Change proposal for a newVDL Mode 4 DLS protocol ...



AERONAUTICAL MOBILE COMMUNICATIONS PANEL (AMCP)

Working Group Maintenance (WGM)

3rd Meeting

Tianjin, China

10-18 December 2001

Agenda Item 8: Review of results of subgroup dealing with VDL Mode 4 ATN issues

Draft change proposal for a new

VDL Mode 4 data link service protocol

Presented by Eurocontrol

SUMMARY

This Working Paper describes the progress made in defining and validating a new simpler DLS protocol for VDL Mode 4 to replace the AVLC. A draft change proposal for the VDL Mode 4 Technical Manual is presented based on the new simplified DLS protocol.

WGM is invited to review the draft change proposal, to agree with the design principles directions and to provide comments on the design and the validation plan of the new DLS protocol.

Following the agreement of WGM with the design principles and directions, the WGM comments will be taken into consideration before producing the final change proposal and validating its functionality.

Introduction

The current ICAO VDL Mode 4 SARPs and Technical Manual specify a Data Link Service (DLS) protocol to be used which is a variation of the AVLC protocol and is derived from material in the VDL Mode 2 Technical Manual.

The VDL Mode 4 community has been considering possible options for optimisation of VDL Mode 4 performance as an ATN subnetwork. One issue is the perceived need for an alternative to the current AVLC DLS protocol.

In the second meeting of WGM, the Working Paper 18 and 20 discussed the potential benefits of using a simplified DLS protocol for VDL Mode 4 instead of the AVLC protocol.

This was supported in principle by WGM and it was acknowledged as a step in a good direction. Furthermore, WGM requested that the work to introduce a new DLS protocol is advanced further, and a complete and validated proposal is made to WGM.

Why a new DLS protocol is required

Following the discussions in the 2nd meeting of WGM, and in preparation for the WGM/3 a paper was drafted to identify the main design issues for the development of the DLS protocol beyond the initial proposal. This paper was presented at the WGM/3 Preparatory Meeting for VDL Mode 4 issues held on the 16th of November 2001 in Bagshot. This paper “A new DLS protocol for VDL Mode 4 datalink - Issues and design proposals” is included as Attachment A to this paper. This paper, in addition confirms the need for a new DLS protocol by identifying the reasons for its introduction.

In Attachment A, the following main reasons for the introduction of a new DLS protocol are identified:

• to remove errors, inconsistencies and ambiguities

• to be able to handle priority messages in an efficient way

• to provide fragmentation and performance benefits both for long and short messages, and

• to reduce the unnecessary complexity of the AVLC protocol

Further details on the above issues are provided in Attachment A section 3.3.

Activities to develop the initial proposal for the new DLS protocol

The initial proposal for an alternative DLS protocol was described in Working Paper 18 of the 2nd WGM meeting.

This proposal described a custom-defined protocol that makes better use of the functionalities defined in other VM4 layers and avoids duplication of functions.

Eurocontrol is the focal point of this activity and is funding the development and validation of the new DLS protocol.

In order to advance further the initial proposal, a WGM Preparatory Meeting was held on the 16th November 2001 to discuss (primarily) the development of the new DLS protocol. LFV, DFS, FAA, ADSI, SAAB and Eurocontrol together with the designing team of the new protocol (Helios Techology, McCallum Wyman Associates) attended this meeting.

This meeting has resulted in the agreement of the main principles and guidelines for the development of the new DLS protocol. More specifically the meeting agreed the following plan:

• In the third meeting of WGM (December 2001) a draft proposal will be presented based on the agreed design guidelines during this preparatory meeting.

• Following the approval of WGM in its 3rd meeting, the proposal will be finalised and validated by inspection and simulation.

• The final proposal, together with the validation details will be presented to WGM/4 meeting, which will be asked to approve the changes to Technical Manual of VM4.

• In developing the proposal, the manufacturers will be kept informed and they will provide comments.

• In developing the proposal particular care will be given to issues that relate to the performance of the VDL Mode 4 datalink.

The detailed minutes of this meeting are presented as Working Paper 15 in this WGM meeting. Appendix A of WP15 provides details of the agreement within the VDL Mode 4 community of WGM on the way ahead to develop the proposal for the new DLS protocol.

After the preparatory meeting on the 16th November, a first draft of a change proposal for the new DLS protocol was circulated for comments among the VDL Mode 4 interested parties. These comments together with the responses of the designing team have been gathered into a paper and are presented here as Attachment B to this paper.

Taking the latest comments from interested parties into account (as described in Attachment B), an updated change proposal has been prepared for consideration by the AMCP/WGM 3rd meeting. This proposal is included as Attachment D to this paper.

