13.1. Feature Description 
IP Distributed Architecture is an architecture with a central system
and numerous “unintelligent” peripheral modules. An access point/OpenScape
4000 SoftGate is essentially “remotely controlled” by the central
system. If the control link fails, the access point/OpenScape 4000 SoftGate
cannot survive autonomously. It must forward signaling messages from
the peripheral modules to the central system. It cannot process these
itself. Therefore, in the event of a failure in the control link with
the central system, the access point/OpenScape 4000 SoftGate has no option
other than to reset itself and wait until the central system restores
it to operational status.
Thus, if the control link between the central system and an access
point/OpenScape 4000 SoftGate fails, the access point/OpenScape 4000
SoftGate can no longer place telephone calls.
On account of these very severe consequences of a failure in the control
link between the OpenScape 4000 central system and the access point/OpenScape
4000 SoftGate, a possibility of “surviving” such failures has been
created. In the event of a fault, signaling survivability switches the
control link from the IP network to an alternative route. The signaling
path is switched over without interruption.
However, signaling survivability does not help against a central system
failure. If a central system is no longer available to control the access
points/OpenScape 4000 SoftGates, a signaling path via CO or alternative
LAN is no help either. In such cases, the entire communication system
(including all access points/OpenScape 4000 SoftGates) fails.
Calls possible with signaling survivability:
- Calls within the access point/OpenScape 4000 SoftGate
-
Full scope of features
- Trunk calls from subscribers in the access point/OpenScape 4000 SoftGate via local trunks
-
Full scope of features (for trunk calls)
- Calls with subscribers in other access points/OpenScape 4000 SoftGates to which an IP connection can still be established for the payload
-
Full scope of featuresCalls with subscribers in the central system and calls with subscribers in access points/OpenScape 4000 SoftGates to which no IP connection can be established for the payload are only possible if the “Payload Survivability” feature is configured for the relevant components. However, even if “Payload Survivability” is configured, only “Basic Call” functionality can be guaranteed.Please refer IP Distributed Architecture > Section 2.9, “Payload Survivability”.Signaling survivability is sold as a performance feature and is configured individually for each access point/OpenScape 4000 SoftGate.Two alternatives are available for the Signaling Survivability feature for each Access Point/OpenScape 4000 SoftGate (see also Section 1.2, “What is Used as an Alternative Route for Signaling?”):
- Signaling Survivability via PSTN network
- Signaling Survivability via alternative LAN
IMPORTANT:
For OpenScape 4000 SoftGates it is recommended to use Signalling Survivability over Alternate LAN.IMPORTANT:
In this context please pay attention to the use of the feature “HSR via UDP” (see Section 1.3, “HSR via UDP”).