Black Box MWU2000-X21 - Manual (Page 60)

60
2.048Mbps Wireless Modem
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For fractional E1/T1, the LIU card performs the loopback. Both clock and data are looped
back. When the Master modem is set for loopback operation, the clock starts drifting from the
clock of the end equipment (under normal conditions, the system clock is supplied by the
Master end equipment). Eventually this will lead to error messages and the link will be
disconnected. Therefore, loopback tests on the Master side should be as short as possible and
should be limited to 1 to 2 minutes at the most. It is recommended to avoid performing
loopback test on the Master unit in Fractional E1/T1 applications, or alternatively to switch
the master/slave definitions of both sides for the duration of the test. For V.35 LIU and RS-
530/X.21 LIU configured to operate with an external clock, the end-equipment (or
alternatively a BER meter) should be connected to the unit during the test in order to supply
the required clock.
Line Interface Unit Type Menu
Table 3-8. Line Interface Unit Type Menu Options
MCP Parameters Menu
The MCP Parameters menu gives you access to the following parameters:
• Network ID
• Master-Slave
• Total Link Delay
• Modem Initialisation String
• Number of Links to Synchronize.