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INTERNET-DRAFT                                             Thierry Ernst
                                                           Hong-Yon Lach
                                                     Claude Castelluccia
                                 Motorola Labs and INRIA Planete, France
                                                            13 July 2001
                   "Network Mobility Support in IPv6:
                  Problem Statement and Requirements"
                  draft-ernst-mobileip-monetv6-00.txt




Status of This Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
   groups may also distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Abstract

   This draft addresses the problems of routing datagrams to nodes
   located in an IPv6 mobile network. A mobile network is one or more
   IP-subnets attached to a mobile router and mobile as a unit. The
   mobile router dynamically changes its point of attachment.
   Applications of mobile networks include networks attached to people
   (PANs) and networks of sensors deployed in an aircraft, a boat, or a
   car.

   This draft defines a terminology and presents a number of specific
   issues faced by mobility of an entire network.  An explicit mobility
   support scheme is required, what we call "network mobility support"
   in contrast with "host mobility support". We have listed a number of
   requirements that need to be addressed by network mobility support.




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                                 Contents

Status of This Memo

Abstract

Introduction

1. Definitions and Problem Statement
   1.1. Motivations
   1.2. Terminology
   1.3. Characteristics
   1.4. Aim of Network Mobility Support
   1.5. Assumption
   1.6. Issues
      1.6.1. Routing Issues
      1.6.2. Addressing Issues
      1.6.3. Network Protocols Issues
      1.6.4. Security Issues

2. Constraints and Requirements
   2.1. Constraints
      2.1.1. Host Mobility Support Constraints
      2.1.2. Addressing Constraints
      2.1.3. IPv6 Constraints
      2.1.4. Security Constraints
   2.2. Requirements
      2.2.2. Wide-Area Mobility Support
      2.2.3. Security
      2.2.4. Transparency
      2.2.5. Optimal Routing
      2.2.6. Minimum Signalling Overload
      2.2.7. Scalability
      2.2.8. Nested Mobility
      2.2.9. Backward Compatibility
      2.2.10. Minimum Impact on Existing Protocols

References

Author's Addresses











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Introduction

   This document addresses the question of routing datagrams to nodes
   located in an IPv6 mobile network, i.e. network mobility support. We
   define a mobile network as an entire network that dynamically changes
   its point of attachment in the Internet and thus its reachability in
   the Internet.

   The first section gives the motivations for network mobility support.
   We then describe mobile networks and we define a new terminology used
   throughout this study (section 1.2). There may exist various kind of
   mobile networks and they obviously have specific characteristics as
   depicted in section 1.3. Section 1.4 explains what this study tries
   to achieve. Section 1.6 concludes this section with a number of
   issues faced by network mobility support.

   Network mobility support in wide-area IPv6 networks has to comply
   with a number of constraints and requirements. Constraints limit the
   implementation and the deployment of a potentially and ideally good
   solution, and solutions need to fulfill a number of requirements.
   Some requirements must be solved whereas other should be solved
   whenever possible. Constraints and requirements for network mobility
   support are discussed in the second section. Most constraints and
   requirements that we have listed are equally applicable to host
   mobility support and network mobility support.  Some of them have
   been debated in the literature as far as host mobility support was
   concerned; we have extended this list to include those related to
   mobile networks.

1. Definitions and Problem Statement

1.1. Motivations

   The purpose of traditional mobility support is to provide continuous
   Internet connectivity to mobile hosts (host mobility support).  There
   are situations where an entire network might move and attach to
   different locations in the Internet topology. In this paper, we refer
   to a network as a set of nodes that share the same IP prefix and that
   are attached to the Internet through a border router. We refer to a
   mobile network as a network whose border router is a mobile router
   which dynamically changes its point of attachment to the Internet and
   thus its reachability in the Internet.

