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RFC 5522 - Network Mobility Route Optimization Requirements for


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Network Working Group                                            W. Eddy
Request for Comments: 5522                                       Verizon
Category: Informational                                       W. Ivancic
                                                                    NASA
                                                                T. Davis
                                                                  Boeing
                                                            October 2009

          Network Mobility Route Optimization Requirements for
  Operational Use in Aeronautics and Space Exploration Mobile Networks

Abstract

   This document describes the requirements and desired properties of
   Network Mobility (NEMO) Route Optimization techniques for use in
   global-networked communications systems for aeronautics and space
   exploration.

   Substantial input to these requirements was given by aeronautical
   communications experts outside the IETF, including members of the
   International Civil Aviation Organization (ICAO) and other
   aeronautical communications standards bodies.

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.

Table of Contents

   1. Introduction ....................................................2
   2. NEMO RO Scenarios ...............................................5
      2.1. Aeronautical Communications Scenarios ......................5
           2.1.1. Air Traffic Services Domain .........................6
           2.1.2. Airline Operational Services Domain .................8
           2.1.3. Passenger Services Domain ...........................9
      2.2. Space Exploration Scenarios ...............................10
   3. Required Characteristics .......................................12
      3.1. Req1 - Separability .......................................13
      3.2. Req2 - Multihoming ........................................14
      3.3. Req3 - Latency ............................................15
      3.4. Req4 - Availability .......................................16
      3.5. Req5 - Packet Loss ........................................17
      3.6. Req6 - Scalability ........................................18
      3.7. Req7 - Efficient Signaling ................................19
      3.8. Req8 - Security ...........................................20
      3.9. Req9 - Adaptability .......................................22
   4. Desirable Characteristics ......................................22
      4.1. Des1 - Configuration ......................................22
      4.2. Des2 - Nesting ............................................23
      4.3. Des3 - System Impact ......................................23
      4.4. Des4 - VMN Support ........................................23
      4.5. Des5 - Generality .........................................24
   5. Security Considerations ........................................24
   6. Acknowledgments ................................................24
   7. References .....................................................25
      7.1. Normative References ......................................25
      7.2. Informative References ....................................25
   Appendix A.  Basics of IP-Based Aeronautical Networking  ........28
   Appendix B.  Basics of IP-based Space Networking ................30

1.  Introduction

   As background, the Network Mobility (NEMO) terminology and NEMO goals
   and requirements documents are suggested reading ([4], [5]).

   The base NEMO standard [1] extends Mobile IPv6 [2] for singular
   mobile hosts in order to be used by Mobile Routers (MRs) supporting
   entire mobile networks.  NEMO allows mobile networks to efficiently
   remain reachable via fixed IP address prefixes no matter where they
   relocate within the network topology.  This is accomplished through
   the maintenance of a bidirectional tunnel between a NEMO MR and a
   NEMO-supporting Home Agent (HA) placed at some relatively stable
   point in the network.  NEMO does not provide Mobile IPv6's Route
   Optimization (RO) features to Mobile Network Nodes (MNNs) other than
   to the NEMO MR itself.  Corresponding Nodes (CNs) that communicate

   with MNNs behind an MR do so through the HA and the bidirectional
   Mobile Router - Home Agent (MRHA) tunnel.  Since the use of this
   tunnel may have significant drawbacks [6], RO techniques that allow a
   more direct path between the CN and MR to be used are highly
   desirable.

   For decades, mobile networks of some form have been used for
   communications with people and avionics equipment on board aircraft
   and spacecraft.  These have not typically used IP, although
   architectures are being devised and deployed based on IP in both the
   aeronautics and space exploration communities (see Appendix A and
   Appendix B for more information).  An aircraft or spacecraft
   generally contains many computing nodes, sensors, and other devices
   that are possible to address individually with IPv6.  This is
   desirable to support network-centric operations concepts.  Given that
   a craft has only a small number of access links, it is very natural
   to use NEMO MRs to localize the functions needed to manage the large
   onboard network's reachability over the few dynamic access links.  On
   an aircraft, the nodes are arranged in multiple, independent
   networks, based on their functions.  These multiple networks are
   required for regulatory reasons to have different treatments of their
   air-ground traffic and must often use distinct air-ground links and
   service providers.

   For aeronautics, the main disadvantage of using NEMO bidirectional
   tunnels is that airlines operate flights that traverse multiple
   continents, and a single plane may fly around the entire world over a
   span of a couple days.  If a plane uses a static HA on a single
   continent, then for a large percentage of the time, when the plane is
   not on the same continent as the HA, a great amount of delay is
   imposed by using the MRHA tunnel.  Avoiding the delay from
   unnecessarily forcing packets across multiple continents is the
   primary goal of pursuing NEMO RO for aeronautics.

   Other properties of the aeronautics and space environments amplify
   the known issues with NEMO bidirectional MRHA tunnels [6] even
   further.

      Longer routes leading to increased delay and additional
      infrastructure load:
         In aeronautical networks (e.g., using "Plain Old" Aircraft
         Communication Addressing and Reporting System (ACARS) or ACARS
         over VHF Data Link (VDL) mode 2) the queueing delays are often
         long due to Automatic Repeat Request (ARQ) mechanisms and
         underprovisioned radio links.  Furthermore, for space
         exploration and for aeronautical communications systems that
         pass through geosynchronous satellites, the propagation delays
         are also long.  These delays, combined with the additional need

         to cross continents in order to transport packets between
         ground stations and CNs, mean that delays are already quite
         high in aeronautical and space networks without the addition of
         an MRHA tunnel.  The increased delays caused by MRHA tunnels
         may be unacceptable in meeting Required Communication
         Performance [7].

      Increased packet overhead:
         Given the constrained link bandwidths available in even future
         communications systems for aeronautics and space exploration,
         planners are extremely adverse to header overhead.  Since any
         amount of available link capacity can be utilized for extra
         situational awareness, science data, etc., every byte of
         header/tunnel overhead displaces a byte of useful data.

      Increased chances of packet fragmentation:
         RFC 4888 [6] identifies fragmentation due to encapsulation as
         an artifact of tunneling.  While links used in the aeronautics
         and space domains are error-prone and may cause loss of
         fragments on the initial/final hop(s), considerations for
         fragmentation along the entire tunneled path are the same as
         for the terrestrial domain.

      Increased susceptibility to failure:
         The additional likelihood of either a single link failure
         disrupting all communications or an HA failure disrupting all
         communications is problematic when using MRHA tunnels for
         command and control applications that require high availability
         for safety-of-life or safety-of-mission.

   For these reasons, an RO extension to NEMO is highly desirable for
   use in aeronautical and space networking.  In fact, a standard RO
   mechanism may even be necessary before some planners will seriously
   consider advancing use of the NEMO technology from experimental
   demonstrations to operational use within their communications
   architectures.  Without an RO solution, NEMO is difficult to justify
   for realistic operational consideration.

   In Section 2 we describe the relevant high-level features of the
   access and onboard networks envisioned for use in aeronautics and
   space exploration, as they influence the properties of usable NEMO RO
   solutions.  Section 3 then lists the technical and functional
   characteristics that are absolutely required of a NEMO RO solution
   for these environments, while Section 4 lists some additional
   characteristics that are desired but not necessarily required.  In
   Appendix A and Appendix B we provide brief primers on the specific
   operational concepts used in aeronautics and space exploration,
   respectively, for IP-based network architectures.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [3].
   Although this document does not specify an actual protocol, but
   rather specifies just the requirements for a protocol, it still uses
   the RFC 2119 language to make the requirements clear.

