Active Recall

Question 1

What are the three types of networks? Briefly describe them.

Answer 1

Local Area Network (LANs) = Allow devices to communicate in a limited area such as a house, on campus or in an office.
Metropolitan Area Network = (MANs) = Designed to extend over a city.
Wide Area Network (WANs) = Allows transmission globally.

Question 2

What does OSI stand for in the OSI model?

Answer 2

Open System Interconnection

Question 3

What are the 7 layers of the OSI model?

Answer 3

Physical layer
Datalink layer
Network layer
Transport layer
Session layer
Presentation layer
Application layer

Question 4

What is the physical layer responsible for?

Answer 4

Transporting individual bits from one node to the next.

Question 5

What happens in the datalink layer and what is it responsible for?

Answer 5

It packs bit into frames, to distinguish each frame from one another and is responsible for transmitting these frames from one network layer device to the next.

Question 6

What is the network layer responsible for? Give an example.

Answer 6

Responsible for source-to-source destination.
Example: If I want to send a message from my iPhone to another iPhone, the network layer ensures this. (iPhones would be the source of the message)

Question 7

What is the transport layer responsible for? Give an example.

Answer 7

Responsible for process-to-process destination.
Example: If I want to send a message on messenger the transport layer ensure that the message will also be received on messenger and not anther app like WhatsApp.

Question 8

What is the session layer responsible for?

Answer 8

Responsible for dialogue control.

Question 9

What is the presentation layer responsible for?

Answer 9

Responsible for encryption, compression, and translation.

Question 10

What is the application layer responsible for?

Answer 10

Responsible for providing services to end users.

Question 11

During Hop-to-Hop delivery, what changes?

Answer 11

MAC address

Question 12

What is the MAC address?

Answer 12

Is a number that uniquely identifies each device on a network.

Question 13

What are the 5 layers of TCP/IP?

Answer 13

Physical layer
Datalink layer
Network layer
Transport layer
Application layer

Question 14

What are the fundamental concepts of the physical layer? Describe them. (There are 3)

Answer 14

Channel = Is the communication path between two devices.
Propagation delay = The amount of time it takes for a signal to travel from its source to its destination.
Bandwidth = Amount of information that can be transmitted per unit of time.

Question 15

What is multiplexing?

Answer 15

Allows for simultaneous transmission of multiple signals across a single data link.

Question 16

There are three types of multiplexing. Name and describe them.

Answer 16

Frequency-Division Multiplexing = Can be applied when the bandwidth of a link is greater than the combined bandwidths of the signals to be transmitted.
Time-Division Multiplexing = Can only be used with a data signal. The usage of high-capacity links is divided into time slots, and each device has a time slot.
Statistical Time-Division Multiplexing = Guarantees the full capacity of a link.

Question 17

What is a circuit switched network? Give an example.

Answer 17

Is a network that is done at the physical layer and consists of switches connected by physical links. Because they are connected by physical links, if the sequence of number 12345 was sent, the receiver would also get the same sequence 12345 as the information follows the same path.

Question 18

What is a packet switched network? Give an example.

Answer 18

Done at the network layer and these are not connected by physical links. Because of this, if the sequence 12345 was sent, the receiver may receive them in any order such as 2314 because this type of network is a first in first served basis.

Question 19

List 3 types of guided media.

Answer 19

Twisted pair cabling
Coaxial cabling
Fiber optical cabling

Question 20

List 3 types of unguided media.

Answer 20

Cellular communication
Radio frequency
Satellite communication

Question 21

What is the purpose of cladding in an optic fiber cable?

Answer 21

The cladding surrounds the core and reduces the pulse from broadening. The light travelling reflects off the cladding and bounces because the cable wont always be straight. This also provides protection from external noises and is much faster than the other types of guided media.

Question 22

What does the term ‘topology’ mean?

Answer 22

The way the network is laid out.

Question 23

What are the 5 categories of topology?

Answer 23

Star
Mesh
Tree
Bus
Ring

Question 24

What does the datalink layer ensure?

Answer 24

Ensures reliable delivery between two physically connected devices.

Question 25

What are the 5 services of the datalink layer?

Answer 25

``` Framing Access control Error detection Error correction Flow control ```

Question 26

What does framing mean?

Answer 26

In the datalink layer the bits are packed into frames so that they are distinguishable from one another.

Question 27

What is access control?

Answer 27

Determines who should have access to the physical layer.

Question 28

What are the two types of error detection? What do they mean?

Answer 28

Single-bit errors = When only one bit has changed. | Burst errors = When two or more bits have changed.

Question 29

What are the three types of error detection methods?

Answer 29

Parity checking LRC CRC

Question 30

What are bridges and switches?

Answer 30

Bridges operate at the physical and datalink layers and has a table for filtering forwarding decisions. Switches are essentially a multiport bridge and is a device that is used to link several separate LANs.

Question 31

What is a random access protocol?

Answer 31

Any computer can send data at any time.

Question 32

What is a controlled access protocol?

Answer 32

Has a central authority telling who goes first, second etc.

Question 33

What is meant by token passing?

Answer 33

Is a ring of computers and a special token that keeps circulating the ring. So if a computer wants to send data, it retains the token and converts the token frame into a data frame transmission and sends it.

Question 34

What is the CSMA/CD algorithm?

Answer 34

1. When a device wants to send data, it first listens to the channels. This is to find out whether a frame is currently being transmitted or received. 2. If no other frame is on the link, send; or if another frame is on the link, wait and then listen again. 3. While sending the data, listen to the feedback signal for a possible collision.

Question 35

There a three levels of energy, zero, normal and abnormal level. What do each of these mean?

Answer 35

Zero = Channel is in idle. Normal = A station is successfully transmitting a frame. Abnormal level = There is a collision, the energy level is twice as the normal level.

Question 36

What is the CSMA/CA algorithm?

Answer 36

1. The source sense the channel until it is idle. 2. Once it finds the idle channel, source waits for a period of time called distributed inter frame space (DIFS). 3. Then the source sends a control frame to destination called request to send (RTS). 4. After receiving RTS, destination waits another period of time called short inter frame space (SIFS), then send a control frame called clear to send (CTS) to the source. 5. The source sends the data after waiting another time equal to SIFS. 6. The destination sends an ACK after waiting another time equal to SIFS.

Question 37

What is full duplex internet?

Answer 37

Data can be sent both ways at the same time.