One document matched: draft-kempf-netlmm-nohost-ps-00.txt
J. Kempf
Internet Draft K. Leung
Document: draft-kempf-netlmm-nohost-ps-00.txt P. Roberts
K. Nishida
G. Giaretta
M. Liebsch
Expires: December, 2005 June, 2005
Problem Statement for IP Local Mobility
(draft-kempf-netlmm-nohost-ps-00.txt)
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Abstract
In this document, the well-known problem of localized mobility management
for IP link handover is given a fresh look. After a short discussion of the
problem and a couple of scenarios, the principal shortcomings of existing
solutions are discussed.
Table of Contents
1.0 Introduction................................................2
2.0 The Local Mobility Problem..................................3
3.0 Scenarios for Localized Mobility Management.................6
4.0 Most Serious Problems with Existing Solutions...............7
5.0 Security Considerations.....................................8
6.0 Author Information..........................................8
7.0 Informative References......................................9
8.0 IPR Statements.............................................10
9.0 Disclaimer of Validity.....................................10
10.0 Copyright Notice..........................................10
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1.0 Introduction
Localized mobility management has been the topic of much work in the IETF
for some time, and it may seem as if little remains to be said on the topic.
The experimental protocols developed from previous work, namely FMIPv6 [1]
and HMIPv6[2], involve host-based solutions that mimic to a greater or
lesser extent the approach taken by Mobile IPv6 [3] for global mobility
management. However, recent developments in the IETF and the WLAN
infrastructure market suggest that it may be time to take a fresh look at
localized mobility management. Firstly, new IETF work on global mobility
management protocols that are not Mobile IPv6, such as HIP [4] and Mobike
[5], suggests that future wireless IP hosts may support a more diverse set
of global mobility protocols. Secondly, the success in the WLAN
infrastructure market of WLAN switches, which perform localized mobility
management without any host involvement, suggests a possible design paradigm
that could be used to accommodate other global mobility management options
on the host while reducing host software complexity and expanding the range
of hosts that could be accommodated.
This document briefly describes the local mobility problem and a few
scenarios where localized mobility management would be desirable. Then, it
describes the two most serious problems with existing protocols: the
requirement for host support, and the complex security interactions required
between the host and the network. More detailed requirements and gap
analysis for existing protocols can be found in [6].
1.1 Terminology
Mobility terminology in this draft follows that in RFC 3753[7], some of
which are included here:
IP Link
A set of routers, mobile nodes, and wireless access points that share
link broadcast capability or its functional equivalent. This definition
covers one or multiple access points under one or several access
routers. In the past, such a set has been called a subnet, but this
term is not strictly correct for IPv6, since multiple subnet prefixes
can be assigned to an IP link in IPv6.
Local Mobility
Local Mobility is mobility over a restricted area of the network
topology. Note that, although the area of network topology over which
the mobile node moves may be restricted, the actual geographic area,
though not unlimited, could be quite large, depending on the mapping
between the network topology and the wireless coverage area.
Localized Mobility Management
Localized Mobility Management is a generic term for protocols dealing
with IP mobility management confined within a restricted, topologically
localized portion of the network. Localized mobility management
signaling is not routed outside a locally restricted part of the
network, although a handover may trigger Global Mobility Management
signaling. Localized mobility management protocols exploit the locality
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of movement by confining movement related changes to a topologically
restricted part of the network when movement is restricted
geographically.
Localized Mobility Management Domain
A Localized Mobility Management Domain consists of the following three
components: wireless or other access points, access routers, localized
mobility management domain gateways which form the boundary to other
networks and may shield other networks from the specialized routing
protocols (if any) run in the Localized Mobility Management Domain; and
(optionally) other internal routers which may also be needed in some
cases to support a specialized routing protocol.
Global Mobility Protocol
A Global Mobility Protocol is a mobility protocol used by the mobile
node to change the global, end-to-end routing of packets when movement
causes a topology change and thus invalidates a global unicast address
on the local IP link currently in active use by the mobile node. The
Global Mobility Protocol allows the mobile node to maintain a mapping
between a permanent rendezvous or home address and a temporary care-of
address for rendezvous with nodes that want to initiate a connection,
and it may also provide direct routing through the rendezvous node
and/or optimized routing directly between correspondent nodes and the
local address. Typically, this protocol will be Mobile IPv6 [1] but it
could also be HIP [4] or Mobike [5] (note: although Mobike is not
considered a mobility management protocol in general, for purposes of
this document, it will be so considered because it manages the address
map and routing between a fixed VPN endpoint address and a changing
local address).
