NEMO Working Group T. Ernst
Internet-Draft Keio University / WIDE
Expires: April 27, 2006 October 24, 2005
Network Mobility Support Goals and Requirements
draft-ietf-nemo-requirements-05
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Abstract
Network mobility arises when a router connecting a network to the
Internet dynamically changes its point of attachment to the Internet
thereby causing the reachability of the said network to be changed in
relation to the fixed Internet topology. Such kind of network is
referred to as a mobile network. With appropriate mechanisms,
sessions established between nodes in the mobile network and the
global Internet can be maintained after the mobile router changes its
point of attachment. This document outlines the goals expected from
network mobility support and defines the requirements that must be
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met by the NEMO Basic Support solution.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. NEMO Working Group Objectives and Methodology . . . . . . . . 4
3. NEMO Support Design Goals . . . . . . . . . . . . . . . . . . 5
3.1. Migration Transparency . . . . . . . . . . . . . . . . . . 5
3.2. Performance Transparency and Seamless Mobility . . . . . . 5
3.3. Network Mobility Support Transparency . . . . . . . . . . 6
3.4. Operational Transparency . . . . . . . . . . . . . . . . . 6
3.5. Arbitrary Configurations . . . . . . . . . . . . . . . . . 6
3.6. Local Mobility and Global Mobility . . . . . . . . . . . . 7
3.7. Scalability . . . . . . . . . . . . . . . . . . . . . . . 7
3.8. Backward Compatibility . . . . . . . . . . . . . . . . . . 7
3.9. Secure Signaling . . . . . . . . . . . . . . . . . . . . . 8
3.10. Location Privacy . . . . . . . . . . . . . . . . . . . . . 8
3.11. IPv4 and NAT Traversal . . . . . . . . . . . . . . . . . . 8
4. NEMO Basic Support One-Liner Requirements . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. Change Log From Earlier Versions . . . . . . . . . . 13
A.1. Changes between version -04 and -05 . . . . . . . . . . . 13
A.2. Changes between version -03 and -04 . . . . . . . . . . . 13
A.3. Changes between version -02 and -03 . . . . . . . . . . . 13
A.4. Changes Between Version -01 and -02 . . . . . . . . . . . 14
A.5. Changes Between Version -00 and -01 . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
Intellectual Property and Copyright Statements . . . . . . . . . . 16
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1. Introduction
Network mobility support (see [1] for the related terminology) is
concerned with managing the mobility of an entire network, viewed as
a single unit, which changes its point of attachment to the Internet
and thus its reachability in the Internet topology. Such a network
is referred to as a mobile network and includes one or more mobile
routers (MRs) which connect it to the global Internet. Nodes behind
the MR(s) (MNNs) are both fixed (LFNs) and mobile (VMNs or LMNs). In
most cases, the internal structure of the mobile network will be
relatively stable (no dynamic change of the topology), but this is
not always true.
Cases of mobile networks include, for instance:
o Networks attached to people (Personal Area Networks or PANs): a
cell-phone with one cellular interface and one Bluetooth interface
together with a Bluetooth-enabled PDA constitute a very simple
instance of a mobile network. The cell-phone is the mobile router
while the PDA is used for web browsing or runs a personal web
server.
o Networks of sensors and computers deployed in vehicles: vehicles
are increasingly embedded with a number of processing units for
safety and ease of driving reasons, as advocated by ITS
(Intelligent Transportation Systems) applications ([4], [5]).
o Access networks deployed in public transportation (buses, trains,
taxis, aircrafts): they provide Internet access to IP devices
carried by passengers: laptop, camera, mobile phone: host mobility
within network mobility or PANs: network mobility within network
mobility, i.e. nested mobility (see [1] for the definition of
nested mobility).
o Ad-hoc networks connected to the Internet via an MR: for instance
students in a train that need both to set up an ad-hoc network
among themselves, and get Internet connectivity through the MR
connecting the train to the Internet.
Mobility of networks does not cause MNNs to change their own physical
point of attachment; however they do change their topological
location with respect to the global Internet. If network mobility is
not explicitly supported by some mechanisms, the mobility of the MR
results in MNNs losing Internet access and breaking ongoing sessions
between arbitrary correspondent node (CNs) in the global Internet and
those MNNs located within the mobile network. In addition, the
communication path between MNNs and correspondent nodes becomes sub-
optimal, and multiple levels of mobility will cause extremely sub-
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optimal routing.
