3Com VCX V7122 User Manual page 211

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ETTINGS
The gateway can either generate its own timing signals, using an internal clock, or recover
them from one of the E1/T1 trunks.
To use the internal gateway clock source configure the following parameters:
TDMBusClockSource = 1
ClockMaster = 1 (for all gateway trunks)
To use the recovered clock option configure the following parameters:
TDMBusClockSource = 4
ClockMaster_x = 0 (for all "slave" gateway trunks connected to PBX#1)
ClockMaster_x = 1 (for all "master" gateway trunks connected to PBX#2)
Assuming that the gateway recovers its internal clock from one of the "slave" trunks
connected to PBX#1, and provides clock to PBX#2 on its "master" trunks.
In addition it is necessary to define from which of the "slave" trunks the gateway recovers its
clock:
TDMBusPSTNAutoClockEnable = 1 (the gateway automatically selects one of the
connected "slave" trunks)
Or
TDMBusLocalReference = # (Trunk index: 0 to 7, default = 0)
To configure the TDM Bus Clock Source parameters see
Settings on page 72.
3Com VCX V7122 SIP VoIP Gateway User Manual
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Configuring the TDM Bus
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