explicit global protocol Dns(role Client, role Server, role Other)
{
    query(Addr, Packet) connect Client to Server;

    choice at Server {
        dummy() connect Server to Other;
        answer(Addr, Packet) from Server to Client;
    } or {
        query(Addr, Packet) connect Server to Other;
        answer(Addr, Packet) from Other to Server;
        answer(Addr, Packet) from Server to Client;
    }
}