HSC Information Processing and Technology/Communications
- 1 Characteristics of Communication Systems
- 2 Examples of Communication Systems
- 3 Transmitting and Recieving
- 3.1 Methods of Data Transmission
- 3.2 Modes of Data Transmission
- 3.3 Processes involved in Data Transmission
- 3.4 Networks
- 3.5 LANs
- 3.6 WANs
- 3.7 Packet Switching
- 3.8 Network Topologies
- 3.9 Network Hardware
- 3.10 Network Software
- 4 Other Information Processes
- 5 Issues Related to Communication Systems
Characteristics of Communication Systems
COMMUNICATION SYSTEM- allows people to send and receive data and information. All communication systems have five basic components:
- DATA SOURCE- produces the data to be sent.
- TRANSMITTER- encodes the data into a single signal suitable for a transmission medium.
- TRANSMISSION MEDIUM- is a channel, such as a cable, is which the signal is transmitted to the destination. Signal may be changed or distorted during transmission.
- RECEIVER- decodes the signal back into the original data or an approximation of the data.
- DESTINATION- is the receiver of the information.
Communication systems are used in information systems when participants need to transmit and receive data and information. Good communication systems have an accurate, reliable and secure transmission medium and should have a minimum delay in communicating. Good communication depends on protocols, handshaking, speed of transmission and error checking which all depends on the information technology used in the communication system.
PROTOCOL- is a set of rules that governs the transfer of data between computers. It defines how the information is transmitted and how errors are detected. Two computers must use the same protocols when communicating otherwise the data transfer may be unsuccessful. Protocols are written into internationally accepted standards such as the OSI reference model.
- OSI REFERENCE MODEL- divides data communications into seven layers. Each layer expresses the standard using a protocol. The bottom layers are responsible for data transfer from one place to another. They specify things such as plugs, format, method of transmission, error checking.
- (See page table below for examples of common protocols).
|TCP/IP||Transmission Control Protocol / Internet Protocol
TCP/IP is the basic communication language or protocol of the Internet. It can also be used as a communications protocol in a private network. When you are set up with direct access to the Internet, your computer is provided with a copy of the TCP/IP program just as every other computer that you may send messages to or get information from also has a copy of TCP/IP.
|HTTP||HyperText Transfer Protocol
The HTTP is the set of rules for exchanging files (text, graphic images, sound, video, and other multimedia files) on the WWW. HTTP is an application protocol.
|FTP||File Transfer Protocol
FTP, a standard Internet protocol, is the simplest way to exchange files between computers on the Internet.
|SMTP||'Simple Mail Transfer Protocol
SMTP is a TCP/IP protocol used in sending and receiving e-mail. However, since it’s limited in its ability to queue messages at the receiving end, it’s usually used with one of two other protocols, POP3 or IMAP, that let the user save messages in a server mailbox and download them periodically from the server.
|IMAP||Internet Message Access Protocol
IMAP is a standard protocol for accessing e-mail from your local server.
|Post Office Protocol (3)
POP3 is the most recent version of a standard protocol for receiving e-mail. POP3 is a client/server protocol in which e-mail is received and held for you by your Internet server.
|MIME||Multi-purpose Internet Mail Extensions
MIME is an extension of the original Internet e-mail protocol that lets people use the protocol to exchange different kinds of data files on the Internet: audio, video, images, application programs, and other kinds, as well as the ASCII handled in the original protocol, the SMTP.
|UDP||User Datagram Protocol
UDP is a communications method (protocol) that offers a limited amount of service when messages are exchanged between computers in a network that uses the IP. UDP is an alternative to the Transmission Control Protocol (TCP) and, together with IP, is sometimes referred to as UDP/IP. Like the TCP, UDP uses the IP to actually get a data unit (called a datagram) from one computer to another.
|Telnet||Telnet is a user command and an underlying TCP/IP protocol for
accessing remote computers.
|IPX||Internetwork Package Exchange
IPX (Internetwork Packet Exchange) is a networking protocol from Novell that interconnects networks that use Novell’s NetWare clients and servers. IPX is a datagram or packet protocol. IPX works at the network layer of communication protocols and is connectionless.
|IEEE (802)||A set of network standards developed by the IEEE Institute of
Electrical and Electronics Engineers.
|FDDI||Fibre Distributed Data Interface
FDDI is a standard for data transmission on fiber optic lines in a LAN that can extend in range up to 200 km. The FDDI protocol is based on the token ring protocol. In addition to being large geographically, an FDDI LAN can support thousands of users.
