manipulation or calculation is necessary to
accomplish this.

Here's why this

This is necessary, required because a Location Recipient that experienced
the location a
problem with the location included in a request needs to tell the
specific SIP entity which added the locationValue in error into the
original request. Since more than one SIP entity can insert
location into a request in transit, all other SIP elements may be
confused by receiving this error header, header field, were it to remain
generic to all entities in the response path. So, This requirement
means that the header has to identify field identifies the Location Inserter who
it is for,
inserted the problematic locationValue, so that all other SIP
entities that read the header field know to ignore it, since it is not for them. it. 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 be interpreted
by each SIP entity along the original path upstream and tell be processed
by both the server that included the invalid locationValue what was wrong with the location and the
UAC who that did not know what the error meant. This will cause not, resulting in confusion if left without this indication. at the UAC.

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 only one of the locationValues. Without this an
identification of which the specific locationValue was in error, both entities
would react react, and one would do so react incorrectly.

When more than one locationErrorValue is present in a
Geolocation-Error header is field, they are separated by a comma. commas.

If more than one locationErrorValue is present in a response, and
intended for the same "inserter=", each error code MUST be unique to
this "inserter=" entity, and the error codes SHOULD MUST 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 field:

Geolocation-Error: 200; code="Retry Location Later";
node="bob.example.com";
inserter="alice.example.com";

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

Table 2: Summary of the Geolocation-Error Header Field

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. For example, Alice includes her
location in an INVITE to Bob. Bob can accept this INVITE, thus
creating a dialog, even though his UA determined the location
contained in the INVITE was bad. There is a Geolocation-Error
header value in the 200 OK to the INVITE informing Alice the INVITE
was accepted but the location provided was bad. The choice of which SIP requests
are
included in table 2 above come from which Methods can are the ones allowed to optionally have contain
the Geolocation header field (see section 4.1). That said, a UAC
MUST ignore a Geolocation-Error header field value if it that did not include a Geolocation
header value in the request part of the transaction.
contain its host-id..

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, header field, is in Figure 3.

Alice Bob
| |
| Request w/ Location |
|------------------------------------------------>|
| |
| |
| 424 (Bad Location Information) |
| with Geolocation-Error containing |
| 200 ("Retry Location Later" (with Later with same data)) data") |
|<------------------------------------------------|
| |

Figure 3. Basic Transaction with 424 and Geolocation-Error Header
Field

The following subsections provide an initial list of location
based errors for any SIP non-100 response, including the new 424
(Bad Location Information) response. These error codes are divided
into 5 categories, each based on receiver (of how the response)
actionable reactions response receiver should react
to these errors.

o 100 1XX "Cannot Process Location"

o 200 2XX "Retry Location Later" (with Later with same data) data"

o 300 3XX "Retry Location Later" (with device Later with updated location) device location"

o 400 4XX "Permission Necessary" To Reveal Location Information to a Third Party"

o 500 5XX "Location Information Denial"

All 5 of the above error codes MUST be implemented to comply with
this specification. Each of these actionable errors is given a 3
digit error code category, meaning any future 1XX, 2XX, 3XX, 4XX,
and 5XX error codes defined will have the same action expected by
X00 categories - just increase categories, although the future error code may provide more
granular meaning. information. If another action is expected to occur with a
newly defined error code, it MUST outside the 100-599 range. 100 unit ranges are OPTIONAL for future
error codes, but they apply here.

4.3.1 Location Error: 100 "Cannot Process Location"

The location error 100 "Cannot Process Location" indicates to a
Geolocation-Error recipient that what they the locationValue supplied in a request, as
far as location is concerned,
request cannot be processed at this time. This only has to do with
the location that the location "inserter=" added to the request, and
not about the overall request that was sent.

Action(s) to be taken by Geolocation-Error receiver to for a 1XX:
This error gives no guidance on what to do next. It is a
general information indication to a SIP "inserter=" entity
that there was an unspecific problem with the location
supplied in the SIP request.

Implementations MAY choose to react in a way as if this the "inserter="
entity received a 2XX or 3XX location error. A 4XX error Implementations MUST
NOT be
misunderstood here, react as if the "inserter=" entity received a 4XX location
error, as that error category involves human intervention to grant,
or not, permission to reveal "inserter=" location when this is
likely not desired.

The text string of "Cannot Process Location" is RECOMMENDED, but not
mandatory for usage in this error. Implementations MAY use another
text string.

An example of this 100 location error is here: is:

Geolocation-Error: 100; code="Cannot Process Location";
node="bob.example.com";
inserter="alice.example.com";
This category covers all 1XX location errors 1XX. errors. The same basic actionable
reaction is expected by when a location "inserter=" entity to receives any
1XX location error.

4.3.2 Location Error: 200 "Retry Location Later" (same data) Later same data"

The location error 200 "Retry Location Later" (same data) Later same data" indicates
to a Geolocation-Error recipient that what they supplied in a
request, as far as location is concerned, cannot be processed at
this time, but there is no need to retry this request, without changing update the location
information, at a later
time - in a new SIP request. It For example, this location error is possible
that
appropriate when the Location Recipient cannot process location at this a
specific time, or when there is there was a timeout during dereferencing, if an LbyR were sent. when a location
URI is dereferenced.

Action(s) to be taken by Geolocation-Error receiver to for a 2XX:
Reactions to a 2XX location error are to try again, without
having to update again after some
period of time has elapsed. The "inserter=" has not identified
problems with the location supplied originally. There provided in the original request,
so there is no constraints on how long this new try has need to wait, update this location unless
there is a the
requestor moves. A Retry-After header field MUST be present in a
the 424 response. response indicating after how long the LR thinks it
can process the location, the error recipient MUST obey this
instruction.

Implementations SHOULD choose to react by preparing, however this
"inserter=" does or can, to queue queuing another message
with the same location information, provided unless the "inserter=" does not move between
the time of the original request and the transmission time of the
new request. entity
knows it has changed locations.

Implementations MAY choose whether or not to inform the user of this error. The text string
of "Retry Location Later" Later same data" is RECOMMENDED, but not
mandatory for usage in this error. Implementations MAY use another text
string to inform the user that location was not received by the UAS
(i.e., the called party).

An example of this 200 location error is here: is:

Geolocation-Error: 200; code="Retry Location Later"; Later same data";
node="bob.example.com";
inserter="alice.example.com";

This category covers all 2XX location errors 2XX. errors. The same basic actionable
reaction is expected by when a location "inserter=" entity to receives any
2XX location error.

If a SIP request has the "routing-allowed" header field parameter
set to "no", and the SIP server believes processing location within the
request is
required in order to service the request properly, a 2XX location
error is sent towards the recipient. This error is the proper error
even when there is no location in the SIP request, but the SIP
request contains a policy statement that location is not to be
viewed during transit towards the ultimate destination.

4.3.3

4.3.2.1 Location Error: 300 "Retry Location Later" (device updated
location) 201 "Linkable Target Identity Required"

The location error 300 "Retry Location Later" (device updated
location) indicates to a Geolocation-Error recipient that what they
supplied in a request, as far as location code 201 "Linkable Target Identity Required" is concerned, cannot be
processed at this time, but to retry this request, once
specifically for the location
information has been updated, event in which a new SIP request.

Action(s) request requires a binding
of the Target's identity to be taken by Geolocation-Error receiver the presence document in order to a 3XX:

3XX location errors indicate know
this is the "inserter=" SIP entity needs Target's location to refresh its location, or make the an appropriate routing
decision. Because Alice could include Bob's location information
supplied more complete, without notifying in her SIP
request, the user of SIP server - in this
error. 3XX error are specific case - needs to be solved by without user
intervention.

This document gives no guidance how
understand this message is accomplished, given the
number of ways a UAC can learn its routed based on Alice's location, or a and not
Bob's. There is no absolute binding between presence documents and
SIP intermediary
can Sight signaling, hence a UAC, as defined in [RFC3693].

This 300 location separate error currently does not indicate what exactly was
wrong with specific behaviors are
necessary.

It is of particular importance is the location supplied, according emergency calling case,
described here [ID-PHONE]. The presence document has a <presence>
element containing an "entity=" attribute identifying who the
presence document is about. The PIDF-LO is a presence document.
[RFC3693] allows unlinkable pseudonyms to be in the Location
Recipient. That "entity="
attribute. This is left problematic for a future effort.

Implementations MAY choose whether or not some (all?) source location based
call routing situations.

The node= routing intermediary makes this locationErrorValue a 201
to inform the user of resolve this
error. The text string problem. In the 424 response, the Retry-After header
value of "Retry Location Later" '0' is RECOMMENDED, REQUIRED, indicating the new request be sent
immediately, but not mandatory for usage with a target identification resolved in this error. Implementation MAY use
another text string to inform the user that location was not
received by
PIDF-LO and SIP request. In presence, the UAS (i.e., entity= attribute is
typically the called party).

A 3XX location error would be used where URI of the Location Recipient
cannot find or cannot parse presentity, meaning something like the location supplied, believing that a
automated refresh and retry could fix
Contact address of the problem. Also, UAC here.

If there is no Retry-After header value, the default is to resend
the SIP request immediately with the corrected entity= attribute
(i.e., emulating a 3XX
location error would Retry-After: 0 header value).

Action(s) to be used when taken by Geolocation-Error receiver for a Location Recipient did not find
any 201:

201 location in a SIP request, but was expecting it. Perhaps an
emergency request was made that error indicate the "inserter=" did not contain location. The retry
in this case would be in properly
identify the form of an UPDATE Method request,
containing location (LbyV or LbyR).

An example Target of this location error is here:

Geolocation-Error: 300; code="Retry Location Later";
node="bob.example.com";
inserter="alice.example.com";

This category covers location errors 3XX. presence document. The same basic actionable
reaction
Retry-After has been received - or is expected by a location "inserter=" entity assumed to any 3XX
location error.

4.3.4 be 0 -
meaning the new SIP request is to be sent immediately.

4.3.3 Location Error: 400 "Permission Necessary"

The location error 400 "Permission Necessary" 300 "Retry Location Later with device updated
location"

The location error 300 "Retry Location Later with device updated
location" indicates to a Geolocation-Error recipient that when what they sent
supplied in a particular SIP request, they included as far as location in that is concerned, cannot be
processed. In order to retry this request without giving
permission in the request for a (or any) new SIP server to look at that request, the
location information (i.e., the <retransmission-allowed> was set to
"no" in the PIDF-LO for B2BUAs, or "routing-allowed=no" as a
Geolocation header parameter for proxy servers) to route the message
at the intended recipient (i.e., the UAS, or the called party). must be updated.

