[Serusers] Timeout for provisional replies

Hello, Currently we've the folling tm-timeouts set: modparam("tm", "fr_timer", 30) modparam("tm", "fr_inv_timer", 180) In my understanding the first timer hits if no final reply for a request (except INVITE) or an ACK for a neg. INVITE-reply arrives within 30 seconds; the second timer hits if no final reply arrives for an INVITE after a provisional reply (the first one?) is received within 180 seconds. But is there a timer for the first provisional reply for an INVITE? I ask because I want to detect if a contact is unreachable. I'd assume that a device answers with "100 trying" (or immediately with 180/183) within some seconds, but which timer do I have to set? Thanks, Andy