For your first project, you will develop a program that teaches about local area networks, specifically, the Ethernet topology. The focus of the project is to teach how computers on such a network contend for transmission, seize it, and transmit them. Obviously, one could also show breakup of messages into packets, or listening and receiving them, but we won't here. A similar project was give in the System simulation course, visit the assignment page for that project (Assignment #5).

It is important to begin working in groups, so, find two other people to work with. If you can't find any one, let us know, we will hook you up with a group. We like to make sure that there is at least one person from the Simulation course in each group. This should not be a problem as more than half of you were in that course last semetser. Begin keeping track of your work in your project notebook, we will ask that you turn it in once this project is finished. You are expected to give a 5 minute presentation about what your user interface will look like on Monday, February 3rd. Set modest goals that you could achieve. On Monday, February 10th, you will be asked to give a 10 minute presentation about your design. Of course, the project itself is due a week later!

The Ethernet model employs a broadcasting approach for networking. A number of stations/nodes/computers are connected to such a network, typically, in a one mile radius. A message broadcasted on the network by one of the stations is picked up by all other stations. Stations can recognize whether messages are for them or not. A message that doesn't belong to a station is, simply, discarded by that station.

The most interesting part of this LAN is the concept of network contention. When a station is ready to transmit a message, it first must determine whether the network is already being used or not. If the network is not seized by any other station, the station that wishes to transmit must first send a small packet containing a unique bit pattern across the network. If no other station is doing the same thing at that time, the transmitting station can now assume ownership of the network and transmit a message. If more than one station are contending for the network at the same time, their bit patterns will collide which intern changes the bit pattern in the network to something different than the bit patterns of all contending stations. Collisions are easyly detected by the contending stations who listen to the network for their own unique bit pattern. To resolve collisions, the following Exponential Backoff Heuristic has been adopted which basically causes the stations involved in a collision to transmit at a later time.

EBF = L² * T * random() where L is the number of seize attempts by the station and T is the time it takes to transmit the stations bit pattern.

Key constraints

• There are up to eight stations.
• Network transmission takes place using a thin coaxial cable (1000,000 bits/sec.).
• Stations give up on transmitting a message after 5 unsuccessful attempts to seize the network.
• The size of each packet for a transmitted message is 1024 bits. Each message shall contain 1 to 10 packets (uniformly dist.) associated with it regardless of its point of origin.
• The packet containing the station's bit pattern (used for contention) is 64 bytes long (there are eight bits in a byte).

Requirements:

Design a Java Applet and the necessary classes for this project that satisfy the following requirements:

• user should be able to choose the number of stations.
• Each station represented graphically, may be, a circle.
• The network represented graphically, may be, by an open-ended line with branches to each circle.
• User needs to be informed of what is going on, may be, through one or more text areas.
• The user should be able to initiate contention by any number of stations at the same time.
• Bit pattern transmission for network contention by stations should be implemented graphically.
• Collisions should be implemented graphically.