Action(s) to be taken by Geolocation-Error receiver to for a 4XX:

4XX 3XX:

3XX location errors indicate to the UAC (i.e., the calling
party) that they need to grant permission to a "inserter=" SIP
intermediary server entity needs
to look at refresh its location, or make the supplied location to
complete information
supplied more complete, without notifying the message routing. This indication MUST require
human user intervention, as the rulemaker of the policy on
whether or not their location is to this
error. 3XX errors may be revealed.

The resolved without user of intervention.

This document gives no guidance how this is accomplished, given the location "inserter=" device
number of ways a UAC can choose to grant
permission to this learn its location, or a SIP intermediary server to allow this request to
be routed, or the user
can deny this Sight a UAC, as defined in [RFC3693].

This 300 location revelation (request by error currently does not indicate what exactly was
wrong with the server). It is location supplied, according to the user's choice as rulemaker. Location
Recipient. That is left for a future effort.

Implementations MUST provide MAY choose whether or not to inform the user, as rulemaker, a clear
indication that permission to consume their location is sought by an
entity other than who that user is calling. of this
error. The text string of
"Permission Necessary" "Retry Location Later with device updated
location" is RECOMMENDED, but not mandatory for usage in this
error. Implementation MAY use another text string to inform the
user that location is being sought was not received by an intermediary the UAS (i.e., not the called
party).

This document gives no guidance how this intervention is
accomplished, given

A 3XX location error would be used where the number of ways a UAC can accomplish this
(i.e., audio prompt or toggle Location Recipient
cannot find or keystroke on their UA).

This 400 cannot parse the location error currently does not indicate exactly supplied. 3XX location
errors should cause a requestor to retry with refreshed location
information, which
SIP server indicates it needs might be sufficient to fix the problem. Also, a
3XX location revealed. That said, the
"node=" FQDN address could error would be supplied, telling the user (via audio
or video indication) which used when a Location Recipient was
expecting to find location in a SIP entity wants this request, but did not find it -
perhaps an emergency request was made that did not contain location. Perhaps
the user can know
The retry in some circumstances whether this is an
appropriate "node=" (domain). All case would be in the form of this is left for an UPDATE Method
request, containing location. If the 424 response contains a future
effort(s).
Retry-After value, there SHOULD NOT be a long delay associated with
a new request - under the guise that if the location had been good,
there would not have been an error to this request.

An example of this 300 location error is here: is:

Geolocation-Error: 400; code="Permission Necessary"; 300; code="Retry Location Later with device
updated location";
node="bob.example.com";
inserter="alice.example.com";

This category covers all 3XX location errors 4XX. errors. The same actionable
solution basic
reaction is expected to be afforded to the UAC user, as rulemaker,
to when a location "inserter=" entity receives any 4XX
3XX location error.

4.3.5

4.3.4 Location Error: 500 "Location 400 "Permission to Reveal Location Information Denial" to
a Third Party"
The location error 500 "Location 400 "Permission to Reveal Location Information Denial" to
a Third Party" indicates to a Geolocation-Error recipient that what they supplied in
sent a request, as
far as location is concerned, has been denied at this time.
This only has to do with the particular SIP Request including location in that the location "inserter="
added to the request, and not about
without giving permission in the overall request for an intermediary SIP
entity to look at that location information (i.e., the
<retransmission-allowed> was
sent. If this were applied set to "no" in the SIP request itself, this would
equate to PIDF-LO for B2BUAs,
or "routing-allowed=no" as a 6XX Global error. Geolocation header field parameter for
proxy servers) to route the request toward the intended recipient
(i.e., the UAS, or the called party).

Action(s) to be taken by Geolocation-Error receiver to for a 1XX:
This error gives no guidance on what to do next, other than to
not try again with this same 4XX:

4XX location supplied.

If errors indicate to the Location Recipient believed UAC (i.e., the calling
party) that merely refreshing, or in
some other way alter or augment they need to grant permission to a SIP
intermediary server to look at the location supplied would work in
a new request, then a 3XX location error SHOULD have been returned
(to to
complete the "inserter="). An example of why this 5XX could have been
returned is if location were sent message routing. This indication MUST require
human user intervention, acting as an LbyR, and the LIS denied the
dereference request from ruleholder of the Location (reference) Recipient, this is
the expected
policy on whether or not location error returned is to be revealed.

The user of the location "inserter=" entity.

Implementations MUST NOT interpret anything else into device can choose to grant
permission to this location
error other than it is considered a location based denial error.
This does not mean the SIP intermediary server to allow this request was denied, to
be routed, or even had an error,
unless the response was a 424. Otherwise, this only has to do with user can deny permission. It is the location part of user's choice
as ruleholder.

Implementations MUST provide the request.

The difference between a 1XX and user, as ruleholder, a 5XX clear
indication that permission to consume their location error is simple. A
1XX location error sought by an
entity that is a case of a Location Recipient either not
knowing or not being able to tell the "inserter=" entity what was
wrong with the location supplied in a SIP request. Whereas, a 5XX
location error is where the location was purposely, and actively
denied (or declined) from being received by the Location Recipient
entity, or its user. This could occur in a UAS or SIP server.

If implementations choose to inform that the UAC user of this error, the is calling. The text
string of "Location "Permission To Reveal Location Information Denial" to a Third
Party" is RECOMMENDED, but not mandatory for usage in this error.
Implementations MAY use another text string.

An example of this location error is here:

Geolocation-Error: 500; code="Location Information Denial";
node="bob.example.com";
inserter="alice.example.com";

This category covers string to inform the user that
location errors 5XX. The same basic actionable
reaction is expected being sought by an intermediary (i.e., not the called
party).

This document gives no guidance how the UAC can seek permission from
the user, given the number of ways a location "inserter=" entity to any 5XX
location error.

4.3.6 Which Scenario Matches Which Error Code?

The following are some additional failure scenarios, with which
error code SHOULD be used for consistency,

- Scheme (sip:, or sips:, or pres:, or another one) of the LbyR URI
isn't supported (100)
- Format (geo or civic) isn't supported (100)
- Cannot parse location (100)
- Can't find LIS (no access UAC can accomplish this (i.e.,
audio prompt or no path (100) toggle or denied access(500))
- Dereference failed (timeout) (200)
- Insufficient keystroke on a UA).

This 400 location info supplied (300)
- Cannot find error indicates exactly which SIP server indicates
that it needs the location in message (300)

4.4 The 'geolocation' Option Tag

This document creates and IANA registers one new option tag:
"geolocation". This option tag is to be used, as defined in RFC
3261, in by the Require, Supported and Unsupported headers. Whenever a
UA "node=" FQDN address supplied,
perhaps telling the user (via audio or video indication) which SIP
entity wants to indicate support for this SIP extension, location. Perhaps the geolocation
option tag is included user can know in a Supported header of the SIP request.

4.5 Using sip/sips/pres as a Dereference Scheme

If some
circumstances whether this is an LbyR URI appropriate "node=" (domain). This
latter feature is included not described in this document.

An example 400 location error is:

Geolocation-Error: 400; code="Permission to Reveal Location
Information to a SIP request, it MUST be a SIP-,
SIPS- or PRES-URI. When PRES: Third Party";
node="bob.example.com";
inserter="alice.example.com";

This category covers all 4XX location errors. The same resolution
is used, if expected to be afforded to the resulting resolution, UAC user, as defined in [RFC3856], resolves to a SIP: or SIPS: URI, this
section applies.

This document IANA registers 3 mandatory to implement URI schemes
for LbyR:

o SIP:
o SIPS:
o PRES:

These 3 are IANA registered in Section 9.6.

These schemes MUST be implemented according to this document.
absoluteURI is not mandatory ruleholder, to implement.

Dereferencing a Target's any
4XX location using SIP- or SIPS-URI is
accomplished by treating the URI as a PRES-URI and generating a
SUBSCRIBE request to a presence server as defined in [RFC3856]
using the 'presence' event package. The resulting NOTIFY will
contain the PIDF, rather MUST contain a PIDF-LO. See Figure 4. for a
basic message flow for a dereference. error.

4.3.5 Location Error: 500 "Location Information Denial"

The NOTIFY contains Alice's
PIDF-LO in Figure 4.

When used in this manner, SIP is a Using Protocol as defined in
[RFC3693] and elements receiving location MUST honor the
'usage-element' rules as defined in this extension.

Alice Location Server Bob
| |
| INVITE w/ LbyR URI |
|-------------------------------------------------------->|
| | |
| 200 (OK) |
|<--------------------------------------------------------|
| | |
| | SUBSCRIBE error 500 "Location Information Denial" indicates to LbyR URI |
| |<-----------------------------|
| | 200 (OK) |
| |----------------------------->|
| | |
| | NOTIFY w/ PIDF-LO |
| |----------------------------->|
| | 200 (OK) |
| |<-----------------------------|
| | |

Figure 4. Location-by-Reference and Dereferencing

In Figure 4., Alice sends Bob her location in an LbyR URI. Bob
receives this LbyR URI a
Geolocation-Error recipient that what they supplied 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 back
to Bob's UA. 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.

The SUBSCRIBE contains a geolocation option tag in either the
Supported or Require header (depending on what strength of support
the UAC wants to apply). The NOTIFY MUST match the subscribing
UAC's option-tag strength for geolocation.

A dereference of an LbyR 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 this PIDF-LO. This is the
purpose of this extension to SIP - to convey location to a specific
destination.

5. Geolocation Examples

This section contains are two examples of messages providing
location. One shows LbyV with coordinates, the other shows LbyR.
The example for (Coordinate format) is taken from [RFC3825]. A
civic format example of the same position on the earth request, as
far as location 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 5.1 shows a "cid:" URI, indicating
this SIP request contains an LbyV message body - which is in the
form of a PIDF-LO. Section 5.2 shows an LbyR URI indicating
location is to be acquired via an indirection dereference mechanism,
which is determined by the scheme of URI supplied.

5.1 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.

INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/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:target123@atlanta.example.com>
;inserted-by="alice@atlanta.example.com"
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: <target123@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"
xmlns:gml="http://www.opengis.net/gml"
entity="pres:alice@atlanta.example.com">
<dm:device id="target123">
<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>
</dm:device>
</presence>
--boundary1--

The Geolocation header field from the above INVITE...

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. The "cid:" eases parsing of message
bodies.

If the Geolocation header field were this instead:

Geolocation: <sips:server5.atlanta.example.com/target123>

...the presence of something other than "cid:" indicates an LbyR is
included in concerned, has been denied at this message. It is expected that any node wanting time.
This only has to
know where user "target123" is would subscribe do with the location that the location "inserter="
added to server5 the request, and not about the overall request that was
sent. If this were applied to
dereference the sips-URI (see Figure 4 for SIP request itself, this message flow, and
Section 5.2 would
equate to a 6XX Global error.

