Why route liste and route group process. More scalable when you add new gateways and new paths either through a WAN or PSTN, creates a route list for the WAN and a route list for the PSTN, the routes pattern that route the calls through the WAN will point to the the WAN’S route list, and the route pattern that routes the calls through the PSTN will point to the route list ‘s PSTN, then for each route list , associate a route group that groups the gateways, GWs of WAN and GWs of PSTN, now when you add a new route pattern through PSTN , you just to point it to the route list ‘s PSTN, instead of creating the same route pattern for each gateways’s PSTN.
Where to do digits manipulation. at different levels, From the route pattern level, route group at the route list details level, at the gateway or sip trunk via the outbound calls section, translation pattern before making a decision of call routing through a route pattern, or transformation pattern associated to the gateway or sip trunk using a partition and CSS applied after a route pattern. Now depending the direction of the calls, to the WAN, to the PSTN, through different Gateways, you have a granular choice to select the best level of manipulation.