• Network: two or more interconnected devices to allow fast data transmission and resource sharing. It can be wireless or wired or both type of connections

• Benefits of networking:

  • ​higher storage - can store files on network storage via Internet

  • resource sharing - sharing output devices such as printers, scanners or being able to use the same software within the network.

  • file sharing - transmission of data between devices

• Each connected device on the network is called “Node”

• LAN (Local Area Network) - connection of computers and devices in a small geographical area.

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    Hardware needed to setup LAN:

•  Minimum two nodes(computers) each containing its Network Interface Card

  • ​The NICs convert the data signals from the nodes into data signals that can be transferred across the network.

• Data transfer medium(wired/wireless)

• Hub/switch(device that connects nodes together)

  • hub: makes them all act as a single segment. Data packets are transmitted across the whole network.

  • switch: can create and connect to different segments of the network, reduces data traffic because data packets are only sent to its own destination

• Wireless Access Point(WAP)

  • allows the user to connect to network and it is built into the router

  • there is no need to do building network

  • there can be performance issues as a result of signal interference

• Router

  • ​manages data packets, allows internal connections between networks, acts as a firewall. It also translates addresses between private and public IP addresses

• Bridge

  • ​stores network addresses and connects two LANs together(only if they are under the same protocol

• Repeater

  • ​connects cables together

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• WAN (Wide Area Network) - connection of bigger number of computers and devices in a larger geographical area

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     Models of Networked Computers

     Peer to Peer:

• all computers have the same status

• data transfer might be slow due to data collisions and shared process power

• suitable for small networks (e.g. home network)

• operates with each peer networked computer, therefore every peer can act as client and request a file from another peer or it can act as a server when another peer requests the download of a file

• the data is available from more than one host

• malware might spread from shared files between peers, no security or antivirus

• can work even if a device goes down

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     Client to Server:

• server based network, at least one computer is assigned as the server

• These servers can include: web server, email server, file server, database server

• It offers services such as software and data to client

• manages traffic, records what people do and provides security

• clients have to sign in

• It allows an organization to control the downloading and use of files

• files can be protected from malware attacks

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• ​2 Client types:

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     Network Topologies

• Bus topology:

  • every device is connected to one single cable

  • all communication is shared by one bus, which ables other computers to see what data is being sent from other devices

  • has terminators at both ends

  • cheap to install and easy to set up

  • data collisions slow the network

  • if the cable has fault whole network will go down

  • only really useful over small areas

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• Mesh topology:

  • fully connected network as each device is connected to all others

  • theres always another route available for data to travel

  • no traffic, no collisions

  • can be very expensive set up due to the cable required

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• Star topology:

  • a hub or switch is used to connect all devices

  • faster network performance

  • greater security

  • fewer data collisions

  • expensive to set up due to additional network devices(hub/switch) and requires a lot of cable

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• Hybrid topology:

  • ​combination of two or more topologies

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    Cloud computing

• The Cloud: network of serves hosted on the internet which offer a range of services to store and process data. It is online services provided by numerous companies. 

• Benefits:

  • accessible via network

  • no need to get or install the software

  • any connected computer can access the service

  • less technical knowledge required

• Drawbacks:

  • no privacy

  • data might get lost, volatile

  • cannot access data if there is a bandwidth issue

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• Wired network: a network cable(can be twisted pair, coaxial or fibre-optic) used to connect to Ethernet by the network router

  • ​copper cable: cheap and easy to install and use, but gets affected by electromagnetic waves and needs repeaters quite often

  • fibre-optic cable: high bandwidth, performs the best and need for repeaters is less often, but it is very expensive to setup and use

• Wireless network: a transmission using radio, microwave or infrared without the use of cables

  • radio waves: cheap to set up, can travel for long distances, but it offers poor security, omni-directional and bounce off when they face a high frequency. Used in TVs, phones or wireless LAN

  • microwave: unidirectional, can travel long distance more resistant to high frequency, offers medium security, but expensive to set up

  • infrared: unidirectional, offers high security, cheap to set up, but cannot travel long distance or penetrate through solid objects such as walls

