The concept of an ingress module accepting calls from other places such as SIP trunks or ISDN trunks is introduced in the section called “Routing calls within a site”.

The ingress stage should, in most cases, normalize both the destination number and the caller ID into the E.164 format. This will assist with both routing and log analysis later on.

The ingress stage may also convert the destination numbers to the addresses of internal users such as user@example.org. This can also be done at the routing stage.