[Serusers] loop call with asterisk

[Bogdan-Andrei IANCU]

Hi Richard,

I guess it's a very thin line between a loop and a spiral. They are very 
similar (even impossible to tell the difference from SIP point of view), 
but first is harmful and the second useful :-).
I haven't went through the RFC, but IMHO is tricky for UAS detect 
properly a loop - I guess that's way everybody relies on MAX_FORWARD to 
end potential loops.
So, depends a lot of what *  consider a loop (how exactly does this) - 
because, as you said, all important hdrs are the same. Btw, is at least 
RURI changing between  outgoing and returning call ( on *) ?
The worst solution will be insert a very simple B2BUA in the middle to 
change at least some tags. But is ugly :-(

regards,
Bogdan


Richard wrote:

>Hi,
>
>I am trying to use * as a PSTN gateway. When a call comes in from PSTN, it
>is forwarded to ser. If for some reason (e.g. call being forwarded back to
>PSTN), ser will just do a record route and send it back to *. When * gets
>this call, it thinks it is a loop and drop the call. I know that this
>question has been raised before. I'd like to see, just from sip respective,
>what's the theoretical way to solve it? Since all major fields are the same,
>e.g. fromuri, touri, cseq, callid, what is the right way to detect loop in
>SIP in this case? Btw, cisco router doesn't have this problem.
>
>Thanks,
>Richard
>
>
>
>
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