2.  NEMO RO Scenarios

   To motivate and drive the development of the requirements and
   desirable features for NEMO RO solutions, this section describes some
   operational characteristics to explain how access networks, HAs, and
   CNs are configured and distributed geographically and topologically
   in aeronautical and space network architectures.  This may be useful
   in determining which classes of RO techniques within the known
   solution space [8] are feasible.

2.1.  Aeronautical Communications Scenarios

   Since aircraft may be simultaneously connected to multiple ground
   access networks using diverse technologies with different coverage
   properties, it is difficult to say much in general about the rate of
   changes in active access links and care-of addresses (CoAs).  As one
   data point, for using VDL mode 2 data links, the length of time spent
   on a single access channel varies depending on the stage of flight.
   On the airport surface, VDL mode 2 access is stable while a plane is
   unloaded, loaded, refueled, etc., but other wired and wireless LAN
   links (e.g. local networks available while on a gate) may come and
   go.  Immediately after takeoff and before landing, planes are in the
   terminal maneuvering area for approximately 10 minutes and stably use
   another VDL mode 2 channel.  During en route flight, handovers
   between VDL mode 2 channels may occur every 30 to 60 minutes,
   depending on the exact flight plan and layout of towers, cells, and
   sectors used by a service provider.  These handovers may result in
   having a different access router and a change in CoA, though the use
   of local mobility management (e.g., [9]) may limit the changes in CoA
   to only handovers between different providers or types of data links.

   The characteristics of a data flow between a CN and MNN varies both
   depending on the data flow's domain and on the particular application
   within the domain.  Even within the three aeronautical domains
   described below, there are varying classes of service that are
   regulated differently (e.g., for emergencies versus nominal
   operations), but this level of detail has been abstracted out for the
   purposes of this document.  It is assumed that any viable NEMO RO
   solution will be able to support a granularity of configuration with
   many sub-classes of traffic within each of the specific domains
   listed here.

2.1.1.  Air Traffic Services Domain

   The MNNs involved in Air Traffic Services (ATS) consist of pieces of
   avionics hardware on board an aircraft that are used to provide
   navigation, control, and situational awareness.  The applications run
   by these MNNs are mostly critical to the safety of the lives of the
   passengers and crew.  The MNN equipment may consist of a range of
   devices from typical laptop computers to very specialized avionics
   devices.  These MNNs will mostly be Local Fixed Nodes (LFNs), with a
   few Local Mobile Nodes (LMNs) to support Electronic Flight Bags, for
   instance.  It can be assumed that Visiting Mobile Nodes (VMNs) are
   never used within the ATS domain.

   An MR used for ATS will be capable of using multiple data links (at
   least VHF-based, satellite, HF-based, and wired), and will likely be
   supported by a backup unit in the case of failure, leading to a case
   of a multihomed MR that is at least multi-interfaced and possibly
   multi-prefixed as well, in NEMO terminology.

   The existing ATS link technologies may be too anemic for a complete
   IP-based ATS communications architecture (link technologies and
   acronyms are briefly defined in Appendix A).  At the time of this
   writing, the ICAO is pursuing future data link standards that support
   higher data rates.  Part of the problem is limited spectrum, pursued
   under ICAO ACP-WG-F, "Spectrum Management", and part of the problem
   is the data link protocols themselves, pursued under ICAO ACP-WG-T,
   "Future Communications Technology".  ACP-WG-T has received inputs
   from studies on a number of potential data link protocols, including
   B-AMC, AMACS, P34, LDL, WCDMA, and others.  Different link
   technologies may be used in different stages of flight, for instance
   802.16 in the surface and terminal area, P34 or LDL en route, and
   satcom in oceanic flight.  Both current and planned data links used
   for Passenger Information and Entertainment Services (PIES) and/or
   Airline Operational Services (AOS), such as the satcom links employed
   by passenger Internet-access systems, support much higher data rates
   than current ATS links.

   Since, for ATS, the MRs and MNNs are under regulatory control and are
   actively tested and maintained, it is not completely unreasonable to
   assume that special patches or software be run on these devices to
   enable NEMO RO.  In fact, since these devices are accessed by skilled
   technicians and professionals, it may be that some special
   configuration is required for NEMO RO.  Of course, simplicity in set
   up and configuration is highly preferable, however, and the desirable
   feature labeled "Des1" later in this document prefers solutions with
   lower configuration state and overhead.  To minimize costs of

   ownership and operations, it is also highly desirable for only widely
   available, off-the-shelf operating systems or network stacks to be
   required, but this is not a full requirement.

   Data flows from the ATS domain may be assumed to consist mainly of
   short transactional exchanges, such as clearance requests and grants.
   Future ATS communications are likely to include longer messages and
   higher message frequencies for positional awareness and trajectory
   intent of all vehicles in motion at the airport and all aircraft
   within a thirty-mile range during flight.  Many of these may be
   aircraft-to-aircraft, but the majority of current exchanges are
   between the MNNs and a very small set of CNs within a control
   facility and take place at any time due to the full transfer of
   control as a plane moves across sectors of airspace.  The set of CNs
   may be assumed to be topologically close to one another.  These CNs
   are also involved in other data flows over the same access network
   that the MR is attached to, managing other flights within the sector.
   These CNs are often geographically and topologically much closer to
   the MR in comparison to a single fixed HA.

   The MNNs and CNs used for ATS will support IP services, as IP is the
   basis of the new Aeronautical Telecommunications Network (ATN)
   architecture being defined by ICAO.  Some current ATS ground systems
   run typical operating systems, like Solaris, Linux, and Windows, on
   typical workstation computer hardware.  There is some possibility for
   an RO solution to require minor changes to these CNs, though it is
   much more desirable if completely off-the-shelf CN machines and
   operating systems can be used.  Later in this document, the security
   requirements suggest that RO might be performed with mobility anchors
   that are topologically close to the CNs, rather than directly to CNs
   themselves.  This could possibly mean that CN modifications are not
   required.

   During the course of a flight, there are several events for which an
   RO solution should consider the performance implications:

   o  Initial session creation with an ATS CN (called "Data Link Logon"
      in the aeronautical jargon).

   o  Transfer of control between ATS CNs, resulting in regional
      differences in where the controlling CN is located.

   o  Aircraft-initiated contact with a non-controlling ATS CN, which
      may be located anywhere, without relation to the controlling CN.

   o  Non-controlling, ATS, CN-initiated contact with the aircraft.

   o  Aircraft transition between one access link to another, resulting
      in change of CoA.

   o  Concurrent use of multiple access links with different care-of
      addresses.

2.1.2.  Airline Operational Services Domain

   Data flows for Airline Operational Services (AOS) are not critical to
   the safety of the passengers or aircraft, but are needed for the
   business operations of airlines operating flights, and may affect the
   profitability of an airline's flights.  Most of these data flows are
   sourced by MNNs that are part of the flight management system or
   sensor nodes on an aircraft, and are terminated at CNs located near
   an airline's headquarters or operations center.  AOS traffic may
   include detailed electronic passenger manifests, passenger ticketing
   and rebooking traffic, and complete electronic baggage manifests.
   When suitable bandwidth is available (currently on the surface when
   connected to a wired link at a gate), "airplane health information"
   data transfers of between 10 and several hundred megabytes of data
   are likely, and in the future, it is expected that the In-Flight
   Entertainment (IFE) systems may receive movie refreshes of data
   (e.g., television programming or recent news updates) running into
   the multi-gigabyte range.

