Information processes and technology topic 3-Communication ...
Characteristics of Communication SystemsA communication system allows its users to send and receive data and informationThe framework in which communication systems function is shown in the diagram below, where it represents Skype/MSN as a communication system.832485-257683000Network Interface CardWirelessEthernet CableFunctions performed within communication systems to send a message:Message creation Organisation of packets at the interface between source and transmitter Signal generation by the transmitter Transmission via a medium Synchronising the exchange Addressing and routing Error detection and correction Security and management All communication systems have five basic components: The data source produces the data to be sent. The transmitter encodes the data into a signal suitable for a transmission' medium. The transmission medium is a channel, such as a cable, in which the signal is~ transmitted to the destination. The signal may be changed or distorted during transmission.The receiver decodes the signal back into the original data or an approximation! of the dataThe destination is the receiver of the information. Protocols in communication:A protocol is a set of rules that governs a communication process‘Handshaking’ is the process of establishing a communication link and agreeing on which protocol to use.A communications protocol must define the following:Rate of transmission (in baud or bps)Whether transmission is to be synchronous or asynchronousWhether data is to be transmitted in half-duplex or full-duplex modeAlso, protocols can include sophisticated techniques for detecting and recovering from transmission errors and for encoding and decoding mon protocols:TCP/IP: Transmission Control Protocol/Internet Protocol – rules that split data into packets for transfer across the internetHTTP: Hyper Text Transfer Protocol – allow the displaying of files containing hypertext links across a network FTP: File Transfer Protocol – the protocol defining the transfer of files over a network or the internetSMTP: Simple Mail Transfer Protocol – sending of e-mail messages POP: Post Office Protocol – retrieves e-mail messagesSSL: Secure Sockets Layer – used for encryption of data for secure data transmissionThe client-server architecture:The client sends a request to the server using its IP address and the port. The server receives the request and responds using the client IP address and port.The client controls the user interface and applicationThe server controls access to the network127635127000Advantages:Centralised resources; given that the server is the centre of the network, it can manage resources that are common to all usersIt is possible to remove or add clients without affecting the operation of the network and without the need for major modificationDisadvantages:Client-server networks can become congested and overload the server with requestsIncreased costs due to the technical complexity of the serverTYPES OF CLIENTSThe client controls the user interface and application . Some examples of clients include; web browsers and e-mail clients.Thin clients:A thin client - a workstation that does not have the capacity to perform meaningful tasks without a server. E.g. a thin client is a network computer without a hard disk drive. They are easy to install and have lower total costs than fat clients.Fat clients:A fat client (or thick client) - a desktop computer connected to a Network that includes a NOS. They may do their own processing without access to the server. They perform the bulk of the processing in client/server applications.They can handle higher bandwidths; operating systems and software that do not run on thin clients can run on fat/thick clients as it has its own resources.Serversserver – computer that controls access to the networkSome examples of servers include:Print servers - control access to printers on the network and queue data waiting to be printedMail servers - receives electronic mail (e-mail) and stores it in the recipient’s mailbox.Web servers - stores and distributes web pages. It allows access over port 80 on its IP address.File servers- a computer that provides file services to workstations and users. It stores files and application software.Proxy servers - a computer that manages printing tasks.NOSNOS(network operating system)- a set of core programs that run on the computer controlling a network. It organizes the whole network as one. E.g. Microsoft Windows NT, and UNIX. They have features such as:Administration – allows the network manager to manage the network users and perform essential tasks such as backing up the files on the shared network disk drives. File management – allows the network users to access and manage their files Security – protects the network resources, users and their files from unauthorised access to the network Sharing resources – enables users to access