Payload survivability requires CO lines at access points, in order to switch alternative routes. If, in example Figure 31 “Payload survivability - source dependent routing configuration”, the IP connection between Berlin and Frankfurt fails, all existing calls will be interrupted. No new calls can be set up until “Good Quality“ has been determined again.

As both an access point in Berlin and the access point in Frankfurt have a local CO line, calls between subscribers in Berlin and Frankfurt can alternatively be switched via the trunk. Of particular note here is that, in the case of IPDA, a OpenScape 4000 system now calls itself via trunk, in order to connect its own subscribers.

The alternative routes are defined as a function of the source group. Thus, in the example, it is unnecessary for AP 99 to have its own trunk access. It can be reached via the trunk access of its source group in AP 98.