Communication System

Communication Systems support people who are working together by enabling them the electronic exchange of data

and information. This presentation will enable the users to access a wide range of information regarding Communication Systems.

The topics in Communication Sytem

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Characteristics of Communication Systems Examples of Communication Systems Transmitting and Receiving Other Information Processes Issues Related To Communication Systems

Every communication system has 5 basic requirements•Data Source (where the data originates)•Transmitter (device used to transmit data)•Transmission Medium (cables or non cable)•Receiver (device used to receive data)•Destination (where the data will be placed)

Characteristics of Communication Systems

The necessity of protocols in communication – a protocol is needed when one computer communicates with another where one of its tasks is to ensure that the data send by the sending device is the same as the data received by the receiving device. A protocol is a set of rules that control a communications link.

A protocol defines the format and meaning of information exchanged by describing parameters such as speed of transmission (bps, baud) transmission mode (answer or originate), handshake, parity, error detection and correction.

The elements that a protocol controls include: the type of language used (e.g. ASCII), type of error checking method used (e.g. checksum), what to do when error is detected (e.g. resend data), way data are sent (asynchronous or synchronous transmission) and how often receiving computer needs to acknowledge that it has received the data.

Handshaking – is the exchange of signals between two devices to establish a communication link for senders and receivers. The computer handshakes to a printer or a modem in order to establish a connection for communicating. For a link between the computer and modem, handshaking involves the signalling of both to each other that they are switched on and ready for work………

…… The computer sends a DTR (Data Terminal Ready) signal to modem through a particular wire used only for this signal. When the modem is ready it sends a DSR (Data Set Ready) signal to computer through a different wire in the connecting cable.

Measuring speed in a communication link : -

Baud rate – the number of distinct signal events or timing intervals in a second. If a device like a modem can only send on-off signals then its bps equals its baud rate.

Measuring speed in a communication link : - Bits per second (bps) – the number of bits that

are transmitted in a second. This measures the speed of communication. Bps is the number of 0s and 1s which are transmitted through the communication link in one second. This includes special bits described in the protocol, including start and stop bits and various error checking bits. Bps is more useful than baud rate as it shows how much data is sent and how fast it is sent.

Methods to check for errors in communications links including: -

Parity bit check – this is a character error detection method. It adds an extra bit to every character or byte transmitted.

Methods to check for errors in communications links including: -

Check sum – adds together the values of all the bytes transmitted in a message block and sends the total as the last data byte of the block.

Methods to check for errors in communications links including: -

Cyclic redundancy check (CRC) – performs a division calculation on the entire block of data to produce a 16- or 32- bit result. Like check sum, CRC is a block error detection method and cannot reveal which byte or bytes in a block are faulty.

Examples of Communication Systems

- E-mail- Voice Mail - Fax- Smart Phone - Instant Messaging- Teleconferencing - Video-conferencing - Groupware - Telephony- E-Commerce - The Internet- Bulletin board system - The Web- Global positioning system

Teleconferencing (as an alternative to a face to face meeting) – or videoconferencing, allows people in different locations to participate in meetings without the problems and expense of travel using microphone and a camera, monitor and speakers.

Teleconferencing

How audio data is transmitted and received – Sound and images must be converted into binary by digitising before it is transmitted.

How video data is transmitted and received – images and sounds can be represented as a series of numbers and therefore 1s and 0s. The process of converting images into binary numbers is called digitisation.

Teleconferencing

Advantages – reduction of costs due to decreased travel and accommodation bills, stimulates face-to-face meetings without travel.

Disadvantages – teleconferencing results in the lack of personal contact which limits the potential to develop interpersonal relationships.

Examples of teleconferencing such as: Business use –Business use of

teleconferencing is becoming common as meetings and conferences can be held in any city nationally or internationally without the need for all participants to b in the same location.

Examples of teleconferencing such as: Distance education –. Unlike a

video lecture, teleconferencing is interactive as it allows the participants to ask and answer questions. Student living in these remote areas can participate in teleconferences, lecture broadcasts and live tutorial sessions.

Electronic commerce

EFTPOS as the transfer of funds electronically at the point of sale – Electronic Funds Transfer – Point of Sale – is an increasingly popular method of purchasing goods and services using a credit card or savings account. The customer swipes the card through EFTPOS terminal, choosing and account and entering their PIN as a password. The funds are transferred from customer’s account to retail store’s account without any cash being handled which is an advantage.

