21 Networks Flashcards
Network
- A collection of two or more computers connected together to share resources and data
- An arrangement of computers and other devices connected together to share resources and data
- All types of computer can be linked in networks.
Network service
An app running on a server which provides facilities or operations such as data storage, printing or communication
Server
A powerful computer that provibes the network with services like
* storing files
* sending/receiving emails
Many networks include servers.
In client-server network, the server -
* Authenticate the user
* Give user access to the files that they have permitted to access
Why are networks used?
Why computers are connected in a network?
A network can support multiple users accessing multiple services at the same time.
Network allows users -
* to access the internet
* to communicate with each other (through email or video)
* to access shared files among serveral users
* to read/write personal files on a central server (Network provides extra storage space and a back-up facility)
* to download data or updates to computer programs
* to send data to peripherals like a shared printer
Types of network
- PAN - Personal Area Network (My phone and car bluetooth)
- LAN - Local Area Network (My home wifi)
- WAN - Wide Area Network (Internet)
PAN
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- Personal Area Network
- Network used for data transmission over short distance by computer devices, such as laptops, moblie phones, tablets, media players and printers
- Devices may belong to oner person or serveral.
- connection of local devices usually wirelessly by radio waves using Bluetooth
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Examples:
* A smartphone connected to wireless earbuds for audio streaming
* A laptop connected to a smartphone for internet tethering.
* Using a smartphone to control a television
* Directly transferring files between two smartphones without needing a Wi-Fi router
* Printing documents wirelessly from a laptop to a Wi-Fi Direct-enabled printer.
* Controlling various smart home devices through a smartphone to manage home automation tasks.
LAN
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- Local Area Network
- A network that covers a relatively small geographical area, often a single site such as a home, a hospital, an office, a school or a factory
- Connection of hardware (cables, routers,..), computers, servers and other hardware devices, usually owned by the organisation
- Wireless Local Area Network (WLAN) at home
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Examples:
* Home: A wireless router allows all the computer devices in a household to access the Internet and share devices such as printer
* Office: Enabling employees to share resources such as printers and files, communicate through email and VoIP, and access company servers for applications and data storage
* Business: Supporting the operations of a large organization, including file sharing, application hosting, communication, and data management across multiple departments and floors of a building.
* School: Facilitating access to educational resources, managing administrative tasks, supporting e-learning platforms, and enabling communication between students and teachers.
* Campus (University, Business): Connecting multiple buildings within a campus to provide seamless access to resources, support collaboration, and manage large-scale IT infrastructure.
WAN
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- Wide Area Network
- A network thet covers a large geographical area
- Connection of two or more LANs (usually under a shared ownership)
- Internet is largest WAN.
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Examples:
* Employees on different sites communicating and sharing data
* A bank using a WAN to connect its ATMs, branches, and data centers globally for reliable and secure financial operations
* Internet
Types of network architecture
- Client-server
- Peer-to-peer (P2P)
Client-server network
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A network that has at least one server (one powerful computer) to provide services to the client computers (individual computers)
The server -
* Authenticate the user
* Give user access to the files that they have permitted to access
Process of a client accessing data/ files from a server:
1. A client will make a connection/ connect to server using its address. The server will know the address of the client that is included in the connection request.
2. Then, the client will make a request for a service/ data to the server.
3. If the request is valid, the server will send the requested data to the client using the address from the initial connection request.
In short, client connects to server using its address»_space; then request for service»_space; If valid request, server serves the request
Additional steps, such as authentication may be required sometimes.
Example 1:
A wants to check her web-based email from her laptop.
1. She uses a web browser to access the website, hosted on a server.
2. The website serves a web page that asks for her username and password. (Authentication)
3. She enters and submit it to the server.
If correct details, the server serves the web page that display her emails and allows her to manage her email. (requested service)
Example 2:
B wants to buy a book from an online store using his smartphone.
1. B opens the online store’s app, which connects to the store’s server.
2. The server displays the store’s homepage with various book categories.
3. B selects a book, and adds it to his cart. The server processes the request and updates the cart. (requested service)
Example 3:
C wants to access her cloud-stored documents from her desktop computer.
1. C opens her cloud storage application, which connects to the cloud server.
2. The server displays a login page. C enters her username and password and submits them. (Authentication)
3. If the credentials are correct, the server displays her stored documents, allowing her to view, download, or upload files. (Requested service)
Peer-to-peer network
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A network that doesn’t have any dedicated servers
Each computer in P2P network can -
* act as both client and server
* provide a service (sharing some files, providing access to a printer)
* request service from any other computer
Examples
1. Some instant messaging systems that allows users to chat in real time where the messages are sent directly to each other
2. Users download and upload files simultaneously, such as movies, software, or large datasets, making file distribution faster and reducing the load on any single server like pirated websites
3. Bitcoin
Network topologies
The arrangement of connections between networked devices is referred to as the network topology.
