Least Cost Routing (LCR) is not strictly limited to calls destined for the PSTN, instead LCR can be used to prevent OnNet calls from being routed OffNet. In this recipe we will cover both uses.
Before we begin this recipe it is helpful to have some information:
DID ranges of locations for which we are implementing LCR
Site codes of locations for which we are implementing LCR
Local numbers per location for Tail End Hop Off
In this recipe we will implement LCR and Tail End Hop Off for calls destined to an office in San Francisco. We will assume the following:
DID Range for this location: +1 415 555 1000 to 1099
Site code for this location: 11
Local numbers for this location: 415 XXX XXXX
To implement Least Cost Routing for a location, we need to perform the following:
Add a new route list that will contain the route group with the gateway or trunk device local to the location for which we are implementing LCR, as well as the Standard Local Route Group:
Add a new route pattern to send local calls to our new route list. Key fields to note here are Route Pattern, Route Partition, and Gateway/Route List*:
Next add a translation pattern (Call Routing | Translation Pattern, then click on Add New) that is responsible for converting E.164 numbers to their internal extensions.
Here the Translation Pattern must match only the DID range for the location. For our recipe the pattern is
\+1415555.10XX. For the partition use something that is globally accessible, for example PT-Global-E164:
For our pattern, it is necessary to set Discard Digits to PreDot and Prefix Digits to the site code—12 in this recipe.
Least cost routing with Tail End Hop off is accomplished by sending calls to locations where the call would cost the least. In addition to Tail End Hop Off, we can accomplish least cost routing by recognizing when a user dials the DID to another user on the same cluster by converting the E.164 number to the local extension and routing over the IP network.
Once more we see the benefits of the logical nature of local route groups. By having localization settings at the gateway level, we don't have to worry about formatting and allow the local gateway to normalize the call as required by the PSTN. In the event that the call cannot be made through the gateway or trunk device at the local site, the call will fall back to the gateway or trunk device local to the originating caller.
Do remember that Tail End Hop Off is not legal in all countries. Check with local regulations before implementing it.