GCSE Computer Science Past Paper Presentation Notes PDF

for Edexcel Ul t i m a t e G C S E The p u t e r S c i e n c e Co m An i m a t e d e s e n t a t i o n s i a...

for Edexcel Ul t i m a t e G C S E The p u t e r S c i e n c e Co m An i m a t e d e s e n t a t i o n s i a Pr4-2 – Transm i ssi o n M e d (C ) 1 2020  Transmission Media 2 (C) 2 020  Wired ne t w o rk s (C) 2020 3  YO Textbook reading UR TUR N! Read page 17 of Chapter 4 – Networks about wired networks from The Ultimate GCSE Computer Science Textbook (C) 4 202 0  http://tiny.cc/transmissionmedia - how transmission media work 5  Wired networks Use cables to connect devices together Usually managed by a switch 6  Types of cable Unshielded Twisted Pair (UTP) cables copper cable 4 twisted pairs of wires known as Ethernet cable Fibre optic cables thin glass tube light is reflected along the tube 7  Copper vs fibre optic Copper Fibre optic Cheaper per metre No electromagnetic interference Already exists in telephone Data can travel longer distances networks (>100m) Data travels faster at speed of light Higher bandwidths 8 (C) 2 020  eless n etw orks Wir (C) 2020 9  10 Wireless networks SE is on: Focus for Edexcel GC Wi-Fi es Wi-Fi uses radio wav Bluetooth Zigbee RFID NF C (C) 2020  YO Textbook reading UR TUR N! Read pages 18-19 of Chapter 4 – Networks about Wi-Fi from The Ultimate GCSE Computer Science Textbook Stop before you get to the benefits and risks (C) 1 202 1 0  Typical home Wi-Fi setup Wi-Fi access point often part of a wireless router Data travels using radio waves Wireless router includes: network switch router (to connect to ISP) wireless access point 1 (C) 2 2 020  Wi-Fi hotspot Found in public buildings Enables any Wi-Fi device to connect to Internet Some places charge for access Usually unencrypted data can be read by anybody on the network better to use an encrypted network scrambles data so it can’t be understood or use a VPN (virtual private network) creates a private connection Can be setup on a mobile phone for personal use known as tethering 1 (C) 2 3 020  Wireless access points Several wireless access points used on a large network Usually connected by cable to a switch Provide coverage across a large area 1 (C) 2 4 020  YO Textbook reading UR TUR N! Read pages 19-20 of Chapter 4 – Networks about benefits, risks and disadvantages of Wi-Fi networks from The Ultimate GCSE Computer Science Textbook (C) 1 202 5 0  Benefits of wireless networks Devices can connect without a cable Devices not restricted to specific location Mobile phone Wi-Fi saves on data costs Bandwidth is big enough for Internet connectivity Any Wi-Fi device can connect if it conforms to Wi-Fi standard has permission to connect Relatively easy to setup in homes no technical experience required Relatively low cost very little cabling required BYOD – bring your own device employees can use their own devices at work 1 (C) 2 6 020  17 Risks of a wireless network Hackers can see data on the network if encryption is not used Hackers do not need physical access to a network they just need wireless access (C) 2020  Other disadvantages of wireless networks Bandwidth usually lower than wired networks but not usually an issue if Internet bandwidth is lower than wireless Obstacles interrupt wireless signals lost data packets = reduced bandwidth Range is limited additional access points needed for large area Interference from electrical signals and microwaves lost data packets = reduced bandwidth Bandwidth is shared with other devices (C) 1 202 8 0  YO Textbook reading UR TUR N! Read pages 20-21 of Chapter 4 – Networks about Bluetooth from The Ultimate GCSE Computer Science Textbook (C) 1 202 9 0  Bluetooth Protocol for wireless communication Range approximately 10 metres No line of sight required Used for portable devices on a personal area network 2 (C) 2 0 020  Bluetooth – typical applications Examples: Using a mobile phone in a car via Bluetooth Using a Bluetooth speaker to play music Tethering a mobile phone’s Internet connection mobile hotspot Reading a text message on an Apple watch connected by Bluetooth 2 (C) 2 1 020  Advantages of Bluetooth widely available on many portable devices no radio frequency licence required no line of sight required passkey can be used to prevent non-authorised devices from connecting lower power consumption than Wi-Fi (C) 2 202 2 0  Limitations of Bluetooth current data transfer rates are slow maximum range of 10 metres can only connect one device to one other device at a time e.g. a Bluetooth headset cannot be used at the same time as a Bluetooth speaker connected to the same mobile phone (C) 2 202 3 0  YO Textbook reading UR TUR N! Read pages 21-22 of Chapter 4 – Networks about Zigbee from The Ultimate