10.1.5.2. Payload Survivability 
Figure 176. Payload survivability: Alternative route for the payload via PSTN
Payload survivability allows internal system
calls to be routed via the CO. The OpenScape 4000 in effect
"calls itself" and establishes an internal call between different parts
of the system. The route for payload survivability is also selected automatically
as a spillover route if the entire capacity of the HG 3575 is already
in use in the IP network.
IMPORTANT:
For information about feature restrictions with
payload survivability, see Chapter
2, “Restrictions”.