SIP Working Group James Polk
Internet Draft Cisco Systems
Expires: September 9, 2009 Brian Rosen
Intended Status: Standards Track (PS) NeuStar
March 9, 2009
Location Conveyance for the Session Initiation Protocol
draft-ietf-sip-location-conveyance-13.txt
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with
the provisions of BCP 78 and BCP 79. This document may contain
material from IETF Documents or IETF Contributions published or made
publicly available before November 10, 2008. The person(s)
controlling the copyright in some of this material may not have
granted the IETF Trust the right to allow modifications of such
material outside the IETF Standards Process. Without obtaining an
adequate license from the person(s) controlling the copyright in
such materials, this document may not be modified outside the IETF
Standards Process, and derivative works of it may not be created
outside the IETF Standards Process, except to format it for
publication as an RFC or to translate it into languages other than
English.
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-
Drafts.
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
reference material or to cite them other than as "work in progress."
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 September 9, 2009.
Copyright Notice
Copyright (c) 2009 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 in effect on the date of
publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your
Polk & Rosen Expires Sept 9, 2009 [Page 1]
Internet Draft Location Conveyance in SIP Mar 2009
rights and restrictions with respect to this document.
Legal
This documents and the information contained therein are provided on
an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE
IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL
WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY
WARRANTY THAT THE USE OF THE INFORMATION THEREIN WILL NOT INFRINGE
ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
Abstract
This document defines an extension to the Session Initiation
Protocol (SIP) to convey geographic location information from one
SIP entity to another SIP entity. The extension covers end to end
conveyance as well as location-based routing, where SIP servers
make routing decisions based on the location of the user agent
clients.
Table of Contents
1. Conventions and Terminology used in this document . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of SIP Location Conveyance . . . . . . . . . . . . . 6
4. SIP Modifications for Geolocation Conveyance . . . . . . . . 7
4.1 The Geolocation Header . . . . . . . . . . . . . . . . . 7
4.2 424 (Bad Location Information) Response Code . . . . . . 11
4.3 The Geolocation-Error Header . . . . . . . . . . . . . . 11
4.4 The 'geolocation' Option Tag . . . . . . . . . . . . . . 20
4.5 Using sip/sips/pres as a Dereference Scheme . . . . . . . 20
5. Geolocation Examples . . . . . . . . . . . . . . . . . . . . 21
5.1 Location-by-value (Coordinate Format) . . . . . . . . . . 22
5.2 Location-by-reference . . . . . . . . . . . . . . . . . . 23
6. SIP Element Behavior . . . . . . . . . . . . . . . . . . . . 24
6.1 UAC Behavior . . . . . . . . . . . . . . . . . . . . . . 25
6.2 UAS Behavior . . . . . . . . . . . . . . . . . . . . . . 28
6.3 Proxy Behavior . . . . . . . . . . . . . . . . . . . . . 33
7. Geopriv Privacy Considerations . . . . . . . . . . . . . . . 36
8. Security Considerations . . . . . . . . . . . . . . . . . . . 37
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . 38
9.1 IANA Registration for New SIP Geolocation Header . . . . 38
9.2 IANA Registration for New SIP 'geolocation' Option Tag . 39
9.3 IANA Registration for New 424 Response Code . . . . . . . 39
9.4 IANA Registration for New SIP Geolocation-Error Header . 39
9.5 IANA Registration for New SIP Geolocation-Error Codes . . 39
9.6 IANA Registration of LbyR Schemes . . . . . . . . . . . 40
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 40
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 41
Polk & Rosen Expires Sept 9, 2009 [Page 2]
Internet Draft Location Conveyance in SIP Mar 2009
11.1 Normative References . . . . . . . . . . . . . . . . . 41
11.2 Informative References . . . . . . . . . . . . . . . . . 42
Author Information . . . . . . . . . . . . . . . . . . . . . 42
Appendix A. Requirements for SIP Location Conveyance . . . . 43
Appendix B. Example of Civic-based PIDF-LO w/ S/MIME . . . . 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:
"cid=" = content-ID URI. See Section 4.1 for more details.
Content-ID - Defined in RFC 2392 as a URL reference to find message
body parts within the same message, to ease parsing.
LbyR = Location-by-Reference
LbyV = Location-by-Value
locationErrorValue - contains an actionable error code from a
Location Recipient, identifying the location "inserter=", and
optionally a test string describing the type of error. There can
be one or more locationErrorValues within a Geolocation-Error
header in a SIP response. See Section 4.3 for more details.
locationValue - contains a URI pointing to a Location Target's
location (as a PIDF-LO), and one or more header parameters about
that URI. There can be one or more locationValues within a
Geolocation header in a SIP request. See Section 4.1 for more
details.
Location Generator - the first IP enabled device that builds the IP
packet that transmits the PIDF-LO containing the Target's
location
Location Information Server (LIS) - a logical server that stores
geolocation records, which correspond to LbyR URIs, which point
to those records.
Location Object - Defined in RFC 4119 as the PIDF-LO (XML scheme)
format which includes the geolocation of Location Target in
either civic address or coordinate form.
Location Recipient - Defined in RFC3693 as any entity that
understands geolocation (LbyR or LbyV) along a message path.
Polk & Rosen Expires Sept 9, 2009 [Page 3]
Internet Draft Location Conveyance in SIP Mar 2009
Does not include entities that process a message containing
geolocation that do not understand geolocation (i.e., layer 3
routers).
Location Server - a logical IP server that transmits a PIDF-LO. This
can be logically combined with the Location Generator, or could
be an intermediary element - such as a LIS.
Location Target - The entity whose location is being sought, whether
or not this entity is aware of this inquiry or is even an IP
device.
Location-by-Reference (more than one meaning)
- a general purpose term meaning a message containing a URI that
points to a PIDF-LO (geolocation of a Location Target) not within
this same message
- a URI that logically locates a geolocation record of a Location
Target. The URI does not point to location within the same
message as the URI.
Location-by-Value - when a message contains the actual location of a
Location Target, in the form of a PIDF-LO, within a part of the
same message, usually pointed to by a "cid=" URI in a Geolocation
header.
Using Protocol - as defined in [RFC3693], a protocol that is deemed
to be in compliance with the security and privacy aspects of the
Geopriv Requirements RFC [RFC3693], with good community
verification.
Instead of using the terms Location-by-Reference (or just
by-reference) and Location-by-Value (or just by-value), this
document will herein use the acronyms LbyR and LbyV, respectively.
The use of "cid=" implies LbyV, therefore, the use of a "cid="
Reference URL, which is *not* a Location-by-Reference (LbyR).
2. Introduction
This document describes how Location can be "conveyed" (that is,
transmitted over the Internet) from one SIP user agent (UA), or in
some circumstances, a proxy server acting in support of a UA, to
another entity using SIP [RFC3261]. Here "Location" is a
description of the physical geographical area where something
currently exists. The phrase "location conveyance" describes
scenarios in which a SIP user agent client (UAC) is informing a user
agent server (UAS) or intermediate SIP server where the UAC is. A
superset of this can also be true as well, in which one UA (UA-1) is
telling another UA-2 where another Target is, meaning not
necessarily where UA-1 is. The key to this is whether UA-1 has
Polk & Rosen Expires Sept 9, 2009 [Page 4]
Internet Draft Location Conveyance in SIP Mar 2009
permission to retransmit that other Target's location. If yes, then
this is valid. If no, then this is breaking a fundamental rule
within this extension.
Location Conveyance is different from a UAC seeking the location the
UAS. Location conveyance is a 'sending location out in the request'
model, where 'asking that someone else's location be in a response'
is not discussed here.
Geographic location in the IETF is discussed in RFC 3693 (Geopriv
Requirements) [RFC3693]. It defines a "Target" as the entity whose
location is being sought. In this case, this is the UA's
(UA) location. A [RFC3693] "Using Protocol" defines how a "Location
Server" transmits a "Location Object" to a "Location Recipient"
while maintaining the contained privacy intentions of the Target
intact. This document describes the extension to SIP for how it
complies with the Using Protocol requirements, where the location
server is a UA or Proxy Server and the Location Recipient is
another UA or Proxy Server.
