Computer Communication Essay
Section 1 Introduction 1. 1 COMMUNICATIONS Computer communications is the process of sharing data, programs, and information between two or more computers. We have discussed numerous applications that depend on communication systems, including: • E-mail – Provides a fast, efficient alternative to traditional mail by sending and receiving electronic documents. • Instant messaging – Supports direct, “live” electronic communication between two or more friends or buddies. • Internet telephone – provides a very low cost alternative to long-distance telephone calls using electronic voice delivery. Electronic commerce – buying and selling goods electronically In this chapter, we will focus on the communication systems that support these many other applications.
Connectivity, the wireless revolution, and communication systems are key concepts and technologies for the 21st century. 1. 2 NETWORKING Networking is a concept related using computer networks to link people and resources. For example, networking means that you can connect your microcomputer by telephone or other telecommunications links to other computers and information sources almost anywhere.
With this connection, you are linked to the world of larger computers and mainframes and their extensive information resources.
Thus, becoming computer competent and knowledgeable becomes a matter of knowing not only about connectivity through networks to microcomputers, but also about larger computer systems and their information resources. A computer network is a communication system that connects two or more computers so that they can exchange information and share resources. Networks can be set up in different arrangements to suit user’s needs 1. 3 TERMS
There are a number of specialized terms that describe computer networks These terms include: • Node- any device is connected to a network. It could be a computer, printer, or data storage device • Client – a node that shares resources with other nodes. Dedicated servers specialize in performing specific tasks. Depending on the specific task, they may be called an application server, communication server, database server, file server, printer server or Web server. • Server – a node that shares resources with other nodes. Dedicated servers specialize in performing specific tasks.
Depending on the specific task, they may be called an application server, communication server, database server, file server, printer server or web server. • Hub- the center or central node for other nodes. This device can be a server or simply a connection point for cables from other nodes. • Network operating systems (NOS)- control and coordinate the activities of all computers and other devices on a network. These activities include electronic communication and the sharing of information and resources. • Distributed processing – a system in which computing power is locate and shared at different locations.
This type of system is common in decentralized organization where divisional offices have their own computer systems. The computer systems in the divisional offices are networked to the organizations main or centralized computer. • Host computer – a large centralized computer, usually a minicomputer or a main frame. • Network manager – a computer specialist, also known as network administrator, responsible for efficient network operations and implementation of new networks. A network may consist only of microcomputers, or it may integrate micro-computers or other devices with larger computers.
Networks can be controlled by all nodes working together equally or by specialized nodes coordinating and supplying all resources. Networks may be simple or complex, self-contained or dispersed over a large geographical area. 1. 4 LOCAL AREA NETWORKS Networks with nodes that are in close physical proximity – within the same building, for instance – are called local area networks (LANs). Typically LANs span distances less than a mile and are owned and operated by individual organizations. LANs are widely used by colleges, universities and other types of organizations to link microcomputers and to share printers and other resources.
The LAN represented is a typical arrangement and provides two benefits are Economy and flexibility. People can share costly equipment. For instance, the four micro computers share the laser printer and the file server, which are expensive pieces of hardware, Other equipment or nods may also be added to the LAN – for instance, more microcomputers a mainframe computer or optical disk storage devices. Additional t he network gateway is a device that allows one LAN to be linked to other LANs or to a larger network. For example, the LAN of one office group may be connected to the LAN of another office group.
There are a variety of different standards or ways in which nodes can be connected to one another and ways in which their communications are controlled in a LAN. The most common standard is known as Ethernet. LANs using this standard are sometimes referred to as Ethernet LANs HOME NETWORKS While LANs have been widely used within organizations for years, they are now being commonly used by individuals in their homes and apartments. These LANs called home networks allow different computers to share resources including a common Internet connection.
Computers can be connected in a variety of ways including electrical wiring, telephone wiring and special cables. One of the simplest ways however is without cables or wireless. A wireless local area network is typically referred to as wireless LAN (WLAN). It uses radio frequencies to connect computers and other devices. All communications pass through the network’s centrally located wireless receiver or base station. This receiver interprets incoming radio frequencies and routes communications to the appropriate devices. METROPOLITAN AREA NETWORKS/REGIONAL NETWORK
The next step up from the LAN is the MAN- the metropolitan area network. Also known as MANs span distances up to 100 miles. These networks are frequently used as links between office buildings that are located throughout a city. Unlike a LAN, a MAN is typically not owned by a single organization. Rather, it is either owned by a group of organizations who jointly own and operate the network or by a single network service provider who provides network services for a fee. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones. WIDE AREA NETWORKS
Wide area networks (WANs) are countrywide and worldwide networks. These networks provide access to regional service (MAN) providers and typically span distances greater than 100 miles. They use microwave relays and satellites to reach users over long distances – for example from Los Angeles to Paris of course, the widest of all WANs is the Internet, which spans the entire globe. The primary difference between a LAN, MAN and WAN is the geographical range. Each may have various combinations of hardware, such as micro-computers, minicomputers, mainframes and various peripheral devices.
