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I am trying to connect USSD connections OpenBTS to Restcomm-Connect over SIP. It seems like this should be possible but I keep running into issues. Hopefully someone has done this before and can be of help.

What I've Done So Far

  • OpenBTS is running and a phone can connect to the radio
  • Restcomm Connect is running and I have created a USSD application to configured for *100# pointing to it.
  • SIP.USSD.Proxy is pointing to the Restcomm SIP port

What Happens When USSD Codes Are Dialed

  • A SIP INVITE goes to the Restcomm server. That looks like this

    INVITE sip:*100#;phone-context=irrelevant.net;user=dialstring@xxx.xx.x.xx:5080 SIP/2.0

    <?xml version="1.0" encoding="UTF-8"?> <ussd-data> <language>en</language> <ussd-string>%s</ussd-string> </ussd-data>

    • The Restcomm server then sends back a 400 Bad request.
    • A notification is left in the Restcomm logs.

      Restcomm cannot process this call because the destination number *100#;phone-context=irrelevant.net;user=dialstringcannot be found or there is application attached to that

We have recompiled OpenBTS removing the line that adds the ;phone-context=irrelevant.net;user=dialstring string source. Thinking that it could be confusing Restcomm. Still no luck.

One theory is that the OpenBTS SIP client needs to authenticate with Restcomm.

Requirements

  • I am not beholden to Restcomm and would be fine with any OpenBTS -> SIP -> HTTP gateway.
  • What is the reference implementation for OpenBTS USSD SIP?
fizzyh2o
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  • what do you get in logs when you remove the `;phone-context=irrelevant.net;user=dialstring` ? Can you send the full INVITE that you receive at Restcomm Connect in that case ? – jeand Apr 20 '17 at 05:29
  • The new invite is INVITE sip:*100#@172.28.6.90:5080 SIP/2.0 The Content-Type is application/vnd.3gpp.ussd+xml The Restcomm notification error is the same but without the extra string. – fizzyh2o Apr 21 '17 at 00:14
  • We would need Restcomm Connect DEBUG logs to be able to investigate and tcpdump traffic on the Restcomm Connect machine. – jeand Apr 21 '17 at 05:08
  • After looking at this more it unfortunately seems that OpenBTS does not support USSD at the level we need to connect to RestComm. – fizzyh2o Apr 26 '17 at 22:27
  • @fizzyh2o - can you say why OpenBTS ended up not working for you? did you try https://github.com/shingy92/ussd-openbts ? - it's a version of OpenBTS recompiled with some extra USSD support – phoenixdown Feb 02 '18 at 18:25

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