Location can be transmitted by-value or by-reference. The location
"value" in this SIP extension is in the form of a Presence
Information Data Format - Location Object, or PIDF-LO, as described
in [RFC4119]. A PIDF-LO is an XML Scheme specifically for carrying
geographic location of a Target. LbyV refers to a UA including a
PIDF-LO as a body part of a SIP request, sending that Location
Object to another SIP element. LbyR refers to a UA or proxy server
including a URI in a SIP request header field which can be
dereferenced by a Location Recipient for a Location Object, in the
form of a PIDF-LO. Dereferencing can be by a SIP UA or a SIP
server.
As recited in RFC 3693, location often must be kept private. The
Location Object (PIDF-LO) contains rules which provides guidance to
the Location Recipient and controls onward distribution and
retention of the location. This document describes the security and
privacy considerations that must be applied to location conveyed
with SIP.
Another use for location is location-based routing of a
SIP request, where the choice of the next hop (and usually, the
outgoing Request-URI) is determined by the location of the UAC which
is in the message by-value or by-reference. This document describes
how location can be conveyed from the UAC, or a proxy acting on its
behalf, to a routing proxy. How the location is actually used to
determine the next hop or Request-URI is beyond the scope of this
document.
We refer to the "emergency case". This refers to a specific,
important use of SIP location conveyance where the location of the
caller is used to determine which Public Safety Answering Point
(PSAP) is expected to receive an emergency call request for help
Polk & Rosen Expires Sept 9, 2009 [Page 5]
Internet Draft Location Conveyance in SIP Mar 2009
(e.g., a call to 1-1-2 or 9-1-1). This is an example of
location-based routing. The location conveyed is also used by the
PSAP to dispatch first responders to the caller's location. There
are special security considerations, which make the emergency case
unique, compared to a normal location conveyance within SIP.
Common terms are in Section 1. Section 3 provides an overview of SIP
location conveyance. Section 4 details the modifications 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 section 4.
3. Overview of SIP Location Conveyance
This document defines a new SIP header: Geolocation. The
Geolocation header field contains a URI which can either be a "cid:"
URI (Content Identification), as defined in [RFC2392], or an LbyR
-- to be dereferenced by a Location Recipient to retrieve the
location of the Target UA.
Where the Geolocation header contains a "cid:", the URI points to a
message body that is in the form of a PIDF [RFC3863], which was
extended in [RFC4119] to include location, as a PIDF-LO. This is
LbyV, the actual location information in the PIDF-LO is included in
the body of the message.
If the URI in the Geolocation header field is a scheme other than
"cid:", another protocol operation is needed by the SIP message
recipient to obtain the location of the Target (UA). This is
LbyR. This document describes how a SIP presence subscription
[RFC3856] can be used as a dereference protocol.
The Geolocation header, either with the PIDF-LO in a body or as a
LbyR URI, can be included by a UA in a SIP request. A SIP proxy
server can assert location of the UA by inserting the header field,
by adding an LbyR URI into the Geolocation header value, even if
there is a locationValue already there. Since body parts cannot be
inserted by a SIP proxy server, LbyV message body cannot be inserted
by a proxy.
The Geolocation header can have parameters that are associated
with a URI in the header field. The "inserted-by" parameter
indicates the host-id of which specific element added this
particular location to the request. This header parameter is
included in every locationValue, and does not appear more than once
per locationValue. The "inserted-by" parameter is especially useful
for Location Recipients that receive more than one locationValue
within a SIP request. Since implementations of a UA or SIP Server
Polk & Rosen Expires Sept 9, 2009 [Page 6]
Internet Draft Location Conveyance in SIP Mar 2009
do not know they will be the last entity before a Location
Recipient, this optional parameter is necessary within each
locationValue.
Retargeting means the Request-URI of the request has changed to
point at a new destination UAS. This is different than message
routing, that all SIP proxies do. If a SIP request is retargeted
based on the location contained or referenced within that message,
the "used-for-routing" parameter is added as a header parameter
within the appropriate locationValue.
There is no mechanism by which the veracity of these parameters can
be verified. They are hints to downstream entities on how the
location information in the message was originated and used.
Transport Layer Security is expected when a request contains a
user's location. Some implementations will choose to have S/MIME to
encrypt message bodies from source to destination.
This document creates a new option tag: geolocation, to indicate
support for this extension by UAs.
A new error response (424 Bad Location Information) is also defined
in this document. Within this response is a new header indicating
location-based errors, call the Geolocation-Error header. This
header has various codes that provide additional information about
the type of location error experienced by a Location Recipient.
The new headers, the header parameters, the new option tag, the new
error response, and Geolocation-Error codes, which are defined in
Section 4., are IANA registered by this document.
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
This document defines and IANA registers a new SIP header:
Geolocation, 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
Polk & Rosen Expires Sept 9, 2009 [Page 7]
Internet Draft Location Conveyance in SIP Mar 2009
/ gen-value ; (from RFC 3261)
retrans-param = "routing-allowed" EQUAL "yes" / "no"
sip-URI, sips-URI and absoluteURI are defined according to RFC 3261.
The pres-URI is defined in RFC 3859 [RFC3859].
The cid-url is defined in [RFC2392] to locate message body
parts. This URI type MUST be present in a SIP request if location
is transmitted LbyV only.
Other protocols used in the Location URI MUST be reviewed against
the RFC 3693 criteria for a Using Protocol.
The Geolocation header MAY have one or more locationValues. SIP
servers inserting a locationValue MUST add the new value as the last
locationValue in the Geolocation header (i.e., the last
locationValue in the header is the most recent one added to the
message). Placement of the "routing-allowed" parameter, when
present, MUST be the last header value in the Geolocation header.
A locationValue has the following independent header 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, 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 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 not identifying 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, the last locationValue is the most recent one added to
the message. This also gives the "used-for-routing" header
parameter added meaning - as the receiving SIP entity knows which
locationURI 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
Polk & Rosen Expires Sept 9, 2009 [Page 8]
Internet Draft Location Conveyance in SIP Mar 2009
header.
The "routing-allowed" header parameter is a global parameter over
any (and all/each) locationValues in the Geolocation header. This
is the reason why the placement of the header parameter is outside
any locationValue, and appears only once, and is always last in the
header value.
This header parameter has values "=yes" or "=no" only. When this
parameter "=yes", any locationValue can be used for routing
decisions along the downstream signaling path by intermediaries.
When this parameter "=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.
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 NOT view the location (because it is not
for intermediaries to view), and if an LbyR is present, SHOULD NOT
dereference it. UASs are allowed to view location in the SIP
request even when the "routing-allowed" header parameter is set to
"no".
The default behavior when this header 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 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.
Polk & Rosen Expires Sept 9, 2009 [Page 9]
Internet Draft Location Conveyance in SIP Mar 2009
The following table extends the values in Table 2&3 of RFC 3261
[RFC3261].
Header field where proxy INV ACK CAN BYE REG OPT PRA
----------------------------------------------------------------
Geolocation R ar o - - o o o o
Header field where proxy SUB NOT UPD MSG REF INF PUB
----------------------------------------------------------------
Geolocation R ar o o o o o o o
Table 1: Summary of the Geolocation Header
The Geolocation header field MAY be included in any one of the above
requests by a UAC. A proxy MAY add the Geolocation header, but MUST
NOT modify any pre-existing locationValue, including any associated
header parameters within an existing Geolocation header value,
unless one of the existing locationValues is used to retarget the
request towards a new destination UAS. This is discussed in section
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 URI, in its own locationValue header value.
A SIP proxy MAY add a Geolocation header 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 SHOULD NOT
occur for at least two reasons,
#1 - SIP Servers are not the best Sighters, as defined by [RFC3693],
of geographically where a UAC can be; meaning the location
information is not necessarily the greatest. There MAY be
exceptions, but this SHOULD be the rule of thumb.
#2 - without appropriate caution to the fact that Location
Recipients might not understand how to process more than one
location, given this document's limited guidance as to what a
Location Recipient should do when receiving more than one
location (i.e., currently no priority instructions are given
for which locationValue to use if there are more than one). A
Location Recipient can easily be confused by too much location
information, producing undesirable results. The <tuple id>
element in the PIDF-LO XML indicates whose location is
contained in the PIDF-LO.
Polk & Rosen Expires Sept 9, 2009 [Page 10]
Internet Draft Location Conveyance in SIP Mar 2009
Location Recipients receiving a location object, received directly
or as the result of a dereference, MUST honor the usage element
rules within that XML document, 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 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 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 to provide more
detail about what was wrong with the location information in the
request. This header MUST be in the 424 response, containing a
locationErrorValue for each invalid locationValue in the request
(i.e., and one-for-one matching if all locationValues in the request
were bad).