Mobility-related terms used in this document are defined in [2],
whereas terms specifically pertaining to network mobility are defined
in [1]. This document is structured as follows: in Section 2 we
define the rough objectives and methodology of the NEMO working group
to handle network mobility issues and we emphasize the stepwise
approach the working group has decided to follow. A number of
desirable design goals are listed in Section 3. Those design goals
then serve as guidelines to define the requirements listed in
Section 4 for basic network mobility support [3].
2. NEMO Working Group Objectives and Methodology
The mechanisms required for handling network mobility issues were
lacking within the IETF standards when the NEMO working group was set
up at the IETF. At that time, work conducted on mobility support
(particularly in the Mobile IP working group) was to provide
continuous Internet connectivity and optimal routing to mobile hosts
only (host mobility support). Such mechanisms speficied in Mobile
IPv6 [6] are unable to support network mobility. The NEMO working
group has therefore been set up to deal with issues specific to
network mobility.
The primary objective of the NEMO work is to specify a solution which
allows mobile network nodes (MNNs) to remain connected to the
Internet and continuously reachable at all times while the mobile
router seving the mobile network changes its point of attachment.
The secondary goals of the work is to investigate the effects of
network mobility on various aspects of internet communication such as
routing protocol changes, implications of real-time traffic and fast
handovers, and optimizations. This should support the primary goal
of reachability for mobile network nodes. Security is an important
consideration too, and efforts should be made to use existing
security solutions if they are appropriate. Although a well-designed
solution may include security inherent in other protocols, mobile
networks also introduce new challenges.
To complete these tasks, the NEMO working group has decided to take a
stepwise approach. The steps in this approach include standardizing
a basic solution to preserve session continuity (NEMO Basic Support)
(see [3]), and studying the possible approaches and issues with
providing more optimal routing with potentially nested mobile
networks (NEMO Extended Support) (see [7]). However, the working
group is not chartered to actually standardize a solution for
extgended support at this point in time. If deemed necessary, the
working group will be rechartered based on the conclusions of the
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discussions.
For NEMO Basic Support, the working group will assume that none of
the nodes behind the MR will be aware of the network's mobility;
thus, the network's movement needs to be completely transparent to
the nodes inside the mobile network. This assumption accommodates
nodes inside the network that are not generally aware of mobility.
The efforts of the Mobile IP working group have resulted in the
Mobile IPv4 and Mobile IPv6 protocols, which have already solved the
issue of host mobility support. Since challenges to enabling mobile
networks are vastly reduced by this work, basic network mobility
support will adopt the methods for host mobility support used in
Mobile IP, and extend them in the simplest way possible to achieve
its goals. The basic support solution, now defined in [3] following
the requirements stated in Section 4 of the present document, is for
each MR to have a Home Agent, and use bi-directional tunneling
between the MR and HA to preserve session continuity while the MR
moves. The MR will acquire a care-of address at its attachment point
much like what is done for mobile nodes (MN), using Mobile IP. This
approach allows nested mobile networks, since each MR will appear to
its attachment point as a single node.
3. NEMO Support Design Goals
This section details the fundamental design goals the solutions will
intend to achieve. Those design goals serve to define the issues and
to impose a list of requirements for forthcoming solutions. Actual
requirements for NEMO Basic Support are in Section 4; NEMO Extended
Support is not yet considered at the time of this writing.
3.1. Migration Transparency
Permanent connectivity to the Internet has to be provided to all
MNNs, since continuous sessions are expected to be maintained as the
mobile router changes its point of attachment. For maintaining those
sessions, MNNs are expected to be reachable via their permanent IP
addresses.
3.2. Performance Transparency and Seamless Mobility
NEMO support is expected to be provided with limited signaling
overhead and to minimize the impact of handovers on applications, in
terms of packet loss or delay. However, although variable delays of
transmission and losses between MNNs and their respective CNs could
be perceived as the network is displaced, it would not be considered
a lack of performance transparency.
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3.3. Network Mobility Support Transparency
MNNs behind the MR(s) do not change their own physical point of
attachment as a result of the mobile network's displacement in the
Internet topology. Consequently, NEMO support is expected to be
performed only be the MR(s). Specific support functions on any other
node than the MR(s) would better be avoided.
