ACP WGN SGN1 WP205

Aeronautical Communication Panel (ACP) WGN

SGN1 – ATN Internet Communication Service

2nd meeting – Montreal, Canada, 19th - 21st May 2004

Opinion of Thailand regarding to the use of

TCP/IP in the ATN implementation

Prepared by Chonlawit Banphawatthanarak

Summary

This paper describes the analysis of four imaginary situations when TCP/IP can be used with ATN. The inputs of the analysis include 1) strengths and weaknesses of each situation, 2) current global trend, and 3) ATN environment in Thailand.
Note that the viewpoints expressed in this paper are partly based on current ATN situation in Thailand.
  1. Introduction

During the 1st meeting of ACP WGN SGN1, the chairman requested participants to submit their state’s position regarding to the use of TCP/IP in the ATN. This paper discusses and analyses alternatives of using TCP/IP in the ATN implementation in view of resource and implementation plan of AEROTHAI, Thailand’s air traffic service provider agency.

  1. Thailand’s current implementation

AEROTHAI has always been a constant participant in the ATNP meetings and am active developer of many in-house ATN-related services and applications. We now have implemented ATN throughout the country and developed certain ATN applications such as AIDC, AMHS, etc. In addition, AEROTHAI is performing ATN trial with Hong Kong since 2001 to test ATN international link. We plans to establish permanent ATN link after the trial is complete in April 2004. The ATN link with Hong Kong uses CLNP with pass-through services. For local links, we utilize IPv4 for WAN connections (between regional centers an Bangkok center) and CLNP for LAN connections (within Bangkok center).

  1. Thailand’s current plan/trend

Currently AEROTHAI is in the process of devising a national plan for ATN implementation. For the network topology, however, we are considering two following configurations.

3.1.International connection – CLNP using ATN Routers

3.2.Local connection – TCP/IP using IP Routers

  1. The Impacts of using TCP/IP with the ATN (Situation-based analysis)

In order to analyze how the usage of TCP/IP will impact ATN, we first need to explore methods to incorporate TCP/IP in ATN. In this document, we examine four possible situations regarding the use of TCP/IP in the ATN: IP subnet, hybrid network with commercial-off-the-shelves (COTS)-based applications, hybrid network with ATN-based applications, and replacement of the ATN with TCP/IP applications. Using strengths and weaknesses of each situation, global trend, and AEROTHAI’s current situation as inputs, we composed analysis based on six criteria: Performance of the system, Availability of the system, Data integrity, Network management, Interoperability, and Implementation timeframe. The results are as followed.

4.1.IP Subnet (using IP in the network level): Use IP as subnet of the ATN using SNDCF.

4.1.1.System performance: System performance may reduce since the use of IP subnet requires more bandwidth (more data to be sent over the network). Additionally, the use of SNDCF will require computational resources and may cause performance reduction in the end system. However, because the system also utilize high-speed data link and advanced IP router, the performance of communication link may increase, thus the increment may offset some of the decrease in other areas.

4.1.2.System availability: This aspect may remain intact because this configuration uses IP as subnet of TP4/CLNP network.

4.1.3.Data integrity: This aspect may remain intact because processes involving with data integrity will be performed in the upper layers of the OSI.

4.1.4.Network management: Some levels of network management mechanisms are needed between the ATN network and the IP subnet by using the already refined network management features of TCP/IP routers.

4.1.5.Interoperability: With the IP SNDCF, the interoperability aspect may be irrelevant. However, validation of IP SNDCF is required.

4.1.6.Implementation timeframe: Currently, the implementation of IP SNDCF is limited. Therefore, to implement this model, we need to establish timeframe to cover the implementation/validation period of IP SNDCF. We estimate the timeframe to extend approximately 6 months to 1 year.

After consideration, we found one particular situation when the implementation of this model may be useful: sharing network infrastructure between existing network (IP) and newly implemented network (ATN). For example, by simply connecting the end system and ATN router directly to the existing IP network, an organization can establish additional ATN network without the cost of additional link. However, the idea of sharing network infrastructure is not very popular in the ATS community because of various reasons, particularly security. For AEROTHAI, this mechanism represents a valid alternative for backup networks. However, further study is required to make a decision.

4.2.Hybrid System using TCP/IP COTS application and application gateway: Implement COTS applications that utilizes TCP/IP network and uses IP/CLNP gateway to perform transformation between applications in IP network and applications in CLNP network.

4.2.1.System performance: The total system performance will depend upon the performance of IP/CLNP gateway because all traffics pass one single system.

4.2.2.System availability: The existence of IP/CLNP gateway creates a single point of failure. This weakness needs to be further addressed.

4.2.3.Data integrity: In this scenario, data integrity depends on the transformation functions of the gateway. This may be complex and expensive, because even though one of the SARPs objectives is to specify relatively common applications for ATS, differences between ATN applications and COTS applications still exist. Thus, the data integrity issue must also be examined thoroughly to avoid incompatibility between ATN application and COTS application.

