Hi again,
I hope I am not being to pushy/obnoxious now, but I was really hoping I could get an anwer from the openser-guru's concerning my issues with the transaction matching code I mentioned in an earlier mail.
I and my co-workers feel that the RFC is quite clear on the subject of matching ACK to 2xx, so I would really like to hear what the objections are, since openser does not behave this way.
What I was trying to do, was simply to stop the ACKs for 3++ in my script by using "t_check_trans()" and if the ACK did match the transaction, the script would end processing.
But I suppose I'm supposed to do this some other way??
Anyway, I hope to hear from someone, indicating what your views on this txn-matching issue is.
Regards Taisto
Taisto Qvist wrote:
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. Also, 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 and I believe the RFC is faily clear
on this.
(It probably boils down to how rfc-isch you want to be.)
[Bogdan] The end-to-end ACK establish a separate transaction (RFC 3261) and these ACKs are not match as part of the INVITE transactions, but correlated with them.
[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.
[Bogdan] but even describe the wait timer. So, there is no contradiction.
[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 main reasons for saying that ACKs for 2xx should not be matched, come from the following 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 "Terminated" state. This is actually necessary to guarantee correct 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, subsequent 2xx will find no match and therefore be passed to the core.
[TQ] It even says "actually necessary 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 retransmitted 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. Or?
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 even explicitly says(sure, not "MUST" but..):
.. 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.
<snip old stuff>
What I would dream of, is simply have some function-parameters to the t_check_trans(<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
Hi guys,
Just to bring some clarifications on the TM module.
once a transaction is completed (negative or 2xx reply), it is put on wait (wait timer - see RFC3261) for catching any potential retransmissions of replies. So, the transaction is completed, but not removed from memory - RFC
does
not say that you need to trash immediately all the transaction information, but even describe the wait timer. So, there is no contradiction.
The ACK (for 2xx)catching is done based on the completed INVITE transaction (from wait timer) - nothing else.
Inaki, could you please detail what you mean by:
<quote> In my opinion OpenSer does a special treatment for ACK in tm mode,
even if
they are for failed transaction (hop-by-hop ACK's) or succesfull INVITE (end-to-end ACK's).
</quote>
Maybe I can explain you more if I understand you question....
Regards, Bogdan