Location Conveyance for the Session Initiation Protocol
draft-ietf-sipcore-location-conveyance-09
The information below is for an old version of the document that is already published as an RFC.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 6442.
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|---|---|---|---|
| Authors | Jon Peterson , James Polk , Brian Rosen | ||
| Last updated | 2020-01-21 (Latest revision 2011-09-04) | ||
| Replaces | draft-ietf-sip-location-conveyance | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
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| IESG | IESG state | Became RFC 6442 (Proposed Standard) | |
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| Responsible AD | Robert Sparks | ||
| IESG note | ** No value found for 'doc.notedoc.note' ** | ||
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draft-ietf-sipcore-location-conveyance-09
Network Working Group James Polk
Internet Draft Cisco Systems
Expires: Mar 4, 2012 Brian Rosen
Intended Status: Standards Track (PS) Jon Peterson
NeuStar
Sept 4, 2011
Location Conveyance for the Session Initiation Protocol
draft-ietf-sipcore-location-conveyance-09.txt
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 SIP extension covers
end-to-end conveyance as well as location-based routing, where SIP
intermediaries make routing decisions based upon the location of the
Location Target.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six
months and may be updated, replaced, or obsoleted by other documents
at any time. It is inappropriate to use Internet-Drafts as
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on Mar 4, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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publication of this document. Please review these documents
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Without obtaining an adequate license from the person(s) controlling
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than English.
Table of Contents
1. Conventions and Terminology used in this document . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview of SIP Location Conveyance . . . . . . . . . . . . . 4
3.1 Location Conveyed by Value . . . . . . . . . . . . . . . 4
3.2 Location Conveyed as a Location URI . . . . . . . . . . . 5
3.3 Location Conveyed though a SIP Intermediary . . . . . . . 5
3.4 SIP Intermediary Replacing Bad Location . . . . . . . . . 7
4. SIP Modifications for Geolocation Conveyance . . . . . . . . 8
4.1 The Geolocation Header Field . . . . . . . . . . . . . . 8
4.2 The Geolocation-Routing Header Field . . . . . . . . . . 10
4.2.1 Explaining Geolocation-Routing header-value States . . 11
4.3 424 (Bad Location Information) Response Code . . . . . . 13
4.4 The Geolocation-Error Header Field . . . . . . . . . . . 14
4.5 Location URIs in Message Bodies . . . . . . . . . . . . . 17
4.6 Location Profile Negotiation . . . . . . . . . . . . . . 17
5. Geolocation Examples . . . . . . . . . . . . . . . . . . . . 18
5.1 Location-by-value (Coordinate Format) . . . . . . . . . . 18
5.2 Two Locations Composed in Same Location Object Example . 20
6. Geopriv Privacy Considerations . . . . . . . . . . . . . . . 22
7. Security Considerations . . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . 24
8.1 IANA Registration for New SIP Geolocation Header Field . 24
8.2 IANA Registration for New SIP Geolocation-Routing Header
Field . . . . . . . . . . . . . . . . . . . . . . . . . . 24
8.3 IANA Registration for New SIP Option Tags . . . . . . . . 25
8.4 IANA Registration for New 424 Response Code . . . . . . . 25
8.5 IANA Registration for New SIP Geolocation-Error Header
Field . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.6 IANA Registration for New SIP Geolocation-Error Codes . . 26
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
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10. References . . . . . . . . . . . . . . . . . . . . . . . . . 27
10.1 Normative References . . . . . . . . . . . . . . . . . 27
10.2 Informative References . . . . . . . . . . . . . . . . . 28
Author Information . . . . . . . . . . . . . . . . . . . . . 29
Appendix A. Requirements for SIP Location Conveyance . . . . 29
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]. This document furthermore uses numerous terms defined
in RFC 3693 [RFC3693], including Location Object, Location
Recipient, Location Server, Target, Rulemaker and Using Protocol.
2. Introduction
Session Initiation Protocol (SIP) [RFC3261] creates, modifies and
terminates multimedia sessions. SIP carries certain information
related to a session while establishing or maintaining calls. This
document defines how SIP conveys geographic location information of
a Target to a Location Recipient (LR). SIP acts as a Using Protocol
of location information, as defined in RFC 3693.
In order to convey location information, this document specifies
three new SIP header fields, Geolocation, Geolocation-Routing and
Geolocation-Error, which carry a reference to a Location Object
(LO), grant permission to route a SIP request based on the
location-value and provide error notifications specific to location
errors respectively. The Location Object (LO) may appear in a MIME
body attached to the SIP request, or it may be a remote resource in
the network.
A Target is an entity whose location is being conveyed, per RFC
3693. Thus, a Target could be a SIP user agent (UA), some other IP
device (a router or a PC) that does not have a SIP stack, a non-IP
device (a person or a black phone) or even a non-communications
device (a building or store front). In no way does this document
assume that the SIP user agent client which sends a request
containing a location object is necessarily the Target. The location
of a Target conveyed within SIP typically corresponds to that of a
device controlled by the Target, for example, a mobile phone, but
such devices can be separated from their owners, and moreover, in
some cases the user agent may not know its own location.
In the SIP context, a location recipient will most likely be a SIP
UA, but due to the mediated nature of SIP architectures, location
information conveyed by a single SIP request may have multiple
recipients, as any SIP proxy server in the signaling path that
inspects the location of the Target must also be considered a
Location Recipient. In presence-like architectures, an intermediary
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that receives publications of location information and distributes
them to watchers acts as a Location Server per RFC 3693. This
location conveyance mechanism can also be used to deliver URIs
pointing to such Location Servers where prospective Location
Recipients can request Location Objects.
3. Overview of SIP Location Conveyance
An operational overview of SIP location conveyance can be shown in 4
basic diagrams, with most applications falling under one of the
following basic use cases. Each is separated into its own subsection
here in section 3.
Each diagram has Alice and Bob as UAs. Alice is the Target, and Bob
is an LR. A SIP intermediary appears in some of the diagrams. Any
SIP entity that receives and inspects location information is an LR,
therefore in any of the diagrams the SIP intermediary that receives
a SIP request is potentially an LR - though that does not mean such
an intermediary necessarily has to route the SIP request based on
the location information. In some use cases, location information
passes through the LS on the right of each diagram.
