Physical Layer

Question 1

How is latency defined? What is the “Round-Trip Time”?

Answer 1

• The time it takes to transmit 1 bit of data from A to B

- The time it takes to send and receive an answer

Question 2

How is the bandwidth defined? (strict sense, telecommunication)

Answer 2

Strict sense: The width of the frequency band. If the width is bigger, more data can be sent simultaneously. (Physical)
Telecommunication: How much data in a certain amount of time can be transmitted (10GB/s)

Question 3

What is a “Baseband”? When is it used and what are its properties?

Answer 3

• (digital) Signal starts at 0Hz and uses the whole range it is called Baseband.
• Single , bidirectional channel
• Used for short distances

Question 4

What is a “Broadband”? When is it used and what are its properties?

Answer 4

• Analog signal
• Transmissions use a percentage of the bandwidth but can be sent simultaneously
• Unidirectional channels (we need atleast 2 for sending and receiving)
• Big distances

Question 5

Describe the coding of a signal from A to B.

Answer 5

Have a look at the image in the slides

Question 6

What is a “backwards error correction” and what a “forward error correction”? And in what context is it used?

Answer 6

In the context of channel encoding.

• Backwards: Retransmission of packet
• Forward: Fix the faulty transmission

Question 7

What is “Modulation”?

Answer 7

Signal or message to sent changes the frequency of the carrier medium.

Question 8

What is “Multiplexing” and what is its usecase?

Answer 8

Multiplexing is e.g. used over fiber optics because they can only transmit one signal at a time. Multiplexing combines multiple signals into one by creating logical sub channels. Often also reffered as “mux” / demux

Question 9

What are “guided” and “unguided” mediums?

Answer 9

• Guided: Wired cable

- Unguided: Wireless

Question 10

Where to use Coaxial cabel?

Answer 10

• Better defence on radiation vs. Twisted pair cable

- Used for TV or connecting mobile antenna to ISP backbone