ACP WG MeetingWGN01-WP17

Agenda Item 2:Develop the ATN Plan

Issues Related to the Implementation of IPv6-based ATN and Applications

Prepared by Henry Lam

Presented by Hoang Tran

SUMMARY

Due to the emerging of IPv6 in the industry, some States are considering to use IPv6 as an alternative protocol for ATN network and ATN applications, such as AMHS. This paper presents some issues related to the implementation of IPv6-based ATN and its applications.

1Introduction

Defined in ICAO Doc 9705 (SARPs), the global ATN network and its applications are based on the CLNP network protocol. Compliance with SARPs will ensure the success of the global ATN network. To implement the non-SARPs compliant IPv6-based ATN, some technical issues need to be addressed.

2Background

The ATN network and its applications, such as AMHS, are based on ISO CLNP network protocol as defined in ICAO Doc 9705 (SARPs). Within some States/Regions such as U.S. and Asia/Pacific Region, work is underway to implement their components of the ATN network and inter-domain connections to other States/Regions. U.S. and Japan will implement SARPs-compliant ATN network as defined in ICAO Doc 9705 and using X.25 as the sub-network protocol as described in Asia/Pacific G/G router ICD[1]. Although ICAO Doc 9705 does not have any restriction on the type of sub-network protocol, X.25 is preferred sub-network protocol for the ATN ground-to-ground network due to the existing of ISO SNDCF standard for using CLNP over X.25.

The U.S. and Asia/Pacific States have completed the inter-domain ATN connection trial over X.25 sub-network and the SARPs-compliant CLNP-based AMHS application will be deployed between U.S. and Japan in August 2003. Besides the Asia/Pacific Region, The U.S. is also planning to establish inter-domain ATN connections with other States/Regions as required to support global ATN services.

Since industry recently has introduced the IPv6, some States/Regions have conducted research on using IPv6 as an alternative for ATN network protocol. EUROCONTROL and its member States have been engaged in the deployment of the IPv6 protocol for the EUROCONTROL backbone network. EUROCONTROL is also researching IPv6-based ATN/AMHS over its EUROCONTROL backbone network.

The U.S. also has an IP sub-network using IPv4 to support AFTN service within its domestic network. The U.S. is currently planing to phase out and replace all of its X.25 PSN with IPv4 within two years.

To successfully integrate the potential IPv6-based ATN/AMHS Routing Domain (RD) into the global ATN, certain related networking, protocol issues and strategies need to be considered.

3Discussion

Use of IPv6 to support ATN services may fall into following categories:

  1. IPv6 as the network protocol to implement ATN;
  2. Implement ATN applications such as AMHS over IPv6; and
  3. IPv6 as the sub-network to support ATN.

For each of above potential usage of IPv6 to support ATN services, the following technical issues are raised.

a)Regarding IPv6 as the network protocol for ATN, it may not be proper to implement it worldwide. Implementing IPv6–based global ATN backbone will violate the SARPs and will require a major revision of the entire SARPs. States may use IPv6 as its ATN network protocol within its RD;

b)States may implement ATN applications over IPv6-based network within their States as a local matter. Such IPv6-based ATN applications need to be converted into SARPs-compliant as interfaced with global ATN; and

c)ATN SARPs does not have any restriction on sub-network layer, therefore using IPv6 as ATN sub-network is fully SARPs-compliant. However, using IPv6-based sub-network will be an issue of incompatibility with X.25 sub-network, which is recommended by SARPs.

4Technical Consideration and Resolution for IPv6-based ATN/AMHS Issues

The following are technical considerations and resolutions for the above three issues related to IPv6-based ATN/AMHS.

4.1IPv6-based ATN Within the State

ICAO Doc 9705 defines CLNP-based ATN network and its applications. CLNP is the mandatory routed protocol for ATN. Also included are the routing protocols such as ES-IS, IS-IS, and IDRP.

The IPv6-based implementation should be restricted as a local matter within RDs. Regarding the interface to the global ATN, the RDs are responsible to provide the gateway needed to convert their IPv6 to SARPs-compliant CLNP protocol.

4.2Dual-stack Gateway for Non-SARPs Compliant ATN Applications

In order to implement global SARPs-compliant ATN applications, all non-SARPs compliance within a RD must be resolved locally by using the “dual-stack” gateway for the inter-domain interface with other ATN SARPs-compliant RDs. As for the AMHS application, the dual-stack gateway should convert IPv6-based AMHS into CLNP-based AMHS.

4.3SARPs-compliant Inter-domain Interface with IPv6 Sub-network

There is no restriction on ATN sub-network layer according to SARPs. Using IPv6 sub-network will not violate the SARPs, however, the following issues may be raised in case a RD uses IPv6 as the sub-network protocol for its inter-domain link.

  1. Availability of SNDCF standard for IPv6; and
  2. Compatibility with other RDs using X.25 sub-network for inter-domain link.

ISO has defined SNDCF for CLNP over Ethernet (ISO 8473-2), X.25 (ISO 8473-3), OSI data link (ISO 8473-4), and ISDN (ISO 8473-5). The SARPs also have guidance for using SNDCFs for Ethernet and X.25 to implement CLNP-based ATN over those sub-networks. Currently, there is no ISO SNDCF for CLNP over IP. In order to implement CLNP/IPv6, the SNDCF must be developed. The SNDCF over IP standard is under development by EUROCONTROL, which was drafted “EUROCONTROL ATN Project The ATN IP SNDCF” [2].

