WCF Intermediary to enable calls between 2 endpoints behind routers without router configuration

I'm de开发者_C百科veloping a synchronization service using WCF and Sync Framework, and I have it working when the endpoints can communicate directly.

The next step I need to implement is to synchronize 2 endpoints where they both are behind routers and the router ip is changing constantly. I am thinking about a publicly available intermediary that should forward the calls between the 2 endpoints. My biggest problem is that I cannot rely on the users to configure the port forwarding on routers so I cannot directly open a connection from the other endpoint or the intermediary.

My idea is based on FogCreek's CoPilot, and other remote assistance solutions (LogMeIn, TeamViewer, etc) which works without any router configuration.

How would you implement it?

You need something like relay in Azure. I would try implement it this way:

Your intermediary will provide two operations:

• Push - client will call this operation when publishing new data for synchronization. Data will be stored on service until other client downloads them.
• Pull - client will call this operation regulary to download any published data stored on intermediary.

Routers with changing IP should not be a problem, because client will be always initiating connection.

If you are not limited to HTTP protocol you can implement this with Net.Tcp binding and use duplex communication. In such case your intermediary will be able to forward synchronized data immediately. But this solution can have additional complexity when dealing with sessions and connections.