3.1 Location Conveyed by Value
We start with the simplest diagram of Location Conveyance, Alice to
Bob, where no other layer 7 entities are involved.
Alice SIP Intermediary Bob LS
| | | |
| Request w/Location | |
|----------------------------------->| |
| | |
| Response | |
|<-----------------------------------| |
| | | |
Figure 1. Location Conveyed by Value
In Figure 1, Alice is both the Target and the LS that is conveying
her location directly to Bob, who acts as an LR. This conveyance is
point-to-point - it does not pass through any SIP-layer
intermediary. A Location Object appears by-value in the initial SIP
request as a MIME body, and Bob responds to that SIP request as
appropriate. There is a 'Bad Location Information' response code
introduced within this document to specifically inform Alice if she
conveys bad location to Bob (e.g., Bob "cannot parse the location
provided", or "there is not enough location information to determine
where Alice is").
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3.2 Location Conveyed as a Location URI
Here we make Figure 1 a little more complicated by showing a
diagram of indirect Location Conveyance from Alice to Bob, where
Bob's entity has to retrieve the location object from a 3rd party
server.
Alice SIP Intermediary Bob LS
| | | |
| Request w/Location URI | |
|----------------------------------->| |
| | Dereference |
| | Request |
| (To: Location URI) |
| |---------------->|
| | |
| | Dereference |
| | Response |
| (includes location) |
| |<----------------|
| Response | |
|<-----------------------------------| |
| | | |
Figure 2. Location Conveyed as a Location URI
In Figure 2, location is conveyed indirectly, via a Location URI
carried in the SIP request (more of those details later). If Alice
sends Bob this Location URI, Bob will need to dereference the URI -
analogous to Content Indirection [RFC4483] - in order to request the
location information. In general, the LS provides the location value
to Bob instead of Alice directly for conveyance to Bob. From a user
interface perspective, Bob the user won't know that this information
was gathered from an LS indirectly rather than culled from the SIP
request, and practically this does not impact the operation of
location-based applications.
The example given in this section is only illustrative, not
normative. In particular, applications can choose to dereference a
location URI at any time, possibly several times, or potentially not
at all. Applications receiving a Location URI in a SIP transaction
need to be mindful of timers used by different transactions. In
particular, if the means of dereferencing the Location URI might
take longer than the SIP transaction timeout (Timer C for INVITE
transactions, Timer F for non-INVITE transactions), then it needs to
rely on mechanisms other than the transaction's response code to
convey location errors, if returning such errors are necessary.
3.3 Location Conveyed though a SIP Intermediary
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In Figure 3, we introduce the idea of a SIP intermediary into the
example to illustrate the role of proxying in the location
architecture. This intermediary can be a SIP proxy or it can be
a back-to-back-user-agent (B2BUA). In this message flow, the SIP
intermediary could act as a LR, in addition to Bob. The primary use
case for intermediaries consuming location information is
location-based routing. In this case, the intermediary chooses a
next hop for the SIP request by consulting a specialized location
service which selects forwarding destinations based on geographical
location.
Alice SIP Intermediary Bob LS
| | | |
| Request | | |
| w/Location | | |
|--------------->| | |
| | Request | |
| | w/Location | |
| |------------------>| |
| | | |
| | Response | |
| |<------------------| |
| Response | | |
|<---------------| | |
| | | |
Figure 3. Location Conveyed though a SIP Intermediary
However, the most common case will be one in which the SIP
intermediary receives a request with location information (conveyed
either by-value or by-reference) and does not know or care about
Alice's location, or support this extension, and merely passes it on
to Bob. In this case, the intermediary does not act as a Location
Recipient. When the intermediary is not an LR, this use case is the
same as the one described in Section 3.1.
Note that an intermediary does not have to perform location-based
routing in order to be a Location Recipient. It could be the case
that a SIP intermediary which does not perform location-based
routing does care when Alice includes her location; for example,
it could care that the location information is complete or that it
correctly identifies where Alice is. The best example of this is
intermediaries that verify location information for emergency
calling, but it could also be for any location based routing - e.g.,
contacting your favorite local pizza delivery service, making sure
that organization has Alice's proper location in the initial SIP
request.
There is another scenario in which the SIP intermediary cares about
location and is not an LR, one in which the intermediary inserts
another location of the Target, Alice in this case, into the
request, and forwards it. This secondary insertion is generally not
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advisable because downstream SIP entities will not be given any
guidance about which location to believe is better, more reliable,
less prone to error, more granular, worse than the other location or
just plain wrong.
This document takes a "you break it, you bought it" approach to
dealing with second locations placed into a SIP request by an
intermediary entity. That entity becomes completely responsible for
all location within that SIP request (more on this in Section 4).
3.4 SIP Intermediary Replacing Bad Location
If the SIP intermediary rejects the message due to unsuitable
location information, the SIP response will indicate there was 'Bad
Location Information' in the SIP request, and provide a location
specific error code indicating what Alice needs to do to send an
acceptable request (see Figure 4 for this scenario).
Alice SIP Intermediary Bob LS
| | | |
| Request | | |
| w/Location | | |
|--------------->| | |
| | | |
| Rejected | | |
| w/New Location | | |
|<---------------| | |
| | | |
| Request | | |
| w/New Location | | |
|--------------->| | |
| | Request | |
| | w/New Location | |
| |------------------>| |
| | | |
Figure 4. SIP Intermediary Replacing Bad Location
In this last use case, the SIP intermediary wishes to include a
Location Object indicating where it understands Alice to be. Thus,
it needs to inform her user agent what location it will include in
any subsequent SIP request that contains her location. In this
case, the intermediary can reject Alice's request and, through the
SIP response, convey to her the best way to repair the request in
order for the intermediary to accept it.
Overriding location information provided by the user requires a
deployment where an intermediary necessarily knows better than an
end user - after all, it could be that Alice has an on-board GPS,
and the SIP intermediary only knows her nearest cell tower. Which is
more accurate location information? Currently, there is no way to
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tell which entity is more accurate, or which is wrong - for that
matter. This document will not specify how to indicate which
location is more accurate than another.