Action(s) to be taken by Geolocation-Error receiver for a 5XX:
This error gives no guidance on what to do next, other than to
not try again with this decoded example). The returning NOTIFY would
contain Alice's same location supplied.

If the Location Recipient determined that merely refreshing, or in
some other way alter or augment the location supplied would work in
a PIDF-LO, as new request, then a 3XX location error would have been more
appropriate. An example of why this 5XX could have been returned is
if it location were included in sent as a
message body (part) of location URI, and the original INVITE here.

5.2 Location-by-reference

Below is an INVITE LS denied the
dereference request with an LbyR URI instead of an LbyV
PIDF-LO message body part shown in Section 5.1. It from the potential Location Recipient, this is up to
the expected location recipient error returned to the "inserter=" entity. In
all likelihood, this is a dereference Alice's function error, meaning this
will not occur when location at is carried by-value in the Atlanta
LIS server containing request.

Implementations MUST NOT make any assumptions about the implications
of this location record. Dereferencing, if done
with SIP, is accomplished by the Location Recipient sending error other than recognizing that a
SUBSCRIBE request to the URI reference for Alice's location. The
received NOTIFY is location based
denial error has occurred. This does not mean the first SIP request containing Alice's UA
location, as was
denied, or even had an error, unless the response was a PIDF-LO message body (see Figure 4 for 424.
Otherwise, this message
flow example). only has to do with the location part of the
request.

The NOTIFY, in this case, difference between a 1XX and a 5XX location error is the SIP request that simple. A
1XX location error is
conveying location, and appropriate when a Location Recipient either
does not know or cannot tell the "inserter=" entity what was wrong
with the INVITE. There is no retransmission
of location supplied 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"
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 SIP request. A 5XX location error
is appropriate when the Location Recipient would need to dereference the sips-URI in the
Geolocation header field to retrieve Alice's location. If was purposely and
actively prevented from retrieving the
atlanta.example.com domain chooses to implement location conveyance
and delivery information. This
could occur in this fashion (i.e., LbyR), it is RECOMMENDED that
entities outside this domain be able a UAS or SIP server.

If implementations choose to reach inform the dereference
server, otherwise UAC user of this model error, the
text string of implementation "Location Information Denial" is only viable within
the atlanta.example.com domain.

6. SIP Element Behavior

Because a device's RECOMMENDED, but not
mandatory for usage in this error. Implementations MAY use another
text string.

An example of this location error is generally considered to be sensitive
in nature, here:

Geolocation-Error: 500; code="Location Information Denial";
node="bob.example.com";
inserter="alice.example.com";

This category covers 5XX location information needs to be protected errors. The same basic reaction
is expected when
transmitted. This can be addressed through securing the a location
information to prevent either viewing "inserter=" entity receives any 5XX
location error.

4.3.6 Which Scenario Matches Which Error Code?

The following scenario/error code mapping MUST be used for
consistency,

- Scheme (sip:, or changing the PIDF-LO.

Section 26 sips:, or pres:, etc.) of [RFC3261] defines the security functionality SIPS by
transporting SIP messages with either TLS location URI
isn't supported - (100)
- Format (geo or IPSec protection
between SIP entities.

If a SIP entity wants to prevent all SIP entities civic) isn't supported - (100)
- Found where location should be, but do not understand what is
there -(300)
- Cannot find LS in a request path
from viewing location URI (no access or just changing the contents of the PIDF-LO, save
those that possess decryption key, the message body needs no path) - (100) or
denied access - (500))
- Dereference failed (timeout) - (200)
- Insufficient location info supplied - (300)

4.4 The 'geolocation' Option Tag

This document creates and IANA registers one new option tag:
"geolocation". This option tag is to be
secure by a means such used, as S/MIME. This would be the case defined in
[RFC3261], in which a
UAC wants to make sure only the destination UAS can read the
PIDF-LO.

6.1 UAC Behavior

A UAC can send location Require, Supported and Unsupported header fields.

4.5 Using sip/sips/pres as a Dereference Scheme

If an LbyR URI is included in a SIP request, either because it MUST be a SIP-,
SIPS- or PRES-URI. When PRES: is
expected to facilitate location-based routing of used, if the request, or
spontaneously (i.e., for a purpose not resulting resolution,
as defined in [RFC3856], resolves to a SIP: or SIPS: URI, this
section applies.

This document but
known to the UAC). Alice communicating her location to Bob IANA registers 3 mandatory-to-implement URI schemes
for LbyR:

o SIP:
o SIPS:
o PRES:

These 3 are registered with IANA in a SIP
request Section 9.6.

These schemes MUST be implemented according to this document.

absoluteURI is not mandatory-to-implement.

Dereferencing a simple example of this. If Alice wanted to include her Target's location using SIP- or SIPS-URI is
accomplished by treating the URI as a message body in an INVITE that also has an SDP message
body, the Content-Type: Multipart MUST be supported by both UAC and
UAS. Multipart comes in many forms (/mixed, /alternative, etc), PRES-URI and
this document does not limit which type of multipart is used, though
future documents MAY specify or limit multipart generating a
SUBSCRIBE request to a subset of all presence server as defined in [RFC3856]
using the choices for a given use.

A UAC conveying location 'presence' event package. The resulting NOTIFY MUST include
contain a locationValue in PIDF-LO. See Figure 4 for a
Geolocation header (see section 4.1) with either an LbyV indication
(a cid-URL), or an LbyR. An LbyV basic message body sent without flow for a
Geolocation header field MUST NOT occur.
dereference. The UAC supporting NOTIFY contains Alice's PIDF-LO in Figure 4.

When used in this
extension manner, SIP is a Using Protocol as defined in
[RFC3693] and elements receiving location MUST include a Supported header with honor the 'geolocation'
option tag.

More than one location format (civic and coordinate) can be included
'usage-element' rules as defined in the same message body part, but all this specification.

Alice Location Server Bob
| |
| INVITE w/ Location URI |
|-------------------------------------------------------->|
| | |
| 200 (OK) |
|<--------------------------------------------------------|
| | |
| | SUBSCRIBE to location parts of the same URI |
| |<-----------------------------|
| | 200 (OK) |
| |----------------------------->|
| | |
| | NOTIFY w/ PIDF-LO MUST point at the same position on the earth, identifying
the same target. The same |
| |----------------------------->|
| | 200 (OK) |
| |<-----------------------------|
| | |

Figure 4. Location-by-Reference and Dereferencing

In Figure 4, Alice sends Bob her location in multiple formats, for
example, a partial or complete geodetic location URI. Bob
receives this location URI in the INVITE and generates a partial or complete
civic, can allow the recipient new
transaction (SUBSCRIBE) to use the most convenient or
preferable format for its use.

Multiple PIDF-LOs are allowed in retrieve Alice's PIDF-LO. If accepted,
the same request, with each allowed
to point at separate positions - however, each PIDF-LO MUST identify
a different Target. 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 locationValue returned in a single SIP the NOTIFY request for from the same
Target. More than one will likely lead to confusion by a Location
Recipient because this extension does not provide guidance on what a
recipient
Server to Bob's UA. This is to do with more than one location, nor does it give any
preference regarding which the first instance between Alice and
Bob that Alice's location is better or worse than another
location in any message, therefore it is sent
only once, from the same request. Location Server to Bob.

The 'geolocation' SUBSCRIBE contains a geolocation option tag is inserted in a either the
Supported or Require header by a
UAC to provide an indication field (depending on what strength of
support for this extension. the UAC requires). The
presence of NOTIFY MUST match the 'geolocation' option tag in a Supported header
without subscribing
UAC's option-tag strength for geolocation.

A dereference of an LbyR URI using SUBSCRIBE is not violating a Geolocation header field in
PIDF-LO 'retransmission-allowed' element value set to 'no', as the same
NOTIFY is the only message informs a in this multi-message set of transactions
that contains the Target's location, with the location recipient
being the only SIP element receiving to receive this request that PIDF-LO. This is the UAC understands
purpose of this
extension, but it does not know or wish extension to SIP - to convey its location at
this time. Certain scenarios exist (location-based retargeting) to a specific
destination.

5. Geolocation Examples

This section contains are two examples of messages providing
location. One shows LbyV with coordinates, the other shows
dereferencable location URI. 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 appear within the <gp:location-info> in 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 required in the Geolocation header field,
which has a different type of URI, based on the different means of
location conveyance. Section 5.1 shows a "cid:" URI, indicating
this SIP request contains an LbyV message body - which is in order the
form of a PIDF-LO. Section 5.2 shows an LbyR URI indicating
location is to retarget be acquired via an indirection dereference mechanism,
which is determined by the
message properly. scheme of URI supplied.

5.1 Location-by-value (Coordinate Format)

This affects how example shows an INVITE message with a UAS or coordinate location. In
this example, the SIP server processes
such request uses a request. sips-URI [RFC3261], meaning
this message is protected using TLS on a hop-by-hop basis.

INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/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:target123@atlanta.example.com>
;inserted-by="alice@atlanta.example.com"
;routing-allowed=no
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: <target123@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"
xmlns:gml="http://www.opengis.net/gml"
entity="pres:alice@atlanta.example.com">
<tuple id="target123">
<status>
<timestamp>2009-07-13T09:00:00Z</timestamp>
<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>2009-07-29T18:00:00Z</gp:retention-
expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
a </gp:geopriv>
</status>
</tuple>
</presence>
--boundary1--

The 'geolocation' option tag SHOULD NOT be used in Geolocation header field from the Proxy-Require
Header, because above INVITE:

Geolocation: <cid:target123@atlanta.example.com>

... indicates the UAC often will not know content-ID location [RFC2392] within the underlying topology
to know which proxy will do multipart
message body of where location information is, with SDP being the retargeting, thus increasing
other message body part. The "cid:" eases message body parsing.

If the Geolocation header field did not contain a "cid:" scheme, for
example, like this location URI:

Geolocation: <sips:server5.atlanta.example.com/target123>

... the
likelihood existence of a request failure by the first hop proxy that does not
understand non-"cid:" scheme indicates this extension, but is required a
location URI, to by inclusion of be dereferenced to learn the
option tag in this header.

A UAC inserting a locationValue MUST include an "inserted-by="
parameter target's location. Any
node wanting to indicate its hostport. This know where user "target123" is copied would subscribe to
server5 to dereference the
"inserter=" parameter of the Geolocation-Error header sips-URI (see Figure 4 for this message
flow, and Section 5.2 for this decoded example). The returning
NOTIFY would contain Alice's location in a response PIDF-LO, as if a Location Recipient determines there is something wrong with the
locationValue it were
included in this request. Because more than one locationValue
can be inserted along the path a message body (part) of the request, this indication original INVITE.

