GCSE OCR Computer Science - Networks and Network Security

LAN

(Local Area Network) covers a small geographical area.

WAN (Wide Area Network)

Connects LANs that are in different geographical locations.

Server

A device which provides service for other devices

Bandwidth

The amount of data that can be transferred in a given time.

Latency

The time taken for a message to travel from one device to another across a network.

Factors affecting network performance (5)

Bandwidth of transmission medium, latency, number of devices, interferences, network traffic

Client-server network

A network managed by the server with devices connected to the server as clients.

Describe the client-server relationship

• The client sends requests to the server

• The server processes the request and responds to it

Advantages of client-server networks (4)

• Easy to manage network security

• Easy to install and update software

• Easy to perform back-ups

• Easy to keep track of files (they are stored centrally)

Disadvantages of client-server networks (3)

• Expensive to set up and needs specialists to maintain

• Server dependance

• Server may be overloaded

Peer-to-peer network

A network in which devices connect directly to each other without a server.

Advantages of peer-to-peer networks (2)

• Easy to maintain

• No dependence on the server

Disadvantages of peer-to-peer networks (3)

• No centralised management

• Machines are prone to slow down when accessed by another device

• Copying files between devices creates duplicates

Topology

The layout of a network

Star topology

All the devices are connected to a central switch or server that controls the network.

Star topology advantages (3)

• If one device fails the rest of the network is unaffected

• Easy to add more devices

• Better performance

Star topology disadvantages (2)

• Can be expensive to connect each device to the central switch or server by cable

• Single point of failure

Mesh topology

Network devices are either directly or indirectly connected to every other device.

Advantage of mesh topology

No single point of failure

Disadvantage of mesh topology

If the network is wired, it can be very expensive as many wires are needed to connect each device.

Full mesh topology

Each device is connected to each other device.

Partial mesh topology

Not all devices are fully connected.

Switch

Connects devices on a network by receiving and transmitting data.

Wireless Access Point (WAP)

A switch that allows devices to connect wirelessly.

Router

Transmits data between at least two networks.

What is the role of routers on the Internet?

Direct data in packets to their destination.

Network Interface Card (NIC)

An internal piece of hardware that allows a device to connect to a network.

Transmission media

The communication channel along which data is transferred.

Ethernet cables

Transfer data between devices on a LAN. (for example CAT 5e or CAT 6 ‘twisted pair’ cables)

Coaxial cables

A single copper wire surrounded by a plastic layer for insulation and a metallic mesh.

Fibre optic cables

High performance cables that transmit data as light over very large distances.

Wireless networks

Use radio waves to transmit data

Advantages of wireless networks (2)

• More convenient - you can move around while still being connected

• Cheaper - fewer wires

Bluetooth

Wireless technology that directly connects two devices over a short range.

Wi-Fi

Wireless technology that can connect multiple devices to a LAN over a wider range.

Network standard

A set of agreed requirements for hardware and software.

Network protocol

A set of rules for how devices communicate and how data is transmitted.

MAC address

A unique identifier assigned to the NIC in a networked device by the manufacturer.

MAC address format

• 48 or 64-bit binary number

• six or eight 8-bit pairs in hex separated by dashes

IP addresses

Used for sending data between TCP/IP networks.

IPv4 address format

• 32 bit address

• represented in denary with four 8-bit segments

IPv6 address format

• 128 bit address

• represented in hexadecimal with eight 16-bit segments separated by colons

TCP/IP

Protocol that dictates how data is sent between networks

Transmission Control Protocol (TCP)

Allows packets to be sent and received between computer systems. (It breaks the data into packets and reorders them)

Internet Protocol (IP)

Controls the routing and addressing of data packets.

Hyper Text Transfer Protocol (HTTP)

Used by web browsers to access websites and communicate with web servers.

HTTP Secure (HTTPS)

A more secure version of HTTP that encrypts all information sent and received.

File Transfer Protocol (FTP)

Used to access, edit and move files between devices on a network.

Post Office Protocol (POP)

Retrieves emails from a server which holds the email and deletes it after you download it.

Internet Message Access Protocol (IMAP)

Retrieves emails from a server which holds the email until you delete it - you only download a copy.

Simple Mail Transfer Protocol (SMTP)

Sends emails and transfers them between servers.

Layer

A self-contained set of protocols that provide a specific function.

Advantages of using layers (2)

• Breaks network communication into manageable pieces for developers.

• Layers can be changed without affecting other layers

World Wide Web (WWW)

A collection of websites that are hosted on web servers and accessed through the http protocol.

Domain Name Service (DNS)

Used to translate domain names into IP addresses.

Domain Name Servers

Store IP addresses matching domain names.

The cloud

Storage remotely accessed through the internet.

Cloud advantages (4)

• Files can be accessed from any device

• Less expensive

• Provides security and back-ups for you

• Easy to increase storage

Cloud disadvantages (4)

• Requires internet connection

• Dependent on host

• Data may be vulnerable to hackers

• Subscription fee

Passive attack

Data travelling on a network is monitored and sensitive information is intercepted.

Active attack

A network is attacked with malware or other planned attacks.

Brute-force attack

Information is gained by cracking passwords using trial and error.

Denial-of-service attack

Hackers stop users from accessing a part of a network or website, usually by flooding the network with useless traffic.

Malware

Malicious software installed on a person’s device without their knowledge or consent.

Viruses

Attach to certain files and are spread by users copying files and activated by users opening them.

Worms

Viruses that self-replicate without the user’s help, so spread very quickly.

Trojans

Malware disguised as legitimate software.

Social engineering

Gaining sensitive information or illegal access to networks by influencing people.

SQL Injection

Pieces of SQL typed into a website’s input box which reveal sensitive information.

Penetration testing

Specialists are employed to simulate potential attacks on a network.

Physical security

Protecting the physical parts of a network from either intentional or unintentional damage.

Anti-malware software

Software that stops malware from damaging a network and the devices on it.

Firewall

Blocks unauthorised access and examines all data entering and leaving the network.

User access levels

Control which parts of a network different users can access.

Passwords

Help prevent unauthorised users accessing the network.

Encryption

Data is translated into a code which only someone with the correct key can access.