   Currently, these flows are often short messages that record the
   timing of events of a flight, engine performance data, etc., but may
   be longer flows that upload weather or other supplementary data to an
   aircraft.  In addition, email-like interactive messaging may be used
   at any time during a flight.  For instance, messages can be exchanged
   before landing to arrange for arrival-gate services to be available
   for handicapped passengers, refueling, food and beverage stocking,
   and other needs.  This messaging is not limited to landing
   preparation, though, and may occur at any stage of flight.

   The equipment comprising these MNNs and CNs has similar
   considerations to the equipment used for the ATS domain.  A key
   difference between ATS and AOS is that AOS data flows are routed to
   CNs that may be much more geographically remote to the aircraft than
   CNs used by ATS flows, as AOS CNs will probably be located at an
   airline's corporate data center or headquarters.  The AOS CNs will
   also probably be static for the lifetime of the flight, rather than
   dynamic like the ATS CNs.  An HA used for AOS may be fairly close
   topologically to the CNs, and RO may not be as big of a benefit for
   AOS since simple event logging is more typical than time-critical
   interactive messaging.  For the small number of messaging flows,
   however, the CNs are geographically (but not necessarily
   topologically) very close to the aircraft, though this depends on how

   applications are written -- whether they use centralized servers or
   exchange messages directly.  Additionally, since AOS communication is
   more advisory in nature than ATS, rather than safety-critical, AOS
   flows are less sensitive to tunnel inefficiencies than ATS flows.
   For these reasons, in this document, we consider AOS data flow
   concerns with RO mechanisms to not be full requirements, but instead
   consider them desirable properties, which are discussed in Section 4.

   Future AOS MNNs and CNs can be expected to implement IPv6 and conform
   to the new IPv6-based ATN Standards and Recommended Practices (SARPS)
   that ICAO is defining.  AOS CNs have similar hardware and software
   properties as described for ATS above.

2.1.3.  Passenger Services Domain

   The MNNs involved in the Passenger Information and Entertainment
   Services (PIES) domain are mostly beyond the direct control of any
   single authority.  The majority of these MNNs are VMNs and personal
   property brought on board by passengers for the duration of a flight,
   and thus it is unreasonable to assume that they be preloaded with
   special software or operating systems.  These MNNs run stock Internet
   applications like web browsing, email, and file transfer, often
   through VPN tunnels.  The MNNs themselves are portable electronics,
   such as laptop computers and mobile smartphones capable of connecting
   to an onboard wireless access network (e.g., using 802.11).  To these
   MNN devices and users, connecting to the onboard network is identical
   to connecting to any other terrestrial "hotspot" or typical wireless
   LAN.  The MNNs are completely oblivious to the fact that this access
   network is on an airplane and possibly moving around the globe.  The
   users are not always technically proficient and may not be capable of
   performing any special configuration of their MNNs or applications.

   The largest class of PIES CNs consists of typical web servers and
   other nodes on the public Internet.  It is not reasonable to assume
   that these can be modified specifically to support a NEMO RO scheme.
   Presently, these CNs would be mostly IPv4-based, though an increasing
   number of IPv6 PIES CNs are expected in the future.  This document
   does not consider the problem of IPv4-IPv6 transition, beyond the
   assumption that either MNNs and CNs are running IPv6 or a transition
   mechanism exists somewhere within the network.

   A small number of PIES MNNs may be LFNs that store and distribute
   cached media content (e.g., movies and music) or that may provide
   gaming services to passengers.  Due to the great size of the data
   stored on these LFNs compared to the anemic bandwidth available air-
   to-ground, these LFNs will probably not attempt to communicate off-
   board at all during the course of a flight, but will wait to update
   their content via either high-speed links available on the ground or

   removable media inserted by the flight crew.  However, if a higher
   bandwidth link were affordably available, it might be used in-flight
   for these purposes, but supporting this is not a requirement.  Data
   flows needed for billing passengers for access to content are
   relatively low bandwidth and are currently done in-flight.  The
   requirements of these data flows are less stringent than those of
   ATS, however, so they are not specifically considered here.

   The PIES domain is not critical to safety-of-life, but is merely an
   added comfort or business service to passengers.  Since PIES
   applications may consume much more bandwidth than the available links
   used in other domains, the PIES MNNs may have their packets routed
   through a separate high-bandwidth link that is not used by the ATS
   data flows.  For instance, several service providers are planning to
   offer passenger Internet access during flight at DSL-like rates, just
   as the former Connexion by Boeing system did.  Several airlines also
   plan to offer onboard cellular service to their passengers, possibly
   utilizing Voice-over-IP for transport.  Due to the lack of
   criticality and the likelihood of being treated independently, in
   this document, PIES MNN concerns are not considered as input to
   requirements in Section 3.  The RO solution should be optimized for
   ATS and AOS needs and consider PIES as a secondary concern.

   With this in consideration, the PIES domain is also the most likely
   to utilize NEMO for communications in the near-term, since relatively
   little regulations and bureaucracy are involved in deploying new
   technology in this domain and since IP-based PIES systems have
   previously been developed and deployed (although not using NEMO)
   [10].  For these reasons, PIES concerns factor heavily into the
   desirable properties in Section 4, outside of the mandatory
   requirements.

   Some PIES nodes are currently using 2.5G/3G links for mobile data
   services, and these may be able to migrate to an IP-based onboard
   mobile network, when available.

2.2.  Space Exploration Scenarios

   This section describes some features of the network environments
   found in space exploration that are relevant to selecting an
   appropriate NEMO RO mechanism.  It should be noted that IPv4-based
   mobile routing has been demonstrated on board the UK-DMC satellite
   and that the documentation on this serves as a useful reference for
   understanding some of the goals and configuration issues for certain
   types of space use of NEMO [11].  This section assumes space use of
   NEMO within the "near-Earth" range of space (i.e., not for
   communications between the Earth and Mars or other "deep space"
   locations).  Note that NEMO is currently being considered for use out

   to lunar distances.  No strong distinction is made here between
   civilian versus military use, or exploration mission versus Earth-
   observing or other mission types; our focus is on civilian
   exploration missions, but we believe that many of the same basic
   concerns are relevant to these other mission types.

   In space communications, a high degree of bandwidth asymmetry is
   often present, with the uplink from the ground to a craft typically
   being multiple orders of magnitude slower than the downlink from the
   craft to the ground.  This means that the RO overhead may be
   negligible on the downlink but significant for the uplink.  An RO
   scheme that minimizes the amount of signaling from CNs to an MN is
   desirable, since these uplinks may be low-bandwidth to begin with
   (possibly only several kilobits per second).  Since the uplink is
   used for sending commands, it should not be blocked for long periods
   while serializing long RO signaling packets; any RO signaling from
   the CN to MNNs must not involve large packets.

   For unmanned space flight, the MNNs on board a spacecraft consist
   almost entirely of LFN-sensing devices and processing devices that
   send telemetry and science data to CNs on the ground and actuator
   devices that are commanded from the ground in order to control the
   craft.  Robotic lunar rovers may serve as VMNs behind an MR located
   on a lander or orbiter, but these rovers will contain many
   independent instruments and could probably be configured as an MR and
   LFNs instead of using a single VMN address.

   It can be assumed that for manned spaceflight, at least multiple MRs
   will be present and online simultaneously for fast failover.  These
   will usually be multihomed over space links in diverse frequency
   bands, and so multiple access network prefixes can be expected to be
   in use simultaneously, especially since some links will be direct to
   ground stations while others may be bent-pipe repeated through
   satellite relays like the Tracking and Data Relay Satellite System
   (TDRSS).  This conforms to the (n,1,1) or (n,n,1) NEMO multihoming
   scenarios [12].  For unmanned missions, if low weight and power are
   more critical, it is likely that only a single MR and single link/
   prefix may be present, conforming to the (1,1,1) or (1,n,1) NEMO
   multihoming scenarios [12].

