Networks

Question 1

Personal area network

Answer 1

Connected devices that are located within a few metres of each other.

Question 2

Local area network

Answer 2

A network that is formed when devices in the same building or on a single site are connected. Eg home, workplace, school.

The infrastructure is owned and maintained by the organisation using it.

Question 3

Wide area network

Answer 3

When two or more networks are connected across a large geographical area. Eg a bank connecting all machines across a country, police connecting to share information.
Largest WAN is Internet.

Many WANs use telecommunication links owned and managed by other companies. Organisations that run their own WAN will often lease bandwidth from telecommunication companies.

Question 4

Client-server network

Answer 4

Allows you to access your files and emails from any authorised device.

Server: shares resources and services with and authorised client. File, Web, email, database print servers.

Client: a program that typically runs on a device used by an end-user eg laptop or mobile phone.

Client sends request to server, server processes this and sends a reply.

Question 5

Peer-to-peer server

Answer 5

No central server. Every computer can be configured to share its resources eg files, software, processing power, bandwidth.

Peers communicate directly with each other if given permission. Computers must be switched on to share resources eg printing.

Question 6

CS vs P2P

Answer 6

Servers are expensive to set up and maintain, P2P has no additional devices.

Servers can be located in secure rooms not accessible to everyone so easy to monitor, P2P is difficult to oversee every workstation.

Backups are done by and stored on servers, P2P users are responsible for their own backups.

If a server fails, many users will be affected eg cannot access files, if one P2P node fails, most users can carry on unaffected.

Question 7

Protocol

Answer 7

A set of rules that govern how computers communicate with each other

Question 8

HTTP

Answer 8

Hypertext Transfer Protocol
Client sends HTTP request, server receives and sends an HTTP response which encapsulates the requested page, client receives and displays the web page.
Dynamic pages have extra steps before the page is returned.

Question 9

HTTPS

Answer 9

Hypertext Transfer Protocol Secure
Encrypts the data between client and server. Provides a digital certificate containing a public encryption key. Your browser uses the public encryption key and only the authorised server has the private key to decrypt it.

Question 10

Client-side processing

Answer 10

Offloads processing to the client, reducing the load on the server.
Can pose a security risk - malicious content can be distributed. Scripts have no access to the OS and little access to the file system.
Software and browsers must be kept up to date to minimise security risk.

Question 11

Server-side processing

Answer 11

Operations that are carried out on the server.
More control over the environment where the scripts are run.
Scripts are hidden on the server.
Servers can be optimised to cope with heavy processing demands.

Question 12

Packet switching

Answer 12

Small data packets from the same conversation may be sent over multiple different routes.
End points are responsible for checking that everything has been received.
Router examines the destination and decides which interface it should be sent to using a routing table.

Question 13

Circuit switching

Answer 13

Used for telephone calls.
A signal is sent across the first connection to request the line. Each telephone switch would then select an appropriate route and reserve capacity on the line and send the request on.
Guaranteed capacity between the source and destination.

Question 14

DNS

Answer 14

Domain Name System
Used to name and organise internes resources.
Each smaller domain is separated from the larger domain by a full stop eg Leeds.gov.uk
TLD = Top Level Domain
2LD = 2nd Level Domain

Domain names are easier to remember than IP addresses. DNS server translates the domain names in the URL into the IP address.

Question 15

TCP/IP stack

Answer 15

Application
Transport
Internet
Link

Question 16

Application layer

Answer 16

Top of the stack
Decides which protocol is needed to transmit data
Passes on to transport layer
Gets data from transport layer when receiving

Question 17

Transport layer

Answer 17

Uses Transmission Control Protocol to establish end-to-end encryption with the recipient computer.
Splits the data into packets and labels them with a packet number, total number of packets and a port number.

Question 18

Internet layer

Answer 18

Adds the source and destination IP address
The IP address and port number form a socket eg 87.17.180.4:80
A socket specifies which device the packet must be sent to and the application being used on that device.

Question 19

Link layer

Answer 19

The physical connection between nodes
Received layered data from the Internet layer to send
Adds the unique MAC address to the packet
Passes layered data back up to the Internet layer when receiving

Question 20

Network threats

Answer 20

Hackers: someone who deliberately gains unauthorised access to a computer system with the intent to cause damage or steal data. Ethical hackers find vulnerabilities in the network.

Data interception and theft: hacker intercepts data as it is being sent between computers. They may alter it and users will be unaware.

Denial of service: a server is bombarded with requests at a level it cannot cope with so it cannot process any requests.

SQL injection: used to manipulate an SQL statement to their own benefit.

Question 21

Firewall

Answer 21

Acts as a barrier between a trusted network and an untrusted network.
Attempts to prevent malware from entering the network.
Can also be configured to prevent certain types of data from leaving the network.

Question 22

Static filtering

Answer 22

A firewall will check the headers of the packets arriving from the untrusted network against a set of rules (packet filters) defined by the network administrator.

Question 23

Stateful inspection

Answer 23

Also known as dynamic filtering
Continuously monitoring incoming and outgoing traffic after a connection is established. Analysing packet types, looking inside the payload of the packet rather than just the header, checking for suspicious activity.
Requires the firewall to maintain a connection table to keep track of all the conversations between trusted and untrusted networks.

Question 24

Proxy server

Answer 24

Sits between the client devices and the firewall.
Provides anonymity to the clients by keeping their true IP addresses hidden.
Can also keep a cache of websites, serving them from its cache wherever possible to speed up user access and reduce traffic.
Schools often use proxy servers to block certain websites.

Question 25

Network Interface Controller

Answer 25

Also known as Network Interface Cards
Used to connect a device to a network.
Converts the data to be sent into appropriate signals eg voltages through a wire or radio waves wirelessly.
Converts received signals back into the digital data.
Each has a unique MAC address.

Question 26

Hub

Answer 26

Repeats all received messages to all connected devices.
Inefficient as it sends data to places other than its intended destination.

Question 27

Switch

Answer 27

Sends received messages to only their intended destination device.
Builds up a table of the MAC addresses of every connected device.

Question 28

Router

Answer 28

Connects two networks, eg a home network to the Internet.
Core routers are used to forward packets to their destination along the backbone of the Internet. They examine the destination and consult a routing table of known networks which indicates which connection is best to use.

Question 29

Modem

Answer 29

Combination of modulator/demodulator
Modulates the electric signal - changes the signal so that it can be sent through a cable that uses a different technology.
Historically used to convert digital electric signal so they could be transmitted over telephone wires in analogue form.

Question 30

Network access devices

Answer 30

Usually supplied by Internet service providers.
Typically contain a Wireless Access Point, router, modem and a switch with 2-4 ports.
Control access to a network using the MAC addresses of the devices trying to connect. Only allows connections to devices with approved addresses.

Question 31

Gateway

Answer 31

Allows the transmission of data between dissimilar networks eg networks that use different protocols.
Can combine a variety of operations eg malware inspection and spam filtering.