/mcpDialing habits describe what end users can dial to reach various types of destinations. Dialing habits can first be classified as numeric dialing (for example, 914085550123) or alphanumeric dialing (for example, bob@ent-pa.com). Typically, different types of destinations require support for different dialing habits. Further dialing habits might have to be defined for services such as call pick-up, voicemail, and others. Also, future growth should be considered so that more users and more sites can be added as needed without redesigning the dial plan. Some dialing habits, typically PSTN dialing habits in particular, need to follow country-specific requirements or established dialing procedures. Identifying dialing habits is most important when defining an enterprise dial plan in order to avoid overlaps between any two dialing habits. Endpoint addressing Each endpoint registered with the enterprise call control must have a unique numeric address. Endpoint addresses in Cisco Unified CM are equivalent to the directory numbers provisioned on the lines of the endpoints. Use fully qualified PSTN numbers (E.164 numbers) with a leading "+" as endpoint addresses. This format is typically referred to as +E.164 format. The benefits of using +E.164 endpoint addresses include: • Wide use in voice networks • No need to develop and maintain an enterprise numbering scheme • Easy creation of correct caller ID presentation for all on-cluster and off-cluster call flows • Easy implementation of directory lookups • Simplified alternate routing to the PSTN in cases of WAN failure or bandwidth constraints • In addition to the primary numeric endpoint addresses, administrators can provision alphanumeric URIs (for example, bob@ent-pa.com) in Cisco Unified CM to serve as aliases for the primary addresses, and users can enter the URI as an alternate way to dial the destination endpoint. Routing The routing portion of the dial plan enables users to reach the correct destinations when they use the defined dialing habits. The primary numeric routing is based on +E.164 numbers. External routes to other transport networks such as the PSTN also use the +E.164 scheme. Endpoint addresses in +E.164 provide +E.164 on-net dialing without any further configuration. All other numeric dialing habits, such as abbreviated inter-site and intra-site dialing, are implemented as overlays by adding the appropriate translation patterns to the dial plan to map from the implemented dialing habit to the +E.164 global routing address format. This allows users to reach the same endpoint by means of different dialing habits, depending on user preference. Alpha-numeric URIs, as aliases for numeric addresses, provide an alternative means of reaching endpoints. The benefits of URI dialing and routing include: • Conformity with the native dialing habit on most video systems • Easier business-to-business connectivity • Direct mapping from instant messaging identifiers to addresses (easier escalation of business-to-business IM sessions to voice and/or video), although technically IM identifiers and SIP URIs are not necessarily identical