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As stated earlier the switch used at UCL is an AVS 32x32 crossbar video switch, controlled from a SparcStation via an RS232 link. The switch is a dumb device which cannot be polled for its state, so a server is used. The server retains the state of the switch, allows connections to be made from an input to an output, breaks connections, and can allow secure access to the switch. It is important that only valid users can change the configuration of the switch, and so this functionality is not normally available directly outside the CMMC.
Within the CMMC, connection to the switch server is via a switch client that uses the SUN RPC mechanism. Many styles of client have been created; simple text, a graphical interface, and via the CMMC directly.
The switch client can send the following requests to the server:
The server responds to these requests by returning the current state of the switch. Due to the nature of the RPC mechanism, many clients can access the server and update its state. When a client changes the state of a connection, other clients may have previously made state changes, therefore the current switch state is returned. This allows connection of manual interfaces to the switch server to monitor the effects of the channel server requests, or to set up complex scenarios outside the scope of the Channel Server's policies.
The full details of this software are available on request, but are not presented here as the details are specific to the AVS switch.