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International Civil Aviation Organization
ACP-WG-I-06/WP-03
WORKING PAPER
07 March 2008
AERONAUTICAL COMMUNICATIONS PANEL (ACP)
WG I – Internet Protocol Suite – 6th MEETING
Canada, Montreal, 17-21 March 2008
Air Ground ATN/IPS
Prepared by Eivan Cerasi (EUROCONTROL)
Summary
This paper proposes that Mobile IP is used as a convergence layer for air-ground
communications with the intention of introducing flexibility and scalability for
both airborne and ground systems.
Air Ground ATN/IPS
1 Introduction
Investigations into IP mobility support for air-ground communications were initiated
by the former ACP SGN1 with the intention to select a specific technical solution.
The list of technical candidate solutions were documented and presented to former
ACP-WGN.
This paper takes into account the state of these investigations as further progressed
within WGI and recent 3GPP and IETF developments.
2 Abbreviations and references
2.1 Abbreviations
3GPP
AAA
AO
AOC
ATS
BU
CN
COTS
CPE
DS-MIP
HA
IETF
MIP
NEMO
NETLMM
PMIP
SLA
3rd Generation Partnership Project
Authentication, Authorization, Accounting
Airline Operator
Airline Operational Communications
Air Traffic Services
Binding Update
Correspondent Node
Commercial-of-the-Shelf
Customer Premises Equipment
Dual Stack Mobile IP
Home Agent
Internet Engineering Task Force
Mobile IPv6
Networks in Motion
Network-based Localized Mobility Management
Proxy Mobile IPv6
Service Level Agreement
2.2 References
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
SGN1 Report
WGI-02/WP12
WGI-03/WP04
WGI-05/WP04
WGI-05/WP08
3GPP TS 23.402, Architecture enhancements for non-3GPP accesses
RFC3775, Mobility Support in IPv6 (Mobile IPv6), RFC 3775
RFC 3963, Network Mobility (NEMO) Basic Support Protocol
Proxy Mobile IPv6 (http://www.ietf.org/internet-drafts/draft-ietf-netlmmproxymip6-11.txt) to be released as proposed standard (see IESG idtracker)
Aeronautical Requirements for NEMO route optimization
(http://www3.tools.ietf.org/html/draft-ietf-mext-aero-reqs-01)
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3 Status of Approaches to IP Mobility
3.1 Current Standard IETF/3GPP Approaches to IP Mobility
Within the IETF two major approaches have been specified to support mobility
through the standardisation of both client-based and network-based mobility.
o Client Mobility
Mobile IPv6 has been standardized by the IETF [7] and is already implemented into
COTS products. Based on the Mobile IP standard, network mobility [8] has been
achieved through a protocol extension thereby defining a NEMO mobile router. With
this extension, a mobile device can behave as a mobile host or mobile router. The
IETF is considering further extensions within the Mobile Extensions for IPv6
(MEXT) Working Group in other areas and has taken on-board aviation and
automotive requirements for NEMO route-optimization [10].
o Network Mobility
The former IETF NETLMM Working Group has defined local mobility management
as a means to provide mobility for IP hosts. The key deliverable of the working group
is Proxy Mobile IPv6 (PMIP). Although, PMIP is under IESG evaluation to become a
standard, initial COTS implementations already exist. Nevertheless, adopting local
mobility management for the ATN IPS requires WGI to also define a solution for
global mobility.
Within the 3GPP partnership project, Technical Specification TS 23.402 [6] considers
several interfaces for the Evolved Packet System (EPS) for Release 8. The
specification identifies different access requirements to be met by making use of a
combination of IETF-related standards namely PMIP and DS-MIPv6 (for access via
non 3GPP networks). The technical specification is due to be completed in 2008.
This paper further considers these two standardised mechanisms. They are also being
considered by the 3GPP partnership project as a means to enable convergence
between 3GPP and non-3GPPP networks. The rationale of this approach is to ensure
that the ATN IPS is based on well established standards adopted by other sectors;
taking advantage of wider and better industry support.
3.2 WGI Status
Although other candidate solutions for IP mobility were presented as part of the
former SGN1 report, they have not been retained by WGI-02/WP12, WGI-03/WP04,
WGI-05/WP04 and WGI-05/WP08. Indeed all four papers propose or assume local
mobility management to enable ATN IPS mobility. The major benefit of adopting
local mobility management for the ATN IPS is to simplify the airborne IP
communications stack by not including any mobility awareness or features.
However, this approach implies that:
1) the ATN IPS mandates all communication service providers to support local
mobility management as presented in WGI-05/WP04; and
2) requires WGI to define a solution for global network mobility (MOBIKE, SHIM6,
HIP and MIPv6 have been suggested).
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As a solution for global mobility is required, this may add complexity to the airborne
stack reducing the initially perceived benefit.
4 Introducing Flexibility for the ATN IPS Mobility
4.1 Directions
The ATN IPS must not only be specified on the basis of standards but also specify
those that are in line with industry trends.