Global Mobility Anchor Point
A node in the network where the mobile node has its fixed home address
that maintains the mapping between the home address and care-of address
for purposes of rendezvous and possibly traffic forwarding. For Mobile
IPv6 [1], this is the home agent. For HIP [4], this is the rendezvous
server. For Mobike [5], this is the VPN tunnel gateway in the home
network.
Intra-Link Mobility
Intra-Link Mobility is mobility between wireless access points within
an IP Link. Typically, this kind of mobility only involves Layer 2
mechanisms, so Intra-Link Mobility is often called Layer 2 mobility. No
IP link configuration is required upon movement since the link does not
change, but some IP signaling may be required for the mobile node to
confirm whether or not the change of wireless access point also
resulted in a change of IP link. If the IP link consists of a single
access point/router combination, then this type of mobility is
typically absent. See Figure 1.
2.0 The Local Mobility Problem
The local mobility problem is restricted to providing IP mobility management
for mobile nodes within a localized mobility management domain. Localized
mobility management domain consists of a group of access routers connected
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to wired or wireless access points on the downlink side and a wired IP core
through one or more aggregation routers on the side that is routed toward
the border router and the Internet. The aggregation routers function as a
localized mobility management domain gateway, although in this case, there
is no specialized routing protocol and the routers function as a standard IP
routed network. This is illustrated in Figure 1, where the aggregation
routers are designated as "AggR". Transitions between service providers in
separate autonomous systems or across broader topological "boundaries"
within the same service provider are excluded.
Figure 1 depicts the scope of local mobility in comparison to global
mobility. The Aggregation Routers AggR A1 and B1 are gateways to the
localized mobility management domain. The Access Routers AR A1 and A2 are in
Localized Mobility Management Domain A, B1 is in Localized Mobility
Management Domain B. Note that it is possible to have additional aggregation
routers between AggR A1 and AggR B1 and the access routers if the domain is
large. Access Points AP A1 through A3 are in Localized Mobility Management
Domain A, B1 and B2 are in Localized Mobility Management Domain B. Other
Aggregation Routers, Access Routers, and Access Points are also possible.
The figure implies a star topology for the localized mobility management
domain deployment, and the star topology is the primary one of interest
since it is quite common, but the problems discussed here are equally
relevant to ring or mesh topologies in which access routers are directly
connected through some part of the network.
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Localized Mobility Localized Mobility
Management Domain A Management Domain B
+-------+ +-------+
|AggR A1| (other AggRs) |AggR B1| (other AggRs)
+-------+ +-------+
@ @ @
@ @ @
@ @ @
@ @ @
@ @ @
@ @ @
+-----+ +-----+ +-----+
|AR A1| |AR A2|(other ARs) |AR B1| (other ARs)
+-----+ +-----+ +-----+
* * *
* * * * *
* * * * *
* * * * *
* * * * *
* * * (other APs) * * (other APs)
/\ /\ /\ /\ /\
/AP\ /AP\ /AP\ /AP\ /AP\
/ A1 \ / A2 \ / A3 \ / B1 \ / B2 \
------ ------ ------ ------ ------
+--+ +--+ +--+ +--+
|MN|----->|MN|----->|MN|-------->|MN|
+--+ +--+ +--+ +--+
Intra-link Local Global
Mobility Mobility Mobility
Figure 1. Scope of Local and Global Mobility Management
As shown in the figure, a global mobility protocol is necessary when a
mobile node (MN) moves between two localized mobility management domains.
Exactly what the scope of the localized mobility management domains is
depends on deployment considerations. Mobility between two access points
under the same access router and within the same IP link (e.g. within the
same VLAN) constitutes Intra-link mobility, and is typically handled by
Layer 2 mobility protocols. If there is only one access point/cell per
access router, then intra-link mobility may be lacking. Between these two
lies local mobility. Local mobility occurs when a mobile node moves between
two access points connected to two different access routers in the same
localized mobility management domain.
Global mobility protocols allow a mobile node to maintain reachability when
a change between access routers occurs, by updating the address mapping
between the home address and care-of address at the global mobility anchor
point, or even end to end by changing the care-of address directly at the
correspondent node. A global mobility management protocol can therefore be
used between access routers for handling local mobility. However, there are
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three well-known problems involved in using a global mobility protocols for
every transition between access routers. Briefly, they are:
1) Update latency. If the global mobility anchor point and/or
correspondent node (for route optimized traffic) is at some distance
from the mobile node's access network, the global mobility update may
require a considerable amount of time, during which time packets
continue to be routed to the old care-of address and are essentially
dropped.