Handshaking is used to establish a communication session for senders and receivers. It refers to a series of messages or signals used to establish whether the devices are compatible and thus able to communicate.
HANDSHAKING is an agreement about which protocol to use to accomplish the exchange of information. Data can only be successfully transferred if this occurs. It is a series of signals that flow between devices during data transmission. Handshaking is needed between devices as they may have different capabilities and may transfer data different ways. Handshaking involves sending signals to indicate the type of protocol to be used. The transmitting device will send this signal and wait for a response. When two devices successfully handshake a connection is made. If unsuccessful the devices ‘hang up’ and try again. There are two methods of handshaking to control the flow of data;
- HARDWARE FLOW CONTROL uses a dedicated connection such as a wire. It is only practical when devices are close enough to be linked by a cable. Common hardware protocol is RTS/CTS (request to send/ clear to send).
- SOFTWARE FLOW CONTROL uses a special code sent with the data and is used for long distance communication. Common software protocol is XON/ XOFF (X stands for transmission). When a break in transmission is required the XOFF command is sent etc.
BANDWIDTH- is the capacity of the channel or transmission medium. The speed of transmission is determined by the transmitting device and the bandwidth. A transmission medium with a high bandwidth can transfer more data. The speed of data transfer is measured by the number of bits per second, or the baud rate.
Bits per Second
BITS PER SECOND (bps) or BIT RATE- is the maximum number of bits that can be transmitted in one second. This includes special bits used in asynchronous transmission and any error checking bits.
BAUD RATE is the maximum number of data symbols or electrical signals that can be transmitted in one second. Because one data symbol may contain more than one bit the baud rate and bit rate may not be the same.
Error Checking Methods
Received data may contain errors caused by interference in the signal or by errors in encoding and decoding the data. Errors must be detected then corrected. Methods include:
PARITY CHECKING is a method of checking for errors in data transmission using an additional bit called a parity bit. This bit is used only for the purpose of identifying if the bits being moved have arrived successfully. The sender and receiver decide whether to send using an odd or even parity bit. For example with 8 bit ASCII:
- 10011010 0 (even parity, 9th parity bit must be 0 to keep it even)
- 11001001 1(odd parity, 9th bit must be a 1 to make it odd)
CHECKSUM is a method of checking for in data transmission by counting the total number of bits in a data packet. A data packet is created by dividing the total data into smaller groups called packets. The count of bits in a data packet is attached to the data packet. It is used by the receiver to check whether all the bits have arrived successfully. If the count matches it is assumed that a complete transmission was successful.
Cyclic Redundancy Check (CRC)
CYCLIC REDUNDANCY CHECK (CRC) is a method of checking for errors in data transmission using a division process. The data is divided into predetermined lengths by a fixed divisor. The remainder of the calculation is attached and sent with the data. When the data is received, the remainder is recalculated. If the remainders do not match, an error in transmission has occurred.
Dealing with Errors
The receiver may drop the packet, such as in IP, they may only acknowledge correct packets as occurs in TCP, or they may request that packets containing errors be resent, as occurs with Ethernet.
PARAMETER is a variable that is given a constant value for a particular application. Communication settings can be changed by the user to ensure a connection between two devices. These settings are often a parameter. Some common parameters include bps, data bits, parity, stop/ start bits, and flow control:
BITS PER SECOND is the speed of transmission
DATA BITS are the number of bits in each group of data. Each group is usually sent as a byte such as 7-bit or 8-bit ASCII.
PARITY is whether the data contains a parity bit for error detection. Parity is odd, even or none.
STOP/ START BITS are the number of stop and start bits used in asynchronous transmission. This parameter is used to identify each byte. The normal range is between 0 and 2 while some systems only use a stop bit.
FLOW CONTROL is the software handshaking protocol.
Examples of Communication Systems
TELECONFERENCING is the use of an electronic transmission to allow a meeting to occur at the same time in different locations. It is an alternative to face-to-face meetings. Teleconferencing uses audio and video communication to go beyond the normal telephone call.
Advantages: Business people such as the managers at head office and at branch office can conduct formal meetings at scheduled time without the need to travel over large distances. As a result, the cost to travel is reduced. Additionally, teleconferencing systems allows decisions to be made faster, and also it allows employees of organisation to interact with one another. Hence, new innovative ideas emerge during the conference.
