Introduction to Animations for

Business Data Communications Systems, Sixth Edition

by William Stallings

Business Data Commuincations, Sixth Edition incorporates a rich set of animations to reinforce the learning experience and to increase the motivation of students. Animations provide a powerful tool for understanding the complex mechanisms of network protocols. A total of 12 animations are used to illustrate protocol behavior. At the relevant point in the book, an icon indicates that a relevant animation is available online for student use. The animations can be used in two ways. In a passive mode, the student can click more or less randomly on the next step at each point in the animation and watch as the given concept or principle is illustrated. The active mode can be used for two types of assignments. First, the student can be given a specific set of steps to invoke and watch the animation, then asked to analyze and comment on the results. Second, the student can be given a specific end point and required to devise a sequence of steps that achieve the desired result. The instructor's supplement includes a set of assignments for each of the animations, plus suggested solutions so that instructors can assess the student's work.

This brief guide serves to introduce the animations and give you some feel for their operation and use in the classroom. There is a useful background article written by the developers.

The animations are located at You can also reach them by going to the book's Web site at and then clicking on the Animations link.

Let's look at a simple example. The Alternating Bit Protocol (ABP), also known as stop-and-wait, is a well-known data link control protocol. From the Animations Web site, under Chapter 17, click on the Alternating Bit Protocol Simulator link, or click on the link from here.

One mode of operation is to click the Run button. This will perform an automatic simulation of the protocol using a predefined sequence of events. One possible assignment is to ask the student to run the simulation for a given time, then halt the simulation and provide a running commentary explaining the action of the protocol.

Another mode of operation is to actively enter actions step by step. This is done by selecting from among the alternative possible actions in the window at the lower-right hand corner of the animation. At startup there is only one possibility: Sender: Send DATA(0). This indicates that a packet is sent with a sequence number bit set to 0. Click on this selection. The result is illustrated in the upper part of the diagram. The window now offers two selections, one of which causes successful delivery and one of which causes a lost packet. A student assignment involves specifying a sequence of actions that the student is to enter and then answer questions about the sequence. For example, certain sequences involve a connection request but no connection response, even though a connection is set up. The student is asked to explain why. Another type of assignment is to describe a desired result and ask the student to generate a sequence that produces that result.

ABP is a relatively simple protocol, so the assignments are relatively simple. More elaborate assignments are possible for more complex protocols, such as TCP. The projects manual includes a number of assignments for each protocol, and a separate solutions guide.