Network architecture describes how a network is arranged and how resources are coordinated and shared. It encompasses a variety of different configurations describe the physical arrangement of the network. Network strategies define how information and resources are shared. 1. 5 CONFIGURATIONS A network can be arranged or configured in several different ways. This arrangement is called the networks’ topology. The four principal network topologies are start, bus, ring, and hierarchical. In a star network, a number of small computers or peripheral devices are linked to a central unit.
The central unit is the network hub and is typically a host computer or file server. All communications pass through this central unit. Control is maintained by polling. That is each connecting device is asked (“polled”) whether it has a message to send. Each device is then in turn allowed to send its message. 1. 6 COMMUNICATION SYSTEMS Communication systems are electronic systems that transmit data from one location to another. Whether wired or wireless every communication system have four basic elements. • Sending and receiving devices. These are often a computer or specialized communication device.
They originate (send) as well as accept (receive) messages in the form of data, information, and or instructions. • Communication channel. This is the actual connecting or transmission medium that carries the message that carries the message. This medium can be a physical wire or cable or it can be wireless. • Connection devices. These devices, also known as communication devices, act as an interface between the sending and receiving devices and the communication channel. They convert outgoing messages into a form and a format that can travel across the communication channel.
They also reverse the process for incoming messages. • Data transmission specifications. These are rules and procedures that coordinate the sending and receiving devices by precisely defining how the message will be sent across the communication channel. For example, if you wanted to send an e-mail to friend, you could create and send the message using your computer, the sending device. Your modem, a connection device, would modify and format the message so that it could travel efficiently across communication channels, such as telephone lines.
The specifics describing how the message is modified, reformatted, and sent would reform it be described in the data transmission specifications. After your message traveled across the channel, the channel, the receiver’s modem, a connection device, would reform it so that it could be displayed on your friend’s computer, on your friend’s computer, the receiving device. (Note: This example presents the basics communication system elements involved in sending e-mail. It does not and is not intended to demonstrate all the specific steps and equipment involved in an e-mail delivery system)
COMMUNICATION CHANNELS Communication channels are an essential element of every communication system. These channels actually carry the data from one computer to another. There are two categories of communication channels. One category connects sending and receiving devices by providing a physical connection, such as wire or cable. The other category is wireless. PHYSICAL CONNECTION Physical connections use a solid medium to connect sending and receiving devices. These connections include telephone lines (twisted pair), coaxial cable, and fiber-optic cable. Telephone lines you see strung on poles consist of twisted pair cable, which is made up of hundreds of copper wires. A single twisted pair culminates in a wall jack into which you can plug your phone and computer. Telephone lines have been the standard transmission medium for years for both voice and data. However, they are now being phased out by more technically advanced and reliable media. • Coaxial cable, a high frequency transmission cable, replaces the multiple wires of telephone lines with a single solid-copper core.
In terms of the number of telephone connections, a coaxial cable has over 80 times the transmission capacity of twisted pair. Coaxial cable is used to deliver television signals as well as to connect computers in a network. • Fiber-optic cable – transmits data as pulses of light through tiny tubes of grass. In terms of the number of telephone connections fiber optic cable has over 26,000 times the transmission capacity of twisted pair cable. Compared to coaxial cable they are lighter and more reliable at transmitting data.
They transmit information using beams of light at light speed instead of pulses of electricity, making them far faster than copper cable. Fiber optic cable is rapidly replacing twisted pair cable telephone lines. WIRELESS CONNECTIONS Wireless connections do not use solid substance to connect sending and receiving devices. Rather, they use the air itself. Primary technologies used for wireless connections:- • Infrared- Uses infrared light waves to communicate over short distances. It is sometimes referred to as line of sight communication because the light can only travel in a straight line.
This requires that sending and receiving devices must in clear view of one another without any obstruction blocking that view. One of the most common applications is to transfer data and information from a portable device such as a note book computer or PDA to a desk top computer. • Broadcast radio- Communication uses special sending and receiving towers called transceivers, which send and receive radio signals from wireless signals. For example cellular telephones and many web enabled devices use broadcast radio to place telephone calls and/or to connect to the internet.
Some end uses and connect their notebook or handheld computers to a cellular telephone to access the web from remote locations. Most of this web-enabled device follows a standard known as 802. 11; this wireless standard is widely used to connect computers to each other and to the internet. • Microwave communication uses high-frequency radio waves. Like infrared, microwave communications provide line of sight communication because microwaves travel in a straight line. Because the waves cannot bend with the curvature of the earth, they can be transmitted only over relatively short distances.
