SIST EN 302 842-4 V1.3.1:2015

EUROPEAN STANDARD
VHF air-ground and air-air Digital Link (VDL)
Mode 4 radio equipment;
Technical characteristics and methods of measurement
for aeronautical mobile (airborne) equipment;
Part 4: Point-to-point functions

2 ETSI EN 302 842-4 V1.3.1 (2015-04)

Reference
REN/AERO-00019-4
Keywords
aeronautical, digital, radio, testing, VHF
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3 ETSI EN 302 842-4 V1.3.1 (2015-04)
Contents
Intellectual Property Rights . 6
Foreword . 6
Modal verbs terminology . 6
Introduction . 7
1 Scope . 8
2 References . 9
2.1 Normative references . 9
2.2 Informative references . 9
3 Definitions and abbreviations . 10
3.1 Definitions . 10
3.1.1 Basic reference model definitions . 10
3.1.2 Service conventions definitions . 10
3.1.3 General definitio ns . 10
3.1.4 Definition of bit order . 10
3.2 Abbreviations . 10
4 General description of VDL Mode 4 mobile station point-to-point services . 12
4.1 General . 12
4.2 Data Link Service (DLS) and Link Management Entity (LME) . 12
4.2.1 General . 12
4.2.2 DLS timers . 15
4.2.3 DLS counters . 16
4.2.4 Toggle bit (T) . 16
4.2.5 State variables (T and T ) . 16
t r
4.2.6 Initialize Bit (IB) . 16
4.2.7 More bit (M) . 17
4.2.8 Priority (pr) . 17
4.2.9 Message fragmentation and concatenation . 17
4.2.10 DLS procedures . 17
4.2.10.1 Selection of DLS procedures. 17
4.2.10.2 Short transmission procedures . 17
4.2.10.3 Long transmission procedures . 18
4.2.11 Linking transmissions . 20
4.2.11.1 Types of linking . 20
4.2.11.2 Combined RTS / DATA DLPDUs . 20
4.2.11.3 Combined DATA / ACK DLPDUs . 20
4.2.11.4 Combined RTS / ACK DLPDUs . 20
4.2.11.5 Combined CTS / ACK DLPDUs . 20
4.2.12 Ground-air link management . 20
4.2.13 Air-air link management . 21
4.3 Additional VSS services . 21
5 Minimum performance specification under standard test conditions . 21
5.1 DLS sublayer . 21
5.1.1 General . 21
5.1.1.1 Services . 21
5.1.1.2 Data transfer . 22
5.1.1.3 DATA DLPDU duplicate suppression and sequencing . 22
5.1.1.4 Error detection . 22
5.1.1.5 Station identification . 22
5.1.1.6 Broadcast addressing . 22
5.1.1.7 DLS Priority . 23
5.1.1.8 DLS Link control DLPDUs . 23
5.1.2 DLS protocol specification . 23
5.1.2.1 State variables . 23
5.1.2.2 DLS burst formats . 23
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4 ETSI EN 302 842-4 V1.3.1 (2015-04)
5.1.3 DLS system parameters . 27
5.1.4 DLS procedures . 29
5.1.4.1 Setting of re-transmission parameter . 29
5.1.4.2 Selection of user data packet for transmission . 29
5.1.4.3 Selection of transmission procedures . 31
5.1.4.4 Short transmission procedures . 31
5.1.4.5 Long transmission procedures . 32
5.1.4.6 No link with sender . 34
5.1.4.7 User data packet reception . 35
5.1.4.8 Receipt of ACK DLPDU . 35
5.1.4.9 Link reset . 36
5.1.4.10 Linking DLS DLPDU transmissions . 37
5.1.4.11 CTRL DLPDU . 38
5.1.4.12 Procedures for air-air communication . 38
5.2 Link management entity sublayer. 38
5.2.1 Services . 38
5.2.1.1 General . 38
5.2.1.2 Link provision . 39
5.2.1.3 Link change notifications . 39
5.2.1.4 CTRL DLPDU . 39
5.2.1.5 Broadcast link management burst . 40
5.2.2 Control (CTRL) parameter formats . 40
5.2.2.1 Encoding . 40
5.2.2.2 General purpose information parameters . 40
5.2.2.3 Mobile-initiated information parameters . 44
5.2.2.4 Ground-initiated modification parameters . 45
5.2.2.5 Ground-initiated information parameters . 48
5.2.3 LME timers and parameters . 50
5.2.3.1 General . 50
5.2.3.2 Timer TL1 (maximum link overlap time) . 51
5.2.3.3 Parameters TL2 (link initialization time) . 51
5.2.3.4 Timer TL4 (leave generation latency) . 51
5.2.4 CTRL DLPDU types and procedures . 51
5.2.5 CTRL transmission procedures . 55
5.2.5a Frequency management procedures . 55
5.2.5.1 Link connectivity procedures . 55
5.2.5.2 Ground Station Identification . 55
5.2.5.3 Link establishment . 56
5.2.5.4 Mobile-initiated handoff . 57
5.2.5.5 Mobile-requested ground-initiated handoff . 58
5.2.5.6 Ground-initiated handoff . 58
5.2.5.7 Ground-requested mobile-initiated handoff . 59
5.2.5.8 Ground-requested broadcast handoff . 59
5.2.5.9 Ground-commanded autotune . 60
5.2.6 VDL Mode 4 Mobile SubNetwork Dependent Convergence Function (SNDCF) . 60
5.2.6.1 Frame mode SNDCF . 60
5.3 Additional VSS requirements . 60
5.3.1 Information transfer request protocol specification . 60
5.3.1.1 Information transfer request parameters . 60
5.3.1.2 Information transfer request transmission procedures . 62
5.3.1.3 Information transfer request acknowledgement procedures . 62
5.3.2 Void . 62
5.3.3 Void . 62
5.3.4 Retransmission procedures . 63
6 General design requirements . 63
7 Protocol test procedures . 63
7.1 General . 63
7.2 Required test rig . 63
7.3 Protocol test-suite description methodology . 64
7.4 Detailed protocol test procedures . 64
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5 ETSI EN 302 842-4 V1.3.1 (2015-04)
7.4.1 Test-suite overview . 64
7.4.2 Declarations . 67
7.4.3 Constraints . 67
7.4.3.1 Abbreviations . 67
7.4.3.1.1 Subfield mnemonics . 67
7.4.3.1.2 Special characters used in the subfield definitions . 68
7.4.3.1.3 Station addresses and positions . 68
7.4.3.1.4 VDL bursts . 69
7.4.3.2 Test cases . 95
7.4.3.2.1 Test case macros . 96
7.4.3.2.2 Test case descriptions . 98
Annex A (informative): Cross reference matrix . 172
History . 185

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6 ETSI EN 302 842-4 V1.3.1 (2015-04)
Intellectual Property Rights
IPRs essential or potentially essential to the present document may have been declared to ETSI. The information
pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found
in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in
respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web
server (http://ipr.etsi.org).
Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee
can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web
server) which are, or may be, or may become, essential to the present document.
Foreword
This European Standard (EN) has been produced by ETSI Technical Committee Aeronautics (AERO).
The present document is part 4 of a multi-part deliverable covering the VHF air-ground and air-air Digital Link (VDL)
Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne)
equipment, as identified below:
Part 1: "Physical layer";
Part 2: "General description and data link layer";
Part 3: "Additional broadcast aspects";
Part 4: "Point-to-point functions".
The present document is accompanied by an equivalent ground-based standard, ETSI EN 301 842 [i.1] parts 1 to 5,
covering the VHF air-ground Data Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of
measurement for ground-based equipment.
NOTE: Minimum Operational Performance Specifications (MOPS) are also being developed for VDL Mode 4.
EUROCAE have previously published Interim MOPS for VDL Mode 4 [i.2] which are a sub set of
ETSI EN 302 842-1 [5], ETSI EN 302 842-2 [6], ETSI EN 302 842-3 [7] and ETSI EN 302 842-4 (the
present document). ETSI EN 302 842-1 [5], ETSI EN 302 842-2 [6], ETSI EN 302 842-3 [7] and
ETSI EN 302 842-4 (the present document) comply with the requirements of EC Mandate M/318 [i.3].

National transposition dates
Date of adoption of this EN: 6 April 2015
Date of latest announcement of this EN (doa): 31 July 2015
Date of latest publication of new National Standard
or endorsement of this EN (dop/e): 31 January 2016
Date of withdrawal of any conflicting National Standard (dow): 31 January 2017

Modal verbs terminology
In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and
"cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of
provisions).
"must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation.
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7 ETSI EN 302 842-4 V1.3.1 (2015-04)
Introduction
The present document states the technical specifications for Very High Frequency (VHF) Digital Link (VDL) Mode 4
aeronautical mobile (airborne) radio transmitters, transceivers and receivers for air-ground and air-air communications
operating in the VHF band, using Gaussian Filtered Frequency Shift Keying (GFSK) modulation with 25 kHz channel
spacing and capable of tuning to any of the 25 kHz channels from 112,000 MHz to 136,975 MHz as defined in ICAO
VDL SARPs [2].
The present document may be used to produce tests for the assessment of the performance of the equipment. The
performance of the equipment submitted for type testing should be representative of the performance of the
corresponding production model.
The present document has been written on the assumption that:
• the type test measurements will be performed only once, in an accredited test laboratory and the measurements
accepted by the various authorities in order to grant type approval;
• if equipment available on the market is required to be checked it will be tested in accordance with the methods
of measurement specified in the present document or a documented alternative approved by the certifying
authority;
• equipment comply with ETSI EN 302 842-1 [5] and ETSI EN 302 842-2 [6].
NOTE: The present document has been produced with a view to maintaining consistency of numbering with the
equivalent standard for ground equipment (ETSI EN 301 842 [i.1]). Where requirements are the same,
they have been given the same number. Some new airborne requirements have been inserted between
requirements that were sequential in ETSI EN 301 842 [i.1]. This has led to a non-standard form of
numbering for new requirements in some places.
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8 ETSI EN 302 842-4 V1.3.1 (2015-04)
1 Scope
The present document applies to the following radio equipment types:
• Very High Frequency (VHF) Digital Link (VDL) Mode 4 aeronautical mobile (airborne) radio transmitters,
transceivers and receivers for air-ground and air-air communications operating in the VHF band, using
Gaussian Filtered Frequency Shift Keying (GFSK) modulation with 25 kHz channel spacing and capable of
tuning to any of the 25 kHz channels from 112,000 MHz to 136,975 MHz as defined in ICAO VDL
SARPs [2].
The present document provides part 4 of the technical specifications.
The present document is designed to ensure that equipment certified to it will be compatible with the relevant ICAO
VDL SARPs [2] and ICAO VDL4 Technical Manual [1].
Manufacturers should note that in future the tuning range for the transmitter and receiver may also cover any 25 kHz
channel from 108,000 MHz to 111,975 MHz.
The present document applies to "aeronautical mobile (airborne and as applicable also ground vehicles)" equipment
which will hereinafter be referred to as "mobile" equipment.
The scope of the present document is limited to mobile stations. The equivalent specification for ground stations is
ETSI EN 301 842 [i.1].
A description of the scope of the VDL Mode 4 system is provided in part 2 of ETSI EN 302 842-2 [6], clause 1.
ETSI EN 302 842-1 [5] deals with tests of the physical layer, ETSI EN 302 842-2 [6] deals with core link layer
functionality and ETSI EN 302 842-3 [7] with additional broadcast functionality. The present document deals with tests
of the datalink layer (DLS) and the link layer sufficient to support point-to-point functionality. Note that, as described in
ETSI EN 302 842-2 [6], a system supporting point-to-point functionality is required to conform to ETSI
EN 302 842-1 [5], ETSI EN 302 842-2 [6] and the specification in the present document.
The present document is organized as follows:
• clause 2 provides references to relevant documents;
• clause 3 provides general definitions, abbreviations and symbols used;
• clause 4 describes the VDL Mode 4 mobile station point-to-point functions;
• clause 5 provides performance specifications for the VDL Mode 4 mobile station;
• clause 6 provides general design requirements;
• clause 7 provides protocol tests for the point-to-point functions of the system;
• annex A provides a detailed cross-reference to the relevant requirements contained in ICAO VDL4 Technical
Manual [1].
Note that the system can support a very wide range of functions. It is not practical to provide specific tests for all
aspects of functionality. The approach used is to provide detailed tests for the core point-to-point functionality and to
provide tests of those remaining requirements which, if wrongly implemented, could cause a deterioration in the service
offered by other VDL Mode 4 stations.
