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 …show more content…
Briefly explain.

Line noise and distortion can cause data communication errors. Errors can occur during data transmission. Data transmitted both analogue and digital is susceptible to many types of noise and errors. The three significant noises that can cause error in data communication digital circuits are:

White noise: white noise also called thermal noise or Gaussian noise. This noise is a relatively continuous type of noise and much like the static you hear on radio between two stations. It will always be present in some degree of transmission media and electronic device and is also dependent on the temperature of the medium. The level of noise increases due to the increased movement of electrons in the medium. The white noise can be removed from the digital signal by passing the signal through a signal regenerator before the noise completely overwhelms the original signal (White 2007).

Impulse noise: Impulse noise or also called noise spike is a noncontinuous noise and the most difficult errors to detect since it occurs randomly. Difficulty comes in separating the noise from the signal. Some of the sources of impulse noise are voltage change, lightning flashes during thunderstorms, fluorescent lights and poor connection in circuits. If the impulse noise interferes with the digital signal, often the original digital signal can be recognized and recovered. The way to prevent impulse noise is by shielding or moving cables (White