New subject: [OpenSER-Users] TM module is not 3261 compliant (matching ACK to 2xx)

18 Feb 2008

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 