Networks Part 2 (Physical Layer)

Question 1

What is the difference between guided and unguided data?

Answer 1

Guided data uses a physical path for data transfer (e.g fibre optic, coaxial cables)

Unguided data uses no physical path (e.g travels through a vacuum/air/water, radio for example)

Question 2

What is “Simplex” transmission?

Answer 2

One way communication, for example, keyboard to computer.

Question 3

What is “Half-Duplex” transmission?

Answer 3

A two way communication link where only one system can talk at a time, for example, walkie talkies.

Question 4

What is “Full-Duplex” communication?

Answer 4

A two way communication link where both systems can transmit data simultaneously, for example telephones.

Question 5

How does “Parallel Transmission” work?

Answer 5

It transmits groups of bits immediately, which increases the bit-rate (amount of bits being sent per second) but tends to be expensive as thicker cables are needed (higher cost for maintenance, installation).

There can also be bit-synchronisation errors due to “bit-skew”.

Question 6

How does “Serial Transmission” work?

Answer 6

Transmits all bits one after another, which results in a slow bit-rate. It is however cheaper and more reliable over longer distances.

Also potentially incurs extra complexity as data must be translated from its internal to its parallel form.

Question 7

What is “Multiplexing?”

Answer 7

Using one channel to transmit multiple systems connection data.

Essentially one channel is shared between users, resulting in better utilisation as the channel is kept busy.

Question 8

What are the three types of multiplexing?

Answer 8

1. Frequency Division (Place users on different bandwidths)
2. Time Division (Give each user a different time slice of channel)
3. Code Division (Shares channel by allocating users different codes)

Question 9

What is a “Line Code”?

Answer 9

A digital signal representation of a bit stream.