[SIPForum-discussion] Time interval between requests

[mtrank at apexvoice.com]

Others may want to comment, because I'm not 100% sure on this, but I
believe you should not send out a CANCEL unless you have received some
type of provisional response from the UAS, like a 100 Trying. Since this
is a re-INVITE, it's more likely that a 100 Trying is *never* going to be
sent.. the UAS will usually send back a 200 OK right away.

In the case of an original INVITE that starts a session, it would seem to
me to be wrong to send a CANCEL without having received a provisional
response first. Before a provisional response arrives, the only new
message that should go out from a UAC is a repeat of the INVITE until the
response arrives. At this stage, if a call is stopped by a human user, I
believe there will be no cancel, the repeats of the INVITE are simply
ceased.

So, using that as a guide, in the case of a re-INVITE, I think the UAC
side should not be sending a CANCEL unless a provisional response has
arrived ( and that will probably never happen ).





> Hi All,
>  
> Is there any time frame mentioned in RFCs which defines time interval
> between REQUESTS? For example, can UAC send CANCEL of a RE-INVITE just
> 0.0004 sec later ?  I tested some SIP servers , but none of them could
> handle the CANCEL properly when it comes just in such a short interval,
> but I  need to refer to RFCs in order to prove this wrong behaviour to
> vendor.
>  
> Thanks,
> Mustafa AYDIN_______________________________________________
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