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GCSE OCR Computer Science Detailed Notes for Chapter 2: Networks
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GCSE OCR Computer Science Detailed Notes for Chapter 2: Networks. Grade 9/A* Quality
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OCR Computer Science Chapter 1 (Components of a Computer System) Detailed Notes
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Computing Revision Nikhil ChidipothuTopic 2 – Networks
LAN - Local Area Network:
Covers a small geographical area. All hardware is owned by the organisation that
uses it.
LANs are either wired or wireless.
Often found in businesses, schools and universities. Homes also use LANs to connect
various devices include PCs, tablets, smart TVs and printers etc.
WAN – Wide Area Network:
WAN connects LANs. It covers a larger geographical area typically anything greater
than a mile.
Uses external hired infrastructure from companies that manage WAN. WAN is more
expensive as a result.
WAN may be connected using fibre or copper telephone lines, satellite links or radio
links. Internet is biggest WAN.
Factors affecting performance of network:
Bandwidth – amount of data transferred in given time. The greater the bandwidth
the better the network.
Available bandwidth is shared between network users. More users mean that
network becomes slower as congestion occurs so users can be limited bandwidth.
Wired connections are faster and more reliable. Fibre optics are faster than coaxial.
Wireless performance is slower – depends on signal quality so obstructions can also
inhibit performance.
Choice of hardware and network topology can affect performance too.
NICs, Switches and Routers:
Network Interface Controller (NIC) – allows a device to connect to a network. Exist
for both wired & wireless connections.
Switches - connect devices to a LAN. They receive data from one device and transmit
it to the device on the network with correct MAC address.
Routers – transmit data between networks in packets. They also perform packet
switching to ensure data ensure data arrives, all in the right order. Connect LAN to
internet
Cables:
Ethernet connect devices to LAN e.g. CAT 5e. These are twisted pair cables.
Coaxial cables are made of single copper wire surrounded by insulation.
Fibre optic cables transmit data as light. High performance and don’t suffer
interference.
Wireless Networks:
Use radio waves to transmit data. You need a WAP to set up wireless network.
Wireless Access Point – switch that allows devices to connect wirelessly.
Hotspots are locations where you can connect to a WAP. To connect devices need
wireless capability.
Wi-Fi:
, Standard for wireless networks – uses 2 radio frequency bands: 2.4GHz and 5GHz.
Bands are split into numbered channels that cover small frequency range. Channels
overlap.
Wi-Fi performance is affected by interference between networks using adjacent
channels.
Client server network:
In a client server there is a central computer that provides all services to the
network.
Files and software are stored on that central computer and then clients send
requests to server.
Server processes to request and responds. This is known as a client-server
relationship. They are most commonly-used in larger offices and organisations.
Advantages of Client Server Disadvantages of Client
Server
Easy to keep track of files Expensive to set up
due to central location
Easier to perform back-ups Server dependence means
and install software that if server goes down all
updates. clients lose access.
Easier to manage network Server may be overloaded
security due to high usage.
Servers are generally very
reliable and are always
running
Peer-to-Peer network:
In a peer-to-peer network, all devices are equal connecting directly to each other
without server.
So you can store files on individual devices and share them with others. These are
often used in smaller businesses and homes.
Advantages of Peer to Peer Disadvantages of Peer to
Peer
Easy to maintain so no No centralised management
expertise or expensive so backups and software
hardware needed updates are harder.
No dependence so if one Copying files can create
device fails whole network duplicates so it’s harder to
can still work manage.
Less reliable so data may be
lost. Machines in network
may slow down.
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