3.4. Operational Transparency
NEMO support is to be implemented at the level of IP layer. It is
expected to be transparent to upper layers so that any upper layer
protocol can run unchanged on top of an IP layer extended with NEMO
support.
3.5. Arbitrary Configurations
The formation of a mobile network can occur in various levels of
complexity. In the simplest case, a mobile network contains just a
mobile router and a host. In the most complicated case, a mobile
network is multihomed and is itself a multi-level aggregation of
mobile networks with collectively thousands of mobile routers and
hosts. While the list of potential configurations of mobile networks
cannot be limited, at least the following ones are desirable:
o Mobile networks of any size, ranging from a sole subnet with a few
IP devices to a collection of subnets with a large number of IP
devices.
o Nodes that change their point of attachment within the mobile
network.
o Foreign mobile nodes that attach to the mobile network.
o Multihomed mobile network: either when a single MR has multiple
attachments to the internet, or when the mobile network is
attached to the Internet by means of multiple MRs (see definition
in [1] and the analysis in [8]).
o Nested mobile networks (mobile networks attaching to other mobile
networks (see definition in [1]). Although the complexity
requirements of those nested networks is not clear, it is
desirable to support arbitrary levels of recursive networks. The
solution should only impose restrictions on nesting (e.g. path
MTU) when this is impractical and protocol concerns preclude such
support.
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o Distinct mobility frequencies (see mobility factor in [2]).
o Distinct access media.
In order to keep complexity minimal, transit networks are excluded
from this list. A transit network is one in which data would be
forwarded between two endpoints outside of the network, so that the
network itself simply serves as a transitional conduit for packet
forwarding. A stub network (leaf network), on the other hand, does
not serve as a data forwarding path. Data on a stub network is
either sent by or addressed to a node located within that network.
3.6. Local Mobility and Global Mobility
Mobile networks and mobile nodes owned by different administrative
entities are expected to be displaced within a domain boundary or
between domain boundaries. Multihoming, vertical and horizontal
handoffs, and access control mechanisms are desirable to achieve this
goal. Such mobility is not expected to be limited for any
consideration other than administrative and security policies.
3.7. Scalability
NEMO support signaling and processing is expected to scale to a
potentially large number of mobile networks irrespective of their
configuration, mobility frequency, size and number of CNs.
3.8. Backward Compatibility
NEMO support will have to co-exist with established IPv6 standards
and not interfer with them. Standards defined in other IETF working
groups have to be reused as much as possible and extended only if
deemed necessary. For instance, the following mechanisms defined by
other working groups are expected to function without modidication:
o Address allocation and configuration mechanisms.
o Host mobility support: mobile nodes and correspondent nodes,
either located within or outside the mobile network, are expected
to continue operating protocols defined by the Mobile IP working
group. This include mechanisms for host mobility support (Mobile
IPv6) and seamless mobility (FMIPv6).
o Multicast support intended for MNNs is expected to be maintained
while the mobile router changes its point of attachment.
o Access control protocols and mechanisms used by visiting mobile
hosts and routers to be authenticated and authorized, gaining
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access to the Internet via the mobile network infrastructure
(MRs).
o Security protocols and mechanisms.
o Mechanisms performed by routers deployed in both the visited
networks and in mobile networks (routing protocols, Neighbor
Discovery, ICMP, Router Renumbering).
3.9. Secure Signaling
NEMO support will have to comply with the usual IETF security
policies and recommendations and is expected to have its specific
security issues fully addressed. In practice, all NEMO support
control messages transmitted in the network will have to be protected
with an acceptable level of security to prevent intruders to usurp
identities and forge data. Specifically, the following issues have
to be considered:
o Authentication of the sender to prevent identity usurpation.
o Authorization, to make sure the sender is granted permission to
perform the operation as indicated in the control message.
o Confidentiality of the data contained in the control message.
3.10. Location Privacy
Location privacy means to hide the actual location of MNNS to third
parties other than the HA are desired. It is not clear to which
extend this has to be enforced, since it is always possible to
determine the topological location by analysing IPv6 headers. It
would thus require some kind of encryption of the IPv6 header to
prevent third parties from monitoring IPv6 addresses between the MR
and the HA. On the other hand, it is at the very least desirable to
provide a means for MNNs to hide their real topological location to
their CNs.
