tm

TM module enables statefuli processing of SIP transactionsi. The main use of stateful logic, which is costly in terms of memory and CPU, is some services inherently need state. For example, transactioni-based accounting (module acc) needs to process transaction state as opposed to individual messages, and any kinds of forkingi must be implemented statefully. Other use of stateful processing is it trading CPU caused by retransmissioni processing for memory. That makes however only sense if CPU consumption per request is huge. For example, if you want to avoid costly DNS resolution for every retransmission of a request to an unresolvable destination, use stateful mode. Then, only the initial message burdens server by DNS queries, subsequent retransmissionsi will be dropped and will not result in more processes blocked by DNS resolution. The price is more memory consumption and higher processing latency.

Jiri Kuthan