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Howto callmanager call flow

The following steps outline what happens within the cluster when a call is placed to a destination outside the cluster. For example, let's assume the call is being placed to the pizza place down the street.

Step 1. The caller dials the phone number of the pizza place.
Step 2. CallManager looks at those digits and finds a pattern that matches it. If it finds multiple patterns that match, it uses the closest (the one with the fewest possible matches).
Step 3. The pattern that the dialed number matches points to a route list that in turn points to one or more route groups.
Step 4. The route list sends the call to the first route group in it's list.
Step 5. The route group points to one or more gateways and sends the call to the first gateway in the group.
Step 6. If the gateway is unable to handle the call, the route group sends the call to the next gateway in it's list if there is one.
Step 7. If no other gateway exists in the group or if the last gateway in the group is unable to route the call, the call is returned to the route list and the route list sends the call to the next route group in the list.
Step 8. The next route group sends the call to the first gateway in the group.
Step 9. After the call reaches a gateway that is able to handle the call, the call is sent out of the system using that gateway.
Step 10. If no gateway is available, the call fails.






Understanding Route Groups and Route Lists
The job of a route group is to send the call to the gateway or gateways to which it points. The route group sends the call to the first gateway in the group, and if that gateway is unable to handle the call, the route group sends the call to the next gateway in the group. This process is repeated until a gateway in the list is identified that is able to handle the call, or there are no more gateways in the group. If the route group is unable to find an available gateway, the call is returned to the route list.

The job of a route list is to send the call to a route group, which in turn sends the call to a gateway. In the example shown in Figure 4-2, the call is first routed across the wide-area network (WAN). If that path is unable to accommodate the call, it is routed to the PSTN. As you can see, depending on which path the call takes, a different number of digits need to be sent. If the call is sent across the Inter-Cluster Trunk (ICT), only five digits are needed, assuming that the remote cluster is using five digit directory numbers. However, if the call goes across the PSTN, 11 digits are needed. To accomplish this, digit manipulation must take place. Digit manipulation occurs when a called (dialed) or calling (Caller ID) number is changed. In this case, the digit translation strips the required number of digits from the called number so that the call can be routed across the chosen path. Because the path the call takes is not known until it reaches the route group, the digit manipulation should take place there.