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Point-to-Point Connection Technology 155
PBX Networking
L1 Clock
To enable PBXs in the ISDN network to communicate with each
other, they must be “clock-aligned”. The L1 protocol master sets
the clock for layer 1, and the L1 protocol slave adopts (synchro-
nises to) this clock.
When planning a PBX networking scheme, you must make sure
that the L1 clock propagates from a master via a number of PBXs.
Example: propagation of the L1 clock
If more than one port with the setting L1 Type = “Slave” is con-
figured on an Forum 523/524 and the setting L1 sync possible
has been activated, then one of the ports is automatically defined
as the L1 clock source. The Forum 523/524 will automatically
switch the clock source to another port configured as an L1 clock
source (if a line fails, for example).
Please note: Reciprocal or circular application of the L1 clock is
not allowed.
Example: In the above case you could reverse the L1 slave/mas-
ter setting for the connection between PBX 1 and PBX 3. However,
if you then activate the setting
L1 sync possible for the port of
PBX 1, this may cause parts of the PBX network to stop function-
ing temporarily.
When applying the L1 clock of trunk lines, you can assume that
the public network is “clock-aligned”. So, in the above example,
you can connect additional trunk lines to one of the PBXs.
PBX 3
PBX 2
Point-to-point
connection
Trunk line
Network
operator
PBX1
M S
M
S
M
M
S
S