   Cases of mobile networks include networks attached to people
   (Personal Area Network or PAN) and networks deployed in aircrafts,
   boats, cars, trains, etc. An Ad-hoc network as defined in manet is
   not to be confused with a mobile network; however it may become a
   mobile network when its border router changes its point of attachment



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   to the Internet. As an example of a mobile network, we could think of
   an airline company that provides permanent on-board Internet
   connectivity.  This allows all passengers to use their laptops to
   connect to remote hosts, download music or video from any provider,
   or browse the web. The Internet could also be used to exchange
   information between the aircraft and air traffic control stations.
   This scenario has already been investigated by Eurocontrol (European
   Organization for the Safety of Air Navigation [8]). During the
   flight, the aircraft changes its point of attachment to the Internet
   and is reachable by different care-of addresses over time, most
   likely owned by distinct Internet service providers.  This scenario
   justifies that mobile networks may be of a big size, containing
   hundreds of hosts and several routers and may attach to very distant
   parts of the Internet topology. Moreover, it shows that we face two
   distinct levels of mobility, node mobility and network mobility,
   since laptops owned by passengers are themselves mobile nodes
   visiting the aircraft mobile network. However, this paper does not
   address the specific issues involved when mobile nodes visit the
   mobile network. We are focusing on the general case.

 1.2. Terminology

   We mostly adopt the terminology already defined in the IPv6 [5] and
   Mobile IPv6 [6] specifications. We also introduce the following new
   terms relevant to mobile networks. A mobile network attaches to the
   rest of the Internet through its border routers which we refer to as
   the mobile routers (MRs). A mobile router has at least two
   interfaces, the first attached to the home link or the foreign link,
   and the other attached to an internal link of the mobile network. We
   call mobile network node (MNN) any host or router located within the
   mobile network, either permanently or temporarily.

   All MNNs located in the same mobile network share a common and
   permanent IP prefix that we call the Mobile Network Prefix. The
   Mobile Network Prefix is a bit string that consists of some number of
   initial bits which identifies the set of subnetworks that compose the
   mobile network. It also identifies the topological location of the
   mobile network when the mobile router is attached to its home link.
   In addition, we call correspondent node (CN) any node external to the
   mobile network that is communicating with one or more MNNs. The
   terminology is summarized in fig.1.

   Mobile Network
      A set of nodes which are mobile, as a unit, with respect to the
      rest of the Internet, i.e. a mobile router and all its attached
      nodes. The mobile router changes dynamically its point of
      attachment to the Internet and thus its reachability in the
      Internet. All nodes in the mobile network share the same IP



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      prefix: the Mobile Network Prefix. Note that a mobile network may
      be composed by one or more IP-subnets.

            ____
           |    |
           | CN |
           |____|
          ___|____________________
         |                        |
         |                        |
         |       Internet         |
         |                        |
         |________________________|
            __|_            __|_
           |    |  Access  |    |
           | AR |  Router  | AR |
           |____|          |____|
        ______|__ foreign   __|_____________ home
                  link               __|_    link
                                    |    |
                                    | MR | Mobile Router
                                    |____|
                              _________|_______  internal
                               __|__     __|__   link
                              |     |   |     |
                              | LFN |   | LFN | Local Fixed Nodes
                              |_____|   |_____|

                            Figure 1: Terminology

   Mobile IP-subnet

      A mobile network that is composed of a single IP-subnet.

   Mobile Router (MR)

      The border router of a mobile network which attaches the mobile
      network to the rest of the Internet. The mobile router has at
      least two interfaces, an external interface, and an internal
      interface.  The mobile router maintains the Internet connectivity
      for the mobile network. It is used as a gateway to route packets
      between the mobile network and the fixed Internet.

   External Interface of a Mobile Router

      The external interface of a mobile router is attached to the home
      link if the mobile network is at home, or is attached to a foreign
      link if the mobile network is in a foreign network.



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   Internal Interface of a Mobile Router

      The internal interface of a mobile router is attached to an
      internal link within the mobile network. This interface is
      configured with the Mobile Network Prefix (see definition below)
      for all the MNNs inside the mobile network.

   Local Fixed Node (LFN)

      Any host or router permanently located within the mobile network
      and that does not change its point of attachment.

   Local Mobile Node (LMN)

      A mobile node that belongs to the mobile network and that changes
      it's point of attachment. The home link of the LMN is a link
      within the mobile network. The LMN may attach to any link within
      the mobile network, or to any link outside the mobile network.

   Visiting Mobile Node (VMN)

      A mobile node that does not belong to the mobile network and that
      changes it's point of attachment. The home link of the VMN is not
      a link within the mobile network. A VMN may attach to a link
      within the mobile network and obtain a careof address on this
      link.