Disadvantages: Users will not be able to see each other face to face and as result there will be little recognition of the nature and personality of other people with whom the users work with. Additionally, there will be no social relationship between people.
AUDIO CONFERENCE- is a single telephone call involving three or more people at different locations. It is a service provided by a telephone company where audio data is transmitted and received using existing phone lines.
VIDEO CONFERENCE- is a meeting that allows people in different locations to see video images if each other on a screen, as well as hear speech. Video conferencing requires a high bandwidth. Video conferencing simulates face-to-face meetings and reduces costs on not buying airfares, accommodation and meals, and saves time and energy involved in travelling. Teleconferencing is frequently used in business and distance education. However it does remove the inter-personal relationship of face-to-face meetings.
MESSAGING SYSTEMS- are used to send messages to people in different locations who may receive the message at a later time. Messaging systems involve the creation, storage, exchange and management of messages, which are sent to an individual, or a group of people. The oldest form of messaging system is letters while tradition systems include the telephone and fax:
- TELEPHONE- is a system for transmitting sounds or speech along telephone lines to distant locations. It is a convenient method of communicating with people around the world. A telephone answering machine is a communication system as it stores messages for hearing at a later time.
- FAX (OR FACSIMILE) MACHINE- is a system of transmitting and reproducing documents by means of signals sent over telephone lines. The fax machine scans a document and converts it into a bit-mapped image, which is compressed and sent over the telephone network to a destination fax machine. This destination machine decompresses the image and reconstructs the original document. Fax machines have become popular as people can quickly transfer a hard copy off a document or send a written message. Computers equipped with a fax modem can perform the same tasks.
VOICE-MAIL (V-MAIL)- allows communication with other people by storing and forwarding spoken messages. The sender dials a voice-mail number and records a message, which is digitally stored on a computer system and can only be retrieved by the intended receiver. To retrieve the message this person dials the voice-mail number using any phone, enters an account number and password. Once in they can delete, save or forward the message to another person. Voice mail combines the features of a telephone answering machine and some of the concepts of email. It provides some advantages over email as more people have access to a phone than a computer, and people often express feelings better with the spoken word. However email is better for sending complex information and different data types.
ELECTRONIC MAIL (EMAIL)- allows communication with other email users by sending and receiving electronic messages using a computer. Email was one of the earliest uses of the Internet. It is a fast, economical and convenient method of sending messages all over the world in minutes. To use email you need a computer that is linked to a network or the Internet, an account with an Internet service provider (ISP), an email address and email software.
EMAIL ADDRESS- anyone with an email address can receive email and email can be written to anyone that has one. Email addresses are unique and obtained free. They consist of two parts separated by @ symbol in the form ‘name’@’domain name’. The first part is the name of the account. The second is the domain name, which is the location of the account on the Internet. It identifies the specific computer or server where the person’s email messages are stored.
EMAIL MESSAGES contain two main parts, the header and body of the message:
- HEADER- is similar to an envelope as it contains information needed to deliver the message. The sender'’ email address is usually automatically inserted. The header contains four main parts that the sender fills in:
- EMAIL ADDRESS (To:) is the address of the person receiving the message, which must be correctly typed.
- CARBON COPY (Cc:) sends the same message to other people apart from the main recipient (optional).
- BLIND CARBON COPY (Bcc:) sends a copy to other people without revealing that these other people got the message (optional).
- SUBJECT is the topic of the message or a brief description (optional).
- BODY- of the message is typed using the email software or imported or copied from a word processor. The user does not have to be online to compose. Messages can be written offline and sent when the user logs on to the network or Internet. This saves ISP on charges. Email messages are often short and typed quickly. Some people use inventive spelling. When email is sent it is stored on the server where the receiver’s account is until the person checks their email. After the email is read, it can be deleted, printed or stored in an appropriate folder for later reference. The user can also:
- REPLY to the email message by clicking the ‘reply’ icon. The address of the original sender and the subject are automatically inserted in to the header of the reply. Leaving the subject the same identifies the ‘thread’ of the message.
- QUOTING is retaining the previous message in the reply so that the original sender remembers the message.
- FORWARDING is sending a message already received to someone else.
Email software also provides a number of features to help create email:
ADDRESS BOOK- is used to store email addresses. This saves time typing the address and avoids having to remember each one.
MAILING LIST- is a group of people who may want to receive the same messages e.g. people working on the same project or with the same interests. Mailing lists are created by entering each address of each person in the list and giving it a name.
