Aastra OpenCom 130 User Guide - Page 157
Master/Slave, 12.1.3 L1 Clock, Connection via, Q.SIG.IP, Example: propagation of the L1 clock
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PBX Networking Connections Note: All layers of the Q.SIG-IP protocol are symmetrical. The following are unnecessary: a Master/Slave setting, clock and synchronisation settings (please refer to Connection via Q.SIG.IP starting on page 158). 12.1.2 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. 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 S2M 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 S0 lines this setting is determined by "L3 master" for both B-channels. 12.1.3 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. Network operator M PBX1 S M M PBX 3 S S S PBX 2 M Trunk line Point-to-point connection Example: propagation of the L1 clock 155