Chapter 4 - Physical Layer Flashcards
Media Access Control sublayer
Converts data into a stream of bits and controls when that data is sent along the physical media
Contention
Computers wait until the circuit is free, then jump in whenever they have data to transmit
Controlled Access
One device is in control of whose turn it is
Controlled Access - Access Request
Client computers send a request to transmit data to a device in charge
Controlled Access - Polling
A signal is sent to client computers asking if they have data to transmit
Roll Call Polling
A controlling device works through a sequence of clients, asking each one in order if they have data to transmit
Hub Polling
AKA token passing. One device starts the poll and passes permission around the circuit.
Contention - Best Use Case
Smaller networks. Less chance of a collision with less device, and waiting for permission to be granted slows things down.
Controlled Access - Best Use Case
Larger networks. Collision and retransmission would slow things down more than requesting permission.
Human Error
The user typed something incorrectly
Network Error
Error during transmission, the data that’s sent isn’t the data that’s received
Corrupted Data
The data sent is changed somewhere along the path to the receiving computer
Lost Data
The data sent never makes it to the destination
Error Rate
The frequency and pattern in which errors occur on a circuit
Burst Error
An error where more than one bit is changed at a time by the condition causing the error
Line Noise
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.
White Noise/Gaussian Noise
Thermal agitation of electrons. Unavoidable on even the most insulated wires, workaround is to increase signal strength.
Impulse Noise/Spikes
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.
