Data Communication

Question 1

what is baseband transmission?

Answer 1

Sending a digital signal over a channel without changing the digtial signal to an analog signal

Question 2

Name 3 types of transmission impairment

Answer 2

Attenuation,
distortion,
noise

Question 3

what is broadband transmission?

Answer 3

Modulating the signal to an analog signal for transmission.

Question 4

What does the Nyquist theorem have to do with communications?

Answer 4

The Nyquist bit rate defines the theoretical maximum bit rate of a noiseless channel.
BitRate = 2.bandwith.log(2)L
where L = number of signal levels used.

Question 5

What does the Shannon capacity have to do with communications

Answer 5

The Shannon capacity gives the highest data rate for a noisy channel:
Capacity = bandwidth.log(2)(1+SNR)

Question 6

A signal travels from point A to point B. At point A, the signal power is 100 W. At point B, the power is 90 W. What is the attenuation in decibels?

Answer 6

10log(10)(90/100)

A: -0.45

Question 7

The attenuation of a signal is –10 dB. What is the final signal power if it was originally 5 W?

Answer 7

0.5W

Question 8

A signal has passed through three cascaded amplifiers, each with a 4 dB gain. What is the total gain? How much is the signal amplified?

Answer 8

12dB

15.85

Question 9

A line has a signal-to-noise ratio of 1000 and a bandwidth of 4000 kHz. What is the maximum data rate supported by this line?

Answer 9

40 MBps

Question 10

A file contains 2 million bytes. How long does it take to download this file using a 56-kbps channel? 1-Mbps channel?

Answer 10

290 s

Question 11

A computer monitor has a resolution of 1200 by 1000 pixels. If each pixel uses 1024 colors, how many bits are needed to send the complete contents of a screen?

Answer 11

12 million

Question 12

A signal with 200 milliWatts power passes through 10 devices, each with an average noise of 2 microwatts. What is the SNR? What is the SNRdB?

Answer 12

10,000

40

Question 13

If the peak voltage value of a signal is 20 times the peak voltage value of the noise, what is the SNR? What is the SNRdB?

Answer 13

400

26

Question 14

What is the theoretical capacity of a channel in the following case?
a. Bandwidth: 20 kHz SNRdB = 40

Answer 14

SNR=10000

capacity = 267 kbps

Question 15

How many bits can fit on a link with a 2 ms delay if bandwidth of link is
1 Mbps?

Answer 15

2,000 bits

Question 16

What is the total delay (latency) for a frame of size 5 million bits that is being sent on a link
with 10 routers each having a queuing time of 2 µs and a processing time of 1 µs. The length
of the link is 2000 km, The speed of light inside the link is 2 x 108 m/s, the link has a
bandwidth of 5 Mbps. Which component of the total delay is dominant? Which one is
negligible?

Answer 16

We have Latency = Delaypr + Delayqu + Delaytr + Delaypg
Delaypr = 10 x 1 μs = 10 μs // Processing delay
Delayqu = 10 x 2 μs = 20 μs // Queuing delay
Delaytr = 5,000,000 bits / (5 Mbps) = 1 s // Transmission delay
Delaypg = (2000 km) / (2 x 108
) = 0.01 s // Propagation delay
This means
Latency = 10 μs + 20 μs + 1s + 0.01 s ≈ 1.01 s
The transmission time is dominant here because the packet size is huge.