• An agency needs to connect several departmental LANs. The interconnection will be made using a LAN to which departmental LANs are connected. The interconnection LAN must operate at 100Mbps. The medium will run through elevator shafts and a machine room, so signal distortion is a concern. What medium would you recommend? Justify.

• Coaxial cable or fiber optic cable is recommended due its ability to withstand interference and function in harsh environments. They can also easily carry 100Mbs without repeaters spaced apart at short distnaces as would shielded twisted pair.

• Suppose a file of 10,000 characters is to be sent over a line at 2400 bps.Calculate the overhead in bits and time in using asynchronous communication. Assume 1 start and stop bit, and 8 bits to send the character itself for each character.

• Total overhead; 2 x 10,000 = 20,000 bits.

• Time overhead; 20,000/2400 = 8.3333 seconds.

• Calculate the overhead in bits and time using synchronous communication. Assume that the data are sent in frames. Each frame consists of 1000 characters=8000 bits, and an overhead of 48 bits per frame.

• 10,000 characters/1000 per frame=10 frames required to transmit file.

• Overhead in bits is 10 x 48 = 480 bits.

• Time overhead is 480/2400 =0.2 seconds.

• What would the answers to parts a and b be for the original file of 100,000 characters?

• Asynchronous communication

• Total overhead; 2 x 100,000 = 200,000 bits.

• Time overhead; 200,000/2400 = 83.333 seconds.

• Synchronous communication

• 100,000/1,000 = 100 frames.

• Overhead in bits; 100 x 48 = 4,800 bits.

• Time overhead; 4,800/2400 = 2 seconds.

• What would the answers to parts a and b be for the original file of 10,000 characters except at a data rate of 9600bps?

• Asynchronous communication
• Total overhead; 2 x 10,000 = 20,000 bits.

• Time overhead; 20,000/9600 = 2.08333 second.

• Synchronous communication
• 10,000/1,000 = 10 frames.

• Overhead in bits; 10 x 48 = 480 bits.

• Time overhead; 480/9600 = 0.05 seconds.

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Ramayya Krishnan rk2x@andrew.cmu.edu