Ringback tone doens't work in some outbound calls

[Faisal.Saoud]

ringback tone doesn't work in some outbound calls, I have attached two calls, one we can hear the ringback tone from the calling ip phone, and another we don't hear the tone.

call flow: IP Phone>CUCM >Sip>VG>Sip>ITSP

the calling number in both:4823 

[b.winter]

Have you compared the calls by yourself? Probably not ...

If you would have compared the calls, then you could have noticed the following:

In the working call, the provides first sends an "UPDATE" and then "RINGING".
In the non-working call, it's is vice-versa. The provider first sends "RINGING" and then an "UPDATE".

Furthermore, the in the working call, the provider includes "P-Early-Media: sendrecv" in the "RINGING" and "UPDATE" messages, but not in the non-working call.

To-Do: Talk to your provider.

[Faisal.Saoud]

@b.winter 

unfortunately, I get a little confused in some sip cases and don't know how to troubleshoot it. If you advise me on a book to help troubleshoot it, I will be thankful. 

[b.winter]

Since I have never used a book or had a training for VGW / CUBE troubleshooting, I personally can't recommend one.
But books and trainings can only provide you theoretical basic knowledge and maybe provide a basic concept / approach (like where to look -CUCM or VGW/CUBE, which tools are available - debugs/show and RTMT, ...). There are probably countless docs, websites, videos, ... in the internet about troubleshooting. But the real learning only happens while doing the troubleshooting.

Like programming: you don't learn real programming by just reading books or watching videos, you learn it by doing the programming on your own.

[Roger Kallberg]

This Cisco Press book is a fantastic source of information on the topic, Understanding Session Border Controllers Comprehensive Guide to (CUBE) Solutions.