ISP Trunk Session ID?

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Asterisk Users 3 Comments

Hi folks,

What I trying to do here is exactly this:

My provider given me a Huawei modem which have 2 phone jacks on it, but instead of using it I rather redirect my POTS number to my PBX. I ran into couple of bumps on the road but now it’s “half-working”. I extracted the SIP user, pass, server info from the modem and even managed to put my PBX into the same VLAN they use, on the exact same IP address like the modem but there is 1 problem:
It seems this modem also sends some session ID to the ISP’s sip server, something what Asterisk doesn’t by default. So if I do this:

1, Let the modem register at the sip service (the phone number can be called and ringing out)
2, Disconnect the modem
3, Let the PBX connect to the SIP server
4, PBX accepts the calls
5, About 5-10 minutes later it stops doing it, when I call the number it shows busy (beep, beep, beep), no matter if I restart Asterisk or not it won’t work anymore just if I do the same trick again

I’m sure the remote SIP server breaks the voip channel or something, it does NOT drop me out tho, my PBX can register any time without problem but no packets will ever come forward me anymore. It’s kind of hard to solve this from 1 side.

There must be some solution for this.

Please help!

Thank You, Sergej

3 thoughts on - ISP Trunk Session ID?

  • hi, you can try to change sip user agent and sdp session s , owner in sip config same as your phone,s (modem). asterisk by default send user agent = asterisk version , s= asterisk , oasterisk. some providers are not happy if they see “asterisk” word 🙂

  • Sorry to chime in here, is it possible to change the “Server: Asterisk
    “, “s=Asterisk”, and “o=” within sip.conf? What are the directives exactly please?

    Thanks in Advance,


  • you can find in [general] section. useragent=asterisk ; Allows you to change the user agent string
    ; The default user agent string also contains the Asterisk
    ; version. If you don’t want to expose this, change the
    ; useragent string. sdpsession=asterisk ; Allows you to change the SDP session name string, (s=)
    ; Like the useragent parameter, the default user agent string
    ; also contains the Asterisk version.
    ;sdpowner=root ; Allows you to change the username field in the SDP owner string, (o=)