GCSE Computer Science Textbook (C) 2 202 4 0  Zigbee Personal Area Network based on: low-energy low data rate close proximity Used for smart home devices Internet of Things (IoT) Devices added in ad-hoc manner 2 (C) 2 5 020  Smart home devices Devices that may use Zigbee include: house alarms light bulbs light switches smart plugs central heating electronic blinds Many are battery powered Zigbee battery life can be a few years 2 (C) 2 6 020  Zigbee vs other wireless methods Zigbee has larger range than Bluetooth also forms its own mesh network smart devices can act as repeaters Zigbee bandwidth is maximum 250 kbps much lower than Wi-Fi BUT sufficient for most smart devices Zigbee not reliant on cloud servers connect directly to a controller 27 (C) 2 020  Zigbee standards Zigbee is a protocol BUT there is no standard way of implementing it Different manufacturers use it in different ways separate controller needed for each manufacturer some are compatible with common controllers: Amazon Echo Show Samsung Smart Things Apple Home Kit Project Connected Home Over IP (CHIP) alliance of manufacturers trying to standardise smart device communication 2 (C) 2 8 020  Example of standards problem Red manufacturer devices can only communicate with red controller other red devices cannot communicate with blue or pink devices blue or pink controller 3 separate mesh networks CHIP aim is for one single mesh network across all manufacturers 2 (C) 2 9 020  http://tiny.cc/zigbeevs - Zigbee vs Z-Wave vs Wi-Fi 3 0  YO Textbook reading UR TUR N! Read page 23 of Chapter 4 – Networks about RFID and NFC from The Ultimate GCSE Computer Science Textbook (C) 3 202 1 0  RFID Radio Frequency Identification Identifies tiny RFID chips e.g. sticker e.g. embedded into product Can be passive (no power required) or active (power required) Contains very small amount of data e.g. monitoring location of parcels each parcel has unique RFID tag tag may be active or passive passive requires individual scanning active can be scanned from a distance 3 (C) 2 2 020  http://tiny.cc/RFIDvsNFC - What is RFID and How RFID Works 33  http://tiny.cc/RFID2 - RFID as Fast as Possible – STOP at 4:06 3 4  NFC Near Field Communication Secure method of RFID Can be both a reader and a tag Used in most smart phones Examples: unlocking doors transport passes credit and debit card payments 35 (C) 2 020  http://tiny.cc/RFIDvsNFC - RFID vs NFC 36  Activity – comparing wireless YO communication methods UR TUR N! Complete the comparing wireless communication methods activity from The Ultimate GCSE Computer Science Textbook (C) 37 202 0  C o m bi n in g wired and wireless n e t w o r k s (C) 2020 38  YO Textbook reading UR TUR N! Read pages 24-25 of Chapter 4 – Networks about combining wired and wireless networks from The Ultimate GCSE Computer Science Textbook (C) 39 202 0  Combining wireless and wired Most networks are a mixture of wired and wireless e.g. copper cables or fibre optic Wi-Fi Bluetooth Zigbee Controllers are connected to the network: Wi-Fi access points Zigbee controllers RFID scanners NFC enabled devices 4 (C) 2 0 020  Activity – mixed YO networks UR 1. Discuss what devices are connected to your school network and what type TUR of connections they use. N! 2. Discuss what devices might be connected to a supermarket network and what type of connections they use. You may want to do this exercise by starting off in pairs and listing as many different devices and connections that you can for each scenario. Then join up with another pair and compare notes. See if you agree and discuss any that you disagree with. Now you are in a group of 4, send out a spy to find out if there are any devices and connections that other groups have got that you have not got on your list. (C) 4 202 1 0  Extension: http://tiny.cc/wirescableswifi - wires, cables and Wi-Fi 4 2  Extension activity – YO Packet Tracer UR If you have access to the free CISCO Packet Tracer software from TUR http://tiny.cc/packettracer then setup a single wireless access point (use a wireless router) with a couple of devices connected to it: 1. Set up the SSID for the wireless router N! 2. Give the wireless router an IP address of 192.168.0.1 and subnet mask of 255.255.255.0 3. Set the wireless router to be a DHCP server 4. Add a laptop 5. Set the same SSID for the laptop as the wireless router 6. Set the laptop to use DHCP for IP addresses 7. Add encryption to the wireless router 8. Setup the encryption on the laptop (C) 4 202 3 0  r k per f or m an ce Netwo (C) 2020 44  YO Textbook reading UR TUR N! Read page 26 of Chapter 4 – Networks about network performance from The Ultimate GCSE Computer Science Textbook (C) 4 202 5 0  Bandwidth How much data can be transferred more frequencies = more data transferable at once Measured in bits per second (bps) 8 Mbps = 8 megabits per second 8 bits = 1 byte 8 Mbps = 1 megabyte per second Higher bandwidth = more data per second increases overall speed of data transfer Analogy: number of lanes on a motorway maximum speed is still 70mph but more cars can travel at once 4 (C) 2 6 020  Activity – YO bandwidth UR TUR N! Complete the bandwidth activity from The Ultimate GCSE Computer Science Textbook (C) 47 202 0  Effect of transmission media on bandwidth Copper suitable up to 100m bandwidth governed by frequencies copper can accommodate Wireless less frequencies available = less bandwidth obstacles reduce strength of signal = less bandwidth distance reduces strength of signal = less bandwidth 48 (C) 2 020  YO Textbook reading UR TUR N! Read page 27 of Chapter 4 – Networks about bandwidth vs network speed from The Ultimate GCSE Computer Science Textbook (C) 4 202 9 0  Bandwidth vs network speed Bandwidth = maximum amount of data that can be transmitted per second Network speed = how much data is actually transmitted per second Network speed can be affected by: interference latency range network traffic bottle necks 5 (C) 2 0 020  Interference Wi-Fi suffers interference from: overlapping Wi-Fi channels baby monitors microwave ovens Copper cables suffer electrical interference from: electrical cables nearby electrical devices Fibre optic cables no interference Interference = loss of data packets packets must be re-transmitted increases time taken 5 (C) 2 1 020  Latency Time difference between receiving a data packet Latency (ms) and when it was sent Measured in seconds Noticeable during live events video conferencing 36 LAN gaming km ,0 00 Satellites ,0 00 km 6 high latency 3 signals travel thousands of miles 5 (C) 2 2 020  Only Network traffic 100 Mbps left Max 1 Gbps Using More devices communicating at once 400 Mbps = less bandwidth available to each device Using 500 Mbps Particularly noticeable with public Wi-F 53 (C) 2 020  Range As range is extended signals become weaker network speed reduces 50 Mbps Applies to both 200 copper Mbps wireless 400 No Mbps signal 5 (C) 2 4 020  Extension activity – YO contention ratios UR TUR N! Find out what a contention ratio is (C) 55 202 0  YO Textbook reading UR TUR N! Read pages 28-29 of Chapter 4 – Networks about network speed expressions from The Ultimate GCSE Computer Science Textbook (C) 56 202 0  Network speed expressions Network speeds measured in bits per second (bps) These multiples of bits are used: kilobits per second (Kbps) 1,000 bits per second megabits per second (Mbps) 1,000,000 bits per second gigabits per second (Gbps) 1,000,000,000 bits per second one byte = 8 bits Measured in bits 8 bits per second = one byte per second NOT bytes 16 Mbps = 2 MB per second 57 (C) 2 020  Base-10 vs base-2 Network speeds use base-10 units: One Kbps = 1,000 bits per second (103) or (10001) One Mbps = 1,000,000 bits per second (106) or (10002) One Gbps = 1,000,000,000 bits per second (109) or (10003) File sizes use base-2 units One KiB (kibibyte) = 1,024 bytes (210) One MiB (mebibyte) = 1024 x 1024 bytes (220) One GiB (gibibyte) = 1024 x 1024 x 1024 bytes (230) 58 (C) 2 020  File size in bits One byte (B) = 8 bits One KiB (kibibyte) = 1,024 bytes (210) = 1024 x 8 bits One MiB (mebibyte) = 1024 x 1024 bytes (220) = 1024 x1024 x 8 bits One GiB (gibibyte) = 1024 x 1024 x 1024 bytes (230) = 1024 x1024 x 1024 x 8 bits 59 (C) 2 020  Expression for time taken Time taken to transfer a file (seconds) = = 6 (C) 2 0 020  Time taken expression - example Time taken to transfer a file File size = 15 MiB (seconds) File size in bytes = 15 x 1024 x 1024 = File size in bits = 15 x 1024 x 1024 x 8 = Network speed = 1 Gbps Network speed = 1 x 1000 x 1000 x 1000 bps 6 (C) 2 1 020  Expression for number of bytes per second Number of bytes per second = Number of MB (megabytes) per second = 6 (C) 2 2 020  Bytes per second expression - example Network speed = 2 Mbps Number of KiB (kibibytes) Network speed = 2 x 1000 x 1000 bps transferred per second = One KiB = 1,024 bytes = One KiB in bits = 1024 x 8 63 (C) 2 020  Expression for number of files per second Number of files/packets per second = = 6 (C) 2 4 020  Files per second expression - example Network speed = 18 Mbps Number of files transferred per Network speed = 18 x 1000 x 1000 bps second = File size = 250 KiB 250 KiB = 250 x 1,024 bytes = 250 KiB in bits = 250 x 1024 x 8 65 (C) 2 020  Activity – network speed YO expressions UR TUR N! Complete the network speed expressions activity from The Ultimate GCSE Computer Science Textbook (C) 66 202 0  YO Questions UR TUR N! Answer the questions on page 31 of The Ultimate GCSE Computer Science Textbook 67 (C) 2 020