This illustrates two nodes communicating over a duplex network link, with A sending packets to B, and B sending an acknowledging for each received packet back to A. Try varying the parameters to see how they affects performance. You can click "emit" multiple times to send more than one packet. If you send too quickly, packets will be queued at the sender before being transmitted on the link (current queue size is shown as "Q:"). If "pipelining" is disabled, then A will only send the next packet after it receives the acknowledgement from the previous. If "pipelining" is enabled, then A will send packets as soon as possible, without waiting for acknowledgement of previous packets.