Dial Plans

Designing and implementing a dial plan has always been one of the more difficult aspects of a voice system. Every decision requires balancing ease of operation for the end user with ease of administration and scalability. Because all companies have different business requirements, a simple one-size-fits-all formula is not applicable.

A dial plan is composed of five components:

• Endpoint addressing
• Path selection
• Calling privileges
• Digit manipulation
• Call coverage

This chapter provides an overview of the decisions that you must make and the guidelines for working through common dial plan issues. The focus is on endpoint addressing and the fundamentals of how a gateway selects an appropriate path for a call. Chapter 10, "Digit Manipulation," covers digit manipulation in more detail. Chapter 11, "Influencing Path Selection," covers methods for influencing the path selection, and Chapter 12, "Configuring Class of Restrictions," covers calling privileges. Call coverage is defined as a group of devices created to handle incoming calls according to specific rules. The call processing system provides call coverage features, such as call park, pickup groups, and automated call distribution (ACD). You can find more information on these features at Cisco.com

This chapter helps you to do the following:

• Design a numbering plan
• Interact with a public switched telephone network (PSTN) numbering plan
• Design a scalable dial plan
• Overcome the issues with overlapping dial plans
• Understand how a gateway processes dial peers