[SIPForum-discussion] SIP Proxy out of sync message

[MÉSZÁROS Mihály]

Hi,

I am experiencing that my SIP proxy is sending out not the same order 
the transactions as it received.

    1. What do you think Is it normal behaviour?

In my case Ack and a re-invite order is mixed during the traversal 
through the proxy.

The Ack message routing and parsing looking for transaction etc. so 
"processing",
takes longer then the "processing" of the "in dialog" re-invite.

So reInvite will be sent out firstly to the UA B (on the TCP) and only 
after the Ack.

The transaction 9 and 10 are pretty close in time, the UA A is sending 
out near the same time.

You can see that ua is firstly sending out ack, and only shortly after 
it is send a reInvite.

Ack has lower cseq(it is correct it is the same as the cseq in the first 
invite), reInvite has +1 bigger cseq value.

    A       UDP         Proxy       TCP         B
1        >Invite>
2      <100 Trying<
3                            >Invite>
4                          <100 Trying<
5                          <180 Ringing<
6      <180 Ringing<
7                            <200 OK<
8      <180 OK<
9        >Ack>
10     >reInvite>
11                            >reInvite>
12                            >Ack>


So the reInvite with higher cseq arriving firstly to UA B.
    2. Should the B queue transactions, and cotrrect the order somehow?
    3. If yes how long should it wait? (AFAIK UAS tranaction processing 
is atomic)
    4. Who can correct the order according to cseq? UAS Core?
    5. When should pass the received message to  UAS transaction?

Between Proxy and B there is TCP connection so it is reliable transport, 
but between the A and proxy there is UDP.

    5. I searched for this situation in RFC3261, but didn't found any guide.
    6. It will be nice if You can send some pointers, where i can find 
details about right behavior of the proxy and UA B in this case..

Any help or suggestion what can guide me to find the correct behavior, 
is highly appreciated!

Many Thanks!
Mihaly MESZAROS