surveillance mode’s european mode’s station surveillance

EUROPEAN ORGANISATION FOR THE SAFETY OF AIR NAVIGATION

EUROCONTROL

EUROPEAN AIR TRAFFIC MANAGEMENT PROGRAMME

European Mode S Station

Surveillance Co-ordination Interface Control

Document

SUR/MODES/EMS/ICD-01 (form. SUR.ET2.ST03.3110-SPC-02-00)

Edition : 2.06 Edition Date : 9 May 2005 Status : Released Issue Class : General Public

DOCUMENT IDENTIFICATION SHEET

DOCUMENT DESCRIPTION

Document Title European Mode S Station Surveillance Co-ordination Interface Control Document

EATMP INFOCENTRE REFERENCE: 05/05/29-01

PROGRAMME REFERENCE INDEX: EDITION: 2.06


EDITION DATE: 9 May 2005

Abstract

Keywords Mode S SSR Monopulse Radar Surveillance Datalink Station PILOT Cluster ATN GDLP SCN IP

CONTACT PERSON: Nicolas EERTMANS TEL: 3363 UNIT: DAS/CSM

DOCUMENT STATUS AND TYPE

STATUS CATEGORY CLASSIFICATION Working Draft � Executive Task � General Public � Draft � Specialist Task � EATMP � Proposed Issue � Lower Layer Task � Restricted � Released Issue �

ELECTRONIC BACKUP

INTERNAL REFERENCE NAME:

HOST SYSTEM MEDIA SOFTWARE Microsoft Windows NT4 Type: Microsoft Word 97

Media Identification:

European Mode S Station Surveillance Co-ordination Interface Control Document


Edition : 2.06 Released Issue Page iii

DOCUMENT APPROVAL

The following table identifies all management authorities who have successively approved the present issue of this document.

AUTHORITY NAME AND SIGNATURE DATE

Author

Laurent HONET

Mode S System TF Chairman

Eric POTIER

Mode S Programme Manager

John LAW



Page iv Released Issue Edition : 2.06

DOCUMENT CHANGE RECORD

The following table records the complete history of the successive editions of the present document.

EDITION DATE REASON FOR CHANGE SECTIONS

PAGES AFFECTED

1.9 3 Jun 1998 POEMS SCN ICD, Contract Amendment baseline.

2.0 29 Jan 2001 First version of the European Mode S SCF ICD.

2.01 13 Mar 2001 Missing NNCOP Clarification SUR/POEMS.TSC.RII/NE008 added.

2.02 19 April 2001 Released Issue. References updated. Chapter 3

2.03 19 Jan 2005 Simplification of TASP initialisation table Table 6-3, 6.3.2.1, 6.4.2

2.04 16 Feb 2005 Inclusion of Internet Protocols Chapter 8

2.05 27 April 2005 Proposed issue following review by MSTF#22. -

2.06 9 May 2005 Released Issue -



Edition : 2.06 Released Issue Page v

TABLE OF CONTENTS

DOCUMENT IDENTIFICATION SHEET.................................................................................ii

DOCUMENT APPROVAL.....................................................................................................iii

DOCUMENT CHANGE RECORD.........................................................................................iv

EXECUTIVE SUMMARY........................................................................................................1

Chapter 1 INTRODUCTION ..................................................................................................2

Chapter 2 SCOPE .................................................................................................................3

Chapter 3 RELATED DOCUMENTS .....................................................................................4

Chapter 4 OVERVIEW OF INTER-SITE CO-ORDINATION ..................................................5

Chapter 5 CLUSTER OPERATION.......................................................................................9

5.1 Introduction ...................................................................................................9

5.2 Standalone operation ....................................................................................9

5.3 Autonomous State.......................................................................................10

5.4 Central Mode................................................................................................10

5.5 Distributed Mode .........................................................................................11

Chapter 6 CLUSTER CO-ORDINATION PROTOCOLS......................................................12

6.1 Introduction .................................................................................................12

6.2 Network Monitoring Protocol (NMP)...........................................................14

6.3 Target Acquisition and Support Protocol (TASP) .....................................16

6.4 New Node & Change-over Protocol (NNCOP)............................................24

Chapter 7 Solution lists .....................................................................................................27

7.1 Introduction .................................................................................................27

7.2 Coverage Maps ............................................................................................27

Chapter 8 SCN Connection Management .........................................................................29

8.1 Introduction .................................................................................................29

8.2 Set-up of SCN connections by OLM...........................................................31



Page vi Released Issue Edition : 2.06

Chapter 9 Network Overload management.......................................................................33

9.1 Preventive Measures for Network Overload ..............................................33

9.2 Corrective Measures for Network Overload...............................................33

Annex A Cluster Controller protocols ..............................................................................34

Annex B Definitions ...........................................................................................................36



Edition : 2.06 Released Issue Page 1

EXECUTIVE SUMMARY

The present document describes the European Mode S Station Surveillance Co-ordination Interface Control Document.



Page 2 Released Issue Edition : 2.06

CHAPTER 1

INTRODUCTION

Eurocontrol is embarking on an implementation of SSR Mode S ground stations. These will form the next generation of SSR systems and enable the introduction of significant benefits to the ATC environment.

Mode S ground stations with overlapping coverage must be co-ordinated to ensure they work correctly from both a surveillance and a data-link point of view. This co-ordination is achieved by a combination of techniques which include using II and SI code allocation, coverage map design (see [Ref.4.]) and providing ground stations with network connections for inter-station co-ordination.

In order to reduce FRUIT and cater for the limited number of II codes available within Mode S, common use of a single II or SI Code within a cluster of ground stations is to be adopted in the European implementation of Mode S. These clustered stations will co-ordinate the handover of aircraft passing between adjacent ground station coverage such that the acquisition performance of the ground stations can be maintained. This will be achieved by means of a Surveillance Co-ordination Network (SCN). The network will enable lockout to be achieved following initial acquisition of an aircraft, thus significantly reducing FRUIT levels and associated garble in the SSR environment.

A Surveillance Co-ordination Function (SCF) provides the information interchange over the SCN to allow interrogators to operate in such a cluster. When operating as part of a cluster the station’s operation is termed ‘Network Aided’. This document describes the protocols necessary to support this operation in any Cluster Mode or State. These Modes include:

(a) Central Mode where the cluster operation is maintained by a Cluster Controller (CC);

(b) Distributed Mode where the cluster operation is maintained by processes operating at each of the ground stations.

In addition to network aided operation within a cluster, the SCF can also support ‘Standalone’ operation when the connection between ground station and the surveillance co-ordination network is disabled.

