How Digital Devices Communicate PDF

UNIT II How Digital Devices Communicate Satellite What is satellite communication?  Satellite communication uses radio waves for wireless communication  Signals are sent between satellites and ground stations on earth  Ground stations transmit the radio wave to antenna within or...

UNIT II How Digital Devices Communicate Satellite What is satellite communication?  Satellite communication uses radio waves for wireless communication  Signals are sent between satellites and ground stations on earth  Ground stations transmit the radio wave to antenna within or connected to a digital devices  The advantage of satellite communication is that the service is always available  The disadvantages of satellite communication is that the service can be interrupted by weather conditions and signals do not pass through solid objects Satellite television  Digital Video Broadcasting (DVB) is the international standard for broadcasting digital television  Digital Video Broadcasting-Satellite (DVB-S) is an example of DVB  A video signal is sent from a broadcaster to a satellite, and sent back to earth to an antenna connected to a set-top box or directly to a television  The set-top box or television decodes the signal to make it watchable TV & radio What is digital television and radio?  Digital Video Broadcasting Terrestrial (DVB-T) and Digital Audio Broadcasting (DAB) are methods of transmitting video and audio signals from transmitters to an antenna  Transmitters are based on earth  Once received by the antenna, signals travel through wires to a television or radio receiver which decodes the signal and converts it into video and/or audio  The advantages of digital television and radio are: o Improved video/audio quality o Access to more channels/stations Wired What are wired methods of communication?  There are a number of wired methods of communication, some are designed to transmit a specific type of data and some are universal Type Use High Definition Multimedia High definition video and audio signals Interface (HDMI) Sony/Phillips Digital Interface Transmit digital audio streams between devices Format (S/PDIF) 3.5mm jack commonly used to connect headphones, speakers Mini-jack and microphones to devices Networking standard for connecting devices to a local area Ethernet network (LAN) Connecting and powering various devices such as printers, flash Universal Serial Bus (USB) drives, keyboards, mice etc. Wireless What are wireless methods of communication?  There are a number of wireless methods of communication, including: Type Use A wireless method of connecting devices to a local area network Wireless Fidelity (Wi-Fi) (LAN) Allows two devices to connect to each other over very short Bluetooth distances Infra-red (IR) Transmits tiny amounts of data over very short distances Near Field Use close proximity RFID (radio frequency identification) Communication (NFC) 4G and 5G Provides internet access to mobile devices Networks Local area networks (LANs) What is a local area network?  A local area network (LAN) is a network which has a small geographical area (under 1 mile)  All of the hardware is owned by the company/organisation/household using it  LANs will use unshielded twisted pair (UTP) cable, fibre optic cable or wireless connections (Wi-Fi) Advantages and disadvantages of LANs Advantages Disadvantages Allows centralised management of updates, backups and If hardware fails, the network may not software installations function properly or even at all Can secure its devices with the use of firewalls, antivirus Networks are more prone to software and other security features to prevent attacks than standalone computers unauthorised access Allows users on the network to share resources such as Access to data and peripherals can be printers and other peripherals slow depending on network traffic Require maintenance to ensure that Allows the users of the network to collaborate and share software is up to date, upgrades and files and folders backups which can be costly Wide area networks (WANs) What is a wide area network?  A wide area network (WAN) is a network which has a large geographical area (over 1 mile)   They are a collection of LANs joined together  The computers on a WAN are connected via routers  The hardware used to connect the networks together is not all owned by the company/organisation/household using it.  For example, telephone lines owned by telecommunication companies  WANs will use fibre optic cable, telephone lines and satellite to connect the LANs together Personal area networks (PANs) What is a PAN?  A personal area network (PAN) is a network that is used for transmission of data between devices in close proximity  A PAN has a very short range (10 metres)  Bluetooth is the most widely used PAN  Typical examples of devices which make use of a PAN are: o Wireless headphones  o Mobile phones o Tablet o Laptop etc. Tethering What is tethering?  Tethering is when a host device shares its internet connection with other connected devices  Commonly used by mobile devices to share its mobile data connection to devices such as laptops and tablets  Tethering can be enabled or disabled as part of the mobile contract  Some network providers charge extra to use this feature Wireless Communications Wi-Fi What is Wi-Fi?  