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Thread: NAT problem

  1. #1
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    NAT problem (mobile2mobile tcp relay)

    Hi,

    I just want to know if anybody can comment following text. Any comments are welcomed:

    Becuse there's NAT on GGSN and after your mobile phone has established PDP context it has assigned IP address from operator private (10.xxx.xxx.xxx typically or 192.168.xxx.xxx) pool it's not possible from outer world behind the operator firewall to access the phone (send UDP packet or establish TCP connection). The only possibility is to establish permanent TCP connection from mobile device to the server located in the network mobile(public Internet in this case).

    After establishing such connection, server knows mobile IP address and can distribute it to the other users in some way (SIP for example). If other mobile wants to communicate with me it uses its established TCP connection (or establish new one, leaving one connection for "controlling" only- as FTP or RTCP protocol are doing...) and send data to the server. Server just simply connect originator TCP conectoion with receiver TCP connection and routes the TCP data stream to the other side... In other words it just resend the data form one end to the other.

    Any comments?
    Thanks a lot for reading.
    Bye
    STeN
    Last edited by stenlik; 2006-05-21 at 06:52.

  2. #2
    Nokia Developer Moderator
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    Re: NAT problem

    Quote Originally Posted by stenlik
    In other words it just resend the data form one end to the other.
    Yes, it is not a very sophisticated approach, but it works. For example mApache (http://research.nokia.com/research/p...ile-web-server) uses (more or less, I do not know the details) this approach.

  3. #3
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    Re: NAT problem

    Yes, you may use a forwarder (if I understood your description correctly). Alternatively, you may use nat traversal techniques to achieve a p2p communication (see hole punching for instance). Doing it for udp is easier than for tcp, given it's connectionless nature.

  4. #4
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    Re: NAT problem

    Hi,

    many thanks for the replies, do you know about soeme opensource (ideally under GNU GPL v2 ) solutions for linux platform??


    Many thanks
    Bye
    STeN

  5. #5
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    Re: NAT problem

    Search for tcp bouncer or tcp relay for the first option.. I recall seeing some free examples..
    For nat traversal, you can either check some p2p client (most implement some way or another) though the concept is quite straight forward.

  6. #6
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    Re: NAT problem

    Hi PushL,

    many thanks for your reply, but tcp realy only is too simple, I need system, which use tcp relay principle, but form my perspective it must have following features:

    - have http/https administration interface, where users can register their nickname(sip address...), password, manage friendlist... and others

    - you connect to the "control" server port form mobile device and then you send ideally SIP REGISTER request (may be also HTTP digest is computed for security reasons...) containing list of services your client is providing. When user is allowed 200 OK is send from server and you can download status of members of your friendlist... or subscribe for their status change

    - togehter with their status you download also list of services they're supporting and you can compare it with your list...

    - then you'll send INVITE request, specifying opponent sip address - it will be realyed by the server to the other side...

    - after session will be established the data flow will be ralyed by server on other "media" port leaving the "control" port only for getting status and establishing sessions...

    I'm probably going to develop something similar (making it as simply as possible) on my own. But before I'll start ANY COMMENTS from you or anybody else are welcomed... May be you know about something better, which is freely available or you have better ideas, solution for something like this...

    Bye

  7. #7
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    Re: NAT problem

    We have a NAT traversal product that let's you control a firewall from the client. It is a DLL that provides the ability to open and close ports on a router/firewall. The solution does not require a server and consumes zero bandwidth. Information and API documentation is available at http://www.zconf.com

    I don't know if it would work for you, but we could do some customization if required.

    Thanks,
    David

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