2) Signaling overhead. The amount of signaling required when a mobile
node moves from one IP link to another can be quite extensive,
including all the signaling required to configure an IP address on the
new link and global mobility protocol signaling back into the network
for changing the home to care-of address mapping. The signaling volume
may negatively impact wireless bandwidth usage and real time service
performance.
3) Location privacy. The change in care-of address as the mobile node
moves exposes the mobile node's topological location to correspondents
and potentially to eavesdroppers. An attacker that can assemble a
mapping between subnet prefixes in the mobile node's access network
and geographical locations can determine exactly where the mobile node
is located. This can expose the mobile node's user to threats on their
location privacy.
These problems suggest that a protocol to localize the management of
topologically small movements is preferable to using a global mobility
management protocol on each IP link move. Note also that if localized
mobility management is provided, it is not strictly required for a mobile
node to support a global mobility management protocol since movement within
a localized mobility management domain can still be accommodated. Without
such support, however, a mobile node experiences a disruption in its traffic
when it moves beyond the border of the localized mobility management domain.
3.0 Scenarios for Localized Mobility Management
There are a variety of scenarios in which localized mobility management is
attractive.
3.1 Large Campus with Diverse Physical Interconnectivity
One scenario where localized mobility management would be attractive is for
a campus wireless LAN deployment in which parts of the campus are connected
by links that are other than 802.3 or in which it is not possible to cover
the campus by one VLAN. In this case, the campus is divided into separate IP
links each served by one or more access routers. This kind of deployment is
served today by wireless LAN switches that co-ordinate IP mobility between
them, effectively providing localized mobility management at the link layer.
Since the protocols are proprietary and not interoperable, any deployments
that require IP mobility necessarily require switches from the same vendor.
3.2 Advanced Cellular Network
Next generation cellular protocols such as 802.16e [8] and Super 3G/3.9G [9]
with all IP network architecture [10] have the potential to run IP deeper
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into the access network than the current 3G cellular protocols, similar to
today's WLAN networks. This means that the access network can become a
routed IP network. Interoperable localized mobility management can unify
local mobility across a diverse set of wireless protocols all served by IP,
including advanced cellular, WLAN, and personal area wireless technologies
such as UWB and Bluetooth. Localized mobility management at the IP layer
does not replace Layer 2 mobility (where available) but rather complements
it. A standardized, interoperable localized mobility management protocol for
IP can remove the dependence on IP layer localized mobility protocols that
are specialized to specific link technologies or proprietary, which is the
situation with today's 3G protocols. The expected benefit is a reduction in
maintenance cost and deployment complexity. See [6] for a more detailed
discussion of the requirements for localized mobility management.
3.3 Picocellular Network with Small But Host-Dense IP Links
Future radio link protocols at very high frequencies may be constrained to
very short, line of sight operation. Even some existing protocols, such as
UWB and Bluetooth, are designed for low power, short range operation. For
such protocols, extremely small picocells become more practical. Although
picocells do not necessarily imply "pico IP links", wireless sensors and
other advanced host applications may end up making such picocellular type
networks host-dense, requiring subnets that cover small geographical areas,
such as a single room. The ability to aggregate many subnets under a
localized mobility management scheme can help reduce the amount of IP
signaling required on IP link movement, both over the air and through the
access network.
4.0 Problems with Existing Solutions
Existing solutions for localized mobility management fall into two classes:
1) Interoperable IP level protocols that require changes to the host's IP
stack and handle localized mobility management as a service provided to
the host by the localized mobility management domain,
2) Proprietary protocols that handle localized mobility for any host but only
for a specific type of link layer, namely 802.11 running on an 802.3 wired
network backhaul.
For Solution 1), the following are specific problems:
1) The host software requirement limits broad usage even if the
modifications are small. The success of WLAN switches indicates that
network operators and users prefer no host software modifications. This
preference is likely to be independent of the lack of widespread Mobile
IPv4 deployment, since it is much easier to deploy and use the network.
2) Future hosts may choose other global mobility management protocols, such
as HIP or Mobike. The existing localized mobility management solutions
all depend on Mobile IP or derivatives.
3) Existing localized mobility management solutions do not support both IPv4
and IPv6.
4) Security for the existing localized mobility management solutions
requires complex security associations with network elements for no
improvement in security over what is available if localized mobility
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management is not used. In addition to the additional signaling required
to set up these security associations, provisioning a mobile node with
credentials for roaming to all the localized mobility management domains
where the mobile node might end up may prove difficult, acting as a
possible barrier to deployment.
