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Hardware decode/mux/recode

The hardware mux path in the CMMC is implemented using the following equipment:

• A AVS 32x32 crossbar video switch controlled from a SparcStation over an RS232 link. The switch is a "dumb" device, in that it cannot be polled as to its state, so switch state information is stored in a switching server running on the SparcStation. The switch needs to be accessed by both manual and CMMC applications, and hence it's API is an RPC mechanism.
• A Panasonic Quad video multiplexor
• Two GPT video systems System 261 video codecs.
• Two BT video codecs. For most purposes the BT and GPT codecs are similar equivalent. Each codec is controlled over an RS232 line from a SparcStation, which is used to set the clock rate, data rate, coding mode, audio mode and so on.

  Each codec supports two primary data interfaces - RS449 and G703 - and is switchable between the two over the control port from software running on the controlling SparcStation. For use over the internet, a codec is connected via it's RS449 interface to a Sun High-speed Serial Interface (HSI) card in a SparcStation. The SparcStation the runs conversion software to remove the H.221 serial line framing protocol ready for packetisation and transmission, and to re-insert it on the received video stream.

  For use over primary rate ISDN, the codec is connected by its G703 interface to a 3-NET ISDN bonding box, which allows multiple basic rate ISDN channels to be used as if they were a single higher rate channel.

  One of the BT codecs has an ISDA card, which provides two 64Kb/s X21 outputs. These are connected to a Newbridge ISDN terminal adaptor, which allows this codec to be used over a basic rate ISDN channel at 64 or 128Kb/s.

• A 3-NET primary-rate ISDN bonding box - this will eventually be controlled over an RS232 line from a SparcStation.
• A Newbridge 1206-S MainStreet ISDN-X21 Terminal Adaptor, controlled over an RS232 line from a SparcStation.
• A Tandberg basic rate ISDN video phone, on loan from NTR.
• A 4 way n-1 audio mixer, connected to the video matrix switch. This allows us to mix audio from distributed applications such as VAT with audio from ISDN video codecs without causing immediate feedback problems. (secondary feedback problems can however still occur).