With globalized call routing, all calls that involve external parties are based on one normalized format. This format is the +E.164 format, that is, a + prefix, followed by a number in E.164 format. Because +E.164 format is a globally unique format, call routing that is based on +E.164 numbers is called globalized call routing.
With globalized call routing, numbers must use the following formats:
- Normalized called-party numbers: The +E.164 format is used for all external destinations during call routing. Per the recommendation in Preferred Architecture for Cisco Collaboration, you should also use the +E.164 format for calling internal phones that have a dedicated external DID number.
- Normalized calling-party numbers: When a call involves at least one external party, then the +E.164 global format is used for the source of the call. Per the recommendation in Preferred Architecture for Cisco Collaboration, you should also use the +E.164 format for calls coming from internal phones that have a dedicated external DID number.
If call sources do not use the normalized format natively, this localized call ingress must be normalized before being routed. This requirement applies to all received calls (coming from gateways, trunks, and phones).
After the call is routed and the path selection (if applicable) is performed, the destination device might need to change the normalized numbers to a local format. This change is referred to as localized call egress.
Localized call egress applies to these situations:
Calling- and called-party numbers for calls that are routed to gateways and trunks: If the PSTN or the telephony system on the other side of a trunk does not support globalized call routing, then the called and calling-party numbers must be localized from the global format. An example would be to change the called-party number +442079460111 to 011442079460111 before sending the call to the PSTN in the United States.
Calling-party numbers for calls that are routed to phones, if the phone user does not want to see caller IDs in the normalized format: An example would be that the user at a U.S. phone wants to see PSTN callers that are located in the same area code as a seven-digit number and not in +1XXXXXXXXXX format. Another example are internal calls from phones that use the normalized format (for example, phones that have a dedicated external DID number) as the directory number. Users typically want to see such callers by an internally used extension and not in full +E.164 format.
Globalized call routing simplifies international dial plans because the core call-routing decision is always based on the same format, regardless of how the number was initially dialed, and regardless of how the number looks at the egress device.