shared files and resources (e.g. printers and modems) Cross-platform access – provides software that will allow workstations using different operating systems to connect to the file server.Examples of Communication SystemsTeleconferencing systems:Teleconferencing (video conferencing) is an alternative to face to face meetings, using electronic hardware and software such as camera and internet connections to transfer video and audio data. Commonly used for education and conferencing.How data is transmitted and received:The video and audio data is captured, digitised (by assigning a number -binary code- to each pixel on the image to represent its colour), transmitted over the internet, and then decoded when received.AdvantagesDisadvantagesFacilitates flexible meeting schedulingAchieves worldwide connectivity; thus avoids expensive travel costsCan be expensive and requires fast processors and high transmission speedsReduces personal contact; lack of social skills developMessaging systems:Email:Users are able to send text messages and attached files to individuals or groups of people via the internet (e.g. used in schools to send notices and make appointments).How data is transmitted and received:Use computers to send and receive text messages and attached documents via the internetAdvantagesDisadvantagesVery fast transmission of mail compared to conventional postal mailCapable of transmitting and receiving text, graphics, sound and video as attachmentsViruses, which can be attached to email messagesOnly available to those who have a computer, internet connection and email addressVoice mail:Voice mail allows transmission of vocal messages between users via telephone systems. How data is transmitted and received:Audio messages are recorded and then transmitted by telephone system for storage (when someone is unavailable)AdvantagesDisadvantagesThe receiver does not have to be present, and messages are stored and can then be later retrieved by the recipientNo extra hardware needed besides a telephoneVoicemail can be viewed as impersonal by callersOnly users with a voice mail account can access its functionalityVoice over internet protocol (VOIP):Purpose: To allow voice calls to be made over a broadband internet connectionParticipants: Residential home users, small businessesData/information: Sound waves converted to digital audio signalsInformation technology: Broadband internet connection, computer, VOIP software (for computer-to-computer connections), microphone, speakers, sound card, modemHow data is transmitted and received:Sound waves are recorded by microphone The computer compresses it into data packets for transmission over the IP networkThe sending computer places an address on each packet telling the network devices where to send themInside of each packet is a payload; a voice recording digitally convertedThe sending computer sends the packet(s) to a router which directs it to the receiverThe receiving computer decodes the transmission to output sound waves AdvantagesDisadvantagesExcept for your normal monthly ISP fee, there is usually no charge for computer-to-computer calls, no matter the distanceVOIP consumes less transmission timePhone conversations can become distorted, garbled or lost because of transmission errors (e.g. packet loss)Susceptible to worms, viruses and hackingOther systems dependent on communication technology:EFTPOS (Electronic Funds Transfer at Point Of Sale):EFTPOS is a financial network for processing credit cards, debit cards and ATM transactions at ‘point of sale’.How data is transmitted and received:Employee swipes card in a magnetic strip readerCustomer enters password/PINCard details collected and funds transferred from customer to retailer’s accountAdvantages:Disadvantages:Easier than manually transferring funds from bank branchEfficient, secure form of paymentBoth buyer and the seller have to pay charges for use of the cardsMany people don’t have bank accounts or prefer to use cashEmerging trendsPay PassTap and Go (tap your visa card against the machine and up to $100 can be paid for using it,E-commerce:E-Commerce - consists of the buying and selling of products or services over electronic systems such as the internet and other computer networks. Can be used with computers, mobile phones, ATMs, telephone, etc.AdvantagesDisadvantagesCustomers are more easily able to compare products and servicesReduced waiting time as products and services are more quickly obtained by customersPotential customers may not like having to reveal their financial and personal information onlineFraud, hacking, identity theft, etc.Electronic banking:Internet banking - involves consumers using the Internet to access their bank account and to undertake banking transactions. They may do account enquiries and the access to the latest rate of interests and schemes.AdvantagesDisadvantagesAllows people greater convenience in the process of banking as electronic banking