Throughout the global ATN IPS, A/G mobiles will be interacting with several access
media technologies with differing communication characteristics depending on
coverage or phase of flight. Furthermore, authorised services over the media may be
regulated differently depending on current and future policies. It is essential that the
ATN IPS introduces flexibility by de-coupling airborne communication capabilities
from communication service provision, indicates a way forward to enhance mobility
and reduces exposure to technical changes for AO and ATS operators.
In building such an ATN IPS, the following key points can be further considered as
guidelines:
o Avoid over-specification in the IPS manual;
o Avoid aviation specific solutions;
o Where feasible make use of standards that are also used by other sectors;
o Resolve client versus network mobility;
o Identify scalability for aircraft equipage;
o Reduce exposure to technical changes;
o Allow any-to-any communications;
o Allow service providers to evolve independently to deliver competitive
services;
o Foresee the optimisation of protocol signalling and use of compression to
make efficient use of bandwidth;
o Reduce impact of mobility on ATS/AOC centres;
o Agree on a target architecture;
o Agree on common security requirements
4.2 Analysis
4.2.1 MIP as an ATN IPS Convergence Layer
By de-coupling service provision, the ATN IPS does not have to consider the innercapabilities of the communication service provider network. De-coupling service
provision implies that the choice of infrastructure technology is left open to the
communication service provider and is not tied to the capabilities of the mobile node.
This can be achieved when an aircraft supports MIPv6, allowing the service provider
to build and maintain an infrastructure that meets its business strategy and goals. In
this context, communication service providers can offer a service based on:
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o Local mobility management (Proxy Mobile IP1): MIPv6 binding updates (BU)
are not sent as the mobile is it is on its home network; or
o Layer2/Layer 3 service: MIPv6 will naturally send binding updates once the
node detects it is not on its home network.
By enabling Mobile IP in the aircraft several benefits can be highlighted:
o Communication service providers have flexibility in building their
infrastructure (Layer2 or Layer3);
o Communication service providers can target the use of PMIP to optimise
bandwidth usage by eliminating BUs;
o The ATN IPS does not have to specify how communication service providers
build their infrastructure;
o No aviation-specific solutions are involved;
o No need to modify airborne communication stacks when service provider
infrastructure changes;
o No need to make use of a routing protocol as a default route can be obtained
through RA/RD.
Thus, flexibility can be achieved by considering Mobile IP as the convergence layer
on A/G links. Depending on the capabilities of the service provider and the location of
the aircraft, Mobile IP will detect when the mobile node is not on its home network
and start sending binding updates.
4.2.2 Global mobility
Global mobility remains an open issue in other to allow a mobile node to be able to
communicate seamlessly between communication service providers or even between
separate local mobility managed networks of the same communication service
provider. A series of protocols have been identified by WGI to fulfil this task and
some additional experimental protocols are being discussed within the IETF.
Within the timeframe of WGI there may be too many open issues related to global
mobility in order to make a selection. As a result, it is proposed to follow the same
approach foreseen within the 3GPP Release 8 draft specifications by making use of
MIPv6 as a global mobility solution which still permits any-to-any communications.
It is also proposed to create a section within the guidance material indicating that
additional means to enable global mobility may be documented in a future edition of
the ATN IPS manual.
4.2.3 Scalability
Scalability should be introduced in order to adapt airborne devices to the type of
aircraft and flight operations (global, regional, local). It should also allow the
integration of new protocol features as the IETF Working Groups and industry
progress and improve the efficiency of mobile protocols.
In this respect, the ATN IPS can identify scalability in terms of:
o Airborne equipage and services;
1
When an unknown or unregistered mobile node enters a PMIP domain, the protocol allows the
service provider to offer a basic layer 3 routed service (MIPv6 BUs will be sent).
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o Communication service provision;
o ATS/AO operators; and
o Protocol enhancements to increase efficiency and add services.
4.2.3.1 Airborne Elements
It may be useful for the ATN IPS to foresee different type of mobile nodes. In
particular it may be useful to specify how traffic other than AOC/ATS can make use
of the air ground communication link. In this respect alignment with the automotive
industry and making use of NEMO for passenger traffic can be envisaged. Although
on-board LANs can be addressed from the ATN IPS address prefix, the benefit of
NEMO is that the passenger traffic will be tunnelled over the ATN IPS to an exit
point of the communication service provider network creating natural segregation
from AOC/ATS traffic and the ATN IPS routed infrastructure. It is to be noted that
the use of NEMO does not impose the use of a routing protocol on the air ground link
to the HA.
Another aspect is to recognise that scalability is desirable in terms of airborne
components. Making use of COTS products opens the potential to equip large aircraft
with multiple routers meeting the performance characteristics and regulatory
requirements of each domain (ATS/AOC/APC). At the other end, it may be
reasonable to allow other aircraft to be IPv6 hosts on the condition that their
communication service provider offers local mobility management.