If more than one location is present in a request (LbyV or LbyR),
and any of the locationValues is good for the Location Recipient to
process, a 424 MUST NOT be sent. The 424 is only appropriate when
the Location Recipient needs a locationValue and there are no
locationValues included in a SIP request that are usable by a
recipient.
A 424 (Bad Location Information) response is a final response within
a transaction, and does not terminate a usage or a dialog.
The UAC can use whatever means it knows of to verify/refresh its
location information before attempting a new request that includes
location. There is no cross-transaction awareness expected by either
the UAS or any SIP intermediary as a result of this error message.
The new 424 (Bad Location Information) error code is IANA registered
in Section 8 of this document. An initial set of location error of
IANA registered Geolocation-Error codes are in Section 4.3 of this
document.
4.3 The Geolocation-Error Header
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 is created here for this purpose.
Polk & Rosen Expires Sept 9, 2009 [Page 11]
Internet Draft Location Conveyance in SIP Mar 2009
Geolocation-Error header is used to convey location specific errors
within a response. Additions to this IANA registered header require
an RFC be published. The Geolocation-Error header 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 MUST contain at least one
locationErrorValue to indicate what was wrong with the original
locationValue in the corresponding request. If a Location Recipient
experienced more than one error a particular locationValue of the
corresponding SIP request, there can be one locationErrorValue per
problem with the locationValue in the request. Each
locationErrorValue contains one 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 entered in
the "sent-by" parameter of the Via header for that entity
[RFC3261]. As stated in section 18 of RFC 3261, the usage of FQDN
is RECOMMENDED. Here are examples of both locationErrorValue
parameters
node="bob.example.com"
inserter="alice.example.com"
Polk & Rosen Expires Sept 9, 2009 [Page 12]
Internet Draft Location Conveyance in SIP Mar 2009
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 request (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 is necessary, a Location Recipient that experienced
the location problem with the 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, were it to remain generic to all
entities in the response path. So, the header has to identify who
it is for, so that all other SIP entities that read the header know
to ignore it, since it is not for them. This is of particular use
if the original UAC did not include a locationValue in the original
SIP request, but a SIP server along the path did insert a
locationValue. The locationErrorValue would travel to each SIP
entity along the original path and tell both the server that
included the locationValue what was wrong with the location and the
UAC who did not know what the error meant. This will cause
confusion if left without this indication.
A worse case is when both the original UAC and a SIP server along
the path included a locationValue, but there was only something
wrong with one of the locationValues. Without this identification
of which locationValue was in error, both entities would react and
one would do so incorrectly.
More than one locationErrorValue in a Geolocation-Error header is
separated by a comma.
If more than one locationErrorValue is in a response, and intended
for the same "inserter=", each error code MUST be unique to this
"inserter=" entity, and the error codes SHOULD NOT conflict in
meaning. In other words, two error codes (within separate
locationErrorValues of the same response) SHOULD NOT give misleading
or inconsistent indications to the location "inserter=".
Here is an example of a Geolocation-Error header
Geolocation-Error: 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].
Polk & Rosen Expires Sept 9, 2009 [Page 13]
Internet Draft Location Conveyance in SIP Mar 2009
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
The Geolocation-Error header field MAY be included in any response
to one of the above SIP requests, so long as Geolocation was in the
request part of the transaction. The choice of which SIP requests
are in table 2 above come from which Methods can optionally have the
Geolocation header (see section 4.1). That said, a UAC MUST ignore
a Geolocation-Error header value if it did not include a Geolocation
header value in the request part of the transaction.
Here is an example of a transaction that has a location error. In
this case, Bob responds with a 424 (Bad Location Information)
response, including a Geolocation-Error header, is in Figure 1.
Alice Bob
| |
| Request w/ Location |
|------------------------------------------------>|
| |
| |
| 424 (Bad Location Information) |
| with Geolocation-Error containing |
| 200 ("Retry Location Later" (with same data)) |
|<------------------------------------------------|
| |
Figure 1. Basic Transaction with 424 and Geolocation-Error Header
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 the response)
actionable reactions to these errors.
o 100 "Cannot Process Location"
o 200 "Retry Location Later" (with same data)
o 300 "Retry Location Later" (with device updated location)
o 400 "Permission Necessary"
o 500 "Location Information Denial"
Polk & Rosen Expires Sept 9, 2009 [Page 14]
Internet Draft Location Conveyance in SIP Mar 2009
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. 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 supplied in a request, as
far as location is concerned, 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 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 "inserter="
entity received a 2XX or 3XX location error. A 4XX error MUST NOT be
misunderstood here, 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 location error is here:
Geolocation-Error: 100; code="Cannot Process Location";
node="bob.example.com";
inserter="alice.example.com";
This category covers location errors 1XX; meaning there MAY be more
specific errors added to this category in future effort(s). The
same basic actionable reaction is expected by a location "inserter="
entity to any 1XX location error.
4.3.2 Location Error: 200 "Retry Location Later" (same data)
The location error 200 "Retry Location 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 to retry this request, without changing the location
Polk & Rosen Expires Sept 9, 2009 [Page 15]
Internet Draft Location Conveyance in SIP Mar 2009
information, at a later time - in a new SIP request. It is possible
that the Location Recipient cannot process location at this time, or
there was a timeout during dereferencing, if an LbyR were sent.
Action(s) to be taken by Geolocation-Error receiver to a 2XX:
Reactions to a 2XX location error are to try again, without
having to update the location supplied originally. There is
no constraints on how long this new try has to wait, unless
there is a Retry-After header in a 424 response.
Implementations SHOULD choose to react by preparing, however this
"inserter=" does or can, to queue another message with the same
location information, provided the "inserter=" does not move between
the time of the original request and the transmission time of the
new request.
Implementations MAY choose whether or not to inform the user of this
error. The text string of "Retry Location Later" 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 location error is here:
Geolocation-Error: 200; code="Retry Location Later";
node="bob.example.com";
inserter="alice.example.com";
This category covers location errors 2XX; meaning there MAY be more
specific errors added to this category in future effort(s). The
same basic actionable reaction is expected by a location "inserter="
entity to any 2XX location error.
If a SIP request has the "routing-allowed" header parameter set to
"no", and the SIP server believes processing location within the
request 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 Location Error: 300 "Retry Location Later" (device updated
location)
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 is concerned, cannot be
processed at this time, but to retry this request, once the location
information has been updated, in a new SIP request.
Action(s) to be taken by Geolocation-Error receiver to a 3XX:
Polk & Rosen Expires Sept 9, 2009 [Page 16]
Internet Draft Location Conveyance in SIP Mar 2009
3XX location errors indicate the "inserter=" SIP entity needs
to refresh its location, or make the location information
supplied more complete, without notifying the user of this
error. 3XX error are to be solved by without user
intervention.
This document gives no guidance how this is accomplished, given the
number of ways a UAC can learn its location, or a SIP intermediary
can Sight a UAC, as defined in [RFC3693].
This 300 location error currently does not indicate what exactly was
wrong with the location supplied, according to the Location
Recipient. That is left for a future effort.
Implementations MAY choose whether or not to inform the user of this
error. The text string of "Retry Location Later" is RECOMMENDED,
but not mandatory for usage in this error. Implementation MAY use
another text string to inform the user that location was not
received by the UAS (i.e., the called party).
A 3XX location error would be used where the Location Recipient
cannot find or cannot parse the location supplied, believing that a
automated refresh and retry could fix the problem. Also, a 3XX
location error would be used when a Location Recipient did not find
any location in a SIP request, but was expecting it. Perhaps an
emergency request was made that did not contain location. The retry
in this case would be in the form of an UPDATE Method request,
containing location (LbyV or LbyR).
An example 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; meaning there MAY be more
specific errors added to this category in future effort(s). The
same basic actionable reaction is expected by a location "inserter="
entity to any 3XX location error.
4.3.4 Location Error: 400 "Permission Necessary"
The location error 400 "Permission Necessary" indicates to a
Geolocation-Error recipient that when they sent a particular SIP
request, they included location in that request without giving
permission in the request for a (or any) SIP server to look at that
location information (i.e., the <retransmission-allowed> was set to
"no") to route the message at the intended recipient (i.e., the UAS,
or the called party).
