Vodavi XTS-IP, Installation Manual

Page: 83 / 196

CO/PBX Connections 3-43
Chapter 3 - System Installation
XTS-IP - Installation Manual
December 2005
ISDN and T1 Clocking
When combining BRIB, PRIB, and T1 cards in one KSU, specific settings and cabling are
important for proper clocking. The Phase Lock Loop circuitry within the MPB synchronizes
the clocking from the Central Office to the clocking of the KSU. Popping, crackling, dropped
calls, and one-way transmission are usually attributed to the clocking not being synchronized
correctly.
Set the clock source switch of LMU1 to the up position for T1 clock source chain and to the
down position for PRI/BRI clock source chain.
Examples - Settings and Cabling
The following examples clarify the clocking and cabling for these cards:
(1) T1IB and (1)PRIB
If both cards in a phone switch are connected to a telephone company clock (not
point-to-point T1), put the T1 clock switch in the enable position (UP) to allow it to receive
clocking from the telephone company directly, and do not install the clock cable.
Set the PRIB clock switch in the disable position (OFF), which allows the PRIB to synchronize
its timing off of the backplane (from the T1 clocking). If the T1 is a point-to-point T1, set the
PRIB in the enable position (ON), the T1 in the disable position (OFF), and do not install the
clock cable.
If using a point-to-point connection (e.g., networking), do not connect clock cable
to a point-to-point circuit.
When the switch is in the “up” position, it should be considered “ON”. When the
switch is in the “down” position, it should be considered “OFF”.
The cable connection follows the same logic - “up” is clock outside (ON) and “down”
is clock inside (OFF). ON means that clocking is coming from outside the KSU and
OFF means that clocking is coming from inside the KSU.