In principle, the IP distributed architecture is dependent on the availability of the IP network. If the IP connection fails between two access points or between the central OpenScape 4000 switch and an access point, no payload connections are possible via IP.

Also, separation of signaling and payload streams is required very often by customers in the following scenario:

The aspect of signaling between the CO and the access point is covered in Section 2.6, “Signaling Survivability”.

If control of the access point is safeguarded through signaling survivability, calls can be made within the access point in all cases. External calls via trunks or tie trunks in other systems are possible if the corresponding connection modules are located in this access point.

Payload survivability uses existing trunks in order to establish payload connections with other access points or with the OpenScape 4000 central system independently of the IP network. In this context, the system calls itself via the trunk.

The procedure followed for payload survivability between a local subscriber and a CO/tie trunk circuit is route-specific.

If the call comes in via the CO/tie trunk circuit, a trunk call is established between the source group into which the call comes and the source group to which the subscriber belongs.

If, on the other hand, the OpenScape 4000 subscriber establishes the call, the call is routed out of the system via the CO using LCR. A CO/tie trunk from the central system cannot be used in this case.

Payload survivability is destination-oriented and is restricted to one OpenScape 4000 system. I. e, hardware gateways NCUI and STMI2/STMI4, and vNCUI (for SoftGate and Enterprise GW) and STMIX/STMIY boards are affected. If other systems are connected to the OpenScape 4000, the networking LCR must be extended. Details can be found in Section 2.9.3, “Payload Survivability in OpenScape 4000 Networks”.