Chapter 2

Question 1

Layered Architecture (1)

Answer 1

1. Makes system easier to understand.

Question 2

Channel properties (4)

Answer 2

1. Bit rate
2. Delay
3. Storage capacity
4. Error rate

Question 3

Bit rate (1)

Answer 3

1. Number of bits per second

Question 4

Delay (1)

Answer 4

How long does it take to get to the end?

Question 5

Storage Capacity (2)

Answer 5

1. How many bits can the channel hold at once

2. Capacity = BitRate * Delay

Question 6

Error rate (1)

Answer 6

1. Probability of bit flipping.

Question 7

Twisted pair (2)

Answer 7

1. Twisted because otherwise the cables would act as an antenna
2. Bandwidth of 500 MHz

Question 8

Coax Cable (1)

Answer 8

1. Bandwidth in order of GHz

Question 9

Optical Fiber (3)

Answer 9

1. Uses light pulses to transmit bits.
2. Receiver transforms light pulses in electric signals.
3. Bandwidth in order of 100 GHz.

Question 10

Radio frequencies (2)

Answer 10

1. Can travel long distances
2. Power of waves falls with distance from the source.
3. f = 1 or 100 MHz based on AM or FM

Question 11

Microwave (3)

Answer 11

1. Needs line of sight because waves travel in straight lines.
2. Do not travel through objects.
3. f = 10Ghz

Question 12

Baseband Transmission (4)

Answer 12

1. Signal occupies frequencies from 0 to a max.
2. NRZ
3. Clock recovery problems
4. Balanced signals.

Question 13

Manchester encoding (1)

Answer 13

1. XOR with the clock signal

Question 14

NRZI (1)

Answer 14

1. Codes 1 as transition and 0 as a non transition.

Question 15

4B/5B (1)

Answer 15

1. 4 bits are mapped into 5 bits so that no more than 3 consecutive 0 can appear.

Question 16

Scrambling (1)

Answer 16

1. Data is XOR with random sequence that is then XORed back from the receiver

Question 17

Passband transmission (2)

Answer 17

1. Signal is inside a certain frequency band which is shifted from the 0
2. Data is sent by modulating phase frequency or amplitude.
3. Frequency and phase are not independent so they can’t be modulated together.

Question 18

Constellation diagram (3)

Answer 18

1. Modulation of the signal is defined in amplitude and phase shift
2. Phase shift is indicated by angle with x axis
3. Amplitude defined by distance from origin

Question 19

Nyquist’s theorem (1)

Answer 19

1. Max data rate of a noiseless channel = 2. 𝑅=2×𝐵 × log2(𝑉)

Question 20

Shannon’s theorem (2)

Answer 20

1. Max data rate in noisy channel = 𝑅= 𝐵 × log2(1+(𝑁/𝑆))

2. S/N = signal to noise radio, x db = 10^(x/10)

Question 21

Multiplexing (1)

Answer 21

1. Sending multiple signals on a single medium.

Question 22

Simplex channels (1)

Answer 22

Only allow unidirectional data.

Question 23

Duplex channels (1)

Answer 23

Allow data to pass through in both directions at the same time.

Question 24

Half-duplex channels (1)

Answer 24

Allows data in both direction but not at the same time.

Question 25

Frequency division Multiplexing FDM (2)

Answer 25

1. Divides frequency spectrum in bands, each user can access a certain band.
2. Guard bands are assigned to keep channels separated.

Question 26

Time division multiplexing TDM (2)

Answer 26

1. Users take turns to send data on a fixed schedule.

2. Guard time is used to protect against small time variations.

Question 27

Code division multiplexing CDM (3)

Answer 27

1. All stations send at the same time using the same frequencies.
2. The receiver has to figure out who and what was sent.

Question 28

CDM How ? ()

Answer 28

1. Each station is assigned a bit sequence.
2. When sending a 1 the station will send the sequence, when sending a 0 it will send the negation of the sequence.
3. The sent sequences are added linearly.
4. The receiver calculates the product between the sent sequence and the stations and then divides by n (size of the bit seqeunce)