Network Working Group H. Tschofenig
Internet-Draft Nokia Siemens Networks
Intended status: Informational H. Schulzrinne
Expires: January 10, 2008 Columbia U.
July 9, 2007
GEOPRIV Layer 7 Location Configuration Protocol; Problem Statement and
Requirements
draft-ietf-geopriv-l7-lcp-ps-03.txt
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Copyright (C) The IETF Trust (2007).
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Abstract
This document provides a problem statement, lists requirements and
captures design aspects for a Geopriv Layer 7 Location Configuration
Protocol L7 (LCP). This protocol aims to allow an end host to obtain
location information, by value or by reference, from a Location
Configuration Server (LCS) that is located in the access network.
The obtained location information can then be used for a variety of
different protocols and purposes. For example, it can be used as
input to the Location-to-Service Translation Protocol (LoST) or to
convey location within SIP to other entities.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Fixed Wired Environment . . . . . . . . . . . . . . . . . 5
3.2. Moving Network . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Wireless Access . . . . . . . . . . . . . . . . . . . . . 9
4. Discovery of the Location Configuration Server . . . . . . . . 11
5. Identifier for Location Determination . . . . . . . . . . . . 13
6. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 20
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
11.1. Normative References . . . . . . . . . . . . . . . . . . . 22
11.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
Intellectual Property and Copyright Statements . . . . . . . . . . 25
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1. Introduction
This document provides a problem statement, lists requirements and
captures design aspects for a Geopriv Layer 7 Location Configuration
Protocol L7 (LCP). The protocol has two purposes:
o It is used to obtain location information (referred as "Location
by Value" or LbyV) from a dedicated node, called the Location
Configuration Server (LCS).
o It enables the Target to obtain a reference to location
information (referred as "Location by Reference" or LbyR). This
reference can take the form of a subscription URI, such as a SIP
presence URI, a HTTP/HTTPS URI, or another URI. The requirements
related to the task of obtaining a LbyR are described in a
separate document, see [4].
The need for these two functions can be derived from the scenarios
presented in Section 3.
For this document we assume that the GEOPRIV Layer 7 LCP runs between
the end host (i.e., the Target in [1] terminology) acting as the LCP
client and the Location Configuration Server acting as an LCP server.
This document is structured as follows. Section 4 discusses the
challenge of discovering the LCS in the access network. Section 5
compares different types of identifiers that can be used to retrieve
location information. A list of requirements for the L7 LCP can be
found in Section 6.
This document does not describe how the access network provider
determines the location of the end host since this is largely a
matter of the capabilities of specific link layer technologies or
certain deployment environments.
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2. Terminology
In this document, the key words "MUST", "MUST NOT", "REQUIRED",
"SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY",
and "OPTIONAL" are to be interpreted as described in RFC 2119 [2],
with the qualification that unless otherwise stated these words apply
to the design of the GEOPRIV Layer 7 Location Configuration Protocol.
The term Location Configuration Server (LCS) refers to an entity
capable of determining the location of an end point and of providing
that location information, a reference to it, or both via the
Location Configuration Protocol (LCP) to the requesting party, in
most cases to the end point itself (or to an authorized entity that
acts on behalf of it).
This document also uses terminology from [1] and [3].
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3. Scenarios
This section describes a few network scenarios where the L7 LCP may
be used. Note that this section does not aim to exhaustively list
all possible deployment environments. Instead we focus on the
following environments:
o DSL/Cable networks, WiMax-like fixed access
o Airport, City, Campus Wireless Networks, such as 802.11a/b/g,
802.16e/Wimax
o 3G networks
o Enterprise networks
We illustrate a few examples below.
3.1. Fixed Wired Environment
Figure 1 shows a DSL network scenario with the Access Network
Provider and the customer premises. The Access Network Provider
operates link and network layer devices (represented as Node) and the
LCS.
