[Serusers] AW: Snom phone (fwd)

Christian Stredicke stredicke at snom.de
Tue Mar 4 08:42:58 CET 2003

the gateway mandates PRACK, that cant be turned off. The OPTIONS can be
avoided if the phone is set to use REFER explicitly.
-----Ursprüngliche Nachricht-----
Von: Robert Messer [mailto:rmesser at abpintl.com] 
Gesendet: Dienstag, 4. März 2003 05:58
An: cs at snom.de
Betreff: RE: Snom phone (fwd)
I will try to modify the code accordingly, however, 
I've been looking at the OPTIONS tag.  Perhaps I can tell the
snom phone not to use PRACK?  I'll look into that.
-----Original Message-----
From: Kevin [mailto:kmoroz at abpintl.com] 
Sent: Monday, March 03, 2003 8:09 PM
To: 'Greg Fausak'
Cc: 'Robert Messer'; sip at august.net; serusers at lists.iptel.org
Subject: RE: Snom phone (fwd)
   According to snom engineering you should put the routing 
information in the first 200 OK we receive.  Can you do that and try it?

You can test against my proxy if you like to see how it should work. 
-----Original Message-----
From: Greg Fausak [mailto:greg at august.net] 
Sent: Monday, March 03, 2003 7:13 PM
To: 'Kevin'
Cc: 'Robert Messer'; sip at august.net; serusers at lists.iptel.org
Subject: RE: Snom phone (fwd)
I initially sent the packet:
> > > This is that packet that came from the last 200 OK <- PROXY:
> > > 
> > > #
> > > U 2003/02/24 07:56:52.503535 -> 
> >
> > > SIP/2.0 200 OK.
> > > Via: SIP/2.0/UDP;branch=z9hG4bK-ng5tokyx448r.
> > > From: "snom man" <sip:4695461245 at augustvoice.net>;tag=8u6ju8wxuc.
> > > To: <sip:2143357976 at augustvoice.net;user=phone>;tag=3CBB0360-532.
> > > Date: Mon, 24 Feb 2003 13:56:43 GMT.
> > > Call-ID: 3c267202b6a8-lgseu8olovlp at
> > > Server: Cisco-SIPGateway/IOS-12.x.
> > > CSeq: 2 INVITE.
> > > Session-Expires: 7200;refresher=uac.
> > > Require: timer.
> > > Allow-Events: telephone-event.
> > > Contact: <sip:92143357976 at;user=phone>.
> > > Record-Route: <sip:2143357976 at;ftag=8u6ju8wxuc;lr>.
> > > Content-Type: application/sdp.
> > > Content-Length: 209.
> > > .
> > > v=0.
> > > o=CiscoSystemsSIP-GW-UserAgent 7543 5694 IN IP4
> > > s=SIP Call.
> > > c=IN IP4
> > > t=0 0.
> > > m=audio 16632 RTP/AVP 0 100.
> > > a=rtpmap:0 PCMU/8000.
> > > a=rtpmap:100 X-NSE/8000.
> > > a=fmtp:100 192-194.
> > > 
This is the 200 OK (response to the INVITE) message as delivered to the
I couldn't figure out what you were saying, so I went back to
the ethereal trace.  After the snom phone receives a 183 status
message, it sends a PRACK to the PROXY.  This PRACK is
OKed, without a Record-route.  The next message is an OK
responding to the original INVITE, which does indeed have a
So, you are saying that the OK to your PRACK needs a record route?
I can do that I think, because the OK to the INVITE does indeed have
a Record-route.
I don't even know what a PRACK is for...
-----Original Message-----
From: Kevin [mailto:kmoroz at abpintl.com] 
Sent: Monday, March 03, 2003 5:19 PM
To: Greg Fausak
Cc: 'Robert Messer'
Subject: FW: Snom phone (fwd)
Hi Greg, 
   Sorry it took so long to get back to you.  Normally it is faster but
as I stated the SIP inter-
operability was last week which caused the delay.  Looks like the issue
is with the 
SER proxy.  If I knew the specification deeper I should have been able
to answer it myself.  Engineering cc’s Jiri on their response to me so
he is aware of the issue.  
-----Original Message-----
The phone updates the route until it receives a 2xx code. The 200 Ok
response does not contain such a route therefore the phone uses the last
route it receives in the 200 – which is empty. Therefore, the phone MUST
send the ACK directly to the gateway. 
§ 12.1.2 of the RFC3261. The dialog is NOT established by the
401-challened request.
The proxy can very easily solve the problem by putting itself into the
routing path of the 200 Ok.
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