   In some modes of spacecraft operation, all communications may go
   through a single onboard computer (or a Command and Data Handling
   system as on the International Space Station) rather than directly to
   the MNNs themselves, so there is only ever one MNN behind an MR that
   is in direct contact with off-board CNs.  In this case, removing the
   MR and using simple host-based Mobile IPv6 rather than NEMO is
   possible.  However, an MR is more desirable because it could be part
   of a modular communications adapter that is used in multiple diverse

   missions to bridge onboard buses and intelligently manage space
   links.  This is cheaper and leads to faster development time than
   re-creating these capabilities per-mission if using simple Mobile
   IPv6 with a single Command and Data Handling node that varies widely
   between spacecraft.  Also, all visions for the future involve
   network-centric operations where the direct addressability and
   accessibility of end devices and data is crucial.  As network-centric
   operations become more prevalent, application of NEMO is likely to be
   needed to increase the flexibility of data flow.

   The MRs and MNNs on board a spacecraft are highly customized
   computing platforms, and adding custom code or complex configurations
   in order to obtain NEMO RO capabilities is feasible, although it
   should not be assumed that any amount of code or configuration
   maintenance is possible after launch.  The RO scheme as it is
   initially configured should continue to function throughout the
   lifetime of an asset.

   For manned space flight, additional MNNs on spacesuits and astronauts
   may be present and used for applications like two-way voice
   conversation or video-downlink.  These MNNs could be reusable and
   reconfigured per-flight for different craft or mission network
   designs, but it is still desirable for them to be able to
   autoconfigure themselves, and they may move between nested or non-
   nested MRs during a mission.  For instance, if astronauts move
   between two docked spacecrafts, each craft may have its own local MR
   and wireless coverage that the suit MNNs will have to reconfigure
   for.  It is desirable if an RO solution can respond appropriately to
   this change in locality and not cause high levels of packet loss
   during the transitional period.  It is also likely that these MNNs
   will be part of Personal Area Networks (PANs), and so may appear
   either directly as MNNs behind the main MR on board or have their own
   MR within the PAN and thus create a nested (or even multi-level
   nested) NEMO configuration.

3.  Required Characteristics

   This section lists requirements that specify the absolute minimal
   technical and/or functional properties that a NEMO RO mechanism must
   possess to be usable for aeronautical and space communications.

   In the recent work done by the International Civil Aviation
   Organization (ICAO) to identify viable mobility technologies for
   providing IP services to aircraft, a set of technical criteria was
   developed ([13], [14]).  The nine required characteristics listed in
   this document can be seen as directly descended from these ICAO
   criteria, except here we have made them much more specific and
   focused for the NEMO technology and the problem of RO within NEMO.

   The original ICAO criteria were more general and used for comparing
   the features of different mobility solutions (e.g., mobility
   techniques based on routing protocols versus transport protocols
   versus Mobile IP, etc.).  Within the text describing each requirement
   in this section, we provide the high-level ICAO criteria from which
   it evolved.

   These requirements for aeronautics are generally similar to or in
   excess of the requirements for space exploration, so we do not add
   any additional requirements specifically for space exploration.  In
   addition, the lack of a standards body regulating performance and
   safety requirements for space exploration means that the requirements
   for aviation are much easier to agree upon and base within existing
   requirements frameworks.  After consideration, we believe that the
   set of aviation-based requirements outlined here also fully suffices
   for space exploration.

   It is understood that different solutions may be needed for
   supporting different domains.  This may mean either different NEMO RO
   solutions or different mobility solutions entirely.  Divergent
   solutions amongst the domains are acceptable, though preferably
   avoided if possible.

   An underlying requirement that would be assumed by the use of Mobile
   IP technology for managing mobility (rather than a higher-layer
   approach) is that IP addresses used both within the mobile network
   and by CNs to start new sessions with nodes within the mobile network
   remain constant throughout the course of flights and operations.  For
   ATS and AOS, this allows the Home Addresses (HoAs) to serve as node
   identifiers, rather than just locators, and for PIES it allows common
   persistent applications (e.g., Voice over IP (VoIP) clients, VPN
   clients, etc.) to remain connected throughout a flight.  Prior
   aeronautical network systems like the prior OSI-based ATN and
   Connexion by Boeing set a precedent for keeping a fixed Mobile
   Network Prefix (MNP), though they relied on interdomain routing
   protocols (IDRP and BGP) to accomplish this, rather than NEMO
   technology.  This requirement applies to the selection in general of
   a mobility management technology, and not specifically to an RO
   solution once NEMO has been decided on for mobility management.

3.1.  Req1 - Separability

   Since RO may be inappropriate for some flows, an RO scheme MUST
   support configuration by a per-domain, dynamic RO policy database.
   Entries in this database can be similar to those used in IPsec
   security policy databases in order to specify either bypassing or
   utilizing RO for specific flows.

3.1.1.  Rationale for Aeronautics - Separability

   Even if RO is available to increase the performance of a mobile
   network's traffic, it may not be appropriate for all flows.

   There may also be a desire to push certain flows through the MRHA
   path, rather than performing RO, to enable them to be easily recorded
   by a central service.

   For these reasons, an RO scheme must have the ability to be bypassed
   by applications that desire to use bidirectional tunnels through an
   HA.  This desire could be expressed through a policy database similar
   to the security policy database used by IPsec, for instance, but the
   specific means of signaling or configuring the expression of this
   desire by applications is left as a detail for the specific RO
   specifications.

   In addition, it is expected that the use of NEMO technology be
   decided on a per-domain basis, so that it is possible that, for some
   domains, separate MRs or even non-NEMO mobility techniques are used.
   This requirement for an RO policy database only applies to domains
   that utilize NEMO.

   This requirement was derived from ICAO's TC-1 [15] - "The approach
   should provide a means to define data communications that can be
   carried only over authorized paths for the traffic type and category
   specified by the user."

   One suggested approach to traffic separation is multi-addressing of
   the onboard networks, with treatment of a traffic domain determined
   by the packet addresses used.  However, there are other techniques
   possible for meeting this requirement, and so multi-addressing is not
   itself a requirement.  The Req1 requirement we describe above is
   intended for separating the traffic within a domain that makes use of
   NEMO based on flow properties (e.g., short messaging flows vs. longer
   file transfers or voice flows).

3.2.  Req2 - Multihoming

   An RO solution MUST support an MR having multiple interfaces and MUST
   allow a given domain to be bound to a specific interface.  It MUST be
   possible to use different MNPs for different domains.

3.2.1.  Rationale for Aeronautics - Multihoming

   Multiple factors drive a requirement for multihoming capabilities.
   For ATS safety-of-life critical traffic, the need for high
   availability suggests a basic multihoming requirement.  The

   regulatory and operational difficulty in deploying new systems and
   transitioning away from old ones also implies that a mix of access
   technologies may be in use at any given time, and may require
   simultaneous use.  Another factor is that the multiple domains of
   applications on board may actually be restricted in what data links
   they are allowed to use, based on regulations and policy; thus, at
   certain times or locations, PIES data flows may have to use distinct
   access links from those used by ATS data flows.

   This drives the requirement that an RO solution MUST allow for an MR
   to be connected to multiple access networks simultaneously and have
   multiple CoAs in use simultaneously.  The selection of a proper CoA
   and access link to use per-packet may be either within or outside the
   scope of the RO solution.  As a minimum, if an RO solution is
   integrable with the MONAMI6 basic extensions (i.e., registration of
   multiple CoAs and flow bindings) and does not preclude their use,
   then this requirement can be considered to be satisfied.

