Multi-Link Network Architecture

Legend

-----          Simplex link (Link 11, 16 or 22)

===          Duplex link (Link 1 or 11B)

JU            Link 16 JTIDS Unit

NU           Link 22 (NILE) Unit

PU           Link 11 Participating Unit

RU           Link 11B Reporting Unit

SU           Link 1 Supporting Unit

FJUA      Link 16 / Link 11 Forwarding Unit

FJUB      Link 16 / Link 11B Forwarding Unit

FJUAB    Link 16 / Link 11 / Link 11B Forwarding Unit

 

Network Design

UK platforms are fitted with a number of TDLs that generally operate with different technical characteristics and message protocols.  The design of individual TDL networks may be reasonably simple, such as that required for Link 11, or highly complex such as the activity necessary to provide an effective Link 16 network.   However, the overall complexity of the TDL Interface design task always increases when individual TDLs are to be operated together and data is to be transferred between them.  In addition, platforms may have multiple TDLs fitted but not necessarily have data forwarding capabilities provided.

Bandwidth, and thus data bearing capacity, is limited on all TDLs.  Even Link 16, which has significantly more capacity than Link 11, has limited capacity for all the information exchange requirements placed upon it.  Moreover, the message formats to be used on the available bandwidth of the TDLs also differ, even at the basic level of the track number blocks to be used.

The TDLs fitted to the available platforms, TDL bandwidth and message capabilities all have to be considered in the context of the tactical situation of the operation being undertaken.  The tactical situation will provide many factors to be considered including, but not limited to:

The overall mission

The area of operations

The Threat

The tactics and sensor / emitter policies for own platforms

Topographical features

Time scales

Consequently, configuring the various TDL networks to achieve the optimum exchange of information requires significant planning.  The complexity of Joint Force TDL requirements means that effective networks cannot be set up on an ad hoc basis.  Similarly, single standing plans are unlikely to be able to meet the needs for the uncertain variety of scenarios in which UK forces may find themselves operating.  There is, therefore, a need for both long-term and dynamic planning to be carried out in support of TDL operations, both at JTFHQ and Component levels.  In general terms, the more capable the required TDL Interface is, the greater the need will be for specialised network planning and design tools and personnel.

The TDL planning process is also becoming increasingly complex both as the number of capable TDL fitted platforms increases and as the TDL Interface increases in its capability.  For example, extending the use of TDL over satellite systems requires an addition planning and liaison activity to be undertaken with satellite operation authorities.

Pre-mission planning consists of evaluating the required information flows, resulting connectivity requirements and subsequently determining which data link platform assets are available to support the required missions.  An integrated multi-link network architecture / interface design must then be developed to satisfy the requirements of the operational commander, and the necessary configuration information must be provided to the operational units to allow them to implement the required multi-link network.  Early and full participation in the overall operational planning process is absolutely essential to the provision of functional TDL networks.

Dynamic planning is also absolutely essential.  While thorough planning of operations should minimise adverse affects, plans should always be expected to require dynamic modification in reaction to events.  The extent to which TDL plans can be dynamically managed depends on the architecture of the TDL Interface.  For example, a network should be changed only when the proposed modifications can reasonably be expected to reach the relevant platforms in time.  This might be a very short period of time for a Link 11 network but for Link 16, where terminal initialisations have to be changed, a significant time limit may apply.

OPTASK LINK

Successful operation of TDL networks requires that the terminals of all participating units are provided with parameters which ensure a common definition of network characteristics; allocation of transmission time slots (where applicable), and coordination of crypto-variable usage on secure Links. 

Once the TDL configuration has been designed as part of the overall planning and approved the OPTASK LINK message is used to provide the detailed instructions necessary for each participating platform to initialise their systems and change existing information as required.

The JDLMO is now central to the operation of the TDL Interface and is the authority that will normally issue the OPTASK LINK for UK national operations.  The JDLMO will also provide liaison for NATO and coalition operations as necessary.  The JDLMO may delegate some aspects of TDL operations to appropriate command elements or platforms within the TDL Interface but this will usually only be for immediate management activity for a particular TDL.

The OPTASK LINK itself allocates specific data link duties and responsibilities to appropriate TDL participants.  If the planning process has operated properly, these duties and responsibilities must align with other elements of the formatted message system such as the OPGEN.  The OPTASK LINK covers Link 1, Link 4, Link 11, Link 11B, Link 14, MIDS / JTIDS (Link 16 / IJMS), ATDL-1, and National Links such as RN Satellite Link 16.  The detailed OPTASK LINK format and user instructions are contained in APP-11, which is the superior document for the OPTASK LINK format.

