C H A P T E R 5 A P P L I C A T I O N E X A M P L E S
V100 Versatile Multiplexer Technical Manual Version 2.2
Page 195 of 231
Unit 0 is configured to accept the stable receive link clock of 128Kbps (“Ext”) from Modem0, which is used
to clock data out of the Doppler buffer. This is turned around as the transmit clock (“RXC”) and given back
to modem as Terminal Timing, it is then sent over the satellite link to Modem1, which recovers the receive
clock and outputs it to V100 Unit1. Unit1 is configured to accept this receive clock (“Ext”), to use it as the
GRX reference (GRX source in CLOCKING menu) and then turn it around (TX clock set to “RXC”) and
output it back to Modem1 as Terminal Timing (“TT”). Modem1 sends this back via the satellite to Modem0
which recovers the receive clock and uses it to clock the Doppler buffer.
Once again, the programming of the clock references is essential to all tributary channels, since they must
use a clock reference to generate all local bit rates. In this example, the Global Receive clock bus (“GRX”)
takes the Port 1 Aggregate RX clock and Port 2, which will be used to connect a router, uses the GRX as
its reference for generating the RX router clock. To go one stage further and operate Port 2 dynamically,
the RX clock source is set to “DBA”. This allows the V100 to smoothly vary the RX clock on Port 2
according to traffic demand.
NOTE: In order to generate a Terminal Timing (“TT”) clock from pins 8 and 15 on the V100
DB15 Data Port 1 and 2 connectors, jumper links JP4 and JP5 on the V100 motherboard must
be set to position 1-2 (i.e. towards the front of the unit). This is their factory default setting, so
in most cases there is no need to remove the lid.
Modem Settings:
In the example above, two Paradise Datacom P300 modems may be used. Modem0 is used to generate
the network clock, since it has a /- 1ppm reference. On the “Change, Tx, Baseband” menu, select
“Continuous Data” then enter the baseband data rate, in this case “128000”. On the “Change, Tx,
Clocking” menu, the TX clock should be set to “TX CLOCK IN” which expects the transmit clock on the TT
clock pair. On the “Change, Rx, Buffer/Clocking” menu, the RX clock should be set to “INTERNAL”. This
will enable the “Change, Rx, Buffer/Clocking,Buffer Size” menu, which allows the user to select a buffer to
accommodate the incoming Doppler shift. Normally, 4mS per satellite transition is sufficient, i.e. a total of
8mS.
Modem1 recovers the clock from the satellite. On the “Change, Rx, Buffer/Clocking” menu, the RX clock
should be set to “SATELLITE” which will disable the Doppler buffer and output the RX clock on the “RT”
clock pair. On the “Change, Tx, Clocking” menu, the TX clock should be set to “TX CLOCK IN” so as to
accept the TT clock back in from the V100.
