Data Link Layer

Table of Contents

Part 1: General review of data link layer 2

a) Explain the working principles of the data link layer. 2

b) Is controlled access better than contention for media access control? Discuss. 2

c) Why is error detection important in this layer? What is being measured? 3

d) Identify three significant noises that can cause errors in data communication digital circuits. Briefly explain. 3

Part 2: General review of error correction 4

a) Why is cyclical redundancy check (CRC) most popular error checking scheme? 4

b) How is Hamming distance used in error correction? Explain. 4

c) Briefly explain how parity is used to find the location of single-bit errors in the forward error correction method? 5

Part 3: Demonstration of data link protocols 5

a) Explain the necessity of data link protocols? 5

b) Asynchronous communication is sometimes called start-stop transmission. Discuss with necessary diagram? 6

c) Explain the Ethernet protocols categories? 6

References 8

Part 1: General review of data link layer

Explain the working principles of the data link layer.

The data link layer sits between the physical layer and the network layer. It is responsible for sending and receiving messages to and from other computers. It is responsible for moving a message from one computer to next computer where the message needs to go. The data link layer performs the main functions and is divided into two sub layers. The first sublayer called logical link control (LLC) sublayer and the second sublayer called media access control (MAC) sublayer. The LLC sublayer software at the sending computer is responsible for transmitting the network layer Protocol Data Unit (PDU) with the data link layer. At the receiving computer the MAC sublayer software takes the data link layer PDU from the LLC sublayer and coverts into a stream of bits and also controls when the physical layer actually transmits the bits over the