An ideal application of physical layer switching is the development and system integration laboratory of a large defense and aerospace project. Typical of this would be the integration of the avionics system of a multi-role single seat, agile combat aircraft. The completed avionics system is made up of numerous subsystems, such as radars, missile warning, visual sensors, flight control, defensive aids, electronic warfare and so on. These are each designed and fully tested individually but their performance must be further tested and verified in a complete functional and representative electromagnetic environment during system integration. The process of integration is incremental and repetitive. As each new subsystem or software capability is added the system must be retested and, in the case of certain subsystems, the overall system might need to be simplified or reconfigured in order to properly test all of its functionality.

Each of the subsystems would be connected to the Physical Layer Switch once only, but routed to any others by changing the configuration. In the case of a combat aircraft, many such subsystems might use Fibre Channel in its arbitrated loop topology as this is the most efficient form of interconnection in the deployed configuration. However, in the laboratory this is not always the most convenient – if a subsystem is to be added to the loop, cables must be disconnected and the new subsystem hooked in. Using a Physical Layer Switch allows arbitrated loops to be created, modified and tested just by changing the configuration with the knowledge that the final integrated system will perform in just that same way when it is eventually deployed in the aircraft.

Physical Layer Switching (PLS) is analogous to an electronic patch panel which operates independently of any routing or link protocols encapsulated in the data transmissions. It can be used to switch serial/digital signals such as Fibre Channel, Ethernet, High Definition video, Firewire and Serial FPDP at up to 4.25Gbps from any input to any output or to any number of outputs (multicasting). Such a PLS passes the protocol completely transparently so that a signal “in” always results in the same signal “out”. A switch can have as many as 288 data ports plus an out-of-band Ethernet control port used to set up the pathways through the PLS and to read the results of periodic diagnostic testing. The routing of the switch can be changed at any time via the control port giving great flexibility in the way the switch can be used. Switches are available in fully packaged form, typically for use in a development laboratory, or are available in VMEbus or CompactPCI formats for deployment in harsh environments in embedded multi-computer systems and subsystems.