responding to peer over public gprs (O2) - PPP

This is a discussion on responding to peer over public gprs (O2) - PPP ; I have a server application that receives data over GPRS using UDP from various mobile clients. There is no problem with the client to server "send", as there is a static ip address to connect to. The problem comes in ...

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Thread: responding to peer over public gprs (O2)

  1. responding to peer over public gprs (O2)

    I have a server application that receives data over GPRS using UDP from

    various mobile clients. There is no problem with the client to
    server "send", as there is a static ip address to connect to.

    The problem comes in returning responses to the client, as the ip
    addresses are assigned by the bearer, and are private.

    Am I correct in saying that this would be resolved by using VPN? I am
    struggling slightly, as this is not my area of expertise.

    To summarise :-

    Client establishes connection to host with static IP address.
    Host needs to respond to client using identification in the UDP.
    Connection to client then needs maintaining.

    If I there is a better group, please advise me. Any help or pointers
    will be much appreciated.
    Jim


  2. Re: responding to peer over public gprs (O2)

    On 2006-02-21, jmlawton@gmail.com wrote:
    > I have a server application that receives data over GPRS using UDP from
    >
    > various mobile clients. There is no problem with the client to
    > server "send", as there is a static ip address to connect to.
    >
    > The problem comes in returning responses to the client, as the ip
    > addresses are assigned by the bearer, and are private.
    >
    > Am I correct in saying that this would be resolved by using VPN? I am
    > struggling slightly, as this is not my area of expertise.


    This is a generic network address translation (NAT) issue. Perhaps
    reading http://en.wikipedia.org/wiki/Network...ss_translation would
    help.

    -Mikko

  3. Re: responding to peer over public gprs (O2)

    Thanks Mikko,
    I think you are right. I quote from that item :-
    "Services that require the initiation of TCP connections from the
    outside network, or stateless protocols such as those using UDP, can be
    disrupted. Unless the NAT router makes a specific effort to support
    such protocols, incoming packets cannot reach their destination"

    I think the point is, that one cannot rely on a public provider (O2,
    Orange) to provide the NAT decoding on the return leg. So when the
    client's UDP arrives at the server with the bearer's general translated
    IP address in it as the source, responses to that address will not
    arrive at the client.

    It is that problem which I need to resolve, having no control over the
    bearer's NAT arrangements.


  4. Re: responding to peer over public gprs (O2)

    On 2006-02-21, jmlawton@gmail.com wrote:
    > I think the point is, that one cannot rely on a public provider (O2,
    > Orange) to provide the NAT decoding on the return leg. So when the
    > client's UDP arrives at the server with the bearer's general translated
    > IP address in it as the source, responses to that address will not
    > arrive at the client.


    Or the NAT device accepts responses until some timer expires. If the
    private host uses static UDP ports when sending, the timer can be kept
    from expiring by pinging the server with useless UDP packets, but then
    one could just use TCP initiated from the private network. TCP
    connections also have timeouts at the NAT gateway, so connection errors
    should be handled well, though.

    -Mikko

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