SIGNATURE- is several lines automatically appended to outgoing email messages and may include an email address, Web site, graphic, occupation or phone number.
ELECTRONIC COMMERCE (E-COMMERCE) is the buying and selling of goods and services via the Internet. It has become a multi-billion dollar source of revenue for the world'’ businesses. It provides 24-hour availability, global reach, the ability to interact and provide customer information, and a multimedia environment. E-commerce is expected to expand into retail areas as each day there are businesses being established which rely entirely on Web sales.
Electronic Funds Transfer (EFT)
EFTPOS (electronic funds transfer at point-of-sale) is a system that allows people to purchase goods and services using a credit or debit card. It is the electronic transfer of money from the customer’s bank account to the retailer’s. It has made shopping easier for customers and allows retailers immediate payment if the connection is made and approved. Each point-of-sale terminal is linked to the computer of the customer’s bank using the account number on the card. Entering the PIN number is a security measure to identify the customer.
ELECTRONIC BANKING allows customers to view their account balances and transaction histories, transfer money between accounts and pay bills using Bpay. It provides services 24 hours a day but cannot counter for cash or cheque withdrawals. However automatic electronic debits are replacing cheques, which are expensive and ineffective as they pass through many hands before the transaction is completed. Some electronic banks require people to download special banking software and install it. Electronic banking raises the issue of security yet all banks are determined to make their online services safe from interference and to secure customer details using data encryption to secure data transfer between the two involved computers.
Transmitting and Recieving
Methods of Data Transmission
DATA TRANSMISSION occurs in two ways:
PARALLEL TRANSMISSION is the transmission of data simultaneously using separate channels.
SERIAL TRANSMISSION is the transmission of data one after the other. It is used to transmit data to peripheral devices, and is used on networks. Serial transmission can be either synchronous or asynchronous:
Synchronous and Asynchronous Transmission
- ASYNCHRONOUS TRANSMISSION is the sending of data by identifying each byte with special start and stop bits. It has become the standard for personal computers.
- SYNCHRONOUS TRANSMISSION requires all the data to be sent at the same rate (the same number of bytes is sent each second). This is synchronised by each device using a clock. Synchronous is faster and more efficient than asynchronous as there are no extra bits. It is used on larger computer systems.
Modes of Data Transmission
DIRECTION OF DATA- can be simplex, half-duplex or full-duplex mode:
- SIMPLEX MODE allows transmission in one direction only from the sender to the receiver e.g. radio.
- HALF-DUPLEX MODE allows transmission in both directions but not at the same time. The sender and receiver take turns e.g. walkie-talkie.
- FULL-DUPLEX allows transmission in both directions at the same time e.g. email. Most communication systems use this mode.
Processes involved in Data Transmission
NETWORK- is a number of computers and their peripheral devices connected together in some way. Each device in a network is called a node. Terminals are any devices that send data to and receive data from another computer system. If a terminal has both memory and processing capabilities it is called an intelligent terminal. Most personal computers are classified this way and called workstations on a network. The simplest form of a network is when two computers are connected directly to each other via a cable yet networks can involve thousands of computers. Networks are classified as LANs or WANs:
LOCAL AREA NETWORKS (LANs) connect computers within a building or group of buildings on one site. LANs cover a small geographical area and the computers are linked by coaxial cable or fibre-optic cable. There are three main advantages in using a LAN:
- sharing limited hardware resources such as printers, hard disks and modems.
- sharing application software such as word processors and DBMSs.
- improved communication among uses by sending electronic messages.
WIDE AREA NETWORKS (WANs) connect computers over hundreds or thousands of kilometres. WANs often consist of a mainframe computer called the host and a number of terminals e.g. EFTPOS and ATM terminals. A WAN may use a private lased line, the normal phone network, or a combination of both:
- PRIVATE LEASED LINE- is dedicated to the network. It offers higher transmission speeds than the PSTN.
- PUBLIC SWITCHED TELEPHONE NETWORK (PSTN) are relatively cheap if computers do not require a constant connection however they are not guaranteed and can be interrupted.
PACKET SWITCHING is a technique that divides messages into small data packets, transmits these packets, and later joins them to form the original message. It is used to send most data over networks and the Internet. It allows multiple users to use the same transmission line by interspersing the data packets from different users. Data packets may not be sent over the same path and could arrive at the destination at different times and in the wrong order. Each packet contains an address and control instruction to reassemble the message in the correct order.