TDL Coordinating Authority (TDLCA) / Joint Interface Control Officer (JICO)

The TDLCA and JICO are terms that may be encountered in TDL operations and both are recognised by NATO.  Current UK Joint Service documentation states that once nominated, the TDLCA will take Coordinating Authority responsibility for the immediate planning and conduct of TDL operations across the [involved] Components.  Since the preponderance of UK Joint TDL operations can be expected to be in support of Air Defence operations, this responsibility will normally fall to the Air Defence Commander (ADC). The TDLCA will normally form a TDL Planning and Coordination cell, led by a Data Link Manager (DLM), also known as the Joint Interface Control Officer (JICO) by the US, to exercise this responsibility.

Since publication of the Joint Service documentation, the UK has established the JDLMO as the permanent UK formation with TDLCA status and only the term JDLMO need be used.   The JDLMO will provide personnel (detached as necessary) to act as the DLM, issuing the OPTASK LINK and monitoring the status of TDL operations in real-time to ensure that appropriate connectivity is maintained between cooperating forces.

The Joint Commander is responsible for the overall planning and provision of TDLs.  However, responsibility for their usage and day-to-day control will normally be delegated through the JTFC to the most appropriate CC capable of acting as TDLCA / DLM for OOA operations.  PJHQ J6 staff will, nevertheless, remain responsible for ensuring that the JTFC’s in-theatre requirements are met.  In particular, the PJHQ will ensure that advanced planning and preparation for the deployment of appropriate TDL assets is undertaken.  Normally, this task will be delegated to the Supporting Commander best equipped to carry out this task (usually, either CINC STC or CINCFLEET).  Once nominated by the JTFC, the TDLCA / DLM will take Coordinating Authority responsibility for the immediate planning and conduct of TDL operations across the Components. However, this situation may change in the future as ISR assets begin to use TDLs to a much greater extent.  The CC and JDLMO specialist personnel acting as the TDLCA / DLM provide a UK organisation that equates to the US JICO system.

The TDLCA / DLM is responsible for:

·                     Ensuring coordinated, accurate and timely TDL operations.

·                     Ensuring effective data flow within and between the TDLs.

·                     Delegating appropriate tactical TDL C2 functions to subordinate TDL users.

·                     Monitoring and ensuring that the TDL network complies with the JTFC’s Electronic Emission Control (EMCON) policy and any appropriate civil transmission or frequency restrictions

Future TDL Migration Typical Current TDL Network

Radio or landline voice communications must be used to overcome shortfalls in automatic data exchange and some interfacing between different TDLs must be carried out by ‘swivel chair’.

UK Migration Strategy

Ideally, a single TDL message standard would be implemented fully across all UK and allied platforms, but technical limitations, evolving capabilities, operational requirements, national considerations and cost, all conspire to prevent this from happening.  Link 16 has been chosen as the UK’s preferred link for the future, but it is expensive and cannot fulfil all operational requirements.  In particular, Link 16 is restricted to Ultra High Frequency Line-Of-Sight (UHF LOS), but the RN has a continuing requirement for Beyond Line-Of-Sight (BLOS) communications when Link 16 relay platforms are not available; unfortunately, High Frequency (HF) does not have sufficient bandwidth to implement Link 16 and so Link 22 has had to be developed.  Additionally, it would be prohibitively expensive to implement Link 16 in all land vehicles and so the cheaper modem-based TDLs such as Variable Message Format (VMF) will be used by land platforms to supplement the facilities offered by Bowman radios.  It would also be wasteful to use Link 16 to interconnect static facilities and so Air C2 System-Wide Exchange Standard (AWCIES) will be used within the NATO Air C2 System (ACCS) programme.  Finally, Surveillance and Control Data Link (SCDL) will be used for high volume imagery information, such as that derived from ASTOR Synthetic Aperture Radar (SAR) and Moving Target Indicator (MTI) equipment.