   It is not this requirement's intention that an RO scheme itself
   provide multihoming, but rather simply to exclude RO techniques whose
   use is not possible in multihomed scenarios.

   In terms of NEMO multihoming scenarios [12], it MUST be possible to
   support at least the (n,1,n) and (n,n,n) scenarios.

   This requirement was derived from ICAO's TC-2 - "The approach should
   enable an aircraft to both roam between and to be simultaneously
   connected to multiple independent air-ground networks."

3.3.  Req3 - Latency

   While an RO solution is in the process of setting up or
   reconfiguring, packets of specified flows MUST be capable of using
   the MRHA tunnel.

3.3.1.  Rationale for Aeronautics - Latency

   It is possible that an RO scheme may take longer to set up or involve
   more signaling than the basic NEMO MRHA tunnel maintenance that
   occurs during an update to the MR's active CoAs when the set of
   usable access links changes.  During this period of flux, it may be
   important for applications to be able to immediately get packets onto
   the ground network, especially considering that connectivity may have
   been blocked for some period of time while link-layer and NEMO
   procedures for dealing with the transition occurred.  Also, when an
   application starts for the first time, the RO scheme may not have
   previous knowledge related to the CN and may need to perform some set

   up before an optimized path is available.  If the RO scheme blocks
   packets either through queueing or dropping while it is configuring
   itself, this could result in unacceptable delays.

   Thus, when transitions in the MR's set of active access links occurs,
   the RO scheme MUST NOT block packets from using the MRHA tunnel if
   the RO scheme requires more time to set up or configure itself than
   the basic NEMO tunnel maintenance.  Additionally, when an application
   flow is started, the RO scheme MUST allow packets to immediately be
   sent, perhaps without the full benefit of RO, if the RO scheme
   requires additional time to configure a more optimal path to the CN.

   This requirement was derived from ICAO's TC-3 - "The approach should
   minimize latency during establishment of initial paths to an
   aircraft, during handoff, and during transfer of individual data
   packets."

3.4.  Req4 - Availability

   An RO solution MUST be compatible with network redundancy mechanisms
   and MUST NOT prevent fallback to the MRHA tunnel if an element in an
   optimized path fails.

   An RO mechanism MUST NOT add any new single point of failure for
   communications in general.

3.4.1.  Rationale for Aeronautics - Availability

   A need for high availability of connectivity to ground networks
   arises from the use of IP networking for carrying safety-of-life
   critical traffic.  For this reason, single points of failure need to
   be avoided.  If an RO solution assumes either a single onboard MR, a
   single HA, or some similar vulnerable point, and is not usable when
   the network includes standard reliability mechanisms for routers,
   then the RO technique will not be acceptable.  An RO solution also
   MUST NOT itself imply a single point of failure.

   This requirement specifies that the RO solution itself does not
   create any great new fragility.  Although in basic Mobile IPv6 and
   NEMO deployments, the use of a single HA implies a single point of
   failure, there are mechanisms enabling the redundancy of HAs (e.g.,
   [16]).  It is assumed that some HA-redundancy techniques would be
   employed to increase robustness in an aeronautical setting.  It
   should also be understood that the use of RO techniques decreases
   dependence on HAs in the infrastructure and allows a certain level of
   robustness to HA failures in that established sessions using RO may

   be able to operate based on Binding Cache entries even after an HA
   failure.  With RO, an HA failure primarily impacts the ability to
   connect new application flows to a mobile network.

   If a failure occurs in a path selected by an RO technique, then that
   RO technique MUST NOT prevent fallback to the MRHA path for affected
   traffic.

   This does not mention specific redundancy mechanisms for MRs, HAs, or
   other networking elements, so as long as some reasonable method for
   making each component redundant fits within the assumptions of the RO
   mechanism, this requirement can be considered satisfied.

   There is no intention to support "Internet-less" operation through
   this requirement.  When an MR is completely disconnected from the
   majority of the network with which it is intended to communicate,
   including its HA, there is no requirement for it to be able to retain
   any communications involving parties outside the mobile networks
   managed by itself.

   This requirement was derived from ICAO's TC-4 - "The approach should
   have high availability which includes not having a single point of
   failure."

3.5.  Req5 - Packet Loss

   An RO scheme SHOULD NOT cause either loss or duplication of data
   packets during RO path establishment, usage, or transition, above
   that caused in the NEMO basic support case.  An RO scheme MUST NOT
   itself create non-transient losses and duplications within a packet
   stream.

3.5.1.  Rationale for Aeronautics - Packet Loss

   It is possible that some RO schemes could cause data packets to be
   lost during transitions in RO state or due to unforeseen packet
   filters along the RO-selected path.  This could be difficult for an
   application to detect and respond to in time.  For this reason, an RO
   scheme SHOULD NOT cause packets to be dropped at any point in
   operation, when they would not normally have been dropped in a non-RO
   configuration.

   As an attempt at optimizing against packet loss, some techniques may,
   for some time, duplicate packets sent over both the MRHA tunnel and
   the optimized path.  If this results in duplicate packets being
   delivered to the application, this is also unacceptable.

   This requirement does not necessarily imply make-before-break in
   transitioning between links.  The intention is that during the
   handoff period, the RO scheme itself should not produce losses (or
   duplicates) that would not have occurred if RO had been disabled.

   This requirement was derived from ICAO's TC-5 - "The approach should
   not negatively impact end-to-end data integrity, for example, by
   introducing packet loss during path establishment, handoff, or data
   transfer."

   It is understood that this may be a requirement that is not easily
   implementable with regards to RO.  Furthermore Req1, Separability,
   may be sufficient in allowing loss-sensitive and duplicate-sensitive
   flows to take the MRHA path.

3.6.  Req6 - Scalability

   An RO scheme MUST be simultaneously usable by the MNNs on hundreds of
   thousands of craft without overloading the ground network or routing
   system.  This explicitly forbids injection of BGP routes into the
   global Internet for purposes of RO.

3.6.1.  Rationale for Aeronautics - Scalability

   Several thousand aircraft may be in operation at some time, each with
   perhaps several hundred MNNs onboard.  The number of active
   spacecraft using IP will be multiple orders of magnitude smaller than
   this over at least the next decade, so the aeronautical needs are
   more stringent in terms of scalability to large numbers of MRs.  It
   would be a non-starter if the combined use of an RO technique by all
   of the MRs in the network caused ground networks provisioned within
   the realm of typical long-haul private telecommunications networks
   (like the FAA's Telecommunications Infrastructure (FTI) or the NASA
   Integrated Services Network (NISN)) to be overloaded or melt-down
   under the RO signaling load or amount of rapid path changes for
   multiple data flows.

   Thus, an RO scheme MUST be simultaneously usable by the MNNs on
   hundreds of thousands of craft without overloading the ground network
   or routing system.  The scheme must also be tolerant to the delay
   and/or loss of initial packets, which may become more pervasive in
   future Internet routing and addressing architectures [17].

   Since at least one traffic domain (PIES) requires connectivity to the
   Internet and it is possible that the Internet would provide transport
   for other domains at some distant point in the future, this
   requirement explicitly forbids the use of techniques that are known
   to scale poorly in terms of their global effects, like BGP, for the

   purposes of RO.  The previous OSI-based ATN system used IDRP and an
   "island" concept for maintaining connectivity to the mobile network
   but was not tested on a large scale deployment.  The Connexion by
   Boeing system used BGP announces and withdrawals as a plane moved
   across the globe in order to maintain connectivity [10].  This was
   found to contribute to a significant amount of churn in the global
   Internet routing tables, which is undesirable for a number of
   reasons, and must be avoided in the future.

