Authorized Self-Study Guide Cisco Voice over IP (CVoice)

Scalable Dial Plans

The North American telephone network is designed around a ten-digit numbering plan that consists of three-digit area codes and seven-digit telephone numbers, as shown in Figure 5-13. For telephone numbers that are located within an area code, the PSTN often uses a seven-digit dial plan. Features within a CO-based PBX, such as Centrex, allow the use of a custom five-digit dial plan for customers who subscribe to that service. PBXs are more flexible and allow for variable-length dial plans containing 3 to 11 digits.

Figure 5-13. Dial Plan Example

Dial plans contain specific dialing patterns for a user who wants to reach a ...