As an aside, it is not envisioned that any SIP-based emergency
services request (i.e., IP-911, or 112 type of call attempt) will
receive a corrective 'Bad Location Information' response from an
intermediary. Most likely, the SIP intermediary would in that
scenario act as a B2BUA and insert into the request by-value any
appropriate location information for the benefit of Public Safety
Answering Point (PSAP) call centers to expedite call reception by
the emergency services personnel; thereby, minimizing any delay in
call establishment time. The implementation of these specialized
deployments is, however, outside the scope of this document.
4. SIP Extensions for Geolocation Conveyance
The following sections detail the extensions to SIP for location
conveyance.
4.1 The Geolocation Header Field
This document defines "Geolocation" as a new SIP header field
registered by IANA, with the following ABNF [RFC5234]:
message-header /= Geolocation-header ; (message-header from 3261)
Geolocation-header = "Geolocation" HCOLON locationValue
*( COMMA locationValue )
locationValue = LAQUOT locationURI RAQUOT
*(SEMI geoloc-param)
locationURI = sip-URI / sips-URI / pres-URI
/ http-URI / https-URI
/ cid-url ; (from RFC 2392)
/ absoluteURI ; (from RFC 3261)
geoloc-param = generic-param; (from RFC 3261)
HCOLON, COMMA, LAQUOT, RAQUOT, and SEMI are defined in RFC3261
[RFC3261].
sip-URI, sips-URI and absoluteURI are defined according to [RFC3261].
The pres-URI is defined in [RFC3859].
http-URI and https-URI are defined according to [RFC2616] and
[RFC2818], respectively.
The cid-url is defined in [RFC2392] to locate message body parts.
This URI type is present in a SIP request when location is conveyed
as a MIME body in the SIP message.
GEO-URIs [RFC5870] are not appropriate for usage in the SIP
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Geolocation header, because it does not include retention and
re-transmission flags as part of the location information. Other URI
schemes used in the location URI MUST be reviewed against the RFC
3693 [RFC3693] criteria for a Using Protocol. Section 4.6 discusses
how URI schemes are communicated using this SIP extension, and what
to do if a URI scheme is received that cannot be supported.
The generic-param in the definition of locationValue is included as
a mechanism for future extensions that might require parameters.
This document defines no parameters for use with locationValue. If a
Geolocation header field is received that contains generic-params,
each parameter SHOULD be ignored, and SHOULD NOT be removed when
forwarding the locationValue. If a need arises to define parameters
for use with locationValue, a revision/extension to this document is
required.
The Geolocation header field MUST have at least one locationValue.
A SIP intermediary SHOULD NOT add location to a SIP request that
already contains location. This will quite often lead to confusion
within LRs. However, if a SIP intermediary adds location, even if
location was not previously present in a SIP request, that SIP
intermediary is fully responsible for addressing the concerns of any
424 (Bad Location Information) SIP response it receives about this
location addition, and MUST NOT pass on (upstream) the 424 response.
A SIP intermediary that adds a locationValue MUST position the new
locationValue as the last locationValue within the Geolocation
header field of the SIP request.
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 [RFC6086],
MESSAGE [RFC3428], REFER [RFC3515],
SUBSCRIBE [RFC3265], NOTIFY [RFC3265],
PUBLISH [RFC3903]
The Geolocation header field MAY be included in any one of the
above listed requests by a UA, and a 424 response to any one of the
requests sent above. Fully appreciating the caveats/warnings
mentioned above, a SIP intermediary MAY add the Geolocation header
field.
A SIP intermediary MAY add a Geolocation header field if one is not
present - for example, when a user agent does not support the
Geolocation mechanism but their outbound proxy does and knows the
Target's location, or any of a number of other use cases (see
Section 3).
The Geolocation header field MAY be present in a SIP request or
response without the presence of a Geolocation-Routing header
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(defined in Section 4.2). As stated in Section 4.2, the default
value of Geolocation-Routing header-value is "no", meaning SIP
intermediaries MUST NOT view (i.e., process, inspect or actively
dereference) any direct or indirect location within this SIP
message. This is for at least two fundamental reasons,
1) to make the possibility of retention of the Target's location
moot (because it was not viewed in the first place); and
2) to prevent a different treatment of this SIP request based on
the contents of the Location Information in the SIP request.
Any locationValue MUST be related to the original Target. This is
equally true for the location information in a SIP response, i.e.,
from a SIP intermediary back to the Target as explained in Section
3.4. SIP intermediaries SHOULD NOT modify or delete any existing
locationValue(s). A use-case in which this would not apply would be
where the SIP intermediary is an anonymizer. The problem with this
scenario is that the geolocation included by the Target then becomes
useless for the purpose or service they wanted to use (include) it
for. For example, 911/emergency calling or finding the nearest
(towing company/pizza delivery/dry cleaning) service(s) will not
yield intended results if the Location Information were to be
modified or deleted from the SIP request.
4.2 The Geolocation-Routing Header Field
This document defines "Geolocation-Routing" as a new SIP header
field registered by IANA, with the following ABNF [RFC5234]:
message-header /= Georouting-header ; (message-header from 3261)
Georouting-header = "Geolocation-Routing" HCOLON
( "yes" / "no" / generic-value )
generic-value = generic-param; (from RFC 3261)
HCOLON is defined in RFC3261 [RFC3261].
The only defined values for the Geolocation-Routing header field are
"yes" or "no". When the value is "yes", the locationValue can be
used for routing decisions along the downstream signaling path by
intermediaries. Values other than "yes" or "no" are permitted for
future extensions. Implementations not aware of an extension MUST
treat any other received value the same as "no".
If no Geolocation-Routing header field is present in a SIP request,
a SIP intermediary MAY insert this header. Without knowledge from a
Rulemaker, the SIP intermediary inserting this header-value SHOULD
NOT set the value to "yes", as this may be more permissive than the
originating party intends. An easy way around this is to have the
Target always insert this header-value as "no".
