Chapter 15: Legacy Integration Planning and Installation Guide
ShoreTel 11.1 203
15.4 Trunk Requirements
The number of digital trunks required between the ShoreTel system and the legacy PBX
depends on the expected traffic between the two systems. To determine the number of
trunks, you need to estimate the number of calls per hour that are placed between the two
systems. When estimating the call volume between the two systems, consider the
The volume of direct calls between users on the two systems
Traffic related to Automated Call Distributor (ADC) calls
Outbound call volume (i.e. when outbound trunking to the PSTN is provided by
one of the systems for all users, such as a PSTN trunk connected to the legacy PBX
that provides long distance services for users on both the legacy and ShoreTel
Inbound call volume (i.e. when inbound services are provided by one system to all
Additionally, you can rely on the estimated calls-per-hour number to determine the number
of trunks to configure between the two systems.
For more information on trunk requirements, see Chapter 5, starting on page 67.
15.5 Coordinated Dialing Plan
With legacy integration, users on both systems can dial one another using abbreviated or
extension dialing. This includes dialing from applications on the systems, such as the
ShoreTel voice mail application, and would also include forwarding a call to an assistant at
an extension on the legacy PBX. To determine the coordinated dialing plan configuration,
you must identify the current numbering of users on both systems. For example:
When the systems are located together, extensions can normally be assigned from a
single numbering plan, or from a single DID number range provided by the local
carrier. In this case, the extensions on the two systems are assigned such that there
is no overlap using the desired extension length.
When systems are at different locations, each system’s numbering plan is often
based on the DID range supplied by the local telephone company. In this case,
overlap of the extension ranges can occur at the currently used extension length.
For example, consider the following situation.
One location is assigned DID range 408-555-2000 through 2999
The second location is assigned range 650-333-2500 through 2799
The systems currently use four-digit dialing matching the trailing 4 digits of the
In this case, there are users on both systems currently assigned extension 2500. To provide
a coordinated dialing plan across the systems, the extensions must be adjusted to make
them unique system-wide. In the integration, four-digit extensions that overlap are made
unique by increasing the extension length across the system. When the extension length is
increased, the first digit becomes the “system” number and the remaining digits are the
“extension.” In the above example, the extension length would be increased to five-digit
dialing, and at the first location would be extensions 52000 through 52999, while users at
the second location would be assigned extensions 32500 through 32799.