IEEE 1588, Grandmaster Switches and Xbar
In recent years people have moved away from proprietary and closed systems for Flight Test Instrumentation (FTI) networks, towards more open and commercially based systems centering around Ethernet. Issues such as synchronization and nondeterministic transport mechanisms that presented adoption problems can be overcome with IEEE-1588 – the Precision Time Protocol (PTP). Using PTP, a single Ethernet connection can be used for discovery, set-up, acquisition and synchronization. One device (the Grandmaster) synchronizes to the global positioning system (GPS) and then synchronizes each device on the network by accurately time stamping packets to and from each device. A PTP enabled data-acquisition system not only offers two channels on the same module sampled at the same time, or even two modules in the same chassis, or even two chassis on the same airframe – but two channels anywhere at the same time, thus drastically reducing the problem of data time correlation.
Xbar is the next generation switching architecture that blends the rugged and live on power-up performance with a flexible crossbar architecture (currently available in the NET/SWI/003). The Xbar technology allows static forwarding tables to be defined and features sophisticated filtering hardware to create high performance Ethernet switches with flexible forwarding and filtering configurations.
In the simple example below, four network devices (DAU-Analog, DAU-Video, Recorder, and an Ethernet-to-PCM gateway) are interconnected through a four port switch. The user-defined static forwarding table used in the Xbar switching fabric is shown as dashed circles. The red points show which devices are connected together and these can be reconfigured at any time by the user. In this example, Ethernet streams from the DAU-Analog are forwarded to both the Recorder and PCM gateway. Ethernet streams from the DAU-Video are forwarded only to the Recorder.