Action(s) to be taken by Geolocation-Error receiver to a 4XX:
Polk & Rosen Expires Sept 9, 2009 [Page 17]
Internet Draft Location Conveyance in SIP Mar 2009
4XX location errors indicate to the UAC (i.e., the calling
party) that they need to grant permission to a SIP
intermediary server to look at the supplied location to
complete the message routing. This indication MUST require
human user intervention, as the rulemaker of the policy on
whether or not their location is to be revealed.
The user of the location "inserter=" device can choose to grant
permission to this SIP intermediary server to allow this request to
be routed, or the user can deny this location revelation (request by
the server). It is the user's choice as rulemaker.
Implementations MUST provide 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. The text string of
"Permission Necessary" 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 by an intermediary (i.e., not
the called party).
This document gives no guidance how this intervention is
accomplished, given the number of ways a UAC can accomplish this
(i.e., audio prompt or toggle or keystroke on their UA).
This 400 location error currently does not indicate exactly which
SIP server indicates it needs the location revealed. That said, the
"node=" FQDN address could be supplied, telling the user (via audio
or video indication) which SIP entity wants this location. Perhaps
the user can know in some circumstances whether this is an
appropriate "node=" (domain). All of this is left for a future
effort(s).
An example of this location error is here:
Geolocation-Error: 400; code="Permission Necessary";
node="bob.example.com";
inserter="alice.example.com";
This category covers location errors 4XX; meaning there MAY be more
specific errors added to this category in future effort(s). The
same actionable solution is expected to be afforded to the UAC user,
as rulemaker, to any 4XX location error.
4.3.5 Location Error: 500 "Location Information Denial"
The location error 500 "Location Information Denial" indicates to a
Geolocation-Error recipient that what they supplied in a request, as
far as location is concerned, has been denied 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. If this were applied to the SIP request itself, this would
Polk & Rosen Expires Sept 9, 2009 [Page 18]
Internet Draft Location Conveyance in SIP Mar 2009
equate to a 6XX Global error.
Action(s) to be taken by Geolocation-Error receiver to a 1XX:
This error gives no guidance on what to do next, other than to
not try again with this same location supplied.
If the Location Recipient believed that merely refreshing, or in
some other way alter or augment the location supplied would work in
a new request, then a 3XX location error SHOULD have been returned
(to the "inserter="). An example of why this 5XX could have been
returned is if location were sent as an LbyR, and the LIS denied the
dereference request from the Location (reference) Recipient, this is
the expected location error returned to the "inserter=" entity.
Implementations MUST NOT interpret anything else into this location
error other than it is considered a location based denial error.
This does not mean the SIP request was denied, or even had an error,
unless the response was a 424. Otherwise, this only has to do with
the location part of the request.
The difference between a 1XX and a 5XX location error is simple. A
1XX location error 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 the UAC user of this error, the
text string of "Location Information Denial" 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 location errors 5XX; meaning there MAY be more
specific errors added to this category in future effort(s). The
same basic actionable reaction is expected by 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)
Polk & Rosen Expires Sept 9, 2009 [Page 19]
Internet Draft Location Conveyance in SIP Mar 2009
- Format (geo or civic) isn't supported (100)
- Cannot parse location (100)
- Can't find LIS (no access or no path (100) or denied access(500))
- Dereference failed (timeout) (200)
- Insufficient location info supplied (300)
- Cannot find 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 the Require, Supported and Unsupported headers. Whenever a
UA wants to indicate support for this SIP extension, the geolocation
option tag is included in a Supported header of the SIP request.
4.5 Using sip/sips/pres as a Dereference Scheme
If an LbyR URI is included in a SIP request, it MUST be a SIP, SIPS
or PRES-URI. When PRES: is used, if the resulting resolution, 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 to implement.
Dereferencing a Target's location using SIP or SIPS MUST be
accomplished by treating the URI as a presence URI and generating a
SUBSCRIBE request to a presence server as defined in [RFC3856]
using the 'presence' event package. The resulting NOTIFY will
contain a PIDF, which MUST contain a PIDF-LO. See Figure 2. for a
basic message flow for a dereference.
When used in this manner, SIP is a Using Protocol as defined in
[RFC3693] and elements receiving location MUST honor the
'usage-element' rules as defined in this extension.
Polk & Rosen Expires Sept 9, 2009 [Page 20]
Internet Draft Location Conveyance in SIP Mar 2009
Alice Location Server Bob
| |
| INVITE w/ LbyR URI |
|-------------------------------------------------------->|
| | |
| 200 (OK) |
|<--------------------------------------------------------|
| | |
| | SUBSCRIBE to LbyR URI |
| |<-----------------------------|
| | 200 (OK) |
| |----------------------------->|
| | |
| | NOTIFY w/ PIDF-LO |
| |----------------------------->|
| | 200 (OK) |
| |<-----------------------------|
| | |
Figure 2. Location-by-Reference and Dereferencing
In Figure 2., Alice sends Bob her location in an LbyR URI. Bob
receives this LbyR URI in the INVITE and generates a new transaction
(SUBSCRIBE) to retrieve the PIDF-LO of Alice. If accepted, the
PIDF-LO will be in the NOTIFY request from the Location Server 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 as is in the
coordinate format example is in appendix B, which is taken from
[RFC4776]. The differences between the two formats are within the
<gp:location-info> of the examples. Other than this portion of each
Polk & Rosen Expires Sept 9, 2009 [Page 21]
Internet Draft Location Conveyance in SIP Mar 2009
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 all the way to Bob's domain.
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="point2d">
<timestamp>2007-12-02T14:00:00Z</timestamp>
Polk & Rosen Expires Sept 9, 2009 [Page 22]
Internet Draft Location Conveyance in SIP Mar 2009
<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 this message. It is expected that any node wanting to
know where user target123 is would subscribe to server5 to
dereference the sips-URI (see Figure 2. for this message flow, and
Section 5.2 for this decoded example). The returning NOTIFY would
contain Alice's location in a PIDF-LO, as if it were included in a
message body (part) of the original INVITE here.
5.2 Location-by-reference
Below is an INVITE request with an LbyR URI instead of an LbyV
PIDF-LO message body part shown in Section 5.1. It is up to the
location recipient to dereference Alice's location at the Atlanta
LIS server containing the location record. Dereferencing, if done
with SIP, is accomplished by the Location Recipient sending a
SUBSCRIBE request to the URI reference for Alice's location. The
Polk & Rosen Expires Sept 9, 2009 [Page 23]
Internet Draft Location Conveyance in SIP Mar 2009
received NOTIFY is the first SIP request containing Alice's UA
location, as a PIDF-LO message body (see Figure 2 for this message
flow example). The NOTIFY, in this case, is the SIP request that is
conveying location, and not the INVITE. There is no retransmission
of location in this usage.
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com
;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <sips:3sdefrhy2jj7@lis.atlanta.example.com>
;inserted-by="bigbox3.atlanta.example.com"
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@pc33.atlanta.example.com>
(...SDP goes here as the only message body)
A Location Recipient would need to dereference the sips-URI in the
Geolocation header field to retrieve Alice's location. If the
atlanta.example.com domain chooses to implement location conveyance
and delivery in this fashion (i.e., LbyR), it is RECOMMENDED that
entities outside this domain be able to reach the dereference
server, otherwise this model of implementation is only viable within
the atlanta.example.com domain.
6. SIP Element Behavior
Because a device's location is generally considered to be sensitive
in nature, location information needs to be protected when
transmitted. This can be addressed through securing the location
information to prevent either viewing or changing the PIDF-LO.
Section 26 of [RFC3261] defines the security functionality SIPS by
transporting SIP messages with either TLS or IPSec protection
between SIP entities.
If a SIP entity wants to prevent all SIP entities in a request path
from viewing or just changing the contents of the PIDF-LO, save
those that possess decryption key, the message body needs to be
secure by a means such as S/MIME. This would be the case in which a
UAC wants to make sure only the destination UAS can read the
PIDF-LO. S/MIME can be used for just signing, and not encrypting, a
PIDF-LO message body to ensure the integrity of the PIDF-LO is
maintained.
Polk & Rosen Expires Sept 9, 2009 [Page 24]
Internet Draft Location Conveyance in SIP Mar 2009
6.1 UAC Behavior
A UAC can send location in a SIP request, either because it is
expected to facilitate location-based routing of the request, or
spontaneously (i.e., a purpose not defined in this document but
known to the UAC). Alice communicating her location to Bob in a SIP
request is a simple example of this. If Alice wanted to include her
location 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), and
this document does not limit which type of Multipart is used, though
future documents MAY specify or limit Multipart to a subset of all
the choices for a given use.
