13 replies to this topic

[rickyk586]

Is there any way to establish a TCP connection between two client sockets without one of them being a server?

Task: To establish a connection between two computers.

Requirements:

• TCP connection (socket)
  
• The two computers to be connected cannot listen to ports/accept connections (like a server does).
  
• The two computers can however initiate a TCP connection (like a client does)
  
• The network path between the two computers cannot be listened to (sniffed).
  
• Any number of computers can be used, and these restrictions only apply to the two computers to be connected.

I am 99% sure that this task is impossible, but there are some pretty smart people out there so I may be wrong...

[WingedPanther]

One way this has been done with some software is to have a third computer which is a server.

[Maurice_Z]

Well, since there is no Server to listen to ports, you can't get any data, no matter how hard you try, I think... That's how far my logic can take me ^^

[rickyk586]

Still no one can answer it??

[DuneMan]

trick one I think

[R-G]

Well, this issue is elementary (not so hard to do in the practice as it sounds like, or as some other issues theoretically could be), but it is definitely not conveniently.

I could give you a nice introduction on this issues without any problems, but I don't have every minute free time, so I recommend that all people that are interested in this issue try to search for it in a digital search engine. I suggest that you use appropriate parameters, so you will receive pure useful information.

[rickyk586]

I would love to hear your answer. I have posted this question on many forums, and have searched the internet many times, and I have concluded that this task is impossible.

The connection requires sync numbers which are randomly generated with each connection, so there is no way to determine what the sync number will be (and there is no way to set the sync number in Java anyways).

[hetra]

Well, maybe a peer model?

Where both computers are both servers and both clients at the same time...

Peer-to-peer - Wikipedia, the free encyclopedia

[zoranh]

You can't have Berkeley socket connection without one side listening, so your requirements (1) and (2) cannot be both met at the same time.

However, you can have an application protocol (like some of P2P protocols) which doesn't define nodes (computers) as client and server, or master and slave, but rather both can initiate any kind of two-way communication at any given time.

You can imagine chess-playing software which defines two players where each player can initiate an action (make a move). None of them is logically a server. However, physically, one of them must have a server socket in order to create socket connection. It's as simple as that.

For more about Berkeley sockets you may refer to Wikipedia article: Berkeley sockets.

[abzero]

Hmm you guys know the topic is 3 years old.

Anyway, the last constraint in the problem is:
Any number of computers can be used, and these restrictions only apply to the two computers to be connected.

So the answer is....use a third computer which can listen,

[dargueta]

Guys, please try not to resurrect old threads like this, as it pushes more recent ones (with people still paying attention) down the list. R-G, rickyk586 and DuneMan have all left the forum, and Maurice_Z hasn't made a post since February.

And abzero/WingedPanther, you're right, but the problem is that once the computers are connected, they can't communicate because they can't listen. I think. I dunno, that's my interpretation, anyway.

[SweetSixteen <3]

How about you have both computers listening for the other? That way both can accept connections and act as either client or server. It can be done, just not the way you're putting it.

Asking to do it your way goes against the very designs of the OSI model, the IP protocol, the TCP protocol, and who knows how many other holy texts in between.