is available 24/7Saves people from going into the bank to withdraw or deposit money – travel time and costsCustomers may be sucked into phishing scams where they disclose their private details to scammers believing them to be the actual bankUnauthorised individuals can intercept banking transactions; gaining access to people’s private banking details which they can use for criminal activities such as fraudTransmitting and Receiving in Communication SystemsTransmission mediaWired transmission: Twisted pairCoaxial pairOptical fibre cableWhat is it?Twisted pairs are stiff copper wires surrounded by insulating material then encased by a conductor like a mesh. ELECTRICAL SIGNALS USED.The twists in the cable reduce interference/noise during transmission. They are also called unshielded twisted pairs. (UTP)Coaxial cables are thick cores of copper surrounded by insulating material. The insulation is enclosed by a woven mesh. The mesh is surrounded by a plastic layer for electrical interference protection. Fibre optic cables are very thin glass strands well protected by insulation.Cost/reliabilityLeast expensive, least reliable, Moderate, Expensive and most reliableSpeed10Mbps, 100 Mbps10Mbps10Mbps to 1GbpsCable length100m185m2000mUsesA twisted pair is installed to an ethernet cable (RJ-45) for use to connect computers in a local area network (LAN)Mostly used for Internet connections and Foxtel (cable television)TopologiesStar, ringBusStar, ringWireless transmission:Microwave:Microwaves are extremely high frequency radio waves waves that can be used for data transmission.Microwaves are also used by fixed traffic speed cameras, and for radar, which is used by aircraft, ships and weather forecasters.Satellite:Use microwave signals between the satellite and its ground stations.Geostationary object (in space) functioning as a repeater or microwave tower.Used for internet connections mainly in remote areas where other internet connections may be unavailableAdvantages: carry very high bandwidth over very large distancesRadio waves:The two types of radio transmission are ‘line-of-sight’ and ‘wide area spread spectrum’.line-of-sight- having a directional antenna in line with another antenna without objects impeding the signal. Disadvantage = eavesdroppingwide area spread spectrum- signals jump from one frequency to another. Advantages= reduces interference and improves securityRadio waves have the longest wavelengths in the electromagnetic spectrum. Radio waves do more than just bring music to your radio; they also carry signals for your television and mobile phones.Infrared:Infrared light-emitting diodes (LEDs) emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiving computers will contain a silicon photodiode which will convert the infrared radiation to an electric current. Wireless signals, mainly used in devices such as remote controls where it is transmission over very short distancesAdvantages: add devices without cablesTransmission speed:Transmission speed is the time it takes data to travel from the source to the destination. The hardware being used and the transmission medium will greatly affect this speed. It can be best described in terms of bandwidth, baudrate and bits per second (bps).Bandwidth: The ability of the transmission medium to handle a particular amount of data in a given time; the higher the bandwidth the more data that can be sentBaud rate: A measure of the speed of transmission in a communication medium; measures how many bits per second a channel can send per secondBits per second (bps): A measure of the speed of transmission in communication medium; measures how many bits of data are transmitted (or received) in one secondApplication level protocols:HTTP: Hyper Text Transfer Protocol – allow the displaying of files containing hypertext links across a network SMTP: Simple Mail Transfer Protocol – sending of e-mail messages SSL: Secure Sockets Layer – used for encryption of data for secure data transmissionCommunication control and addressing level protocols:TCP/IP: Transmission Control Protocol/Internet Protocol – rules that split data into packets for transfer across the internetTCP: Responsible for breaking data down into IP packets before they are sent, and for assembling the packets when they arriveIP: Responsible for ‘routing’ each packet to the correct destinationTransmission level protocols:Ethernet: The Ethernet protocol allows for bus, star, or tree topologies, depending on the type of cables used and other factorsAsynchronous – uses start and stop bitsSynchronous – no start/stop bitToken ring: A token ring network is local areas network (LAN) in which all computers are connected in a ring or star topology and a bit (or token) passing scheme is used in order to prevent the collision of data between two computers that want to send messages at the same time.Strategies for error detection and error correction:Parity:- Parity is the method used to