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+---------------------------+
| |
| Access Network Provider |
| |
| +--------+ |
| | Node | |
| +--------+ +----------+ |
| | | | LCS | |
| | +---| | |
| | +----------+ |
| | |
+-------+-------------------+
| Wired Network
<----------------> Access Network Provider demarc
|
+-------+-------------------+
| | |
| +-------------+ |
| | NTE | |
| +-------------+ |
| | |
| | |
| +--------------+ |
| | Device with | Home |
| | NAPT and | Router |
| | DHCP server | |
| +--------------+ |
| | |
| | |
| +------+ |
| | End | |
| | Host | |
| +------+ |
| |
|Customer Premises Network |
| |
+---------------------------+
Figure 1: DSL Scenario
The customer premises consists of a router with a Network Address
Translator with Port Address Translation (NAPT) and a DHCP server as
used in most Customer Premises Networks (CPN) and the Network
Termination Equipment (NTE) where Layer 1 and sometimes Layer 2
protocols are terminated. The router in the home network (e.g.,
broadband router, cable or DSL router) typically runs a NAPT and a
DHCP server. The NTE is a legacy device and in many cases cannot be
modified for the purpose of delivering location information to the
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end host. The same is true of the device with the NAPT and DHCP
server.
It is possible for the NTE and the home router to physically be in
the same box, or for there to be no home router, or for the NTE and
end host to be in the same physical box (with no home router). An
example of this last case is where Ethernet service is delivered to
customers' homes, and the Ethernet NIC in their PC serves as the NTE.
Current Customer Premises Network (CPN) deployments frequently show
the following characteristics:
1. CPE = Single PC
1. with Ethernet NIC (PPPoE or DHCP on PC); there may be a
bridged DSL or cable modem as NTE, or the Ethernet NIC might
be the NTE
2. with USB DSL or cable modem [PPPoA, PPPoE, or DHCP on PC]
Note that the device with NAPT and DHCP of Figure 1 is not
present in such a scenario.
2. One or more hosts with at least one router (DHCP Client or PPPoE,
DHCP server in router; VoIP can be soft client on PC, stand-alone
VoIP device, or Analog Terminal Adaptor (ATA) function embedded
in router)
1. combined router and NTE
2. separate router with NTE in bridged mode
3. separate router with NTE (NTE/router does PPPoE or DHCP to
WAN, router provides DHCP server for hosts in LAN; double
NAT)
The majority of fixed access broadband customers use a router. The
placement of the VoIP client is mentioned to describe what sorts of
hosts may need to be able to request location information. Soft
clients on PCs are frequently not launched until long after bootstrap
is complete, and are not able to control any options that may be
specified during bootstrap. They also cannot control whether a VPN
client is running on the end host.
3.2. Moving Network
An example of a moving network is a "WIMAX-like fixed wireless"
scenario that is offered in several cities, like New Orleans, Biloxi,
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etc., where much of the communications infrastructure was destroyed
due to a natural disaster. The customer-side antenna for this
service is rather small (about the size of a mass market paperback
book) and can be run off battery power. The output of this little
antenna is a RJ-45 Ethernet jack. A laptop can be plugged into this
Ethernet jack. The user would then run a PPPoE client to connect to
the network. Once the network connection is established, the user
can run a SIP client on the laptop.
The network-side antenna is, for example, connected through ATM to
the core network, and from there to the same BRASs that serve regular
DSL customers. These Broadband Remote Access Servers (BRASs)
terminate the PPPoE sessions, just like they do for regular DSL.
The laptop and SIP client are, in this case, unaware that they are
"mobile". All they see is an Ethernet connection, and the IP address
they get from PPPoE does not change over the coverage area. Only the
user and the network are aware of the laptop's mobility.
Further examples of moving networks can be found in busses, trains,
and airplanes.
Figure 2 shows an example topology for a moving network.
