This applet illustrates how a message goes from the source machine to the destination machine across one or more networks. Between the source and destination machines are intermediate nodes called routers that connect the networks. The networking software on the source machine, the routers, and on the destination machine is organized into layers with one type of protocol per layer. The sequence of layers is called the protocol stack. The protocol stack used in the Internet is called the TCP/IP protocol stack. This name is used since the Transmission Control Protocol (TCP) and the Internet Protocol (IP) are two of the most important protocols in this protocol stack. From top-down the protocol layers in the TCP/IP protocol stack are: application, transport, network, data link, and physical.
Click the Start button to watch a simulation of a message being sent from the application layer of the source machine to the application layer of the destination machine. The message moves down through the protocol layers on the source machine, up through the protocol layers on the router, back down through the protocol layers on the router, and then finally up through the protocol layers on the destination machine. Each protocol layer is shown in a different color.
Besides showing the basic concept of how a message must traverse the protocol layers, this applet illustrates several other concepts including encapsulation and fragmentation. The radio buttons can be used to illustrate fragmentation. The first set of radio buttons is used to select the maximum size of a message that can be sent across the first network. The second set of radio buttons is used to select the maximum size of a message that can be sent across the second network. Change which radio buttons are selected and then click the Start button to see when fragmentation occurs. For more information about how to use the applet and the concepts it is illustrating, follow the links below.
What concepts is this applet illustrating?
Acknowledgements and Developer Information
Current Version: February 2004
Copyright (C) Mark A. Holliday. All rights reserved.