User guide

Point-to-Point Connection Technology154
PBX Networking
Point-to-Point Connection
Technology
Protocol: Q.SIG or DSS1
The Q.SIG protocol, designed for ISDN point-to-point connections,
is the preferable choice as the transmission protocol; alterna-
tively, the DSS1 protocol, designed for ISDN dial-up connections
in the Euro-ISDN, can be used. Certain PBX networking features
can only be used with the Q.SIG protocol, however. In particular,
the connection designation as internal or external call and also the
name of the caller cannot be transmitted via the DSS1 protocol.
Both protocols implement communication on several protocol layers:
z L1: Layer 1 defines the physical line properties and the
electrical coding of signals.
z L2: Layer 2 enables communication via individual error-
protected channels that are independent of each other.
z L3: Layer 3 defines the administration of the individual
channels and implements the features designed for ISDN.
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 protocol 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. Nor-
mally 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.