A UAC conveying location MUST include a locationValue in a
Geolocation header (see section 4.1) with either an LbyV indication
(a cid-URL), or an LbyR. An LbyV message body sent without a
Geolocation header field MUST NOT occur. The UAC supporting this
extension MUST include a Supported header with the 'geolocation'
option tag.
More than one location format (civic and coordinate) can be included
in the same message body part, but all location parts of the same
PIDF-LO MUST point at the same position on the earth, identifying
the same target. The same location in multiple formats, for
example, a partial or complete geodetic and a partial or complete
civic, can allow the recipient to use the most convenient or
preferable format for its use.
Multiple PIDF-LOs are allowed in the same request, with each allowed
to point at separate positions - 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 in a single SIP request for 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 is to do with more than one location, nor does it give any
preference regarding which location is better or worse than another
location in the same request.
The 'geolocation' option tag is inserted in a Supported header by a
UAC to provide an indication of support for this extension. The
presence of the 'geolocation' option tag in a Supported header
without a Geolocation header field in the same message informs a SIP
element receiving this request that the UAC understands this
extension, but it does not know or wish to convey its location at
this time. Certain scenarios exist (location-based retargeting) in
which location is required in a SIP request in order to retarget the
message properly. This affects how a UAS or SIP server processes
such a request.
Polk & Rosen Expires Sept 9, 2009 [Page 25]
Internet Draft Location Conveyance in SIP Mar 2009
The 'geolocation' option tag SHOULD NOT be used in the Proxy-Require
Header, because the UAC often will not know the underlying topology
to know which proxy will do the retargeting, thus increasing the
likelihood of a request failure by the first hop proxy that does not
understand this extension, but is required to by inclusion of the
option tag in this header.
A UAC inserting a locationValue MUST include an "inserted-by="
parameter to indicate its hostport. This is copied to the
"inserter=" parameter of the Geolocation-Error header in a response
if a Location Recipient determines there is something wrong with the
locationValue in 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 problem in the
response, and who 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 the network (DHCP or LLDP-MED), the UAC MAY learn its LbyR
URI (from DHCP for example). If the latter is the case, the UAC MAY
SUBSCRIBE to this LbyR URI, using the 'presence' event package, to
get and store its own location.
The act of dereferencing a Target's LbyR will be challenged by the
LIS where this location record is - providing a good deal of
protection, SHOULD still be treated as equivalent to possession of
the location information itself and thus TLS SHOULD be used when
transmitting LbyR hop-by-hop along the path to the Location
Recipient, for protection reasons. This is not to be confused with
a possession model, 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 location record. The Ruleholder from [RFC3693]
is still very much in control - for any entity possessing the LbyR.
If the Location Generator wishes to control whether any location
included in the SIP request or added along the signaling path of
this request can be viewed for routing decisions, the Location
Generator adds a Geolocation header value including the
"routing-allowed=no" parameter. This header parameter provides
specific policy rules for each locationValue (if there is more than
one inserted along the signaling path) within the SIP request. A
UAC SHOULD include the "routing-allowed" header parameter, with or
without a locationValue, to each SIP request supporting this
specification to ensure the UAC's policy for intermediaries which
might add a locationValue of the Target downstream. The UAC
understands that the default behavior for SIP servers is to consider
this value to be present, and that it is set to "no".
The UAC MUST understand there is no feedback mechanism to inform the
Polk & Rosen Expires Sept 9, 2009 [Page 26]
Internet Draft Location Conveyance in SIP Mar 2009
Target if a SIP server has included a locationValue downstream.
If a UAC has already conveyed location in the original request of a
transaction, and wants to update its location information (for
whatever reason) after the original request is sent, or after a
dialog is created (regardless of how the UAC conveyed location
previously, as an LbyV or LbyR) - this is done by a UAC sending an
UPDATE request [RFC3311] containing the geolocation option tag and
Geolocation header with the new locationValue (LbyV or LbyR) to the
original destination UAS.
A PIDF includes identity information. It is possible for the
identity in the PIDF to be anonymous. Implementations of this
extension SHOULD consider the appropriateness of including an
anonymous identity in the location information where a real identity
is not required. When using LbyR, the LbyR MUST NOT contain 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 is inappropriate for use in
protecting a PIDF, as the sender does not have a secure identity of
the recipient.
6.1.1 UAC Receiving a Location Failure Indication
Location Recipients can be either, or both, destination UASs and
intermediate servers that use the location information for
location-based routing decisions. If a sent request fails based on
the location information in the request, a 424 (Bad Location
Information) response is sent back to the UAC. The 424 MUST have a
Geolocation-Error header containing one or more locationErrorValues
in the response message. A locationErrorValue has a header
parameter indicating which entity inserted the locationValue
correlated to this error, called the "inserter=" parameter. This
"inserter=" parameter (in the locationErrorValue) is copied from the
"inserted-by=" parameter (from the locationValue) by the Location
Recipient (UAS or proxy) sending the error response. A UAC
receiving a Geolocation-Error in any response type MUST review the
"inserter=" parameter in the locationErrorValue to see if it
indicates this UAC. If locationErrorValue does not match, the
locationErrorValue MUST be ignored. If a locationErrorValue is in a
424, and the "inserter=" entity is not this UAC, the response SHOULD
be treated as a 400 response. If locationErrorValue does indicate
this UAC, this UAC MUST process the response, including the
Geolocation-Error code (defined in section 4.3). Further, UAC MUST
Polk & Rosen Expires Sept 9, 2009 [Page 27]
Internet Draft Location Conveyance in SIP Mar 2009
ignore a Geolocation-Error header value, even for this UAC, even in
a 424 response if the UAC did not include a Geolocation header value
(with locationValue) in the request part of the transaction.
A UAC MAY reattempt a new request if it believes it can correct the
stated failure in the Geolocation-Error header, unless the location
error is a 5XX level error - which clearly states in Section 4.3 not
to do this. A UAC MUST follow all the guidance that pertains to
UACs from Section 4.3 (Geolocation-Error header), heeding what to do
in case it receives any of the error codes articulated in that
section.
Any UAC that inserted location into a request SHOULD be prepared to
receive the Geolocation-Error header in any response, looking to
determine if a locationErrorValue is meant for the UAC, and to react
accordingly.
If a UAC includes location in a request, and either the UAS does not
determine errored location was critical to the transaction and
accept the request, or the request failed for reason other than
location, any response MAY contain a Geolocation-Error header
containing a locationErrorValue with the details of the location
error.
6.2 UAS Behavior
If the Geolocation header field is present in a received SIP
request, the type of URI contained in the locationValue will
indicate if location is an LbyV in a message body (part) or LbyR,
requiring an additional dereference transaction. If the LbyR URI is
sip:, sips: or pres:, and the UAS wants to learn the UAC's location,
the UAS MUST initiate a SUBSCRIBE to the URI provided to retrieve
the PIDF-LO being conveyed by the UAC as defined in [RFC3856]. If
successful, the PIDF-LO will be returned in the NOTIFY request from
the remote host. The UAS is not REQUIRED to dereference the LbyR if
it does not want to (by configuration or user choice). It is
RECOMMENDED the UAS render the location sent to it, however it is
configured to do so.
A Require header with the 'geolocation' option tag indicates the
UAC is requiring the UAS understand this extension or else send
an error response. A 420 (Bad Extension) with a 'geolocation'
option tag in an Unsupported header would be the appropriate
response in this case.
It is possible, but undesirable, for a message to arrive with a body
containing an LbyV, but with no Geolocation header field value
pointing to it (potentially no Geolocation header field at all). In
this case, the recipient MAY still read and use the message body.
Unless stated otherwise by future standards-track publication(s), a
LbyR URI only has meaning within the Geolocation header field and
Polk & Rosen Expires Sept 9, 2009 [Page 28]
Internet Draft Location Conveyance in SIP Mar 2009
MUST NOT appear in any other SIP header field.
There are 2 Geolocation header parameters,
o "inserted-by="
o "used-for-routing"
The "inserted-by=" parameter informs a Location Recipient which SIP
element added this locationValue to the SIP request. This parameter
is mandatory for each locationValue in the request. The value in
the "inserted-by=" parameter is copied into the "inserter="
parameter in each locationErrorValue if there is an error in the
location to be reported back to the location sender. See section
6.2.1.