   Mobile Network Node (MNN)

      Any host or router located within the mobile network, either
      permanently or temporarily. A MNN could be any of a MR, LFN, VMN,
      or LMN.

   Node behind the MR

      A synonym for a mobile network node (MNN). See corresponding
      definition.

   Correspondent Node (CN)

      Any node located outside the mobile network that corresponds with
      any of the MNNs. By extension, we say that CNs corresponding with
      MNNs of a mobile network are CNs of this mobile network.

   Access Router

      Any subsequent point of attachment of the mobile network at the
      network layer. Basically, a router on the home link or the foreign



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      link.

   Home subnet prefix

      A bit string that consists of some number of initial bits of an IP
      address which identifies the home link within the Internet
      topology. (i.e. the IP subnet prefix corresponding to the mobile
      node's home address, as defined in [6]).

   Foreign subnet prefix

      A bit string that consists of some number of initial bits of an IP
      address which identifies a foreign link within the Internet
      topology.

   Mobile Network Prefix

      The network prefix that is common to all IP addresses in the
      mobile network when the mobile router is attached to the home
      link. For a mobile network containing only one subnet, the Mobile
      Network Prefix is the prefix of this subnet ("home subnet prefix"
      as defined in [6]). Note that the Mobile Network Prefix may not be
      the home prefix.

 1.3. Characteristics

   Structure of the mobile network

      The internal structure of a mobile network is preserved while it
      is moving. As a result of the mobility of the mobile network, MNNs
      do not change their point of attachment; however, MNNs move from
      the point of view of their CNs.  From a routing perspective, a
      mobile network may therefore be virtually perceived as a single
      node (the MR) with a topologically correct address or prefix. The
      topological location of a MNN being dependent of the location of
      the MR, the knowledge of the topological location of the MR is
      sufficient for routing datagrams from a CN towards a MNN.

   Mobile Router is a transit point

      All packets sent from any CN to a MNN necessarily transit through
      the MR. As a result, providing the CN with the current location of
      the MR in the Internet topology may be sufficient for optimally
      routing packets intended to a MNN.

   Size of the mobile network

      A mobile network may comprise one or more subnetworks. Its size



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      could scale from a sole subnetwork with a few IP devices, such as
      in the case of a PAN, to a collection of subnets with hundreds of
      IP devices, such as in a train.

   Large number of CNs

      A mobile network may have a very large number of CNs.  For
      instance, each passenger in a train may be considered a MNN.  Each
      of them may be communicating with a few CNs. As a result, the
      total number of CNs would be several times as large as the number
      of MNNs and could scale up to a few thousands.

   Nested mobility

      A mobile network may comprise mobile nodes (local mobile nodes or
      visiting mobile nodes) and even other mobile networks. For
      instance, a bus is a mobile network whereas passengers are mobile
      nodes or even mobile networks themselves if they carry a PAN.

   Various mobility frequencies

      Mobile networks may not move with the same speed and frequency.
      For instance, a PAN connected to the Internet via a WLAN, or a car
      connected to the Internet via GSM are likely to change their point
      of attachment very quickly, while an aircraft or a boat may be
      connected to the Internet via the same satellite link for a couple
      of hours. Obviously, mobile networks may not move at all for a
      large amount of time.

   Multi-homing

      A mobile network may be multi-homed. By multi-homing, we mean that
      the MR may have two or more active interfaces connected to
      distinct parts of the Internet, or the mobile network may be
      connected to the Internet via tow or more MRs. In the first case,
      we could think of a unique device used to connect a car both to
      the cellular phone network and to a navigation satellite.  In the
      second case, we may think of a PAN where the GSM is used to
      connect the PAN to the cellular phone network whereas a PDA is
      used to collect bus timetables from the city bus network.

   Routers in the mobile network

      All routers in the Internet are considered to run a number of
      protocols such as a routing protocol, Neighbor Discovery, ICMP,
      and others. This also applies to any router in the mobile network,
      including the mobile router.




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   Ad-hoc network

      An ad-hoc network that changes its point of attachment to the
      Internet may be seen as a mobile network.

   Idle Mobile Network

      A mobile network that does not engage in any communication outside
      the network may be considered as idle from the point of view of
      the fixed Internet, although there may be internal traffic between
      any two MNNs.

