[OpenSER-Devel] [Serdev] Possible bug in the tm module in the presence of packet loss/branches

[Maxim Sobolev]

Dan Pascu wrote:
> On Friday 07 March 2008, Maxim Sobolev wrote:
>> Klaus Darilion wrote:
>>>> The correct behavior of the tm module in this case would be to
>>>> continue with INVITE re-transmits until we get provisional response
>>>> and immediate CANCEL once that response comes in.
>>> Is this really the correct behavior? Is this behavior defined in RFC
>>> 3261?
>> --- RFC 3261 ---
>>     Once the CANCEL is constructed, the client SHOULD check whether it
>>     has received any response (provisional or final) for the request
>>     being cancelled (herein referred to as the "original request").
>>
>>     If no provisional response has been received, the CANCEL request
>> MUST NOT be sent; rather, the client MUST wait for the arrival of a
>> provisional response before sending the request.
>> --- RFC 3261 ---
>>
>> According to my reading yes, UAC should wait either arrival of the
>> first provisional response or expiration of Timer B (doing due
>> retransmits in the meantime for unreliable transports) and send CANCEL
>> if provisional reply comes in.
> 
> In the paragraph quoted above I do not see any reference to TimerB or to 
> keep retransmitting the initial INVITE on a branch that did not send a 
> provisional reply, even after the caller has canceled the call. The only 
> thing I read in there is that if a branch has not sent a provisional 
> reply until the branch is about to be canceled, either because other 
> branch has picked up the call or because the caller has canceled the call 
> himself, then a CANCEL should not be transmitted on the branch without a 
> provisional reply. This behavior is already honored by openser, AFAIK.

No, it's not. UAC (SER/OpenSER) that wants to cancel branch should wait 
for the provisional reply to come back and then send CANCEL. Neitehr SER 
nor OpenSER does that. The only question is whether or not is should 
keep re-transmitting INVITE in the meantime.

-Maxim