Technology and Engineering · High school

The journey of packets

Split a message into packets and send it; cut a line and watch the routers deliver them another way.

In the learning section below the figure, predict, try, complete the tasks and check yourself with short questions.

Fig. 1The journey of packets

Press Send; tap a station to cut its line; type your own values below

Sent: 0
Arrived: 0/8
Resent: 0
Lost: 0
Total time: 0 ms

Order of arrival

no packets yet

Nothing sent yet.

Message size

Unit

8 packets; at most 1460 bytes per packet, 11.68 KB at most in total (1 KB = 1000 bytes).

Loss rate

The chance that a packet is dropped in a station’s queue (congestion).

Line delay

Propagation time of the lower line; the upper line is a little longer. The timeout follows from it: 183 ms.

Learn

Progress is kept on this page only; no points are given.

1Predict
2Try
3Explain

If you send a message while the upper line is cut, what happens to the message?

Gold cartridge: one packet (its sequence number on top)Purple label: a resent packetDot in the tube: the receiver’s acknowledgement (ACK)The numbers come from the figure’s own model and the values you enter; the default times are example values in milliseconds, not measurements of a real connection. Losses are picked by seeded randomness at the rate you enter: the same values and the same send give the same result. In this figure the first router spreads packets one by one over two lines; in real networks the packets of one connection usually follow the same path, which changes only when a link fails or the load shifts. The receiver acknowledges every packet separately, and a packet whose acknowledgement does not come back before the timeout (now 183 ms) is sent again (a simplified form of TCP retransmission). The router notices a cut line after 25 ms.

How does a web page reach you? The journey of packets on the internetRead the article

The journey of packets

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