Dial plans comprised of the branch prefix and local number length for IP Office users should not exceed 15 digits. The Branch Prefix field and the Local Number Length field appear in IP Office Manager under System Telephony SM tab.

The branch prefix enables IP Office users to have short extension numbers within the local branch but appear to the rest of the enterprise to have unique full enterprise-wide numbers in enterprise canonical format. If a number is configured in the Branch Prefix field, it causes automatic conversion of the IP Office users’ extension numbers in calls to and from the SM Line. The branch prefix is added as a prefix to the IP Office user’s extension number when it appears as the calling number in calls sent to the SM Line. Similarly, it is added to the extension number when it appears in Diversion-Header or History-Info in calls sent over the SM Line to centralized voicemail.

In calls received from the SM Line, if the called number starts with the branch prefix, the prefix is removed and the IP Office will try to target the remaining number locally, to a non-centralized extension or hunt group. If there is no match, IP Office will target it to any matching system short code. If the called number does not start with the branch prefix, the whole number is checked for a match against system short codes.

Centralized users (SIP or ATA) can call local IP Office users in the same branch by dialing the full enterprise number composed of the branch prefix plus local extension number, and IP Office will remove the branch prefix and target the local extension. This may be needed if short-form dialing is not set up on the centralized Avaya Aura® Communication Manager for Sunny day and the Centralized users are accustomed to dialing the full number.

IP Office users cannot call other local IP Office users in the same branch by dialing the full enterprise number composed of the branch prefix plus local extension number.

When a call is made by any source on the IP Office system and short code matching targets the SM Line, if the target (the dialed number) starts with the branch prefix, the branch prefix is removed and the call is targeted locally. This does not apply if the target is the extension number of a Centralized user or Centralized group configured on the IP Office. In this case, the call is handled as specified below and in Sunny day it will be sent to Session Manager.

The branch prefix is expected to be used in Distributed enterprise branch deployments and it is expected to be left blank in Centralized enterprise branch deployments. In Mixed enterprise branch deployments, the branch prefix can be left blank or used. If left blank, the IP Office users’ extension numbers will have to be the full enterprise number. If used, the IP Office users’ extension numbers will be shorter than the Centralized users’ extension numbers.

The Local Number Length field sets the default length for extension numbers. If an extension number of a different length is configured, a warning appears. The Local Number Length field can be left blank. In Mixed enterprise branch deployments, if the Branch Prefix field is not blank, and the Centralized users and IP Office users have extension numbers of different lengths, then it is recommended to leave the Local Number Length field blank.

The extension number configured on IP Office for the Centralized user is the user’s enterprise-wide number. This is the same number that is configured for that user on Session Manager, which is the number that the centralized phone uses when registering to Session Manager in Sunny day and when registering to IP Office in Rainy day.

Centralized users’ extension numbers can be up to 13 digits in length. IP Office users’ extensions can be up to 9 digits in length.

The IP Office Branch Prefix field, which causes number modifications for IP Office users’ extension numbers, does not impact Centralized users’ extension numbers when they appear as calling number or as called number.

Centralized users may have extension numbers that are not related to the local IP Office branch prefix or numbers that begin with the same digits as the IP Office branch prefix. If Centralized users have extension numbers that begin with the same digits as the IP Office branch prefix, the Centralized users’ extension numbers look like the IP Office users’ extension numbers to the rest of the enterprise. This enables users to keep their numbers when migrating from a Distributed enterprise branch to a Centralized enterprise branch.

Calls to centralized users, which can arrive from different sources, are sent to the SM Line in Sunny day and are targeted to the Centralized user’s extension locally in Rainy day. Both Sunny day and Rainy day call handling are done automatically by matching the called number to the Centralized user’s extension number.

IP Office can manage calls to Centralized users that are dialed to the Centralized user’s full extension number, or calls that are dialed using short-form dialing. To support short-form dialing, the global parameter Short Form Dialing Length must be configured. The Short Form Dialing Length field appears in IP Office Manager under System > Telephony tab > SM tab. Configuration of this feature allows IP Office to treat the last N digits (where N is the number configured for the Short Form Dialing Length) as an alias to that user’s extension number.

The Sunny day conversion from the dialed short-form number (for example, 1111) to the enterprise canonical extension number (for example, 5381111) is done by the Communication Manager Feature Server (CM-FS) or Communication Manager Evolution Server (Communication Manager-ES) based on the caller’s location. When a Centralized user makes a call in Sunny day, the call goes directly from the Centralized phone to Session Manager, and IP Office is not involved at this stage. Session Manager first sends the call to the Communication Manager-FS or Communication Manager-ES responsible for calling the Centralized user for origination-side features. That Communication Manager performs the called-number conversion from the dialed short-form to the enterprise canonical number, and sends the call back to Session Manager with the called number modified to the enterprise-canonical number. Session Manager then sequences the call to other applications, if any, and then routes the call based on the enterprise-canonical number. This conversion in Communication Manager is based on Communication Manager configuration of a per-branch location via ip-network-map and ip-network-region forms, as well as Communication Manager per-location AAR analysis to identify the short-form dialed number and per-location route pattern which modifies the called number before sending to Session Manager.

For Rainy day calls made from one Centralized user to another Centralized user, the IP Office Short Form Dialing Length has to be set.