Typical Future TDL Network (circa 2020)

 

TDL Issues

 

Interoperability

In the context of the information exchange, interoperability means that a system, unit or forces of any service or nation can transmit data to and receive data from any other system, unit or forces of any service or nation, and use the exchanged data to operate effectively together.  Interoperability is the key to the entire TDL integration process.  The level of interoperability achieved can be considered in a number of different layers.  A large number of different aspects of the system must fit together in order that all the levels of interoperability are achieved.  In addition to achieving the physical transfer of messages between platforms (Radio Frequency (RF) Interoperability), it is essential that the messages sent over the link contain the data necessary to achieve the IER (Data Interoperability) and that they conform with the protocols defined for Link operation (Protocol Interoperability).  The information contained in the messages must also complement the operational procedures defined for conducting the mission, task or battle.  Finally, on reception, the information must be displayed and interpreted correctly by the receiving operators (Human Computer Interface (HCI) and ‘Brain-to-Brain’ Interoperability) and, if appropriate, forwarded onto other TDLs in a correct and timely manner so that an entire force can share the same tactical information at the same time.  To achieve interoperability, it is essential that agreed standards are laid down and followed.  TDL documentation comprises a suite of NATO, national and individual platform documents.  An overview of this documentation is given in Appendix B.  However, subscribing to standards does not, of itself, guarantee interoperability because dissimilar platforms have different capabilities and they may not implement the agreed standards in the same way or to the same degree.

Network Management

Correct platform implementation, effective participant preparation and adherence to agreed procedures should ensure that TDL operations are largely transparent to end-users.  However, complete adherence to these principles is rarely achieved and dynamic network management may be needed to identify and correct problems as they occur.  Facilities are therefore required to monitor the conduct of TDL operations, to recognise abnormal data exchanges, to identify the source of any errors and to implement timely corrective measures.  The integrity of the network as a whole may sometimes take priority over the needs of a single participant and, if a workable solution cannot be found, non-compliant platforms should be considered for exclusion from the network.

OPNET Management 

Operational NETwork (OPNET) Management is the real-time, on-line monitoring and maintenance of TDL operations. OPNET Management includes monitoring and analysing network and platform parameters, and reassignment of network functions (Network Time Reference (NTR), Initial Entry MIDS / JTIDS Unit (IEJU), Navigation Controller (NC) / Secondary Navigation Controller (SNC), etc) and assets (timeslot allocations, etc).  The aim of OPNET Management is to achieve and maintain optimal network performance and information exchange by monitoring the interface, and responding quickly and efficiently to changes in network use, MIDS / JTIDS Unit (JU) availability and JU geographic distribution.

Voice Coordination

Although most TDLs have built-in mechanisms for managing each of their networks, voice coordination remains essential and must be considered to be part of the total interface, albeit that the actual voice net used will vary with the size and complexity of the data link architecture it supports.  If circumstances demand, different voice net functions may have to be carried out on the same voice circuit.

Timeliness

The term real-time is often taken to mean the provision of a quick or an immediate response, but a better concept is one of timeliness in which data is acquired and processed in ‘real-time’ such that situations may be dealt with, as they develop, in a timely and effective manner.  Different tasks will have different time requirements.  For example, several minutes may be available to react to the sighting of slow moving enemy vehicles, but only seconds may be available to deal with penetrating enemy aircraft.  More demanding still will be the coordination and cueing of weapons systems from a variety of remote sensors.  Data links must therefore be configured and managed to ensure that the latency of key information is minimised; where appropriate, some data reporting may need to be constrained to avoid slow update cycles.  It may also be necessary to restrict certain functions to specific links (e.g. ASW to Link 11 and AAW to Link 16), rather than duplicate data on all TDLs.

Cooperative Engagement Capability (CEC) 

CEC is a USN C2 Air Defence platform capability that exchanges active radar plot data between CEC platforms. The data is independently processed at each unit by common software processes into composite tracks that are thus sourced from a number of active sensors.  Common processing such as position, IFF and kinematic data is also used to establish common Identity.  This system increases the accuracy of object tracking to a degree sufficient to allow a platform’s weapon system to be cued and directed using other platforms sensor data even if the weapon system platform does not itself have sensor contact with the object.

Common Tactical Picture (CTP) 

The CTP is compiled as a result of the frequent and accurate exchange of tactical information between cooperating platforms.  The CTP allows the detailed coordination of platform activity and weapon employment (e.g. target allocations between Link 16 equipped fighters operating within a Fighter Engagement Zone (FEZ).  Historically the CTP was first compiled using voice reports, data exchanged being limited by the abilities of operators to handle voice exchanges.  TDLs have significantly enhanced this process although other sources of data are also used.