Thus microwave is a good medium for sending data between buildings in a city or a large college campus. For longer distances, the waves must be relayed by means of microwaves stations with microwave dishes or antennas. These stations can be installed on towers, high buildings, and mountaintops. • Blue tooth is a short range wireless communication standard that uses microwaves to transmit data over short distances of up to approximately 33 feet. Unlike traditional microwaves. Bluetooth does not require line of sight communication.
Rather it uses radio waves that can pass through nearby walls and other nonmetal barriers. It is anticipated that within the next few years, this technology will be widely used to connect a variety of different communication devices. • Satellite communication uses satellite orbiting about 22,000 miles above the earth as microwave relay stations. Many of these are offered by Intelsat, the International Telecommunications satellite Consortium, which is owned by 114 governments and forms a worldwide communications system. Satellites rotate at a precise point and speed above the earth.
They can amplify and relay microwave signals from one transmitter on the ground to another. Satellite can be used to send and receive large volumes of data from a satellite. Downlink refers to receiving data from satellite. The major drawback to satellite communication is that bad weather can sometimes interrupt the flow of data. One of the most interesting applications of satellite communication for global positioning. A network of satellites owned and managed by the Defense Department continuously sends location information to earth.
Global positioning system (GPS) devices use that information to uniquely determine the geographic location of the device. Available in some automobiles to provide navigational support, these systems are often mounted into the dash with a monitor to display maps and speakers to provide spoken directions. |Channel Description | |Twisted pair Copper wire, standard voice telephone line | |Coaxial cable Solid copper core, more than 80 times the capacity of twisted pair. |Fiber-optic Light carries data, more than 26,000 times the capacity of twisted pair. | |Infrared Infrared light travels in a straight line | |Broadcast radio Radio waves used by cellular telephones and other wireless devices | |Microwave High-frequency radio waves, travels in straight line throughout the air. | |Satellite Microwave relay station in the sky, used by GPS devices. CONNECTED DEVICES A great deal of computer communication takes place over telephone lines. However, because the telephone was originally designed for voice transmission, telephones typically send and receive analog signals, which are continuous electronics waves. Computers, in contrast, send and receive digital signals. MODEMS The word modem is short for modulator-demodulator. Modulation is the name of the process of converting from analog digital. The modem enables digital microcomputers to communicate across analog telephone lines.
This communication includes both voice and data communications. The speed with which modems transmit data varies. This speed, called transfer speed or transfer rate, is typically measured in bits of per second (bps). The higher the speed, the faster you can send and receive information. These are four basic types of modems: external, internal, PC Card and wireless. • The external modem stands apart from the computer and typically is connected by a cable to the computer’s serial port. Another cable connects the modem to the telephone wall jack. The internal modem consists of a plug-in circuit board inside the system unit. A telephone cable connects the modem to the telephone wall jack. • The PC card modem is a credit card size expansion board that is inserted into portable computers. A telephone cables connects the modem to the telephone wall jack. • A wireless modem may be internal, external, or a pc card. Unlike the other modems, it does not use cables. Instead, wireless modems send and receive through the air. CONNECTION SERVICE
Standard telephone lines and conventional modems provides what is called a dial-up service. Although still the most popular type of connection service. Although still the most popular type of connection service, dial-up service is quite slow, and many users find it inadequate to meet their communication needs. For years, large corporations have been leasing special high-speed lines from telephone companies. These lines-known as T1, T2, T3, and T4 lines- support all digital communications, do not require conventional modems, and provide very high capacity.
Unfortunately this type of connection is very expensive. And cost several thousand dollars. While the special high-speed lines are too costly for most individuals, there are affordable connections that provide significantly higher capacity than standard dial-up service. These include DSL, cable and satellite. For comparison of typical user connection • Digital subscriber line (DSL) – uses existing telephone lines to provide high-speed connections. ADSL (asymmetric digital subscriber line) is one of the most widely used types of DSL.
This technology is widely available in most areas. • Cable modems use existing television cables to provide high-speed connections as fast as a T1 or DSL connection, at a lower cost. Although cable connections reach 90 percent of the homes in America, all cable companies do not support cable modems. Industry observers, however, predict 100 percent availability within the next few years. • Satellite/air connection services use satellites and the air download (down link) or send data to users at a rate seven times faster than dial-up connections.