NETWORK TOPOLOGY is the physical arrangement of the devices in a network. Types include:
- STAR TOPOLOGY- has a central computer WITH EACH DEVICE CONNECTED DIRECTLY TO IT. The central computer serves as a switch. It receives messages and sends them to the destination device. This topology requires extra cabling as each device is connected to the central computer rather than the next device. If one cable is broken the network can still operate. Yet if the central computer fails, the whole network fails. It is also limited by the processing power of the central computer. Star networks use a time sharing device that allocates a certain amount of CPU time to each user. It is the most common topology for a mainframe.
- BUS TOPOLOGY- is an arrangement where all devices are connected to a direct line called a bus. Each device has a unique identity and can only recognise the signals intended for it. Devices check the bus and retrieve their messages as data travels along the bus. Each device is considered to be connected to every other device and can communicate directly along the bus to any other device. Bus topology is one of the easiest to set up and can still operate if one node fails. It is used by Ethernet and PowerTalk.
- RING TOPOLOGY-is an arrangement where all devices are attached so that the path is in the shape of a continuous circle. Each device in the ring has a unique address. Data flows in one direction, moving from device to device until arriving at its destination. Token ring is the most common form of access for a ring topology.
Network Access Methods
NETWORK ACCESS METHODS for dealings with multiple users wanting to access the network at the same time include:
- ETHERNET- the first industry-standard LAN access method, or protocol, based on a bus topology. It is defined in a standard called IEEE 802.3. Ethernet allows data to be transmitted simultaneously to all nodes on the network in both directions. Addressing information allows each node to recognise and receive individual data packets intended for it. With these packets travelling simultaneously collisions will occur and cause errors. To overcome this Ethernet uses (CSMA/CD).
- CARRIER SENSE MULTIPLE ACCESS AND COLLISION DETECTION (CSMA/CD)- all nodes have the ability to sense signals on the network. When a node wishes to transmit it ‘listens’ to the bus for signals. When there is no signals it transmits. A collision may occur if two nodes sense a clear bus at the same time. When a collision is detected each device stops transmitting and retransmits at a later time.
- TOKEN RING- a LAN access method, or protocol, based on a ring topology. The token ring operates by continually passing special data packets called tokens between nodes on the network. Workstations with data to send capture a free token and attach data along with addressing information. A busy token with data cannot be used by other nodes. When the data arrives at the destination, it is replaced with an acknowledgment and sent back to the original sending node.
NETWORK HARDWARE- special purpose hardware devices are needed to successfully construct a network.
Network Interface Cards
NETWORK INTERFACE CARD (NIC)- is required by every computer connected to a network. An NIC is an expansion card that fits into an expansion slot on a computer or other device so that it can be connected to the network. Most NICs require a network cable connection and have connectors on the card for different cable types. The type of NIC depends on the type of network. NICs package data according to the rules of the network operating system.
SERVER- is a computer that provides services to other computers on the network. Individual computers log on to the server, which gives them access to files, applications or peripheral devices. Types include:
- FILE SERVER- is a controlling computer in a network that stores the programs and data shared by users. These can be retrieved by any node that has access rights.
- PRINT SERVER- is a computer in a network that controls one or more printers and stores data to be printed. It can be used with or without a file server.
- MAIL SERVER- is a computer in a network that provides email facilities. It stores incoming mail for distribution to users and forwards outgoing mail to appropriate devices.
- WEB SERVER is a computer in a network that provides a connection to the Internet. All Net traffic is directed through it.
Devices used to determine the path between networks include:
- ROUTER- a device that determines where to send data packets between at least two networks. Its decision is based upon its current understanding of the networks. A router maintains a table of the available routes and their conditions. It uses this together with distance and cost algorithms to determine the best route for a given data packet. Data packets often travel through a number of network and routers before arriving at their destination.
- SWITCH- a device that directs data packets along a path. May include the function f a router although switches are a faster and simpler mechanism, as they don’t maintain a knowledge of the networks. A switch is not always required as many LANs are organised so each node inspects each data packet.
The actual interconnection between networks is achieved using a:
- BRIDGE- a combination of hardware and software to link to similar networks. Often connects LANs that use the same protocol such as Ethernet. A bridge examines each data packet on a LAN and forwards any data packets addressed to a connected LAN. Bridges are faster than routers because they connect networks using the same protocol.
- GATEWAY- a combination of hardware and software to link two different types of networks. This usually involves converting different protocols.