   Idle Mobile Network Node

      A MNN that does not engage in any communication.

 1.4. Aim of network mobility support

   The purpose of network mobility support is to provide MNNs with an
   uninterrupt Internet connectivity and to route datagrams between CNs
   and MNNs by the most optimal path in both directions.

 1.5. Assumption

   We limit the scope of our study to mobile networks that are stub
   networks, i.e.  the mobile network does not forward traffic not
   intended to itself.

 1.6 Issues

   Mobility of networks has an impact on routing, addressing, and a
   number of network protocols.

  1.6.1. Routing Issues

      All packets sent to a MNN must transit through the current AR of
      the mobile network and the MR itself. As a result of mobility, the
      path to the mobile network is varying according to the AR to which
      the MR is currently attached. We have to investigate how this path
      could be determined in order to route packets via the most optimal
      path. Particularly, we need to examine if this is best solved by
      routing protocols or by some transient means as this is done for
      mobile hosts. We need to investigate:

         o if there is a need for a CN to determine that the node it is
         corresponding with is in a mobile network.

         o if there is a need to determine the topological location of



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         the mobile network or the mobile network node.

         o if there is a need to determine the AR where the mobile
         network is currently attached.

         o if correspondent nodes should be aware of the topological
         location of the mobile network or the mobile network node or if
         this should this be transparent to them

         o if forwarding should be established from a former AR to a
         latter one.

  1.6.2. Addressing Issues

         o Impact on MR

         Following existing IPv6 specifications, any host is in theory
         required to obtain a topologically correct address on the link
         on which it is currently attached to. We must investigate if
         this can alternatively be done for a single host or for a
         router and for a mobile network. If yes, this means that the
         external interface of the mobile network is configured with the
         foreign prefix.  We also have to investigate if the
         configuration of the MR's interface with a new address has an
         impact on the MNNs.

         o Impact on MNNs

         As for MNNs, they don't actually change their own point of
         attachment, then it is very questionable whether MNNs should
         also get a topologically correct address that actually reflects
         their topological [and hierarchical] location in the Internet.
         If we conclude that mobile network nodes should get a
         topologically correct address, we have to determine how this
         could be performed internally in the mobile network. If we
         renumber, we have to investigate how to maintain connections
         and how and where to advertise the new address; if we do not
         renumber, we have to investigate how to perform optimal routing
         between CNs and MNNs.

  1.6.3. Network Protocols Issues

      As seen in section 1.3, all routers in a mobile network are
      routers like the others and have to run a number of protocols.
      Following the existing IPv6 specifications, they particularly
      should run at least an instance of a routing protocol, and other
      protocols like Neighbor Discovery, etc. We therefore have to
      investigate how the network protocols running in the mobile



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      network must interact with the network protocols running in each
      subsequent visited network and how the mobile router is going to
      interact with the ARs it attaches to.  This raises a number of
      issues for each network protocol, as listed in the following
      sections.

         o Impact on Neighbor Discovery

         One task of Neighbor Discovery is to send Router Advertisements
         and Router Solicitations. When the mobile router is attached to
         some AR in a visited network, it should receive such Router
         Advertisements from its current AR. We have to investigate how
         those Router Advertisements should be processed by the mobile
         router and how the mobile router should interact with this
         instance of the protocol running at the AR. We also have to
         investigate what is the impact on this protocol when the mobile
         network leaves its point of attachment.

         o Impact on the Visited Network

         We have to investigate if the subsequent ARs and the other
         routers in the visited network should be aware that the
         visiting mobile node is a router and not a host. In addition,
         we have to examine if it is necessary to let them know that
         there is an entire network behind the mobile router. In such a
         case, a network route may have to be propagated in the visited
         network and this raises an additional number of issues as
         discussed in the section about routing protocols.

         o Impact on Routing Protocols

         We have to investigate how the mobile router interacts with the
         routing protocols running at each of its subsequent ARs. The
         impact may not be the same whether the mobile network is
         limited to a single IP-subnet or a number of IP-subnets.
         Indeed, a single mobile IP-subnet may not need to run an
         instance of a routing protocol whereas a mobile network
         comprising more than one router may. We have to evaluate what
         kind of routing protocols may run in a mobile network and how
         it interacts with the routing protocol running at each of its
         subsequent ARs.