Due to the existing of SNDCF standard for X.25 and availability of X.25 network, X.25 is a preferred sub-network protocol for ATN by many States/Regions. Both U.S. and Asia/Pacific Region use X.25 sub-network for their inter-domain connection with other States/Regions. Therefore, any State/Regional ATN using IPv6 inter-domain sub-network will not be compatible with that of both the U.S. and Asia/Pacific Region ATN. This issue is discussed below using the U.S. ATN network as an example.

4.3.1The Current U.S. ATN Implementation

The U.S. ATN network and AMHS are SARPs-compliant. The current U.S. ATN implementation is a CLNP network with CLNP over X.25 sub-network for inter-domain connections to other States/Regions. The context diagram of the global ATN including U.S. ATN with X.25 sub-network, and RD A implementing ATN with IPv6 sub-network, is depicted in the Figure 1.

Figure 1. Context Diagram of Global ATN

Within the U.S domain there are two types of router: IS and boundary router RG/G. RG/G_A is the U.S. RG/G router, which connects to RD A. The U.S RG/G has the following characteristics.

  • Support CLNP routed protocol.
  • Support IS-IS routing protocol within U.S RD.
  • Support ES-IS routing protocol within U.S. RD.
  • Support IDRP routing protocol with other RDs.
  • Support X.25 sub-network.
  • Support Ethernet sub-network.

On the side of RD A, RG/G_US is the G/G boundary router provides the connection to the U.S. RD. Different from the U.S. RG/G_A router, the RD A RG/G_US router provides a CLNP/IPv6 interface instead of CLNP/X.25. A solution should be provided to resolve the sub-network incompatibility between the U.S. and RD A.

4.3.2Approach to Resolve U.S - RD A Inter-domain Incompatibility

In order to resolve the sub-network incompatibility between the U.S. and RD A, a sub-network protocol conversion must be conducted. The conversion can be done on either the U.S. side or RD A.

U.S. proposes to use a Commercial-off-the-shelf (COTS) router, which supports CLNP over both X.25 and IPv6 to convert its X.25 interface to IPv6, such that the connection between the U.S. and RD A can be established. This dual sub-network support router will function as a gateway to provide RD A a CLNP/IPv6 interface.

Figure 2. Context Diagram of Global ATN with Modified U.S. ATN Architecture

In Figure 2, router RIX is the dual sub-network support router providing the CLNP/X.25 within U.S. RD and CLNP/IPv6 interface to RD A. The U.S. RD is extended to include RIX router.

Currently, the available RIX router from COTS does not support IDRP. The U.S RIX router assumes to have the following characteristics.

  • Support CLNP routed protocol.
  • Support IS-IS routing protocol within U.S. RD.
  • Support X.25 sub-network.
  • Support IPv6 sub-network.

Since the router RIX does not support IDRP routing protocol, the inter-domain routing between RIX and RG/G_US can only be static. Also there will be no IDRP routing between RG/G_A and RIX.

4.3.3Impact of Using RIX Router on ATN Routing

By using the above approach, both RG/G_A- RIX and RIX -RG/G_US link will not have dynamic routing capability since RIX does not support IDRP routing protocol. The impact of this approach depends on whether RG/G_US router supports IDRP dynamic routing.

4.3.3.1RG/G_US Router With IDRP Dynamic Routing Capability

In case RG/G_US router supports IDRP dynamic routing, both RG/G_Aand RG/G_US router can still run IDRP with each other over RG/G_A- RIX -RG/G_US inter-domain connection, since IDRP PDUs are encapsulated inside CLNP PDUs and therefore can be relayed by RIX router. From CLNP network routing point of view, the inter-domain connection between RG/G_Aand RG/G_US are CLNP link with IDRP routing protocol and RIX router virtually does not exist. Therefore, there will be no impact on the global ATN.

4.3.3.2RG/G_US Router Without IDRP Dynamic Routing Capability

Assuming the RG/G_US router does not supports IDRP dynamic routing, the inter-domain RG/G_A-RG/G_US connection can only use static routing. Since RD A boundary router lacks the dynamic IDRP routing capability, the RD A has to be considered a sub-domain. Therefore the global ATN will lose one inter-domain node, and in turn global ATN will lose some of its dynamic routing capability.

5Summary

The issues related to the implementation of IPv6-based ATN are summarized as:

  1. Using IPv6-based network to support ATN services is not SARPs-compliant and such implementation should be restricted within RDs. Using IPv6 protocol as the global ATN will result in a major revision of entire SARPs, and will be time consuming to re-engineer and conduct technical research
  2. The ATN applications based on non-SARPs compliant IPv6 network should be resolved within the RD as a local matter by using dual-stack gateway. It is a local matter to develop such a dual-stack gateway
  3. To implement ATN over IPv6 sub-network, the related SNDCF must be developed
  4. The IPv6 sub-network based ATN can be integrated into global ATN network with U.S. ATN by using the approach presented in this paper. The use of IPv6 sub-network as ATN inter-domain and the U.S. proposed approach may or may not cost global ATN Inter-domain automatic routing capability. It depends on the characteristic of the boundary router in the RD, which implements IPv6-based network for ATN.

6References

[1] Asia/Pacific Regional Router Interface Control Document for Aeronautical Telecommunication Network (ATN) Ground-Ground Router, Issue 1.4, March 2003.

[2] EUROCONTROL ATN Project The ATN IP SNDCF, Issue 1.1, Tony Whyman, ATN Ref: DIS/COM/ProATN-Sup/DCI/AW_105, May 23 2002.

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