# Message Segmentation

With this interactive applet, you will see why packet switching can have a smaller end-to-end delay than message switching. In this applet there are four nodes: a source (node A), a destination (node B), and two intermediate store-and-forward switches. Each packet sent from the source must be transmitted over three links before it reaches the destination. Each of these links has a transmission rate of 4 kbps and an optional propagation delay of one second.

Each small rectangle represents 1 kbit of data. When you press Start, the rectangles are grouped into one packet in the source's transmit buffer. The packet is transmitted to the first switch, where it must be stored before it can be forwarded. The packet then continues towards the destination.

To simulate message switching, set the packet size equal to the message size. To simulate packet switching, set the packet size to less than the message size. To examine the effect of link propagation delays, check the appropriate boxes for optional propagation delays. It is highly recommended that you calculate the end-to-end delay analytically and then verify your calculation with the applet.

This applet was coded by Shuchun Zhang in 1997 as part of course work at the University of Pennsylvania.