10.18  

Path Replacement 
 
In general, path replacement is supported in all protocols (CorNet N,
CorNet NQ, QSig), provided it is permitted in the CDB.
The following problem can occur in a network consisting of multiple HiPath systems: Station A calls station B which has programmed call forwarding to station C. Station A and C are on the same system, called Node 1 in the figure. B is on Node 2. A call from a station with programmed call forwarding immediately seizes two trunks between the two systems mentioned. This is not necessary. The solution is path replacement (optimization) -- even for more than two affected systems.
 Figure 10-2   Path optimization between networked systems
 
There is no path optimization on connections with IP telephones.  
What's more, path optimization is only carried out in IP-networked HiPath 3000/5000 systems, and not between HiPath 3000 and other systems Path optimization is not performed in an IP network between a HiPath 3000 and HiPath 4000 or OpenScape Voice system because uninterrupted switching is not possible for the connection. In a mixed network of HiPath 3000 and HiPath 4000 systems, the IP cross connect to HiPath 4000 must be configured in a separate trunk group.
The following generally applies:
 •   Path replacement is only initiated after the connection is set up. The Rerouting feature performs replacements in the ringing phase.
 •   Path replacement is activated from the primary end (this is usually the previously held station).
 •   If HiPath 3000 acts as the secondary end, it attempts deferred path replacement (see below for prerequisites)
Path replacement is performed in the following situations:
 •   After transfer scenarios
 •   Connect after call forwarding or call forwarding no answer
(if it can be recognized using the facility information)
Exceptions:
 •   Connection after group ringing or group call.
 •   Basic call without features
 •   If, after feature transfer, only TDM devices in the same node are involved in a call, the IP route is also replaced (there is no path replacement for TDM devices in different nodes connected via IP trunking).
 •   There is no path replacement for conferences.
 •   Path replacement is interrupted if another feature is activated during path replacement execution.
The DMC (Direct Media Control) feature uses path replacement messages as a carrier message for additional DMC information.