5.2 Location-by-reference

Below is
necessary to show which locationValue had the problem an INVITE request with a location URI that is not a "cid:"
- instead of an LbyV PIDF-LO message body part as shown in Section
5.1. The Location Recipient will dereference Alice's location at
the
response, and who Atlanta Location Server the locationErrorValue is for. For example:

Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice@atlanta.example.com"

If a UAC does not learn and store its location locally (a GPS chip)
or from URI is pointing towards.
Dereferencing, if done using SIP, is accomplished by the network (DHCP or LLDP-MED), Location
Recipient sending a SUBSCRIBE request to the UAC MAY learn its LbyR URI (from DHCP reference for
Alice's location. The received NOTIFY is the first SIP request
containing Alice's UA location, as a PIDF-LO message body (see
Figure 4 for this message flow example). If The NOTIFY, in this case,
and not the latter INVITE, is the case, SIP request that is conveying location.
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"
;routing-allowed=no
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@pc33.atlanta.example.com>

(...SDP goes here as the UAC can
SUBSCRIBE only message body)

A Location Recipient would need to this LbyR URI, using dereference the 'presence' event package, sips-URI in the
Geolocation header field to
get and store its own retrieve Alice's location.

The act of dereferencing a Target's LbyR will be challenged by If the
LIS where this
atlanta.example.com domain chooses to implement location record conveyance
and delivery in this fashion, it is - providing a good deal of
protection, SHOULD still RECOMMENDED that entities
outside this domain be treated as equivalent able to possession of reach the dereference server, unless
location information itself and thus TLS SHOULD be used when
transmitting LbyR hop-by-hop along the path to is intentionally restricted within the Location
Recipient, for protection reasons. This atlanta.example.com
domain.

6. SIP Element Behavior

Because a device's location is not generally considered to be confused with
a possession model, sensitive
in which possessing the LbyR grants
authorization to dereference the URI. Any entity dereferencing the
LbyR MUST pass whatever authentication and authorization rules are
on the LIS for this nature, location record. The Ruleholder from [RFC3693]
is still very much in control - for any entity possessing the LbyR.

If information needs to be protected when
transmitted. This can be addressed through securing the Location Generator wishes to control whether any location
included in the SIP request
information to prevent either viewing or added along changing the signaling path PIDF-LO.

Section 26 of
this request can be viewed for routing decisions, [RFC3261] defines the Location
Generator adds SIPS security functionality by
transporting SIP messages with either TLS protection between SIP
entities.

If a Geolocation header value including SIP entity wants to prevent all SIP entities in a request path
that do not possess a decryption key from viewing or changing the
"routing-allowed=no" parameter. This header parameter provides
specific policy rules for each locationValue (if there is more than
one inserted along
contents of the signaling path) within PIDF-LO, the SIP request. message body needs to be secure by a
means such as S/MIME.

6.1 UAC Behavior

A UAC SHOULD include the "routing-allowed" header parameter, with or
without a locationValue, might choose to each send location in a SIP request supporting this
specification to ensure the UAC's policy for intermediaries which
might add a locationValue facilitate
location-based routing of the Target downstream. The UAC
understands that the default behavior request, or for some other purpose.
Alice communicating her location to Bob in a SIP servers request is a simple
example of this. If Alice wanted to consider
this value to be present, and include her location as a
message body in an INVITE that it is set to "no".

The UAC also has an SDP message body, the
Content-Type: Multipart MUST understand there be supported by both UAC and UAS.
Multipart comes in many forms (/mixed, /alternative, etc), and this
document does not limit which type of multipart is no feedback mechanism used, though
future documents might specify or limit multipart to inform a subset of
all the
Target if choices for a SIP server has included given use.

A UAC conveying location MUST include a locationValue downstream.

If in a
Geolocation header (see section 4.1) with either an LbyV indication
(a cid-URL), or a dereferencable location URI. Requests containing
an LbyV message body sent MUST also contain a Geolocation header
field. The UAC has already conveyed supporting this extension MUST include a Supported
header with the 'geolocation' option tag.

More than one location format (civic and coordinate) can be included
in the original request same message body part, but all location parts of the same
PIDF-LO MUST point at the same position on the earth, identifying
the same target. The same location in multiple formats, for
example, a
transaction, partial or complete geodetic and wants a partial or complete
civic, allows the recipient to update select the most preferred format for
its use. Additional complementary location information (for
whatever reason) after the original request is sent, or after a
dialog is created (regardless of how can be in
the UAC conveyed location
previously, second format as an LbyV or LbyR) - this is done by a UAC sending an
UPDATE request [RFC3311] containing well.

Multiple PIDF-LOs are allowed in the geolocation option tag and
Geolocation header same request, with the new locationValue (LbyV or LbyR) each allowed
to point at separate positions - however, each PIDF-LO MUST identify
a different Target (i.e., in the
original destination UAS.

A PIDF includes identity information. It is possible for entity= attribute in the
identity <presence>
element of the presence document). 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). A SIP
request SHOULD include only one location per target in the PIDF a single SIP
request. More than one will likely lead to be anonymous. Implementations of confusion by a Location
Recipient because this extension SHOULD consider the appropriateness of including an
anonymous identity in the location information where does not provide guidance on what a real identity
recipient is not required. When using LbyR, to do with more than one location for the LbyR MUST NOT contain same target
(which could point to different positions), nor does it give any
user identifying information. For example, use something
unidentifiable like

3fg5t5yqw@example.atlanta.com

rather than

aliceishere@example.atlanta.com).

Use of self-signed certificates
preference regarding which location is inappropriate for use more or less reliable than
another location in
protecting a PIDF, as the sender does not have a secure identity same request.

The presence of the recipient.

Mentioned in more detail in later 'geolocation' option tag in section 6.2, SIP MUST NOT
attempt to overcome rules and behaviors conveyed a Supported header
field without a Geolocation header field in the same message informs
a PIDF-LO.
Therefore, UACs SHOULD take care when setting their
<retransmission-allowed> flag to "yes", as when Alice tells Bob her
location with SIP element receiving this flag set to "yes", as long as request that the
<retention-expiry> time is UAC understands this
extension, but it does not indicating the location information
needs know or wish to be deleted - Bob convey its location at
this time. Certain scenarios exist (location-based retargeting) in
which location is free required in a SIP request in order to tell Carol where Alice is.
This is an implicit byproduct of how retarget the PIDF-LO rule-set is, as of
this writing. This is
message properly. Indicating support with a configuration issue, but something worth
mentioning here.

6.1.1 UAC Receiving geolocation option tag
affects how a Location Failure Indication

Location Recipients can be either, UAS or both, destination UASs and
intermediate servers SIP server processes such a request. For
example, it ought to understand that use erroring the location information for
location-based routing decisions. If a sent request fails based on
the because
there was no location information in the request, a 424 (Bad Location
Information) response request is sent back likely not going to result
in the UAC. location appearing in the subsequent request.

The 424 MUST have a
Geolocation-Error header containing one or more locationErrorValues 'geolocation' option tag SHOULD NOT be used in the response message. A locationErrorValue has a Proxy-Require
header
parameter indicating which entity inserted field, because often the locationValue
correlated UAC will not know the underlying
topology to this error, called know which proxy will do the "inserter=" parameter. This
"inserter=" parameter (in retargeting, thus
increasing the locationErrorValue) likelihood of a request failure at the first hop
proxy that does not understand this extension, as is copied from required by
inclusion of the option tag in this header field.

A UAC inserting a locationValue MUST include an "inserted-by="
parameter (from to indicate its hostport. This is copied to the locationValue) by
"inserter=" parameter of the Geolocation-Error header field in a
response if a Location Recipient (UAS or proxy) sending determines there is something wrong
with the error response. A UAC
receiving a Geolocation-Error locationValue in any response type MUST review this 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
"inserter=" parameter problem
in the locationErrorValue to see if it
indicates this UAC. If locationErrorValue does not match, response, and who the locationErrorValue MUST be ignored. If a locationErrorValue is in for. For
example:

Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice@atlanta.example.com"

If a
424, UAC does not learn and store its location locally (a GPS chip)
or from the "inserter=" entity is not this UAC, network (DHCP or LLDP-MED), the response SHOULD
be treated as a 400 response. If locationErrorValue does indicate
this UAC, this UAC MUST process MAY learn its
location URI (from DHCP for example). If the response, including latter is the case,
the
Geolocation-Error code (defined in section 4.3). Further, UAC MUST
ignore a Geolocation-Error header value, even for can SUBSCRIBE to this UAC, even in
a 424 response if location URI, using the UAC did not include 'presence'
event package, to get and store its own location.

The Location Server will likely challenge requests to dereference a Geolocation header value
(with locationValue) in the request part
Target's location URI. The location URI SHOULD be treated as
equivalent to possession of the transaction.

A UAC MAY reattempt a new request if it believes it can correct the
stated failure in location information itself and thus
TLS SHOULD be used when transmitting any location URI hop-by-hop
along the Geolocation-Error header, unless path to the location
error Location Recipient, for protection reasons.
This is a 5XX level error - which clearly states in Section 4.3 not to do this. A UAC MUST follow all be confused with a 'possession model', in which
possessing the guidance that pertains to
UACs from Section 4.3 (Geolocation-Error header), heeding what location URI grants authorization to do
in case it receives any of dereference the error codes articulated in that
section.
URI. Any UAC that inserted entity dereferencing the location into a request SHOULD be prepared to
receive URI MUST pass whatever
authentication and authorization rules are on the Geolocation-Error header in any response, looking LS to
determine if a locationErrorValue acquire this
location. The Ruleholder from [RFC3693] is meant still very much in
control - for any entity possessing the UAC, and to react
accordingly. LbyR.

If a UAC includes location in a request, and either the UAS does not
determine errored location was critical Location Generator wishes to control whether any location
included in the transaction and
accept the request, SIP request or added along the signaling path of
this request failed can be viewed for reason other than
location, any response MAY contain routing decisions, the Location
Generator adds a Geolocation-Error Geolocation header
containing a locationErrorValue with the details of the location
error.

6.2 UAS Behavior

If field value including the Geolocation
"routing-allowed=no" parameter. This header field parameter
provides specific policy rules for each locationValue (if more than
one locationValue is present in a received SIP
request, inserted along the type of URI contained in signaling path) within the locationValue will
indicate if location is an LbyV in a message body (part) or LbyR,
requiring an additional dereference transaction. If
SIP request. A UAC SHOULD include the LbyR URI is
sip:, sips: "routing-allowed" header
field parameter, with or pres:, and the UAS wants without a locationValue, to learn each SIP
request supporting this specification to ensure the UAC's location, policy for
intermediaries which might add a locationValue of the UAS MUST initiate Target
downstream. The default behavior for SIP servers is to consider
this value to be present, with a SUBSCRIBE to the URI provided value of "no".

