IPT HSC 2017 - Communication Systems PDF

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HSC IPT Topic 2 (HSC Score 94)...

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IPT 2017 – 9.3 Communication Systems Characteristics of Communication system Communication systems as being those systems which enable users to send and receive data and information The framework in which communication systems function, demonstrated by the following model:

Use applications to create and transmit messages Establish a communications link and describe the steps that take place in its establishment The functions performed within the communication systems in passing messages between source and destination, including: Message Creation • Messages are usually created at the source before transmission • Messages are created with software application, usually involving the collection of message data • Examples: o Writing emails using email clients e.g. Gmail o Web server retrieving requested HTML files to transmit to web browser o DBMS server extracting records to transmit to client application Organisation of packets at the interface between source and transmitter • To prepare a data packet for transmission, the data packet travels from the application level to the transmission level. • Each protocol wraps the data packet from the layer above with its own header and trailer • Some protocols include the address of the receiver and some protocols include error correction and detection code • At the receiver's end, each protocol strips off its corresponding header and trailer , performs error checks and passes the data packet to the next protocol Signal generation by the transmitter • Transmitter: physical hardware that generates or encodes the data onto the medium creating a signal • Represents individual bits or patterns of bits as a wave (i.e. signal) • Rules of transmission level protocol determine o Which characteristics are altered

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o How each pattern of bits is encoded o Speed of transmission o The control and synchronisation of the exchange Examples of transmitter devices: o Switches o Routers o Cable modems o Bluetooth devices o Mobile phones

Transmission • Occurs as the signal travels or propagates through the medium • Transmitter creates each waveform and maintains it on the medium for a small period of time • Data is usually split into packets and are not sent continuously due to occurrence of errors • As some transmitters wait for acknowledgement from the receiver, this may double transmissions times • Flow control is used by protocols to reduce transmission times Synchronising the exchange • Accurately decoding symbols requires the receiver to sample the incoming signal using the same timing used by the transmitter during encoding • This synchronising process ensures each symbol or waveform is detected by the receiver • Synchronous transmission transfers large data packets at a time • Preambles are included at the start of each data packet to ensure initial synchronisation of the receive and transmit clocks • Another element is embedded within the data packet to ensure synchronisation is maintained throughout transmission of each frame Addressing and routing • Requires TCP/IP protocols • As data packets pass through may different links and each data packet forming a file may travel over quite different paths, efficient routing is required. • An Ethernet switch contains all addresses of attached devices, frames can be directed down the connection that leads to the receiver • Routers use IP addresses within IP datagrams as well as their routing table to determine the next destination for the frame Error detection and correction • As messages descend through each level, many protocols calculate checksums or CRC values to include into the header/footer as error detection methods • On the receiving end, each protocol performs the calculation, making sure the checksum and CRC values match the original Security and management • Protocols usually restrict access based on username and passwords or encrypt messages during transmission • E.g. POP servers require users to be authenticated before retrieving their email messages • E.g. SSL uses public key decryption to secure critical data transfers

The roles of protocols in communication Handshaking and its importance in a communications link • An agreement between 2 devices (in the process of communication) on which protocol to use to connect and exchange information. • Involves sending signals to indicate the type of protocol to use. • A connection is made when the 'handshake' is successful Hardware flow control (HFC) • Dedicated connection such as a wire.

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Only practical when devices are physically close enough to be connected using a cable E.g. RTS/CTS (request to send/clear to send)

Software flow control (SFC) • A special code sent with the data - used for long distance communication • XON/XOFF where X' stands for transmit (signal to wait or problem occurred/ ready to communicate)

Identify and describe specified protocols at different stages of the communication OSI (Open Systems Interconnection) Reference Model IPT Presentation Level • OSI Application Layer: o Where data created by software applications is organised in a format understood by the receiver application • OSI Presentation Layer: o Data is reorganised into a form suitable for subsequent transmission (e.g. compression of an image) o Protocols operating on this levels include HTTP, DNS, FTP, SMTP, POP, IMAP and SSL IPT Communication Control and Addressing Level • OSI Session Layer: o Where communication with the network is established and maintained o Determines when a communication session is started and when it ends o Includes security to ensure a user has appropriate access rights • OSI Transport Layer: o Manages the correct transmission of each packet of data o Ensures that packets that fail to reach the destination is retransmitted o TCP operates on this layer • OSI Network Layer: o Where packets are directed to their destination o IP operates on this layer - addresses and forwards packets to their destination o No attempt for error correction/detection o Routers - directing packets along best path IPT Transmission Level • OSI Data Link Layer: o Defines how transmission media is shared o Device drivers that control physical transmission hardware operates on this layer o These determine the final size of data packets, speed of transfer and other physical characteristics o Switches and Ethernet protocol operates on this level to direct messages to their destination o Other data link protocols: Token Ring, SONET and FDDI • OSI Physical Layer: o Performs the transfer o Consists of hardware (i.e. transmission media) o Converts bits into signals to transmit along the medium