* Bus
* Ring
* Star
* Mesh
Bus network topology
- A bus network consists of a single cable to which each networked device is connected.
- Messages are sent along the cable in the form of electronic signals.
- At the end of each cable, there is terminator to absorb signals that have reached the end of the cable, preventing them from bouncing back and causing interference.
- Only one message can be sent at any one time.
- When more than one network devices send a message at the same time, a collision occurs, making all the messages unreadable.
- It is used in modern cars and some aircraft.
- CAN - Controller Area Network
CSMA/CD
- Carrier Sense Multiple Access with Collision Detection
- to deal with multiple devices sending a message at the same time in bus network
- to minimize collisions and efficiently manage data transmission
How it works:
1. Check if bus is busy.
2. If not busy then send message, else go to 1.
3. Listen to see if message received correctly.
4. If message not received correctly then go to 5, else go back to listening for messages.
5. Wait any amoiunt of time, go to 1 to retry sending message.
Making each device wait any amount of time before checking whether it is safe to send, prevents the different senders from repeatedly sending at the same time.
Advantages and disadvantages of bus network topology
Pros:
* Relatively cheap to install since only one cable is needed
* Easy to add/remove extra network devices
* Easy to implement
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Cons:
* If the cable is damaged, the whole network will fail.
* It can be difficult to identify where a fault is on the cable.
* More devices»_space; more collisions»_space; slower
* Security risk: all data sent is received by all devices on the network
Ring network topology
- Network in which the** cable connects one network device to another** in a closed loop/ ring
- Messages sent all travel in the same direction.
- Data is passed from one device to the next around the ring untill it reaches its destination.
Advantages and disadvantages of ring network topology
Pros:
* There are no data collisions.
* Adding extra devices doesn’t affect the perfromance of the network.
* Easy to add extra network devices
Cons:
* If the cable is damaged/ a networked device fails, the whole network will fail.
* Adding/ removing a device invloves shutting down the network temporarily.
* It can be difficult to identify where a fault is on the network.
* More expensive to install than bus network as it requires more cable to complete the ring
Star network topology
- Each network device is connected to a central point (hub/ switch)
- A central hub receives and directs messages to the correct recipients.
- It is most widely used.
Advantages and disadvantages of star network topology
Pros:
* A damaged cable won’t stop the whole network from working, just the network device connected to it.
* Security and efficiency: Switch sends the message to only the intended devices. Not all devices will see the message.
* It’s easy to locate faults.
* A new device can be added or removed without haveing to close the whole network down.
Cons:
* If the central point (hub/switch) fails, the whole network will fail
* It’s expansive to install as a lot of cables and switch or hub is needed.
Mesh network topology
In a fully connected mesh network,
every devices is connected to every other network device.
* A large number of failures could happen, and the rest of the network devices would still be able to communicate.
In a partially connected mesh network,
some network devices may be connected to multiple other devices or one device.
* The ability to carry on working correctly depends on how many connections to each device are avaliable.
- Each device will pass the message on to the other devices within the network.
- Very fault tolerant
- Largest mesh network = Internet
- are used to communicate between sensors in the IoT
- esp devices are mobile
Advantages and disadvantages of mesh network topology
Pros:
* Very fault tolerant (esp in fully connected): if one device fails, message can be rerouted.
* Very high performance: each network device is liekly to be connected to multiple other devices.
* In a wireless network, each node extends the range of the network.
Cons:
* Diffifcult and expansive to install wired network
* Can be difficult to manage due to the number of connecitons within the network.
Communication media in network
- methods used to connect and transmit data between computers and other networked devices
- Wired
- Wireless
Wired communication media
- Involve a physical conneciton between computer and the network
- Copper wire: electrical signals
- Fibre optic cable: light signals: transmit data faster and allows signals to travel over greater distancess
Pros:
* Reliable and stable network
* Not easy to intercept or eavesdrop on data
* Less prone to be interfernce or security breaches than wireless connectivity
Cons:
* Expensive to install and reconfigure
* Requires many cables at a premises
* ** Limit the mobility/ portablity** of connected devices
Wireless communication media
- doesn’t require a physical connection between devices.
- Radio signals
- ** Infra-red ligh**t: limited distances
Methods: - Moblie phone network
- Buletooth
- WiFi
Pros:
* No cables needed
* Device mobility and flexible network access from various locations
* Easier to expand the range of the network.
Cons:
* Interference from other wireless devices can adverselt affect the performance.
* Walls, ceilings and other physical objects can adversely/negatively affect the performance
* Data is less secured, hence needs encryption to prevent eavesdropping or interception