Mandating and Recommendation Phrases
a) "Shall":
- The use of the word "Shall" indicates a mandated criterion; i.e. compliance with the particular procedure
or specification is mandatory and no alternative may be applied.
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9 ETSI EN 302 842-4 V1.3.1 (2015-04)
b) "Should":
- The use of the word "Should" (and phrases such as "It is recommended that.", etc.) indicates that though
the procedure or criterion is regarded as the preferred option, alternative procedures, specifications or
criteria may be applied, provided that the manufacturer, installer or tester can provide information or data
to adequately support and justify the alternative.
2 References
2.1 Normative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
Referenced documents which are not found to be publicly available in the expected location might be found at
http://docbox.etsi.org/Reference.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
The following referenced documents are necessary for the application of the present document.
[1] ICAO Doc 9816 (First Edition 2004): "Manual on VHF Digital Link (VDL) Mode 4 -
Part 2: Detailed Technical Specifications".
[2] ICAO Annex 10 to the Convention on International Civil Aviation: "Aeronautical
Telecommunications, Volume III: Communication Systems, Part I: Digital Data Communication
Systems, chapter 6", including Amendment 88 (applicable 14/11/13)".
[3] ICAO 9705-CD: "Manual of Technical Provisions for the Aeronautical Telecommunication
Network (ATN)".
[4] Void.
[5] ETSI EN 302 842-1 (V1.3.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio
equipment; Technical characteristics and methods of measurement for aeronautical mobile
(airborne) equipment; Part 1: Physical layer".
[6] ETSI EN 302 842-2 (V1.4.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio
equipment; Technical characteristics and methods of measurement for aeronautical mobile
(airborne) equipment; Part 2: General description and data link layer".
[7] ETSI EN 302 842-3 (V1.4.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio
equipment; Technical characteristics and methods of measurement for aeronautical mobile
(airborne) equipment; Part 3: Additional broadcast aspects".
2.2 Informative references
References are either specific (identified by date of publication and/or edition number or version number) or
non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the
referenced document (including any amendments) applies.
NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee
their long term validity.
The following referenced documents are not necessary for the application of the present document but they assist the
user with regard to a particular subject area.
[i.1] ETSI EN 301 842 (all parts): "VHF air-ground Data Link (VDL) Mode 4 radio equipment;
Technical characteristics and methods of measurement for ground-based equipment".
[i.2] EUROCAE ED-108A: "MOPS for VDL Mode 4 Aircraft Transceiver for ADS-B", July 2001.
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10 ETSI EN 302 842-4 V1.3.1 (2015-04)
[i.3] EC Mandate M/318: "Mandate to CEN/CENELEC/ETSI for standardisation in the field of air
traffic management systems and Galileo local components".
3 Definitions and abbreviations
3.1 Definitions
3.1.1 Basic reference model definitions
See ETSI EN 302 842-2 [6], clause 3.1.1.
3.1.2 Service conventions definitions
See ETSI EN 302 842-2 [6], clause 3.1.2.
3.1.3 General definitions
For the purposes of the present document, the terms and definitions given in ETSI EN 302 842-1 [5] clause 3.1.3,
ETSI EN 302 842-2 [6] clause 3.1.3 and the following apply:
long transmission procedure: procedure that allows transfer of DATA packets in reserved slots, avoiding the loss rates
and delays associated with random access
NOTE: This includes the ability to link sequences of DATA packets, providing continuous transfer in reserved
slots.
More bit (M): bit that controls message fragmentation and concatenation
NOTE: It is set to zero to indicate the end of a message. It is set to 1 to indicate that it is part of a fragmented
message and that there are more fragments to follow.
Network Setup Connection Oriented Protocol (NSCOP): protocol that enables a ground-air link between mobiles
priority (pr): priority of a message, or, in the case of an RTS, the priority of the requested data
short transmission procedure: procedure for the sending of a single data packet. It contains a reservation for a
subsequent acknowledgement
Toggle bit (T): bit that allows detection and rejection of duplicate DLPDUs
NOTE: The T bit is alternately set to 1 and 0 on each successive DATA transmission, except for retransmissions.
Zero-Overhead Connection-Oriented Protocol (ZOCOP): protocol that enables an air-air link between mobiles
3.1.4 Definition of bit order
In the tables included in the present document to illustrate the format of bursts, the following order is implied:
a) bit order in each burst subfield are indicated by subscript numbers. Bit 1 indicates the least significant bit; and
b) bits are transmitted octet by octet, starting with the first octet in each table, and within each octet the rightmost
bit (as shown in the tables) is transmitted first.
3.2 Abbreviations
For the purposes of the present document, the following abbreviations apply:
ACK ACKnowledgement (burst)
ADM ADMinistration identifier
ADS-B Automatic Dependent Surveillance-Broadcast
ARS Administration Region Selector
ATN Aeronautical Telecommunication Network
CMD CoMmanD
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11 ETSI EN 302 842-4 V1.3.1 (2015-04)
CPR Compact Position Reporting
CRC Cyclic Redundancy Code
CTRL ConTRoL (DLPDU)
CTS Clear To Send (burst)
DISC DISConnect
DLE Data Link Entity
DLPDU Data Link Protocol Data Unit
DLS Data Link Service
DM Disconnected Mode (DLPDU)
DTE Data Terminal Equipment
EC European Commission
erid extended reservation ID
FRMR FRaMe Reject (DLPDU)
GFSK Gaussian Filtered Frequency Shift Keying
GSC Global Signalling Channel
GSIF Ground Station Information Frame
hex hexadecimal
HO Hand Off
IA International Alphabet
IA-5 International Alphabet - 5
IB Initialize Bit
ICAO International Civil Aviation Organization
ID IDentity
INFO INFOrmation (DLPDU)
ISO International Organization for Standardization
IS-SME Intermediate System - System Management Entity
LCR Link Connection Refused
LE Link Establishment
lg length
LME Link Management Entity
M More bit
MAC Media Access Control
MOPS Minimum Operational Performance Specification
NACK Negative ACKnowledgement
neg negotiation
NETs Network Entity Titles
NM Nautical Mile
NSCOP Network Setup Connection Orientated Protocol
O Optional
p priority
PCO Point of Control and Observation
PI Parameter Identifier
pr priority
QoS Quality of Service
Res Reserved header bits
RF Radio Frequency
rid reservation ID
RSP ReSPonse
RTS Request To Send (DLPDU)
SARPs Standards And Recommended Practices
seq sequence
SNDCF SubNetwork Dependent Convergence Function
SZOM Start Zero Overhead Mode (DLPDU)
T Toggle bit
UCTRL Unacknowledged ConTRoL data broadcast (DLPDU)
UDATA Unacknowledged DATA broadcast (DLPDU)
UINFO Unacknowledged user INFOrmation data broadcast (DLPDU)
VDL VHF Digital Link
VHF Very High Frequency
VME VDL Management Entity
VSS VDL Mode 4 Specific Services
ZOCOP Zero-Overhead Connection-Oriented Protocol
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12 ETSI EN 302 842-4 V1.3.1 (2015-04)
4 General description of VDL Mode 4 mobile station
point-to-point services
4.1 General
A description of VDL Mode 4 is provided in ETSI EN 302 842-2 [6]. This clause provides a description of the datalink
layer and associated services of the VSS and LME required to support point-to-point communications.
