NEMO Working Group                                 Thierry Ernst, Editor
Internet-Draft                                            WIDE and INRIA
                                                               May, 2003
                                                          February, 2004

           "Network Mobility Support Goals and Requirements"

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   Network mobility arises when a router connecting an entire network to
   the Internet dynamically changes its point of attachment to the
   Internet therefrom causing the reachability of the entire network to
   be changed in the topology. Such kind of network is referred to as a
   mobile network. Without appropriate mechanisms, sessions established
   between nodes in the mobile network and the global Internet cannot be
   maintained while the mobile router changes its point of attachment.
   The required support mechanisms will be provided in two phases. The
   first phase, referred to as NEMO Basic Support is to provide session
   continuity while the necessary optimizations mechanims referred to as
   NEMO Extended Support might be provided later. This document outlines
   the goals expected from network mobility support and defines the
   requirements that must be met by NEMO Basic Support solutions.

Table of Contents

   1.   Introduction . . . . . . . . . . . . . . . . . . . . . . . . 03

   2.   Terminology. . . . . . . . . . . . . . . . . . . . . . . . . 04

   3.   NEMO Working Group Goals and Methodology . . . . . . . . . . 04

   4.   NEMO Support Design Goals . . . . . . . . .  . . . . . . . . 05

   5.   NEMO Basic Support One-liner Requirements  . . . . . . . . . 09

   6.   Changes From  Previous Version . . . . . . . . . . . . . . . 11 10

   A.   Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . 11

   B.   References . . . . . . . . . . . . . . . . . . . . . . . . . 12

   C.   Editors' Addresses . . . . . . . . . . . . . . . . . . . . . 12

   D.   Full Copyright Statement . . . . . . . . . . . . . . . . . . 13

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

1. Introduction

   Network mobility support 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 kind of 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 in effect be relatively stable
   (no dynamic change of the topology), but this is not a general

   Cases of mobile networks include for instance:

      - 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

      - networks of sensors and computers deployed in vehicles: vehicles
      are more and more embedded with a number of processing units for
      safety and ease of driving reasons, as advocated by ITS
      (Intelligent Transportation Systems) applications.

      - 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).

      - ad-hoc networks connected to the Internet via a MR: for instance
      students in a train that both need to set up an ad-hoc network
      among themselves and to 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 happen to 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 into MNNs losing Internet access and breaking ongoing
   sessions entertained 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 arbitrary
   correspondent nodes (CN) becomes sub-optimal, whereas multiple levels
   of mobility will cause extremely sub-optimal routing.

   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.

   This document is structured as follows: in section 3, we define the
   goals and methodology of the NEMO working group and we emphasize the
   stepwise approach the working group has decided to follow. A number
   of desirable design goals are listed in section 4. Those design goals
   serve as guidelines to edict the requirements for basic network
   mobility support.

2. Terminology

   Mobility-related terms used in this document are defined in
   [MOBILITY-TERMS] whereas terms pertaining to network mobility
   specifically are defined in [NEMO-TERMS].

3. NEMO Working Group Goals and Methodology

   The primary goal 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
   network they are attached to changes its point of attachment.
   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 realtime traffic and fast
   handovers, optimizations.  These should all support the primary goal
   of reachability for mobile network nodes. Security is an important
   consideration too, and efforts should be made to use existing
   solutions if they are appropriate.  Although a well-designed solution
   may include security inherent in other protocols, mobile networks
   also introduce new challenges.

   For doing so, the NEMO working group has decided to take a stepwise
   approach by standardizing a basic solution to preserve session
   continuity (NEMO Basic Support), and at the same time study the
   possible approaches and issues with providing more optimal routing
   with potentially nested mobile networks (NEMO Extended Support).
   However, the working group is not chartered to actually standardize a
   solution to such route optimization at this point in time.

   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 will be made to
   accommodate nodes inside the network that are not generally aware of

   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 is for each MR to have a Home
   Agent, and use bidirectional tunneling between the MR and HA to
   preserve session continuity while the MR moves. The MR will acquire a
   Care-of-address from 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.

4. NEMO Suppport Design Goals

   This section details the fundamental design goals the solutions will
   tend to achieve. Those design goals will serve to edict and
   understand the requirements defined for forthcoming solutions. Actual
   requirements for NEMO Basic Support are in the next section, whereas
   NEMO Extended Support has not yet been considered.

      - Migration Transparency: a permanent connectivity to the Internet
      has to be provided to all MNNs while continuous sessions are
      expected to be maintained as the mobile router changes its point
      of attachment. For doing so, MNNs are expected to be reachable via
      their permanent IP addresses.

      - Performance Transparency and Seamless Mobility: NEMO support is
      expected to be provided with limited signaling overhead and to
      minimize the impact of handover over 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.

      - Network Mobility Support Transparency: MNNs behind the MR(s)
      don't 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 by the sole
      MR(s) and specific support functions on any other node than the
      MR(s) would better be avoided.

      - Operational Transparency: NEMO support is to be implemented at
      the IP layer level. 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.

      - Arbitrary Configurations: The formation of a mobile network can
      exist 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 multi-homed 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 configurations 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

         o foreign mobile nodes that attach to the mobile network,

         o multi-homed 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 [NEMO-TERMS]),

         o nested mobile networks (mobile networks attaching to other
           mobile networks, see definition in [NEMO-TERMS]. Although the
           complexity requirements of those nested networks is not
           clear, it is desirable to support arbitrary levels of
           recursive networks, and only in the case where this is
           impractical and protocol concerns preclude this support
           should the solution impose restrictions on nesting
           (e.g. path MTU),

         o distinct mobility frequencies, frequencies (see mobility factor in

         o distinct access medium.

