Understanding the SRX Series Survivable Call Server Dial Plan

One of the most fundamental components of an SRX Series survivable call server (SRX Series SCS) Integrated Convergence Services deployment is its call routing dial plan. An enterprise implements a dial plan that defines the patterns and routes that enable users to make calls directed to their intended destinations based on digits the user dials. In most cases, these digit strings conform to patterns.

For example, many enterprise telephony systems define dialing patterns used for calls as follows:

• For calls inside the company, they use five or six numbers for their digit pattern.
• For calls outside the company, they use a single digit such as 9 followed by a string of digits used to reach a local PSTN number, or other telephony service.
• For long-distance calls, they use 9 followed by 1, and then ten digits.
• For international calls, they use 9 followed by the three-digit IDD number—a two- or three- digit country code, a two- or three-digit area code, and the subscriber number (which normally consists of seven digits).

Normally the SRX Series media (SRX Series MGW) gateway relies on the peer call server to route calls for it. When the SRX Series MGW peer call server is unreachable, the SRX Series SCS takes control to provide call handling and call routing services for analog telephones and fax machines and SIP phones registered to the SRX Series SCS. For this to occur, a local dial plan must exist to specify how calls are routed. This dial plan is referred to as the local SRX Series SCS dial plan. As much as possible, it should emulate the peer call server dial plan to give users a seamless experience.

You configure an SRX Series MGW dial plan’s route patterns to enable the peer call server to route calls using trunks at the SRX Series MGW branch. An SRX Series SCS dial plan differs in purpose. It is used by the SRX Series only and is comprehensive in that it includes route patterns and route policies for all calls routed from behind the SRX Series MGW.

Note: You can create a single dial plan that includes route patterns for both the SRX Series MGW and the SRX Series SCS, and route policies for the SRX Series SCS, or you can create separate ones for them.

A dial plan consists of route patterns, each of which has:

• A digit pattern that specifies a pattern against which called numbers are matched. If a number matches the pattern and the station’s class of restriction configuration allows the call, then the call is routed.
• One or more trunk groups specifying the trunks used to route a matching call.
• A call type, which can specify emergency, intrabranch, interbranch, local, long-distance, international, or custom.
• Optionally, a digit transform rule that identifies how the called number is manipulated before it is transmitted.

For a dial plan to take effect, you must configure the following information:

• Stations and their class of restriction polices.
• The trunks to be used.
• Trunk groups, specifying their trunks.
• The dial plan. For the dial plan, you must configure its route patterns and route policies.

Related Topics

• Understanding SRX Series Integrated Convergence Services Features and Functions
• Understanding SRX Series Integrated Convergence Services Media Gateway Trunks
• Understanding Trunk Group Reusability for SRX Series Integrated Convergence Services