The specifications in the present document provide air-to-ground and air-to-air point-to-point services based on the
ICAO Technical Manual. The present document includes:
• Point-to-point data and control data transfer functions from the DLS.
• Point-to-point link control within the LME.
Note that the present document covers the mobile response to the establishment, termination and handover of links
between ground stations. Decisions made by ground stations to establish, terminate or handover links between ground
stations are local issues and beyond the scope of these specifications.
In most respects, the VDL Mode 4 mobile station follows the provisions of the ICAO standards material for VDL
Mode 4. Within the ICAO standard, there are some requirements which apply explicitly only to ground stations.
Requirements on ground stations are covered in ETSI EN 301 842 (all parts) [i.1].
The scope of the present document is for an mobile station supporting point-to-point applications. Hence the ability to
support broadcast communication is not included in the present document.
Note that, although certain protocols will not be used by the mobile station, the ability to recognize the use by ground
stations of these protocols and to respond in a consistent manner is an mobile station requirement and is included in the
present document.
4.2 Data Link Service (DLS) and Link Management Entity
(LME)
4.2.1 General
The Data Link Service (DLS) provides a point-to-point protocol supporting both air-to-ground and air-to-air exchanges.
For air-to-ground exchanges, connection management is handled by the LME, using a Negotiated Setup
Connection-Orientated Protocol (NSCOP). For air-to-air exchanges, the DLS defines a ZOCOP protocol with link
establishment and disestablishment controlled by timers, allowing rapid link negotiation between aircraft.
The specifications in the present document assume that VDL Mode 4 will be used with a network based on ATN
protocols (see ICAO ATN SARPs [3]). It should be noted that, in future, it could support other network protocols.
The DLS is a simple information exchange protocol which provides:
a) Explicit acknowledgement of each DATA packet.
b) Mechanisms to provide data transfer in reserved slots, avoiding loss rates and delays associated with random
access. This includes the ability to link sequences of DATA packets, providing continuous transfer in reserved
slots.
c) Packet fragmentation, to allow long user data packets to be transferred across the link in fragments optimally
matched to the link conditions.
d) Duplicate detection and suppression via a simple toggle-bit mechanism.
e) Explicit support for the 15 priority levels defined for the ATN, including the ability for high priority messages
to be sent in the middle of a fragmented low priority message.
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As illustrated in figure 4.1, the DLS:
• Provides services to external users in order to support point-to-point, multi-cast and broadcast
communications.
• Provides services to the LME to support link management.
• Supports services between peer DLSs.
• Uses the services of the VSS in order to send and receive messages.
DLS User
LME
DLS
Peer DLS
VSS
Figure 4.1: Functions of the DLS
Figure 4.2 illustrates the use of various services provided by the DLS and VSS in supporting the DLS User and the
LME.
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14 ETSI EN 302 842-4 V1.3.1 (2015-04)
DLS User LME
Directed Data Broadcast Data
(INFO, CTRL) (UDATA)
Connection Management (IB/SZOM)
Message Segmentation (M-bit)
Delivery Order (T-bit)
DLS
Short Long Short Long
Acknowledged Acknowledged Unacknowledged Unacknowledged
Information
Unicast Request
Transfer
Reservation
Request
VSS
General
Response Retransmission
Protocol
Figure 4.2: Services provided by the DLS and VSS
Protocols for short unacknowledged broadcast data have already been specified in the core link layer functionality
(ETSI EN 302 842-2 [6]).
A DLS Burst consists of:
• Burst ID (fixed or variable).
• One or two DLPDUs.
The following DATA DLPDUs (data link protocol data units) are defined:
• CTRL: Used by the LME to establish and maintain links for NSCOP communication.
• INFO: Contains a user data field.
• UDATA: Either a UCTRL or a UINFO. Enables the broadcast of user data - it is unacknowledged.
The following RTS DLPDUs are defined:
• CTRL_RTS: Sent to request the sending of link maintenance data.
• INFO_RTS: A request to send user data (for long transmission procedures).
• UDATA_RTS: A request to send broadcast data.
The following ACK, CTS and other DLS link control DLPDUs are defined:
• UDATA_CTS: This DLPDU is a clear to send in response to a UDATA_RTS.
• INFO_ACK: An acknowledgement of the previous INFO DLPDU.
• INFO_CTS: A clear to send (for long transmission procedures).
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15 ETSI EN 302 842-4 V1.3.1 (2015-04)
• CTRL_ACK: An acknowledgement of the previous CTRL DLPDU.
• FRMR: Used to reset the link.
• FRMR_ACK: Sent to acknowledge receipt of FRMR.
• DM/DISC (Disconnected Mode): Used to indicate that a DLS DLPDU has been received when no link has
been initialized.
• DM/FRMR - Used to indicate that a DLS DLPDU has been received when the link is in the process of being
initialized.
• SZOM: sent in combination with an INFO, INFO_RTS or INFO_ACK to establish a link for ZOCOP
communication.
Table 4.1 shows the DLS burst types.
Table 4.1: DLPDU contents
Toggle More Bit Priority Negotiation Initialize Length
Bit (T) (M) (pr) subfield (neg) bit IB (lg)
CTRL
INFO
UDATA
CTRL_RTS
INFO_RTS
UDATA_RTS
UDATA_CTS
INFO_ACK
INFO_CTS
CTRL_ACK
CTRL_CTS
FRMR_ACK
FRMR
DM/DISC
DM/FRMR
SZOM
Where:
• Toggle Bit (T): This is used for duplicate detection and rejection.
