3.5 Fundamentals Of Computer Networks Flashcards
Computer network definition:
Devices connected together that allow these devices to share information and resources
Benefits of compute networks:
- sharing files is easier (network users can access files, work on them at same time, copy files between machines)
- can share the same hardware (printers) between multiple devices
- can install/update software on all computers at once (not one-by-one)
- can communicate across a network cheaply & easily (email)
- user accounts can be stored centrally (users can log in from any device on the network)
Risks of computer networks:
- can be expensive to set up (often need lots of extra hardware)
- can be vulnerable to hacking
- malware can easily spread between networked computers
- some dependent on 1+ servers, if servers go down it can be disruptive for people using network
- large networks difficult to manage, may require employing a specialist to maintain them
Main types of computer network:
- Personal Area Network (PAN)
- Local Area Network (LAN)
- Wide Area Network (WAN)
Personal Area Network (PAN)
= connects devices in a very short range
- normally centred around a single user
- often used to transmit between mobile/wearable devices
- use common wireless tech (Bluetooth) to connect devices
Bluetooth = strong but short range so ideal for connecting devices in same room
- handy as don’t require additional hardware (can create on the move)
Local Area Network (LAN)
= covers a small geographical area located on a single site
- all hardware owned by organisation that uses it
- can be wired (ethernet cables) or wireless (wi-fi)
- often in businesses, schools, universities
- many homes have it to connect various devices (PCs, tablets, printers, smart TV)
Wide Area Network (WAN)
= connects LANs in different geographical locations
- organisations hire infrastructure from telecommunication companies, who own and manage WAN (as very expensive to set up)
- so under collective/distributed ownership
- may be connected using telephone lines (copper/fibre optic), satellite links, or radio links
- internet = one big WAN
Switch:
Connects devices on a LAN
Router:
Transmits data between different networks different networks (mostly to connect to internet)
What is a Network Interface Card (NIC)
= piece of hardware inside a device, allows it to connect to networks
(For both wired and wireless connections)
What are local wireless networks called?
= WLANs (wireless LANs)
Wi-Fi = specific family of WLAN protocols
What is a WAP?
WAP = wireless access point device
Needed to set up wireless network, allows devices to connect
What do wireless networks use to transmit data?
Radio waves
Benefits of wireless networks (compared to wired networks):
- convenient, device can automatically connect to network & move around while connected
- can be cheaper & better for environment (don’t need wires)
- very easy to add more users (don’t need to install extra wired/do a complex setup)
Risks of wireless networks (compared to wired networks):
- generally less secure, access points usually visible to all devices (not just trusted ones) = can allow hackers to gain access
- distance from WAP, interference from other wireless networks, physical obstructions = reduce signal strength, limit to how far network can reach
- lower bandwidth & less reliable
List different cables used to connect devices on a wired network:
- fibre optic cable
- CAT 6/5e, twisted copper cable
- coaxial cable
Twisted pair of copper wires (CAT 6/5e) cable:
- common type of Ethernet cable
- pair of copper wires twisted together to reduce internal interference
- cheaper
- decent bandwidth (used for LANs)
Coaxial cable
- single copper wire surrounded by plastic layer for insulation & metallic mesh to provide shielding from outside interference
- very cheap
- low bandwidth
Fibre optic cable:
- transmits data as light
- high performance & expensive
- don’t have interference
- can transmit over very large distances at high bandwidth without loss of signal quality
network topology definition:
The layout of a network
List the common network topologies:
- star topology
- bus topology
Star topology:
= all devices are connected to a central switch or server that controls the network
- central switch allows many devices to access server simultaneously
- may be wired/wireless
Pros of star topology:
- if device fails/cable disconnects, rest of network is unaffected
- simple to add more devices (each device connected to switch using separate cable)
- better performance, data goes straight to central device so all devices transmit data at same time
- fewer data collisions
Cons of star topology:
- in wired networks, every device needs cable to connect to central server/switch = expensive
- central switch = expensive piece of hardware
- is problem with switch/server, whole network affected
- max no. of possible connections determined by switch, if more is needed, need to buy a new one
Bus topology:
= use a single ‘backbone’ cable (bus) to connect to all devices
= 2 terminators places at ends of bus to stop data reflecting back along bus (reflected signals cause interference & potentially make network unusable)
- only wired networks
Pros of bus topology:
- network unaffected if device fails