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+--------------------------+
| Wireless |
| Access Network Provider |
| |
| +----------+|
| +-------+ LCS ||
| | | ||
| +---+----+ +----------+|
| | Node | |
| | | |
| +---+----+ |
| | |
+------+-------------------+
| Wireless Interface
|
+------+-------------------+
| | Moving Network |
| +---+----+ |
| | NTE | +--------+ |
| | +---+ Host | |
| +-+-----++ | B | |
| | \ +--------+ |
| | \ |
|+---+----+ \ +---+----+ |
|| Host | \ | Host | |
|| A | \+ B | |
|+--------+ +--------+ |
+--------------------------+
Figure 2: Moving Network
3.3. Wireless Access
Figure 3 shows a wireless access network where a moving end host
obtains location information or references to location information
from the LCS. The access equipment uses, in many cases, link layer
devices. Figure 3 represents a hotspot network found, for example,
in hotels, airports, and coffee shops. For editorial reasons we only
describe a single access point and do not depict how the LCS obtains
location information since this is very deployment specific.
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+--------------------------+
| Access Network Provider |
| |
| +----------+|
| +-------| LCS ||
| | | ||
| +--------+ +----------+|
| | Access | |
| | Point | |
| +--------+ |
| | |
+------+-------------------+
|
+------+
| End |
| Host |
+------+
Figure 3: Wireless Access Scenario
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4. Discovery of the Location Configuration Server
When a Target wants to retrieve location information from the LCS it
first needs to discover it. Based on the problem statement of
determining the location of the Target, which is known best by
entities close to the Target itself, we assume that the LCS is
located in the access network. Several procedures have been
investigated that aim to discover the LCS in such an access network.
DHCP-based Discovery:
In some environments the Dynamic Host Configuration Protocol
(DHCP) might be a good choice for discovering the FQDN or the IP
address of the LCS. In environments where DHCP can be used it is
also possible to use the already defined location extensions. In
environments with legacy devices, such as the one shown in
Section 3.1, a DHCP based discovery solution may not be possible.
DNS-based Discovery:
With this idea the end host obtains its public IP address (e.g.,
via STUN [5]) in order to obtain its domain name (via the usual
reverse DNS lookup). Then, the SRV or NAPTR record for that
domain is retrieved. This relies on the user's public IP address
having a DNS entry.
Redirect Rule:
A redirect rule at a device in the access network, for example at
the AAA client, will be used to redirect the L7 LCP signalling
messages (destined to a specific port) to the LCS. The end host
could then discover the LCS by sending a packet to almost any
address (as long it is not in the user's home network behind a
NAT). The packet would be redirected to the respective LCS being
configured. The same procedure is used by captive portals whereby
any HTTP traffic is intercepted and redirected.
Multicast Query:
An end node could also discover a LCS by sending a multicast
request to a well-known address. An example of such a mechanism
is multicast DNS (see [6] and [7]).
The LCS discovery procedure raises deployment and security issues.
When an end host discovers a LCS it must be ensured that
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1. it does not talk to a man-in-the-middle, and
2. that the discovered entity is indeed an authorized LCS.
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5. Identifier for Location Determination
The LCS returns location information to the end host when it receives
a request. Some form of identifier is therefore needed to allow the
LCS to retrieve the Target's current location (or a good
approximation of it) from a database.
The chosen identifier needs to have the following properties:
Ability for Target to learn or know the identifier:
The Target MUST know or MUST be able to learn the identifier
(explicitly or implicitly) in order to send it to the LCS.
Implicitly refers to the situation where a device along the path
between the end host and the LCS modifies the identifier, as it is
done by a NAT when an IP address based identifier is used.
Ability to use the identifier for location determination:
The LCS MUST be able to use the identifier (directly or
indirectly) for location determination. Indirectly refers to the
case where the LCS uses other identifiers internally for location
determination, in addition to the one provided by the Target.
Security properties of the identifier:
Misuse needs to be minimized whereby off-path adversary MUST NOT
be able to obtain location information of other Targets. A on-
path adversary in the same subnet SHOULD NOT be able to spoof the
identifier of another Target in the same subnet.