A separate specification ([Ref.1.]) exists for the European Mode S ground station and the Cluster Controller (CC). This Interface and Control Document defines the interfacing required between the co-ordination network nodes.

[Ref.2.] describes the proposed SCF messages coded in ASTERIX format which is the standard to be used for the European Mode S equipment.




CHAPTER 2

SCOPE

This specification defines the interface requirements and the message protocols necessary to ensure compatibility between all nodes connected as part of a European Mode S cluster.




CHAPTER 3

RELATED DOCUMENTS

The following documents should be read in conjunction with this specification:

[Ref.1.] Eurocontrol Mode S Station Functional Specifications; SUR/MODES/EMS-SPE-01 (form. SUR.ET2.ST03.3114-SPC-01-00), 3.11, 9 May 2005.

[Ref.2.] EUROCONTROL Standard Document For Surveillance Data Exchange Part 5 Category 017 Mode S Surveillance Coordination Function Messages, SUR.ET2.ST03.3111-SPC-02-00, Edition: 1.0, October 2004 + Annex A: Co-ordinate transformation algorithms for the hand-over of targets between POEMS interrogators.

[Ref.3.] European Mode S Station Coverage Map Interface Control Document, SUR/MODES/EMS-ICD-03 (form. SUR.ET2.ST03.3113-SPC-01-00), 1.16, 9 May 2005.

[Ref.4.] Coverage map definitions for POEMS interrogators, DA255D006/1.3, 5 August 1997.




CHAPTER 4

OVERVIEW OF INTER-SITE CO-ORDINATION

In order to co-ordinate surveillance activity Mode S radars are connected via a ground network. The overall network topology consists of a large number of interconnected nodes. Some of these nodes which operate with the same II or SI code are grouped into clusters. The nodes within a cluster co-ordinate their Mode S surveillance activities via the network and using a Surveillance Co-ordination Function (SCF). Each cluster will consist of a number of nodes - radar nodes and the Cluster Controller (CC) node. In Central Mode, surveillance co-ordination in the cluster will be controlled by the CC. However, if the CC fails or is not present the radars will act as a ‘distributed’ system. In the Distributed Mode the radars will be responsible for the co-ordination between the nodes. This section describes the Surveillance Co-ordination Function (SCF) at the individual cluster nodes which provide the inter-site co-ordination.

The SCF can be considered to consist of two parts, the Communication Process and the Co-ordination Process. Figure 4-1 shows a simplified schematic of this two-part SCF.




The Communications Process continually synthesises the network topology i.e. the Communications Process knows which nodes can be accessed through the network. The Network Monitoring Protocol (NMP) is used to obtain information on which nodes can currently be seen. The messages within the Network Monitoring Protocol are known as Network Information Messages (NIMs).

The Communications Process uses the NMP to continuously examine the network topology, determine the cluster stability and define the Mode and State in which the node should be operating.

Depending on the Mode and State, the Communication Process at each cluster node selects the appropriate operating parameters, which consist of:

(a) a selected coverage map indicating the surveillance, lockout and datalink coverage to be maintained;

(b) the II or SI code to be used by the station;

GSCo-ordination

Process

CCCo-ordination

Process

GSCo-ordination

Process

RF Head andInterrogator

RF Head andInterrogator

CCCommsProcess

GSCommsProcess

GSCommsProcess CC-GS

ConnectionCC-GS

Connection

Co-ordinationEnvironment

CommunicationsEnvironment

GS-GSConnection

Key: CC - Cluster Controller, GS - Ground Station

Figure 4-1 SCF System Schematic




(c) and where the lockout override shall be applied.

When the SCF connection to the SCN is enabled, the station’s surveillance operation is ‘Network Aided’ in that the station uses the network derived information to initiate and support the tracking of targets. When the network connection is disabled the station is now said to be operating surveillance ‘Standalone’ and the station must acquire and track targets solely through the use of all-calls, and its own internal roll call.

When operating standalone or network aided and no stable cluster configuration can be selected, the Communication Process selects the Autonomous State. In this State the station coverage map and II or SI code are selected to ensure that it does not interfere with any other station having overlapping coverage.

The Co-ordination Process uses the parameters described in 4.4 to perform track acquisition and support using the Target Acquisition and Support Protocol (TASP). This protocol provides target handover between sites and track information to sites which have had a track miss, see section 6.3.

The Cluster Controller will operate one other Protocol, sending instructions to the radar nodes. This protocol is the Central Mode System Control Protocol, described in Appendix A.

Figure 4-2 provides an overview of the Surveillance Co-ordination Function (SCF). The Communication Process provides the coverage map and II or SI code to the Co-ordination Process.




Network AidedSurveillanceOperation

OperatingModes

SurveillanceCo-ordination

Protocols(Messages passed

over the SCN)

Central Distributed

Target Acquisition andSupport

Target Acquisition andSupport

Solution List

State 0 - ...State 1 - ......State n - ...

Coverage map, II or SI code selectionDependent on ‘Mode’ and ‘Cluster Stability’, select a solution.

Cluster Mode & State DeterminationCentral ‘Mode’ if CC part of cluster; otherwiseDistributed ‘Mode’.If Cluster is unstable for greater than 3 x T2

then choose Autonomous ‘State’else choose ‘State’ according to the network topology.

Cluster Stability DeterminationAt T2 expiry, establish if the cluster is stable elsedeclare cluster to be unstable.

Network Topology DeterminationSend NIMs (containing nodes seen and local station status)to all networked nodes. Use received NIMs tosynthesise Network Topology.

Note that Standaloneoperation can beforced by disabling theconnection to the SCNthereby forcing theNMP to select the‘Autonomous state’. Itshall then be possibleto re-load thecoverage map and IIor SI code parametersassociated with allstates.

To enter networkaided operation theconnection to the SCNshall be enabled. TheNMP shall then selectthe appropriate ‘Mode’and ‘State’.

Key to ModeTransitions

CtoD:DtoC:

These Modetransitions shall bemade between theDistributed Mode andCentral Mode,maintaining the same‘State’.

Standalone

Network Information Messages (NIMs)

NetworkMonitoringProtocol

SurveillanceCo-ordinationNetwork (SCN)

CtoD

DtoC

Solution List

State 0 - ...State 1 - ......State n - ...