There is no feedback mechanism to retrieve
the PIDF-LO being conveyed by inform the UAC as defined in [RFC3856]. Target if a SIP server
has included a locationValue downstream. If
successful, the PIDF-LO will be returned a UAC has already
conveyed location in the NOTIFY original request from
the remote host. The UAS is not REQUIRED of a transaction, and
wants to dereference update its location information (for whatever reason) after
the LbyR if
it does not want to (by configuration original request is sent, or user choice). It after a dialog is
RECOMMENDED the UAS render the location sent to it, however it created, this is
configured to do so.

A Require
done by sending an UPDATE request [RFC3311]. The UPDATE will include
a geolocation option tag and Geolocation header field with the 'geolocation' option tag indicates new
locationValue to the
UAC is requiring original destination UAS.

A presence document includes identity information (in the UAS understand "entity="
attribute of the <presence> element), although the identity could be
an unlinkable pseudonym [RFC3693]. Implementations of this
extension or else send
an error response. A 420 (Bad Extension) with a 'geolocation'
option tag in SHOULD consider the appropriateness of including an Unsupported header would be
unlinkable pseudonym as the appropriate
response identity in this case.

It is possible, but undesirable, for the location information
where a message real identity is not required. See the concerns raised in
section 4.3.2 about unlinkable pseudonyms in relation to arrive with a body
containing an LbyV, but their
potential problems with no Geolocation header field value
pointing requests that need to it (potentially no Geolocation header field at all). In
this case, route based on the recipient MAY still read and use
location contained in the message.

When using LbyR, the message body.
Unless stated otherwise by future standards-track publication(s), a
LbyR location URI only has meaning within the Geolocation header field and MUST NOT appear in contain any other SIP header field.

There are 3 Geolocation header parameters,

o "inserted-by="
o "used-for-routing"
o "routing-allowed"

The "inserted-by=" parameter informs a Location Recipient which SIP
element added this locationValue to the SIP request. This parameter user
identifying information. For example, use something unidentifiable
like

3fg5T5yqWowhGLn54wg4NgHlkDsFn@example.atlanta.com

rather than

aliceishere@example.atlanta.com).

Use of self-signed certificates is mandatory inappropriate for each locationValue use in
protecting a PIDF, as the request. The value in sender does not have a secure identity of
the "inserted-by=" parameter recipient.

Although this is copied into the "inserter="
parameter discussed in each locationErrorValue if there is an error more detail in the later in section 6.2,
SIP entities MUST NOT bypass rules and behaviors conveyed in a
PIDF-LO. UACs SHOULD take care when setting their
<retransmission-allowed> flag to "yes". When Alice tells Bob her
location with this flag set to be reported back "yes", Bob is free to tell Carol
where Alice is (as long as the <retention-expiry> time has not
elapsed, indicating that the location sender. See section
6.2.1.

The "used-for-routing" parameter information should be
deleted). This is included in an implicit byproduct of the locationValue if PIDF-LO rule-set, as
of this writing. This decision is a SIP server used configuration issue, but is
worth mentioning here.

6.1.1 UAC Receiving a Location Failure Indication

Location Recipients that use the location in the request to determine how to
route information for
location-based routing decisions can be either destination UASs or forward the message towards the ultimate destination. If
there are more than one locationValues
intermediate servers. If a request fails based on the location
information in the Geolocation header,
and it request, a 424 (Bad Location Information)
response is possible that different locationValues were used sent back 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 UAC. The 424 MUST have a locationValue,
Geolocation-Error header field containing one or more
locationErrorValues in the response message. A locationErrorValue
has a "used-for-routing" header field parameter is
added indicating which entity inserted the
locationValue correlated to this error, called the applicable locationValue. "inserter="
parameter. This "inserter=" parameter should be
present in each locationValue used along (in the path. locationErrorValue)
is copied from the "inserted-by=" parameter (from the locationValue)
by the Location Recipient (UAS or proxy) sending the error response.
A
"used-for-routing" UAC receiving a Geolocation-Error in any response type MUST check
whether the "inserter=" parameter in the locationErrorValue
indicates this UAC.

o If locationErrorValue does not match, the locationErrorValue
MUST NOT ever be removed from a
locationValue in ignored.

o If a request.

The "routing-allowed" parameter locationErrorValue is exclusively for SIP servers, and
will be discussed in section 6.3.

Additional locationValues inserted into a request SHOULD be placed
the order they were generated, 424, and the "inserter=" entity
is not rearranged. This informs a
Location Recipient which was this UAC, the last locationValue in response SHOULD be treated as a 400
response.

o If locationErrorValue does indicate this UAC, this UAC MUST
process the message
that was used to route response, including the message. This is for troubleshooting and
management reasons.

Individual header parameters Geolocation-Error code
(defined in any received locationValue MUST NOT
be modified or deleted section 4.3), taking the action described in transit to that
section for the ultimate destination.

A UAS received error code.

Additionally, the UAC MUST NOT send location ignore a Geolocation-Error header field
value, even for this UAC, even in a 424 response message, as there can be
any number of issues/problems with receiving location, and if the UAC
or proxy servers cannot error did not
include a response. Therefore, Geolocation header field value (with locationValue) in the UAS,
request part of the transaction.

A UAC MAY reattempt a new request if it
wants to send can correct the stated
failure in the Geolocation-Error header field, unless the location
error is a 5XX level error - Section 4.3 clearly states not to do
this. A UAC its location, SHOULD MUST follow all the guidance that pertains to UACs from
Section 4.3 (Geolocation-Error Header Field), heeding what to do so
when it receives any of the error codes articulated in that section.

Any UAC that inserted location into a new request MUST be prepared to
receive the Geolocation-Error header field in a
separate transaction. This document gives no guidance which SIP
request any response, looking
to use, but SIP MESSAGE is determine if a viable choice.

A UAS MAY include locationErrorValue is meant for the UAC, and to
react accordingly.

If a 'geolocation' option tag UAC includes location in the Supported header
of a response, indicating it request, and either the UAS does understand this extension, even if not
determine errored location was not in a request critical to the UAS.

A transaction and
accept the request, or the request failed for reason other than
location, any response MAY contain a Geolocation-Error header field
containing a locationErrorValue with the details of the location
error.

6.2 UAS wishing to dereference an LbyR URI contained Behavior

If the Geolocation header field is present in a received
request will use SIP
request, the 'presence' event package type of URI contained in a SUBSCRIBE request
to the URI. If accepted, the PIDF-LO locationValue will return to the UAS
indicate if location is in a
NOTIFY request. If there are any errors during dereferencing, message body (part) or in requires an
additional dereference transaction. If the PIDF-LO itself, location URI is sip:,
sips: or pres:, and the UAS will error the original request wants to learn the
UAC with a locationErrorValue indicating what UAC's location, the
UAS concluded was
wrong with the location. This is MUST SUBSCRIBE to include any dereferencing
problems encountered.

Section 4.5 of this document called for the IANA registration of 3 provided URI schemes (sip:, sips:, and pres:) that are mandatory to implement
for dereferencing.

A UAS MUST be prepared to receive subsequent location updates from retrieve the UAC, either LbyV or LbyR (regardless of how PIDF-LO being
conveyed by the UAS received
location previously from this UAC). The UAC as defined in [RFC3856]. If successful, the
Target's PIDF-LO will convey location
using be returned in the UPDATE [RFC3311] method to NOTIFY request from the UAS, and not a reINVITE.

If there
remote host. The UAS is more than one location (any combination of LbyV and
LbyR), this document does not give guidance what a Location
Recipient does with each location. There are no priority or
more-trusted indications given by this document. All this is
considered application specific, and out-of-scope of this document.
This document makes it clear that if when there are more than one
location, each in REQUIRED to dereference the location
URI if location is not needed to process the same PIDF-LO MUST be about request. It is
RECOMMENDED the same Target
(identifier) and point at UAS display the same position on location to the earth. If there
is more than one PIDF-LO user, or otherwise
render the location appropriately.

A Require header field with different Target identifiers, then the 'geolocation' option tag indicates
the UAC is merely telling requires that the UAS where more than one Target is, and
there should not be any conflict.

Within any PIDF-LO, there is understand this extension, sending an
error response if it does not. A 420 (Bad Extension) with a <retransmission-allowed> element that
can
'geolocation' option tag in an Unsupported header field would be set to "yes" or "no". These are the only possibilities. If
Alice conveys her location to Bob (as has been described throughout
appropriate response in this document) case.

It is possible, but undesirable, for a message to arrive with a <retransmission-allowed> element set body
containing an LbyV, but with no Geolocation header field value
pointing to "no",
then Bob 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 publication(s), a
location URI only has meaning within the Geolocation header field
and MUST NOT inform appear in any other element where Alice is. If SIP header field.

There are 3 Geolocation header field parameters,

o "inserted-by="
o "used-for-routing"
o "routing-allowed"

The "inserted-by=" parameter informs a Location Recipient which SIP
entity 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
<retransmission-allowed> element "inserter="
parameter in each locationErrorValue if there is set an error in the
location to be reported back to "yes", then Bob can
inform other elements where Alice is, but only until the
<retention-expiry> element, also location sender. See section
6.2.1.

The "used-for-routing" parameter is included in the PIDF-LO, allows Bob to
[RFC4119]. As a byproduct of this, that means that locationValue if Alice conveys
her
a SIP server used the location in the request to Bob with a <retransmission-allowed> element set determine how to
"yes", and
route or forward the <retention-expiry> time message towards the ultimate destination. If
there are more than one locationValues in the Geolocation header
field, it is not requiring Bob possible that different locationValues were used to
delete Alice's location yet, then Bob
route the message at different points along the path traversed by
the request. This is free to tell anyone else
where Alice is. Whenever Bob conveys Alice's location,
<retention-expiry> timer MUST be maintained allowed, as it is (i.e., not
changed). The <dm:device id> element identifies consistent with the rule
that Alice whenever a message is the
target of this location. RFC 4119 implicitly allows this behavior,
thus SIP routed based upon a locationValue, a
"used-for-routing" parameter is not going added to change this behavior the applicable
locationValue. This parameter MUST be present in each locationValue
used along the path. A "used-for-routing" parameter MUST NOT be
removed from occurring.

6.2.1 UAS Generating a Location Failure Indication

If a UAS receives location locationValue in a request, but determines there request.