REPEATER- is used to rebuild a fading signal (caused by long distances or electromagnetic field interference) to its original strength and shape before transmitting it onwards. It ensures data is received as it was sent. A network repeater is used in a LAN to connect network segments. They are less intelligent than a bridge or gateway.
HUB- is a central connecting device in a network. Data arrives at the hub from one or more devices and is forwarded out using just one cable. A hub can include a router. Most were originally passive (data simply passed through without change). Intelligent hubs are more frequently used today. These contain a CPU and network operating system, which allows them to perform some server functions.
- WIRE TRANSMISSION transfers the data through wires and cables, which must be, protected from damage, take up space and can be difficult to install. However wire transmission can carry large amounts of data with little interference from other signals. Two types of transmission are used. Baseband networks use the entire capacity of the cable to transmit only one signal at a time. Broadband networks divide the cable so that several signals can be transmitted at once. Types include:
- TWISTED-PAIR consists of two thin copper wires twisted to form a spiral. This reduces the amount of interference from other cabling. Two main types are unshielded twisted-pair (UTP) which is the most common and shielded twisted-pair, which is used, in ‘noisy’ environments where its shield protects from excessive electromagnetic interference. Twisted-pair is slowest medium with a bandwidth up to 60Kbps.
- COAXIAL CABLE consists of a single copper wire surrounded by an insulator, grounded shielding and an outer insulator. Shielding allows data to be transmitted with little distortion. Commonly used over distances less than a few kilometres. Bandwidth is 10Mbps.
- FIBRE-OPTIC CABLE uses a small laser of light to carry data in small glass fibres free from electromagnetic interference, securely and at high speeds without errors. These are replacing conventional copper-wire cables. Bandwidth is in excess of 400Mbps where a single strand can carry thousands of phone conversations. However it is expensive.
- WIRELESS TRANSMISSION moves the data through air and space without the need for a fixed physical connection between source and destination e.g. radio. Wireless LANs use radio waves, not cables. Wireless LANs are not popular due to problems in maintaining signal quality and concerns about electromagnetic radiation. Wireless transmission involves:
- MICROWAVE is a high frequency radio signal sent through space in a straight line from one antenna to another. Antennas are placed on tall buildings or mountaintops to continue transmission over long distances. Microwave is faster than phone lines or coaxial and even though it is reasonably error free, weather conditions and objects can obstruct the signal and affect transmission.
- SATELLITE. These are specialised transmitters and receivers that are launched by a rocket and placed in orbit around earth. A signal is sent from one ground station to the satellite, which receives and retransmits it to another ground station. Each ground station uses a satellite dish to send and receive. Satellites can transmits large amounts of data over long distances at great speeds. There are hundreds currently operating and used for weather forecasting, television broadcasting, and radio and Internet communications.
- MOBILE PHONES transmit data to a grid of cellular stations, which are linked to the wireless transmission telephone network. Mobiles use radio waves to communicate with the cellular station. They are a portable device, yet monthly fees are higher than those for a normal phone in most countries.
NETWORK SOFTWARE must be installed on each computer in a network. This software contains the ‘rules’ for communication and determines how the network devices send and receive data. Network software is organised by a network administrator.
The Role of the Network Administrator
NETWORK ADMINISTRATOR- is a person who manages a network within an organisation. Their responsibilities include network security, installing new applications, distributing software upgrades, monitoring daily activity, enforcing licensing agreements, developing a storage system and providing routine backups. These are completed using the network operating system.
NETWORK OPERATING SYSTEM (NOS)- is an operating system that is designed primarily to support computers connected to a LAN. Examples include Microsoft’s Windows NT and Novell’s Netware. One part of the NOS resides in each node and another resides in the server. It controls the flow of data between the network devices and requests for data, organises messages from nodes until the network is ready to process each message. Tasks include:
- ADMINISTRATION- adds, removes and organises users, installs hardware devices and software applications, and carries out maintenance operations such as backup.
- FILE MANAGEMENT- gives users access to remote hard disks on the server and provides a file system and the ability to manage a network directory.
- APPLICATIONS- handles requests from users to share data and applications.
- RESOURCE MANAGEMENT- allows network devices to be shared, assigns users to printers, and orders print jobs.
- SECURITY- monitors and restricts access to network resources.
