[Users] BYE before 200 OK?

Bogdan-Andrei Iancu bogdan at voice-system.ro
Fri Sep 2 20:17:47 CEST 2005

Hi there,

Iqbal wrote:

> no BYE should occur, after 200 OK, your UAC should send ACK to 
> openser, and openser  ACK to gateway, it seems as if the pstn GW is 
> not getting the ACK's
> Iqbal
> Michael Ulitskiy wrote:
>> Hello,
>> Can someone please enlighten me on if this is allowed to send BYE
>> before 200 OK? I thought that BYE should be used only after dialog
>> established, but now I have a SIP PSTN termination provider and they
>> appear to be sending BYE with route headers right after 183 Session 
>> Progress
>> in some cases.
>> So the session looks like the following:
>> UAC                                OpenSER PSTN                       
>> Provider UAS
>> INVITE to openser
>>                                         180 Trying back to UAC
>>                                         INVITE to UAS
>> 180 Trying back to openser
>> 183 Session progress back to openser
>>                                       183 Session Progress back to UAC
>> BYE to openser with Route headers
>>                                       BYE to UAC (loose_routing)
>> 200 OK to openser
>>                                       200 OK to UAS
>> Is it ok?
No this is not OK - BYE must be use only if the call was established via 
a 200 OK. If UAC want to terminate the call before the 200 OK, it must 
use CANCEL; for same result, UAS must reply with a negative reply. If 
they do not act like this, the INVITE transaction will remain active 
(until some timeout hits).

But double check if the BYE doesn't belong to a different dialog. 
Otherwise, I would say the UAS GW is broken here......

>> And there's even more to it. I don't know if above is OK or not, but 
>> I would thought that now the session is ended. Nonetheless in exactly 
>> 50 seconds I'm getting
>> 183 Session progress back to openser
>>                                       183 Session progress back to UAC
>> -- in another 60 seconds
>> 183 Session progress back to openser
>>                                       183 Session progress back to UAC
>> -- this happens 6 times every 60 seconds and then
>> 408 Request Timeout back to openser
>>                                        ACK to UAS
>>                                        408 Request Timeout to UAC
>> ACK to openser
>> Do you think it's a provider bug? Another question is how openser is 
>> routing replies that cannot be matched to transaction
>> as I think transaction has already been deleted after BYE and latest 
>> 183 replies were routed
>> by some other principle. Could please someone comment on this?
no, the previous BYE does not stop the INVITE transaction on proxy - 
only a UAC CANCEL or UAS final reply can do it (or proxy timeout).
The INVITE transaction ends when the 408 is received from the UAS.
Since replies are still generated by the GW for the INVITE, again, check 
if the BYE belongs to INVITE dialog.......

If not, the GW is twice broken :-/: first because of BYE before 200 and 
second for keep sending replies foe INVITE after BYE.


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