• Ethernet: focused on LANs, transmission medium, networking technology that includes the protocol, port, cable, and computer chip needed to plug a desktop or laptop to transmit data

• Ethernet Collisions:

  • -data collision occurs when two end systems transmit data at the same time

  • -CSMA/CA protocol is used to reduce collisions, we use CSMA/CA with RTS (Request to Send) / CTS (Clear to Send)

  • This is how it works:

  1. The node listens to the network channel to determine whether data are being transmitted by another node

  2. If the network is busy then the node waits a random period of time. The node keeps listening and waiting until the network becomes clear

  3. The node sends an RTS signal to the WAP, which returns a CTS signal once the network has been confirmed to be clear

  4. The node then transmits the data

  5. The receiver send an acknowledgement back to the sender

  6. If no acknowledgement is received the data need to be retransmitted

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• Bit Streaming

  • flow of bits over a communication path

  • bits arrive with the same order they are sent

• There are two types of Bit Streaming:

  • ​Real time- when the bit stream content is transmitted as it is produced

    • ​the content is being generated as it is being delivered such as when viewing a sporting event, it is filmed by a camera connected to a computer. It is encoded, but it cannot be fast-forwarded or paused.

  • On demand- when the bit stream content is transmitted at a time chosen by the user

    • ​the delivery of the media and the playing of the media are two separate processes. The incoming media data are received into a buffer created on the user’s computer. The user’s machine has media player software that takes the media data from the buffer and plays it. It can be paused, or fast-forwarded

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     The World Wide Web (WWW) and the Internet

• Internet is an infrastructure, network of networks, collection of connected computers.

• The world wide web is the collection of websites and web pages accessed using the internet

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     Hardware that is used to support the internet:

• modems

  • connects your home internet to Internet Service Provider

  • converts digital signals to analogue signals or vice versa

• PSTN(Public Switched Telephone Network)

  • ​bi-directional communication channel used for telephone calls via circuit switching.

• dedicated lines

  • ​allows the user to host website and telephone calls, continuous access on web, but it can be only bought and cannot be shared

• cell phone network

  • mobile data

  • this is provided by mobile phone companies acting as ISPs. The mobile phone, equipped with the appropriate software, communicates with a standard cell tower to access the wireless telephone network, which in turn provides a connection to the Internet

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• Internet Protocol(IP)- A protocol that specifies the size of the packets that a message is broken down into, and the address of the recipient device

• IPv4- a method of addressing that uses 32-bit numbers to specify internet/network addresses

  • split into 4 blocks by using dots(”.”)

  • the values can be between 0-255

  • e.g. 342.45.320.23

• IPv6- a method of addressing that uses 128-bit numbers to specify internet/network addresses

  • split into 8 blocks by using colons(”:”)

  • the values are hexadecimal and can be between 0000-FFFF

  • e.g. 2001:0db8:85a3:0000:0000:8a2e:0370:7334

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    Public IP address:

• assigned to every computer that connects to the Internet, where each IP is unique

• two computers with the same IP address cannot exist

• users have no control over their assigned IP addresses. It is assigned by the ISP

• It can be static or dynamic

  • static: can be used for primarily hosting web pages or services on the internet

  • dynamic: it is chosen from a pool of available addresses and changes each time one connects to the Internet

    Private IP address:

• An IP address is considered private if the IP number falls within one of the IP address ranges reserved for private networks such as a LAN

• If the private network is connected to the Internet then each computer will have a private IP as well as a public IP. Private IP is used for communication within the network whereas the public IP is used for communication over the Internet.

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    Uniform Resource Locator(URL)

• every document on the internet has an unique URL

• it is consist of 3 main parts: domain, protocol and filepath

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    Domain Name Service(DNS)

• This is the system used to find the computer which hosts the website you are looking for

• It is a collection of IP addresses

    How URL is used to locate a resource on the WWW with the role of DNS:

1. type in the URL address to your browser

2. URL address will be sent to ISP and it looks up the IP address of the URL in DNS

3. when it finds the matching IP address, it sends back the IP address and redirects you to the website

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                                                                                                                                                                               by: Elif Nur Cholak