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When this Geolocation-Routing header-value is set to "no", this
means no locationValue (inserted by the originating UAC or any
intermediary along the signaling path) can be used by any SIP
intermediary to make routing decisions. Intermediaries that attempt
to use the location information for routing purposes in spite of
this counter indication could end up routing the request improperly
as a result. Section 4.4 describes the details on what a routing
intermediary does if it determines it needs to use the location in
the SIP request in order to process the message further. The
practical implication is that when the Geolocation-Routing
header-value is set to "no", if a cid:url is present in the SIP
request, intermediaries MUST NOT view the location (because it is
not for intermediaries to consider when processing the request), and
if a location URI is present, intermediaries MUST NOT dereference
it. UAs are allowed to view location in the SIP request even when
the Geolocation-Routing header-value is set to "no". An LR MUST by
default consider the Geolocation-Routing header-value as set to
"no", with no exceptions, unless the header field value is set to
"yes".
A Geolocation-Routing header-value that is set to "no" has no
special security properties. It is at most a request for behavior
within SIP intermediaries. That said, if the Geolocation-Routing
header-value is set to "no", SIP intermediaries are still to process
the SIP request and send it further downstream within the signaling
path if there are no errors present in this SIP request.
The Geolocation-Routing header field satisfies the recommendations
made in section 3.5 of RFC 5606 [RFC5606] regarding indication of
permission to use location-based routing in SIP.
SIP implementations are advised to pay special attention to the
policy elements for location retransmission and retention described
in RFC 4119.
The Geolocation-Routing header field cannot appear without a
header-value in a SIP request or response (i.e., a null value is not
allowed). The absence of a Geolocation-Routing header-value in a SIP
request is always the same as the following header field:
Geolocation-Routing: no
The Geolocation-Routing header field MAY be present without a
Geolocation header field in the same SIP request. This concept is
further explored in Section 4.2.1.
4.2.1 Explaining Geolocation-Routing header-value States
The Geolocation header field contains a Target's location, and MUST
NOT be present if there is no location information in this SIP
request. The location information is contained in one or more
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locationValues. These locationValues MAY be contained in a single
Geolocation header field, or distributed among multiple Geolocation
header fields. (See section 7.3.1 of RFC3261.)
The Geolocation-Routing header field indicates whether or not SIP
intermediaries can view and then route this SIP request based on the
included (directly or indirectly) location information. The
Geolocation-Routing header field MUST NOT appear more than once in
any SIP request, and MUST NOT lack a header-value. The default or
implied policy of a SIP request that does not have a
Geolocation-Routing header field is the same as if one were present
and the header-value were set to "no".
There are only 3 possible states regarding the Geolocation-Routing
header field
- "no"
- "yes"
- no header-field present in this SIP request
The expected results in each state are:
If the Geolocation-Routing Only possible interpretations:
-------------------------- -----------------------------
"no" SIP intermediaries MUST NOT process
included geolocation information
within this SIP request.
SIP intermediaries inserting a
locationValue into a Geolocation
header field (whether adding to an
existing header-value or inserting the
Geolocation header field for the first
time) MUST NOT modify or delete the
received "no" header-value.
"yes" SIP intermediaries can process
included geolocation information
within this SIP request, and can
change the policy to "no" for
intermediaries further downstream.
Geolocation-Routing absent If a Geolocation header field exists
(meaning a locationValue is already
present), a SIP intermediary MUST
interpret the lack of a
Geolocation-Routing header field as if
there were one present and the
header-value is set to "no".
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If there is no Geolocation header
field in this SIP request, the default
Geolocation-Routing is open and can be
set by a SIP intermediary or not at
all.
4.3 424 (Bad Location Information) Response Code
This SIP extension creates a new location-specific response code,
defined as follows,
424 (Bad Location Information)
The 424 (Bad Location Information) response code is a rejection of
the request due to its location contents, indicating location
information that was malformed or not satisfactory for the
recipient's purpose, or could not be dereferenced.
A SIP intermediary can also reject a location it receives from a
Target when it understands the Target to be in a different location.
The proper handling of this scenario, described in Section 3.4, is
for the SIP intermediary to include the proper location in the 424
Response. This SHOULD be included in the response as a MIME message
body (i.e., a location value), rather than as a URI; however, in
cases where the intermediary is willing to share location with
recipients but not with a user agent, a reference might be
necessary.
As mentioned in Section 3.4, it might be the case that the
intermediary does not want to chance providing less accurate
location information than the user agent; thus it will compose its
understanding of where the user agent is in a separate <geopriv>
element of the same PIDF-LO [RFC4119] message body in the SIP
response (which also contains the Target's version of where it is).
Therefore, both locations are included - each with different
<method> elements. The proper reaction of the user agent is to
generate a new SIP request that includes this composed location
object, and send it towards the original LR. SIP intermediaries can
verify that subsequent requests properly insert the suggested
location information before forwarding said requests.
SIP intermediaries that are forwarding (as opposed to generating) a
424 response MUST NOT add, modify, or delete any location appearing
in that response. This specifically applies to intermediaries that
are between the 424 response generator and the original UAC.
Geolocation and Geolocation-Error header fields and PIDF-LO body
parts MUST remain unchanged, never added to or deleted.
Section 4.4 describes a Geolocation-Error header field to provide
more detail about what was wrong with the location information in
the request. This header field MUST be included in the 424 response.
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It is only appropriate to generate a 424 response when the
responding entity needs a locationValue and there are no values in
the request that are usable by the responder, or when the responder
has additional location information to provide. The latter case is
shown in Figure 4 of section 3.4. There, a SIP intermediary is
informing the upstream UA which location to include in the next SIP
request.
A 424 MUST NOT be sent in response to a request that lacks a
Geolocation header entirely, as the user agent in that case may not
support this extension at all. If a SIP intermediary inserted a
locationValue into a SIP request where one was not previously
present, it MUST take any and all responsibility for the corrective
action if it receives a 424 to a SIP request it sent.
A 424 (Bad Location Information) response is a final response within
a transaction, and MUST NOT terminate an existing dialog.