Identify client processing and server processing The client - server model The role of the client and the server • Server: provides particular processing resources and services to each client machine • Client: perform independent local processing, manages all interactions with end users (i.e. provides a user interface) • A form of distributed processing, occurs sequentially Thin clients and fat clients • Fat Client: clients that has applications installed which are executed by the CPU within the client

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Thin Client: terminals that only perform basic processing tasks (e.g. transmitting and receiving data, displaying info), relies on servers to perform more complicated processing

Examples of clients • Web browsers • Email clients • Database applications • Personal computers Examples of servers • File Servers o Consists of distributed processing o All workstations data is saved on the file server o The client PC (i.e. Fat Client) must request for a file and the file server sends it o The file server stores all data and applications • Client Servers o Consists of centralised processing o Consists of thin clients o All processing happens on the server • Print servers • Mail servers • Web servers • Database servers

Describe the advantages and disadvantages of client - server architecture Advantages of client servers Centralisation • Servers handle all the administration, access rights and resource allocation • All files are stored on the server, management and navigation of files is easier • More secure to protect all data in a centralised area Back-Up and Recovery • Easy to back - up and recover files from the server Flexibility of Server • Server can be easily upgraded (i.e. adding new resources and systems) • Plays different roles for different kinds of clients

Disadvantages of client server Congestion • Too many requests from clients may lead to congestion in the server • Overloading of servers can lead to breakdowns Server Failure • If server fails, whole network breaks down with it Cost • Professional IT staff is required to maintain and manage the servers and other hardware/software • Expensive installation and maintenance

IPT 2017 – 9.3 Communication Systems Examples of Communication systems For given examples, identify the participants, information/data, information technology, need and purpose For given examples explain how data is transmitted and received For given examples, identify the advantages and disadvantages of the system Teleconferencing Systems • • •

Teleconferencing: the use of electronic transmission to allow a meeting to occur at the same time in different locations (e.g. audio or video conference) Audio conference: a single telephone call between three or more people (all at different locations) where audio data is transmitted and received using telephone lines Video conference: a meeting that allows people in different locations to see and hear each other through the transmission of video and audio data, usually requires special communication arrangements because of the high bandwidth required to transmit video data

Advantages • Reduces costs (e.g. travelling and accommodation costs) • Saves time and energy otherwise expended into travelling Disadvantages • Removes inter-personal relationship and social interactions which can be achieved through a face-to-face meeting • Face-to-face meetings are more effective when ideas need clarification and to develop partnerships/friendships Information system diagram • Purpose: to exchange information • Participants: people involved in the conference • Data: Audio, text, images, video, chart • Information: Exchanged discussions • Hardware: Computer, webcam, speaker, microphone, cables, router, modem, projector, screens, internet connection • Software: audio software, teleconferencing software, video software, operating system, anti-virus software, application software (e.g. excel, database), web browser • Information processes: transmitting and receiving, displaying

Messaging Systems • •

Involve the creation, storage, exchange and management of messages. Used to send messages to people in different locations.

Traditional systems Telephone • A system for transmitting sounds or speech between distant locations through telephone lines • A telephone answering system is a type of messaging system that stores messages and allows the receiver to hear the message at a later time Fax • Fax machines is a system of transmitting and reproducing documents through the use of signals that travel along telephone lines • The fax machine scans a document and converts the document into a bit-map image that is compressed and transmitted along telephone lines to a destination fax machine. • The destination fax machine will decompress the image and restore the document to the original format before printing.

IPT 2017 – 9.3 Communication Systems Voicemail • Voicemail allows communication between people by storing and forwarding spoken messages. A sender will record a message which will be stored on a system from where it can be retrieved at a later date by the intended receiver. This receiver dials into the voice-mail system, entering their account details to retrieve the voicemail. • An advantage that voicemail has over email is that more people have access to a telephone rather than a computer equipped for email use. • Additionally, voice tone is better interpreted through a voicemail Electronic Mail • Electronic mail allows communication between users by sending and receiving electronic messages using a computer. • Fast, economical and a convenient way to send messages to people in any location. • Requirements: o Internet connection o Email provider o Email ID o Computer/Device • Email address structure: 'name'@ 'domain name' o 'Name': name of the account (usually the username) o 'Domain name': location of the person's account on the internet • Email message structure: o Email address (To:) is the address of the main recipient (cannot see BCC but can see CC) o Carbon Copy (Cc:) sends the same message to other people ( can see other CC and the main recipient) o Blind Carbon Copy (Bcc:) sends a copy of the message to other people that are not revealed ( can see all other recipients) o Subject: topic of the message • Other terminology: o Quoting: when the previous message is retained so that the original sender remember the message o Forwarding: involves sending messages you have received to someone else o Address book: used to store email addresses o Mailing List: a group of people who may want to receive the same messages o Signature: several lines automatically appended to outgoing email messages (e.g. email address, Web site, graphic, occupation or telephone number) Advantages of messaging systems • Reduce costs of travelling of having a face-to-face meeting • Saves time of meeting people in person Disadvantages of messaging systems • Reduces face-to-face social interaction • Danger of misinterpretation Information system diagram - Messaging Systems • Purpose: to allow communication between users • Participants: people involved in the communication link • Data: Audio, text, images, video, • Information: Everyday conversation, discussions, attachments (files) • Hardware: PC, telephone, fax machine, screen, cables, router, modem, internet connection, email server • Software: web browser, operating system, anti-virus software, email software • Information processes: processing, transmitting and receiving, displaying