• More Bit (M): This is set to
...

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.VHF air-ground and air-air Digital Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne) equipment;Part 4: Point-to-point functions49.090On-board equipment and instruments33.060.99Druga oprema za radijske komunikacijeOther equipment for radiocommunicationsICS:Ta slovenski standard je istoveten z:EN 302 842-4 V1.3.1SIST EN 302 842-4 V1.3.1:2015en,fr,de01-oktober-2015SIST EN 302 842-4 V1.3.1:2015SLOVENSKI
STANDARD
EUROPEAN STANDARD SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 2
Reference REN/AERO-00019-4 Keywords aeronautical, digital, radio, testing, VHF ETSI 650 Route des Lucioles F-06921 Sophia Antipolis Cedex - FRANCE
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ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 3 Contents Intellectual Property Rights . 6 Foreword . 6 Modal verbs terminology . 6 Introduction . 7 1 Scope . 8 2 References . 9 2.1 Normative references . 9 2.2 Informative references . 9 3 Definitions and abbreviations . 10 3.1 Definitions . 10 3.1.1 Basic reference model definitions . 10 3.1.2 Service conventions definitions . 10 3.1.3 General definitions . 10 3.1.4 Definition of bit order . 10 3.2 Abbreviations . 10 4 General description of VDL Mode 4 mobile station point-to-point services . 12 4.1 General . 12 4.2 Data Link Service (DLS) and Link Management Entity (LME) . 12 4.2.1 General . 12 4.2.2 DLS timers . 15 4.2.3 DLS counters . 16 4.2.4 Toggle bit (T) . 16 4.2.5 State variables (Tt and Tr) . 16 4.2.6 Initialize Bit (IB) . 16 4.2.7 More bit (M) . 17 4.2.8 Priority (pr) . 17 4.2.9 Message fragmentation and concatenation . 17 4.2.10 DLS procedures . 17 4.2.10.1 Selection of DLS procedures. 17 4.2.10.2 Short transmission procedures . 17 4.2.10.3 Long transmission procedures . 18 4.2.11 Linking transmissions . 20 4.2.11.1 Types of linking . 20 4.2.11.2 Combined RTS / DATA DLPDUs . 20 4.2.11.3 Combined DATA / ACK DLPDUs . 20 4.2.11.4 Combined RTS / ACK DLPDUs . 20 4.2.11.5 Combined CTS / ACK DLPDUs . 20 4.2.12 Ground-air link management . 20 4.2.13 Air-air link management . 21 4.3 Additional VSS services . 21 5 Minimum performance specification under standard test conditions . 21 5.1 DLS sublayer . 21 5.1.1 General . 21 5.1.1.1 Services . 21 5.1.1.2 Data transfer . 22 5.1.1.3 DATA DLPDU duplicate suppression and sequencing . 22 5.1.1.4 Error detection . 22 5.1.1.5 Station identification . 22 5.1.1.6 Broadcast addressing . 22 5.1.1.7 DLS Priority . 23 5.1.1.8 DLS Link control DLPDUs . 23 5.1.2 DLS protocol specification . 23 5.1.2.1 State variables . 23 5.1.2.2 DLS burst formats . 23 SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 4 5.1.3 DLS system parameters . 27 5.1.4 DLS procedures . 29 5.1.4.1 Setting of re-transmission parameter . 29 5.1.4.2 Selection of user data packet for transmission . 29 5.1.4.3 Selection of transmission procedures . 31 5.1.4.4 Short transmission procedures . 31 5.1.4.5 Long transmission procedures . 32 5.1.4.6 No link with sender . 34 5.1.4.7 User data packet reception . 35 5.1.4.8 Receipt of ACK DLPDU . 35 5.1.4.9 Link reset . 36 5.1.4.10 Linking DLS DLPDU transmissions . 37 5.1.4.11 CTRL DLPDU . 38 5.1.4.12 Procedures for air-air communication . 38 5.2 Link management entity sublayer. 38 5.2.1 Services . 38 5.2.1.1 General . 38 5.2.1.2 Link provision . 39 5.2.1.3 Link change notifications . 39 5.2.1.4 CTRL DLPDU . 39 5.2.1.5 Broadcast link management burst . 40 5.2.2 Control (CTRL) parameter formats . 40 5.2.2.1 Encoding . 40 5.2.2.2 General purpose information parameters . 40 5.2.2.3 Mobile-initiated information parameters . 44 5.2.2.4 Ground-initiated modification parameters . 45 5.2.2.5 Ground-initiated information parameters . 48 5.2.3 LME timers and parameters . 50 5.2.3.1 General . 50 5.2.3.2 Timer TL1 (maximum link overlap time) . 51 5.2.3.3 Parameters TL2 (link initialization time) . 51 5.2.3.4 Timer TL4 (leave generation latency) . 51 5.2.4 CTRL DLPDU types and procedures . 51 5.2.5 CTRL transmission procedures . 55 5.2.5a Frequency management procedures . 55 5.2.5.1 Link connectivity procedures . 55 5.2.5.2 Ground Station Identification . 55 5.2.5.3 Link establishment . 56 5.2.5.4 Mobile-initiated handoff . 57 5.2.5.5 Mobile-requested ground-initiated handoff . 58 5.2.5.6 Ground-initiated handoff . 58 5.2.5.7 Ground-requested mobile-initiated handoff . 59 5.2.5.8 Ground-requested broadcast handoff . 59 5.2.5.9 Ground-commanded autotune . 60 5.2.6 VDL Mode 4 Mobile SubNetwork Dependent Convergence Function (SNDCF) . 60 5.2.6.1 Frame mode SNDCF . 60 5.3 Additional VSS requirements . 60 5.3.1 Information transfer request protocol specification . 60 5.3.1.1 Information transfer request parameters . 60 5.3.1.2 Information transfer request transmission procedures . 62 5.3.1.3 Information transfer request acknowledgement procedures . 62 5.3.2 Void . 62 5.3.3 Void . 62 5.3.4 Retransmission procedures . 63 6 General design requirements . 63 7 Protocol test procedures . 63 7.1 General . 63 7.2 Required test rig . 63 7.3 Protocol test-suite description methodology . 64 7.4 Detailed protocol test procedures . 64 SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 5 7.4.1 Test-suite overview . 64 7.4.2 Declarations . 67 7.4.3 Constraints . 67 7.4.3.1 Abbreviations . 67 7.4.3.1.1 Subfield mnemonics . 67 7.4.3.1.2 Special characters used in the subfield definitions . 68 7.4.3.1.3 Station addresses and positions . 68 7.4.3.1.4 VDL bursts . 69 7.4.3.2 Test cases . 95 7.4.3.2.1 Test case macros . 96 7.4.3.2.2 Test case descriptions . 98 Annex A (informative): Cross reference matrix . 172 History . 185
ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 6 Intellectual Property Rights IPRs essential or potentially essential to the present document may have been declared to ETSI. The information pertaining to these essential IPRs, if any, is publicly available for ETSI members and non-members, and can be found in ETSI SR 000 314: "Intellectual Property Rights (IPRs); Essential, or potentially Essential, IPRs notified to ETSI in respect of ETSI standards", which is available from the ETSI Secretariat. Latest updates are available on the ETSI Web server (http://ipr.etsi.org). Pursuant to the ETSI IPR Policy, no investigation, including IPR searches, has been carried out by ETSI. No guarantee can be given as to the existence of other IPRs not referenced in ETSI SR 000 314 (or the updates on the ETSI Web server) which are, or may be, or may become, essential to the present document. Foreword This European Standard (EN) has been produced by ETSI Technical Committee Aeronautics (AERO). The present document is part 4 of a multi-part deliverable covering the VHF air-ground and air-air Digital Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne) equipment, as identified below: Part 1: "Physical layer"; Part 2: "General description and data link layer"; Part 3: "Additional broadcast aspects"; Part 4: "Point-to-point functions". The present document is accompanied by an equivalent ground-based standard, ETSI EN 301 842 [i.1] parts 1 to 5, covering the VHF air-ground Data Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for ground-based equipment. NOTE: Minimum Operational Performance Specifications (MOPS) are also being developed for VDL Mode 4. EUROCAE have previously published Interim MOPS for VDL Mode 4 [i.2] which are a sub set of ETSI EN 302 842-1 [5], ETSI EN 302 842-2 [6], ETSI EN 302 842-3 [7] and ETSI EN 302 842-4 (the present document). ETSI EN 302 842-1 [5], ETSI EN 302 842-2 [6], ETSI EN 302 842-3 [7] and ETSI EN 302 842-4 (the present document) comply with the requirements of EC Mandate M/318 [i.3].