Figure 4-2 Overview of the Surveillance Co-ordination Function




CHAPTER 5

CLUSTER OPERATION

5.1 Introduction

5.1.1 The following definitions of Operation, State and Mode have been adopted:

(a) Operation - Two types have been defined:

(i) Network aided, where the SCF’s connection to the SCN is enabled;

(ii) Standalone where, the SCF’s connection to the SCN is disabled.

(b) State - This describes the unique II or SI code and coverage maps (surveillance, datalink, lock-out, intermittent lock-out and lock-out override) with their associated parameters (including power, probability of reply and interlace patterns).

(c) Mode - When a node is in Network Aided operation it can operate in

(i) Central Mode i.e. the Cluster Controller Communication Process selects each station State or

(ii) Distributed Mode i.e. the Communication Process at the radar node determines and selects the State.

5.1.2 The possible Mode and State transitions are shown in figure 4.2.

5.2 Standalone operation

5.2.1 The ground station is in standalone operation when its connection to the SCN is disabled and it is functioning in an autonomous State. This operational State may be used for commissioning, maintenance, emergency operations etc.

5.2.2 Following successful power up tests manual and automatic enabling of the connection between the ground station and the SCN shall be possible to put the station into Network Aided operation. The Communication Process then selects the appropriate Mode.

5.2.3 Before effectively entering Network Aided operation, the ground station shall be in standalone operation during at least 10 scans.

Note: This is to minimise the network load, when a new radar enters the cluster.




5.3 Autonomous State

5.3.1 When the station is operating in an autonomous State, the coverage map and II or SI code are chosen to ensure the station does not interfere with any other station having overlapping coverage.

5.3.2 Interrogators in the Autonomous State derive all their surveillance acquisitions by All-Call. TASP is not run with any other node on the network.

5.3.3 The Autonomous State is selected on power up, when the station is operating standalone, or when the available network connections are not able to support a stable cluster.

5.3.4 The SCF will attempt to promote the node from the autonomous State to another State at the earliest opportunity.

5.4 Central Mode

5.4.1 The CC is responsible for selecting interrogators to acquire targets, to monitor the targets positions and to manage track support functions.

5.4.2 On entering the Central Mode the CC examines the network topology to select the State of each station. The CC informs the connecting cluster stations with a ‘Move Node to New Cluster State’ message. The CC will compile a global roll-call which is used to control track acquisition and track support. The global roll-call will be created and updated using ASTERIX Cat 48 messages from the ATCC output of all radar nodes in the network.

5.4.3 When operating in Central Mode, the CC uses the following protocols:

(a) Network Monitoring Protocol (NMP)

(b) Central Mode System Control Protocol (see appendix A for details)

The CC shall send Track Data messages to the radar nodes, when the CC detects a track miss in the category 48 output of that radar.

The SCFs are responsible for operating the following protocols:

(a) Network Monitoring Protocol (NMP);

(b) Central Mode System Control Protocol (see appendix A for details);

(c) The acceptance of Track Data messages from the CC.

5.4.4 The following transitions are possible from Central Mode:

(a) Central Mode: the CC announces the new Central State.

(b) Distributed Mode: the SCF determines a new Distributed State from the solution list.




5.5 Distributed Mode

5.5.1 Nodes enter Distributed Mode when either the CC fails or is not present (i.e. the CC plays no active part in the operation of the cluster).

5.5.2 In Distributed Mode, the individual interrogator SCFs are responsible for:

(a) determining the network topology, the cluster stability and selection of the state i.e. the function of the Communication Process (refer to section 4.1).

(b) the operation of the surveillance protocols i.e. the function of the Co-ordination Process (refer to section 4.1).

5.5.3 During Distributed Mode operation, the SCFs use the following protocols:

(a) Network Monitoring Protocol (NMP)

(b) Track Acquisition and Support Protocol (TASP)

(c) New Node / Change-over Protocol (NNCOP).

5.5.4 The following transitions are possible from Distributed Mode:

(a) Distributed Mode: the SCF determines a new Distributed State from the solution list.

(b) Central Mode: NMP announces the presence of a CC which will provide the Central State.




CHAPTER 6

CLUSTER CO-ORDINATION PROTOCOLS

6.1 Introduction

6.1.1 This section details the protocols required to support Surveillance Co-ordination Functions operating within the cluster configuration on the Surveillance Co-ordination Network.

6.1.2 The following definitions are used for co-ordination protocols:

(a) A Surveillance Co-ordination Network (SCN) is a predefined group of nodes as listed in the SCF.

(b) The network topology is a list of nodes in the SCN, which are operating as network aided,

(c) In distributed mode, nodes in a SCN determining the same network topology will form a ‘stable’ cluster. The cluster will become ‘unstable’ when all nodes in the cluster do not determine the same network topology. Cluster stability is not relevant in central mode.

Note: When a node is operating as Standalone, it is still a member of the group of nodes in a SCN. This is to allow the node to join the desired cluster when it starts to operate as Network Aided.

The following timers are used for co-ordination protocols and shall be operational parameters:

(a) T1 for the sending of Network Information Messages (range: 0.1 - 2 seconds, with 0.1 second increments),

(b) T2 for the determination of the network topology and the cluster stability (range: 0.4 - 8 seconds, with 0.1 second increments),

(c) T3, T4 and T5 to detect messages lost in the network (T3 range: 3 - 15 seconds, T4 range: 1 - 5 seconds, T5 range: 1 - 10 seconds, all with 0.1 second increments).

Note: It is recommended that T2 is set to be greater than T1, and preferably greater than twice the longest T1 setting of any node in the cluster. In distributed mode a node will only change state following connection/disconnection of another node after the first T2 expiry following T2 expiry on all other nodes. Therefore, changes in distributed mode state may take a period of up to twice the longest T2 period setting of any node in the cluster.




6.1.3 The SCF manages the network and the clusters, i.e. :

(a) Determines the network topology,

(b) Determines the cluster stability;

(c) Determines the Cluster Mode and State;

(d) Runs co-ordination protocols to ensure cluster surveillance operation.

The message types referred to in the following sections are described in [Ref.2.].

6.1.4 In ‘Distributed Mode’, the SCF processes the information, indicated in Figure 6-1, received from the PAF (see [Ref.1.], section 7.3.2.) and received over the SCN. The SCF also sends messages over the SCN.

In ‘Central Mode’, the SCF processes the information indicated in Figure 6-2, received over the SCN from the CC. The SCF also sends messages over the

SCN to the CC.