Electronic commerce

Electronic banking on the Internet – E-commerce (electronic commerce) involves conducting a business and making sales over a network such the Internet making ii convenient for customers to purchase goods as they ‘browse’ as many stores at they want 24.7 without leaving their home.

Transmitting and receiving in communication systems:

Communication concepts including: - Protocols – a protocol of information

exchanged by describing parameters such as speed of transmission (bps, baud), transmission mode (answer or originate), handshake, parity, error, detection and correction.

Examples include: Exports-modem, Z-modem, smtp, http and NETBIOS.

Communication concepts including: - Handshaking – is the process by which

two devices initiate communications. It enables a communications protocol to be agreed upon. Bandwidth (bps) is a measure of how much information can flow along a data pipe.

Communication concepts including: - Error detection / correction – Error

correction methods – these protocols attempt to correct any detected transmission errors. Retransmission is where the receiving computer requests that part of the message to be sent again and it may involve only the corrupted blocks of the message being transmitted or the whole message being transmitted. Retransmission is the most common error correction method.

Serial Transmission

Data is transmitted, on a single channel, one bit at a time one after another

often used to send data to a printer

- Sender Transmitted Receiver received

101 0 0 1 1 0

Parallel Transmission

-each bit has it’s own piece of wire along which it travels- Much faster than serial because of way bits processed.

R

ecei

ver

rece

ived

Sender transm

itted

10011001

All bits are sent simultaneously

Simplex: One direction only

Transmission Direction

Half duplex: Both directions but only one direction at a time

Full duplex: send and receive both directions at once

RING – consists of nodes in a closed loop or circle. Each node is part of a loop linking all the nodes together and nodes are attached to the cable at various points around the ring. Traffic can be one-way around the loop or can travel in both directions if a double loop is used. Its advantages include: a single cable is used to connect all the nodes making it extremely cheap, takes up less space and easy to fault-find in terms of broken cable. Its disadvantages include: if the ring is broken or cable is faulty the network ceases to operate, the ring must be broken to add or remove nodes, and it’s slow as it goes around the entire circle.

3 Types of LANs

3 Types of LANs

STAR – is a network topology that consists of computers attached to a central point or node (a device such as a computer connected to a network) which can be a computer like a mainframe, hub with links going out to computers that are workstations and servers. Star networks are popular and most common in LANs.

Its advantages include: each node has its own cable and doesn’t need to share the line with other nodes, if a cable to a node is broken then only that node is affected while the rest of the network can operate normally, new links to the central node can be easily added or existing links easily removed without affecting the rest of the network.

Its disadvantages include if the central node fails then the entire network will cease to operate, more cabling is needed than for other network topologies which is uneconomical.

BUS – this uses a cable in single line with two end points. At each end point there is terminator that prevents signals at the end of the cable from being reflected back into the network. In a BUS network each node is connected to a single cable and it is mostly used for small LANs.

Its advantages include: it’s easy and cheap to set up as it requires less cables, nodes can be easily added and removed and if a node goes down the network is unaffected.

Its disadvantages include: because the one cable carries all the data, collisions (data traffic jams) become more common as more nodes are added or when multiple terminals transmit at the same time.

Nowadays, bus networks are often replaced with a star network

3 Types of LANs

Network Hardware – a PC needs specialised hardware to become part of a network which includes a network card and cables.

Servers – a computer that supplies a service to other nodes on the network, taking a responsibility for certain tasks such as file sharing, printing, and database and Internet access to network to users.

1. File Server – computer dedicated to the task of sharing disk space, files and sometimes a printer. It uses the NOS to allowing many registered users to access files and programs at the same time.

2. Print server – computer that manages printing tasks whereby printers are attached to them and can be accessed by all network users in the network environment.

Servers –Mail server – this computer stores, receives and distributes electronic mail for users.

1. Web server – computer that stores and ‘serves’ webpages to users on either intranet or the internet.

2. Proxy server – this computer acts as a temporary store for data moving between LAN and other network like the Internet.

NETWORK TOPOLOGIES (categorizing by shape)

Other information processes in communication systems

Collecting refers to the process of obtaining data from a source external

to the system. Data can be collected in either digital or analog form. A computer can directly process digital data but needs to digitise analog data before attempting to process.

The phone as a collection device with voice mail –the callers are: given a series of options then requested to press a key on the phone’s keypad corresponding to their chosen option used in bill payment and product ordering systems and caller has to enter their credit card number allowing entered data to be immediately digitised and processed by computer.

