PBX Networking
159
Master/Slave
For an ISDN connection, it is possible to determine which PBX is the protocol master
and which the protocol slave. This relationship can be determined for all three pro-
tocol layers independently of one another.
For each protocol layer, the PBX at the other end always has to be suitably configured.
If one PBX is the protocol master for a layer, the other PBX must be the protocol slave
for this same layer. Normally all three protocol layers are configured identically. In the
case of a trunk line, the network operator is the protocol master for all three layers.
Note
In the case of an S
2M
line, it is also possible to determine for each useful channel
which end can administer a channel (master = internally seized or slave = externally
seized). On S
0
lines this setting is determined by “L3 master” for both B-channels.
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 (synchronises 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 configured on an
OpenCom 100 and the setting L1 sync possible has been activated, then one of the
ports is automatically defined as the L1 clock source. The OpenCom 100 will automat-
ically 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.
PBX 3
PBX 2
Point-to-point
connection
Trunk line
Network
operator
PBX1
MS
M
S
M
M
S
S
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