Similar to how dial-plan normalization rules manipulate the digits a user dials, trunk translation rules are used to manipulate how numbers are modified before being delivered to a particular trunk. Often these formats vary by gateway, PBX, or telephony provider. Examples of modifications include adding an external prefix for calls going to a PBX, or prepending the international dialing code for international calls.
It’s important to identify all the required rules for each trunk during the planning phases of a deployment.