Duplex channel wrapper.
The duplex channel wrapper is listening to more duplex input channels. When it receives some message,
it wraps the message and sends it via the only duplex output channel.
On the other side the message is received by duplex channel unwrapper. The unwrapper unwraps the message
and uses the duplex output channel to forward the message to the correct receiver.
The receiver can also send the response message. Then it goes the same way back.
Notice, the 'duplex channel wrapper' can communication only with 'duplex channel unwrapper'.
It cannot communicate with one-way 'channel unwrapper'.