check data in asynchronous transmission, where one character is checked at a time. The eighth bit of the byte is the parity bit, which is used to check the accuracy of transmission. The parity checking can be either odd or even.When 01010111 are sent, there is an odd parity. When 01011111 are sent, there is an even parity, thus an error.Checksum:-- If the 1 digits of a binary code are added they give a total which is called a checksum. The receiving computer calculates the checksum and compares it to the transmitted checksum, and if they do not match, an error is detected.if the total of the bytes is lower than 255, that is the checksumadd all except for the last, divide by 255 if greater, get remainder, if there’s an error, then the addition of the byte values, divided by 255 gets a different same remainderWhat is the checksum for the message 0000001000000010 = 2 (checksum)Cyclic redundancy check (CRC):- the transmitted data is treated as one large binary sum . The sum is then divided by a constant and the remainder is sent to the receiver. The receiver then works out the sum of the transmitted data, divides it by the same constant and compares the remainder with the transmitted data. CRC has the highest probability of detecting errors.TREAT THE MESSAGE AS 1 BIG BINARY. GET THE VALUE AND DIVIDE BY A CONSTANT. THE REMAINEDER IS THE CRC.Star networks are where one central node (computer or other network device) and distant nodes are connected along communications lines that radiate as spokes from the central node.Advantages:Fast; if the central computer is fastNon-centralised failure will not cause the entire network to failMultiple nodes can be easily connectedFiles can be simultaneously accessed by multiple nodesDisadvantages:The network operation depends on the functioning of the central node; hence, the failure of the central node leads to the failure of the entire networkNetwork topologies:Star networks:Bus networks are where several devices are connected to a single communications channel.Advantages:It is easy to handle and implement; only one main lineCheaper; no extra hardware is required (such as a central server)Easy error detection since there is only one main line and few connectionsDisadvantages:Slow; can perform well only for a limited number of nodesIf the main line (bus) is broken, transmission will failBus networks: Ring networks are where there is a continuous circle, with nodes around the circumference.Advantages:Cheaper, a central server is not required for the management of this topologyEasily set up/implemented – using cablesDisadvantages:If one node of the ring breaks down or a part of the network is disconnected, the network will not workRing networks: Hybrid networks are where a combination of any two or more of the basic topologies.Advantages:Able to be used where different types of networks are required Disadvantages:Expensive, errors may be hard to detect within the networkHybrid networks: Wireless networks:Wireless networks are where the data packets are converted into radio frequencies which travel through the air to the receiving node.Advantages:Cables aren’t needed to connect the nodes together; portable applications are available, e.g. laptops, wireless printers, etc.Easy to add stations as there are no cables requiredDisadvantages:Disconnections are more common than with cable connectionsQuality of transmission is not as high as other methodsDevices which are not Wi-Fi enabled cannot be connected to the networkWireless signal can be intercepted and accessed by hackerswithin the networkData collisions CSMA/CD is used by bus or star topologies when data collides. When a node needs to put data onto the network it must first 'listen' to the line for a carrier signal. It can transmit data after it determines that no carrier signal is detected on the network. Since no other device is transmitting it places it’s on carrier signal onto the line to prevent other nodes from transmitting. If a node were to detect a carrier signal present it would wait until the signal is turned off. Network hardwareHubs:Hubs- A multiport device used to connect computers in a local area network. They send data to many locations at the same time. In a network with hubs data Passes network traffic to all devices connected, therefore slowing down the network.They are cheap and use Half duplex transmission, therefore inefficient under high network trafficSwitches:Switches- A multi-port device that allows small sections of LANs to connect and switch traffic directly from the source to the destination. They:Transmit to the destination port onlyEnables faster data transmission as it reduces collisionsAre more expensive and fasterLimit traffic to a certain nodeRouters:Router - stores information about its surrounding networks and the paths it can use to access them. They:direct data traffic, which is protocol dependentSelects the best path on the network to route data (efficient) by