LOGON is the procedure used to gain access to the network. The user is identified by a user ID and password. The ID usually conforms to a limited length and the password often must contain one digit. The password is a security measure and must not be readily available or easily guessed and must be kept secure. The password file should be encrypted and protected from unauthorised access. Network systems may require users to frequently change passwords as a security measure. The logon procedure usually allows the user two or three attempts to enter the correct ID and password. Mistakes can occur in typing or the communication link. After logging on the user is given access to only those features authorised by the network administrator. The correct logoff procedure should always be carried out to clear the communication line for another user.
The Internet, Intranets and Extranets
INTRANET- is a private network that uses a similar interface to the Web. It usually has a connection to the Internet and consists of many interlinked LANs. The main purpose of an intranet is to share information (e.g. staff news, policies) and computing resources among the employees of and organisation. When access to the Net is provided it is through firewalls.
FIREWALL- monitors the flow of data in both directions to maintain the security of the organisation.
EXTRANET- is an intranet that is accessible to customers, suppliers or others outside the organisation. Provides such information as product descriptions, answers to frequently asked questions, warranties and how to contact customer service.
Other Information Processes
COLLECTING data for a communication system involves generating the data to be transmitted. Collecting data involves a range of collection devices to gather different types of data. The choice of device depends on the application and the type of data to be transmitted. Some devices include:
- ATM terminals for electronic banking
- EFTPOS terminals for a retail store
- telephones for voice mail
- keyboards for email
- video cameras for a surveillance system.
PROCESSING of data in a communication system is the manipulation of the data. After collection the data must be converted into a form for transmission. This involves encoding and decoding: • ENCODING involves converting data from its original form into another form for transmission. • DECODING converts the data from the form used for transmission back into its original form.
The type of encoding or decoding depends on whether the original data is in analog or digital form:
• ANALOG DATA is represented by using continuous variable physical quantities such as voltages. Most natural events in the real world are therefore in analog form. Sounds, images and video are in analog form. Analog signals are pulses, usually electrical or optical, in the form of a continuous wave.
• DIGITAL DATA is represented in the form of digits or numbers. IT works with data in digital form. Digital signals are represented using a series of 0s and 1s.
Encoding and Decoding Methods
The form of the data and the transmission signal affect the quality of the data received and the cost of transmission. The quality of analog data depends on maintaining the exact wave as it moves through wire or space. It is corrupted there is no way of regenerating the wave. It is possible to regenerate digital data because it only involves distinguishing between a 0 and a 1. There are four encoding and decoding possibilities in transmission:
- ANALOG DATA TO ANALOG SIGNAL. The wave shape of the data is encoded into the signal e.g. a telephone.
- DIGITAL DATA TO ANALOG SIGNAL. A series of 0s and 1s is encoded into a continuous wave e.g. a modem modulates (encodes) digital data from a computer into analog signals for a phone line. When this is received by another modem it demodulates (decodes) it back to digital data.
- DIGITAL DATA TO DIGITAL SIGNAL. A series of 0s and 1s is transmitted by sending it through a channel as a series of on and off pulses e.g. a LAN where the computer or a peripheral devices encodes the data. Low error rate.
- ANALOG DATA TO DIGITAL SIGNAL. The wave shape of the data is encoded into a series of 0sand 1s e.g. TV. This is called digitising. Images are digitised by scanners using a process called sampling.
CLIENT-SERVER ARCHITECTURE describes the software relationships between the client (user) and the server. A client sends a request to the server according to an agreed protocol and the server responds. It provides a convenient way to interconnect programs that are distributed across different locations in a network. Most business applications and the Internet use client-server architecture. The Web browser is a client program that requests services from a Web server to complete the request.
DISPLAYING is the presentation of information in the form of text, images, audio, video or numbers. A range of software and hardware combinations are used including:
- TELEPHONE- displays audio information. A phone contains a transmitter that converts sound into a signal suitable for the transmission medium and a receiver to convert it back to sound. A phone also displays voice mail messages.
- EFTPOS TERMINAL- displays information about EFTPOS transactions. The terminal contains a screen to display the name and price of the product being purchased. When the customer’s bank is contacted the terminal displays the approval is funds are available. It then provides a receipt.
Issues Related to Communication Systems
Issues Related to Messaging Systems
MESSAGING SYSTEMS have improved communication but raised issues:
- SOCIAL CONTEXT. Ideas delivered by messaging systems appear less forceful and caring than those delivered personally. MSs have difficulty when communication depends on expression of feelings.
- DANGER OF MISINTERPRETATION. Communication often depends on the context inflection on a person’s voice and body language. Misinterpretation can occur with email, or phone etc.
- POWER RELATIONSHIPS. MSs may change the relationship between people in an organisation. The normal communication through middle management is affected.
