[Serusers] How to drop a redundant/broken SIP reply message?

[Hendrik Scholz]

Hi!

On Dec 24, 2009, at 12:35 AM, Frank Durda IV wrote:
> is what you normally get, with the two
> 18x messages coming one or two seconds apart.

The reason for this usually is that Softswitches map every
ISUP message to a SIP message and even if there isn't
any 'new' information they still send something downstream.
We see this on another Softswitch as well.

> However, if the called number is busy, you get
>
> 100 Trying
> 183 Session Progress (no SDP payload)
> 486 Busy Here
>
> What the calling party experiences for that is a second
> or two of ring-back commencing with the 183 Session
> progress, then a busy signal.   That's very non-compliant.

I'd call that expected behaviour ;)
Imagine this case: I call you on your cell. You pull your phone out
of your bag,  see my number and after a few seconds decide to reject  
my call.
In that case a 486 will be send to me a few seconds after the 183.
As a matter of fact my phone does play a ringtone for a few
seconds as your phone is actually ringing. Whether the tone
was locally generated or sent from the network/you is a different
story.

I do see the issue with the client first generating the ringtone locally
followed/mixed with a network provided one. Note that
the early media might include a precall announcement, advise
of charge or simply a custom ringtone.
I believe it is also common to play announcements as early media
to work around some billing things.

I do not have a solution at hand to supress the 183 you experience but
wanted to mention a few scenarios in which the 183 does make sense
from a user experience point of view.

Just my $.02,
  Hendrik

--
Hendrik Scholz
VoIP System Engineer
hendrik.scholz at freenet-ag.de
Tel.: +49 (0) 431 9020552
Fax: +49 (0) 431 9020559

freenet Cityline GmbH
Ein Unternehmen der freenet Group
Am Germaniahafen 1-7
D-24143 Kiel

www.freenet.de

Geschäftsführung: Stephan Esch, Andreas Jürgensen, Bodo Rebetge,  
Andreas Sand
Sitz der Gesellschaft: Kiel
HRB 6202 KI, Amtsgericht Kiel