4.4 The Geolocation-Error Header Field
As discussed in Section 4.3, more granular error notifications
specific to location errors within a received request are required
if the location inserting entity is to know what was wrong within
the original request. The Geolocation-Error header field is used for
this purpose.
The Geolocation-Error header field is used to convey
location-specific errors within a response. The Geolocation-Error
header field has the following ABNF [RFC5234]:
message-header /= Geolocation-Error
; (message-header from 3261)
Geolocation-Error = "Geolocation-Error" HCOLON
locationErrorValue
locationErrorValue = location-error-code
*(SEMI location-error-params)
location-error-code = 1*3DIGIT
location-error-params = location-error-code-text
/ generic-param ; from RFC3261
location-error-code-text = "code" EQUAL quoted-string ; from RFC3261
HCOLON, SEMI, and EQUAL are defined in RFC3261 [RFC3261]. DIGIT is
defined in RFC5234 [RFC5234].
The Geolocation-Error header field MUST contain only one
locationErrorValue to indicate what was wrong with the locationValue
the Location Recipient determined was bad. The locationErrorValue
contains a 3-digit error code indicating what was wrong with the
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location in the request. This error code has a corresponding quoted
error text string that is human understandable. The text string is
OPTIONAL, but RECOMMENDED for human readability, similar to the
string phrase used for SIP response codes. That said, the strings
are complete enough for rendering to the user, if so desired. The
strings in this document are recommendations, and are not
standardized - meaning an operator can change the strings - but MUST
NOT change the meaning of the error code. Similar to how RFC 3261
specifies, there MUST NOT be more than one string per error code.
The Geolocation-Error header field MAY be included in any response
to one of the SIP Methods mentioned in Section 4.1, so long as a
locationValue was in the request part of the same 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. Bob merely
includes a Geolocation-Error header value in the 200 OK to the
INVITE informing Alice the INVITE was accepted but the location
provided was bad.
If, on the other hand, Bob cannot accept Alice's INVITE without a
suitable location, a 424 (Bad Location Information) is sent. This
message flow is shown in Figures 1, 2 or 3 in Sections 3.1, 3.2 and
3.3 respectively.
If Alice is deliberately leaving location information out of the LO
because she does not want Bob to have this additional information,
implementations should be aware that Bob could error repeatedly in
order to receive more location information about Alice in a
subsequent SIP request. Implementations MUST be on guard for this,
by not allowing continually more information to be revealed unless
it is clear that any LR is permitted by Alice to know all that Alice
knows about her location. A limit on the number of such rejections
to learn more location information SHOULD be configurable, with a
RECOMMENDED maximum of 3 times for each related transaction.
A SIP intermediary that requires Alice's location in order to
properly process Alice's INVITE also sends a 424 with a
Geolocation-Error code. This message flow is shown in Figure 4 of
Section 3.4.
If more than one locationValue is present in a SIP request and at
least one locationValue is determined to be valid by the LR, the
location in that SIP request MUST be considered good as far as
location is concerned, and no Geolocation-Error is to be sent.
Here is an initial list of location based error code ranges for any
SIP response, including provisional responses (other than 100
Trying) and the new 424 (Bad Location Information) response. These
error codes are divided into 3 categories, based on how the response
receiver should react to these errors. There MUST be no more than
one Geolocation-Error code in a SIP response, regardless of how many
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locationValues there are in the correlating SIP request. There is no
guidance given in this document as to which locationValue, when more
than one was present in the SIP request, is related to the
Geolocation-Error code; meaning that, somehow not defined here, the
LR just picks one to error.
o 1XX errors mean the LR cannot process the location within the
request
A non-exclusive list of reasons for returning a 1XX is
- the location was not present or could not be found,
- there was not enough location information to determine
where the Target was,
- the location information was corrupted or known to be
inaccurate,
o 2XX errors mean some specific permission is necessary to process
the included location information.
o 3XX errors mean there was trouble dereferencing the Location URI
sent.
Dereference attempts to the same request SHOULD be limited to 10
attempts within a few minutes. This number SHOULD be configurable,
but result in a Geolocation-Error: 300 error once reached.
It should be noted that for non-INVITE transactions, the SIP
response will likely be sent before the dereference response has
been received. This document does not alter that SIP protocol
reality. This means the receiver of any non-INVITE response to a
request containing location SHOULD NOT consider a 200 OK to mean the
act of dereferencing has concluded and the dereferencer (i.e., the
LR) has successfully received and parsed the PIDF-LO for errors and
found none. The end of section 3.2 discusses how transaction timing
considerations lead to this requirement.
Additionally, if an LR cannot or chooses not to process location
from a SIP request, a 500 (Server Internal Error) SHOULD be used
with or without a configurable Retry-After header field. There is no
special location error code for what already exists within SIP
today.
Within each of these ranges, there is a top level error as follows:
Geolocation-Error: 100 ; code="Cannot Process Location"
Geolocation-Error: 200 ; code="Permission To Use Location
Information"
Geolocation-Error: 300 ; code="Dereference Failure"
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If an error recipient cannot process a specific error code (such as
the 201 or 202 below), perhaps because it does not understand that
specific error code, the error recipient SHOULD process the error
code as if it originally were a top level error code where the X in
X00 matches the specific error code. If the error recipient cannot
process a non-100 error code, for whatever reason, then the error
code 100 MUST be processed.
There are two specific Geolocation-Error codes necessary to include
in this document, both have to do with permissions necessary to
process the SIP request; they are
Geolocation-Error: 201 ; code="Permission To Retransmit Location
Information to a Third Party"
This location error is specific to having the Presence Information
Data Format (PIDF-LO) [RFC4119] <retransmission-allowed> element set
to "no". This location error is stating it requires permission
(i.e., PIDF-LO <retransmission-allowed> element set to "yes") to
process this SIP request further. If the LS sending the location
information does not want to give this permission, it will not
change this permission in a new request. If the LS wants this
message processed with the <retransmission-allowed> element set to
"yes" it MUST choose another logical path (if one exists) for this
SIP request.