3.11. IPv4 and NAT Traversal
IPv4 clouds and NAT are likely to co-exist with IPv6 for a long time,
so it is desirable to ensure mechanisms developed for NEMO will be
able to traverse such clouds.
4. NEMO Basic Support One-Liner Requirements
The NEMO WG is to specify a unified and unique "Network Mobility
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Basic Support" solution, hereafter referred to as "the solution".
This solution is to allow all nodes in the mobile network to be
reachable via permanent IP addresses, as well as maintain ongoing
sessions as the MR changes its point of attachment to the Internet
topology. This is to be done by maintaining a bi-directional tunnel
between an MR and its Home Agent.
The NEMO Working Group, after some investigation of alternatives, has
decided to reuse the existing Mobile IPv6 [6] mechanisms for tunnel
management, or extend it if deemed necessary.
The list of requirements below has been imposed on the NEMO Basic
Support solution. The requirements have mostly been met by the
resulting specification which can now be found in [3].
R01: The solution MUST be implemented at the IP layer level.
R02: The solution MUST set up a bi-directional tunnel between a
Mobile Router and its Home Agent (MRHA tunnel)
R03: All traffic exchanged between an MNN and a CN in the global
Internet MUST transit through the bi-directional MRHA tunnel.
R04: MNNs MUST be reachable at a permanent IP address and name.
R05: The solution MUST maintain continuous sessions (both unicast
and multicast) between MNNs and arbitrary CNs after IP handover of
(one of) the MR.
R06: The solution MUST not require modifications to any node other
than MRs and HAs.
R07: The solution MUST support fixed nodes, mobile hosts and
mobile routers in the mobile network.
R08: The solution MUST allow MIPv6-enabled MNNs to use a mobile
network link as either a home link or a foreign link.
R09: The solution MUST ensure backward compatibility with other
standards defined by the IETF. In particular, this includes:
R09:1: The solution MUST not prevent the proper operation of
Mobile IPv6 (i.e. the solution MUST allow MIPv6-enabled MNNs to
operate either the CN, HA, or MN operations defined in [6])
R10: The solution MUST treat all the potential configurations the
same way (whatever the number of subnets, MNNs, nested levels of
MRs, egress interfaces)
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R11: The solution MUST support at least 2 levels of nested mobile
networks, while, in principle, arbitrary levels of recursive
mobile networks SHOULD be supported.
R12: The solution MUST function for multihomed MRs and multihomed
mobile networks as defined in [1].
R13: NEMO Support signaling over the bi-directional MUST be
minimized
R14: Signaling messages between the HA and the MR MUST be secured:
R14.1: The receiver MUST be able to authenticate the sender.
R14.2: The function performed by the sender MUST be authorized
for the content carried.
R14.3: Anti-replay MUST be provided.
R14.4: The signaling messages MAY be encrypted.
R15: The solution MUST ensure transparent continuation of routing
and management operations over the bi-directional tunnel (this
includes e.g. unicast and multicast routing protocols, router
renumbering, DHCPv6)
R16: When one egress interface fails, the solution MAY preserve
sessions established through another egress interface.
5. Security Considerations
As this document only provides a discussion about design goals and
describes neither a protocol nor an implementation or a procedure,
there are no security considerations associated with it.
6. IANA Considerations
This document requires no IANA actions.
7. Acknowledgments
The material presented in this document takes most of its text from
discussions and previous documents submitted to the NEMO working
group. This includes initial contributions from Motorola, INRIA,
Ericsson and Nokia. We are particularly grateful to Hesham Soliman
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(Ericsson) and the IETF ADs at the time (Erik Nordmark and Thomas
Narten) who greatly helped to set up the NEMO working group. We are
also grateful to all the following people whose comments highly
contributed to the present document: T.J. Kniveton (Nokia), Alexandru
Petrescu (Motorola), Christophe Janneteau (Motorola), Pascal Thubert
(Cisco), Hong-Yon Lach (Motorola), Mattias Petterson (Ericsson) and
all the others people who have expressed their opinions on the NEMO
mailing lists (formely known as MONET). Thierry Ernst wishes to
personally acknowledge his previous employers, INRIA, and Motorola
for their support and direction in bringing this topic up to the IETF
-- particularly Claude Castelluccia (INRIA) and Hong-Yon Lach
(Motorola).
8. References
8.1. Normative References
[1] Ernst, T. and H. Lach, "Network Mobility Support Terminology",
draft-ietf-nemo-terminology-04 (work in progress), October 2005.