Collecting (continued)

EFTPOS terminal as a collection device for

electronic banking – (Electronic Funds Transfer- Point of Sale) is a collection device for electronic banking and can be used for: to pay for a purchase customer selects the account type (credit, savings or cheque) enters their PIN and amount is directly withdrawn from customer’s bank account or added to their credit card statement

Processingthis is an information system process that converts digital data

into information within the information system.

Sending of attachments with email – an email (Electronic Mail) is the transmission of memos and messages over a network. Users can email to a single recipient or broadcast it to multiple users. Attachments are computer files such as text, video, sound pictures or programs sent with an email message.

Processing (continued)

this is an information system process that converts digital data into information within the information system.

Encoding and decoding methods – communication systems frequently convert data signals between analog and digital. The parts of a communication link that use analog signals (e.g. from telephone to local exchange) must convert all data to analog before transmission.

Processing (continued)

this is an information system process that converts digital data into information within the information system.

Client-server architecture – shares the processing between client and server computers on a network.

Client controls the user interface and application logic – the processing in client server networks is shared or distributed between server and client.

Processing (continued)

this is an information system process that converts digital data into information within the information system.

Server controls access to the database – sometimes more than one user wants to access the same data record at the same time. The database software at the server can lock

those records in use.

Displaying is the process by which the information stored within

the system is made available for its users. This is a necessary process within a communication system as it produces the output.

The phone as display device with voice mail – a telephone is a display device for voice mail as the output is audio, not graphical. A caller’s telephone number and name can be recalled on the screen of a mobile phone.

Displaying (continued)

is the process by which the information stored within the system is made available for its users. This is a necessary process within a communication system as it produces the output.

EFTPOS terminal as display device for electronic banking – the EFTPOS terminal will display the type of account user has selected, amount of cash to be withdrawn / amount to spend on the transaction. It asks for pin number, display processing messages and then whether the transaction has been approved or not.

Issues related to communication systems

Usage of communication systems to share knowledge not just data – main role of communication systems is to share knowledge. Most communication systems are privately controlled an owned thus these powerful organisations and individuals control the information they pass on to receivers who also have control over the knowledge.

Issues related to messaging systems – increasing business and personal communications occur via email or other Internet messaging solutions like chat rooms or instant messaging clients.

Ideas delivered by this means appear less forceful and caring than ideas delivered personally

Danger of being misinterpreted Power relationships – communications via electronic

means restrict relationships as inter-personal socialisation is limited.

Privacy and confidentiality Electronic junk mail – this is one a user receives countless

unrequested emails from unknown people or spammers.

Implications of Internet trading including – purchasing goods and services over the Internet has become common recently with payments transacted via a credit card. In today’s ‘cashless’ society, even people low on cash can purchase goods via a credit card, an EFTPOS terminal or instant credit checks, encouraging spending but resulting in increasing debt levels.

Trading over the Internet and its commercial implications – many businesses which are based entirely on the Internet may have a great website and product but have neglected to plan their supply chain as thoroughly and thus consumers face lengthy delays when purchasing items.

Difficulties of censoring content on the Internet – censorship is a major issue concerning control of the Internet where its contents (inappropriate websites, newsgroups, emails, chat rooms) should be censored but because the Internet is worldwide the responsibility of censorship becomes a problem whether the user, content provider or ISP (Internet Service Provider) should be responsible.

Issues arising from Internet banking including: Security of banking details – Internet banking

customers have a right to the privacy of their transactions and financial details. When account details are entered into a response form on a webpage, the user has no control over the computer systems it passes through before reaching its destination. The encryption (data security coding) systems used on many web browsers and web servers aren’t totally secure as many have been broken by ‘hackers’.

Issues arising from Internet banking including: Changing nature of work – jobs have been

eliminated due to increased Internet emphasis. Replacements generally require skills in IT and web support services causing the existing staff to retrain or find alternative jobs.

Issues arising from Internet banking including:

Branch closure and job loss –This has had a major impact on customer access to traditional banking services, has increased customer dissatisfaction with the banks and reduced employment in the banking industry.

The emerging trend of accessing media such as radio and video across the Internet – communication technologies are converging into one technology – ‘convergent technology’ - as multimedia and the Internet have already converged, radio and TV has started to converge with the Internet through live audio and video Internet broadcasts. ….

The web has started to converge with cable TV with the provision of fully interactive cable broadcast services and web services are now appearing on broadcast digital TV. Telephones and mobile phones can now purchased with high resolution LCD screens and built-in web browser and email software while a PC is no longer needed to access the Internet with set top boxes that turn the TV into a web browser.