The following list discusses frequently mentioned identifiers and
their properties:
Host MAC Address:
The Target's MAC address is known to the end host, but not carried
over an IP hop and therefore not accessible to the LCS in most
deployment environments (unless carried in the L7 LCP itself).
ATM VCI/VPI:
The VPI/VCI is generally only seen by the DSL modem. Almost all
routers in the US use 1 of 2 VPI/VCI value pairs: 0/35 and 8/35.
This VC is terminated at the DSLAM, which uses a different VPI/VCI
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(per end customer) to connect to the ATM switch. Only the network
provider is able to map VPI/VCI values through its network. With
the arrival of VDSL, ATM will slowly be phased out in favor of
Ethernet.
Switch/Port Number:
This identifier is available only in certain networks, such as
enterprise networks, typically available via proprietary protocols
like CDP or, in the future, 802.1ab.
Cell ID:
This identifier is available in cellular data networks and the
cell ID may not be visible to the end host.
Host Identifier:
The Host Identifier introduced by the Host Identity Protocol [8]
allows identification of a particular host. Unfortunately, the
network can only use this identifier for location determination if
the operator already stores an mapping of host identities to
location information. Furthermore, there is a deployment problem
since the host identities are not used in todays networks.
Cryptographically Generated Address (CGA):
The concept of a Cryptographically Generated Address (CGA) was
introduced by [9]. The basic idea is to put the truncated hash of
a public key into the interface identifier part of an IPv6
address. In addition to the properties of an IP address it allows
a proof of ownership. Hence, a return routability check can be
omitted. It is only available for IPv6 addresses.
Network Access Identifiers:
A Network Access Identifier [10] is used during the network access
authentication procedure, for example in RADIUS [11] and Diameter
[12]. In DSL networks the user credentials are, in many cases,
only known by the home router and not configured at the Target
itself. To the network, the authenticated user identity is only
available if a network access authentication procedure is
executed. In case of roaming the user's identity might not be
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available to the access network since security protocols might
offer user identity confidentiality and thereby hiding the real
identity of the user allowing the access network to only see a
pseudonym or a randomized string.
Unique Client Identifier
The DSL Forum has defined that all devices that expect to be
managed by the TR-069 interface be able to generate an identifier
as described in Section 3.4.4 of the TR-069v2 DSL Forum document.
It also has a requirement that routers that use DHCP to the WAN
use RFC 4361 [13] to provide the DHCP server with a unique client
identifier. This identifier is, however, not visible to the
Target when legacy NTE device are used.
IP Address:
The Target's IP address may be used for location determination.
This IP address is not visible to the LCS if the end host is
behind one or multiple NATs. This may not be a problem since the
location of a host that is located behind a NAT cannot be
determined by the access network. The LCS would in this case only
see the public IP address of the NAT binding allocated by the NAT,
which is the expected behavior. The property of the IP address
for a return routability check is attractive to return location
information only to the address that submitted the request. If an
adversary wants to learn the location of a Target (as identified
by a particular IP address) then it does not see the response
message (unless he is on the subnetwork or at a router along the
path towards the LCS).
On a shared medium an adversary could ask for location information
of another Target. The adversary would be able to see the
response message since it is sniffing on the shared medium unless
security mechanisms, such as link layer encryption, are in place.
With a network deployment as shown in Section 3.1 with multiple
hosts in the Customer Premise being behind a NAT the LCS is unable
to differentiate the individual end points. For WLAN deployments
as found in hotels, as shown in Section 3.3, it is possible for an
adversary to eavesdrop data traffic and subsequently to spoof the
IP address in a query to the LCS to learn more detailed location
information (e.g., specific room numbers). Such an attack might,
for example, compromise the privacy of hotel guests.
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6. Requirements
The following requirements and assumptions have been identified:
Requirement L7-1: Identifier Choice
The L7 LCP MUST be able to carry different identifiers or MUST
define an identifier that is mandatory to implement. Regarding
the latter aspect, such an identifier is only appropriate if it is
from the same realm as the one for which the location information
service maintains identifier to location mapping.
