Connecting modern computers to legacy tactical equipment

System integrators and engineers can link the old to the new with ATDS and NTDS interface boards.

Before the advent of radio technology, a warfighter’s view of the battlefield was limited to line of sight and information provided by scouts. It was impossible to have a real-time, wide angle view of the theater. Nowadays, organizations like NATO use several radio links to exchange real-time tactical information between aircraft, land vehicles, and ships, extending detection capabilities.

Link-11 (also known as TADIL A) is a digital radio link NATO has used for decades. Although military links have progressed with Link-16 and Link-22, there remain field systems that require Link-11 support. Using high-frequency (HF) or ultra-high-frequency (UHF) radios, Link-11 is half-duplex and operates in polled mode, where only one net participant is permitted to broadcast tactical information at any given time. A designated Net Control Station governs the broadcast order. Each participant on the Link-11 network consists of two components – the Tactical Data System (DTS) computer that receives data from sensors, navigation systems, and operators, and forwards them over a wired, point-to-point data link to the Data Terminal Set (DTS) for distribution to net participants over the radio.

In the opposite direction, the DTS retrieves incoming tactical digital information from other net participants and forwards it to the TDS for processing. The data link between TDS and DTS may be serial or parallel. MIL-STD-188-203-1A specifies the serial link as Airborne Tactical Data Systems (ATDS) and the parallel, Naval Tactical Data Systems (NTDS).

Connecting to modern systems

Since Link-11’s introduction in the early 1960s, computing capabilities have advanced tremendously, providing faster information processing. However, many modern computers still need to interface with legacy equipment. To accomplish this, system integrators and engineers can add ATDS and NTDS interface boards. When selecting an interface board, form factor availability and multi-OS support are two factors to consider. Availability and support for a large number of buses and operating systems enable developers to target more market segments.

Military network topology has changed since Link-11 was originally developed. Militaries worldwide now gravitate toward linking systems together through Ethernet-based networks instead of point-to-point interfaces such as ATDS. However, due to risk mitigation and budget cuts, organizations often require connecting legacy equipment to Ethernet. Because it may not be feasible to add Ethernet interfaces to legacy equipment, an independent converter box like the IXI ATDS-to-Ethernet converter may need to sit between the legacy equipment and network.

The legacy equipment uses ATDS to connect to the converter which then forwards the data over Ethernet. Since Ethernet is inherently unsecure, the ATDS-to-Ethernet converter should encrypt all Ethernet data, protecting the tactical data against network adversaries. Another challenge with Ethernet is that packets may drop before reaching their destinations when using a UDP based protocol. The ATDS-to-Ethernet converter may offer a redundant Ethernet capability to significantly increase network reliability. If one network path is not available, operation continues without delay or interruption on the surviving path.

Due to signal degradation, short cables are typically used to connect ATDS equipment. Yet organizations may require linking two ATDS components separated by great distances. For example, the TDS and DTS may be located on opposite ends of an aircraft or in different rooms in a simulation laboratory. These hurdles can be overcome by bridging two ATDS-to-Ethernet converters through Ethernet, and then linking each converter to the ATDS equipment. ATDS data is translated to Ethernet packets on one converter and then translated back to ATDS on the second converter. The converters are typically mounted near the legacy equipment to make the ATDS cable run as short as possible. With this strategy, ATDS equipment that resides miles apart, even in different cities, can communicate with one another.

TDS and DTS equipment interfaces through ATDS or NTDS. Typically, legacy equipment has one interface but not the other, preventing for example an ATDS TDS from connecting directly to an NTDS DTS. However, organizations may desire to link this equipment, particularly if budget constraints prohibit procuring additional assets. One solution is to use an NTDS-to-ATDS bridge, which provides a transparent hardware and protocol conversion, allowing TDS and DTS equipment to communicate over heterogeneous data links.

Budget constraints extend the service life of legacy equipment and restrict acquisition of newer equipment. The U.S. military began replacing the Link-11 system in the early 1980s, yet legacy equipment is still being used and maintained. As militaries across the globe migrate toward open architecture communication interfaces such as Ethernet, solutions such as ATDS interface boards, ATDS-to-Ethernet converters, and NTDS-to-ATDS bridges can help organizations meet these challenges.
IXI Technology
About the author: Bryan Ly is senior software engineer at IXI Technology.

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