PAF

- Track Initialisation (section 6.3.2.1)- Track Update (section 6.3.2.2)- Track Miss (update with no measured position, section 6.3.2.3)- Track Drop (section 6.3.2.4)

SCF SCN. Network Information (section 6.2)

. Track Data Request (section 6.3.3.1)

. Track Data (section 6.3.3.2)

. Cancellation of Track Data (section 6.3.3.3)

. Track Data Stop (section 6.3.3.4)

. Track Data Stop Acknowledgement (section 6.3.3.5)- New Node / Change-over (section 6.4)- New Node / Change-over reply (section 6.4)

PAF

SCF

Figure 6-1 Distributed Mode Information Flow between SCF/SCF and PAF/SCF

SCF SCN. Network Information (section 6.2)

. Track Data (appendix B)

. Move Node to new Cluster State (section 6.2)

. Move Node to new Cluster State Ack (section 6.2)

CC

Figure 6-2 Central Mode information Flow between the SCF and the SCN




Note: In Central Mode and Distributed Mode, track data is passed to the PAF from the SCN, for the initiation and maintenance of tracks.

6.2 Network Monitoring Protocol (NMP)

6.2.1 This section defines how the Network Topology is maintained and how the states, modes and operations at a node are determined and selected.

The syntax of the state tables is as follows:

(a) States, Modes And Operations are defined in CAPITALS.

(b) The events and corresponding conditions are specified in the first column. Events are in Italic, conditions for the events are in normal font.

(c) A reaction to an event and its corresponding condition can be the change to another state as shown by the other columns. In addition an action could be initiated or a message could be sent to create a compatible reaction at the other node. In a particular cell, a state change is specified first and actions or messages are specified below the separating line.

(d) Non-specified events will be ignored.

6.2.2 Monitoring the network topology

Table 6-1 shows the operation in which network monitoring shall be performed. The figure also shows under which events and conditions the network monitoring shall be changed.

Table 6-1 Monitoring Network Topology

EVENTS & CONDITIONS

STAND ALONE OPERATION

NETWORK AIDED OPERATION

SCF /SCN CONNECTION ENABLED


SCF / SCN CONNECTION DISABLED

STAND ALONE OPERATION

T1 EXPIRY

• NODE WITH LOWER ADDRESS


− SEND NIM TO THE NODE WITH THE LOWER ADDRESS

RECEIVE NIM

• NIM RECEIVED FROM NODE WITH HIGHER ADDRESS


− REPLY WITH NIM

− ADD NODE TO NETWORK TOPOLOGY

RECEIVE NIM

• NIM RECEIVED FROM NODE WITH LOWER ADDRESS


− ADD NODE TO NETWORK TOPOLOGY




The protocol consists of the following stages:

(a) At T1 expiry, the node sends to other nodes of lower address, and which are members of the same SCN, a Network Information Message (NIM).

(b) When a node receives a NIM, the node will add the originating node to the network topology. The receiving node will then send a NIM to the originating node if the originating node is a node of a higher address.

The 16 bit address of a node is composed of Source Area Code (MSB) and Source Identity Code (LSB) as defined in [Ref.2.]. The NIMs indicate the network topology as seen by transmitting node at (not after) the last T2 expiry, or the currently seen topology if there has been no T2 expiry ever.

6.2.3 Monitoring the Cluster Mode, Stability and State

Table 6-2 specifies on which events and under which conditions state and mode changes shall occur.

Table 6-2 Monitor and Select States

EVENTS & CONDITIONS DISTRIBUTED MODE CENTRAL MODE

AUTONOMOUS STATE DISTR. STATES CENTRAL STATES

T2 EXPIRY

• CC PRESENT

CENTRAL MODE

− CLEAR NETWORK TOPOLOGY

CENTRAL MODE


CENTRAL MODE


RECEIVE “MOVE NODE TO NEW CLUSTER STATE”

N/A TO DISTRIBUTED MODE N/A TO DISTRIBUTED MODE CENTRAL MODE

− DETERMINE AND SELECT NEW STATE

− SEND “MOVE NODE TO NEW CLUSTER STATE ACK”.

T2 EXPIRY

• CC NOT PRESENT • STABLE CLUSTER

DISTR. MODE


− DETERMINE AND SELECT NEW STATE

DISTR. MODE


− DETERMINE AND SELECT STATE

DISTR. MODE


− DETERMINE AND SELECT STATE

T2 EXPIRY

• CC NOT PRESENT • UNSTABLE CLUSTER • UNSTABLE FOR LESS

THAN 3 X T2

DISTR. MODE


DISTR. MODE


DISTR. MODE


T2 EXPIRY

• CC NOT PRESENT • UNSTABLE CLUSTER • UNSTABLE FOR MORE

THAN 3 X T2

DISTR. MODE


DISTR. MODE


− DETERMINE AND SELECT AUTONOMOUS STATE

DISTR. MODE


− DETERMINE AND SELECT AUTONOMOUS STATE

Note: The state (entry in the solution list) will be selected dependent on the Network Topology. In general the state will remain the same. Only when nodes are added, removed or in case of hardware failures in the cluster or network, will the state change.




At T2 expiry, if a CC is present in the network topology (detected by its address), the Communication Process selects the ‘Central Mode’, otherwise the ‘Distributed Mode’ is selected. In both modes the cluster stability is assessed. This assessment is achieved by analysing the content of the most recent NIM received from each node within the last T2 period. If all nodes of the cluster see the same network topology, then the cluster is stable.

In ‘Distributed Mode’, the Communication Process determines and selects, from the solution list, the State according to the Network Topology if the cluster is stable.

In ‘Distributed Mode’, if the cluster is unstable, the state is not changed unless the cluster has been unstable for greater than T2 x 3 seconds. In this case the Communication Process selects the autonomous State.

After all processing associated with T2 expiry, the network topology is cleared in preparation for the next T2 period.

In ‘Central Mode’, the State is determined by the CC and included in the ‘Move Node To New Cluster State’ message. The SCF Communication Process will select the State contained in this message. It shall then send back to the CC the ‘Move Node to New Cluster State Acknowledgement’ message.

6.3 Target Acquisition and Support Protocol (TASP)

6.3.1 This protocol enables the acquisition of targets and the support of target misses through co-ordination over the SCN.

To facilitate the acquisition of targets, the protocol ensures that all interrogators are aware of any new tracks entering their coverage. To facilitate the support of target misses, the protocol ensures that a radar node, having one or more track misses in regions covered by other radars of the cluster, can maintain the track using track information from all these radars until successful surveillance is resumed.

PAF PAF

SCF SCN SCF

Node A Node B

PAF

Figure 6-3 Information and Message Flow between Nodes A and B




The TASP operates upon reception of information from the PAF or upon reception of messages from the SCN (excluding NIMs). At any node, TASP shall operate for all other nodes in the cluster.