- PRIVACY AND CONFIDENTIALITY. A characteristic of MSs is that the messages are stored (e.g. email messages are stored on servers and can be accessed by the service providers) therefore there is no guarantee of privacy and confidentiality.
- ELECTRONIC JUNK MAIL. Unwanted mail is a problem for MSs. People can send a message to one or thousands of people (spamming) very easily. If a person receives hundreds per day it wastes time and prohibiting this practice would be difficult and compromise free society.
- INFORMATION OVERLOAD. This term refers to the enormous amount of information that people have to absorb. MSs are a source of information. The large amount of email received by some people has increased their workload and stress levels. There is often an expectation that people will reply quickly to an email than to a letter written down by someone else.
Issues Related to the Internet
INTERNET TRADING or e-commerce, is increasing at a staggering rate to meet the needs of consumers. The Net provides significant advantages for consumers such as more information about products and services, global shopping and increased competition resulting in lower prices. Some implications include:
- TAXATION. Present governments have been unable to tax Internet transactions. This increased Net business will reduce the money governments receive from their goods and services.
- EMPLOYMENT RAMIFICATIONS. The increase in Net trading requires more people to be employed in the IT industry and may result in fewer shop fronts and people required to run them.
- NATURE OF BUSINESS. Traditional businesses that provide interaction opportunities are being challenged. People can complete some of their business at home without travelling.
- TRADE BARRIERS. The developments in communication technology have made trade barriers irrelevant. The issue of where one country ends and another begins is open to question. People are buying and selling on the Net with little thought given to such issues.
CENSORSHIP is one of the most controversial issues to have arisen with the Net as it provides access to a large amount of offensive material especially to children. Some believe offensive material should be banned while others believe this would compromise free society. There have been unsuccessful attempts to censor material on the Net by governments and law enforcement bodies worldwide. The Internet Industry Association (IIA) represents Australian ISPs. It has released a code that deals with censorship of online content. The code requires ISPs to remove offensive content from their servers and to block access to classified material on overseas sites. The federal government has passed a law requiring ISPs to subscribe to this code. The difficulty with enforcing censorship is the enormous number of Web sites and the thousands of new ones published daily. Monitoring on a global basis is impossible. Clearly a multinational agreement is necessary however this would be difficult to obtain and regulate. The prime responsibility of preventing children from offensive material lies with the parents and carers.
The Internet now provides radio and video:
RADIO is being broadcasted by Web sites from around the world. These stations cater for a range of tastes.
VIDEO is also being provided online. It is replacing videotapes and other media. It allows organisations to create unlimited video channels, which are used for sales, training, communication and other purposes. Video on the Net saves time, reduces costs and provides global ability viewing. The size and quality of the video is currently less than TV broadcast but will improve with advances in technology and increased bandwidth.
Issues Related to Electronic Banking
INTERNET BANKING has raised issues:
- SECURITY. All banks are determined to make their online services secure from interference and customer details secure. Data encryption is used to secure data transfer between computers.
- CHANGING NATURE OF WORK. People working for the bank do not carry out the services for the online bank. Banks require more people with IT skills and fewer with banking skills.
- BRANCH CLOSURES AND JOB LOSSES. With many people using Net banking, ATMs and EFTPOS there is less need to access the facilities provided by a branch resulting in closures and job losses.
Working from Home
TELECOMMUTING is working from home and electronically communicating with the office. It is expected to increase. Factors that will affect this include availability of bandwidth, the perceived value of telecommuting, and the opportunities to work collaboratively across distances. The Internet has allowed a new type of organisation to develop whose employees work almost entirely through telecommunication with an occasional face-to-face meeting. The main advantages of telecommuting include a greater flexibility in work hours, saving money on food, transport and clothing, and saving time. It also benefits people who are physically impaired or required to look after children. The employer saves time on overheads such as office space and furniture. Disadvantages include a lack or missing of social and professional contact offered by an external workplace, loneliness and isolation. Telecommuting can also blur the line between work and home life. The home is no longer a place where the pressures of work can be forgotten and work may be interrupted by domestic chores.
A virtual organisation or company is one whose members are geographically apart, usually working by computer e-mail and groupware while appearing to others to be a single, unified organization with a real physical location. Groupware refers to programs that help people work together collectively while located remotely from each other.
Virtual organisations are organisations structured around the communication system. The components of an organisation are linked using information technology rather than by a defined space such as an office