The "routing-allowed" parameter is exclusively for SIP servers, and
will be discussed in section 6.3.

Additional locationValues inserted into a request MUST be placed
the order they were generated, and not rearranged. This informs a
problem with
Location Recipient which was the location last locationValue in the request, it is the responsibility
of the UAS to inform whomever inserted location into message
that request
there was a problem experienced. The Geolocation used to route the message. This is for troubleshooting and
management reasons.

Individual header field parameters in any received locationValue
MUST NOT be modified or deleted in transit to the
request has a locationValue, providing the ultimate
destination.

A UAS a URI indicating
where the Target's MUST NOT send location is. The Location Target identified in
the PIDF-LO may or may not a response message, as there can be the location inserter, or the
generator
any number of issues/problems with receiving location, and the request (the UAC
or SIP server). Ultimately,
location is in proxy server(s) cannot reply to a PIDF-LO. This is either in response with an error
response. If the request as UAS wants to send its location to a
message body (LbyV), or UAC, it has to be dereferenced from the LbyR in
the locationValue can do
so in the request. LbyR records are typically kept
on a LIS, which can challenge all dereference requests. All
PIDF-LOs have new request within a Location Target identifier. separate transaction. This document
gives no recommendation about which SIP request to use, but SIP
MESSAGE is who the
location is about. The "inserted-by=" parameter of the
locationValue tells the a viable choice.

A UAS who inserted that locationValue. This
"inserted-by=" parameter is copied into MAY include a 'geolocation' option tag in the "inserter=" parameter Supported header
field of
the locationErrorValue generated by the Location Recipient (the
UAS), in a response, when indicating it wants to inform the does understand this extension,
even if location
"inserter=" entity there was not included in a problem with request to the UAS.

A UAS wishing to dereference an location it
received.

There can be more than one locationValues URI contained in a request. The
"inserter=" parameter received
request will use the 'presence' event package in a SUBSCRIBE request
to the locationErrorValue URI. If accepted, the LS will distinguish it
from being misunderstood by entities that did not insert return the errored
location. PIDF-LO to the UAS
in a NOTIFY request. If there is one valid locationValue are any errors during dereferencing,
or in a request, even if all the
others have errors with them, a 424 (Bad Location Information)
response MUST NOT be sent. The Location Recipient (the UAS) is
RECOMMENDED PIDF-LO itself, the UAS will respond to send the original
request with a locationErrorValue for each errored
locationValue, indicating what the UAS concluded
was wrong with unique "inserter=" parameters to make sure the
right entities know which locations were in error.

As hinted at, a location "inserter=" can be a UAC or it can be an
in-signaling-path SIP server, who is acting as a UAC locator. location. This
means the SIP server is including its version of where it thinks the
UAC is, geographically. This "inserter=" has to be in the form of
an LbyR include any dereferencing
problems encountered.

Dereferencing for sip:, sips: and pres: URI in a locationValue, because SIP servers schemes are not allowed
mandatory-to-implement.

A UAS MUST be prepared to insert message bodies, as of the time of this publication, receive subsequent location updates from
all
the way back to RFC3261.

Each locationErrorValue has an error code, letting UAC, either LbyV or LbyR (regardless of how the UAS received
location previously from this UAC). The UAC will convey updated
location
"inserter=" entity know what was wrong with using the location supplied.
See Section 4.3 for UPDATE [RFC3311] method to the 5 actionable responses UAS, and not a UAC can take from
reINVITE. The UAS MUST NOT reject updated location arriving in a locationErrorValue.
reINVITE though, as other dialog parameters might be changing also
(in which a reINVITE is appropriate).

If the there is more than one location "inserted-by=" entity, meaning either the UAC (any combination of LbyV and
LbyR), this document does not give guidance about what a Location
Recipient does with each location. There are no priority or
proxy
more-trusted indications specified by this document. All this is
considered application-specific, and out-of-scope for this document.
If more than one location is present in the message path, chose to indicate that PIDF-LO, location was so
important
elements in the request same PIDF-LO MUST apply to include a 'geolocation' option tag the same Target
(identified in a
Require header, the response SHOULD be a 424 (Bad Location
Information) back to "entity=" attribute) and point at the "inserter=" entity (knowing same
position on the response
will ultimately go to earth. If there is more than one PIDF-LO with
different Target identifiers, then the UAC regardless) if is merely telling the UAS
where more than one Target is, and there needs to should not be any conflict.

Within any PIDF-LO, there is a
locationErrorValue sent because <retransmission-allowed> policy
element that can be set to "yes" or "no". These are the only
possibilities. If Alice conveys her location was bad. Only entities
identified in a locationErrorValue as the "inserter=" entity will
pay attention to Bob (as has been
described throughout this locationErrorValue. All other entities document) with a <retransmission-allowed>
element set to "no", then Bob MUST
ignore NOT inform any locationErrorValue not directed towards them. See
section 4.3 for more information on this, including all other element
where Alice is. If the location
specific errors and Geolocation-Error header parameters.

In <retransmission-allowed> element is set to
"yes", then Bob can inform other elements where Alice is, but only
as long as the above scenario ('geolocation' option tag <retention-expiry> policy element, also in a Require
header), the only other response can be
PIDF-LO, allows [RFC4119]. As a 420, but only byproduct of this, that means that
if Alice conveys her location to Bob with a <retransmission-allowed>
element set to "yes", and the UAS <retention-expiry> time does not support this Geolocation extension
require Bob to SIP, delete Alice's location yet, then Bob is free to tell
anyone else where Alice is. The entity= attribute in the 424 <presence>
element identifies who is
sent.

If the location "inserted-by=" entity placed target of each location, preventing
confusion. Whenever Bob conveys Alice's location,
<retention-expiry> timer MUST be maintained as is (i.e., not changed
from when Bob received it). RFC 4119 implicitly allows this
behavior, and the 'geolocation'
option tag in a Supported header, behavior does not change when SIP is the response can be Using
Protocol.

6.2.1 UAS Generating a 424 if it
chooses, but also can be any other SIP response, including Location Failure Indication

If a 200
OK. A locationErrorValue UAS receives location in a Geolocation-Error header that request, but determines there is not
in a 424 (Bad Location Information) response is considered
informational by the Location Recipient, and not considered
important enough to reject
problem with the request based solely on bad location
information.

For example, Alice INVITEs Bob in the request, it is the responsibility
of the UAS to a dialog, and includes geolocation
in inform the entity that inserted the problematic
location into that request. Bob can accept The Geolocation header field in the INVITE with a 200 OK and still
add
request has a locationErrorValue in locationValue, providing the 200 OK UAS a location URI
indicating "yes, I accept
your request, and btw, something was wrong with where the Target's location you
provided (in is. The Location Target
identified in the INVITE)". What was wrong with PIDF-LO may or may not be the location is
indicated by inserter,
or the Geolocation-Error code. Who this
locationErrorValue is for is indicated by generator of the "inserter=" parameter.

Each locationErrorValue request. Ultimately, location is destined for one "inserter=" entity.
This gives in a Location Recipient one mechanism to tell each inserter
what
PIDF-LO. This is either in the request as a message body (LbyV), or
obtained by initiating a dereference transaction on a Location Recipient concluded was wrong with what
Server identified in the
"inserter=" included (as far as location is concerned). Therefore,

o there MUST be URI. Location Servers typically
challenge all dereference requests. All PIDF-LOs have a locationErrorValue for each Location
Target identifier. The "inserted-by=" parameter of the
locationValue that
was considered bad by tells the UAS to ensure each upstream location
inserter understands which error code(s) SIP entity inserted that
locationValue. This "inserted-by=" parameter is intended for them
(and which to ignore).

o there MUST NOT be more than one copied into the
"inserter=" parameter of the locationErrorValue in generated by the
response per locationValue
Location Recipient (the UAS), in a response, when it wants to inform
the request.

o location "inserter=" entity there MUST NOT was a problem with the
location it received.

There can be more than one locationErrorValue to the same locationValue in a request. The
"inserter=" parameter in the request.

o there MUST NOT be a locationErrorValue in will prevent
entities that did not insert the response for a errored location from
misunderstanding whether the locationErrorValue applies to them.

If there is one valid locationValue in a request, even if all the request that was not in error, according to
others have errors with them, the Location Recipient.

Here is an example of Recipient MUST NOT send a Geolocation-Error header

Geolocation-Error: 400; code="Permission Necessary";
node="server42.example2.com";
inserter="alice.example.com";
424 (Bad Location Information) response. The above example says that the Location Recipient is
server42.example.com, and this entity believes it cannot route this
message without knowing
(the UAS) MUST send a locationErrorValue for each errored
locationValue, with unique "inserter=" parameters to make sure the "inserter="'s location. This
right entities know which locations were in error.

As hinted at, a location
may "inserter=" can be in the request, a UAC or it may need can be an
in-signaling-path SIP server acting as a UAC locator. This
means the SIP server is including its version of where it thinks the
UAC is, geographically. This "inserter=" has to be in the request and form of
an dereferencable location URI in a locationValue, because SIP
servers are not allowed to insert message bodies.

Each locationErrorValue has an error code, letting the location
"inserter=" entity know what was
not. wrong with the location supplied by
that entity. See Section 4.3 for the 5 actionable responses a UAC
can take from a locationErrorValue.

If the location is encrypted, server42 doesn't know it is "inserted-by=" entity, meaning either the UAC or
proxy in the message path chose to indicate that location was
sufficiently important to include a 'geolocation' option tag in the
request. server42.example.com sends a
Require header field, any error response SHOULD be a 424 (Bad
Location Information) response with a locationErrorValue indicating a 400
location error, which means it requires permission back to view Alice's
location the "inserter=" entity (knowing the
response will ultimately go to proceed with processing her signaling. Section 4.3
highlights this example, stating the user, Alice, MUST be made aware
of this location revelation request. This document does not give
any guidance how Alice is UAC regardless) if there needs to
be informed (i.e., audio, visual,
etc). Alice can grant permission or choose not to, knowing this SIP
request attempt (to this destination, at this time) will fail. The
problem could be corrected if a future SIP request were good locationValue sent to travel
through properly process the request. Only
entities identified in a different server than server42 (or it might not). locationErrorValue as the "inserter="
entity will pay attention to this locationErrorValue. All other
entities MUST ignore any locationErrorValue not directed towards
them. See Section section 4.3 for further rules about more information on this, including all
the location-specific errors and Geolocation-Error header
and field
parameters.

In the locationErrorValue.

This document says nothing about what above scenario ('geolocation' option tag in a Location Recipient Require
header field), the only other response can be a 420, if the UAS
does with
more than one 'good' locationValue not support this Geolocation extension to SIP.