- aren’t dependant on a central switch working to keep network running
- relatively cheap to set up, less wiring needed
- hardware needed (bus cable,terminations) cheaper to buy & maintain than switches
Cons of bus topology:
- data collisions common, then data must be reset which slows network down
- more devices added = more likely data collisions so unsuitable for large networks
- devices must wait for bus to be available to send any data to avoid data collisions = slows network down
- if bus cable breaks, splits network into separate parts which don’t have terminators at each end = lots of reflected signals, can shut down entire network
Network protocol definition
A set of rules for how devices communicate and how data is transmitted across a network
- how communication between 2 devices should start/end
- how data should be organised
- what devices should do if data goes missing
List common network protocols:
- Ethernet
- Wi-Fi
- TCP (Transmission control protocol)
- UDP (User data gram protocol)
- IP (Internet protocol)
- HTTP (Hypertext Transfer Protocol)
- HTTPS (Hypertext Transfer Protocol Secure)
- FTP (File Transfer Protocol)
- email protocols:
- SMTP (Simple Mail Transfer Protocol)
- IMAP (Internet Message Access Protocol)
Purpose & use of Ethernet:
= family of protocols that operates on the link layer
- handles transmission of data between devices on LANs
- for wired connections
Purpose & use of Wi-Fi:
= standard family of protocols for WLANs (link layer)
TCP (Transmission Control Protocol)
= establishes connection between sending & receiving devices
- then splits data into numbered packets (can be reassembled at destination)
- communicates with receiving device to check all packets have been transferred correctly
- sending device gets confirmation when transfer complete
UDP (User Datagram Protocol)
= breaks down data into packets without numbering them
- unnumbered packets read by receiving device in order they arrive (may not be order sent)
- only sends each packet once, doesn’t check if they have been received
= saves time, don’t know if packets have gone missing in transit
IP (internet protocol)
= establishes connections between routers & handing network traffic
- IP address = unique number assigned to every device connected to IP network
- directs data packets to destination using packet switching, each packet sent through series of routers which read packet’s IP address to decide which router to send packet to next
- packet switching = efficient as many possible routes packet can take, packets reach receiving device quickly, even if traffic
HTTP (Hyper Text Transfer Protocol)
= used by web browsers to access websites & communicate with web servers
HTTPS (Hyper Text Transfer Protocol Secure)
= more secure version of HTTP, encrypts all info sent & received
FTP (File Transfer Protocol)
= used to access, edit, move files between devices on a network
IMAP (Internet Message Access Protocol)
= used to retrieve emails from a server
SMTP (Simple Mail Transfer Protocol)
= Used to send emails & transfer mails between servers
Need for network security?
They are vulnerable to attacks by criminals
Protects against damage, cyber attacks & unauthorised access
Methods of network security:
- authentication
- encryption
- firewall
- MAC address filtering
Authentication
= makes sure anyone trying to access network is who they say they are, prevents unauthorised people for accessing data from network
- passwords
- biometrics
- email confirmation
- CAPTCHA
Encryption
= when data is translated into code which only someone with correct key can access (unauthorised users can’t read it), essential for sending data over a network securely
- encrypted text = cipher text
- non-encrypted text = plain text
Firewall
= anti-malware software which examines all data entering & leaving a network & blocks any potential threats
- used to prevent unauthorised access to a companies network
MAC address filtering
= checks unique identification (MAC address) of each device that tries to connect to network & only lets allowed devices to join network, blocks others
makes sure only people on a network are trusted users
User access levels (authentication)
= control which parts of network different groups of users can access
- limits no. of people with access to important data, help to prevent attacks from within an organisation
4 layer TCP/IP model: (protocols operating on that layer)
- application layer(4) = HTTP, HTTPS, FTP, SMTP, IMAP
- transport layer(3) = TCP, UDP
- internet layer(2) = IP
- link layer(1) = Wi-Fi, Ethernet
Application layer
= provides networking services to applications
= where network applications (web browser, email programs) operate
Transport layer
= sets up communications between 2 devices(hosts), splits data into packets & checks packets correctly sent/delivered
= hosts agree settings (language, size of packets)
Internet layer
= adds IP addresses to data packets, directs packets between devices & handles traffic, used by routers
= routes packets across network
Link layer
= passes data over physical network, responsible for how data is sent as electrical signals over cables, wireless & other hardware, interprets signals using device drivers
- where network hardware (NIC - Network Interface Card) & device drivers sit
