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V100 Versatile Multiplexer Technical Manual Version 2.2
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Relay (SVR) card has the same footprint as the voice daughtercard and attaches in the same way to the
voice motherboard. On the rear panel, connectors 1 to 4 only are activated.
When fitted, the SVR card operates transparently with the analogue voice motherboard with no user
intervention and does not restrict any of the normal clear voice functions normally available from the
V100. All normal forms of analogue traffic are therefore still supported, including fax and data modem
relay. All four channels may be operated with or without STU traffic, with different compression algorithms
and with different line interfaces, just as before.
STU-IIB or STU-III telephones may be operated in secure mode at three digitisation rates; 2400bps,
4800bps or 9600bps. The V100 SVR card requires 5200bps, 7600bps and 12400bps to perform the relay
function at each rate respectively and so when in relay mode, a slightly higher bandwidth is use by the
channel. It is advisable to take this into consideration when planning bandwidth budgets.
In operation it is normal to establish a non-secure call from the connected Secure Telephone Unit (STU) in
the normal way. Once established, the users confirm their identity verbally and then enter secure mode at
either end. During this process, the STU devices perform a training sequence similar to that of a dialup
modem, which is demodulated, transferred by the V100 to the remote end and remodulated in both
directions. Once the training sequence is complete, the STU devices send encrypted data to each other
transparently via the V100. When the call ends, the STU devices may either return to clear voice mode or
terminate the call in the normal way. At no time does the V100 decrypt or decipher the secure
information.
