The AMO REFTA is used to edit the reference clock table (REFTA). The system references this table which contains the interfaces used for synchronization with the corresponding priorities. The priorities define which interface and priority must be used for synchronization for every system. It also defines the sequence in the case of possible failures. Also the interfaces are defined which are never used or only for special error cases occurring in the network during a synchronization process.

The safety equipment processes the error counter according to a patented procedure. The error counters generally provide the network provider with important information about the layer-1 quality of the network connections. The reference clock table provides a complete overview of the synchronization state of the system. Comparing different reference clock tables with the network synchronization plan provides a quick overview of the network situation with regard to synchronization and layer-1 errors.

The points are weighted in the error counters according to their importance for the synchronization quality and increased for transmission if the errors occurred in layer 1. The error counters are reduced by 5% at hourly intervals as long as the system is synchronous. The error counters therefore always show quality differences for the interface and thus for the connected equipment and routes in relation to the last hours. Serious errors remain visible over a longer period of time (1 to 2 days). As soon as the error counter for an interface is no longer 0, the "History error messages" file containing error messages for the relevant interfaces should be consulted. The OpenScape 4000 error messages can be used to find network errors - even in the transmission network and transmission equipment.

A bit slip, for example, is penalized with 150 points, a short interrupt < 1 sec with 1,500 points, a longer interrupt with 1,500 points x seconds, an excessive frequency departure during regulation start or an excessive jitter with 32,000 points. A record contains 16,000 points at startup. A record is not accepted - even if it has the highest priority - once the error counter exceeds 42,000 points. A record of this kind is accepted after a minimum of 30 minutes and "paroled" with error points below 42,000 if it has the highest priority.

If no records can be referenced (during tests) because of error counters, all error counters are halved.

In special cases, the barring column (= YES or = NO) provides a means of direct access for quick intervention in network synchronization. It is mainly used in rare network errors to turn the synchronization direction without the need to switch off the remaining interfaces. Setting the disable function to "YES" for a record with a certain priority has the same effect as setting the priority to 0. As priority changes from and to zero are possible by simply switching the record on and off, turning the synchronization direction in these rare network errors by switching on and off the interfaces would be unreasonable.

Clock supplier: The selected interface used for synchronization is marked "X" in the REFTA.

Only one clock supplier can be active for LTUs 1-15. As LTUs 17-99 (IPDAs) are connected asynchronously via LAN, synchronization is not possible with the system's central clock generator. Consequently, a separate IPDA can be selected in each interface and used for synchronization. This is also marked "X" in the REFTA.