            oo In case the mobile network is running the same routing
            protocol as its ARs, it is questionable whether the mobile
            network should participate or not in the routing protocol
            running in the visited network.  If it does, the mobile
            network can be seen as a partition of the local network. The
            topology computed by the routing protocol becomes more



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            dynamic and we have to evaluate how existing protocols are
            able to handle this case. Moreover, mobility may cause a
            routing table partition.

            oo In case the mobile network doesn't participate in the
            routing protocol running in the visited network, the mobile
            network can be seen as a kind of Autonomous System that is
            running an instance of an Internal Gateway Protocol.

         routing protocol running in the mobile network and the routing
         protocol running in the visited network. In addition, we must
         determine what routing protocol is suitable within the mobile
         network. We also have to evaluate the impact on routing
         protocols when the mobile router is multi-homed, when the
         mobile network comprises more than one mobile router, and when
         the mobile network itself receives another mobile network.

  1.6.4. Security Issues

      All security concerns that usually apply to host mobility support
      also apply to network mobility support. We may face a number of
      additional ones that complement the addressing issues, network
      protocols issues, and routing issues depicted in the previous
      sections.



























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2. Constraints and Requirements

 2.1. Constraints

  2.1.1. Host Mobility Support constraints

      LMNs and VMNs that operate Mobile IPv6 must still be able to use
      the same protocol once located in a mobile network.  If needed,
      the solution to support mobile networks has to provide the
      necessary Mobile IPv6 extensions.

  2.1.2. Addressing constraints

      The network part of IP addresses is used for routing and
      identifying the subnetwork in the topology. Every interface
      attached to a subnetwork must have a unique address with the
      network part identifying the subnetwork.

  2.1.3. IPv6 constraints

      In order not to re-invent the wheel, any solution has to be based
      on IPv6 protocols. It is also desirable that it becomes an
      integral part of the existing protocol suite. It is desirable to
      introduce new features as extensions to the existing protocols
      with minimum modifications.

  2.1.4. Security constraints

      Any solution must comply with IPv6 security policies.






















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 2.2. Requirements

   Requirements relative to mobility of hosts are discussed in most
   published papers in the field of mobile networking as found in [1]
   and also [7, 4]. [OTHERS]. Most of them are equally applicable to
   network mobility support, with some additions.


  2.2.2. Wide-Area mobility support

      A truly worldwide mobility support requires international
      standards in order to move between heterogeneous networks, i.e.
      wide-area mobility. A lack of international standardization would
      prevent from this.  We must avoid a situation where distinct
      Internet Service Provider would develop distinct network mobility
      support schemes which are unable to inter-operate with each other.
      Not only standard between countries and organizations is required,
      but also between networks in which different policies may apply.
      Indeed, nothing but administrative and security policies should
      prevent a mobile network to attach anywhere in the Internet. For
      doing so, we need a mobility support scheme that fits well into
      the existing standards, that is easy to deploy and that does not
      require too much additional services in the network.

  2.2.3. Security

      Unlike fixed nodes, MNNs are more exposed to security issues and
      identity usurpation. Mobility support must provide MNNs and their
      CNs with at least as good security as for fixed nodes and single
      mobile nodes. In practice, network mobility support signalling
      must be exchanged in a secure manner and must ensure the
      following:

         o Confidentiality

         Mobility support must ensure confidentiality of all control
         datagrams transmitted between MNNs and CNs in any direction to
         insure MNNs' confidentiality.  If requested, only the recipient
         must be able to decrypt the content of the datagram.

         o Authentication       All control messages must be
         authenticated by recipients in order to prevent intruders to
         usurp the identity of a MNN. Mobility support shouldn't leave
         more room for intruders to usurp an identify nor to perpetrate
         any kind of attack against MNNs or CNs.

         o Authorization




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         Mobility support must ensure that a node which performs a
         mobility management operation is effectively authorized to
         perform such an operation.

         o Location Privacy

         Mobility support has to provide means for to keep the location
         of MNNs secret to any third party.  It shouldn't be possible to
         determine the topological location of a mobile network and its
         MNNs by monitoring control messages exchanged between any two
         nodes.  In practice, MNNs may wish to hide their location to
         some or all of their CNs.  The network administrator may also
         wish to hide the location of the mobile network to all CNs
         without discrimination between MNNs.