      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.

      - Local Mobility and Global Mobility: mobile networks and mobile
      nodes owned by administratively different 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 type is not expected to be limited for any consideration
      other than administrative and security policies.

      - 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.

      - Backward Compatibility: NEMO support will have to co-exist with
      existing IPv6 standards without interfering 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 modidications:

         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 keep 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 entertained by MNNs are expected to be
           maintained while the mobile router changes its point of

         o Access control protocols and mechanisms used by visiting
           mobile hosts and routers to be authenticated and authorized
           to gain access to the Internet via the mobile network
           infrastructure (MRs).

         o Security protocols and mechanisms

         o Mechanisms performed by routers deployed both in the visited
           networks and in mobile networks (routing protocols, Neighbor
           Discovery, ICMP, Router Renumbering, ...).

      - Secure Signaling: NEMO support will have to comply with 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 ensure 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.

      - Location Privacy: means to hide the actual location of MNNS to
      third parties other than the HA are desired. In which extend this
      has to be enforced is not clear 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 to monitor IPv6 addresses between the MR and
      the HA. On the other hand, it is at the very least desirable to
      provide means for MNNs to hide their real topological location to
      their CNs.

      - 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 developped for NEMO will be able to traverse such

5. NEMO Basic Support One-liner Requirements

   The NEMO WG will specify a unified and unique solution for "Basic
   Network "Network Mobility Support". Basic
   Support" solution. The solution will 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 will be done by maintaining a
   bidirectional tunnel between a MR and its Home Agent. The Working
   Group will investigate reusing the existing Mobile IPv6 mechanisms
   for the tunnel management, or extend it if deemed necessary.

   The following requirements are placed on the NEMO Basic Support
   solution, hereafter referred to as "the solution":

   R01: The solution MUST be implemented at the IP layer level.

   R02: The solution MUST set up a bi-directional tunnel between a
        MR and its Home Agent.

   R03: All traffic exchanged between a MNN and a CN in the global
        Internet MUST transit through the bidirectional 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. This include particularly:

        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 [MIPv6])

   R10: The solution MUST treat all the potential configurations the
        same way (whatever the number of subnets, MNNs, nested levels
        of MRs, egress interfaces, ...)
   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 MR and multihomed
        mobile networks as defined in [NEMO-TERMS]). Particularly:

        R12.1: The solution MUST function for multi-MR mobile networks

        R12.2: The solution MUST function for multi-egress

        R12.3: The solution MUST function for MR with multiple global
               addresses on an egress interface.


   R13: NEMO Support signaling over the bidirectional 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 SHOULD MAY be encrypted [ACCORDING TO
               "MAY" (?)]

   R15: The solution MUST ensure transparent continuation of routing and
        management operations over the bi-directional tunnel when the MR
        is away from home. (this
        includes e.g. unicast and multicast routing protocols, router
        renumbering, DHCPv6, etc)

   R16: The solution MUST not impact on the routing fabric neither on
        the Internet addressing architecture. [ACCORDING TO IETF56
        minutes, SHOULD BE REMOVED]

   R17: The solution MUST ensure backward compatibility with other
        standards defined by the IETF [SPECIFIC PROTOCOLS SHOULD BE
        BE INCLUDED HERE INSTEAD OF R09.] Particularly:

   R18: The solution SHOULD MAY preserve sessions established through
        another egress interface when one fails [PROPOSED BY EDITOR OF

6. Changes since last version Between Versions

 6.1. 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

   - R17 moved to R09 and contains former R09 as a sub-case.

   - R18: relaxed from "SHOULD" to may based on Vijay Devarapalli
   comment (030718)

 6.2 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 "a 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

A. 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
   (Ericsson) and the IETF ADs (Erik Nordmark and Thomas Narten) who
   highly 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: TJ 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 (formely MONET)
   mailing list. Thierry Ernst wish to personally grant support to its
   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).

B. References

   [IPv6-NODE]      John Loughney
                    "IPv6 Node Requirements"
                    Work in progress.

   [MobileIPv4]     Charles Perkins
                    "IP Mobility Support"
                    RFC 2002, IETF, October 1996.

   [MobileIPv6]     David B. Johnson and C. Perkins.
                    "Mobility Support in IPv6"
                    Work in progress.

                    "Mobility Related Terminology
                    Work in progress.

   [NEMO-TERMS]     Thierry Ernst and Hong-Yon Lach
                    "Terminology for Network Mobility Support",
                    Work in progress.

   [RFC1122]        R. Braden (editor).
                    "Requirements for Internet Hosts - Communication
                    Layers".  IETF RFC 1122, October 1989.

   [RFC2119]        S. Bradner
                    "Key words for use in RFCs to Indicate Requirement
                    Levels", BCP 14, RFC 2119, IETF, March 1997.

   [RFC2460]        S. Deering and R. Hinden.
                    "Internet Protocol Version 6 (IPv6) Specification"
                    IETF RFC 2460, December 1998.

C. Editors's Addresses

   Questions about this document can be directed to the NEMO working
   group chairs:

      Thierry Ernst,
      Keio University.
      5322 Endo, Fujisawa-shi,
      Kanagawa 252-8520, Japan.
      K-square Town Campus
      1488-8 Ogura, Saiwai-ku, Kawasaki
      Kanagawa, 212-0054 Japan
      Phone : +81-466-49-1100 +81-44-580-1600
      Fax   : +81-466-49-1395 +81-44-580-1437
      Email :

      T. J. Kniveton
      Communications Systems Lab
      Nokia Research Center
      313 Fairchild Drive
      Mountain View, California 94043, USA
      Phone : +1 650 625-2025
      Fax   : +1 650 625-2502
      EMail :

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