Solution 2 has the following problems:
1) Existing solutions only support WLAN networks with Ethernet backhaul and
therefore are not available for advanced cellular networks or
picocellular protocols, or other types of wired backhaul.
2) Each WLAN switch vendor has its own proprietary protocol that does not
interoperate with other vendor's equipment.
3) Because the solutions are based on layer 2 routing, they may not scale up
to a metropolitan area, or local province.
Having an interoperable, standardized localized mobility management protocol
that is scalable to topologically large networks, but requires no host
involvement is a highly desirable solution.
5.0 Security Considerations
Localized mobility management has certain security considerations, one of
which - need for localized mobility management domain to host security - was
touched on in this document. Existing localized mobility management
solutions increase the need for host to localized mobility management domain
signaling and provisioning of the mobile node with credentials without
increasing the security beyond what is available if no localized mobility
management solution is used. A more complete discussion of the security
requirements for localized mobility management can be found in [6].
6.0 Acknowledgements
The authors would like to thank Youngjune Gwon, DoCoMo Labs USA, for writing
the first draft of this document.
7.0 Author Information
James Kempf
DoCoMo USA Labs
181 Metro Drive, Suite 300
San Jose, CA 95110
USA
Phone: +1 408 451 4711
Email: kempf@docomolabs-usa.com
Kent Leung
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134
USA
EMail: kleung@cisco.com
Phil Roberts
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Motorola Labs
Schaumberg, IL
USA
Email: phil.roberts@motorola.com
Katsutoshi Nishida
NTT DoCoMo Inc.
3-5 Hikarino-oka, Yokosuka-shi
Kanagawa,
Japan
Phone: +81 46 840 3545
Email: nishidak@nttdocomo.co.jp
Gerardo Giaretta
Telecom Italia Lab
via G. Reiss Romoli, 274
10148 Torino
Italy
Phone: +39 011 2286904
Email: gerardo.giaretta@tilab.com
Marco Liebsch
NEC Network Laboratories
Kurfuersten-Anlage 36
69115 Heidelberg
Germany
Phone: +49 6221-90511-46
Email: marco.liebsch@ccrle.nec.de
8.0 Informative References
[1] Koodli, R., editor, "Fast Handovers for Mobile IPv6," Internet Draft, a
work in progress.
[2] Soliman, H., editor, "Hierarchical Mobile IPv6 Mobility Management,"
Internet Draft, a work in progress.
[3] Johnson, D., Perkins, C., and Arkko, J., "Mobility Support in IPv6,"
RFC 3775.
[4] Moskowitz, R., Nikander, P., Jokela, P., and Henderson, T., "Host
Identity Protocol", Internet Draft, work in progress.
[5] Kivinen, T., and Tschopfening, H., "Design of the MOBIKE Protocol",
Internet Draft, work in progress.
[6] Kempf, J., Leung, K., Roberts, P., Giaretta, G., Liebsch, M., Nishita,
K., and Gwon, Y., "Requirements and Gap Analysis for Localized Mobility
Management", Internet Draft, work in progress.
[7] Manner, J., and Kojo, M., "Mobility Related Terminology", RFC 3753,
June, 2004.
[8] IEEE, "Air Interface for Mobile Broadband Wireless Access Systems",
802.16e, 2005.
[9] "DoCoMo's Proposals for 3G Long Term Evolution - Technologies for Super
3G", TSG-RAN Future Evolution Workshop, Toronto, Canada, 2-3 November,
2004.
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[10] 3GPP, "All-IP Network (AIPN) Feasibility Study", Chris Sancho, ed.,
3GPP TR 22.978, 2005.
9.0 IPR Statements
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not be available; nor does it represent that it has made any independent
effort to identify any such rights. Information on the procedures with
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Copies of IPR disclosures made to the IETF Secretariat and any assurances of
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implementers or users of this specification can be obtained from the IETF
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The IETF invites any interested party to bring to its attention any
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may cover technology that may be required to implement this standard.
Please address the information to the IETF at ietf-ipr@ietf.org.
10.0 Disclaimer of Validity
This document and the information contained herein are provided on an "AS
IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS
SPONSORED BY (IF ANY), THE INTERNET SOCIETY 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 HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS
FOR A PARTICULAR PURPOSE.
11.0 Copyright Notice
Copyright (C) The Internet Society (2005). This document is subject to the
rights, licenses and restrictions contained in BCP 78, and except as set
forth therein, the authors retain all their rights.
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