  2.2.4. Transparency

         o Mobility Transparency

         With respect to the layer separation of the Internet protocol
         suite, handover of IP sessions should be transparent at layers
         above the network layer. At least, there shouldn't be an abrupt
         interruption of the IP sessions.  This means that a mobile
         network is always reachable regardless of its point of
         attachment.  Particularly, mechanism have to be added so that
         transiting datagrams are forwarded to the current location of
         the mobile network.

         o Operational Transparency

         From an application's point of view, continuous access to the
         Internet must be maintained regardless of the location of the
         mobile network. Moreover, it is required that the application
         does not need to perform any action to remain connected. This
         means that mobility support should be performed at the network
         layer. It is the responsibility of the network protocols to
         support connectivity of the network in an absolute transparent
         manner to the applications.

         o Mobility management transparency for MNNs

         We have seen that MNNs appear to move from the point of view of
         their CNs although do not change their point of attachment
         within the mobile network. Mobility management of a mobile
         network is therefore better seen as MR's responsibility and
         should be transparent to MNNs. MNNs should have no
         responsibility in network mobility management. They should only
         be concerned about managing their own mobility if they



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         themselves appear to change their point of attachment. However,
         MNNs may encounter variable delays of transmission and loss
         with their respective CNs as the network is moving.

         o Performance Transparency

         Network mobility support should exhibit low latency, incur
         little or no data loss, minimum delays, scale to a large
         internetwork, incur minimum signalling load, bandwidth
         consumption for datagrams delivery and memory requirements, as
         seen in [3]. The solution is termed "efficient" provided
         mobility is supported without performance degradation of the
         Internet. Loss and delays should indeed range into those
         experimented for communication flows between two fixed nodes.
         Moreover, both local-area mobility and wide-area mobility need
         to be handled as efficiently. At last, the addition of network
         mobility support shouldn't impact the performance of upper
         layers. In order to limit losses during hand-offs and to avoid
         degradation of performance at the upper layers, it may be
         necessary to perform seamless handovers.

         o Layers Independence

         Support of mobility is best managed at the network layer. A
         change of topological location therefore shouldn't have any
         repercussion at other layers of the TCP/IP reference model.  If
         this is respected, compatibility with existing transport and
         application layers is maintained.  Support of mobility in
         transport and application protocols is not the focus of this
         study.

  2.2.5. Optimal routing

      The amount of traffic intended for the mobile network is
      understandably more significant than in the case of a single
      mobile node. Non-optimal routing therefore becomes an even more
      important issue that it was already for mobile nodes. Avoiding
      triangle routing reduces bandwidth consumption and transmission
      delays.

  2.2.6. Minimum signalling overload

      Routing packets efficiently from a CN to the current location of
      the mobile network may be performed at the cost of control
      traffic. The cost of this control traffic has to be balanced
      against the expected gain of optimal routing. Minimizing the
      amount of control traffic has always been an important concern for
      host mobility support.  Due to a potentially large number of CNs,



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      this becomes an even more important concern for network mobility
      support.

  2.2.7. Scalability

      Scalability has always been an important concern in the design of
      new protocols. As far as host mobility is concerned, mobility
      support has to take into consideration a growing number of mobile
      hosts and should even assume that a major part of the nodes
      composing the Internet are mobile in the near future. This means
      that signalling load and memory consumption should scale to an
      important number of mobile nodes. Network mobility support has to
      address scalability in two ways:

         o Large number of mobile networks       Scaling to a large
         number of mobile networks as hosts mobility support is required
         to scale to a large number of mobile nodes.

         o Large number of correspondent nodes       Scaling to the size
         of large mobile networks comprising hundreds of MNNs
         communicating with an important number of CNs.

      In other words, mobile network support must be able to support
      large mobile networks containing hundreds of nodes like a train
      and corresponding with thousands of CNs, and a very large number
      of small mobile networks such as PANs comprising a few IP devices.
      Scaling to a large number of CNs indeed deserves more
      consideration than scaling to a large number of mobile networks.

