Re: [OpenSER-Users] TM-module and ACK to 2xx (doesnt terminate txn?)

El Thursday 14 February 2008 09:01:52 Taisto Qvist escribió: Please, don't require Disposition-Notification in mails sent to a maillist. Thanks.

Oups, I seemed to have my maillist-subscription disabled so I never got the answers.... I seems like we dont agree on the interpretation of the txn handling for invite. Sure, there is a timer for handling retransmitted responses, but thats in earlier states than Terminated. Sure, there is nothing that says that the inner workings of your transactions must exactly behave as the statemachine diagrams in the rfc as long as the external behavior stays the same, but still, I think that the ACK for 2xx should not match the INVITE txn. (It probably boils down to how rfc-isch you want to be.) [TQ] Where does it say that ACKs establish a separate transaction? There is no defined ACK transaction, only INVITE/nonInvite, server and client. The ACK is either a part of the INVITE txn, or its a separate request, but I would never call it a standalone transaction. The real purpose of txn's (in my view), is to enable/simplify forking, and to handle retransmissions. Retransmissions of ACK and 2xx, are done by the UAC/UAS, so there is no need for a ack-txn. [TQ] I'd say there is. Where does it describe that this wait-timer should be used for all responses, or for matching ALL acks? My two main reasons for saying that ACKs for 2xx should not be matched, come from the following two texts. (17.1.1.2, and 17.2.1) 17.1.1.2 (client invite txn) The client transaction MUST be destroyed the instant it enters the operation. The reason is that 2xx responses to an INVITE are treated differently; each one is forwarded by proxies, and the ACK handling in a UAC is different. Thus, each 2xx needs to be passed to a proxy core (so that it can be forwarded) and to a UAC core (so it can be acknowledged). No transaction layer processing takes place. Whenever a response is received by the transport, if the transport layer finds no matching client transaction (using the rules of Section 17.1.3), the response is passed directly to the core. Since the matching client transaction is destroyed by the first 2xx, core. [TQ] It even says "actually nessesary to guarantee...." Since the txn's are there to (among other things) absorb retransmissions, the receiving the 2xx MUST destroy the txn, so that when the next retransmission of 2xx is received, it is not consumed by the txn layer. This is what your txn-layer does for 3++ right? Any additional 3++ received on a txn while waiting for Timer D to expire, will just be consumed, and the proxy core will never have to process it. 17.2.1. (server invite txn) The purpose of the "Confirmed" state is to absorb any additional ACK messages that arrive, triggered from retransmissions of the final response. ..snip... Once the transaction is in the "Terminated" state, it MUST be destroyed immediately. [TQ] The Confirmed state is there to absorb retransmissions, not the terminated. When receiving 2xx you go directly to terminated bypassing confirmed. Also, in 18.2.1 the text explicitly says: .. Note that when a UAS core sends a 2xx response to INVITE, the server transaction is destroyed. This means that when the ACK arrives, there will be no matching server transaction, and based on this rule, the ACK is passed to the UAS core, where it is processed. Thats faily clear right? :-) The think that puzzles my a little bit though, is that you must have added "extra" code for this matching...? I mean, you're using the ;branch=z9xxxx for transaction matching right, if its there? And the ACK for 2xx doesnt have the same branch, indicating a "new txn". So matching ALL ACKs would imply that for any ACK that doesnt match a txn, your really checking up Call-Id's, tags and stuff, just to be able to match this ACK to the 2xx? Or are you checking callid's, cseq's, tags, and stuff, for ALL requests in your txn matching? Now, I been working on a sip-stack the last few years myself, and I naturally know that there is often a need to match the ACK, and the stack I've build has similar functions, it just doesnt do it on the txn layer, where we try to be as RFC-isch as possible. What I would like, is simply have some function-parameters to the t_check_trans(<DEFANGED_param>), or even better in my little mind, a "modparam("tm", "ack_2xx_matching", 1)". I am looking forward to hearing your reply, and in the mean time, thanks to all of you developers for an extraordinary software :-) Regards Taisto Qvist even if