Recognised Air Picture (RAP) or Recognised Maritime Picture (RMP) 

The RAP is an electronically-produced display from primary radar, secondary radar and ESM sources covering a three-dimensional volume of interest in which all detected air and surface contacts have been evaluated against specific threat parameters and then assigned a recognition category and track number.  The RAP is usually disseminated using TDLs to provide support for operations and missions in the air environment.

The RMP is the fullest achievable agreed level of identification and tracking of all surface and sub-surface contacts in the area of interest.  TDLs will be used to assist in disseminating the RMP. The RMP is normally associated with the RAP of the same area but may extend further and includes data, not necessarily real-time, from other sources.

Joint Operational Picture  (JOP)

The compilation of current intelligence, force deployments, logistical and tactical information to aid decision-making and control at the operational level.

Relay Requirements

Many TDLs are carried on UHF bearers and are thus constrained by radio horizon and LOS limitations, typically around 300nm.  MIDS / JTIDS Link 16 can, however, achieve air-to-air ranges of 500nm in extended range mode, although only with a reduction of data capacity and lessening of Electronic Counter Measures (ECM) resistance.  Surface-to-surface and surface-to-air ranges will be much shorter.  In most cases, these ranges will not be sufficient to meet theatre-wide operational needs and, consequently, Link 16 relays will be required. Operation of other TDLs, such as Link 11 at HF can be utilised.  For many TDL operations, suitable airborne platforms must, therefore, be tasked to carry out the relay mission throughout the expected period of TDL operation.  These platforms will be those with multiple radio capability and long endurance and, as such, are currently likely to be large High Value Assets (HVA)s which, to meet the needs of relay, may need to be positioned in sub-optimal locations for their primary role (including in areas of increased threat).  For this reason, dedicated UAVs may provide the best solution in the future.

Data Looping

Data looping is the unnecessary reception of the same data by an Interface Unit from two or more TDL paths.  To avoid looping, it is necessary to ensure that only one data forwarder is established for any one specified connectivity path.  Special protocols have to be observed by CIUs including ensuring that data transmitted by a CIU is not forwarded and that CIUs do not process data that has been forwarded.

Emission Control

Most TDL operations depend upon using electronic emissions.  The EMCON policy for a JTF, which will be coordinated and promulgated by the JTFC, must therefore consider the requirements of TDL operations in order to establish a balance between the needs for surveillance / control and security / surprise.  Procedures for the rapid change of EMCON state should be promulgated by the JTFC, along with the level of authority to order such changes.  TDLs can also be used to help to overcome limitations imposed by EMCON restrictions.  For example, EMCON restrictions that compromise one element’s organic surveillance and warning capability may be ameliorated by TDL information from another element operating under less restrictive EMCON (e.g. air picture and AD warning information could be provided by an Airborne Warning and Control System (AWACS) ac to a maritime unit operating under emissions silence).

Track Number (TN) Assignment

The range of available TNs for the reporting of own unit and sensor tracks differs between TDLs.  A significant element in the pre-mission planning process to generate the OPTASK LINK is the assignment of unique blocks of TNs to each participating platform for surveillance and data forwarding.

Data Registration

Data registration is a condition of correct relative alignment between local and remote track positional data.  Three types of data registration exist as follows:

a.            Internal registration of own sensor data within a platform.

b.            Sensor registration where Link 16 PPLI data is used as a means for correcting locally produced track data to the Link 16 position reference (WGS 84).

c.            Remote registration where a TDL requires platforms to account for other platform's errors upon reception.   

Link 11 has a form of remote registration that is similar to that used by Link 16.  However this is not the same process as the Link 11 Gridlock which may be implemented quite differently in different Link 11 platforms.  Note that there is no use of a common grid between Link 11 and Link 16 and that forwarding units do not adjust forwarded track reports to account for differences between the two TDLs.

Air Control

Air control refers to the function of a unit controlling one or more aircraft.  Control may be made through digital or voice means.  Voice control of high performance aircraft has the advantages that controller intentions can be made as explicit as language allows and information and orders can be broadcast and received by all units listening to the radio channel.  The disadvantages, however, are a lack of EMCON facilities, vulnerability to ECM and the need to duplicate verbal instructions and orders onto data links for the wider dissemination of target allocations and engagement intentions.  By contrast, digital control allows for secure, ECM resistant transmissions, whilst also allowing for the dissemination of this data onto other data links.  However, digital control is limited by the need for platforms to process pre-formatted messages, which requires the coordinated implementation by all units of the applicable message standards.