Wireless fidelity (Wi-Fi) is a common standard for wireless networks  Wi-Fi is common in most homes and offices to connect devices such as laptops, tablets & smart phones  Using Wi-Fi, devices communicate with a hotspot or a wireless access point (WAP), which can be a standalone device or built into a router or switch   Wi-Fi may be preferred over Bluetooth when: o High speed data transfer is required o Long range communication is required o Many devices are needed to be connected at the same time Advantages Disadvantages  Portability - Easy to move around,  Speed - Slower data transfer than Ethernet location is only limited by range  Security - Less secure than Ethernet  Cost - Less expensive to setup and add  new devices Range - Relies on signal strength to the WAP, signals can be obstructed (up to  Compatibility - Most devices are 100m) manufactured with a built in Wi-Fi adapter Bluetooth What is Bluetooth?  Bluetooth is another common standard for wireless networks  Bluetooth is common in most homes and offices to connect devices such as headphones, controllers, keyboards & mice  Bluetooth is used typically for a direct connection between two devices  When two devices pair, they both exchange a cryptographic key  The keys are used to generate a secret shared key which is used to encrypt the data between the two devices and create a Wireless Personal Area Network (WPAN)  Connected devices continuously change their transmitting frequency between 79 different channels to avoid interference and improve the reliability of the connection  This is known as the frequency hopping spread spectrum (FHSS) Advantages Disadvantages   Speed - Very slow transfer speeds Compatibility - Ideal for personal devices and ad-hoc connections  Security - Data can be intercepted by  anyone in range Power - Very low power consumption  Range - Short range (30m) Differences between Bluetooth and Wi-Fi Bluetooth Wi-Fi Maximum number of connections 7 30 Transmission frequency 2.4Ghz 2.4Ghz, 5Ghz Maximum range (meters) 30 meters 100 meters (depending on obstructions) Maximum transfer speed 3 Mbytes / Sec 75 Mbytes / Sec (Depending on the standard being used) GPS What is GPS?  Global Positioning System (GPS) is a satellite system used to track the exact location of an object  GPS uses orbiting satellites to receive, amplify and transmit signals  Radio frequencies are used to communicate between satellites and ground stations  GPS requires a direct line of sight Advantages Disadvantages   Expensive setup and maintenance Wide coverage area   Signal interference due to weather or Real-time data transmission obstacles  Improved communication in remote  Limited bandwidth and capacity locations   Privacy concerns and potential for Accurate location tracking Surveillance 3G & 4G What is 3G & 4G?  3G and 4G are references to the 3rd and 4th generation of mobile data networks  They provide mobile devices with wireless access to the internet  Each generation has a faster transfer rate and an improved capacity for more users o 3G - 256 Kbps (kilobits per second) o 4G - 100+ Mbps (megabits per second)  The current generation (5G) has even faster speeds and lower latency Infra-red (IR) What is infra-red?   Infra-red is a wireless communication method used to transfer very small amounts of data to a device in direct line of sight  Commonly used in remotes to control devices such as: o Televisions o Audio receivers o Home entertainment equipment etc.  Uses light waves which can cause: o Walls or obstacles to block the signal o Sunlight to affect the signal  It is a reliable and cost effective solution for many short-range wireless communication needs NFC What is NFC?  Near field communication (NFC) is a subset of RFID which allows communication between two devices in very close proximity  NFC can be either: o Passive - uses energy from the reader o Active - has it's own power source  Smartphones use active NFC to allow contactless payments by tapping a smartphone on a reader  Smartphones can also exchange data using NFC by tapping together (usually back to back) Advantages Disadvantages  Convenient  Limited range  Secure  Slow data transfer rate (not suitable for transferring large  Very fast files)   Low Compatibility power consumption Factors Influencing Digital Communication Bandwidth & latency What is bandwidth?   Bandwidth is the amount of data that can be carried by a connection in one second  Measured in bits per second (bit rate)  A smaller bandwidth means that less data can be sent and the network can slow down, potentially to the point of becoming unusable Impact on user experience  A higher bandwidth means more data can be sent and received in one second  Higher bandwidth can improve: o Upload and download speeds o Online gaming o Streaming high definition video  To stream content, enough data to play a few seconds is downloaded and stored in a temporary area of memory called a buffer  As the contents of the buffer are played, more data is downloaded at the same time to keep the buffer full  If the buffer ever becomes empty playback will pause  To stream successfully, data must be downloaded to the buffer at a faster rate than it is being emptied What is latency?  Latency is the delay between data being sent and received  If there is a big delay between the two, more data will be on the network causing collisions  This can lead to even more packets of data being sent as the error rate will increase Impact on user experience  Playing games online smoothly, requires a high bandwidth  A high latency can cause lag and the game will not respond as quickly as a users commands  This can cause big issues when users are playing fast paced games or playing against other users with a lower latency (have an advantage due to quicker response times)  Streaming sport content with a high latency can cause micro-stutters and ruin a users watching experience Speed & volume of data transfer What else can affect the speed & volume of data transfer? Factor Description  Devices that emit electromagnetic signals such as microwaves and fridges can Interference disrupt wireless signals Transfer Wired connections can carry more frequencies, meaning a higher bandwidth method compared to wireless