If the "inserted-by=" location entity placed the 'geolocation'
option tag in a request (i.e., which to
choose to use). This scenario MAY Supported header field, the response can be addressed a 424 if
it chooses, but also can be any other SIP response, including a 200
OK. A locationErrorValue in a future effort.

Further, more than one error code Geolocation-Error header field that
is allowed not in a 424 (Bad Location Information) response is considered
informational by the
locationErrorValue - each having one "inserter=" parameter. The
error codes destined for the same inserter MUST NOT contradict the
meaning of the problem Location Recipient, and does not cause the
Location Recipient had with a particular
locationValue.

6.3 Proxy Behavior

[RFC3261] states message bodies cannot be added by proxies.
However, proxies are permitted to add a header reject the request solely because of bad
location information.

For example, Alice INVITEs Bob to a dialog, and includes geolocation
in the request. This
implies that a proxy Bob can accept the INVITE with a 200 OK and still
add a Geolocation locationValue locationErrorValue in the 200 OK indicating "yes, I accept
your request, and btw, something was wrong with
LbyR URI, but not LbyV message body.

It is allowed, but NOT RECOMMENDED, for more than one SIP element to
insert the location into a request along its path. As described earlier you
provided in this document, each insertion of the INVITE". The specific problem with the location into a SIP request is
accompanied
indicated by the Geolocation-Error code. The "inserter=" parameter
identifies the Location Inserter this locationErrorValue is intended
for.

Each locationErrorValue is destined for one "inserter=" entity.
This gives a new locationValue in Location Recipient a Geolocation header. Also
described earlier, each locationValue MUST contain an "inserted-by="
value indicating mechanism to a tell each inserter
what the Location Recipient which host inserted
location into a particular request.

However, if concluded was wrong with the location is already in a SIP request,
the "inserter=" entity included. Therefore,

o there MUST be a SIP server
SHOULD NOT add another LbyR locationErrorValue for each locationValue that identifies
was considered bad by the same target UAS to ensure each upstream location
inserter understands which error code is intended for the
inserter (and which to ignore).

o there MUST NOT be more than one locationErrorValue in the
PIDF-LO (in
response per locationValue in the <dm:device id> element) to request.

o there MUST NOT be more than one locationErrorValue with the same
"inserter=" entity in the request. This
will likely cause confusion at

o there MUST NOT be a locationErrorValue in the Location Recipient as to which to
use.

A proxy is permitted to read any locationValue, and response for a
locationValue in the associated
body, if request that was not S/MIME protected, in transit if present, and can use error, according to
the contents Location Recipient.

Here is an example of the a Geolocation-Error header field to make location-based retargeting
decisions, if retargeting requests based on location is a function
of

Geolocation-Error: 201; code="Linkable Target Identity Required";
node="server42.example.com";
inserter="alice.example.com";

The above example says that proxy. Retargeting is defined in [RFC3261]. However, if the Geolocation header parameter "routing-allowed" Location Recipient is present
server42.example.com, and
set to "no", or is not present (knowing the default behavior is "no"
if not present, with or without a Geolocation header), SIP servers
MUST NOT view the contents of this entity cannot verify the LbyV message body. Further, SIP
servers MUST NOT attempt to dereference an LbyR. Target's
identity within this message. This is because typically needed in order to
make routing decisions for the SIP request, likely request where the entity=
attribute has an unlinkable pseudonym obscuring a location target's
identity from the originating UAC, did signaling. This is not give the
SIP server permission desire because if Alice's
message is to view be routed based on the location within in the SIP request.
How a SIP server indicates it requires permission to view a
request's location in order request,
server42 has to properly process verify that this request is in
section 6.3.2.

If the Geolocation header parameter "routing-allowed" Alice's location. The
appropriate action is present in to send a SIP request, the value MUST NOT be changed during processing of
the request. If 424 (Bad Location Information)
response with the Geolocation above (201) Geolocation-Error header parameter "routing-allowed"
is value. We do
not present, SIP servers are to treat the location within the want Alice's request as if routed based on Bob's location.

See Section 4.3 for further rules about the Geolocation-Error header parameter "routing-allowed" were present
and set to "no".

In the spirit of informing implementers of B2BUAs
field and SBCs, each
server type really should adhere to the above proxy guidance locationErrorValue.

This document says nothing about what a Location Recipient does with
respect
more than one 'good' locationValue in a request (i.e., which to
choose to use). This scenario MAY be addressed in a future effort.

Further, more than one error code is allowed in the "Routing-allowed" header parameter, understanding
that there are no IETF police, and the specific behaviors of these
types of SIP servers
locationErrorValue - each having one "inserter=" parameter.

6.3 Proxy Behavior

[RFC3261] states message bodies cannot presently be defined. In other words, if
the particular type of SIP server mentioned here is added by proxies.
However, proxies are permitted to add a header field to a request.
This means that a proxy can add a Geolocation locationValue header
field with a dereferencable location URI, but not the ultimate
destination of this a LbyV message
body.

It is allowed, but NOT RECOMMENDED, for more than one SIP element to
insert location into a request and supports along its path. As described earlier
in this SIP extension, document, each policy rule within the Geolocation header needs to remain
intact and unchanged.

No type insertion of location into a SIP server can delete request is
accompanied by a "Routing-allowed" new locationValue in a Geolocation header
parameter, but if one field.
Also described earlier, each locationValue MUST contain an
"inserted-by=" value indicating to a Location Recipient the host
that inserted a specific location into a particular request.

If, however, location is not yet present, any already in a SIP request, a SIP server MAY
SHOULD NOT add a
"Routing-allowed" header parameter with another location URI that identifies the value set same target
in the PIDF-LO (in the entity= attribute) to "no" only. the same request. This
will likely cause confusion at the Location Recipient as to which to
use.

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, header field, which would be a
local policy decision, the new locationValue MUST be added to the
end of the header field (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. header field.

A proxy wishing to dereference an LbyR a location URI contained in a
received request will use the 'presence' event package in a
SUBSCRIBE request to the URI. If accepted, the PIDF-LO LS will return the
PIDF-LO to the proxy in a NOTIFY request. If there are any errors
during dereferencing, or in the PIDF-LO itself, the proxy will send
an 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.

6.3.1 Proxy Behavior with Geolocation Header Field Parameters

SIP servers MUST NOT delete any existing Geolocation locationValue
(URI or header field parameter) from a request. An existing
locationValue
(URI or header parameter) MAY only be modified 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

According to this specification, the default value of any
Geolocation header value "routing-allowed" is "no". This parameter
does not have to be present to deny SIP servers along the signaling
path the ability to view the target's location. This parameter MAY
be added in transit by a SIP server, and MUST be with a value of
"no". Other modifications of the 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,
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 the proxy can make no other modification.

A SIP server MAY add a new Geolocation locationValue to a SIP
request. The proxy server SHOULD NOT insert a locationValue of a Location Target
unless it is reasonably certain it knows the actual geographic
location of the Location Target, for Target (for example, if it thoroughly
understands the topology of the underlying access network and it can
identify the device reliably (in location reliably, even in the presence of, for example, of NAT
or VPN). Routing errors are likely if the SIP server inserts an
incorrect locationValue.

A server adding a locationValue added to an existing Geolocation header field
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"
<sips:3sdefrhy2jj7@ls7.atlanta.example.com>;
inserted-by="ls7.atlanta.example.com"

Notice the locationValue added by the proxy "ls7" is last among
locationValues. This practice Proxies MUST be done for add locationValue at the end of all added
locationValues.
locationValues that are already present in the request.

If this request was then retargeted by an intermediary using the
locationValue inserted by the server, server "ls7", 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";
<sips:3sdefrhy2jj7@ls7.atlanta.example.com>;
inserted-by="ls7.atlanta.example.com"; used-for-routing

It is conceivable that an initial routing decision is made on
one locationValue, and subsequently another routing decision is
made on a different locationValue further towards the ultimate
destination. This retargeting decision can be made on a newly
inserted locationValue. While unusual, newly
inserted locationValue. While unusual, it can occur. In such a
case, proxies MUST NOT remove any existing "used-for-routing" header
field parameter. In this instance, the SIP server retargeting based
on another locationValue MUST add the "used-for-routing" header
field parameter to the locationValue used for retargeting by this
server. This will result in a Geolocation header field indicating
that the request has been retargeted more than once, which is
allowed.

A Proxy that inserts or adds locationValue into a request MAY move a
'geolocation' option tag that is in a Supported header field into a
Require header field if this proxy deems geolocation to be
sufficiently important to Location Recipient(s) of this request.

A proxy can read any locationValue present, and the associated body,
if not S/MIME protected, and can 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. Retargeting
is defined in [RFC3261]. However, if the Geolocation header field
parameter "routing-allowed" is present and set to "no", or is not
present (the default behavior is "no" if "routing-allowed" is not
present, whether or not a Geolocation header field is present), SIP
servers MUST NOT view the contents of the location message body.
Further, SIP servers MUST NOT attempt to dereference a location URI.
This is because the Location Inserter (likely the originating UAC)
did not give the SIP server permission to view the location within
the SIP request. How a SIP server indicates it can occur. In such requires permission
to view a
case, proxies request's location in order to properly process this
request is described in section 6.3.2.

If the Geolocation header field parameter "routing-allowed" is
present in a SIP request, the value MUST NOT remove any existing "used-for-routing" header
parameter. In this instance, be changed during
processing of the request. If the Geolocation header field
parameter "routing-allowed" is not present, SIP server retargeting based on
another locationValue servers MUST add treat
the location within the request as if the "used-for-routing" header field parameter
"routing-allowed" were present and set to "no".

B2BUAs and SBCs should also adhere to the locationValue used for retargeting by this server.
This will result in a Geolocation above proxy guidance with
respect to the "Routing-allowed" header looking as field parameter. In other
words, if it were
retargeting more than once, which would be true - the particular type of SIP server mentioned here supports
this SIP extension and is not the desired
outcome.

A Proxy that inserts or adds locationValue into a request MAY move a
'geolocation' option that is in a Supported ultimate destination of this SIP
request, each policy rule within the Geolocation header into field MUST
remain intact and unchanged.

No SIP server can delete a Require "Routing-allowed" header field
parameter, but if this proxy deems geolocation to be that important one is not yet present, any SIP server MAY add a
"Routing-allowed" header field parameter with the value set to
Location Recipient(s) of this request. "no"
only.

6.3.2 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 6.2.1.), 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 sections be
inconsistent. 6.2.1.).
The one thing point to add is that a proxy does not need to examine
location contained in a request. Section 6.2.1. only applies to
proxies that are needing, monitoring need to monitor or policing police location within requests (for
whatever reason).