The following sections and the state tables define the operation of TASP. In these sections only the operation between two nodes (node A and node B) is described : Node A will be receiving information from the PAF and will be providing resulting messages to node B. Node B will be processing these messages from node A and will be sending appropriate reply messages to node A. The configuration is as shown in figure 6.5. It should be noted that for every track of node A, state tables must be maintained for all other nodes in the same cluster as Node A.

The syntax of the state tables is as follows:

(a) States are defined in CAPITALS. For a particular node, states are maintained for the relationship between that node (node A) and all other nodes (e.g. node B) per track. The following states are recognised:

(i) NULL; the track of node A is not in the overlapping coverage of node A and node B, according to the coverage maps in both nodes.

(ii) SENDING TRACK DATA, node A sends Track Data messages to node B to assist node B in the (re-)acquisition of the target. The track data message sent will be from the latest track update, be it measured or extrapolated.

(iii) RECEIVING TRACK DATA, node A is receiving Track Data messages from node B or is waiting to receive Track Data messages as a result of a Track Data Request message.

(iv) EXCHANGING TRACK DATA, the node A and node B are both sending and receiving Track Data messages. This state could be caused by e.g. misses in both radar on the track during the same period. The track data message sent will be from the latest track update, be it measured or extrapolated.

(v) ACQUIRED, the track is in the overlapping coverage of both radar and both radar have acquired the target.

(b) The events and corresponding conditions are specified in the first column of the table. Events are in Italic, conditions for the events are in normal font. A more detailed description from each event is given in sections 6.3.2 and 6.3.3.

(c) A reaction to an event and its corresponding condition can be the change to another state as shown in the other columns. In addition to the state change an action could be initiated or a message could sent to create a compatible reaction in the other node. If an action is initiated or messages are generated, it will be shown in the cell under the separating line.

(d) Non-specified events shall be ignored.




Table 6-3 TASP Initialisation

EVENT & CONDITIONS INITIAL STATE & ACTIONS

TRACK INITIATED

• TRACK DATA NOT RECEIVED FROM B IN THE LAST SCAN PERIOD • TRACK NOT IN THE COVERAGE OF NODE B

NULL

TRACK INITIATED

• TRACK DATA RECEIVED FROM B IN THE LAST SCAN PERIOD • TRACK NOT IN THE COVERAGE OF NODE B

NULL

− SEND CANCELLATION OF TRACK DATA TO B

TRACK INITIATED

• • TRACK IN THE COVERAGE OF NODE B

SENDING TRACK DATA

− SEND TRACK DATA TO B




Table 6-4 TASP State Table

STATES

EVENT & CONDITIONS

NULL

SENDING TRACK DATA

ACQUIRED

RECEIVING TRACK DATA

EXCHANGING TRACK DATA

TRACK UPDATE

• TRACK UPDATE WITH MEASURED POSITION

• TRACK IN THE COVERAGE OF NODE B

SENDING TRACK DATA

− SEND TRACK DATA

SENDING TRACK DATA

− SEND TRACK DATA

ACQUIRED ACQUIRED

− SEND CANCELLATION OF TRACK DATA

− STOP AND RESET TIMER T3

SENDING TRACK DATA



− SEND TRACK DATA TRACK UPDATE


• TRACK NOT IN THE COVERAGE OF NODE B

NULL NULL

− SEND TRACK DATA STOP

− RESET AND START T4

NULL NULL


− STOP AND RESET T3

NULL




− RESET AND START T4 TRACK UPDATE


• BAD ALTITUDE (CREDIBILITY CHECK FAILED)

NULL NULL



NULL NULL



NULL




− RESET AND START T4 TRACK UPDATE

• TRACK UPDATE WITH NO MEASURED POSITION



− SEND TRACK DATA

− SEND TRACK DATA REQUEST



− SEND TRACK DATA








− SEND TRACK DATA

TRACK UPDATE



NULL NULL



NULL NULL NULL



TRACK DROP

(NOTE : NO STATE MEANS THAT THE TRACK IS KILLED AND

DO NOT EXIST ANYMORE FOR THE NODE. T4 IS ONLY

ASSOCIATED TO THE EVENT OF RECEIVING THE TRACK DATA STOP ACKNOWLEDGEMENT AND IS NOT ASSOCIATED TO

ANY TRACK)

NO STATE NO STATE



NO STATE



NO STATE



NO STATE






STATES

EVENT & CONDITIONS

NULL

SENDING TRACK DATA

ACQUIRED



RECEIVE TRACK DATA REQUEST

• TRACK INITIATED AND MAINTAINED


NULL



SENDING TRACK DATA

SENDING TRACK DATA

− SEND TRACK DATA


− SEND TRACK DATA





NULL



NULL



NULL



NULL



NULL




• TRACK NOT INITIATED AND NOT MAINTAINED

STATE : NO APPLICABLE STATE

(THE TRACK DOES NOT EXIST AT THE PAF LEVEL NOR AT THE SCF LEVEL) FOR THIS EVENT WITH THE MENTIONED CONDITION


− RESET AND START T4 (SEE ALSO NOTE FOR THE « TRACK DROP » EVENT) RECEIVE TRACK DATA


• RECEIVED TRACK DATA CORRELATES WITH THE TRACK UPDATE

NULL



SENDING TRACK DATA



ACQUIRED



ACQUIRED



SENDING TRACK DATA



RECEIVE TRACK DATA


NULL SENDING TRACK DATA

ACQUIRED RECEIVING TRACK DATA

− RESET AND START TIMER T3


− RESET AND START TIMER T3

RECEIVE CANCELLATION OF TRACK DATA

NULL ACQUIRED ACQUIRED RECEIVING TRACK DATA


RECEIVE TRACK DATA STOP


NULL

− SEND TRACK DATA STOP ACK.