connections Blockages Walls and furniture can block wireless signals, lowering the bandwidth available Distance The strength of a wired and wireless signals reduces as data has to travel further Wired & wireless communication What are the advantages and disadvantages of wired & wireless communication? Wired Wireless Speed Fast data transfer Slower than wired Portabilit Location is limited by physical cable Location only limited by range y Security Better physical security Less secure, easier to intercept data Range Less affected by interference Affected by interference Cables can be trip hazards, need routing Safety None along walls, under floors Cables are cheap, more devices means No cables required, may require a wireless Cost more cables needed access point to be purchased Broadband, mobile broadband & cellular networks  Internet Service Providers (ISP) provide access to high speed internet (broadband)  ISPs use fibre optic or copper cable to create a wide area network (WAN) What is fibre optic?  Fibre optic is a type of cable that uses light to transmit data on a wide area network (WAN)  Fibre transmits data at a much higher speed and has a much higher bandwidth compared to copper cables   Fibre optic cable does not suffer from interference which makes them the most secure option to send sensitive data  Fibre optic cables can cover a long distance without any degradation, they can span cities and countries What is copper cable?  Copper is a type of cable originally used in telecommunication to transmit voice signals, forming the traditional landline phone network  The ability to use copper to deliver network traffic on a wide area network (WAN) made the internet possible  Copper cables degrade over time which limits their range compared to fibre optic  Copper cable suffers from interference which can disrupt data quality  Copper transmits data at a much slower rate, and has a much lower bandwidth compared to fibre optic Identifying Devices IP Addresses What is an IP address?  An IP (Internet Protocol) address is a unique identifier given to devices which communicate over the Internet (WAN)  IP addresses can be allocated by a network administrator or assigned dynamically by a Dynamic Host Configuration Protocol server (DHCP)  IP addresses make it possible to deliver data to the right device  A device connecting to a network will be given an IP address, if it moves to a different network then the IP address will change IPv4  Internet Protocol version 4 is represented as 4 blocks of denary numbers between 0 and 255, separated by full stops  Each block is one byte (8 bits), each address is 4 bytes (32 bits)   IPv4 provides over 4 billion unique addresses (232), however, with over 7 billion people and countless devices per person, a solution was needed IPv6  Internet Protocol version 6 is represented as 8 blocks of 4 hexadecimal digits, separated by colons  Each block is 2 bytes (16 bits), each address is 16 bytes (128 bits)  IPv6 could provide over one billion unique addresses for every person on the planet (2128) MAC Addresses What is a MAC address?  A MAC (Media Access Control) address is a universally unique identifier given to devices which communicate over a local area network (LAN)  MAC addresses are static, they can never change  MAC addresses make it possible for switches to efficiently forward data to the intended recipient  Any device that contains a Network Interface Card (NIC) has a MAC address assigned during manufacturing  A device connecting to a local network already has a MAC address, if it moves to a different network then the MAC address will stay the same   A MAC address is represented as 12 hexadecimal digits (48 bits), usually grouped in pairs  The first three pairs are the manufacturer ID number (OUI) and the last three pairs are the serial number of the network interface card (NIC)  There are enough unique MAC addresses for roughly 281 trillion devices  MAC addresses can be used to: o Restrict or allow access to a network o Identify a device on a network o Track a device o Assign 'static' or 'fixed' IP addresses Device name What is a device name?  A device name is a way for users to describe/name a device so that it is easier to identify on a network  Device names are not used by devices to communicate as they are not always unique  Device names are set by users in the devices operating system or from a router Components of a Network Cables What cables are used in a wired network?  A wired network is a network where physical cables are used to join devices together and transmit data  The most common types of cables in a wired network are: o Ethernet o Fibre optic What is Ethernet?   Ethernet is a wired networking standard to carry electrical signals between devices on a local area network (LAN)  Ethernet is common in most offices and homes to connect devices such a desktop computers & servers  Ethernet uses twisted pair cables (CAT5) to allow duplex communication What is fibre optic?  Fibre optic is a type of cable that uses light to transmit data on a wide area network (WAN)  Fibre transmits data at a much higher speed and has a much higher bandwidth compared to copper cables  Fibre optic cable does not suffer from interference which makes them the most secure option to send sensitive data  Fibre optic cables can cover a long distance without any degradation, they can span cities and countries Wireless Access Points What is a wireless access point (WAP)?  The Wireless Access Point (WAP) allows wireless devices to connect to a local area network (LAN)  The WAP connects to a Switch or Hub via an Ethernet cable  The WAP range is limited so the use of multiple Wireless Access Points can be used for complete coverage or a home/business Router & gateway What is a router?  