1.3.3 Networks (TCP/IP Stack and Packets)

Question 1

What are the four layers in the TCP/IP stack?

Answer 1

Application Layer
Transport Layer
Network Layer
Link Layer

Question 2

What does the application layer do?

Answer 2

It specifies what protocol needs to be used to relate the application being sent.

Question 3

What does the transport layer do? [3]

Answer 3

• Uses TCP to establish an end-to-end connection between the source and recipient computer.
• It splits data into packets, and labels them with their packet number, the total number of packets and the port number being used for communication.
• If any packets get lost, the transport layer requests retransmissions of these lost packets.

Question 4

What does the network layer do? [3]

Answer 4

• It adds the source and destination IP addresses.
• Routers operate on this layer. The router uses the IP addresses to forward the packets.
• The socket addresses are used to specify which device the packets must be sent to, and the application being used on that device.

Question 5

What is a socket address?

Answer 5

The combination of the IP address and the port number.

Question 6

What is the link layer?

Answer 6

• The connection between the network devices. It adds the MAC address identifying the Network Interface Cards of the source and destination computers.
• For devices on the same network, the destination MAC is the address of the recipient computer. Otherwise, it is the MAC address of the router.

Question 7

Some data has reached its destination. What happens moving up the TCP/IP stack?

Answer 7

Link: Removes the MAC address
Network: Removes the IP addresses
Transport: Removes the port number and reassembles the packets
Application: Presents the data to the recipient, in the form it was requested in.

Question 8

Who typically owns infrastructure used in WANs?

Answer 8

Third parties

Question 9

What is the TCP/IP stack?

Answer 9

A stack of networking protocols which work together, used in sending and receiving data.

Question 10

What is the Domain Name System?

Answer 10

The system used to name and organise internet resources.

Question 11

How does the DNS work?

Answer 11

It is a hierarchy. Each smaller domain is separated from the larger domain by a full stop.

Question 12

Give an example of a TLD (top level domain)

Answer 12

.com

Question 13

Give an example of a 2LD (second level domain)

Answer 13

.co.uk

Question 14

What are packets?

Answer 14

Segments of data.

Question 15

What three parts can a packet be split up into?

Answer 15

• Header
• Payload
• Trailer

Question 16

What does the header of a packet contain?

Answer 16

• Sender and recipient IP addresses
• Protocol being used (allows recipient to understand how to interpret packet)
• Order of packets
• Time to Live (tells packet when to expire, so it doesnt travel forever)

Question 17

What does the payload of a packet contain?

Answer 17

Raw data to be transmitted

Question 18

What does the trailer of a packet contain?

Answer 18

Checksum, or cyclic redundancy check (detects whether any errors have occured during transmission)

Question 19

What are the two methods used in networks to exchange data?

Answer 19

Packet switching
Circuit Switching

Question 20

What is packet switching?

Answer 20

A method of communication, where data is communicated using packets across a network using the most efficient route. This route can vary for each packet.

Question 21

Packet Switching Advantages

Answer 21

• Multiple methods to ensure data arrives intact (eg checksums)
• Multiple routes can be used between paths. If one path breaks, another can be used.
• Packets can be transferred over very large networks, allowing global communication.

Question 22

Packet Switching Disadvantages

Answer 22

• Time is spent deconstructing and reconstructing the data packets
• Must wait for all packets to arrive before the data can be received.

Question 23

What is Circuit Switching?

Answer 23

A method of communication, where a direct link is created between two devices.
This direct link is maintained for the duration of the entire conversation between devices.

Question 24

What is a requirement for circuit switching?

Answer 24

The two devices must be able to transfer and receive data at the same rate.

Question 25

Advantages of circuit switching

Answer 25

• Data arrives in a logical order, which results in a quicker reconstruction of the data
• Two users can hold a call without delay in speech

Question 26

Disadvantages of circuit switching

Answer 26

• Bandwidth is wasted during periods of time in which no data is being sent.
• Devices must transfer and receive data at the same rate.
• Ties up sections of the network which cannot be used by others until transmission has been completed.

Question 27

What is an IP address?

Answer 27

• A numerical address made of 4 numbers, each between 0 and 255.
• It uniquely identifies a device on a network.
• It is a logical identifier.