Practical VoIP Using VOCAL

Feature Activation

The FS state machine model is the same for executing one feature. This model is illustrated in Figure 13-12. This model does not support multiple features on the same server.

Figure 13-12. Generic state machine on FS

Walkthrough of Feature Activation

The following process describes what happens when the FS creates a new CallInfo:

1. When an INVITE message arrives, the FS does the following:

   1. Creates a new CallInfo, which holds info about the call leg, current state, timers, and feature data (for example, last caller’s number, possible proxy locations, proxy status, and anonymous blocking data).

   2. Pulls the user port from the RequestUrl and From fields.

   3. Searches for called or calling features:

      1. Searches FsUsers map for RequestUrl:-user.

         If not found, goes to Step ii.

         If found, retrieves the called feature and the state machine begins at START (illustrated as circle A in Figure 13-11). See Step 2.

      2. Searches FsUsers map for From:-user.

         If not found, deletes CallInfo and the message processing is finished.

         If found, retrieves the calling feature and the state machine begins at START. See Step 2.

2. At START, the feature has a choice of what to do with the INVITE message:

   1. The feature executes one or more operators until it cannot continue because it needs a response message. Eventually, the SIP stack provides an automatically generated response to allow this process to complete.

   2. The feature transitions ...