National transposition dates Date of adoption of this EN: 6 April 2015 Date of latest announcement of this EN (doa): 31 July 2015 Date of latest publication of new National Standard or endorsement of this EN (dop/e):
31 January 2016 Date of withdrawal of any conflicting National Standard (dow): 31 January 2017
Modal verbs terminology In the present document "shall", "shall not", "should", "should not", "may", "need not", "will", "will not", "can" and "cannot" are to be interpreted as described in clause 3.2 of the ETSI Drafting Rules (Verbal forms for the expression of provisions). "must" and "must not" are NOT allowed in ETSI deliverables except when used in direct citation. SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 7 Introduction The present document states the technical specifications for Very High Frequency (VHF) Digital Link (VDL) Mode 4 aeronautical mobile (airborne) radio transmitters, transceivers and receivers for air-ground and air-air communications operating in the VHF band, using Gaussian Filtered Frequency Shift Keying (GFSK) modulation with 25 kHz channel spacing and capable of tuning to any of the 25 kHz channels from 112,000 MHz to 136,975 MHz as defined in ICAO VDL SARPs [2]. The present document may be used to produce tests for the assessment of the performance of the equipment. The performance of the equipment submitted for type testing should be representative of the performance of the corresponding production model. The present document has been written on the assumption that: • the type test measurements will be performed only once, in an accredited test laboratory and the measurements accepted by the various authorities in order to grant type approval; • if equipment available on the market is required to be checked it will be tested in accordance with the methods of measurement specified in the present document or a documented alternative approved by the certifying authority; • equipment comply with ETSI EN 302 842-1 [5] and ETSI EN 302 842-2 [6]. NOTE: The present document has been produced with a view to maintaining consistency of numbering with the equivalent standard for ground equipment (ETSI EN 301 842 [i.1]). Where requirements are the same, they have been given the same number. Some new airborne requirements have been inserted between requirements that were sequential in ETSI EN 301 842 [i.1]. This has led to a non-standard form of numbering for new requirements in some places. SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 8 1 Scope The present document applies to the following radio equipment types: • Very High Frequency (VHF) Digital Link (VDL) Mode 4 aeronautical mobile (airborne) radio transmitters, transceivers and receivers for air-ground and air-air communications operating in the VHF band, using Gaussian Filtered Frequency Shift Keying (GFSK) modulation with 25 kHz channel spacing and capable of tuning to any of the 25 kHz channels from 112,000 MHz to 136,975 MHz as defined in ICAO VDL SARPs [2]. The present document provides part 4 of the technical specifications. The present document is designed to ensure that equipment certified to it will be compatible with the relevant ICAO VDL SARPs [2] and ICAO VDL4 Technical Manual [1]. Manufacturers should note that in future the tuning range for the transmitter and receiver may also cover any 25 kHz channel from 108,000 MHz to 111,975 MHz. The present document applies to "aeronautical mobile (airborne and as applicable also ground vehicles)" equipment which will hereinafter be referred to as "mobile" equipment. The scope of the present document is limited to mobile stations. The equivalent specification for ground stations is ETSI EN 301 842 [i.1]. A description of the scope of the VDL Mode 4 system is provided in part 2 of ETSI EN 302 842-2 [6], clause 1. ETSI EN 302 842-1 [5] deals with tests of the physical layer, ETSI EN 302 842-2 [6] deals with core link layer functionality and ETSI EN 302 842-3 [7] with additional broadcast functionality. The present document deals with tests of the datalink layer (DLS) and the link layer sufficient to support point-to-point functionality. Note that, as described in ETSI EN 302 842-2 [6], a system supporting point-to-point functionality is required to conform to ETSI EN 302 842-1 [5], ETSI EN 302 842-2 [6] and the specification in the present document. The present document is organized as follows: • clause 2 provides references to relevant documents; • clause 3 provides general definitions, abbreviations and symbols used; • clause 4 describes the VDL Mode 4 mobile station point-to-point functions; • clause 5 provides performance specifications for the VDL Mode 4 mobile station; • clause 6 provides general design requirements; • clause 7 provides protocol tests for the point-to-point functions of the system; • annex A provides a detailed cross-reference to the relevant requirements contained in ICAO VDL4 Technical Manual [1]. Note that the system can support a very wide range of functions. It is not practical to provide specific tests for all aspects of functionality. The approach used is to provide detailed tests for the core point-to-point functionality and to provide tests of those remaining requirements which, if wrongly implemented, could cause a deterioration in the service offered by other VDL Mode 4 stations. Mandating and Recommendation Phrases a) "Shall": - The use of the word "Shall" indicates a mandated criterion; i.e. compliance with the particular procedure or specification is mandatory and no alternative may be applied. SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 9 b) "Should": - The use of the word "Should" (and phrases such as "It is recommended that.", etc.) indicates that though the procedure or criterion is regarded as the preferred option, alternative procedures, specifications or criteria may be applied, provided that the manufacturer, installer or tester can provide information or data to adequately support and justify the alternative. 