Practical VoIP Using VOCAL

Chapter 13. CPL Feature Server

This chapter looks at the role of the Call Processing Language (CPL) Feature server, including the different types of features that it supports and how you can write your own CPL features. In our development of VOCAL, we implemented features such as Call Forward, Call Screening, and Call Blocking. The Feature server (FS) can also execute arbitrary CPL scripts written by users, but it is difficult to link new features to the original provisioning screens without having the in-depth knowledge and experience of Vovida’s developers. The new, not yet implemented, provisioning system, discussed in Chapter 19, offers a more user-friendly approach to linking new features to GUI screens.

What Are Features?

Features are enhanced functions that enable customers to do more than simply call and receive phone calls. Core system features such as Call Forward No Answer are provided by the network. Other set-based features such as Transfer are dependent on the design of the phone set. Set-based features are also known as phone-based or user-based features. Another way of grouping features is determining whether they are calling features or called features. Calling features such as Call Blocking are activated when a user makes a call, which may prevent the user from dialing a 1-900 toll number. Called features such as Call Screening are activated when a user receives a call, which may prevent someone from calling the user. Before going into detail about how these ...