4.2.4.Network Management: Both ATN and TCP/IP networks have their own network management systems. Therefore, in order to establish network management in this situation, close cooperation among all involving parties are required along with a set of standards to specify the process.

4.2.5.Interoperability: This aspect also greatly depends upon the transformation functions of gateway. However, bilateral agreements should be developed to solve any interoperability issues that arise during the implementation.

4.2.6.Implementation Timeframe: Using configuration in the figure 2 as the baseline, there are two separate systems in the setup: TCP/IP application and gateway. Both systems may be implemented independently, however, we estimated that the time required for gateway implementation would exceed that of the TCP/IP application. Also the validation period of the gateway must be included.

For this situation, it was concluded in the ICAO ACP meeting that the implementation and maintenance responsibility of IP/CLNP gateway will rest upon those who wish to implement non-compliant systems. Additionally, states that implement non-compliant systems should develop bilateral agreements with neighboring states that implement compliant systems, to solve any problems that may occur. For AEROTHAI, we are following the development on this issue.

4.3.Hybrid System using modified ATN application for TCP/IP and application gateway: Implement the modified ATN applications instead of SARPS compliant. The modified ATN applications use TCP/IP in place of TP4/CLNP.

4.3.1.System performance: The performance may not be impacted because the transformation functions of gateway are based on the same applications for both networks.

4.3.2.System availability: Like in situation 4.2, the existence of IP/CLNP gateway creates the single point of failure, a major weakness that needs to be addressed further.

4.3.3.Data integrity: Because the applications on both networks are based on the same application, the transformation functions of the IP/CLNP gateway should be simple and data integrity should be intact.

4.3.4.Network Management: This is the same as in situation 4.2.

4.3.5.Interoperability: This aspect should be left intact because the applications’ upper layers are based on the same specifications.

4.3.6.Implementation Timeframe: The timeframe of this situation will be similar to that of situation 4.2 because both situations use gateway. However, due to the use of ATN application as baseline, the timeframe may be significantly shorter depending on the developers’ experience with ATN applications.

The system configuration in this situation is also considered non-compliant implementation at present. Therefore, state using this configuration shall bear responsibility of the gateway implementation. Currently, Eurocontrol is considering the use of either situation 4.2 or 4.3. For AEROTHAI, we consider situation 4.3 to be more plausible compare to situation 4.2 and we are also following the development on this issue closely.

4.4.Replacement: Direct use of TCP/IP as replacement of ATN. This situation will occur only when ICAO agrees to the use of TCP/IP as future replacement of the ATN. As described in situation 4.2 and 4.3, there are two alternatives on selecting application to use with TCP/IP: COTS applications or modified ATN applications. Both situations still require application gateway because there will be ATN systems available. However, for this situation, ICAO should specify particular countries/organizations to implement application gateways in their region.

4.4.1.System performance: As described in situation 4.2 and 4.3, the performance of this system depends upon the transformation functions of gateway.

4.4.2.System availability: This configuration still requires IP/CLNP gateway, which will create a single point of failure in the system. The availability will greatly depend upon the management of this single point of failure.

4.4.3.Data integrity: For data integrity, two scenarios are considered. The first scenario: if the COTS applications are chosen, then the transformation functions of the gateway can be complex as described in situation 4.2. Therefore, the data integrity will become an important issue because transferring data between systems with COTS applications and systems with ATN applications will be problematic. Therefore, ICAO should address this issue in its standards. The second scenario: if the ATN applications are modified to use TCP/IP, then the transformation functions of the gateway will not be as complicated as in the first scenario. Consequently, the data integrity issue will be irrelevant.

4.4.4.Network Management: The network management aspect shall be reviewed thoroughly by ICAO thus this aspect should be irrelevant.

4.4.5.Interoperability: Standard documents by ICAO should address this aspect thoroughly thus this aspect should be irrelevant.

4.4.6.Implementation Timeframe: ICAO will have to complete several researches and investigations in order to make decision to recommend TCP/IP as replacement of TP4/CLNP. Furthermore, ICAO will have to develop SARPs and other relevant standard documents to ensure compatibility. Moreover, the actual implementation/transition will require a long period of time and some additional validation period. Consequently, the implementation of this situation may not start in the near future, but in a medium-term to long-term future.

As stated early that there is a possibility of this situation be implemented in a medium-term to long-term period, pending the decision of ICAO, it will not be appropriate to start considering this option at present. For AEROTHAI, we expect this situation to raise awareness from members of the working groups toward using TCP/IP in the future. However, further studies on the topic should be encouraged.

  1. Conclusion:

The analysis discusses basic strengths and weaknesses of four possible situations. For any organization, a more detailed analysis incorporating financial and technical aspect should be conducted prior to any decision to implement any particular alternative.

  1. Action by the meeting:

The WGN1 is invited to review the document and discuss any additional comments in the working group.