WGI is invited to discuss to this subject to determine if it is part of the scope of the
ATN IPS manual.
4.2.3.2 Communication Service Providers
As described in section 4.2.1, communication service providers can select one or
more technical solutions to meet their infrastructure needs. It is to be recognised that
both Mobile IP and local network mobility management rely on the existence of the
Home Agent (HA) which may be a single point of failure. It is important to note that
the current global air-ground data link providers already rely on such architecture by
routing all traffic through one or two global locations demonstrating the feasibility of
home agents. To address these aspects, specifications for home agent reliability are
being developed within the IETF and Global-HAHA is foreseen to enhance global
scalability.
Such options can be documented in terms of ATN IPS guidance for communication
service providers.
4.2.3.3 ATS/AO Providers
Mobile IPv6 mobile nodes communicate with corresponding nodes (CN). A
correspondent node is not required to support any mobility features if bi-directional
tunnelling is used between the CN and HA but must be Mobile IP aware if route
optimisation if required.
The CN is the end–system in terms of Mobile IP but does not have to be the endsystem in terms of air-ground communications. The CN functionality can be
integrated as part of the communication service provider network CPE implying that
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the ATS or AO end-systems do not need to support anything else other than IP. This
decouples communication service provision from the ground end-systems and reduces
their exposure to technical changes.
WGI is invited to discuss to this subject to determine if it is part of the scope of the
ATN IPS manual
4.2.3.4 Protocol Enhancements
The IETF MEXT Working Group charter covers solutions to enable dual-stack
operation, mechanisms to support high-availability home agents, allowing the use of
multiple interfaces in mobile nodes, ways to employ Mobile IPv6 in the presence of
firewalls, address the specific needs of automotive and aviation communities for route
optimisation in network mobility and support for AAA is needed as a continuation of
earlier work on bootstrapping. Currently, the Working Group is tackling the below
items:
o Binding Revocation for IP Mobility
o MIPv6 home link operation in various SDOs
o 4283bis to extend MN identifier to other identifiers
o Mobile IPv6 Bootstrapping for the Authentication Option Protocol
o Interaction between Mobile IPv6 and IPsec/IKE by PF_KEY extensions
o IP Tunneling Optimization in a Mobile Environment
o Generic Notification Message for Mobile IPv6
o GRE requirements for IPv6 mobility
o Virtual Home Link configuration for Mobile IPv6
o Extend DSMIPv6 Home Network Support
Primarily, extensions involve the setting of bits within the Mobile IPv6 headers.
Depending on the capabilities of the originator/receiver, these extensions will be used
or not thereby providing a form of backwards compatibility. In view of the WGI
timescales, it is too early to include any of these provisions within the ATN IPS.
However, as these protocols are based on extensions to Mobile IP, it indicates to ATN
IPS communications service providers and airborne manufacturers the potential
roadmap for protocol enhancements and allows them to operate and manage the coexistence of several types of mobile nodes over time.
It is proposed to create a section within the guidance material indicating that technical
evolutions can be achieved by making use of Mobile IPv6 extensions which allows
co-existence and backwards compatibility.
4.2.4 Security
It is important to recognise that authentication is already performed at application
level complemented by out-band systems e.g. flight plans, surveillance.
Currently, ATS network operators manage secured networks and do not encrypt data
within their environment. Equally, communication service providers operate secure
networks and commit to contractual SLA for security. As a minimum, security would
need to be applied at the access link. In the case of the ATN IPS it is proposed that
security model is agreed and that measures are specified for the access links e.g. MNId based authentication, ingress filtering, encryption of MIP signalling, protection
against rogue mobiles, DoS attacks etc.
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4.2.5 Basic Architecture
Making use of Mobile IP, the above sections lead to the architecture illustrated in the
below figure.
Table 1 - Basic Architecture
4.3 Conclusions
This paper has been prepared in order to specify a flexible framework for the ATN
IPS A/G. In viewing Mobile IPv6 as a convergence layer, it allows service providers
to select the technology of their choice to transport IPv6 packets, reduces the exposure
to changes in technology, is in line with practices of other sectors, balances the
provisions within the ATN IPS manual, allows any-to-any communications, provides
global mobility, allows targeted security measures and does not introduce aviation
specific mechanisms.
4.4 Recommendations
WGI is invited to:
1) Remove the mandated support for local network mobility management on
service providers;
2) Mandate Mobile IPv6 for mobile nodes in the ATN IPS manual, discuss the
use of NEMO for non ATS/AOC flows and the support for hosts;
3) Agree to insert guidance material to document service flexibility for service
providers (PMIP, Layer 2/3)
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4) Agree to insert guidance material to document that global mobility options
other than MIP may be considered in the future editions
5) Agree to insert guidance material to document mobile node evolutions through
IETF Mobile IPv6 extensions
6) Agree to prepare guidance material indicating that the CN functionality can be
part of service provision and not necessarily part of the ATS/AOC endsystems
7) Define a security model between the mobile node and the service provider
access point.
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