How are E.164 called-party numbers normalized on a globalized call-routing environment in Cisco UCM?

In a globalized call-routing environment within Cisco UCM, the fundamental principle is to standardize all incoming called-party numbers into a globally unique format, typically E.164 with a leading plus sign (e.g., +14085551212). This normalization must occur at the ingress point of the call (e.g., the gateway or trunk receiving the call from the PSTN) before Cisco UCM attempts to route it. This approach simplifies the internal routing logic, as all subsequent routing decisions are made based on a single, consistent number format, regardless of how the number was originally dialed or presented by the carrier.

B. Normalization is not required. This is incorrect. A globalized call-routing design fundamentally relies on normalization to provide a scalable and consistent dial plan across multiple sites.
C. Normalization is achieved by stripping or translating the called numbers to internally used directory numbers. This is misleading. While normalization involves stripping/translating numbers, the goal is to convert them to a global E.164 standard, not necessarily to a short, internal-only directory number. In a globalized model, the internal directory numbers themselves are configured in the E.164 format.
D. Normalization is achieved by setting up calling search spaces and partitions at the SIP trunks for PSTN connection. This is incorrect. Calling Search Spaces (CSS) and partitions are mechanisms for call routing control and class-of-service, not for number manipulation. They determine which translation patterns are accessible, but they do not perform the normalization themselves. ---

1. Cisco Collaboration System 12.x Solution Reference Network Design (SRND)

Reference: Chapter: Dial Plan, Section: Globalized Call Routing.

Quote/Paraphrase: The SRND states, "With globalized call routing, the goal is to have a directory number (DN) in the full E.164 format, including the + sign... All other types of numbers, such as abbreviated internal numbers or numbers from the PSTN, are converted to the +E.164 format at the ingress point to the Unified CM cluster." This directly supports the principle that normalization happens at call ingress before routing.

2. Implementing Cisco Collaboration Core Technologies (CLCOR 350-801) Official Cert Guide, 1st Edition

Reference: Chapter 6, Section: "Globalized Call Routing".

Quote/Paraphrase: The guide explains that a key aspect of globalized call routing is to "normalize all inbound call-dialed numbers to the +E.164 format at the ingress gateway." This reinforces that the process is tied to the ingress point of the call, making it a prerequisite for internal routing.