2 References 2.1 Normative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. Referenced documents which are not found to be publicly available in the expected location might be found at http://docbox.etsi.org/Reference. NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. The following referenced documents are necessary for the application of the present document. [1] ICAO Doc 9816 (First Edition 2004): "Manual on VHF Digital Link (VDL) Mode 4 - Part 2: Detailed Technical Specifications". [2] ICAO Annex 10 to the Convention on International Civil Aviation: "Aeronautical Telecommunications, Volume III: Communication Systems, Part I: Digital Data Communication Systems, chapter 6", including Amendment 88 (applicable 14/11/13)". [3] ICAO 9705-CD: "Manual of Technical Provisions for the Aeronautical Telecommunication Network (ATN)". [4] Void. [5] ETSI EN 302 842-1 (V1.3.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne) equipment; Part 1: Physical layer". [6] ETSI EN 302 842-2 (V1.4.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne) equipment; Part 2: General description and data link layer". [7] ETSI EN 302 842-3 (V1.4.1): "VHF air-ground and air-air Digital Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for aeronautical mobile (airborne) equipment; Part 3: Additional broadcast aspects". 2.2 Informative references References are either specific (identified by date of publication and/or edition number or version number) or non-specific. For specific references, only the cited version applies. For non-specific references, the latest version of the referenced document (including any amendments) applies. NOTE: While any hyperlinks included in this clause were valid at the time of publication ETSI cannot guarantee their long term validity. The following referenced documents are not necessary for the application of the present document but they assist the user with regard to a particular subject area. [i.1] ETSI EN 301 842 (all parts): "VHF air-ground Data Link (VDL) Mode 4 radio equipment; Technical characteristics and methods of measurement for ground-based equipment". [i.2] EUROCAE ED-108A: "MOPS for VDL Mode 4 Aircraft Transceiver for ADS-B", July 2001. SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 10 [i.3] EC Mandate M/318: "Mandate to CEN/CENELEC/ETSI for standardisation in the field of air traffic management systems and Galileo local components". 3 Definitions and abbreviations 3.1 Definitions 3.1.1 Basic reference model definitions See ETSI EN 302 842-2 [6], clause 3.1.1. 3.1.2 Service conventions definitions See ETSI EN 302 842-2 [6], clause 3.1.2. 3.1.3 General definitions For the purposes of the present document, the terms and definitions given in ETSI EN 302 842-1 [5] clause 3.1.3, ETSI EN 302 842-2 [6] clause 3.1.3 and the following apply: long transmission procedure: procedure that allows transfer of DATA packets in reserved slots, avoiding the loss rates and delays associated with random access NOTE: This includes the ability to link sequences of DATA packets, providing continuous transfer in reserved slots. More bit (M): bit that controls message fragmentation and concatenation NOTE: It is set to zero to indicate the end of a message. It is set to 1 to indicate that it is part of a fragmented message and that there are more fragments to follow. Network Setup Connection Oriented Protocol (NSCOP): protocol that enables a ground-air link between mobiles priority (pr): priority of a message, or, in the case of an RTS, the priority of the requested data short transmission procedure: procedure for the sending of a single data packet. It contains a reservation for a subsequent acknowledgement Toggle bit (T): bit that allows detection and rejection of duplicate DLPDUs NOTE: The T bit is alternately set to 1 and 0 on each successive DATA transmission, except for retransmissions. Zero-Overhead Connection-Oriented Protocol (ZOCOP): protocol that enables an air-air link between mobiles 3.1.4 Definition of bit order In the tables included in the present document to illustrate the format of bursts, the following order is implied: a) bit order in each burst subfield are indicated by subscript numbers. Bit 1 indicates the least significant bit; and b) bits are transmitted octet by octet, starting with the first octet in each table, and within each octet the rightmost bit (as shown in the tables) is transmitted first. 3.2 Abbreviations For the purposes of the present document, the following abbreviations apply: ACK ACKnowledgement (burst) ADM ADMinistration identifier ADS-B Automatic Dependent Surveillance-Broadcast ARS Administration Region Selector ATN Aeronautical Telecommunication Network CMD CoMmanD SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 11 CPR Compact Position Reporting CRC Cyclic Redundancy Code CTRL ConTRoL (DLPDU) CTS Clear To Send (burst) DISC DISConnect DLE Data Link Entity DLPDU Data Link Protocol Data Unit DLS Data Link Service DM Disconnected Mode (DLPDU) DTE Data Terminal Equipment EC European Commission erid extended reservation ID FRMR FRaMe Reject (DLPDU) GFSK Gaussian Filtered Frequency Shift Keying GSC Global Signalling Channel GSIF Ground Station Information Frame hex hexadecimal HO Hand Off IA International Alphabet IA-5 International Alphabet - 5 IB Initialize Bit ICAO International Civil Aviation Organization ID IDentity INFO INFOrmation (DLPDU) ISO International Organization for Standardization IS-SME Intermediate System - System Management Entity LCR Link Connection Refused LE Link Establishment lg length LME Link Management Entity M More bit MAC Media Access Control MOPS Minimum Operational Performance Specification NACK Negative ACKnowledgement neg negotiation NETs Network Entity Titles NM Nautical Mile NSCOP Network Setup Connection Orientated Protocol O Optional p priority PCO Point of Control and Observation PI Parameter Identifier pr priority QoS Quality of Service Res Reserved header bits RF Radio Frequency rid reservation ID RSP ReSPonse RTS Request To Send (DLPDU) SARPs Standards And Recommended Practices seq sequence SNDCF SubNetwork Dependent Convergence Function SZOM Start Zero Overhead Mode (DLPDU) T Toggle bit UCTRL Unacknowledged ConTRoL data broadcast (DLPDU) UDATA Unacknowledged DATA broadcast (DLPDU) UINFO Unacknowledged user INFOrmation data broadcast (DLPDU) VDL VHF Digital Link VHF