reading the packet address and understanding the network topologyEnables fast data transmission as it reduces collisionsConnects different networkBridges and gateways:Bridges - used to connect two LANs together in a simple network topology which use the same protocol to communicate. Gateways- devices that provide the ability for one protocol to talk to a different one . They are more complex than bridges and will translate data in one protocol to another protocol for work interface cards (NIC):NIC- a circuit board that is installed in a slot inside a PC. The NIC is where the network cable plugs into the computer.Provides a physical link to a computer network; this connection allows computers to communicate with servers, as well as other computers on the network.The job of the NIC is to control the sending, receiving and error checking of all data exchanged between the PC and the other network devices.Mobile phones:Transmit and receive voice calls via radio wavesCables:Connects communication systems together, allowing for data transmitting and receivingWireless access points:A wireless access point (WAP) is a device that allows wireless communication devices to connect to a wireless network. Common hardware devices that connect to a WAP include laptop computers.Bluetooth devices:Bluetooth is a wireless network protocol for exchanging data over short distances (using short length radio waves) from fixed and mobile devices, creating personal area networks (PANs). Common hardware devices that connect to Bluetooth include mobile phones to send and receive data.Backbone linkBackbone link- typically fibre or high capacity coaxial cable. It is designed to connect central nodes (such as hubs and switches) and carries a much higher volume of data than UTP or standard coaxial cable. Users would not normally connect directly to a backbone.OSI modelThe bottom layers are responsible for transfer of data from one place to another. They include protocols that specify the type of plugs, the format of data, the method of transmission and error checking. The top layers examine the exchange of data between application programs. They include protocols that specify file transfer, passwords and network management. OSI (Open?Systems?Interconnection model)- a theoretical model that describes defined layers in a network operating system. There are 7 layers:Layer 7, Application layer- provides the interface for the application programs. 403796512319000Layer 6, Presentation layer-converts formats specific to system to formats that are generic. It also provides encryption and compression.Layer 5, Session layer- Facilitates the starting, handling and ending of connections between nodes. It also synchronises streams of data.Layer 4, Transport layer-Ensures that reliability and flow control are ensured by choosing the correct protocols, e.g. TCP. It also uses port numbers to differentiate between different applications on the same node. If the packet/frame fails then the transport will begin resending.Layer 3, Network layer- It provides addressing across the internet. It determines the best path for the data. The source and destination is added to the packets. It also handles congestion control and packet sequencing. This includes switching?and?routing?technologies, such as routers and hubs.Layer 2, Data link layer- It translates messages from the Network layer into bits for the Physical layer to transmit. It also makes sure that there is reliable transfer between 2 nodes, while dealing with physical addressing. Layer 1, Physical layer-It sends the data through physically, e.g. electrical impulse, light or radio signal. It provides the physical means, e.g. twisted cables, cards.ASCII basicsA= 65The remainder goes on the left, then minus that remainder and divide.Keep dividing by 2, no remainder = 0, remainder =1Keep dividing to 1/2, since can’t have fractions, then 0 or 1 It is from bottom to top.3377565-134493000Internet, intranets and extranets:The Internet consists of a worldwide network of computer networks that use the TCP/IP network protocols to facilitate data transmission and exchange.An Intranet is a private computer network that uses the protocols of the Internet. An intranet is not accessible by computers on the outside of the private network.An Extranet is a private network that uses Internet protocols. It can be viewed as part of a company's intranet that is extended to users outside the company, usually via the Internet.Other Information Processes in Communication SystemsCollecting:A phone is a collection device for the use of voice mailAn EFTPOS terminal is a collection device for electronic bankingDigital data:Digital Data is data that is stored and transmitted in two possible states; each digit can be either on or off, represented using electrical impulses that are of high or low voltageMuch of our technology relies on digital dataComputers use the binary system to store and transmit