SENDING TRACK DATA


SENDING TRACK DATA


SENDING TRACK DATA



SENDING TRACK DATA



RECEIVE TRACK DATA STOP



(THE TRACK DOES NOT EXIST AT THE PAF LEVEL NOR AT THE SCF LEVEL) FOR THIS EVENT

− SEND TRACK DATA STOP ACKNOWLEDGEMENT RECEIVE TRACK DATA STOP

ACKNOWLEDGEMENT

• TRACK NOT INITIATED OR NOT MAINTAINED


(THE TRACK DOES NOT EXIST AT THE PAF LEVEL NOR AT THE SCF LEVEL) FOR THIS EVENT


RECEIVE TRACK DATA STOP ACKNOWLEDGEMENT


NULL


SENDING TRACK DATA


ACQUIRED









STATES

EVENT & CONDITIONS

NULL

SENDING TRACK DATA

ACQUIRED



T3 EXPIRY

• LAST TRACK UPDATE WITH NO MEASURED POSITION

NULL














T4 EXPIRY



(THE TRACK DOES NOT EXIST AT THE PAF LEVEL NOR AT THE SCF LEVEL) FOR THIS EVENT WITH THE MENTIONED CONDITION


− RESET AND START T4 T4 EXPIRY


NULL



SENDING TRACK DATA



ACQUIRED









The sections that follow (6.3.2 and 6.3.3) provide general guidance information about TASP and should be used to aid the understanding of the state tables, which forms the basis of the requirement.

6.3.2 Information from the PAF

This section explains that part of the state table describing the operation of the SCF at node A when receiving information from the PAF. This section only applies to an SCF operating in ‘Distributed Mode’.

6.3.2.1 Track Initialisation

If the track is in the overlapping coverage with node B provided that the network overload prevention measure is not active, then the SCF initialises the state for node B to SENDING TRACK DATA. This allows the other sensors in the cluster to be informed about the existence of the track.

In all other cases the NULL state is selected.

6.3.2.2 Track Update

When during the track update, node A detects that the track has (re-)entered the overlapping coverage of node B and when the network overload prevention measure is not active, then node A sets the state to SENDING or EXCHANGING TRACK DATA. This allows the other sensors in the cluster to be informed about the existence of the aircraft, when it enters their coverage.

In case the state is RECEIVING or EXCHANGING TRACK DATA and the track is updated with a measured position, a Cancellation of Track Data




message is sent and the state is set to ACQUIRED or SENDING TRACK DATA respectively.

Node A returns to the NULL state, when the track is no longer in the surveillance coverage of node B. A Track Data Stop message is sent in case node A has been sending Track Data messages.

6.3.2.3 Track Miss (Track update with no measured position)

When radar node A detects a miss and when the network overload prevention measure is not active, it sends a Track Data Request message to all radar with overlapping coverage (for example node B) and selects the RECEIVING or EXCHANGING TRACK DATA state.

6.3.2.4 Track Drop

For an explanation of the conditions to drop a track see [Ref.1.]: section 7.3.2.3.

When a track is dropped at node A, node A sends Track Data Stop messages to the other nodes in the cluster. The track and state tables for the track cease to exist.

6.3.3 Messages to/from the SCN

This section explains that part of the state table describing the operation of the SCF at node A and node B when receiving or sending messages through the SCN. All sections of 6.3.3 apply to an SCF operating in ‘Distributed Mode’.

6.3.3.1 Reception of Track Data Request

Receipt at node A of a Track Data Request Message from node B indicates that node B requires track support following a miss for its track.

If the track is initiated and maintained at node A and in the coverage of node B according to the maps at node A, node A selects the SENDING or EXCHANGING TRACK DATA state and it sends Track Data to node B. On entry of those states node A sends the Track Data message immediately using the most recent track update. Afterwards it sends Track Data to node B each time the track is updated at node A.

In all other cases node A sends to node B a Track Data Stop message.

6.3.3.2 Reception of Track Data

Reception of Track Data occurs at node A;

(a) in the RECEIVING or EXCHANGING TRACK DATA states, when node A has had requested support for this track from node B, or;




(b) in any state (mostly NULL) or before a state has been defined, when node B has detected that a track has entered the surveillance coverage of node A.

The received track data may be used by the PAF at node A to initialise a new track or maintain an existing one. On receipt of a track data message from node B, the SCF at node A shall:

(a) if the last track update at node A was achieved using a measured position, node A selects the ACQUIRED or SENDING TRACK DATA state or it remains in the NULL state. Node A also sends a Cancellation of Track Data message to node B;

(b) if the last track update at node A was not achieved using measured position, node A remains in the same state.

On receipt of a Track Data message from node B, node A shall stop the timer T3. Timer T3 is only active in the RECEIVING TRACK DATA and EXCHANGING TRACK DATA states, it will be activated on transition to those states and reset and started again on each track-data message. On exit of those states the timer will be reset and stopped.

6.3.3.3 Reception of Cancellation of Track Data

On receipt of a Cancellation of Track Data Message from node B, node A stops the sending of track data by selecting the ACQUIRED state (after the SENDING TRACK DATA state) or RECEIVING TRACK DATA state (after the EXCHANGING TRACK DATA state).

6.3.3.4 Reception of Track Data Stop

On receipt of a Track Data Stop message from node B, node A sends a Track Data Stop Acknowledgement and stops the timer T3 , if it is active (See section 6.3.3.2).

Before sending the Track Data Stop, node B will have selected the NULL state or will have dropped the track. Node A will select the SENDING TRACK DATA state for node B if it is maintaining a track for the aircraft (the existing state is not NULL). Node B will receive track data from node A until;

(a) Node A also detects that the track has left the coverage of node B.

(b) Node B re-acquires the target, because the aircraft has returned to the coverage of node B.

When an aircraft enters or exits the coverage of a sensor, Track Data messages will be exchanged until both nodes agree on the “in coverage” or “out of coverage” situation. This use of Track Data messages and Track Data Stop message will compensate for map inaccuracies.




6.3.3.5 Reception of Track Data Stop Acknowledge

On receipt of a Track Data Stop Acknowledge message from node B, node A shall stop the timer T4.

The sending of Track Data Stop shall be guarded by acknowledgement, which should be received before timer T4 expires. If this acknowledgement is not received before the expiry of T4 , the Track Data Stop will be repeated and the T4 timer reset and re-started.

Note: In case the network connection has been broken, the loop of sending Track Data Stop, time out T4 and resending Track Data Stop will be interrupted by NMP.

6.3.4 Duplicate Address;

The protocol allows target acquisition and target support for duplicate Mode S address tracks.

(a) Whenever a message is received with a Mode S Address for which two or more tracks are present in the receiving node, TASP should be run for every track with that address.

(b) When an SCF receives two or more Track Data messages with different positions but the same address, it is up to the PAF to maintain the tracks correctly, even if there are e.g. duplicates or triplicates (see [Ref.1.], section 7.3.2.2 [E2]).

(c) If a node has tracks with duplicate Mode-S addresses, it shall assign a Duplicate Address Reference Number to each track (DRN).