Requirement L7-2: Mobility Support
The L7 LCP MUST support a broad range of mobility from devices
that can only move between reboots, to devices that can change
attachment points with the impact that their IP address is
changed, to devices that do not change their IP address while
roaming, to devices that continuously move by being attached to
the same network attachment point.
Requirement L7-3: Layer 7 and Layer 2/3 Provider Relationship
The design of the L7 LCP MUST NOT assume a business or trust
relationship between the VSP and the ISP/ASP. Requirements for
resolving a reference to location information are not discussed in
this document.
Requirement L7-4: Layer 2 and Layer 3 Provider Relationship
The design of the L7 LCP MUST assume that there is a trust and
business relationship between the L2 and the L3 provider. The L3
provider operates the LCS and needs to obtain location information
from the L2 provider since this one is closest to the end host.
If the L2 and L3 provider for the same host are different
entities, they cooperate for the purposes needed to determine end
system locations.
Requirement L7-5: Legacy Device Considerations
The design of the L7 LCP MUST consider legacy devices, such as
residential NAT devices and NTEs in an DSL environment, that
cannot be upgraded to support additional protocols, for example,
to pass additional information towards the Target.
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Requirement L7-6: VPN Awareness
The design of the L7 LCP MUST assume that at least one end of a
VPN is aware of the VPN functionality. In an enterprise scenario,
the enterprise side will provide the LCS used by the client and
can thereby detect whether the LCS request was initiated through a
VPN tunnel.
Requirement L7-7: Network Access Authentication
The design of the L7 LCP MUST NOT assume prior network access
authentication.
Requirement L7-8: Network Topology Unawareness
The design of the L7 LCP MUST NOT assume end systems being aware
of the access network topology. End systems are, however, able to
determine their public IP address(es) via mechanisms, such as STUN
[5] or NSIS NATFW NSLP [14] .
Requirement L7-9: Discovery Mechanism
The L7 LCP MUST define a mandatory-to-implement LCS discovery
mechanism.
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7. Security Considerations
A discussion about security aspects can be found in another document.
[Editor's Note: The security related content was previously in this
document and will be published in a separate document soon.]
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8. IANA Considerations
This document does not require actions by IANA.
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9. Contributors
This contribution is a joint effort of the GEOPRIV Layer 7 Location
Configuration Requirements Design Team of the IETF GEOPRIV Working
Group. The contributors include Henning Schulzrinne, Barbara Stark,
Marc Linsner, Andrew Newton, James Winterbottom, Martin Thomson,
Rohan Mahy, Brian Rosen, Jon Peterson and Hannes Tschofenig.
We would like to thank the GEOPRIV working group chairs, Andy Newton,
Randy Gellens and Allison Mankin, for creating the design team.
The design team members can be reached at:
Marc Linsner: mlinsner@cisco.com
Rohan Mahy: rohan@ekabal.com
Andrew Newton: andy@hxr.us
Jon Peterson: jon.peterson@neustar.biz
Brian Rosen: br@brianrosen.net
Henning Schulzrinne: hgs@cs.columbia.edu
Barbara Stark: Barbara.Stark@bellsouth.com
Martin Thomson: Martin.Thomson@andrew.com
Hannes Tschofenig: Hannes.Tschofenig@siemens.com
James Winterbottom: James.Winterbottom@andrew.com
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10. Acknowledgements
We would like to thank the IETF GEOPRIV working group chairs, Andy
Newton, Allison Mankin and Randall Gellens, for creating this design
team. Furthermore, we would like thank Andy Newton for his support
during the design team mailing list, for setting up Jabber chat
conferences and for participating in the phone conference
discussions.