The "used-for-routing" parameter is included in the locationValue if
a SIP server used the location in the request to determine how to
route or forward the message towards the ultimate destination. If
there are more than one locationValues in the Geolocation header,
and it is possible that different locationValues were used to route
the message at different times of this request's journey. This is
allowed, as it is consistent with the rule that anytime a message is
routed based upon a locationValue, a "used-for-routing" parameter is
added to the applicable locationValue. This parameter should be
present in each locationValue used along the path. A
"used-for-routing" parameter MUST NOT ever be removed from a
locationValue in a request.
Additional locationValues inserted into a request SHOULD be placed
the order they were generated, and not rearranged. This informs a
Location Recipient which was the last locationValue in the message
that was used to route the message. This is for troubleshooting and
management reasons.
Individual header parameters in any received locationValue MUST NOT
be modified or deleted in transit to the ultimate destination.
A UAS MUST NOT send location in a response message, as there can be
any number of issues/problems with receiving location, and the UAC
or proxy servers cannot error a response. Therefore, the UAS, if it
wants to send a UAC its location, SHOULD do so in a new request in a
separate transaction. This document gives no guidance which SIP
request to use, but SIP MESSAGE is a viable choice.
A UAS MAY include a 'geolocation' option tag in the Supported header
of a response, indicating it does understand this extension, even if
location was not in a request to the UAS.
A UAS wishing to dereference an LbyR URI contained in a received
request will use the 'presence' event package in a SUBSCRIBE request
to the URI. If accepted, the PIDF-LO will return to the UAS in a
NOTIFY request. If there are any errors during dereferencing, or in
Polk & Rosen Expires Sept 9, 2009 [Page 29]
Internet Draft Location Conveyance in SIP Mar 2009
the PIDF-LO itself, the UAS will error the original request to the
UAC with a locationErrorValue indicating what the UAS concluded was
wrong with the location. This is to include any dereferencing
problems encountered.
Section 4.5 of this document called for the IANA registration of 3
URI schemes (sip:, sips:, and pres:) that are mandatory to implement
for dereferencing.
A UAS MUST be prepared to receive subsequent location updates from
the UAC, either LbyV or LbyR (regardless of how the UAS received
location previously from this UAC). The UAC will convey location
using the UPDATE [RFC3311] method to the UAS.
If there 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 the same PIDF-LO MUST be about the same Target
(identifier) and point at the same position on the earth. If there
is more than one PIDF-LO with different Target identifiers, then
the UAC is merely telling the UAS where more than one Target is, and
there should not be any conflict.
6.2.1 UAS Generating a Location Failure Indication
If a UAS receives location in a request, but determines there is a
problem with the location in the request, it is the responsibility
of the UAS to inform whomever inserted location into that request
there was a problem experienced. The Geolocation header in the
request has a locationValue, providing the UAS a URI indicating
where the Target's location is. The Location Target identified in
the PIDF-LO may or may not be the location inserter, or the
generator of the request (the UAC or SIP server). Ultimately,
location is in a PIDF-LO. This is either in the request as a
message body (LbyV), or it has to be dereferenced from the LbyR in
the locationValue in the request. LbyR records are typically kept
on a LIS, which can challenge all dereference requests. All
PIDF-LOs have a Location Target identifier. This is who the
location is about. The "inserted-by=" parameter of the
locationValue tells the UAS who inserted that locationValue. This
"inserted-by=" parameter is copied into the "inserter=" parameter of
the locationErrorValue generated by the Location Recipient (the
UAS), in a response, when it wants to inform the location
"inserter=" entity there was a problem with the location it
received.
There can be more than one locationValues in a request. The
"inserter=" parameter in the locationErrorValue will distinguish it
Polk & Rosen Expires Sept 9, 2009 [Page 30]
Internet Draft Location Conveyance in SIP Mar 2009
from being misunderstood by entities that did not insert the errored
location.
If there is one valid locationValue 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 to send a locationErrorValue for each errored
locationValue, 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 Sighter, as
defined in RFC3693. 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 URI in a locationValue,
because SIP servers are not allowed to insert message bodies, as of
the time of this publication, from all the way back to RFC3261.
Each locationErrorValue has a error code, letting the location
"inserter=" entity know what was wrong with the location supplied.
See Section 4.3 for the 5 actionable responses a UAC can take from
a locationErrorValue.
If the location "inserted-by=" entity, meaning either the UAC or
proxy in the message path, chose to indicate that location was so
important in the request to include a 'geolocation' option tag in a
Require header, the response SHOULD be a 424 (Bad Location
Information) back to the "inserter=" entity (knowing the response
will ultimately go to the UAC regardless) if there needs to be a
locationErrorValue sent because the location was bad. Only entities
identified in a locationErrorValue as the "inserter=" entity will
pay attention to this locationErrorValue. All other entities MUST
ignore any locationErrorValue not directed towards them. See
section 4.3 for more information on this, including all the location
specific errors and Geolocation-Error header parameters.
In the above scenario ('geolocation' option tag in a Require
header), the only other response can be a 420, but only if the UAS
does not support this Geolocation extension to SIP, else the 424 is
sent.
If the location "inserted-by=" entity placed the 'geolocation'
option tag in a Supported header, the response can be a 424 if it
chooses, but also can be any other SIP response, including a 200
OK. A locationErrorValue in a Geolocation-Error header that is not
in a 424 (Bad Location Information) response is considered
informational by the Location Recipient, and not considered
important enough to reject the request based solely on bad location
information.
For example, Alice INVITEs Bob to a dialog, and includes geolocation
in the request. Bob can accept the INVITE with a 200 OK and still
add a locationErrorValue in the 200 OK indicating "yes, I accept
Polk & Rosen Expires Sept 9, 2009 [Page 31]
Internet Draft Location Conveyance in SIP Mar 2009
your request, and btw, something was wrong with the location you
provided (in the INVITE)". What was wrong with the location is
indicated by the Geolocation-Error code. Who this
locationErrorValue is for is indicated by the "inserter=" parameter.
Each locationErrorValue is destined for one "inserter=" entity.
This gives a Location Recipient one mechanism to tell each inserter
what the Location Recipient concluded was wrong with what the
"inserter=" included (as far as location is concerned). Therefore,
o there MUST be a locationErrorValue for each locationValue that
was considered bad by the UAS to ensure each upstream location
inserter understands which error code(s) is intended for them
(and which to ignore).
o there MUST NOT be more than one locationErrorValue in the
response per locationValue in the request.
o there MUST NOT be more than one locationErrorValue to the same
"inserter=" in the request.
o there MUST NOT be a locationErrorValue in the response for a
locationValue in the request that was not in error, according to
the Location Recipient.
Here is an example of a Geolocation-Error header
Geolocation-Error: 400; code="Permission Necessary";
node="server42.example2.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 the "inserter="'s location. This location
may be in the request, or it may need to be in the request and was
not. If location is encrypted, server42 doesn't know it is in the
request. server42.example.com sends a 424 (Bad Location
Information) response with a locationErrorValue indicating a 400
location error, which means it requires permission to view Alice's
location 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 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 to travel
through a different server than server42 (or it might not).
See Section 4.3 for further rules about the Geolocation-Error header
and the locationErrorValue.
This document says nothing about what a Location Recipient does with
Polk & Rosen Expires Sept 9, 2009 [Page 32]
Internet Draft Location Conveyance in SIP Mar 2009
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
locationErrorValue - each having one "inserter=" parameter. The
error codes destined for the same inserter MUST NOT contradict the
meaning of the problem 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 to a request. This
implies that a proxy can add a Geolocation locationValue with
LbyR URI, but not LbyV message body.
It is allowed, but NOT RECOMMENDED, for more than one SIP element to
insert location into a request along its path. As described earlier
in this document, each insertion of location into a SIP request is
accompanied by a new locationValue in a Geolocation header. Also
described earlier, each locationValue MUST contain an "inserted-by="
value indicating to a Location Recipient which host inserted
location into a particular request.
However, if location is already in a SIP request, a SIP server
SHOULD NOT add another LbyR that identifies the same target in the
PIDF-LO (in the <dm:device id> element) to the same request. This
will likely cause confusion at the Location Recipient as to which to
use.
A proxy is permitted to read any locationValue, and the associated
body, if not S/MIME protected, in transit if present, 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 parameter "routing-allowed" is present 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 the LbyV message body. Further, SIP
servers MUST NOT attempt to dereference an LbyR. This is because
the SIP request, likely from the originating UAC did not give the
SIP server permission to view the location within the SIP request.
