Hello Joe, On Fri, Aug 04, 2017 at 03:45:12PM -0400, Joe Baran wrote: t_check_trans() is the traditional method of retransmission dampening, and does different things depending on what type of message is being processed. For most requests, however, it resends the last reply (if the transaction is known) and ends route script execution for that message. If the transaction is not matched, it just returns false and execution carries on. You can read more about the details here: https://kamailio.org/docs/modules/5.0.x/modules/tm.html#tm.f.t_check_trans But in order to use t_check_trans(), an actual transaction has to be created, and that is fairly expensive from a performance point of view (in strictly relative terms). The purpose of t_precheck_trans() is to provide a lightweight retransmission detection mechanism which does not require a transaction to actually be created and destroyed in order to detect retransmissions. You can read more about the rationale here: http://blog.miconda.eu/2014/10/kamailio-42-tips-10-lightweight.html Long story short: t_check_trans() only detects retransmissions if an actual transaction was created (via t_newtran() or, most commonly, via t_relay()). t_precheck_trans() is a lighter-weight wrapper around it which does not require that in order to detect and suppress retransmissions. -- Alex -- Alex Balashov | Principal | Evariste Systems LLC Tel: +1-706-510-6800 / +1-800-250-5920 (toll-free) Web: http://www.evaristesys.com/, http://www.csrpswitch.com/