data, i.e. the digits 1 and 0Analog data:analogue data is represented in a continuous form in which there are many different possibilitiesAnalogue data can be represented as a wave It is more difficult to handle this type of data as transmitting it accurately involves sending it in its exact form, and because there are so many more variables it is more easily corrupted.Processing:Encoding and decoding analog and digital signals:Communication systems use both analog and digital data, for this reason it is often necessary to encode and decode signalsAnalog data to analog signal - Telephone conversations are the best example here. The system encodes speech and transmits it from sender to receiver. Digital data to analog signal - A digital device will often have to display data in an analog form for humans to understand. This will require encoding the 0’s and 1’s.Digital data to digital signal - This form of transmission has both sender and receiver speak the same language. One computer on a network is able to communicate directly with another computer. Analog data to digital signal - The analog data is encoded to a series of 0’s and 1’s by dividing the data into two groups across an illogical line.32994605143500Real life example- modemsModem converts the digital data from your PC into an analog signal before sending it through the telephone link - the modulation step (the 'mo' in modem). The modem on the receiving computer converts the analog data from its telephone line back into digital before passing it to the computer - the demodulation step (the 'dem' in modem). Types of modulationWaveDescription + diagramAmplitude modulation28873454127500the change of peak of the wave indicates a 0 or 1. A high peak equals an 1. Frequency modulation2882265-635000A higher frequency indicates a 1, a lower frequency indicates a 0.Phase modulation27171651905000A change of phase indicates a o or 1NRZ-L modulationNon return to zero level modulation uses a high voltage to indicate a zero, and an low voltage to indicate an 1.2811145-852805000NRZ-I modulationNon return to zero level inverted modulation uses a high voltage to indicate a zero, and an zero voltage to indicate an 1. The polarity of the bit is reversed when a 1 bit is encountered.2764790-42291000Manchester encoding27647905905500Bits are translated depending on the transitions.?a 0 is indicated by a 0 to 1 transition at the centre of the bit a 1 is indicated by a 1 to 0 transition at the centre of the bit. 148082020193000(HIGH LOW = zero) (LOW HIGH = 1) QAM2750185-580199500Quadrature Amplitude ModulationWaves that have specific shape (amplitude and phase) represent agreed upon codes.(duplicate the wave, then take it back and reduce depending on amplification.Formation of data packets:A packet is the unit of data that is routed between an origin and a destination on a networkThe structure of a packet depends on the type of packet it is and on the protocol. Normally, a packet has a header and a payloadFor example, an IP packet includes;The source IP addressThe destination IP addressThe sequence number of the packetsThe type of service, etc.The payload is the data it carriesRouting:Routing is the process of selecting paths in a network along which to send network trafficRouting is performed for many kinds of networksEncryption and decryption:Encryption is the process of transforming information (referred to as plaintext) using an algorithm (called cipher) to make it unreadable to anyone except those possessing special knowledge, who obtain the ‘key’.Decryption is the reverse process where the receiver requires the ‘key’ to decrypt the data.Error checking:Parity bit checkCheck sumCyclic redundancy check (CRC)Displaying:A phone is also a display device for the use of voice mailAn EFTPOS terminal is also a display device for electronic bankingNetwork administration tasks:Adding/removing usersAssigning users to printersGiving users file access rightsInstallation of software and sharing with usersClient installation and protocol assignmentNetwork-based applications Logon and logoff proceduresWhere user enters username and password to validate access. A user session is opened and the user can access resources they have rights to. Log-off disconnects that user form network – important for security as open network can be used by unauthorised usersIssues Related to Communication SystemsTeleconferencing systems:Changing the nature of work as individuals around the world can work on a project and share informationMay lose interpersonal skills as communication via microphones and speakers Messaging systems:Cyber bullyingMisinterpretation (may not understand abbreviation, cannot see facial expressions)PrivacyEmployers have rights to read employee emails sent from workSocial networking companies may sell user information without user’s knowledgeChild grooming for sexual assault (using fake Facebook accounts)Diminishing of interpersonal