Networks

Wide area network (WAN)

any network in which the computers communicate using resources supplied by a 'third party carrier' e.g. BT

how does a WAN connect 2 or more remote locations

Uses cables, telephone lines, satellites or radio waves

List organisations that use a WAN and why

Large companies with many offices e.g. banks

Govs - employees in many locations

Research organisations: located in more than 1 place

Advantages of WAN

reliability, consistent speed, lower susceptibility to interference and improved physical security.

Disadvantages of WAN

installation cost, reduced mobility and cable faults.

What is a NIC

A network interface card: a hardware that connects a device to a network and gives it a MAC address so it can be identified - provides a network interface

Which devices are NICs bulit into

they are built into every networked device

can a device have more than 1 network interface?

Yes it can have more than one netowrk interface.

What is a MAC address?

Media Access Control address: An address associated with a device/network adapter which is used for local communication

What does MAC filtering do?

allows or blocks a device from accessing a network depending on its MAC address

What is MAC addresses represented in normally?

hexadecimal

What does a switch do?

connects devices on a LAN and forwards data using MAC addresses

How does a switch do what it does?

learns which AC addresses are reachable through its ports --> forwards frames towards appropriate device

what does a router do?

connects different networks and forwards packets using IP addressing, they select where packets should be forwarded next

What does a router do at home?

connects the home LAN to the Internet - routes packets between home LAN and internet

What is a WAP and what does it do?

Wireless Access Point: allows wireless devices to connect to a network

What is wireless transmission

uses radio waves for communication however is susceptible to interference from nearby objects

Advantages of wireless networks 3

no need to lay cables, easy to connect new devices, devices can be portable within the range of the access point

disadvantages of wireless networks 4

can be less reliable than wired networks, if many devices try to use the same access point at the same time, the connection can be very slow, connection speed reduces the further the device is from the access point, can be less secure than wired connections.

What is an IP address and what does it do?

An Internet Protocol address: where packets of data are sent to or received from

wireless network

a network using radio waves

wired network

a network using cables

routing definition

directing IP packets to their destinations

what are packets

one unit of data sent through an IP network

What does packet switching do?

divides data into packets that are routed and reassembled at the destination

What do packets contain?

the payload, the header

what is the payload in a packet?

This is the actual chunk of user data from the file

what does the header in a packet contain?

vital metadata needed to route and rebuild the file, including: sender's IP address, receiver's IP address, sequence number, total number of packets in transmission

What is a PAN/ what does it do?

Personal Area Netowork: connects personal devices that are in close proximity (~10m) to an individual

Example of PAN

bluetooth

ownership of PAN

owned + controlled by 1 individual

What is a LAN + what does it do?

Local Area Network: connects multiple computers + peripheral devices together over a small contained geographic infrastructure

Ownership of LAN

hardware owned + managed by person or organisation running it (privately owned)

examples of LAN

school network connecting student worksattions to a shared school printer/server, home network

Advantages of networks

Computers can share resources e.g. printers, Files can be accessed through any computer in the network, Data is easy to back up as it is stored centrally on the server

Disadvantages of networks

Purchasing the network hardware is expensive, Managing a large network is complicated, Viruses may be able to infiltrate the network and infect every computer

List all the network hardware needed to connect a stand alone computer to a WAN

NIC in device, a switch/hub, modem, router, WAP

what does a modem do?

connect to the Internet - usually combined with router inside a single device

List all the network security methods

authentication, encryption, firewall, MAC address filtering

what is authentication?

process of verifying that a user is who they claim to be before giving access to a system or network.

examples of authentication

username and password, pin, biometrics, two factor authentication

what does encryption do?

the encoding of data from plaintext to ciphertext so intercepted data cannot be easily understood without the appropriate decryption key

what is a key

a sequence of numbers used to encrypt or decrypt using a maths formula

What is a symmetric encryption

The same private key is used to encrypt and decrypt a message - must be given to recipient of your message to decrypt data securely (that's why it's private)

what is asymmetric encryption

uses a public/private key pair: a public key used to encrypt and private key to decrypt

why is an asymmetric encryption more secure than a symmetric key?

because you never have to send or reveal your decryption key (as it is private

Common wireless security standards

WEP (wired equivalent privacy), WPA (Wifi protected access)

what represents a weak encryption (opposite for strong encryption)

Code may be broken in time to use the information - wouldn't be worth the effort trying

What does a firewall do?

separates a trusted and untrusted network and monitors network traffic and applies security rules to allow or block connections

What is port blocking

preventing access to certain ports on a network - usually done by a firewall

what is packet filtering

checking packets and dropping those that don't match filtering rules

what is MAC address filtering

checks a device's MAC address to determine whether it should be allowed or blocked from connecting

Disadvantages of MAC address filtering

MAC address can be faked

what is a protocol

a set of rules for communication between devces ona netowkr

What is TCP?