   This requirement was derived from ICAO's TC-6 - "The approach should
   be scalable to accommodate anticipated levels of aircraft equipage."

   The specific scaling factor for the number of aircraft used in our
   version of the requirement is an order of magnitude larger than the
   estimated equipage cited in an ICAO draft letter-of-intent to ARIN
   for an IPv6 prefix allocation request.  There were several other
   estimates that different groups had made, and it was felt in the IETF
   that using a larger estimate was more conservative.  It should be
   noted that even with this difference of an order of magnitude, the
   raw number is still several orders of magnitude lower than that of
   estimated cellular telephone users, which might use the same protocol
   enhancements as the cellular industry has also adopted Mobile IP
   standards.

3.7.  Req7 - Efficient Signaling

   An RO scheme MUST be capable of efficient signaling in terms of both
   size and number of individual signaling messages and the ensemble of
   signaling messages that may simultaneously be triggered by concurrent
   flows.

3.7.1.  Rationale for Aeronautics - Efficient Signaling

   The amount of bandwidth available for aeronautical and space
   communications has historically been quite small in comparison to the
   desired bandwidth (e.g., in the case of VDL links, the bandwidth is 8
   kbps of shared resources).  This situation is expected to persist for
   at least several more years.  Links tend to be provisioned based on
   estimates of application needs (which could well prove wrong if
   either demand or the applications in use themselves do not follow
   expectations) and do not leave much room for additional networking
   protocol overhead.  Since every byte of available air-ground link
   capacity that is used by signaling for NEMO RO is likely to delay
   bytes of application data and reduce application throughput, it is
   important that the NEMO RO scheme's signaling overhead scales up much
   more slowly than the throughput of the flows RO is being performed

   on.  This way, as higher-rate data links are deployed along with more
   bandwidth-hungry applications, the NEMO RO scheme will be able to
   safely be discounted in capacity planning.

   Note that in meeting this requirement, an RO technique must be
   efficient in both the size and number of individual messages that it
   sends, as well in the ensemble of messages sent at one time (for
   instance, to give RO to multiple ongoing flows following a handover),
   in order to prevent storms of packets related to RO.

   This requirement was derived from ICAO's TC-7 - "The approach should
   result in throughput which accommodates anticipated levels of
   aircraft equipage."

3.8.  Req8 - Security

   For the ATS/AOS domains, there are three security sub-requirements:

   1.  The RO scheme MUST NOT further expose MNPs on the wireless link
       than already is the case for NEMO basic support.

   2.  The RO scheme MUST permit the receiver of a binding update (BU)
       to validate an MR's ownership of the CoAs claimed by an MR.

   3.  The RO scheme MUST ensure that only explicitly authorized MRs are
       able to perform a binding update for a specific MNP.

   For the PIES domain, there are no additional requirements beyond
   those of normal Internet services and the same requirements for
   normal Mobile IPv6 RO apply.

3.8.1.  Rationale for Aeronautics - Security

   The security needs are fairly similar between ATS and AOS, but vary
   widely between the ATS/AOS domains and PIES.  For PIES, the traffic
   flows are typical of terrestrial Internet use and the security
   requirements for RO are identical to those of conventional Mobile
   IPv6 RO.  For ATS/AOS, however, there are somewhat more strict
   requirements, along with some safe assumptions that designers of RO
   schemes can make.  Below, we describe each of these ATS/AOS issues,
   but do not further discuss PIES RO security.

   The first security requirement is driven by concerns expressed by ATS
   communications engineers.  The concern is driven by current air-
   ground links to a craft and their lack of security, which has allowed
   eavesdroppers to track individual flights in detail.  Protecting the
   MNP from exposure has been expressed as a requirement by this
   community, though the security of the RO system should not depend on

   secrecy of the MNP.  The RO scheme should use some reasonable
   security mechanisms in order to both protect RO signaling via strong
   authentication and encrypt the MNP from being visible over air-ground
   links.

   The second security requirement is driven by the risk of flooding
   attacks that are started by an attacker redirecting an MNP's traffic
   to some target victim CoA.  To protect bindings to bogus CoAs from
   being sent, the RO scheme must somehow validate that an MR actually
   possesses any CoAs that it claims.  For the purposes of aeronautics,
   it is safe to assume ingress filtering is in place in the access
   networks.

   To protect against "rogue" MRs or abuse of compromised MRs, the RO
   scheme MUST be capable of checking that an MR is actually authorized
   to perform a binding update for a specific MNP.  To meet this
   requirement, it can be assumed that some aeronautical organization
   authority exists who can provide the required authorization, possibly
   in the form of a certificate that the MR possesses, signed by the
   aeronautical authority.

   It is also reasonable to assume trust relationships between each MR
   and a number of mobility anchor points topologically near to its CNs
   (these anchor points may be owned by the service providers), but it
   is not reasonable to assume that trust relationships can be
   established between an MR and any given CN itself.  Within the
   onboard networks for ATS and AOS, it is reasonable to assume that the
   LFNs and MRs have some trust relationship.

   It is felt by many individuals that by the time the IP-based ATN
   grows into production use, there will be a global ATN-specific Public
   Key Infrastructure (PKI) usable for ATS, though it is agreed that
   such a PKI does not currently exist and will take time to develop
   both technically and politically.  This PKI could permit the
   establishment of trust relationships among any pair of ATS MNNs, MRs,
   or CNs through certificate paths, in contrast to the more limited
   amount of trust relationships described in the previous paragraph.
   While it has been suggested that early test and demonstration
   deployments with a more limited-scale PKI deployment can be used in
   the near-term, as a global PKI is developed, some parties still feel
   that assuming a global PKI may be overly bold in comparison to
   assuming trust relationships with anchor points.  It is always
   possible to scale the anchor point assumption up if a PKI develops
   that allows the CNs themselves to become the anchor points.  It is
   not possible to go back down in the other direction if a global PKI
   never emerges.

   This requirement was extrapolated from ICAO's TC-8 - "The approach
   should be secure" and made more specific with help from the MEXT
   working group.

3.9.  Req9 - Adaptability

   Applications using new transport protocols, IPsec, or new IP options
   MUST be possible within an RO scheme.

3.9.1.  Rationale for Aeronautics - Adaptability

   The concepts of operations are not fully developed for network-
   centric command and control and other uses of IP-based networks in
   aeronautical and space environments.  The exact application
   protocols, data flow characteristics, and even transport protocols
   that will be used in either transitional or final operational
   concepts are not completely defined yet, and may even change with
   deployment experience.  The RO solution itself should allow all
   higher-layer protocols, ports, and options to be used.

   This requirement was derived from ICAO's TC-9 - "The approach should
   be scalable to accommodate anticipated transition to new IP-based
   communication protocols."

4.  Desirable Characteristics

   In this section, we identify some of the properties of the system
   that are not strict requirements due to either being difficult to
   quantify or to being features that are not immediately needed, but
   that may provide additional benefits that would help encourage
   adoption.

4.1.  Des1 - Configuration

   For ATS systems, complex configurations are known to increase
   uncertainty in context, human error, and the potential for reaching
   undesirable (unsafe) states [18].  Since RO alters the communications
   context between an MNN and CN, it is desirable that a NEMO RO
   solution be as simple to configure as possible and also easy to
   automatically disable if an undesirable state is reached.

   For CNs at large airports, the Binding Cache state management
   functions may be simultaneously dealing with hundreds of airplanes
   with multiple service providers and a volume of mobility events due
   to arrivals and departures.  The ability to have simple interfaces
   for humans to access the Binding Cache configuration and alter it in
   case of errors is desirable, if this does not interfere with the RO
   protocol mechanisms themselves.