Next steps

The are some issue that require further work in the development of the new DLS proposal. These are namely the setting the timers and the QoS parameters. Furthermore the air to air protocol needs a further review. Finally some issues in relation to LME need some further work. These issues will be progressed and agreed together with the VDL Mode 4 interested parties in WGM.

Following the completion of the above remaining work and the consideration of the comments and suggestion from the WGM/3 meeting, the DLS proposal will be tested and validated for correct operation and interaction with the other VDL Mode 4 protocols as required.

In Attachment A, section 5.3 the details of the proposed validation plan for the change proposal of the DLS protocol are presented. In summary the main validation method will be a detailed inspection process backed up by analysis and simple modelling and simulation where necessary. An independent validation team (i.e. one that was involved in the drafting process) will also be used for this work in order to bring fresh eyes to the work, making it easier to spot inconsistencies and errors in the protocol and to ensure that the protocol has been well documented.

The finalised change proposal together with the validation report will be presented to the forth meeting of WGM.

Recommendation

WGM is invited to:

• Review the draft change proposal for a new DLS protocol;

• Agree with the design principles and directions of the change proposal;

• Provide comments on the change proposal;

• Provide comments on the validation plan of the change proposal.

Attachment A

A new DLS protocol for the

VDL Mode 4 datalink:

Issues and design proposals

Document information

|Document title |A new DLS protocol for VDL Mode 4 datalink: Issues and design proposals |

|Author |Mike Shorthose, Helios Technology |

| |Tony Whyman, McCallum Whyman Associates |

|Produced by |Helios Technology Ltd |

| |Chamberlain House |

| |High Street |

| |Bagshot |

| |Surrey |

| |GU19 5AE |

| |Tel: +44 1276 452 811 |

| |Fax: +44 1276 472 897 |

|Produced for |Nikos Fistas, Eurocontrol |

|Helios contact |Dr Michael G Shorthose |

| |Tel: +44 1276 452 811 |

| |Fax: +44 1276 472 897 |

| |Email: mike.shorthose@helios-tech.co.uk |

|Produced under contract |N/A |

|Version |0.1 |

|Date of release |8 November 2001 |

|Document reference |P196D003 |

Contents

Document information 1

Contents 2

1 Introduction 3

1.1 Overview 3

1.2 Background 3

1.3 Scope of work 4

1.4 Contents 4

1.5 References 4

2 Analysis of point to point data requirements 5

2.1 Introduction 5

2.2 Data transfer requirements 5

2.3 VDL Mode 4 burst length 6

2.4 Impact on design 7

3 Rationale for introducing a new protocol 8

3.1 Introduction 8

3.2 Summary of protocols 8

3.2.1 AVLC 8

3.2.2 Transmit/Acknowledge 8

3.3 Comparative analysis of protocols 9

3.3.1 Performance for transmit/acknowledge transactions (short user data) 9

3.3.2 Performance for transmit/acknowledge transactions (long user data) 9

3.3.3 Priority handling 10

3.3.4 Leave event generation 10

3.3.5 Protocol complexity 11

3.3.6 Removal of errors, inconsistencies and ambiguities 11

3.4 Conclusion 11

4 Protocol design issues 12

4.1 Introduction 12

4.2 Baseline scenario 13

4.3 Reserving a slot for the acknowledgement 14

4.4 Uplink transfer in ground reserved slots 15

4.5 Acknowledgement of downlink in ground reserved slots 15

4.6 Linking messages 16

4.7 Use of regular mobile transmissions on the data channel 18

4.8 Use of sync bursts on the GSCs 18

4.9 Request to send/clear to send 19

4.10 Multiple acknowledgement in the same burst 19

4.11 Summary 19

5 Way ahead 21

5.1 Issues to be addressed by WG-M 21

5.2 Work programme 21

5.3 Validation plans 22

Introduction

1 Overview

This document has been produced by Helios Technology Ltd (Helios) and McCallum Whyman Associates (MWA) under contract to Eurocontrol. The contract concerns the drafting and validation of a new DLS protocol for the VDL Mode 4 data link system.

The purpose of this document is to set out the rationale for introducing a new DLS protocol and to set out the design issues which need to be addressed prior to commencement of drafting.

2 Background

ICAO has approved SARPs for VDL Mode 4. Within ICAO, the AMCP Working Group M (AMCP/WGM) is responsible for maintaining (and updating) the VDL Mode 4 Manual on Technical Details and Specifications.

The ICAO VDL Mode 4 documents specify the Data Link Service (DLS) protocol to be used. The currently specified DLS protocol is a variation of the AVLC protocol and is derived from material in the VDL Mode 2 Technical Manual.

