C: Client;  R1: Router;
R2: Router; R3: Router;
R4: Router; S: Server;

pipe R1--R2: Tunnel 1 [color=red]
     R2==R3: Tunnel 2 [color=green]
     R3==R4: Tunnel 3 [color=blue, line.type=triple]
{
    C->S: \plRequest;
    C<-S: \prResponse;
};
