Many kinds of high-performance embedded computing systems in the military market have an appetite for high-speed data from sensors. Often such input is presented as one or more channels of analog data, and, in some cases, the sensor data is provided directly to the processing system. However, in other cases, the sensor data is converted to digital data by a smaller system near the sensor itself and then sent over one or more fiber optic links to the processing system. For these applications, Serial Front Panel Data Port (FPDP), or ANSI/VITA 17.1-2003, provides a simple point-to-point protocol with low overhead, high throughput and minimum latency.

Serial FPDP overcomes a key limitation of parallel FPDP: its distance limitations. It does so by using a serial interface based on the Fibre Channel physical layer. Serial FPDP retains the frame format of the original standard thus simplifying the exchange of data between parallel and serial implementations. As a result, Serial FPDP makes it easy to exchange data from local chassis and legacy systems using parallel interfaces to remote chassis through a Serial FPDP connection.

When Serial FPDP was originally deployed, it was based on the fiber optic transceivers that were readily available at the time. The fastest version of Serial FPDP uses a bit rate of 2.5 Gbaud, providing of 247 Mbytes/s after 8B/10B encoding. As sensor technology improved, the sensor-to-processor interface often combined multiple Serial FPDP links to meet the ever increasing need for bandwidth. Although this approach provides the necessary throughput, it adds complexity at both ends of the link to manage splitting the data at the source and then aligning the resulting fiber optic streams at the destination. Because there is no standard method for doing this, link aggregation becomes an application-specific part of the problem.

The latest version of Serial FPDP, VITA 17.2, addresses these requirements in two ways. First, the choices for raw bit rates are expanded to include 3.125, 4.25, 5.0 and 6.25 Gbaud, allowing each link to operate up to 2.5x faster than before. Second, the standard now includes the capability to aggregate links in sets of 1x, 2x, 4x, 6x, 8x or 12x, allowing a single logical link to consist of multiple underlying physical links. The net result is that a stream of sensor data of up to 75 Gbaud (7.5 Gbytes/s) can now be considered a single Serial FPDP link.

Sonar is among the key applications that have used FPDP, including such major sonar upgrade programs as the SQQ-89 sonar upgrade for the guided missile (DDG) class of destroyers, the sonar for the New Attack Submarine (NSSN) and the P3 Aircraft. The SQQ-89 Sonar transmit and receive systems are used on Arleigh Burke Class (Aegis) Guided Missile Destroyers. The sonar suite aboard the vessel class is the Lockheed Martin SQQ-89(V)6, which includes Edo Corporation AN/SQS-53C bow-mounted active search and attack sonar and the AN/SQR-19B passive towed array. The suite was upgraded to SQQ-89(V)15 to allow deployment of the Lockheed Martin AN/WLD-1 Remote Minehunting System (Figure 1).