If a proxy inserted a locationValue into a request, it SHOULD MUST 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 6.1.1.) that
included a locationValue a request, which then receives an error to
that locationValue.

This location inserting location-inserting proxy SHOULD be (at least) transaction
stateful for the response. If the proxy is configured as a
stateless proxy, and it inserts location, it MUST process and
monitor all SIP responses, looking for locationErrorValues that
indicate it was the "inserter=" to learn that the location it
supplied was in error. It SHOULD react
accordingly according to the error code
received. This document gives no guidance what the proxy should do
to rectify the bad location information, since the proxy is not the
SIP response destination, but a future document MAY could address this.

The "routing-allowed" parameter's purpose is to indicate if SIP
servers along the signaling path should bother looking at the LbyV
location message body or dereferencing the LbyR. location URI. There are
two values specified here for this parameter: "yes" and "no". If
the "routing-allowed" parameter is set to "yes", and the SIP server
determines this SIP request
needs to should be routed based on the location of the target's
location, this parameter gives the server permission to look at the location
(or dereference it). If
location (or dereference it). If this parameter is set to "no",
then the SIP server MUST NOT view the location message body or
dereference the location URI within this SIP request. If the SIP
server believes it cannot process this message properly because it
needs to learn the target's location in order to route the message,
then it MUST return a 424 (Bad Location Information) response,
indicating it requires permission (error code 400) to view the
location.

Here is an example of a Geolocation-Error header field

Geolocation-Error: 400; code="Permission to Reveal Location
Information to a Third Party";
node="server42.example.com";
inserter="alice.example.com";

The above example says that the Location Recipient is
server42.example.com, and this entity believes it cannot route this
message without knowing permission to view the Target's location.
Regardless of whether there is a Geolocation header value parameter,
such as

routing-allowed=no

or this parameter is not present in the SIP request (as shown 400
error example above). The default behavior is to act as if the
parameter is present and set to "no". Server42 MUST get permission
to view the Target's location by reading a routing-allowed header
parameter saying "yes", otherwise a 400 error is sent back to the
inserter= entity to get permission.

Section 4.3 highlights this example, stating the user, Alice, MUST
be made aware of this parameter location revelation request. This document
does not give any guidance how Alice is set to "no", then the SIP
server MUST NOT view the LbyV be informed (i.e., audio,
visual, etc). Alice can grant permission or dereference the LbyR within choose not to, knowing
this SIP request. If the SIP server believes it cannot process request attempt (to this
message properly because it needs to learn the target's location in
order destination, at this time) will
fail. The problem might not recur if a future SIP request were to route the message, then it MUST return
travel through a 424 (Bad Location)
response, indicating different server than server42 (or it requires permission (error code 400) to view
the location. might again).

7. Geopriv Privacy Considerations

Location information is considered by most to be highly
sensitive information, requiring protection from eavesdropping,
and altering in transit. [RFC3693] articulates rules to
be followed by any protocol wishing to be considered a "Using
Protocol", specifying how a transport protocol meets 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.

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 be large. Normal
RFC 3261 procedures of reverting to TCP when the MTU size is
exceeded would be invoked.

8. 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 (although 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 LbyV 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 user. This
extension is especially sensitive. That said, there is the ability,
according to [RFC3693] to have an anonymous identity for the
target's location. This is accomplished by use of an unlinkable
pseudonym in the entity= attribute of the <presence> element
[RFC4479]. Though, this can be problematic for routing messages
based on location (covered several times in the document above).

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
unable to meet this requirement, alert users, 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

This SIP extension offers the default ability to require permission
to view location while the SIP request is such that in transit. The default
for this is set to "no", and there is an error explicitly describing
how an intermediary asks for permission to view the Target's
location.

Because target locations can be placed on a remote server, called a
Location Server accessible with the possession of a URI. The
concept of an LbyR location URI,
this URI has its own security considerations. It is tempting to
assume that the dereference of this URI 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 a target's 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 of 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 specification does not constrain the dereference protocol
to use TLS. That specification is left entirely to the dereferencing
protocol documents.

There is no end-to-end integrity on any locationValue or
locationErrorValue header field parameter end-to-end (or middle-to-end if the
value was inserted by a intermediary), so recipients of either
header field need to implicitly trust the header field contents, and
take whatever precautions each entity deems appropriate give these facts. given this
situation. Any idea of using SIP Identity is lost as soon as it is
realized that the Geolocation header value can be added to by
intermediaries in the signaling path.

9. 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).

[Editor's Note: RFC-Editor - within the IANA section, please
replace "this doc" with the assigned RFC number,
if this document reaches publication.]

9.1 IANA Registration for the SIP Geolocation Header Field

The SIP Geolocation header Header Field is created by this document, with
its definition and rules in Section 4.1 of this document, to and should
be added to the sip-parameters, IANA sip-parameters registry, in the portion titled
"Header Field Parameters and Parameter Values".

Predefined
Header Field Parameter Name Values Reference
---------------- ------------------- ---------- ---------
Geolocation inserted-by= no [this doc]
Geolocation used-for-routing yes [this doc]
Geolocation routing-allowed yes [this doc]

9.2 IANA Registration for New SIP Option Tag

The SIP option tag "geolocation" is created by this document, with
the definition and rule in Section 4.4 of this document, to be added
to the IANA sip-parameters within IANA. registry.

9.3 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 4.2 of this document.

9.4 IANA Registration of New Geolocation-Error Header Field

The SIP Geolocation-error header field is created by this document,
with its definition and rules in Section 4.3 of this document, to be
added to the sip-parameters, IANA sip-parameters registry, in the portion titled
"Header Field Parameters and Parameter Values".

Predefined
Header Field Parameter Name Values Reference
----------------- ------------------- ---------- ---------
Geolocation-Error inserter= no [this doc]
Geolocation-Error node= no [this doc]
Geolocation-Error code= no yes* [this doc]
* see section 9.5 for the newly created values.

9.5 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 in the IANA sip-parameters within
IANA.
registry. Details of these error codes are in Section 4.3 of this
document.

Geolocation-Error codes
-----------------------
Geolocation-Error codes provide reason for the error discovered by
Location Recipients, categorized by action to be taken by error
recipient to be placed into SIP responses to inform the location
inserter of the error.

Code Description Reference
---- --------------------------------------------------- ---------
100 "Cannot Process Location" General location error, [this doc]
meaning location in the request cannot be
processed at this time. No actionable guidance.
Can be treated as a 200 or 300 error by error
recipient.

200 "Retry Location Later" (with Later with same data) Location data" The location [this doc]
cannot be processed at this time. Error recipient
should try again with same data.

201 "Linkable Target Identity Required" [this doc]
Target's identity cannot be unlinkable within
the presence element's entity= attribute. This
is necessary for routing SIP requests based
on Target's location (and some other entity's).

300 "Retry Location Later" (with Later with device updated location) location" [this doc]
Location cannot be processed at this time. Error
recipient should try again with same data.

400 "Permission Necessary" To Reveal Location Information to a Third Party"
Permission from calling user [this doc] to reveal location [this doc]
in request before request can be processed. This
is a routing by location error. User MUST be
informed of permission request.

500 "Location Information Denial" Request was actively [this doc]
denied because of the location in the request.
Recipient should not try again.

9.6 IANA Registration of LbyR Location URI Schemes

This document directs IANA to create a new set of parameters in a
separate location from SIP and Geopriv, called the "Location
Reference URI" registry, containing the URI scheme, the
Content-Type, and the reference. Below is an example of how it
could look reference, as follows:

URI Scheme Content-Type Reference
---------- ------------ ---------
SIP: [this doc]
SIPS: [this doc]
PRES: [this doc]

Additions to this registry require an industry specification. must be defined in a permanent and
readily available specification (this is the "Specification
Required" IANA policy defined in [RFC5226])..

10. 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, Ted Hardie, Shida Shubert, Umesh Sharma, Richard
Barnes, Dan Wing, Matt Lepinski and Jacqueline Lee for constructive
feedback and nits checking.

A special

Special thanks to Paul Kyzivat for his help with the ABNF in this
document, to Dan Wing for help with the S/MIME example,
document and to Robert Sparks for many helpful comments and the
proper building construction of the Geolocation-Error header. header field.

And finally, to Spencer Dawkins for giving this doc a good scrubbing
to make it more readable.

11. References

11.1 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
[RFC2392] E. Levinson, " Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, 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

[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., 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.

[RFC3515] R. Sparks, "The Session Initiation Protocol (SIP) Refer
[RFC3903] Niemi, A., A, "Session Initiation Protocol (SIP) Extension
for Event State Publication", RFC 3903, October 2004.

[RFC5234] Crocker, D., Ed., and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234, January 2008.

[IANA-civic] http://www.iana.org/assignments/civic-address-types-
Registry

[RFC5491] J. Winterbottom, M. Thomson,

[RFC5226] T. Narten, H. Tschofenig, "GEOPRIV PIDF-LO
Usage Clarification, Considerations, and Recommendations ", Alvestrand, "Guidelines for Writing an IANA
[RFC4479] J. Rosenberg, "A Data Model for Presence", RFC 4479, July
2006

11.2 References - Informative

[RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
"Geopriv Requirements", RFC 3693, February 2004

[RFC4483] E. Berger, "A Mechanism for Content Indirection in SIP", RFC
[RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
[RFC4776] H. Schulzrinne, " Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
Information ", RFC 4776, October 2006

[ID-PHONE] B. Rosen, J. Polk, "ECRIT Phone BCP",
Author Information

James Polk
Cisco Systems
3913 Treemont Circle
Colleyville, Texas 76034

33.00111N
96.68142W

Phone: +1-817-271-3552
Email: jmpolk@cisco.com

Brian Rosen
NeuStar, Inc.
470 Conrad Dr.
Mars, PA 16046

40.70497N
80.01252W

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 If a motivational statement below each requirements that
requirement is not obvious in intent intent, a motivational statement is
included below it.

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 to guarantee 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 if 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 If location having has been conveyed, and the UA
moves, it needs a means the UAC must be able to update the location previously
conveyed to
party of this location change. other parties.

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 [RFC4119] is a mandatory to implement format for
location conveyance within SIP, whether included LbyV or
LbyR.

Motivation: interoperability with other IETF location protocols and
mechanisms
Mechanisms.

UAC-9 There must be a mechanism for the UAC to request the UAS send
its location 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
happen because the UAC does not implement this extension, or it can
be that
because the UAC implements the extension, but does not know
where it the Target is. This may be, for example, due to the
failure of the access network to provide a location
acquisition
mechanisms mechanism the UAC understands. supports. 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 also apply to the UAS 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
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 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.