Geolocation-Error: 202 ; code="Permission to Route based on Location
Information"
This location error is specific to having the Geolocation-Routing
header value set to "no". This location error is stating it requires
permission (i.e., the Geolocation-Routing header value set to "yes")
to process this SIP request further. If the LS sending the location
information does not want to give this permission, it will not
change this permission in a new request. If the LS wants this
message processed with the <retransmission-allowed> element set to
"yes" it MUST choose another logical path (if one exists) for this
SIP request.
4.5 Location URIs in Message Bodies
In the case where an LR sends a 424 response and wishes to
communicate suitable location by reference rather than by value, the
424 MUST include a content-indirection body per RFC 4483.
4.6 Location Profile Negotiation
The following is part of the discussion started in Section 3, Figure
2, which introduced the concept of sending location indirectly.
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If a location URI is included in a SIP request, the sending user
agent MUST also include a Supported header field indicating which
location profiles it supports. Two option tags for location profiles
are defined by this document: "geolocation-sip" and
"geolocation-http". Future specifications MAY define further
location profiles per the IANA policy described in Section 8.3.
The "geolocation-sip" option tag signals support for acquiring
location information via the presence event package of SIP
([RFC3856]). A location recipient who supports this option can send
a SUBSCRIBE request and parse a resulting NOTIFY containing a
PIDF-LO object. The URI schemes supported by this option include
"sip", "sips" and "pres".
The "geolocation-http" option tag signals support for acquiring
location information via an HTTP ([RFC2616]). A location recipient
who supports this option can request location with an HTTP GET and
parse a resulting 200 response containing a PIDF-LO object. The URI
schemes supported by this option include "http" and "https". A
failure to parse the 200 response, for whatever reason, will return
a "Dereference Failure" indication to the original location sending
user agent to inform it that location was not delivered as intended.
If the location URI receiver does not understand the URI scheme sent
to it, it will return an Unsupported header value of the option-tag
from the SIP request, and include the option-tag of the preferred
URI scheme in the response's Supported header field.
See [ID-GEO-FILTERS] or [ID-HELD-DEREF] for more details on
dereferencing location information.
5. Geolocation Examples
5.1 Location-by-value (in Coordinate Format)
This example shows an INVITE message with a coordinate location. In
this example, the SIP request uses a 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>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
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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:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
xmlns:gml="http://www.opengis.net/gml"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
entity="pres:alice@atlanta.example.com">
<dm:device id="target123-1">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</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. The other message
body part is SDP. The "cid:" eases message body parsing and
disambiguates multiple parts of the same type.
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If the Geolocation header field did not contain a "cid:" scheme, for
example, it could look like this location URI:
Geolocation: <sips:target123@server5.atlanta.example.com>
... the existence of a non-"cid:" scheme indicates this is a
location URI, to be dereferenced to learn the Target's location. Any
node wanting to know where the target is located would subscribe to
the SIP presence event package [RFC3856] at
sips:target123@server5.atlanta.example.com
(see Figure 2 in Section 3.2 for this message flow).
5.2 Two Locations Composed in Same Location Object Example
This example shows the INVITE message after a SIP intermediary
rejected the original INVITE (say, the one in section 5.1). This
INVITE contains the composed LO sent by the SIP intermediary which
includes where the intermediary understands Alice to be. The rules
of RFC 5491 [RFC5491] are followed in this construction.
This example is here, but ought not be taken as occurring very
often. In fact, this example is believed to be a corner case of
location conveyance applicability.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIPS/2.0/TLS pc33.atlanta.example.com;branch=z9hG4bK74bf0
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188512@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
Geolocation-Routing: no
Accept: application/sdp, application/pidf+xml
CSeq: 31863 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>
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<?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:gbp="urn:ietf:params:xml:ns:pidf:geopriv10:basicPolicy"
xmlns:dm="urn:ietf:params:xml:ns:pidf:data-model"
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="target123-1">
<gp:geopriv>
<gp:location-info>
<gml:location>
<gml:Point srsName="urn:ogc:def:crs:EPSG::4326">
<gml:pos>32.86726 -97.16054</gml:pos>
</gml:Point>
</gml:location>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>802.11</gp:method>
</gp:geopriv>
<dm:deviceID>mac:1234567890ab</dm:deviceID>
<dm:timestamp>2010-11-04T20:57:29Z</dm:timestamp>
</dm:device>
<dm:person id="target123">
<gp:geopriv>
<gp:location-info>
<cl:civicAddress>
<cl:country>US</cl:country>
<cl:A1>Texas</cl:A1>
<cl:A3>Colleyville</cl:A3>
<cl:RD>Treemont</cl:RD>
<cl:STS>Circle</cl:STS>
<cl:HNO>3913</cl:HNO>
<cl:FLR>1</cl:FLR>
<cl:NAM>Haley's Place</cl:NAM>
<cl:PC>76034</cl:PC>
</cl:civicAddress>
</gp:location-info>
<gp:usage-rules>
<gbp:retransmission-allowed>false
</gbp:retransmission-allowed>
<gbp:retention-expiry>2010-11-14T20:00:00Z
</gbp:retention-expiry>
</gp:usage-rules>
<gp:method>triangulation</gp:method>
</gp:geopriv>
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<dm:timestamp>2010-11-04T12:28:04Z</dm:timestamp>
</dm:person>
</presence>
--boundary1--
6. Geopriv Privacy Considerations
Location information is considered by most to be highly sensitive
information, requiring protection from eavesdropping and altering in
transit. [RFC3693] originally articulated rules to be followed by
any protocol wishing to be considered a "Using Protocol", specifying
how a transport protocol meets those rules. [RFC6280] updates
the guidance in RFC3693 to include subsequently introduced
entities and concepts in the geolocation architecture.
RFC5606 explores the difficulties inherent in mapping the GEOPRIV
architecture onto SIP elements. In particular, the difficulties of
defining and identifying recipients of location information are
given in that document, along with guidance in Section 3.3.2 on the
use of location by-reference mechanisms to preserve confidentiality
of location information from unauthorized recipients.
