Fig. 5

An interactive connection chain. Host h_i can only know host h_i+1 is connected with it. It has no idea about the connecting situation after h_i+1 in the downstream of the connection chain. If we monitor the outgoing connection from the host h_i, what we know is the TCP/IP packets coming from h_i and going to host h_i + 1, rather than any other hosts from h_i+2 to h_n+1. But if there is a session between h_i and h_n+1, each packet sent from host h_i must be acknowledged by host h_i+1 first and then forwarded to the following hosts until to the destination host h_n+1 of the chain. Even though the echo of a send from h_i comes from host h_i+1 from the point of h_i, this packet is actually echoed by the destination host, rather than its directly connected host