Kamailio can behave as a stateful proxy through the TM module. However, "stateful" in this context refers to transaction state, not dialog state. Certain applications may benefit from an awareness of "calls" in the proxy, not just SIP transactions. For example, a common need is to limit the number of calls that can be made concurrently by an endpoint, account, user group, etc. In order to count the number of calls in progress, it is necessary for the proxy to be aware of whole dialogs, not just transactions, and to provide some means of programmatically classifying these dialogs. This is just one common application discussed for illustrative purposes; there are many others. The dialog module provides dialog awareness for the Kamailio proxy. Its functionality is to keep track of the current dialogs, to offer information about them (e.g. how many dialogs are active), and to manage various characteristics of dialogs. The module exports several functions that can be used directly from the configuration route script as well as functions for the RPC interface. This module also provides an API foundation on which to build more complex dialog-oriented functionality in other Kamailio modules.
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