If the Geolocation header parameter "routing-allowed" is present in
a SIP request, the value MUST NOT be changed during processing of
the request. If the Geolocation header parameter "routing-allowed"
is not present, SIP servers are to treat the location within the
request as if the header parameter "routing-allowed" were present
and set to "no".
In the spirit of informing implementers of B2BUAs and SBCs, each
Polk & Rosen Expires Sept 9, 2009 [Page 33]
Internet Draft Location Conveyance in SIP Mar 2009
server type really should adhere to the above proxy guidance with
respect to the "Routing-allowed" header parameter, understanding
that there are no IETF police, and the specific behaviors of these
types of SIP servers cannot presently be defined. In other words, if
the particular type of SIP server mentioned here is not the ultimate
destination of this SIP request and supports this SIP extension,
each policy rule within the Geolocation header needs to remain
intact and unchanged.
No type of SIP server can delete a "Routing-allowed" header
parameter, but if one is not yet present, any SIP server MAY add a
"Routing-allowed" header parameter with the value set to "no" only.
More than one Geolocation locationValue in a message is permitted,
but can cause confusion at the recipient. If a proxy chooses to add
a locationValue to a Geolocation header, which would be a local
policy decision, the new locationValue MUST be added to the end of
the header (after previous locationValue(s)). This is done to
create an order of insertion of locationValues along the path.
Proxies MUST NOT modify the order of locationValues in a geolocation
header.
A proxy wishing to dereference an LbyR URI contained in a received
request will use the 'presence' event package in a SUBSCRIBE request
to the URI. If accepted, the PIDF-LO will return to the proxy in a
NOTIFY request. If there are any errors during dereferencing, or in
the PIDF-LO itself, the proxy will error the original request to the
UAC with a locationErrorValue indicating what the proxy concluded
was wrong with the location. This is to include any dereferencing
problems encountered.
6.3.1 Proxy Behavior with Geolocation Header Parameters
SIP servers MUST NOT delete any existing Geolocation locationValue
(URI or header 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 this Geolocation header
field MUST NOT occur. For example, an existing Geolocation
locationValue in a request of:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice123@atlanta.example.com";
can be modified by a proxy to add the "used-for-routing" parameter,
like this:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice123@atlanta.example.com";
used-for-routing
Polk & Rosen Expires Sept 9, 2009 [Page 34]
Internet Draft Location Conveyance in SIP Mar 2009
if this is the locationValue the proxy used to make a retargeting
decision based upon, but make no other modification.
A SIP server MAY add a new Geolocation locationValue to a SIP
request. The proxy SHOULD NOT insert a locationValue of a Location
Target unless it is reasonably certain it knows the actual location
of the Location Target, for example, if it thoroughly understands
the topology of the underlying access network and it can identify
the device reliably (in the presence of, for example, NAT or VPN).
Routing errors are likely if the SIP server inserts an incorrect
locationValue.
A server adding a locationValue to an existing Geolocation header
would look like:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice123@atlanta.example.com",
<sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
inserted-by="lis1.atlanta.example.com"
Notice the locationValue added by the proxy is last among
locationValues. This practice MUST be done for all added
locationValues.
If this request was then retargeted by an intermediary using the
locationValue inserted by the server, the intermediary would add a
"used-for-routing" parameter like this:
Geolocation: <cid:alice123@atlanta.example.com>;
inserted-by="alice123@atlanta.example.com",
<sips:3sdefrhy2jj7@lis1.atlanta.example.com>;
inserted-by="lis1.atlanta.example.com"; used-for-routing
It is conceivable that an initial routing decision is made on
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, it can occur. In such a
case, proxies MUST NOT remove any existing "used-for-routing" header
parameter. In this instance, the SIP server retargeting based on
another locationValue MUST add the "used-for-routing" header
parameter to the locationValue used for retargeting by this server.
This will result in a Geolocation header looking as if it were
retargeting more than once, which would be true - and is the desired
outcome.
A Proxy that inserts or adds locationValue into a request MAY move a
'geolocation' option that is in a Supported header into a Require
header if this proxy deems geolocation to be that important to
Location Recipient(s) of this request.
Polk & Rosen Expires Sept 9, 2009 [Page 35]
Internet Draft Location Conveyance in SIP Mar 2009
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. The one thing 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 or policing location within
requests (for whatever reason).
If a proxy inserted a locationValue into a request, it SHOULD be
ready to examine the response to that request, in case there is one
or more location errors in the response. To a great degree, this
scenario has the proxy behaving as a UAC (see section 6.1.1.) that
included a locationValue a request, which then receives an error to
that locationValue.
This location inserting proxy SHOULD be 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 location it supplied was in error. It SHOULD react
accordingly to the error code received. This document gives no
guidance what the proxy should do to rectify the bad location
information, but a future document MAY address this.
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]:
Polk & Rosen Expires Sept 9, 2009 [Page 36]
Internet Draft Location Conveyance in SIP Mar 2009
"The Using Protocol will typically facilitate that the keys
associated with the credentials are transported to the
respective parties, that is, key establishment is the
responsibility of the Using Protocol."
[RFC3261] and the documents it references define the key
establishment mechanisms.
Quoting requirement #6 of [RFC3693]:
"(Single Message Transfer) In particular, for tracking of
small Target devices, the design should allow a single
message/packet transmission of location as a complete
transaction."
When used for tracking, a simple NOTIFY or UPDATE normally is
relatively small, although the PIDF itself can get large. Normal
RFC 3261 procedures of reverting to TCP when the MTU size is
exceeded would be invoked.
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 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
extension especially sensitive.
When location is inserted by a UAC, which is RECOMMENDED, it can
decide whether to reveal its location using hop-by-hop methods. UAC
implementations MUST make such capabilities conditional on explicit
user permission, and SHOULD alert a user that location is being
conveyed. Proxies inserting location for location-based routing are
unable to meet this requirement, and such use is NOT RECOMMENDED.
Polk & Rosen Expires Sept 9, 2009 [Page 37]
Internet Draft Location Conveyance in SIP Mar 2009
Proxies conveying location using this extension MUST have the
permission of the Target to do so.
One facet within this extension is such that locations can be placed
on a remote server, accessible with the possession of a URI. The
concept of an LbyR URI has its own security considerations. It is
tempting to assume that the dereference would have authentication,
authorization and other security mechanisms that limit the access to
information. Unfortunately, this might not be true. The access
network the UAC is connected to can be the source of location
reference, and it might not have any credentialing mechanism
suitable for controlling access to location. Consider,
specifically, a nomadic user connected to an access network in a
hotel. The UAC has no way to provide a credential acceptable to
the hotel Location Server (LS) to any of its intended Location
Recipients. The recipient of a reference does not know if a
reference has appropriate authorization policies or not. The LS
should provide location to any requestor.
Accordingly, possession of the reference should be considered
equivalent to possession of the value, and the reference should be
treated with the same degree of care as the value. Specifically,
TLS MUST be used to protect the security of the reference. Notice
that this does not constrain the dereference protocol to use TLS.
That specification is left entirely to the dereferencing protocol
documents.
There is no integrity on any locationValue or locationErrorValue
header parameter end-to-end (or middle-to-end if the value was
inserted by a intermediary), so recipients of either header need to
implicitly trust the header contents, and take whatever precautions
each entity deems appropriate give these facts.
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).
9.1 IANA Registration for the SIP Geolocation Header
The SIP Geolocation header is created by this document, with its
definition and rules in Section 4.1 of this document, to be added to
the sip-parameters, in the portion titled "Header Field Parameters
and Parameter Values".
Polk & Rosen Expires Sept 9, 2009 [Page 38]
Internet Draft Location Conveyance in SIP Mar 2009
Predefined
Header Field Parameter Name Values Reference
---------------- ------------------- ---------- ---------
Geolocation inserted-by= no [this doc]
Geolocation used-for-routing no [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 sip-parameters within IANA.
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
The SIP Geolocation-error header is created by this document, with
its definition and rules in Section 4.3 of this document, to be
added to the sip-parameters, 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 [this doc]
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 sip-parameters within
IANA. 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.
Polk & Rosen Expires Sept 9, 2009 [Page 39]
Internet Draft Location Conveyance in SIP Mar 2009
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 same data) Location [this doc]
cannot be processed at this time. Error recipient
should try again with same data.
300 "Retry Location Later" (with device updated location) [this doc]
Location cannot be processed at this time. Error
recipient should try again with same data.
