Point-to-Point Connection Lines
PBX Networking
137
The external S
0
-ports of a gateway can also be used for a direct connection.
Connection via an Active Transmission System
For distances exceeding the range of a direct connection, an active trans-
mission system can increase the range to up to 50 km. Normally the L1 master
is the transmission system for the two connected PBXs. For the protocol
layers L2 and L3, one PBX is normally the protocol master and the other PBX
is the protocol slave.
Connection by an active transmission system
Note:
The active transmission system itself gets its L1 clock either
from the network operator or from a clock generator connected
by wire.
Connection via the Public Network
Point-to-point connections via the public network of a network operator can
be used for bridging distances beyond 50 km. Due to the long distance
involved, for technical reasons it is not possible to synchronise the L2 protocol.
Consequently, the public network is normally the protocol master for protocol
layers L1 and L2. One PBX is therefore the L3 master and the other PBX the
L3 slave.
Point-to-point connection via a public network
PBX 1
L1 slave
L2 master
L3 master
PBX 2
L1 slave
L2 slave
L3 slave
Transmission
System
L1 master
PBX 1
L1 slave
L2 slave
L3 master
PBX 2
L1 slave
L2 slave
L3 slave
Public
network
L1 master
L2 master