[2] Manner, J. and M. Kojo, "Mobility Related Terminology",
RFC 3753, June 2004.
[3] Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
"Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
January 2005.
8.2. Informative References
[4] "CALM - Medium and Long Range, High Speed, Air Interfaces
parameters and protocols for broadcast, point to point, vehicle
to vehicle, and vehicle to point communication in the ITS
sector - Networking Protocol - Complementary Element", ISO
Draft ISO/WD 21210, February 2005.
[5] Ernst, T. and K. Uehara, "Connecting Automobiles to the
Internet", Proceedings 3rd International Workshop on ITS
Telecommunications (ITST), November 2002.
[6] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
IPv6", RFC 3775, June 2004.
[7] Ng, C., "Network Mobility Route Optimization Problem
Statement", draft-ietf-nemo-ro-problem-statement-01 (work in
progress), October 2005.
[8] Ng, C., Ernst, T., Paik, E., and M. Bagnulo, "Analysis of
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Multihoming in Network Mobility Support",
draft-ietf-nemo-multihoming-issues-04 (work in progress),
October 2005.
[9] Thubert, P., Wakikawa, R., and V. Devarapalli, "NEMO Home
Network Models", draft-ietf-nemo-home-network-models-05 (work
in progress), June 2005.
[10] Deering, S. and R. Hinden, "Internet Protocol Version 6
(IPv6)", IETF RFC 2460, December 1998.
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Appendix A. Change Log From Earlier Versions
The discussions behind the changes in the lattest versions of this
documents are reflected in the "issue" web page:
http://www.sfc.wide.ad.jp/~ernst/nemo/
A.1. Changes between version -04 and -05
Added a reference to [7]
Split references into Normative and Informational
Cosmetics changes
A.2. Changes between version -03 and -04
- Issue B1: English brush up
- Issue B2: Added a reference to [4] and [5] when speaking about
usages.
- Issue B3: The following paragraph from section 1 was partly
removed; the remaining part was moved to section 2 and rephrased:
"The mechanisms required for handling such mobility issues are
currently lacking within the IETF standards. Traditional work
conducted on mobility support (particularly in the Mobile IP working
group) is to provide continuous Internet connectivity and optimal
routing to mobile hosts only (host mobility support) and are unable
to support network mobility. The NEMO working group has therefore
been set up to deal with issues specific to network mobility. The
purpose of this document is thus to detail the methodology that will
be followed by the NEMO working group, its goals, and to define
requirements for network mobility support."
- Issue B4: Effectively removed former requirements about "impact on
the routing fabric".
A.3. Changes between version -02 and -03
- Mostly cosmetic changes
- Merged section Terminology into Introduction
- Cross-references with other NEMO WG docs
- Changed the introducion of section Section 4 and added reference to
NEMO Basic Support's resulting specification.
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A.4. Changes Between Version -01 and -02
- removed sub-items in R12 (sub-cases are contained into the
definition of multihoming)
- minor typos
- R15: Added "multicast"
- R14.4: SHOULD softened to MAY according to discussion at IETF56th
meeting.
- R17 moved to R09 and contains former R09 as a sub-case.
- R18: relaxed from "SHOULD" to may based on Vijay Devarapalli
comment (030718)
A.5. Changes Between Version -00 and -01
- title of documents: included the word "goals"
- entire document: some rewording
- section 4: changed title of section to "NEMO Design Goals".
- section 4: removed "MUST" and "MAY"
- section 4: more text about location privacy
- section 4: changed "Administration" paragraph to "Local and Global
Mobility". Text enhanced.
- section 5: R02: replace "between MR and MR's HA" with "an MR and
its HA" R11: specified at least 2 levels R12: replaced "support" with
"function" and add "multihomed MR" R13.x renumbered to R12.x since
part of R12 (editing mistake) R13 and R18: new requirements proposed
by editor and minor changes in the formulation of other Requirements
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Author's Address
Thierry Ernst
Keio University / WIDE
Jun Murai Lab., Keio University.
K-square Town Campus, 1488-8 Ogura, Saiwa-Ku
Kawasaki, Kanagawa 212-0054
Japan
Phone: +81-44-580-1600
Fax: +81-44-580-1437
Email: ernst@sfc.wide.ad.jp
URI: http://www.sfc.wide.ad.jp/~ernst/
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