400 "Permission Necessary" Permission from calling user [this doc]
to reveal location 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
denied because of the location in the request.
Recipient should not try again.
9.6 IANA Registration of LbyR 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
URI Scheme Content-Type Reference
---------- ------------ ---------
SIP: [this doc]
SIPS: [this doc]
PRES: [this doc]
Additions to this registry require an industry specification.
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, Paul Kyzivat,
Shida Shubert, Umesh Sharma, Richard Barnes, Ted Hardie, Matt
Polk & Rosen Expires Sept 9, 2009 [Page 40]
Internet Draft Location Conveyance in SIP Mar 2009
Lepinski and Jacqueline Lee for constructive feedback and nits
checking.
A special thanks to Paul Kyzivat for his help with the ABNF in this
document, to Dan Wing for help with the S/MIME example, and to
Robert Sparks for many helpful comments and the proper building of
the Geolocation-Error header.
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
Requirement Levels", RFC 2119, March 1997
[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., "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.
[RFC2976] S. Donovan, "The SIP INFO Method", RFC 2976, Oct 2000
Polk & Rosen Expires Sept 9, 2009 [Page 41]
Internet Draft Location Conveyance in SIP Mar 2009
[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.
[IANA-civic] http://www.iana.org/assignments/civic-address-types-
registry
11.2 References - Informative
[RFC3693] J. Cuellar, J. Morris, D. Mulligan, J. Peterson. J. Polk,
"Geopriv Requirements", RFC 3693, February 2004
[RFC3825] J. Polk, J. Schnizlein, M. Linsner, "Dynamic Host
Configuration Protocol Option for Coordinate-based Location
Configuration Information", RFC 3825, July 2004
[RFC4776] H. Schulzrinne, " Dynamic Host Configuration Protocol
(DHCPv4 and DHCPv6) Option for Civic Addresses Configuration
Information ", RFC 4776, October 2006
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
Polk & Rosen Expires Sept 9, 2009 [Page 42]
Internet Draft Location Conveyance in SIP Mar 2009
Appendix A. Requirements for SIP Location Conveyance
The following subsections address the requirements placed on the
UAC, the UAS, as well as SIP proxies when conveying location. There
is a motivational statement below each requirements that is not
obvious in intent
A.1 Requirements for a UAC Conveying Location
UAC-1 The SIP INVITE Method [RFC3261] must support location
conveyance.
UAC-2 The SIP MESSAGE method [RFC3428] must support location
conveyance.
UAC-3 SIP Requests within a dialog should support location
conveyance.
UAC-4 Other SIP Requests may support location conveyance.
UAC-5 There must be one, mandatory to implement means of
transmitting location confidentially.
Motivation: interoperability
UAC-6 It must be possible for a UAC to update location conveyed
at any time in a dialog, including during dialog
establishment.
Motivation: in case a UAC has moved prior to the establishment of a
dialog between UAs, the UAC must be able to send new location
information. In the case of location having been conveyed,
and the UA moves, it needs a means to update the conveyed to
party of this location change.
UAC-7 The privacy and security rules established within [RFC3693]
that would categorize SIP as a 'Using Protocol' must be met.
UAC-8 The PIDF-LO [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
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
Polk & Rosen Expires Sept 9, 2009 [Page 43]
Internet Draft Location Conveyance in SIP Mar 2009
the original UAC with the UAS's location.
UAC-10 There must be a mechanism to differentiate the ability of the
UAC to convey location from the UACs lack of knowledge of its
location
Motivation: Failure to receive location when it is expected can be
because the UAC does not implement this extension, or it can
be that the UAC implements the extension, but does not know
where it is. This may be, for example, due to the failure of
the access network to provide a location acquisition
mechanisms the UAC understands. These cases must be
differentiated.
UAC-11 It must be possible to convey location to proxy servers
along the path.
Motivation: Location-based routing.
A.2 Requirements for a UAS Receiving Location
The following are the requirements for location conveyance by a UAS:
UAS-1 SIP Responses must support location conveyance.
Just as with UAC-9, UAS-1 has been DEPRECATED by the SIP WG,
due to the many problems this requirement would have caused
if implemented. The solution is for the above UAS to send a
new request to the original UAC with the UAS's location.
UAS-2 There must be a unique 4XX response informing the UAC it did
not provide applicable location information.
In addition, requirements UAC-5, 6, 7 and 8 apply to the UAS
A.3 Requirements for SIP Proxies and Intermediaries
The following are the requirements for location conveyance by a SIP
proxies and intermediaries:
Proxy-1 Proxy servers must be capable of adding a Location header
field during processing of SIP requests.
Motivation: Provide the capability of network assertion of location
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
Polk & Rosen Expires Sept 9, 2009 [Page 44]
Internet Draft Location Conveyance in SIP Mar 2009
tunnels and roaming mechanisms, it may be difficult for a
network to reliably know the location of the endpoint. Proxy
assertion of location is NOT RECOMMENDED unless the sip
signaling network has reliable knowledge of the actual
location of the Targets.
Proxy-2 There must be a unique 4XX response informing the UAC it
did not provide applicable location information.
Appendix B. Example of INVITE with S/MIME encrypted Civic PIDF-LO
This appendix gives an *EXAMPLE* (meaning this might contain errors
based on future review) of a SIP INVITE request that points to the
same position on the earth as the coordinate based example that is
in section 5.1 in the body of this document:
The INVITE request is TLS hop-by-hop encrypted, and the
LbyV message body is S/MIME encrypted. This example
shows the location message body in its unencrypted form for clarity.
The message body lines below that have the '$' signs are S/MIME
encrypted. In this example, the SDP is not S/MIME encrypted. A
complete list of IANA registered CAtypes can be found at
[IANA-civic].
INVITE sips:bob@biloxi.example.com SIP/2.0
Via: SIP/2.0/TLS pc33.atlanta.example.com
;branch=z9hG4bK74bf9
Max-Forwards: 70
To: Bob <sips:bob@biloxi.example.com>
From: Alice <sips:alice@atlanta.example.com>;tag=9fxced76sl
Call-ID: 3848276298220188511@atlanta.example.com
Geolocation: <cid:target123@atlanta.example.com>
;inserted-by="alice@atlanta.example.com"
Supported: geolocation
Accept: application/sdp, application/pidf+xml
CSeq: 31862 INVITE
Contact: <sips:alice@pc33.atlanta.example.com>
Content-Type: multipart/mixed; boundary=boundary1
Content-Length: ...
--boundary1
Content-Type: application/sdp
...SDP goes here
--boundary1
Content-Type: application/pkcs7-mime;
smime-type=enveloped-data; name=smime.p7m
Content-ID: <target123@atlanta.example.com>
Polk & Rosen Expires Sept 9, 2009 [Page 45]
Internet Draft Location Conveyance in SIP Mar 2009
$ Content-Type: application/pidf+xml
$
$ <?xml version="1.0" encoding="UTF-8"?>
$ <presence xmlns="urn:ietf:params:xml:ns:pidf"
$ xmlns:gp="urn:ietf:params:xml:ns:pidf:geopriv10"
$ xmlns:cl="urn:ietf:params:xml:ns:pidf:geopriv10:civicAddr"
$ entity="pres:alice@atlanta.example.com">
$ <tuple id="sg89ae">
$ <timestamp>2007-07-09T14:00:00Z</timestamp>
$ <status>
$ <gp:geopriv>
$ <gp:location-info>
$ <cl:civicAddress>
$ <cl:country>US</cl:country>
$ <cl:A1>Texas</cl:A1>
$ <cl:A3>Colleyville</cl:A3>
$ <cl:HNO>3913</cl:HNO>
$ <cl:A6>Treemont</cl:A6>
$ <cl:STS>Circle</cl:STS>
$ <cl:PC>76034</cl:PC>
$ <cl:NAM>Haley's Place</cl:NAM>
$ <cl:FLR>1</cl:FLR>
$ <cl:civicAddress>
$ </gp:location-info>
$ <gp:usage-rules>
$ <gp:retransmission-allowed>no</gp:retransmission-allowed>
$ <gp:retention-expiry>2007-07-27T18:00:00Z</gp:retention-
$ expiry>
$ </gp:usage-rules>
$ <gp:method>DHCP</gp:method>
$ <gp:provided-by>www.example.com</gp:provided-by>
$ </gp:geopriv>
$ </status>
$ </tuple>
$ </presence>
--boundary1--
Polk & Rosen Expires Sept 9, 2009 [Page 46]