The router is responsible for routing data packets between different networks  An example of data the router can direct is, sending internet traffic to the right devices in your home  The router manages and prioritise data traffic, which can help to keep connections stable  The router will assign IP addresses to the devices on the network  The router acts as a gateway What is a gateway?   A gateway is a device that bridges the connection between two different types of network  Gateways translate between different network protocols  For example, a local area network (LAN) to a wide area network (WAN) Switch & boosters What is a switch?  A Switch allows multiple wired devices to connect to a local area network (LAN)  The Switch is an active device, which means it can inspect network data and route it to the correct device, thus reducing traffic on the network  A Switch can contain extra Software to allow administration/configuration What is a booster?  A booster is a device used to amplify a network signal in order to extend the normal range  Boosters can be used with both wired and wireless networks  Wireless access points can be be configured to act as a booster (repeater mode) Server What is a server?  A server is a dedicated computer that shares its resources with devices that connect to it  Devices that connect to a server are known as clients  Common examples of servers include: o File o Web o Print o Authentication o Application Server Function File  Allows access to shared and private resources   Stores the content of websites and processes requests made via HTTP to Web access them  Manages print jobs and organises the queue so that individual printers are not Print overloaded Authenticatio  Stores usernames and passwords that can be checked when a user logs in n  Authenticated users receive a certificate that allows access to resources Application  Allows clients access to applications that run directly from the server  A single computer can perform multiple server functions depending on its resources (memory & processor) Connecting to the Internet Web browser What is a web browser?  A web browser is a software application used to locate, retrieve, and display content on the World Wide Web (WWW)  Web browsers are used to display web pages which include images, videos and other files  Most web browsers have the following features: o Home page o Ability to bookmark favourites o Keep a history of visited websites o Hyperlinks which allow users to navigate between pages Internet Service Provider (ISP) What is an ISP?  An Internet Service Providers (ISP) is a company that provides access to the Internet to users and businesses  The ISP provides internet access by leasing equipment and telecommunication lines to users that are required to access the internet  IPS generally charge a subscription fee for access to the internet Search Engines What are Search Engines?  Search engines are tools that locate and display web pages related to the search terms entered by the user   They are essential for navigating the vast amount of information on the internet  They index millions of web pages and use algorithms to rank the relevance of each page to the search terms How do search engines work?  Search engines work in several stages: o Crawling o Indexing o Ranking  Crawling is when web crawlers scour the internet daily to retrieve new websites  Indexing is how websites are categorised based on the content of their web pages, keywords and metadata  Ranking is how websites are ranked and listed on search engine pages - this depends on many factors to display the most relevant results Filter software What is filter software?  Filter software uses two lists stored in a database to allow or block access to websites  URLs entered by a user are compared against both lists  The two lists are: o Whitelist - URLs on the whitelist are allowed and the website can be viewed o Blacklist - URLs on the blacklist are not allowed and the website is blocked  URLs that cannot be found on either list are allowed  Filter software is used by schools and parents to protect children from accessing age inappropriate content  Administrators can add and remove URLs from the lists Benefits of using a Local Area Network (LAN) Benefits of using a Local Area Network (LAN) What are the benefits of a LAN?  Users can share peripherals such as printers   Shared access to the internet  Users can access their files from any computer on the network  Communication can be made easier via email and social networks  Users can share files and folders easily such as central databases and spreadsheets  Servers can be used to provide centralised backups, updates and security  Media streaming (movies, music and gaming) What are the drawbacks of a LAN?  There is an increased security risk to data  Malicious software can infiltrate the network and render it unusable  Servers and switches can provide a central point of failure, resulting in users not being able to complete tasks using their computer  Factors can impact the performance of the network such as the number of users and data on the network at one time Peer-to-Peer & Client-Server Networks Peer-to-peer networks What is a peer-to-peer network?  A peer is a computer on a network which is equal to all other computers  Each peer on the network o Often have their own printer attached o Will provide access to their own files o Is responsible for their own backups o Is responsible for their own security o Is responsible for carrying out their own backups  A network with no server providing services is a peer-to-peer network  Most homes will have a peer-to-peer network model Advantages Disadvantages  Very easy to set up and maintain  Users will need to manage their own backups  Very cheap to set up because there is no expensive hardware to purchase  Users will need to manage their own software updates  No specialist knowledge or staff are required to run the network  The network can be less secure Client-server networks What is a client-server network?  