Intersite Prefix

The intersite dialing prefix (ISP) is optional and customer wide, and it tells the dial plan that the user is making an on-net call, and that the digits to follow must be in the format of a site location code (SLC) and an extension number. The ISP is a single digit number in the range 0 to 9 and must be unique within the customer’s network. The ISP is deployment configurable to any value, but must not overlap with the PSTN dialing prefix or emergency number. The ISP is an optional configurable value within a customer’s dial plan.

Note

Customer wide means that the same ISP must be used for all of a customer’s sites. If the first site that is provisioned begins with the digit 8, then all other sites should also begin with the digit 8.

Under one service provider you can have the ISP as 7 for one customer and 8 for another customer.

A standalone ISP is not supported, but rather, the ISP is implemented as the first digit of the SLC, for the following reasons:

• Corporate Directory Support*If the ISP is not included in the site code, then after directory lookup, you must manually insert the ISP before call completion.
• Callback Support*If the ISP is not included in the site code, then the calling party number is not contained in the ISP. You must manually insert the ISP before call completion.

ISP does not apply to Type 4 Dial Plans.