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Chapter 3 — DPNSS1/DASS2 features description and implementation Page 771 of 1536
DPNSS1 Route Optimization
The DPNSS1 Route Optimization feature has been developed to optimize
trunk usage within a DPNSS1 network, by replacing non-optimum call paths
through a DPNSS1 private network with optimum paths. An optimum path is
the path that uses only the first choice routes to link two PBXs across the
network. The first choice is determined by the programming of the network
numbering and routing at each PBX. This optimization applies to established
simple voice calls which were routed during set-up, or transferred or
attendant-extended to another party.
Route optimization is initiated by the originating PBX, after recognizing that
a DPNSS1 call may have been set up over a non-optimum path due to
alternative routing or call modification. If the call is ringing, the originating
PBX waits for an answer signal before initiating optimization. If the call has
been transferred, on answer, or attendant-extended to a another party, then the
transfer or extension signaling sequence initiates the optimization.
The originating PBX sends a Route Optimization Request message, which
contains a Call Reference Number (CRN) field, to the terminating PBX. The
CRN is used as a destination address to route the call back to the originating
PBX and uniquely identify the call being optimized (the Originating Line
Identity sent in the Initial Service Request Message is used for this purpose).
The set-up message for the backward call contains a field that identifies the
call set-up as route optimization. This causes the call, throughout its path, to
be restricted to only first choice routes.
If the route optimization request call set-up successfully gets back to the
originating PBX, a conference is established at the originating node between
the originating party, the original path still carrying the speech, and the silent
new path. A message of acknowledgment is returned to the terminating PBX
on the new path. Upon receiving this acknowledgment, the terminating PBX
replaces the old path with the new (optimized) path, and sends a connect
indication across the new path to the originating PBX. The old path is
silenced. Upon receiving the connect indication, the originating PBX
terminates the conference, connects the originating party to the optimized
path, and clears the original path.
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