(d) All track data messages sent for a track which has a known duplicate address shall include the DRN assigned to that track ([Ref.2.]).

(e) If track data is received from node A with a DRN and this track data correlates with an existing track, the DRN will be inserted in subsequent Cancellation of Track Data messages sent for this track for node A.

(f) If a Track Data message is received from node A without a DRN and this track data correlates with an existing track, subsequent Cancellation of Track Data message sent for this track to node A will not include DRN.

(g) When a node receives a Cancellation of Track Data message with a DRN included, it will only process this message for the track, which has the same DRN assigned to it.

(h) The SCF shall ignore a Cancel Track Data message, which does not contain a DRN, if a DRN is expected.

6.4 New Node & Change-over Protocol (NNCOP)

This NNCOP protocol is used by a node when entering a cluster or when executing channel change-over. This protocol is only used in Distributed




Mode. The protocol shall be executed for all other nodes in the cluster. The purpose of the protocol is;

(a) to inform the other nodes (e.g. node B) in the cluster in case of a change-over (e.g. node A);

(b) to reduce the network load when a new node enters the cluster or in case of a change-over.

Figure 6.8 describes the NNCOP for Node A sending and receiving messages from Node B.

Table 6-5 NNCOP State Table

EVENTS TASP NOT RUNNING TASP RUNNING

A IS SWITCHING TO A NEW STATE, WHICH IS A STATE OF THE DISTRIBUTED MODE OR A HAS EXPERIENCED A SWITCH-OVER

• CREATE TASP STATE TABLES

FOR B (SET STATES TO NULL) • SEND NEW NODE / CHANGE-

OVER MESSAGE TO B • START TIMER T5

RECEPTION OF NEW NODE / CHANGE-OVER MESSAGE FROM B

TASP RUNNING • CREATE TASP STATE TABLES

FOR B (SET STATES TO NULL) • SET INITIAL STATES FOR TASP

STATE TABLES FOR B • SEND NEW NODE / CHANGE-

OVER REPLY MESSAGE TO NODE B

• SET INITIAL STATES FOR TASP

STATE TABLES FOR B • SEND NEW NODE / CHANGE-

OVER REPLY MESSAGE TO NODE B

TIMER T5 EXPIRED • SEND NEW NODE / CHANGE-

OVER NODE MESSAGE TO B • RESTART TIMER T5

RECEPTION OF NEW NODE / CHANGE-OVER REPLY MESSAGE FROM NODE B

TASP RUNNING • SET INITIAL STATES FOR TASP

STATE TABLES FOR B • STOP T5

A DETECTS NEW NODE B • CREATE TASP STATE TABLE

(SET STATES TO NULL)

The sections that follow (6.4.1 and 6.4.2) provide general guidance information about NNCOP and should be used to aid the understanding of the state tables, which forms the basis of the requirement.

6.4.1 State Definition

TASP RUNNING, in this state TASP is active at node A for node B.

TASP NOT RUNNING, in this state TASP is inactive at node A for node B.

6.4.2 Constraints

(a) The “New Node / Change-over” message and the “New Node / Change-over Reply” message include the unique Mode-S addresses of aircraft tracked by the sending node which are located in the overlapping coverage with the receiving node.




(b) The “Set Initial States for the TASP State Table” process initialises the state for the track node pair to ACQUIRED, if the mode S Address has been received in the message from that node, else the state shall be set to NULL. Note that this process modifies all states in the TASP State Table for node B and no TASP actions are permitted for node B while the process is running.

(c) For the “New Node / Change-over” message and the “New Node / Change-over Reply” message, the following processing is required:

(i) In the sending node no duplicate Mode S Addresses shall be sent.

(ii) In the receiving node, received Mode-S addresses corresponding to two or more tracks shall be ignored. The TASP state shall be set to NULL for these tracks.




CHAPTER 7

SOLUTION LISTS

7.1 Introduction

7.1.1 Each node SCF on the cluster determines the network topology and cluster stability and hence from this selects the State to be used. Each State has an associated solution list entry which specifies the coverage map, the II and/or SI code configuration to be used, and the site specific set-up, including Mode Interlace Pattern, Radiated Power (for range and azimuth) settings, etc.

7.2 Coverage Maps

7.2.1 For further information refer to [Ref.1.], [Ref.3.]and [Ref.4.]. These documents contain all requirements related to coverage maps.

7.2.2 Each cluster node will store and access coverage maps. There will be one Coverage Map for each possible State.

7.2.3 A map at a ground station is built up from a number of cells with the exception of the lockout override map which is defined on a per sector basis. Each cell represents a volume of airspace approximately 5NM x 5NM (refer to Reference 5 for further details) and with a vertical extent defined as the minimum and maximum altitude at which the station can provide cover. Each radar node that has any vertical overlap with the cell of another node is listed for that cell.

7.2.4 A coverage map shall consist of:

(a) Surveillance map;

(b) Intermittent lock-out map;

(c) Lock-out map;

(d) Datalink map;

(e) Lock-out override map.

7.2.5 Surveillance map

A bit is assigned to each radar that could carry out surveillance in the cell volume. The bits are set to ‘1’ for radars that are expected to carry out surveillance in the cell volume and set to ‘0’ for radars not providing surveillance coverage for that cell.




7.2.6 Intermittent lock-out map

This map defines where the ground station shall apply intermittent lock out.

7.2.7 Lock-out map

This map defines where the ground station shall have Lock-out responsibility and apply lock out.

7.2.8 Datalink map

The datalink bit is used to indicate whether the station informs the GDLP and Local User on the full acquisition of targets which enter the cell. Full acquisition is defined as confirmation of a non-zero value for the ‘Mode S sub-network version’ field of BDS 1,0.

7.2.9 Lock-out override map

This map defines the sectors to be used for lock-out override.

7.2.10 In addition the Solution Lists will include Mode Interlace Pattern, Power settings associated with the site Range and Azimuth requirements and other parameter settings that are determined as necessary for the operation of each and every State.




CHAPTER 8

SCN CONNECTION MANAGEMENT

8.1 Introduction

The Connection Management Service facilitates connection of the SCF to the SCN to enable the operation of the Cluster Co-ordination Protocols defined in section 6. The Connection Management Service is part of the Output Link Management (OLM) defined in [Ref.1.].

Connection management only operates when the SCF is operating network-aided, either in central or in distributed mode.

Cluster Co-ordination Protocols

Connection Management (OLM)

Network (e.g. X.25, TCP/IP)

The “connections” to be managed are ‘full duplex’ logical links between ground station SCFs via the SCN. For the purposes of this document, it is assumed that the SCN will provide interfaces complying to:

• ITU-T Recommendation X.25 (1988) or,

• TCP/IP internet standards as defined by RFC793 and RFC791.