  2.2.8. Nested mobility

      Network mobility support must allow VMNs to visit the mobile
      network and LMNs to leave it. Basically, a VMN should be able to
      operate Mobile IPv6 or any forthcoming standard. Network mobility
      support should therefore consider both mobile networks and mobile
      nodes, otherwise it may hardly interact with host mobility
      support. In practice, it should handle visiting mobile nodes as
      optimally as if networks where fixed. It is also advisable to
      consider the special case where the correspondent node is itself
      mobile or located in a mobile network.

  2.2.9. Backward compatibility

      Backward compatibility corresponds to the ability to leave the
      actual protocol suite unchanged. This was an important issue for
      IPv4 since it is not possible to require all hosts to implement
      new features in order to manage mobility. On the other hand, the
      emergence of IPv6 is an opportunity for making the necessary



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      changes. Backward compatibility is not an issue at the time being
      although IPv6 itself has to interwork with IPv4. Indeed, IPv6
      offers the possibility to add new features until the IPv6
      specification is fully ratified. There is still scope for adding
      new capabilities if needed.

  2.2.10. Minimum Impact on Existing Protocols

      In order to provide a deployable solution and to allow wide-area
      mobility, a good solution should better make use of the existing
      protocols whenever possible and impose minimum changes or
      extensions on the existing ones.







































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References

   [1] Pravin Bhagwat, Satish Tripathi, and Charles Perkins. Network
   Layer Mobility: an Architecture and Survey. IEEE Personal
   Communications, 3(3):54, June 1996.

   [2] Editor R. Braden. Requirements for Internet Hosts - Communication
   Layers.  Request For Comments 1122, Internet Engineering Task Force
   (IETF), October 1989.

   [3] Ramon Caceres and Venkata N. Padmanabhan. "fast and scalable
   handoffs for wireles internetworks".  In Proc. of the Second ACM/IEEE
   International Conference on Mobile Computing and Networking
   (MobiCom), Rye, New York, USA, November 1996. Bell Laboratories and
   University of California at Berkeley.

   [4] Claude Castelluccia.  A Hierarchical Mobility Management Scheme
   for IPv6. Third Symposium on Computers and Communications (ISCC'98),
   Athens, Greece, June 1998. http://sirac.inrialpes.fr/planete

   [5] S. Deering and R. Hinden. Internet Protocol Version 6 (IPv6)
   Specification.  Request For Comments 2460, Internet Engineering Task
   Force (IETF), December 1998.

   [6] David B. Johnson and C. Perkins. Mobility Support in IPv6.
   Internet Draft draft-ietf-mobileip-ipv6-14.txt, Internet Engineering
   Task Force (IETF), July 2001. Work in progress.

   [7] Andrew Myles and David Skellern. Comparing Four IP Based Mobile
   Host Protocols. In Joint- European Networking Conference. Macquarie
   University, Sydney, Australia, May 1993.

   [8] Thomas Quinot. An IPv6 architecture for Aeronautical
   Telecommunication Network. Master's thesis, Ecole Nationale
   Sup'erieure des T'el'ecommunications Paris, EUROCONTROL - European
   Organization for the Safety of Air Navigation - ISA project (IPv6,
   Satellite communication and ATMode for ATN), 1998.
   http://www.eurocontrol.fr/.













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Author's Addresses

    Questions about this document can be directed to the authors:


      Thierry Ernst
      Motorola Labs Paris and INRIA - PLANETE team Grenoble
      ZIRST - 655 avenue de l'Europe
      38330 Montbonnot Saint Martin, France
      http://www.inrialpes.fr/planete/
      Phone: +33 4 76 61 52 69
      Email: Thierry.Ernst@inrialpes.fr

      Hong-Yon Lach
      Motorola Labs Paris, Lab Manager,
      Networking and Applications Lab (NAL)
      Espace Technologique - Saint Aubin
      91193 Gif-sur-Yvette Cedex, France
      Phone: +33 1 69 35 25 36
      Email: Hong-Yon.Lach@crm.mot.com

      Claude Castelluccia
      INRIA - PLANETE team Grenoble
      ZIRST - 655 avenue de l'Europe
      38330 Montbonnot Saint Martin, France
      Phone: +33 4 76 61 52 15
      Email: Claude.Castelluccia@inrialpes.fr
























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