User's Manual 264 Document #: LTRT-68822
Mediant 2000
3. Click Submit to apply your changes.
4. Save the changes to flash memory, see 'Saving Configuration' on page 396.
21.2.2 Clock Settings
In a traditional TDM service network such as PSTN, both ends of the TDM connection must
be synchronized. If synchronization is not achieved, voice frames are either dropped (to
prevent a buffer overflow condition) or inserted (to prevent an underflow condition). In both
cases, connection quality and reliability is affected.
PSTN line clock (see 'Recovering Clock from PSTN Line' on page 264)
Internal clock (see 'Configuring Internal Clock as Clock Source' on page 265)
Note: When the device is used in a ‘non-span’ configuration, the internal device clock
must be used (as explained above).
21.2.2.1 Recovering Clock from PSTN Line Interface
This section provides a brief description for configuring synchronization based on
recovering clock from the PSTN line (Trunk) interface. For a full description of the clock
parameters, see 'PSTN Parameters' on page 619.
To configure synchronization based on clock from PSTN line:
1. In the TDM Bus Settings page, do the following:
a. Set the 'TDM Bus Clock Source' parameter (TDMBusClockSource) to Network to
recover the clock from the line interface.
b. Select the trunk from which the clock is derived, using the 'TDM Bus Local
Reference' parameter (TDMBusLocalReference).
Note: The E1/T1 trunk should recover the clock from the remote side (see below
description of the 'Clock Master' parameter).
c. Enable automatic switchover to the next available "slave" trunk if the device
detects that the local-reference trunk is no longer capable of supplying the clock
to the system:
a. Set the 'TDM Bus PSTN Auto FallBack Clock' parameter
(TDMBusPSTNAutoClockEnable) to Enable.
b. Enable the device to switch back to a previous trunk that returns to service if
it has higher switchover priority, using the 'TDM Bus PSTN Auto Clock
Reverting' parameter (TDMBusPSTNAutoClockRevertingEnable).
c. In the Trunk Settings page, configure the priority level of the trunk for taking
over as a local-reference trunk, using the 'Auto Clock Trunk Priority'
parameter (AutoClockTrunkPriority).
2. Set the PSTN trunk to recover/derive clock from/to the remote side of the PSTN trunk
(i.e. clock slave or clock master): In the Trunk Settings page, set the 'Clock Master'
parameter (ClockMaster) to one of the following:
• Recovered - to recover clock (i.e. slave)
• Generated - to transmit clock (i.e. master)
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