For X.25, a ‘full duplex’ logical link refers to an established Switched Virtual Circuit (SVC). For TCP/IP, a ‘full duplex’ logical link refers to an established TCP connection.

The table specifies the environment of Connection Management. The Cluster Co-ordination Protocols use the SCF Connection Management Service by passing to it the data to be transmitted and the destination ground station address.




Figure 8-1 represents an example of an X.25 configuration with 3 stations and

a Cluster Controller and Figure 8-2 represents an example of an IP configuration with 3 stations and a Cluster Controller

OLM

DTE DTE

C

HANNEL1

C

HANNEL2

DCE DCE

OLM

DTE DTE

C

HANNEL1

C

HANNEL2

DCE DCE

DCE DCE

OLM

DTE DTE

C

HANNEL1

C

HANNEL2

XX..2255 WWiiddee AArreeaaNNeettwwoorrkk

Node 1: EMS

Node 2: EMS

Node 4: EMS

DTE DTE

Node 3: CC

DCE DCE

Figure 8-1 Example SCN Cluster using X.25




8.2 Set-up of SCN connections by OLM

The OLM of new nodes will attempt to establish a single connection with each of the existing nodes. The OLM will try connecting to both SCN addresses of the remote node until a full-duplex logical link is established.

The OLM will only accept a single SCN connection request from each other node.

The OLM will only allow a single SCN connection between two nodes.

In the event of colliding connection requests between 2 nodes, the node with the lower address (SAC/SIC, SAC being the most significant byte) shall accept the connection initiated by the other node, while the node with the higher address shall not.

In case no connection has been established, or an existing connection is broken, the node shall periodically repeat the connection attempt.

OLM

C H A N N E L 1

C H A N N E L 2

OLM

C H A N N E L 1

C H A N N E L 2

OLM C H A N N E L 1

C H A N N E L 2

Node 4: IP-enabled EMS

Node 3: IP-enabled CC

Node 2: IP-enabled EMS Node 1: IP-enabled EMS

IP addresses

IP addresses

IP addresses

IP addresses

Figure 8-2 Example SCN Cluster using IP




Note: The higher level protocols using Connection Management have been designed to be robust enough to deal with the occasional loss of a message.




CHAPTER 9

NETWORK OVERLOAD MANAGEMENT

Flow management is a system level problem, when network overload occurs one or all data providers to the network may be the cause of the overload. As such each data provider should reduce its contribution to the load using a set of pre-programmed measures. This sections specifies the action taken on the Surveillance Co-ordination Network.

9.1 Preventive Measures for Network Overload

The following measures will reduce the load:

(a) Both the Track Data messages and the Cancellation of Track Data messages shall be packed together on an 22.5° secto r basis as defined in the ASTERIX Standard (Part 1), which would reduce network load (less messages, less acks) and processor load (less context switches due to interrupts caused by messages and acks).

(b) When entering Network Aided Mode, the NNCOP protocol shall be used to limit network loading.

9.2 Corrective Measures for Network Overload

In case the message has not been sent during a period of Pno seconds, the radar shall go to “Standalone” operation. Pno is an operational parameter and shall be between 1 and 100 seconds with an accuracy of 0.5 seconds

Note: The radar will go to Standalone operation to avoid oscillation between Autonomous State and one of the Distributed Mode States, because the network load might allow NMP to be run but the network might overload if TASP is added.




ANNEX A

CLUSTER CONTROLLER PROTOCOLS

A.1 Network Monitoring Protocol

The Cluster Controller (CC) shall send NIMs to radar nodes according to section 6.2.1. This will enable the radar nodes to detect the presence of a CC. The CC shall then run the Central Mode System Control Protocol to determine and deliver the State of each radar node.

A.2 Central Mode System Control Protocol

When the cluster is operating in Central Mode all stations will receive configuration commands from the CC. The CC will determine the Cluster State using NIMs and deliver the Cluster State to each ground station. The CC will send ‘Move Node to New Cluster State’ messages when new station States are selected.

When the cluster is operating in Central Mode a failure detected by the CC, anywhere within the cluster, must be notified to the network such that the cluster is protected. This will be done by the CC broadcasting a ‘Move Node to New Cluster State’ message to all cluster nodes to select the State which ensures that the failed station does not interfere with any cluster station having overlapping coverage. When the failure has been resolved and the cluster is operating satisfactorily the CC shall determine the new Cluster State and deliver this to each ground station.

The sending of ‘Move Node To New Cluster State’ shall be guarded by acknowledgement, which should be received by the CC before a CC timer expires. If this acknowledgement is not received before the expiry of the CC timer , the ‘Move Node To New Cluster State’ will be repeated and the CC timer reset and re-started.

Note: In case the network connection has been broken, the loop of sending ‘Move Node To New Cluster State’, CC time out and resending ‘Move Node To New Cluster State’ will be stopped by NMP, as soon as another state change is needed.

A.3 Track Acquisition and Support

The CC maintains through the reception of ASTERIX cat 48 messages from radar nodes a global roll call from which it co-ordinates the cluster activity.

The CC operates at CC defined intervals when detecting through ASTERIX cat 48 messages the following events:




(a) a track initialisation, send Track Data messages to the other nodes with overlapping coverage, which have not yet initiated the track;

(b) a track update, send Track Data messages to the other nodes when the track is detected in their coverage and the track is not yet initiated and maintained by that radar node;

(c) a track miss, send a Track Data message to the node with the track miss;

(d) a track drop.

A.4 Duplicate Mode S Address

The duplicate Mode-S address situation will be recognised by the CC (same mode-S address, different positions). In case a radar node needs Track Data messages for a track with a duplicate address, these messages shall be sent to the node by the CC. The PAF will use the position to correlate the tracks (see also [Ref.1.]) .




ANNEX B

DEFINITIONS

ASTERIX All purpose Structured Radar Information Exchange. CC Cluster Controller GDLP Ground Data Link Processor. II Interrogator Identifier LSB Least Significant Bit NMP Network Monitoring Protocol. NIM Network Information Messages NNCOP New Node & Change-over Protocol MSB Most Significant Bit RDP Radar Data Processing SCF Surveillance Co-ordination Function. SCN Surveillance Co-ordination Network SI Surveillance Identifier TASP Track Acquisition and Support Protocol

surveillance mode’s european mode’s station surveillance

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