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Understanding the Dial Plan

The ISDN gateway uses the dial plan to determine how to route calls between IP and ISDN networks. When the ISDN

gateway receives a request to initiate a new IP to ISDN or ISDN to IP call, it examines the called number (if available),

and uses the dial plan to determine whether to reject the call, find out which number should be called to initiate the

outgoing part of the call, and check the allowed call bandwidth.

There are a number of different ways in which you can use the dial plan. For example, you can use the dial plan to

enable users to use a particular bandwidth for an IP to ISDN call. You can also use the dial plan to enable the ISDN

gateway to join incoming ISDN calls to the correct conference on an MCU. (For example dial plans, refer to Example Dial

Plan Rules.)

The dial plan is actually divided into two; an IP to ISDN dial plan and an ISDN to IP dial plan. If the incoming part of a

connection is from an IP endpoint, the IP to ISDN dial plan is used; from an ISDN endpoint, the ISDN to IP dial plan is

used. The behavior of the two dial plans is near identical, and the sections below only make a distinction between the

two where differences exist.

Refer to the sections below for more information about the use and administration of dial plans:

● Rules

● Using Rules

● Rule Ordering

Rules

Dial plans are administered using rules. Rules and their addition and control are near identical for the IP to ISDN and

ISDN to IP dial plans.

Each rule comprises the following three parts:

● a condition that must be matched for the rule to be invoked.

The condition can be set to match any called number, to match a call that has no called number, or can specify

the called number by specific number or pattern.

● an action that is carried out if the rule is invoked.

The action can be to reject the call, to place the call using the original dialed number, or to specify the number/

address to call.

● a set of additional parameters that modify the action:

❍ Call type: use this option to specify whether the call is a normal video call, a telephone call, or a

video call that supports legacy ISDN endpoints that use n x 64kbps.

❍ Maximum bandwidth: use this option to limit the bandwidth available to for calls to particular

numbers, or to allow users to select their own bandwidth (for more information, see

Adding and

Updating Dial Plan Rules).

❍ ISDN port: use this option if you need to specify the ISDN port for a particular type of call.

Using Rules

Each dial plan comprises a set of rules. When the ISDN gateway receives a new incoming call, it selects the appropriate

dial plan, then compares the called number (if available) to the condition of each rule in that dial plan until a match is

found. When a match is found, no more rules are checked, and the action of the matching rule is used to determine what

should be done next; typically the outgoing part of the connection will be initiated, calling a number specified by the

action, or the connection will be rejected and the incoming part terminated.

If a dial plan contains no rules, or if no rules' conditions match the called number calls are rejected by default.

For more information on adding and modifying dial plan rules, see

Adding and Updating Dial Plan Rules.

Rule Ordering

Rules are always checked in the same order for each incoming call. This means a dial plan may be designed to handle

specific calling cases first, then general calls if no specific cases match. For example, a dial plan may be set up to call a

particular person's endpoint if an incoming call is received to a specific number, but all other incoming calls get

connected to an operator's endpoint. Such a dial plan might look like this:

1. Condition: Called number is "6056" / Action: Call with the original called number.

Codian ISDN GW 3200 Series User Guide Version 1.0(1.18)