4.2.  Des2 - Nesting

   It is desirable if the RO mechanism supports RO for nested MRs, since
   it is possible that, for PIES and astronaut spacesuits, PANs with MRs
   will need to be supported.  For oceanic flight, ATS and AOS may also
   benefit from the capability of nesting MRs between multiple planes to
   provide a "reachback" to terrestrial ground stations rather than
   relying solely on lower rate HF or satellite systems.  In either
   case, this mode of operation is beyond current strict requirements
   and is merely desirable.  It is also noted that there are other ways
   to support these communications scenarios using routing protocols or
   other means outside of NEMO.

   Loop-detection, in support of nesting, is specifically not a
   requirement at this stage of ATN and space network designs, due to
   both the expectation that the operational environments are carefully
   controlled and inherently avoid loops and the understanding that
   scenarios involving nesting are not envisioned in the near future.

4.3.  Des3 - System Impact

   Low complexity in systems engineering and configuration management is
   desirable in building and maintaining systems using the RO mechanism.
   This property may be difficult to quantify, judge, and compare
   between different RO techniques, but a mechanism that is perceived to
   have lower impact on the complexity of the network communications
   system should be favored over an otherwise equivalent mechanism (with
   regards to the requirements listed above).  This is somewhat
   different than Des1 (Configuration), in that Des1 refers to operation
   and maintenance of the system once deployed, whereas Des3 is
   concerned with the initial design, deployment, transition, and later
   upgrade path of the system.

4.4.  Des4 - VMN Support

   At least LFNs MUST be supported by a viable RO solution for
   aeronautics, as these local nodes are within the ATS and AOS domains.
   If Mobile IPv6 becomes a popular technology used by portable consumer
   devices, VMNs within the PIES domain are expected to be numerous, and
   it is strongly desirable for them to be supported by the RO
   technique, but not strictly required.  LMNs are potentially present
   in future space exploration scenarios, such as manned exploration
   missions to the moon and Mars.

4.5.  Des5 - Generality

   An RO mechanism that is "general purpose", in that it is also readily
   usable in other contexts outside of aeronautics and space
   exploration, is desirable.  For instance, an RO solution that is
   usable within Vehicular ad hoc Networks (VANETs) [19] or consumer
   electronics equipment [20] could satisfy this.  The goal is for the
   technology to be more widely used and maintained outside the
   relatively small aeronautical networking community and its vendors,
   in order to make acquisitions and training faster, easier, and
   cheaper.  This could also allow aeronautical networking to possibly
   benefit from future RO scheme optimizations and developments whose
   research and development is funded and performed externally by the
   broader industry and academic communities.

5.  Security Considerations

   This document does not create any security concerns in and of itself.
   The security properties of any NEMO RO scheme that is to be used in
   aeronautics and space exploration are probably much more stringent
   than for more general NEMO use, due to the safety-of-life and/or
   national security issues involved.  The required security properties
   are described under Req8 of Section 3 within this document.

   Under an assumption of closed and secure backbone networks, the air-
   ground link is the weakest portion of the network and most
   susceptible to injection of packets, flooding, and other attacks.
   Future air-ground data links that will use IP are being developed
   with link-layer security as a concern.  This development can assist
   in meeting one of this document's listed security requirements (that
   MNPs not be exposed on the wireless link), but the other requirements
   affect the RO technology more directly without regard to the presence
   or absence of air-ground link-layer security.

   When deploying in operational networks where network-layer security
   may be mandated (e.g., virtual private networks), the interaction
   between this and NEMO RO techniques should be carefully considered to
   ensure that the security mechanisms do not undo the route
   optimization by forcing packets through a less optimal overlay or
   underlay.  For instance, when IPsec tunnel use is required, the
   locations of the tunnel endpoints can force sub-optimal end-to-end
   paths to be taken.

6.  Acknowledgments

   Input from several parties is indirectly included in this document.
   Participants in the Mobile Platform Internet (MPI) mailing list and
   BoF efforts helped to shape the document, and the early content was

   borrowed from MPI problem statement and proposed requirements
   documents ([21], [13]).  The NEMO and MONAMI6 working group
   participants were instrumental in completing this document.  The
   participants in the MEXT interim meeting February 7th and 8th of 2008
   in Madrid were critical in solidifying these requirements.  Specific
   suggestions from Steve Bretmersky, Thierry Ernst, Tony Li, Jari
   Arkko, Phillip Watson, Roberto Baldessari, Carlos Jesus Bernardos
   Cano, Eivan Cerasi, Marcelo Bagnulo, Serkan Ayaz, Christian Bauer,
   Fred Templin, Alexandru Petrescu, Tom Henderson, and Tony Whyman were
   incorporated into this document.

   Wesley Eddy's work on this document was performed at NASA's Glenn
   Research Center, primarily in support of NASA's Advanced
   Communications Navigations and Surveillance Architectures and System
   Technologies (ACAST) project, and the NASA Space Communications
   Architecture Working Group (SCAWG) in 2005 and 2006.

7.  References

7.1.  Normative References

   [1]   Devarapalli, V., Wakikawa, R., Petrescu, A., and P. Thubert,
         "Network Mobility (NEMO) Basic Support Protocol", RFC 3963,
         January 2005.

   [2]   Johnson, D., Perkins, C., and J. Arkko, "Mobility Support in
         IPv6", RFC 3775, June 2004.

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

7.2.  Informative References

   [4]   Ernst, T. and H-Y. Lach, "Network Mobility Support
         Terminology", RFC 4885, July 2007.

   [5]   Ernst, T., "Network Mobility Support Goals and Requirements",
         RFC 4886, July 2007.

   [6]   Ng, C., Thubert, P., Watari, M., and F. Zhao, "Network Mobility
         Route Optimization Problem Statement", RFC 4888, July 2007.

   [7]   ICAO Asia/Pacific Regional Office, "Required Communication
         Performance (RCP) Concepts - An Introduction", Informal South
         Pacific ATS Coordinating Group 20th meeting, Agenda Item 7,
         January 2006.

   [8]   Ng, C., Zhao, F., Watari, M., and P. Thubert, "Network Mobility
         Route Optimization Solution Space Analysis", RFC 4889,
         July 2007.

   [9]   Kempf, J., "Goals for Network-Based Localized Mobility
         Management (NETLMM)", RFC 4831, April 2007.

   [10]  Dul, A., "Global IP Network Mobility", Presentation at IETF
         62 Plenary, March 2005.

   [11]  Ivancic, W., Paulsen, P., Stewart, D., Shell, D., Wood, L.,
         Jackson, C., Hodgson, D., Northam, J., Bean, N., Miller, E.,
         Graves, M., and L. Kurisaki, "Secure, Network-centric
         Operations of a Space-based Asset: Cisco Router in Low Earth
         Orbit (CLEO) and Virtual Mission Operations Center (VMOC)",
         NASA Technical Memorandum TM-2005-213556, May 2005.

   [12]  Ng, C., Ernst, T., Paik, E., and M. Bagnulo, "Analysis of
         Multihoming in Network Mobility Support", RFC 4980,
         October 2007.

   [13]  Davis, T., "Mobile Internet Platform Aviation Requirements",
         Work in Progress, September 2006.

   [14]  ICAO WG-N SWG1, "Analysis of Candidate ATN IPS Mobility
         Solutions", Meeting #12, Working Paper 6, Bangkok, Thailand,
         January 2007.

