Chapter 4 - Physical Layer

Question 1

Media Access Control sublayer

Answer 1

Converts data into a stream of bits and controls when that data is sent along the physical media

Question 2

Contention

Answer 2

Computers wait until the circuit is free, then jump in whenever they have data to transmit

Question 3

Controlled Access

Answer 3

One device is in control of whose turn it is

Question 4

Controlled Access - Access Request

Answer 4

Client computers send a request to transmit data to a device in charge

Question 5

Controlled Access - Polling

Answer 5

A signal is sent to client computers asking if they have data to transmit

Question 6

Roll Call Polling

Answer 6

A controlling device works through a sequence of clients, asking each one in order if they have data to transmit

Question 7

Hub Polling

Answer 7

AKA token passing. One device starts the poll and passes permission around the circuit.

Question 8

Contention - Best Use Case

Answer 8

Smaller networks. Less chance of a collision with less device, and waiting for permission to be granted slows things down.

Question 9

Controlled Access - Best Use Case

Answer 9

Larger networks. Collision and retransmission would slow things down more than requesting permission.

Question 10

Human Error

Answer 10

The user typed something incorrectly

Question 11

Network Error

Answer 11

Error during transmission, the data that’s sent isn’t the data that’s received

Question 12

Corrupted Data

Answer 12

The data sent is changed somewhere along the path to the receiving computer

Question 13

Lost Data

Answer 13

The data sent never makes it to the destination

Question 14

Error Rate

Answer 14

The frequency and pattern in which errors occur on a circuit

Question 15

Burst Error

Answer 15

An error where more than one bit is changed at a time by the condition causing the error

Question 16

Line Noise

Answer 16

AKA distortion. Degradation of the performance of a communication circuit due to equipment or natural disturbances, manifests as extra bits, missing bits, or flipped bits.

Question 17

White Noise/Gaussian Noise

Answer 17

Thermal agitation of electrons. Unavoidable on even the most insulated wires, workaround is to increase signal strength.

Question 18

Impulse Noise/Spikes

Answer 18

Primary error source in data communications, caused by voltage changes in adjacent lines, lightning flashes, fluorescent lines. Lasts as long as 1/100 of a second and can obliterate a group of data.