[Serusers] fr_inv_timer in tm module

Dear all, When i was reading about tm module ( http://www.iptel.org/ser/doc/modules/txt/tm.txt ) I found this section ... ****************************************************************************************************** 1.3.2. fr_inv_timer (integer) Timer which hits if no final reply for an INVITE arrives after a provisional message was received (in seconds). Default value is 120 seconds. Example 1-2. Set fr_inv_timer parameter ... modparam("tm", "fr_inv_timer", 200) ***************************************************************************************************** But I could not understand here what is the meaning of "provisional message" and how fr_inv_timer behave.. Please some one teach me about this with some example... thanks in advance.. --------------------------------- Do you Yahoo!? New and Improved Yahoo! Mail - Send 10MB messages!