We would also like to thank Murugaraj Shanmugam, Ted Hardie, Martin
Dawson, Richard Barnes, James Winterbottom, Tom Taylor, Otmar Lendl,
Marc Linsner, Brian Rosen, Roger Marshall, Guy Caron, Doug Stuard,
Eric Arolick, Dan Romascanu, Jerome Grenier, Martin Thomson, Barbara
Stark, Michael Haberler, and Mary Barnes for their WGLC review
comments.
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11. References
11.1. Normative References
[1] Cuellar, J., Morris, J., Mulligan, D., Peterson, J., and J.
Polk, "Geopriv Requirements", RFC 3693, February 2004.
[2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[3] Schulzrinne, H. and R. Marshall, "Requirements for Emergency
Context Resolution with Internet Technologies",
draft-ietf-ecrit-requirements-13 (work in progress),
March 2007.
11.2. Informative References
[4] Marshall, R., "Requirements for a Location-by-Reference
Mechanism used in Location Configuration and Conveyance",
draft-marshall-geopriv-lbyr-requirements-01 (work in progress),
March 2007.
[5] Rosenberg, J., Weinberger, J., Huitema, C., and R. Mahy, "STUN
- Simple Traversal of User Datagram Protocol (UDP) Through
Network Address Translators (NATs)", RFC 3489, March 2003.
[6] Aboba, B., Thaler, D., and L. Esibov, "Link-local Multicast
Name Resolution (LLMNR)", RFC 4795, January 2007.
[7] Cheshire, S. and M. Krochmal, "Multicast DNS",
draft-cheshire-dnsext-multicastdns-06 (work in progress),
August 2006.
[8] Moskowitz, R., "Host Identity Protocol", draft-ietf-hip-base-08
(work in progress), June 2007.
[9] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[10] Aboba, B., Beadles, M., Arkko, J., and P. Eronen, "The Network
Access Identifier", RFC 4282, December 2005.
[11] Rigney, C., Willens, S., Rubens, A., and W. Simpson, "Remote
Authentication Dial In User Service (RADIUS)", RFC 2865,
June 2000.
[12] Calhoun, P., Loughney, J., Guttman, E., Zorn, G., and J. Arkko,
"Diameter Base Protocol", RFC 3588, September 2003.
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[13] Lemon, T. and B. Sommerfeld, "Node-specific Client Identifiers
for Dynamic Host Configuration Protocol Version Four (DHCPv4)",
RFC 4361, February 2006.
[14] Stiemerling, M., "NAT/Firewall NSIS Signaling Layer Protocol
(NSLP)", draft-ietf-nsis-nslp-natfw-14 (work in progress),
March 2007.
[15] Peterson, J., "A Presence-based GEOPRIV Location Object
Format", RFC 4119, December 2005.
[16] Hardie, T., "LoST: A Location-to-Service Translation Protocol",
draft-ietf-ecrit-lost-05 (work in progress), March 2007.
[17] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
draft-ietf-sip-identity-06 (work in progress), October 2005.
[18] Peterson, J. and C. Jennings, "Enhancements for Authenticated
Identity Management in the Session Initiation Protocol (SIP)",
RFC 4474, August 2006.
Tschofenig & Schulzrinne Expires January 10, 2008 [Page 23]
Internet-Draft Geopriv L7 LCP; Problem Statement July 2007
Authors' Addresses
Hannes Tschofenig
Nokia Siemens Networks
Otto-Hahn-Ring 6
Munich, Bavaria 81739
Germany
Phone: +49 89 636 40390
Email: Hannes.Tschofenig@nsn.com
URI: http://www.tschofenig.com
Henning Schulzrinne
Columbia University
Department of Computer Science
450 Computer Science Building
New York, NY 10027
US
Phone: +1 212 939 7004
Email: hgs+ecrit@cs.columbia.edu
URI: http://www.cs.columbia.edu
Tschofenig & Schulzrinne Expires January 10, 2008 [Page 24]
Internet-Draft Geopriv L7 LCP; Problem Statement July 2007
Full Copyright Statement
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Tschofenig & Schulzrinne Expires January 10, 2008 [Page 25]
