Question

Since, two methods with the same parameters but different return values will not compile. What is the best way to define this interface without loosing clarity?

public interface IDuplexChannel<T, U>
{
    void Send(T value, int timeout = -1);
    void Send(U value, int timeout = -1);
    bool TrySend(T value, int timeout = -1);
    bool TrySend(U value, int timeout = -1);
    T Receive(int timeout = -1);
    U Receive(int timeout = -1);
    bool TryReceive(out T value, int timeout = -1);
    bool TryReceive(out U value, int timeout = -1);
}

I considered using out params but that would make it a little awkward to use.

public interface IDuplexChannel<T, U>
{
    void Send(T value, int timeout = -1);
    void Send(U value, int timeout = -1);
    bool TrySend(T value, int timeout = -1);
    bool TrySend(U value, int timeout = -1);
    void Receive(out T value, int timeout = -1);
    void Receive(out U value, int timeout = -1);
    bool TryReceive(out T value, int timeout = -1);
    bool TryReceive(out U value, int timeout = -1);
}

Generic version, a little unwieldy but it works.

public interface IDuplexChannel<T, U>
{
    void Send(T value, int timeout = -1);
    void Send(U value, int timeout = -1);
    bool TrySend(T value, int timeout = -1);
    bool TrySend(U value, int timeout = -1);
    V Receive<V>(int timeout = -1) where V : T, U;
    bool TryReceive(out T value, int timeout = -1);
    bool TryReceive(out U value, int timeout = -1);
}

Answer 1

The main problem is you are trying to view the duplex channel from both ends at the same time. Data travels both ways on a duplex channel, but there are still definite endpoints. What you send on one end is what you receive on the other.

public interface IDuplexChannel<TSend, TReceive>
{
    void Send(TSend data);
    TReceive Receive();
}

That said, you should be using WCF anyway, especially since you’re using .NET 4.0.

Edit: Pictures

        "PERSON" A                                     "PERSON" B
            O            int ----------------->            O
           -|-           <-------------- string           -|-
           / \                                            / \
IDuplexChannel<int, string>                     IDuplexChannel<string, int>