2018 Past Paper

Question 1

What does TTL stand for?

Answer 1

Time to live

Question 2

What is TTL?

Answer 2

a value in an IP packet that tells a network router whether or not the packet has been in the network too long and should be disregarded

Question 3

How do routers impact the TTL?

Answer 3

TTL initially set to number between 1-255. Each router that receives the packet subtracts at least 1 from the count.

Question 4

What happens if TTL is 0?

Answer 4

router disregards it and sends an ICMP message back to the originating host

Question 5

What is the transmission delay, Tx?

Answer 5

time taken to put bits onto the wire

Question 6

what is the equation for working out the Tx?

Answer 6

Tx = b/r
where b = no of bits
r=data rate (b/s)

Question 7

What is the propagation delay, Tp?

Answer 7

time taken for a signal to traverse a link

Question 8

what is the equation for working out the Tp?

Answer 8

Tp=d/Ss
where d = distance of link, m
Ss= speed of signal in m/s

Question 9

Differences between client-server and P2P?

Answer 9

• in client-server there is a specific server and specific clients connected to a server, whereas with P2P client and server are not distinguished
• in client-server data is stored in centralised server, whereas P2P each peer has its own data
• in client server the client requests service and the server responds with it, in P2P each node can request service but also provide

Question 10

What is the role of CSS in the development of a web-based application?

Answer 10

applies presentation to webpage, like layout, font, colours

Question 11

What

advantages does the use of CSS have over alternatives?

Answer 11

• ease of presenting different styles to different users
• more formatting options
• faster download time

Question 12

What does the onload property of tag in DOM API do?

Answer 12

• occurs when object has been loaded
• can be used to check the visitors browser type and browser version and load the proper version of webpage based on info

Question 13

is false ==”0” true or false?

Answer 13

true

both sides converted to numbers and then the comparison is performed

Question 14

What is a WebSocket?

Answer 14

protocol for creating a fast 2-way channel between a web browser and a server
Used for allowing interaction between web browser and a web server

Question 15

Why does WebSockets not need HTTP?

Answer 15

• doesnt rely on HTTP as it is its own protocol

- overcomes limitations with HTTP to allow low latency communications

Question 16

What is latency?

Answer 16

term used to indicate any kind of delay that happens in data communication over a nework

Question 17

Name different types of events in the DOM that can be

handled with Javascript

Answer 17

onclick
keypress
mouseover

Question 18

What is a port number?

Answer 18

a way to identify a specific process to which a network message is forwarded when it arrives at server

Question 19

Why do we need port numbers as well as IP addresses?

Answer 19

IP address is a numerical label assigned to each device, the port number is used to direct data to the correct location within device

Question 20

What is the tuple that uniquely identifies a TCP connection?

Answer 20

protocol
source IP address
source port
target IP address
target port

Question 21

What service does the Domain Name System (DNS) provide?

Answer 21

has a directory of domain names and translates them into IP addresses

Question 22

Which level

of the Internet reference model is the DNS protocol located at? And why?

Answer 22

application layer

- allows the application to translate a name into a network address

Question 23

Advantage and disadvantage of Symmetric encryption?

Answer 23

ad- fast

dis - have to exchange key used to encrypt before decrypt

Question 24

Advantage and disadvantage of Asymmetric encryption?

Answer 24

ad - eliminates the need to share the key

dis - takes longer