A client is a computer on the network, these connect to the server via a switch  A server is a computer on a network which often has a single purpose, for example o Managing access to the Internet o Managing printing o Providing email services o Providing backups o Controlling security  Servers are often more powerful than the client machines  Servers are seen as more significant than the client machines and can require specialist hardware and software  A network which uses a server is called a client-server model  Most companies, organisations and schools will use a client-server network model Advantages Disadvantages   Servers can be expensive to purchase, Managing backups of the network is setup and maintain easier as it is done from one central point   A specialist network manager would be Updating and installing new software can required as servers require specialist IT be done centrally instead of having to log knowledge on to each machine   Servers can be a single point of failure, Security of files can be managed easily meaning all users would lose access to the network if the server fails Methods of Securing a Network Usernames & Passwords How does a password help?  Passwords are a digital lock to prevent unauthorised access to an account  Passwords are used to authenticate a user to the network  They are often stored as an encrypted/ciphered text entry in a database, ensuring that even with unauthorised access to a database, a hacker would not be able to gain access to the individual passwords of users  Strong passwords and regular password changes are important to maintain security Firewalls What is a firewall?  A firewall is a barrier between a network and the internet  A firewall prevents unwanted traffic from entering a network by filtering requests to ensure they are legitimate  It can be both hardware and software and they are often used together to provide stronger security to a network o Hardware firewalls will protect the whole network and prevent unauthorised traffic o Software firewalls will protect the individual devices on the network, monitoring the data going to and from each computer Encryption What is encryption?  Encryption is a method of scrambling data so that unauthorised users cannot understand it  Encryption methods use 'keys', which are specialised programs designed to scramble or unscramble data  Encryption uses complex mathematical algorithms to scramble the data  There are two common methods of encryption: o Symmetric  o Public key Symmetric encryption  The sender uses a key to encrypt the data before transmission  The receiver uses the same key to decrypt the data  It's usually faster, making it ideal for encrypting large amounts of data  The significant downside is the challenge of securely sharing this key between the sender and receiver  If an unauthorised user captures the key, they can decrypt all messages intercepted in transmission Structure of Symmetric Encryption Public key encryption  Public key encryption uses two keys: o a public key for encryption o and a private key for decryption  Receivers openly share their public key  Senders use this public key to encrypt the data  The receiver's private key is the only key that can decrypt the data and is kept locally on their side  The public and private keys are created at the same time and are designed to work together in this way  It is typically slower than symmetric encryption  It is generally used for more secure and smaller data transactions, e.g. passwords, bank details Structure of Public Key Encryption WEP/WPA What is WEP?  Wireless Encryption Protocol (WEP) is a method of encrypting data being transmitted on a wireless network  Each device on the network uses the same key to encrypt and decrypt data  It is a less secure encryption method due to all devices on the network sharing the same key  Eavesdropping software (packet sniffers) can be used to intercept data packets and identify the key What is WPA?  Wi-fi Protected Access (WPA) is a more secure method of encrypting data being transmitted on a wireless network  Each device connected to the network receives a different key  New keys are used for every packet transmitted on the network Virtual private networks (VPN) What is a VPN?  A VPN allows users to remotely connect to private local area networks (LANs)  All data sent and received using a VPN is encrypted  Common uses of a VPN include: o Remotely accessing a companies network (working from home) o Making secure payments  o Hiding web activities o Bypassing geolocation rights management or online censorship File access rights What are file access rights?  File access rights can be set to determine different levels of access to specific files/folders  Examples of file permissions include: o Read - can read the contents of a file only o Write - can make changes to file contents and/or create new files o Delete - can delete files o Execute - can run applications/launch software Transaction logs & backups What is a transaction log?  A transaction log is a secure file on a network that keeps a record of every action performed by devices on a network  Transactions logs include: o Device & data access o Timestamps o User IDs o Successful/failed login attempts  Transaction logs don't directly protect a network, they help administrators monitor any identify any unusual activity  Backups are another indirect method of protecting a network  Keeping copies of data in a secure place on the network in the event of a data breach/loss