IPT 2017 – 9.3 Communication Systems Other systems dependent on communication technology such as: Electronic commerce • Buying and selling of goods and services via the Internet • Provides 24-hour availability, global reach, the ability to interact and provide customer information in a multimedia environment Advantages • Easy and convenient • No travel needed • Easy to search and compare prices of products • 24/7 access Disadvantages • Security of money transactions (i.e. credit card) • Wait time • Delivery errors • Cannot physically see/touch the product • Large tax implications for business and customers Information system diagram - Electronic Commerce • Purpose: provides platform for the buying/selling of goods and services via the Internet • Participants: Customers and traders • Data: Audio, text, images, video, • Information: Product information, product reviews, contact details etc. • Hardware: PC, telephone, cables, router, modem, internet connection • Software: web browser, operating system, anti-virus software, • Information processes: processing, transmitting and receiving, displaying

EFTPOS (electronic funds transfer at point-of-sale) • A system that allows the purchase of goods and services using a credit/debit card. • Transfers money electronically from the customer's bank account to the retailer's bank account • Point-of-sale terminal is linked to the computer of the customer's bank through the account number • PIN number is a security measure to identify the customer. • Connection must be approved before money is transferred. • Hardware: scanner, printer, keypad, screen, terminal, cables, till, modem, router • Software: secure connection (https, ssl), browser, EFTPOS software, transaction processing system Electronic banking • Allows customers to view their account balances and transaction histories, transfer money and pay bills online. • Cannot cater for cash or cheque withdrawals • Raises the issue of security, data encryption is often used to secure the data transfer between the customer and the bank. Advantages: • Easy and convenient • No travel needed • 24/7 access Disadvantages: • Security of money transactions • Chance of errors in transfers or transactions

IPT 2017 – 9.3 Communication Systems Information system diagram - Electronic banking • Purpose: allows customers to view account balances and transaction histories and pay bills via Internet • Participants: Clients, bank staff • Data: text, images, • Information: Account balance, transaction history, bill information, • Hardware: PC, telephone, cables, router, modem, internet connection • Software: web browser, operating system, anti-virus software, • Information processes: processing, transmitting and receiving, displaying

Transmitting and receiving in communication systems For a given scenario, choose and justify the most appropriate transmission media Transmission media including: Wired Transmission • Transfers data through wires/cables • Wires/cables must be protected from external damage and takes up physical space • Can carry large amounts of data without interference Unshielded Twisted Pair (UTP) • Widely used, due to low cost and ease of installation. • Structure: Two thin insulated copper wires, twisted together to from a spiral. • The twisting of the cables reduce electrical interference between adjacent pairs of wires • Can only transmit data over a limited distance (100m or less) • Max bandwidth is 60Kb/sec (CAT 6) - a slow transmission medium • Usually coded in a blue colour Shielded Twisted Pair (STP) • Individual pairs have additional insulation covering to prevent outside interference • Used in noisy environment as its shield protects against excessive electromagnetic interference. • More difficult to install and less common compared to UTP • Usually coded in a blue colour

Coaxial cable • Structures: o Consists of a central copper wire core, surrounded by insulation o Braided metal shielding surround insulation to absorb unwanted external signals, preventing interference, allowing the data to be transmitted with little distortion o Plastic sheath protects cable from physical damage o At each end, a terminating resistor is used to prevent transmitted signals from being reflected back down the cable • Advantages: o Can be used over a longer distance (500m - 1km) o Max Bandwidth of 10Mb/sec o Thick outer shielding provides insulation against outside interference

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Disadvantages: o Difficult to install o Expensive compared to twisted pair cables

Fibre-optic cable • Structure: o Thin, solid strands of glass that transmit info as pulses of light. o Core is made up of high-purity glass (6-50 microbes in diameter) in which light pulses travel to o Core is encased with cladding (125 microbes in diameter) made up of a different type of glass o Primary buffer provides some protection as outer plastic covering o Overall diameter = 250 microbes • Advantages: o Unaffected by electromagnetic interference o High maximum bandwidth (500mb/sec - 1Gb/sec) - allowing a large amount of data to be transmitted at a time o Secure transmission o Can transmit several km o Mostly error-free • Disadvantages o Very expensive o Very difficult installation requiring specialists o Easy to break glass core

Repeaters • Signals can be corrupted when travelling long distances or due to interference from electromagnetic fields • Repeaters is used to rebuild fading signal to original strength and shape • Used in a LAN to connect network segments

Wireless Transmission • Involves transmission of data without cables/wires

IPT 2017 – 9.3 Communication Systems Advantages of Wireless Communication • Enabled instant transmission of information to consumers • Working professionals can access Internet anywhere with Wi-Fi →...