How do ISPs and/or 3-G services block VOIP, is it by port number?

Discussion in 'UK VOIP' started by tinnews, Oct 6, 2012.

  1. tinnews

    tinnews Guest

    As per the subject, how do ISPs and/or 3-G internet providers block
    VOIP (if they do)? If it's blocked by stopping traffic on specific
    ports one can presumably bypass the block by using different port
    numbers, however if they actually look at packets to see what's in
    them this wouldn't work.

    I want to use VOIP on an 3G connection, the conditions of
    use explicitly say that you *can* use VOIP but that to do this you
    have to ask them to enable it on your connection. The problem is that
    there is no clue as to how to ask for it to be enabled and no one that
    I have spoken to at Orange has any idea about this either.

    Alternatively I guess one might be able to set up an ssh tunnel for
    the VOIP ports but I'm not quite sure of the details of how one might
    do this, does anyone have any ideas/pointers?
    tinnews, Oct 6, 2012
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  2. tinnews

    Chris Davies Guest

    They could trivially block traffic to port 5061 or traffic to known
    SIP end points. Or they could do packet inspection and drop packets
    containing VoIP traffic.

    Make a note of the date/time you called about this matter, who you spoke
    you, and the outcome. Then go ahead any try VoIP anyway.

    You really do not want to be tunnelling time-sensitive UDP traffic over
    a TCP connection if you can possibly help it. If you get really stuck,
    take a look at the VPN capability of I've not used it myself
    but ISTM that it's intended to help get around ISP port blocks.

    Chris Davies, Oct 6, 2012
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  3. As Chris says, this isn't a great idea - you'd do a lot better to use
    an individual-packet-based VPN, such as OpenVPN. For any VPN solution
    to work, you'll need an endpoint outside the network you're trying to
    tunnel out of - a server you run, or a public or commercial server if
    such are available.
    Roger Burton West, Oct 7, 2012
  4. tinnews

    tinnews Guest

    OK, thanks for the feedback and ideas. I can run OpenVPN (on my home
    Linux system) but it feels like overkill for the requirements I have.
    I'll explore the alternative ports approach first.
    tinnews, Oct 8, 2012
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