While older satellite services could not upload (uplink) or send data to satellites and had to rely on slow dial-up connections, newer two-way satellite connections are now available. While slower than DSL and cable modems, satellite /air connections are available almost anywhere that a satellite-receiving disk can be aimed at the southern skies. Several factors affect how data is transmitted. These factors include band width and protocols BANDWIDTH
Bandwidth is a measurement of the width or capacity of the communication channel, effectively; it means how much information can move across the communication channel in a given amount of time. There are three categories of bandwidth. • Voice band, also known as voice grade and low bandwidth, is used for standard modems and dial-up service uses this bandwidth. While effective for transmitting text documents, it is slow for many types of transmission including high-quality audio and video. Typical speeds are 56 to 96 kbps. Medium band is the bandwidth used in special leased lines to connect minicomputers and mainframes as well as to transmit data over long distances. Unlike voice band and broadband, medium band is not typically used by individuals • Broadband is the bandwidth used for high-capacity transmissions. Micro-computers with DSL, cable, and satellite connections as well as other more specialized high-speed devices use this bandwidth. It is capable of effectively meeting most of today’s communication needs, including transmitting high-quality audio and video.
Speeds are typically 1. 5mbps, although much higher speeds are possible. PROTOCOLS For data transmission to be successful, sending and receiving devices must follow a set of communication rules for the exchange of information. These rules for exchanging data between computers are known as protocols. The standard protocol for the Internet is TCP/IP (transmission control protocol/Internet protocol). The essential features of this protocol involve 1) Identification sending and receiving devices and (2) reformatting information for transmission across the Internet. Identification: Every computer on the Internet has a unique numeric address called an IP address (Internet Protocol address). The internet uses IP addresses to deliver e-mail and to locate Web sites. Because these numeric addresses are difficult for people to remember and use, a system was developed to automatically convert text- based addresses to numeric IP addresses. • This system uses a domain name server (DNS) that converts text-based addresses to IP addresses, For example, whenever you enter a URL, say www. mcgraw-hill. com a DNS converts this to an IP address before a connection can be made. Reformatting – Information sent or transmitted across the Internet usually travels through numerous interconnected networks. Before the message is sent, it is reformatted or broken down into small parts called packets. Each packet is then sent separately over the Internet, possibly traveling different routes to one common destination. AT the receiving end, the packets are reassembled into the correct order. |NETWORKS | Section 2 BACKGROUND
Technological innovations in networking are taking place at a rapid pace. Only a decade ago, the narrowband telephone modem was essentially the only Internet access technology available. Since then, a broad range of broadband techniques have been developed: DSL, cable, but also wireless technologies that will ultimately provide high-quality access via mobile phones. This is only the beginning: It is envisaged that in the near future virtually all electronic devices will be assigned an Internet address, and it Cannot be predicted what other innovations will bring.
Section 3 EMERGING 3. 1 THE WIRELESS EMERGING The single most dramatic change in connectivity and communications in the past five years has been the wide spread use of mobile or wireless telephones. This wireless technology allow individual to stay connected with one another from almost anywhere at any time. While this wireless technology was originally extended from voice communication it is now becoming widely used to support all kinds of communication especially computer communication.
In addition recently released wireless technology promise to allow a wide variety of nearby devices to communicate with one another without any physical connection. You can share high speed printer, share data file and collaborate on working document with a nearby co-worker without having your computer connected to cable or telephone wireless communication. Other wireless technology allow individual to connect to the internet and share information from almost everywhere in the world. Section 4 Conclusion
Communication has extended our uses for the microcomputer enormously. The mobile telephone and other wireless technologies are revolutionizing how we use computers today. You can connect your microcomputer to the other people micro computer, to the internet and to other larger computer located throughout the world. The results are increased productivity – for you as individual and for the groups and organizations of which are a member. Communication systems are the electronic systems that transmit data over communication lines from one location to another.
You might use a wearable computer and a satellite communication system to access the internet from almost anywhere. You might work for an organization whose computer system is spread throughout a building, or even throughout the country or world. Or you might use telecommunication lines-telephone lines-to tap into information located in an outside data bank. You could then transmit it to your microcomputer for your own working and analysis. You can even set up a network in your home or apartment using existing telephone lines. Or you can set up a wireless network.
Then you can share files, use one internet connection, and play interactive games with others in your home. Competent end users need to understand the concept of connectivity, the impact of the wireless revolution, and the Clements of a communication system. Additionally, they need to understand the basics of communications channel channels connection devices, data transmission, networks, networks architectures, and network. REFERENCE Communication and Networks By Oleary ———————– DATA TRANSMISSION Bandwidth measures capacity of communication channel, Protocols are rules for exchanging data.
Computer networks connect computers, A node may be a client, hub, or host computer, Node, client, hub, NIC, NOS, distributed processing, host computer, and network manager are specialized network terms Network architecture describes how a computer network is configured and what strategies are employed. Configurations include star, bus, ring and hierarchical.. Strategies include terminal, client-server and peer-to peer. NETWORK ARCHITECTURE Communications networks differ in geographical size. LANs, including home networks, connect nearby devices; MANs connect buildings in a city. WANs are countrywide and worldwide networks. NETWORK TYPES