Transmission Control Protocol: breaks up messages in to packets and reassembles them, detects errors, resends lost messages

what is IP

Internet protocol: routes the individual packets from 1 IP address to antoehr

what is the TCP/IP protocol stack

a protocol stack that defines 4 layers that allow communication on the Internet

what are the 4 layers in the TCP/IP stack?

application, transport, internet and link layers

what design is the TCP/IP stack

modular design: each layer responsible for a small part of commuincation process

What protocols are used on the application layer?

HTTP, HTTPS, SMTP, IMAP

what happens in the application layer?

Applications such as email clients and web browsers create data to send in this layer

What is HTTP and what does it do/how it works?

Hypertext Transfer Protocol: used to request and transfer web resources between a client and web server.

What is HTTPS and what does it do/how it works?

Hypertext Transfer Protocol Secure: provides an encrypted version of HTTP for more secure web transactions. Uses encryption to protect data transferred between a browser and web serve

examples of where HTTPS is used

sensitive data such as logins or payment information is transmitted.

What is SMTP and what does it do?

Simple Mail Transfer Protocol: Used to send email from an email client to a mail server and to transfer email between mail servers.

What is IMAP and what does it do?

Internet Message Access Protocol: used to access email stored on a mail server and synchronise it across devices.

What does the transport layer do overall?

Creates connection between 2 computers or 'hosts

What happens at sender side in transport layer/

Data is split into segments when using TCP.

Segments contain sequence numbers so they can be put back into the correct order.

Port numbers identify the sending and receiving applications.

What happens at receiver side on transport layer?

Segments are reassembled in the correct order.

With TCP, missing data can be detected and retransmitted.

The completed data is passed to the correct application.

What protocols are used on the transport layer?

TCP (Transmission control protocol)

what does TCP do? 3

breaks data into segments before transmission, uses sequence numbers so the data can be reassembled in the correct order at the destination, detects missing or corrupted data and requests retransmission.

What happens at sender end of internet layer?

Adds the source and destination IP addresses to the packet.

Determines how packets are routed across networks towards the destination.

what happens at receiver end of internet layer?

Checks the destination IP address.

Processes/removes the IP header information.

Passes the data up to the Transport Layer.

what protocol acts on internet layer and what does it do?

IP (Internet Protocol): Responsible for addressing and routing packets across networks using IP addresses so that they reach the correct destination.

What is the link layer responsible for?

Responsible for how data is physically transmitted across the network.

what does the link layer work with?

It works with hardware such as NICs (Network Interface Cards), cables and wireless connections, as well as device drivers.

what protocol acts in link layer?

MAC (Media Access Control)

what happens at receiver end of application layer?

Uses the correct protocol to correctly display the data, webpage or email for user.

Which way do you go through the layers if sending data?

Termianl A --> application layer --> tranpsort layer --> Internet layer --> Link layer --> Link layer of router --> internet

Which way do you go through the layers if receiving data?

link layer (router) --> Internet (router) --> link layer of router --> link layer of terminal B --> internet layer (of TB etc.) --> transport layer --> application layer

example of sending data through layers?

Application: computer application produces data for sending, transport: splits data into packets, internet :sends and routes the packets, link: physical hardware and cables

Example of receiving data through layers

Link layer (router): removes MAC address + passes packets up to internet layer, Internet layer (router): removes IP addresses + passes packets up to transport layer, transport layer (TB: reassembles packets + passes data to application layer, application layer (TB) : uses correct protocol to display data

Advantages of layers

Layers self contained: the functionality of one layer can be changed without affecting the functionality of other layers, Different hardware/software operates on a particular layer --> interoperability between providers + systems

--> manufacturer's routers operating on the internet layer, will operate with another manufacturer's NICs operating on the Link layer

Senders and receivers using different software + hardware can communicate using the same layer protocols