Very High Frequency VME VDL Management Entity VSS VDL Mode 4 Specific Services ZOCOP Zero-Overhead Connection-Oriented Protocol SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 12 4 General description of VDL Mode 4 mobile station point-to-point services 4.1 General A description of VDL Mode 4 is provided in ETSI EN 302 842-2 [6]. This clause provides a description of the datalink layer and associated services of the VSS and LME required to support point-to-point communications. The specifications in the present document provide air-to-ground and air-to-air point-to-point services based on the ICAO Technical Manual. The present document includes: • Point-to-point data and control data transfer functions from the DLS. • Point-to-point link control within the LME. Note that the present document covers the mobile response to the establishment, termination and handover of links between ground stations. Decisions made by ground stations to establish, terminate or handover links between ground stations are local issues and beyond the scope of these specifications. In most respects, the VDL Mode 4 mobile station follows the provisions of the ICAO standards material for VDL Mode 4. Within the ICAO standard, there are some requirements which apply explicitly only to ground stations. Requirements on ground stations are covered in ETSI EN 301 842 (all parts) [i.1]. The scope of the present document is for an mobile station supporting point-to-point applications. Hence the ability to support broadcast communication is not included in the present document. Note that, although certain protocols will not be used by the mobile station, the ability to recognize the use by ground stations of these protocols and to respond in a consistent manner is an mobile station requirement and is included in the present document. 4.2 Data Link Service (DLS) and Link Management Entity (LME) 4.2.1 General The Data Link Service (DLS) provides a point-to-point protocol supporting both air-to-ground and air-to-air exchanges. For air-to-ground exchanges, connection management is handled by the LME, using a Negotiated Setup Connection-Orientated Protocol (NSCOP). For air-to-air exchanges, the DLS defines a ZOCOP protocol with link establishment and disestablishment controlled by timers, allowing rapid link negotiation between aircraft. The specifications in the present document assume that VDL Mode 4 will be used with a network based on ATN protocols (see ICAO ATN SARPs [3]). It should be noted that, in future, it could support other network protocols. The DLS is a simple information exchange protocol which provides: a) Explicit acknowledgement of each DATA packet. b) Mechanisms to provide data transfer in reserved slots, avoiding loss rates and delays associated with random access. This includes the ability to link sequences of DATA packets, providing continuous transfer in reserved slots. c) Packet fragmentation, to allow long user data packets to be transferred across the link in fragments optimally matched to the link conditions. d) Duplicate detection and suppression via a simple toggle-bit mechanism. e) Explicit support for the 15 priority levels defined for the ATN, including the ability for high priority messages to be sent in the middle of a fragmented low priority message. SIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 13 As illustrated in figure 4.1, the DLS: • Provides services to external users in order to support point-to-point, multi-cast and broadcast communications. • Provides services to the LME to support link management. • Supports services between peer DLSs. • Uses the services of the VSS in order to send and receive messages.
Figure 4.1: Functions of the DLS Figure 4.2 illustrates the use of various services provided by the DLS and VSS in supporting the DLS User and the LME. LMEDLS UserDLSPeer DLSVSSSIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 14
Figure 4.2: Services provided by the DLS and VSS Protocols for short unacknowledged broadcast data have already been specified in the core link layer functionality (ETSI EN 302 842-2 [6]). A DLS Burst consists of: • Burst ID (fixed or variable). • One or two DLPDUs. The following DATA DLPDUs (data link protocol data units) are defined: • CTRL: Used by the LME to establish and maintain links for NSCOP communication. • INFO: Contains a user data field. • UDATA: Either a UCTRL or a UINFO. Enables the broadcast of user data - it is unacknowledged. The following RTS DLPDUs are defined: • CTRL_RTS: Sent to request the sending of link maintenance data. • INFO_RTS: A request to send user data (for long transmission procedures). • UDATA_RTS: A request to send broadcast data. The following ACK, CTS and other DLS link control DLPDUs are defined: • UDATA_CTS: This DLPDU is a clear to send in response to a UDATA_RTS. • INFO_ACK: An acknowledgement of the previous INFO DLPDU. • INFO_CTS: A clear to send (for long transmission procedures). Directed Data(INFO, CTRL)Short AcknowledgedLongAcknowledgedShortUnacknowledgedLongUnacknowledgedUnicast RequestReservationInformationTransferRequestGeneralResponseProtocolRetransmissionConnection Management (IB/SZOM)Message Segmentation (M-bit)Delivery Order (T-bit)Broadcast Data(UDATA)DLSVSSDLS UserLMESIST EN 302 842-4 V1.3.1:2015

ETSI ETSI EN 302 842-4 V1.3.1 (2015-04) 15 • CTRL_ACK: An acknowledgement of the previous CTRL DLPDU. • FRMR: Used to reset the link. • FRMR_ACK: Sent to acknowledge receipt of FRMR. • DM/DISC (Disconnected Mode): Used to indicate that a DLS DLPDU has been received when no link has been initialized. • DM/FRMR - Used to indicate that a DLS DLPDU has been received when the link is in the process of being initialized. • SZOM: sent in combination with an INFO, INFO_RTS or INFO_ACK to establish a link for ZOCOP communication. Table 4.1 shows the DLS burst types. Table 4.1: DLPDU contents
Toggle Bit (T) More Bit (M) Priority (pr) Negotiation subfield (neg) Initialize bit IB Length (lg) CTRL
INFO
UDATA
CTRL_RTS
INFO_RTS
UDATA_RTS
UDATA_CTS
INFO_ACK
INFO_CTS
CTRL_ACK
CTRL_CTS
FRMR_ACK
FRMR
DM/DISC
DM/FRMR
SZOM
Where: • Toggle Bit (T): This is used for duplicate detection and rejection. • More Bit (M): This is set to zero to indicate the end of a message. It is set to 1 to indicate that it is part of a fragmented message and that there are more fragments to follow. • priority (pr): This is the priority of the message. • negotiation subfield (neg): This indicates the link management parameters to be used for air-to-air link control. • Initialize Bit (IB): This bit causes the receiver to initialize the Tt and Tr state variables and to cle
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