Polycom MGC Administrator Administrator's Manual page 369

The list of network types that can be connected to the MCU is displayed
in the Item=Value box.
3. Click on the network type to be used for clocking in the Item = Value
box. The following table describes which network type should be
selected for clocking when the MCU is connected to various networks.
Table 5-16: Clocking Options
Networks
connected to
the MCU
ISDN only or
ISDN with any of
the following
networks: ATM,
H.323, MPI
ATM only
H.323 only
Network selected
Notes
for clocking
ISDN The primary and the backup
clock must be set on spans of
the same network type.
Internal Clock
Internal Clock
MGC Administrator's Guide
5-133