AW: [Serusers] PRACK

Reinhard Hainz rhainz at
Fri Jun 27 11:06:09 CEST 2003


the situation is more complicated.
The environemet:

A ... a "traditional" phone in the PSTN world
B ... an other "traditional" phone in PSTN
C ... a cisco gw connecting PSTN to IP (SIP)
D ... a SIP-Server (ser)
E ... a phone number configured in ser, that is forwared to the number
of B (using URI rewriting from ser)

The request flow is as follows:

1. A is connected (over PSTN) to C
2. C sends an INVITE to D (URI: E - this is the To-Header, too)
3. D rewrites the INVITE for E to an INVITE to B
4. D sends an INVITE to C for B (E is the record-route)
5. C sends both E a PRACK
6. D sends itself a PRACK for B (but i am not forwarding it)

The question is - why does cisco send this PRACK at all. Wenn I use the
same configuration which IP-Phones only, then no PRACK are send.

At 5. the phone B rings (but no ring tone at A), and after accepting the
call at B the call is established and works. 


-----Ursprüngliche Nachricht-----
Von: serusers-bounces at [mailto:serusers-bounces at] Im
Auftrag von Andy Blen
Gesendet: Donnerstag, 26. Juni 2003 15:18
An: Reinhard Hainz; serusers at
Betreff: Re: [Serusers] PRACK

I don't think the problem is on SER side, SER supports PRACKs
Feel free to send us network dumps so that we look at the problems you


At 02:59 PM 6/26/2003, Reinhard Hainz wrote:

>is ser supporting the SIP Request PRACK ? I get this Requests when i am
forwarding an incoming call from a cisco router back to it (with an
other number) à the destination telephone rings but i do not hear the
signals (ringing) on my calling phone. When the called phone accepts the
call then everything works fine.
>In more detail:
>The cisco router sends 2 PRACK Requests: 
>    * to the phone that is the destination of the forward (after
>    * to the phone with the forwarding set 
>But not to the phone which initialises the call.
>Serusers mailing list
>serusers at

Andy Blen Services 

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