In the AMCP Working Group M 2nd meeting (May 2001), there was much discussion on the potential benefits of using an alternative DLS protocol, for which an initial proposal was presented at the meeting.

The initial proposal for a new DLS protocol is a custom-defined protocol that makes better use of the functionalities defined in other VM4 layers and avoids duplication of functions.

However, this initial proposal remains at an early stage of development, and no validation of the new protocol has yet been performed. For these reasons it was not considered for adoption by WGM.

Nevertheless, the WGM agreed that there is interest in considering further this initial proposal and in examining again the issue when the analysis, testing and validation of the new protocol is complete.

3 Scope of work

The new DLS protocol that was presented to AMCP/WGM is described in detail in working paper 18 of the 2nd WGM [1, 2, 3].

The aim of the Eurocontrol contract is to complete the proposal for a new DLS protocol for VDL Mode 4 along the lines of the initial proposal described in [1,2,3].

In addition, it is intended that the new protocol will be tested and validated for correct operation and interaction with the other VDL Mode 4 protocols as required.

A change proposal will also be prepared for consideration by AMCP/WGM.

4 Contents

The document is presented as follows:

• Section 2 provides an analysis of the point to point data load that VDL Mode 4 might support. The purpose is to provide an operational context for the protocol design.

• Section 3 summarises the rationale for introduction of a simpler protocol.

• Section 4 presents the designs issues associated with the introduction of a new protocol. A simple analysis is presented of the throughput performance of Mode 4 in order to assess the likely impact of each elements of the design.

• Section 5 summarises the way ahead for the work including a description of the validation approach.

5 References

[1] “Alternative approach to VDL Mode 4 data link service”, Mike Shorthose, Tony Whyman, N Fistas, presented by Eurocontrol to AMCP WG-M/2 as WP18, Finland, 25 April – 3 May 2001

[2] “Using VDL Mode 4 as an ATN Datalink”, Tony Whyman, Attachment A to AMCP/WG M/2 – WP18

[3] “FEC modelling in VDL Mode 4”, Mike Shorthose, Nikos Fistas, Further attachment to AMCP/WG M/2 – WP18

[4] “VDL Mode 4 Data Link Management”, Tony Whyman, Doc Ref MWA/VDL4/1. draft 0.1, 24 October 2001

[5] “European ATN Simulation: Phase 2 Report: ATN Traffic and Mobility Scenarios”, Mike Shorthose, Piotr Schielman, Andrew Sage, Andrew Ives, Helios Technology Ltd, DED6/ATN/NPT/LOGICA_DOC/12.2, 11 October 1999

[6] “European ATN Simulation: VDL Mode 2 Simulation Report”, Bob Eberlein (ARINC), Mike Shorthose (Helios Technology Ltd), DED6/ATN/NPT/LOGICA_DOC/12.3.2, 13 April 2000.

Analysis of point to point data requirements

1 Introduction

In order to decide on an appropriate DLS protocol for VDL Mode 4, it is useful to consider the type of point to point communication that it might support. This section presents an operational context for consideration of the DLS design. The operational context consists of a representative data load for a future time frame (approximately 2015) based on previous Eurocontrol analysis.

The operational context has been established in order to:

• illustrate the type of point to point messages that VDL Mode 4 must transfer efficiently

• provide a basis for comparing the transfer characteristics of AVLC and a new simpler protocol.

• inform the process of designing a new protocol so that it achieves the maximum possible transfer efficiency.

2 Data transfer requirements

Reference [5] describes data scenarios put together for Eurocontrol as part of a modelling contract to investigate European ATN scenarios. Reference [5] drew upon an accepted reference base for its conclusions including:

• ‘Operational Requirements for Air Traffic Management (ATM) Air/Ground Data Communications Services’, Eurocontrol, Edition 1.0, 15 January 1998,

and covered the three major types of air/ground point to point communication: ATSP, AAC and AOC.

The results provided in [5] were structured in a number of ways including:

• timescale

• phase of flight

and included the length of user data associated with each message in each transaction and the frequency of each transaction..

For the purpose of the analysis presented here, all transactions are included for the latest timeframe (2015) considered in [5] – no attempt has been made to divide out, for example, pre-flight messages. The data load therefore represents an upper limit for the load per aircraft/ground station pair in the timeframe up to 2015.

Figure 2-1 illustrates the user data size and message frequency obtained from [5].

Figure 2-1: Message frequency for ATS/AAC/AOC messages

It can be seen that:

• the message load is dominated by the ATS class

• most ATS messages are short ( ................
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