skillsE-commerce:Hacking Loss of jobs as machine replace humansGlobalisation: access to unreliable sellers – loss of moneyElectronic banking:Jobs and bank branches close as ATM machines replace bank tellersExtra costs for businesses who need to train staff in ITE-crime more common (phishing scams, key logging)EFTPOS:Similar to e-commerceChanging nature of work (working from home):Advantages:Flexibility over when to work when productivity is high and when it suits private life (taking care of children)Save costs on travelAllows disabled and rural workers to find jobsReduced office needs for employersDisadvantages:Need self-motivated staff who can cope with isolationVirtual communities:Network of individuals who pursue similar interests; e.g. forums created in Facebook and online dating sitesAdvantages: People from around the world can communicateDisadvantages: Young people can become addictedLoss of social skillsThe Internet:The need for ethical behaviour when using the internetDo not attack others through insulting messages – cyber bullyingDo not copy and paste information without proper referencing – plagiarism Do not impersonate others to extract personal data – follow netiquette These behaviours make the internet safe and enjoyable for everyone.Issues that have arisen from internet useAvailability of material normally restrictedInternet saturated with pornography and children with internet access can easily view sites if no filter (leading to sexualisation of children)Internet used to spread child pornography in file sharing sites (abuse of children)Australian Government implementing a mandatory filter: will this restrict material that is legally availableDomination of content and control of access to internet Previously, large media organisations decided what news people would receive. But individuals have greater control and power through blogs – where they can report news.Access to internet controlled by a few large companies. There is less competition, leading to higher internet prices, which limits access to the poor. Current and emerging trends in communicationsBlogs:BLOGS- a web page that serves as a publically, accessible personal journal for an individual.Other users can read; entries are dated & have a journal design.Only updated by blog owner.Current and emerging trends are:Interactive blogsBlogs in educationGroup blogs are now possibleWikis:A Wiki is a piece of server software that allows users to freely create and edit Web page content using any Web browser.Can be updated by any internet user with a wiki accountPowerful educational resource – but the information may not be accurateRSS feeds:RSS FEEDS- A format for delivering regularly changing web content.A user subscribes to a feed by entering the users URL by clicking on the feed icon in a browser that activates the subscription process. It allows the users to avoid manually inspect which feeds they want to read. Podcasts:Podcasts are audio files that deliver content over the Internet Users subscribe for podcasts through specific software. It may be on the internet and users will be notified through email or the software.They can be uploaded for download or streamed direct from the site. Online radioInternet Radio is an audio service transmitted via the internet.It involves streaming media, giving listeners a continuous stream of audio that cannot be paused or replayed.Audio data is transmitted serially over the local network or internet in TCP or UDP packets. TV and video on demandVideo on Demand - where a user has access to the companies video database and from there, is able to make a selection appropriate to their needs.The downside of VOD is the large file size that the videos have, this impedes on the speed of the transfer and consumes the users downloads (assuming they are on a capped plan) 4G 4G as the name implies, is the fourth generation in the mobile networking standard with speeds up to 1gpbs.The fourth generation of mobile networking technology requires new hardware to support newer features. This includes: Gaming and high demand services like video conferencing and streaming.All prior features in 1G, 2G, and 3Gup to 30x faster than initial 3G speeds 4G also utilises packet switching telephony only which means packets do not need to be routed, improving reliability and efficiency.3G technologies for mobile communications3G refers to the Third Generation of mobile telephone technology.3G technology is intended for the true multimedia cell phone - usually called smartphones.3G has the following enhancements over 2.5G and previous networks:Several times higher data speedEnhanced audio and video streamingVideo-conferencing support Web and WAP browsing at higher speedsIPTV (TV through the Internet) support.3G application services include mobile internet access, wide-area voice calls, mobile TV and video calls, all in a mobile environment. ................
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