TDL Frequency Clearance Requirements

In order for a TDL user to transmit data, clearance to radiate or to use the appropriate part of the Electromagnetic (EM) spectrum must be obtained from the relevant military authorities; this is generally only applicable during peacetime operations.  For those TDL bearers that operate in the standard voice communication parts of the spectrum, such as Link 11 UHF and HF, clearance to use particular frequencies and waveforms is given by the allocation of the appropriate (in this case) UHF or HF frequencies in the OPTASK LINK or OPTASK COMMS.  Permission to use the selected radio frequencies will have been obtained by the originator of the OPTASK, normally from a standing list of allocated frequencies.

JTIDS / MIDS Restrictions

JTIDS / MIDS is, however, a special case in that this TDL radiates in part of the spectrum in which civil aviation navaids and identification systems radiate and that is owned by the national civil aviation authorities.  JTIDS / MIDS transmissions are required to operate on a non-interference basis with these civil systems (Distance Measuring Equipment (DME), Identification Friend or Foe (IFF) and Global Positional System (GPS)).  Tactical Air Navigation (TACAN) is a military system that makes use of combined military DME and VOR transmissions and is thus subject to the same DME restrictions.  The nature of JTIDS / MIDS transmissions and the need to guarantee non-interference requires a formal certification and radiation clearance process for JTIDS / MIDS users.  JTIDS / MIDS terminals are required to undergo a testing and certification process before being allowed to radiate.  The JDLMO is the military body with responsibility for ensuring observance of the civil requirements.

Time Slot Duty Factor (TSDF)  

Frequency clearance agreements define the total emissions which can be generated by a MIDS community within a given geographic area, and also the number of emissions which can originate from a single source within that area. The terminology used to indicate the maximum or actual number of emissions is known as the TSDF and is usually represented in the form ‘m/n’ where ‘m’ is a percentage indicator of the maximum number of transmissions allowed for the total community, and ‘n’ is a percentage indicator of the maximum number of transmissions allowed for a single user – e.g. 100/50.  Some national frequency clearance agreements specify a three part TSDF, e.g. 100/50/20, where the third value represents alternative single user limitations. TSDF is calculated by counting time slots (100 TSDF represents 1536 time slots per 12 seconds); the ‘equivalent TSDF’ can be calculated by counting pulses (100 TSDF represents 396,288 pulses per 12 seconds).

Interference Protection Feature (IPF)

The JTIDS / MIDS terminal implements features to protect against inadvertent or incorrect operation thus providing Electro Magnetic Compatibility (EMC) with civil DME equipment.  In order to comply with frequency clearance restrictions, the terminal contains IPF software, which is set by operator action, as follows:

IPF 0 No Protect (Combat) 

The COMBAT mode offers no IPF protection.  This mode is not authorised for use during peacetime.  It is intended for combat or other extraordinary situations where operational requirements dictate.  In these cases, deviations in the distribution of limited frequencies, pulse width or energy emitted in the IFF band, which would otherwise result in the cessation of terminal operation in the full or partial IPF protection modes, will be allowed.

IPF 1 Partial Protect (Exercise)

This is the normal NATO mode of operation.  The terminal monitors its own emissions and automatically inhibits transmission if the following parameters do not meet specification requirements agreed by military and civilian aviation authorities:

·                     Frequency hop.

·                     Pulse width.

·                     Spurious emissions in the IFF guard bands.

IPF 2 Full Protect (Peacetime)  

This mode incorporates all protection features of IPF Partial Protect.  This mode also provides the following additional protection:

·                     Automatically inhibits transmissions if any attempt is made to transmit in more than 304 time slots (slightly less than 20% of the time slots).

·                     Prevents assignment of adjacent time slots or more than 608 time slots in a network (slightly less than 40% of the time slots).

·                     Prevents selection of the high power mode, multi-net operation and communications in other than Communications Mode 1.

·                     Prevents transmissions in disallowed time slots.

UK Frequency Clearance Agreement (FCA) 

The current UK FCA provides specific restrictions on JTIDS / MIDS operations within the UK FIR.   The restrictions are fall into two primary categories either for aircraft or for surface (maritime or land) platforms.  The restrictions apply limitations on the distances that either DME beacons or SSR installations should be avoided by while operating JTIDS / MIDS.  The differences in the two types of platforms restrictions are due to the length of time that platforms might spend affecting the DME or SSR installations.

The FCA is updated each year and restrictions are promulgated through single and joint service channels.  In order to avoid this document potentially being out of date the restriction details are therefore not promulgated in this document.