In a SIP deployment, location information may be added by any of
several elements, including the originating user agent or a proxy
server. In all cases, the Rule Maker associated with that location
information decides which entity adds location information and what
access control rules apply. For example, a SIP user agent that does
not support the Geolocation header may rely on a proxy server under
the direction of the Rule Maker adding a Geolocation header with a
reference to location information. The manner in which the Rule
Maker operates on these devices is outside the scope of this
document.
The manner in which SIP implementations honor the Rule Maker's
stipulations for access control rules (including retention and
retransmission) is application-specific and not within the scope of
SIP protocol operations. Entities in SIP networks that fulfill the
architectural roles of the Location Server or Location Recipient
treat the privacy rules associated with location information per
the guidance in [RFC6280] section 4.2.1. In particular, RFC4119
(especially 2.2.2) gives guidance for handling access control rules;
SIP implementations should furthermore consult the emendations in
RFC5606.
7. Security Considerations
Conveyance of physical location of a UA raises privacy concerns,
and depending on use, there probably will be authentication and
integrity concerns. This document calls for conveyance to
be accomplished through secure mechanisms, like S/MIME encrypting
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message bodies (although this is not widely deployed), TLS
protecting the overall signaling or conveyance location by-reference
and requiring all entities that dereference location to authenticate
themselves. In location-based routing cases, encrypting the
location payload 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. Data can only be encrypted to a
particular, anticipated target, and thus if multiple recipients need
to inspect a piece of data, and those recipients cannot be predicted
by the sender of data, encryption is not a very feasible choice.
Securing the location hop-by-hop, using TLS, protects the message
from eavesdropping and modification in transit, but exposes the
information to all proxies on the path as well as the endpoint. In
most cases, the UA has no trust relationship with the proxy or
proxies providing location-based routing services, so such
end-to-middle solutions might not be appropriate either.
When location information is conveyed by reference, however, one can
properly authenticate and authorize each entity that wishes to
inspect location information. This does not require that the sender
of data anticipate who will receive data, and it does permit
multiple entities to receive it securely, but it does not however
obviate the need for pre-association between the sender of data and
any prospective recipients. Obviously, in some contexts this
pre-association cannot be presumed; when it is not, effectively
unauthenticated access to location information must be permitted. In
this case, choosing pseudo-random URIs for location by-reference,
coupled with path encryption like SIPS, can help to ensure that only
entities on the SIP signaling path learn the URI, and thus restores
rough parity with sending location by-value.
Location information is especially sensitive when the identity of
its Target is obvious. Note that 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 in the document above). Moreover, anyone fishing for
information would correlate the identity at the SIP layer with that
of the location information referenced by SIP signaling.
When a UA inserts location, the UA sets the policy on whether to
reveal its location along the signaling path - as discussed in
Section 4, as well as flags in the PIDF-LO [RFC4119]. UAC
implementations MUST make such capabilities conditional on explicit
user permission, and MUST alert the user that location is being
conveyed.
This SIP extension offers the default ability to require permission
to process location while the SIP request is in transit. The
default for this is set to "no". There is an error explicitly
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describing how an intermediary asks for permission to view the
Target's location, plus a rule stating the user has to be made aware
of this permission request.
There is no end-to-end integrity on any locationValue or
locationErrorValue header field parameter (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 given this
situation.
8. IANA Considerations
The following are the IANA considerations made by this SIP
extension. Modifications and additions to all 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.]
8.1 IANA Registration for the SIP Geolocation Header Field
The SIP Geolocation Header Field is created by this document, with
its definition and rules in Section 4.1 of this document, and should
be added to the IANA sip-parameters registry with the following
actions
1. Update the Header Fields registry with
Registry:
Header Name compact Reference
----------------- ------- ---------
Geolocation [this doc]
8.2 IANA Registration for the SIP Geolocation-Routing Header Field
The SIP Geolocation-Routing Header Field is created by this document,
with its definition and rules in Section 4.2 of this document, and
should be added to the IANA sip-parameters registry with the
following action
1. Update the Header Fields registry with
Registry:
Header Name compact Reference
----------------- ------- ---------
Geolocation-Routing [this doc]
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8.3 IANA Registration for Location Profiles
This document defines two new SIP option tags: "geolocation-sip" and
"geolocation-http" to be added to the IANA sip-parameters Options
Tags registry.
Name Description Reference
----------- ------------------------------------------ ---------
geolocation-sip The "geolocation-sip" option tag signals [this doc]
support for acquiring location information
via the presence event package of SIP
(RFC 3856). A location recipient who
supports this option can send a SUBSCRIBE
request and parse a resulting NOTIFY
containing a PIDF-LO object. The URI
schemes supported by this option include
"sip", "sips" and "pres".
geolocation-http The "geolocation-http" option tag signals [this doc]
support for acquiring location information
via an HTTP ([RFC2616]). A location
recipient who supports this option can
request location with an HTTP GET and
parse a resulting 200 response containing
a PIDF-LO object. The URI schemes
supported by this option include "http"
and "https".
The names of profiles are SIP option-tags, and the guidance in this
document does not supersede the option-tag assignment guidance in
[RFC3261] (which requires a Standards Action for the assignment of a
new option tag). This document does however stipulate that
option-tags included to convey the name of a location profile per
this definition MUST begin with the string "geolocation" followed by
a dash. All such option tags should describe protocols used to
acquire location by reference: these tags have no relevance to
location carried in SIP requests by value, which use standard MIME
typing and negotiation.
8.4 IANA Registration for 424 Response Code
In the SIP Response Codes registry, the following is added
Reference: RFC-XXXX (i.e., this document)
Response code: 424 (recommended number to assign)
Default reason phrase: Bad Location Information
Registry:
Response Code Reference
------------------------------------------ ---------
Request Failure 4xx
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424 Bad Location Information [this doc]
This SIP Response code is defined in section 4.3 of this document.
