5.20.2. Methods of Preventing Network Loops 
- Method: Prevention of network loops by checking for prohibited connections in the
node
connecting matrix. Potential loops can be avoided right from the network planning
stage. For
this purpose, specific connections are barred in a node connecting matrix based on
virtual
originating/destination node numbers. This matrix, which is initialized to permit
all
connections, is administered by AMO KNMAT. The check for prohibited connections is
carried
out in all nodes involved in a connection. When applying this method, note the following
carefully:
- The traffic paths are restricted; this can adversely affect the load distribution in the network.
- Not all loops can be prevented.
- CONN=D is set for all NPIs.
- Method: Limitation of network loops with TRANSIT-COUNTER This counter prevents endless loops in the network. Threshold values are set for incoming circuits or trunk groups in each node. In each transit node the currently active counter in the network protocol is incremented and compared with the threshold value. If the threshold value is reached, the connection is cleared and an advisory issued. If nodes of variants up to and including Hicom 3000 V3.2 are involved in a connection, the TRANSIT-COUNTER information is lost. In general, a connection (or several connections) cannot be set up if a threshold value is set too low.
- Method: Prevention of network loops by temporarily reducing classes of service. LCR classes of service can be reduced or removed using the AMO KNLCR for combinations of virtual originating and destination nodes. This prevents occupation of a specific LCR route or generally prevents further routing in this network node for combinations of virtual originating and destination nodes.