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SIP URI technical question

  • 14-05-2019 12:36pm
    #1
    Shadeymate
    Registered Users Posts: 8 ✭


    We're using Blueface as our VoIP provider in our SME office.

    In the Blueface web portal, we have Blueface SIP accounts and URI's in the format as below:

    sip:username@ip_address:9876

    The IP address is that of our dedicated ISP Modem for VoIP. The SIP account has a known good working PSTN attached to it. It all works fine.

    However the port 9876 is not open on the dedicated ISP Modem (checking with nmap -sU ip_address -p 9800-9900). I can web-login to the ISP modem, but there is nothing relevant that I can find in regards to port 9876.

    So I don't really understand how phone calls are working correctly (both inbound and outbound)? Anyone able to shed some light or tell me where to start looking?


Comments

  • #2
    tsue921i8wljb3
    Closed Accounts Posts: 5,017 ✭✭✭tsue921i8wljb3


    Shadeymate wrote: »
    We're using Blueface as our VoIP provider in our SME office.

    In the Blueface web portal, we have Blueface SIP accounts and URI's in the format as below:

    sip:username@ip_address:9876

    The IP address is that of our dedicated ISP Modem for VoIP. The SIP account has a known good working PSTN attached to it. It all works fine.

    However the port 9876 is not open on the dedicated ISP Modem (checking with nmap -sU ip_address -p 9800-9900). I can web-login to the ISP modem, but there is nothing relevant that I can find in regards to port 9876.

    So I don't really understand how phone calls are working correctly (both inbound and outbound)? Anyone able to shed some light or tell me where to start looking?

    Port 9876 is the port that you are using for SIP with Blueface. Your device registers with Blueface on startup, then periodically re-registers keeping the SIP communication channel open. The port is not open to the internet.

    Calls do not use this port. When a call is made or received your device and the Blueface server negotiate ports and codecs over Session Description Protocol (SDP) which uses the SIP channel. The port(s) used for calls are not open permanently either, only when required.

    https://www.3cx.com/blog/voip-howto/sdp-voip2/

    My advice is if it is working to leave it alone. I've had issues before with one way audio due to NAT in certain routers and it can be a pain to fix.


  • #3
    Mr. G
    Moderators, Technology & Internet Moderators Posts: 4,621 Mod ✭✭✭✭Mr. G


    Shadeymate wrote: »
    The SIP account has a known good working PSTN attached to it. It all works fine.

    nmap won’t help you here, you’re using NAT. I’d correctly configured, you shouldn’t be able to connect to the port on your public IP.

    What VoIP device are you using for blueface? Can you post your config?


  • #4
    Shadeymate
    Registered Users Posts: 8 ✭Shadeymate


    Alondra Prehistoric Pantry wrote: »
    Port 9876 is the port that you are using for SIP with Blueface. Your device registers with Blueface on startup, then periodically re-registers keeping the SIP communication channel open. The port is not open to the internet.

    Calls do not use this port. When a call is made or received your device and the Blueface server negotiate ports and codecs over Session Description Protocol (SDP) which uses the SIP channel. The port(s) used for calls are not open permanently either, only when required.

    https://www.3cx.com/blog/voip-howto/sdp-voip2/

    My advice is if it is working to leave it alone. I've had issues before with one way audio due to NAT in certain routers and it can be a pain to fix.

    This is great info, thanks. I asked the question as we are investigating switching ISP providers (and IP addresses, and modems). Blueface support say that we can simply go ahead and switch Providers/IPs/modems and the phones will briefly drop then reconnect okay.

    Which kind of makes me a bit nervous because of all the IP + port stuff going on in the SDP connection protocol.


  • #5
    tsue921i8wljb3
    Closed Accounts Posts: 5,017 ✭✭✭tsue921i8wljb3


    Shadeymate wrote: »
    This is great info, thanks. I asked the question as we are investigating switching ISP providers (and IP addresses, and modems). Blueface support say that we can simply go ahead and switch Providers/IPs/modems and the phones will briefly drop then reconnect okay.

    Which kind of makes me a bit nervous because of all the IP + port stuff going on in the SDP connection protocol.

    Blueface are correct. You should be able to switch ISPs without issue. There should be no configuration changes needed. It's one of the benefits of VoIP in that your phone system is not tied to one ISP.


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