8.5 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 4.4 of this document, to be
added to the IANA sip-parameters registry with two actions
1. Update the Header Fields registry with
Registry:
Header Name compact Reference
----------------- ------- ---------
Geolocation-Error [this doc]
2. In the portion titled "Header Field Parameters and Parameter
Values", add
Predefined
Header Field Parameter Name Values Reference
----------------- ------------------- ---------- ---------
Geolocation-Error code yes [this doc]
8.6 IANA Registration for the SIP Geolocation-Error Codes
This document creates a new registry for SIP, called
"Geolocation-Error Codes." Geolocation-Error codes provide reason
for the error discovered by Location Recipients, categorized by
action to be taken by error recipient. The initial values for this
registry are shown below.
Registry Name: Geolocation-Error Codes
Reference: [this doc]
Registration Procedures: Specification Required
Code Default Reason Phrase Reference
---- --------------------------------------------------- ---------
100 "Cannot Process Location" [this doc]
200 "Permission To Use Location Information" [this doc]
201 "Permission To Retransmit Location Information to a Third Party"
[this doc]
202 "Permission to Route based on Location Information" [this doc]
300 "Dereference Failure" [this doc]
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Details of these error codes are in Section 4.4 of this
document.
9. Acknowledgements
To Dave Oran for helping to shape this idea.
To Dean Willis for 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, John Elwell, Thomas Stach,
Jacqueline Lee and Adam Roach for constructive feedback and nits
checking.
Special thanks to Paul Kyzivat for his help with the ABNF in this
document and to Robert Sparks for many helpful comments and the
proper construction of the Geolocation-Error header field.
And finally, to Spencer Dawkins for giving this doc a good scrubbing
to make it more readable.
10. References
10.1 Normative References
[RFC3261] J. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J.
Peterson, R. Sparks, M. Handley, and E. Schooler, "SIP:
Session Initiation Protocol", RFC 3261, May 2002.
[RFC4119] J. Peterson, "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
[RFC2392] E. Levinson, "Content-ID and Message-ID Uniform Resource
Locators", RFC 2392, August 1998
[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
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Instant Messaging" , RFC 3428, December 2002
[RFC3311] J. Rosenberg, "The Session Initiation Protocol (SIP) UPDATE
Method", RFC 3311, October 2002
[RFC3265] Roach, A, "Session Initiation Protocol (SIP)-Specific
Event Notification", RFC 3265, June 2002.
[RFC6086] C. Holmberg, E. Burger, H. Kaplan, "Session Initiation
Protocol (SIP) INFO Method and Package Framework", RFC 6086,
January 2011
[RFC3515] R. Sparks, "The Session Initiation Protocol (SIP) Refer
Method", RFC 3515, April 2003
[RFC3903] Niemi, 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.
[RFC4479] J. Rosenberg, "A Data Model for Presence", RFC 4479, July
2006
[RFC4483] E. Berger, "A Mechanism for Content Indirection in SIP", RFC
4483, May 2006
[RFC5491] J. Winterbottom, M. Thomson, H. Tschofenig, "GEOPRIV PIDF-LO
Usage Clarification, Considerations, and Recommendations ",
RFC 5491, March 2009
[RFC5870] A. Mayrhofer, C. Spanring, "A Uniform Resource Identifier
for Geographic Locations ('geo' URI)", RFC 5870, June 2010
[RFC2616] R. Fielding, J. Gettys, J., Mogul, H. Frystyk, L.,
Masinter, P. Leach, T. Berners-Lee, "Hypertext Transfer
Protocol - HTTP/1.1", RFC 2616, June 1999
10.2 Informative References
[RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
"Geopriv Requirements", RFC 3693, February 2004
[RFC2818] E. Rescorla, "HTTP Over TLS", RFC 2818, May 2000
[RFC5606] J. Peterson, T. Hardie, J. Morris, "Implications of
'retransmission-allowed' for SIP Location Conveyance",
RFC5606, Oct 2008
[ID-GEO-FILTERS] R. Mahy, B. Rosen, H. Tschofenig, "Filtering Location
Notifications in SIP", draft-ietf-geopriv-loc-filters, "work
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in progress", March 2010
[ID-HELD-DEREF] J. Winterbottom, H. Tschofenig, H. Schulzrinne, M.
Thomson, M. Dawson, "A Location Dereferencing Protocol Using
HELD", "work in progress", June 2011
[RFC6280] R. Barnes, M. Lepinski, A. Cooper, J, Morris, H.
Tschofenig, H. Schulzrinne, "An Architecture for Location
and Location Privacy in Internet Applications",
draft-ietf-geopriv-arch, "work in progress", October 2010
Authors' Addresses
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
Jon Peterson
NeuStar, Inc.
Email: jon.peterson@neustar.biz
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. This
is from the original requirements draft that has since evolved into
the solution document (that is above). This has been kept for
historical reasons.
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If a requirement is not obvious in 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: 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: if a UAC has moved prior to the establishment of a
dialog between UAs, the UAC must be able to send location
information. If location has been conveyed, and the UA
moves, the UAC must be able to update the location previously
conveyed to 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.
Motivation: interoperability with other IETF location protocols and
Mechanisms.
UAC-9 There must be a mechanism for the UAC to request the UAS send
its location.
UAC-9 has been DEPRECATED by the SIP WG, due to the many
problems this requirement would have caused if implemented.
The solution is for the above UAS to send a new request to
the original UAC with the UAS's location.
UAC-10 There must be a mechanism to differentiate the ability of the
UAC to convey location from the UACs lack of knowledge of its
location
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Motivation: Failure to receive location when it is expected can
happen because the UAC does not implement this extension, or
because the UAC implements the extension, but does not know
where the Target is. This may be, for example, due to the
failure of the access network to provide a location
acquisition mechanism the UAC 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.
The SIPCORE WG reached consensus that this be allowed, but
not to communicate the UAS's location; rather for a SIP
intermediary to inform the UAC which location to include in
its next SIP request (as a matter of correcting what was
originally sent by the UAC).
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.
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 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 can have
widely varying access network arrangements, including VPN
tunnels and roaming mechanisms, it can be difficult for a
network to reliably know the location of the endpoint.
Proxies SHOULD NOT assert location of an endpoint unless the
SIP signaling network has reliable knowledge of the actual
location of the Targets.
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Proxy-2 There must be a unique 4XX response informing the UAC it
did not provide applicable location information.
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