   [15]  Davis, T., "Aviation Global Internet Operations Requirements",
         ICAO WG-N, Sub-Working-Group N1, Information Paper #4 (IP4),
         September 2006.

   [16]  Wakikawa, R., "Home Agent Reliability Protocol", Work
         in Progress, July 2009.

   [17]  Zhang, L. and S. Brim, "A Taxonomy for New Routing and
         Addressing Architecture Designs", Work in Progress, March 2008.

   [18]  ICAO, "Threat and Error Management (TEM) in Air Traffic
         Control", ICAO Preliminary Edition, October 2005.

   [19]  Baldessari, R., "C2C-C Consortium Requirements for NEMO Route
         Optimization", Work in Progress, July 2007.

   [20]  Ng, C., "Consumer Electronics Requirements for Network Mobility
         Route Optimization", Work in Progress, February 2008.

   [21]  Ivancic, W., "Multi-Domained, Multi-Homed Mobile Networks",
         Work in Progress, September 2006.

   [22]  CCSDS, "Cislunar Space Internetworking: Architecture", CCCSDS
         000.0-G-1 Draft Green Book, December 2006.

   [23]  NASA Space Communication Architecture Working Group, "NASA
         Space Communication and Navigation Architecture Recommendations
         for 2005-2030", SCAWG Final Report, May 2006.

Appendix A.  Basics of IP-Based Aeronautical Networking

   The current standards for aeronautical networking are based on the
   ISO OSI networking stack and are referred to as the Aeronautical
   Telecommunications Network (ATN).  While standardized, the ATN has
   not been fully deployed and seems to be in only limited use compared
   to its full vision and potential.  The International Civil Aviation
   Organization (ICAO) is a part of the United Nations that produces
   standards for aeronautical communications.  The ICAO has recognized
   that an ATN based on OSI lacks the widespread commercial network
   support required for the successful deployment of new, more
   bandwidth-intensive ATN applications, and has recently been working
   towards a new IPv6-based version of the ATN.

   Supporting mobility in an IP-based network may be vastly different
   than it is in the OSI-based ATN, which uses the Inter-Domain Routing
   Protocol (IDRP) to recompute routing tables as mobile networks change
   topological points of attachment.  ICAO recognizes this and has
   studied various mobility techniques based on link, network,
   transport, routing, and application protocols [14].

   Work done within ICAO has identified the NEMO technology as a
   promising candidate for use in supporting global, IP-based mobile
   networking.  The main concerns with NEMO have been with its current
   lack of route optimization support and its potentially complex
   configuration requirements in a large airport environment with
   multiple service providers and 25 or more airlines sharing the same
   infrastructure.

   A significant challenge to the deployment of networking technologies
   to aeronautical users is the low capability of existing air-ground
   data links for carrying IP-based (or other) network traffic.  Due to
   barriers of spectrum and certification, production of new standards
   and equipment for the lower layers below IP is slow.  Currently
   operating technologies may have data rates measured in the several
   kbps range, and it is clear that supporting advanced IP-based
   applications will require new link technologies to be developed
   simultaneously with the development of networking technologies
   appropriate for aeronautics.

   In addition to well-known commercial data links that can be adapted
   for aeronautical use, such as Wideband Code-Division Multiple Access
   (WCDMA) standards or the IEEE 802.16 standard, several more
   specialized technologies either exist or have been proposed for air-
   ground use:

   o  VHF Data Link (VDL) specifies four modes of operation in the
      117.975 - 137 MHz range that are capable of supporting different
      mixes of digital voice and data at fairly low rates.  The low
      rates are driven by the need to operate within 25 kHz channels
      internationally allocated for aeronautical use.  VDL mode 2 is
      somewhat widely deployed on aircraft and two global service
      providers support VDL access networks.  Experiences with VDL mode
      2 indicate that several kbps of capacity delivered to a craft can
      be expected in practice, and the use of long timers and a
      collision avoidance algorithm over a large physical space
      (designed to operate at 200 nautical miles) limit the performance
      of IP-based transport protocols and applications.

   o  Aircraft Communications and Reporting System (ACARS) is a
      messaging system that can be used over several types of underlying
      RF data links (e.g., VHF, HF, and satellite relay).  ACARS
      messaging automates the sending and processing of several types of
      event notifications over the course of a flight.  ACARS in general
      is a higher-level messaging system, whereas the more specific
      "Plain Old ACARS" (POA) refers to a particular legacy RF interface
      that the ACARS system employed prior to the adoption of VDL and
      other data links.  Support for IP-based networking and advanced
      applications over POA is not feasible.

   o  Broadband Aeronautical Multi-carrier Communications (B-AMC) is a
      hybrid cellular system that uses multi-carrier CDMA from ground-
      to-air and Orthogonal Frequency Division Multiplexing (OFDM) in
      the air-to-ground direction.  B-AMC runs in the L-band of spectrum
      and is adapted from the Broadband-VHF (B-VHF) technology
      originally developed to operate in the VHF spectrum.  L-band use
      is intended to occupy the space formerly allocated for Distance
      Measuring Equipment (DME) using channels with greater bandwidth
      than are available than in the VHF band, where analog voice use
      will continue to be supported.  B-AMC may permit substantially
      higher data rates than existing deployed air-ground links.

   o  All-Purpose Multi-Channel Aviation Communications System (AMACS)
      is an adaptation of the Global System for Mobile Communications
      (GSM) physical layer to operate in the L-band with 50 - 400 kHz
      channels and use VDL mode 4's media access technique.  AMACS may
      permit data rates in the several hundred kbps range, depending on
      specific channelization policies deployed.

   o  Project 34 (P34) is a wideband public-safety radio system capable
      of being used in the L-band.  P34 is designed to offer several
      hundred kbps of capacity specifically for IP-based packet
      networking.  It uses OFDM in 50, 100, or 150 kHz channels and

      exact performance will depend on the particular operating band,
      range (guard time), and channelization plan configured in
      deployment.

   o  L-Band Data Link (LDL) is another proposal using the L-band based
      on existing technologies.  LDL adapts the VDL mode 3 access
      technique and is expected to be capable of up to 100 kbps.

Appendix B.  Basics of IP-based Space Networking

   IP itself is only in limited operational use for communicating with
   spacecraft currently (e.g., the Surry Satellite Technology Limited
   (SSTL) Disaster Monitoring Constellation (DMC) satellites).  Future
   communications architectures include IP-based networking as an
   essential building block, however.  The Consultative Committee for
   Space Data Systems (CCSDS) has a working group that is producing a
   network architecture for using IP-based communications in both manned
   and unmanned near-Earth missions, and has international participation
   towards this goal [22].  NASA's Space Communications Architecture
   Working Group (SCAWG) also has developed an IP-based multi-mission
   networking architecture [23].  Neither of these is explicitly based
   on Mobile IP technologies, but NEMO is usable within these
   architectures and they may be extended to include NEMO when/if the
   need becomes apparent.

Authors' Addresses

   Wesley M. Eddy
   Verizon Federal Network Systems
   NASA Glenn Research Center
   21000 Brookpark Road, MS 54-5
   Cleveland, OH  44135
   USA

   EMail: weddy@grc.nasa.gov

   Will Ivancic
   NASA Glenn Research Center
   21000 Brookpark Road, MS 54-5
   Cleveland, OH  44135
   USA

   Phone: +1-216-433-3494
   EMail: William.D.Ivancic@grc.nasa.gov

   Terry Davis
   Boeing Commercial Airplanes
   P.O.Box 3707  MC 0Y-96
   Seattle, WA  98124-2207
   USA

   Phone: 206-280-3715
   EMail: Terry.L.Davis@boeing.com

 

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