how can make EDI socket service ..?

We are currently delivery a EDIproject and have hit issue.
we want to interact SAP R/3 system and our customer system only through a VAN which Tcp Socket.
we can only connect our customer with Tcp socket.
because our customer have no plan new EDI standard development, XML others.
we can make client socket service by B2B Integrator and EDI adapter but we learned to need server socket service.
But I don’t know how can create server socket or invoke service.