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@freenet-ag.de Tel.: +49 (0) 431 9020552 Fax: +49 (0) 431 9020559
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