Communication System

“Communication Systems” are electronic systems that transmit data from one location to another. Every communication system has four basic elements which are as follows:

1) Sending and receiving devices: These may be computers or specialized communication devices.

2) Communication channel: This is the actual medium that carries the message. It may be a physical cable or it can be wireless.

3) Connection devices: These act as the interface between the sending and receiving devices and the communication channel. They convert messages into packets that can travel across the communication channel.

4) Data transmission specifications: These are procedures that coordinate the sending and receiving devices by defining the way in which the messages will be sent across the communication channel.

For example, when you send an e-mail, your computer would be the “sending device”. Your modem would be the “connection device” which would modify the message so that it could travel efficiently across the “communication channel” which is the telephone line. How the message is modified and sent would be described in the “data transmission specifications”. At the receiving end, another modem modifies it once again so that it can be displayed on the “receiving device” which would be another computer.

Communication Channels: You know that communication channels are an essential element of every communication system. There are two categories of communication channels. One category connects sending and receiving devices by providing a physical connection such as a wire or cable. The other category is wireless.

“Physical Connections” use a solid medium to connect sending and receiving devices. They include telephone lines, coaxial cable and fiber-optic cable.

Telephone lines 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.

Coaxial cable is a high-frequency transmission cable and consists of a single solid-copper core. 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 glass. Compared to coaxial cable, fiber-optic cable is lighter and more reliable at transmitting data as compared to coaxial cable.

Wireless Connections: Wireless connections use air to connect sending and receiving devices. They do not use any solid substances like wires and cables. Primary technologies used for wireless connections are infrared, broadcast radio, microwave and satellite.

“Infrared” uses infrared light waves to communicate over short distances. Since the light waves travel in a straight line, sending and receiving devices must be in clear view of one another. One of the most common applications is to transfer data from a portable device such as a notebook computer or PDA to a desktop computer.

“Broadcast radio” uses radio signals to communicate with wireless devices. Cellular telephones and many Web-enabled devices use broadcast radio to place telephone calls and to connect to the Internet. Some users connect their notebook or handheld computers to a cellular telephone to access the Web. Most Web-enabled devices follow a standard known as “Wi-Fi (i.e. wireless fidelity)”.

“Microwave” communication uses high-frequency radio waves. Microwaves travel in a straight line and therefore can be transmitted across relatively short distances. Microwave is a good medium for sending data between buildings in a city or a large college campus. For longer distances, the waves are relayed by microwave stations with microwave dishes or antennas. “Bluetooth” is a short-range wireless standard that uses microwaves.

“Bluetooth” is the name of a new technology that promises to change the way we use machines. We see a large number of cables in our offices, homes and everywhere else. We often have a hard time trying to figure out which cable needs to go where. Bluetooth is essentially a cable-replacement technology which tries to solve this problem.

Conceived initially by Ericsson, Bluetooth is a small, cheap radio chip to be plugged into computers, printers, mobile phones, etc. It creates a wireless personal area network (PAN) and provides a way to connect and exchange information between two devices over distances of about 30 feet. It aims to simplify data synchronization between Internet devices and other computers.

“Satellite” communication uses satellites orbiting above the earth as microwave relay stations. Satellites can amplify and relay microwave signals from one transmitter on the ground to another. They can be used to send and receive large volumes of data.

The “Global Positioning System (GPS)” is a network of 24 satellites developed by the United States Department of Defense which continually sends location information to the earth. GPS devices use that information to determine the geographical location of the device. GPS devices provide navigational support in some automobiles. They are sometimes mounted with a monitor to display maps and with speakers to provide spoken directions to the driver.

Let us look at a summary of communication channels.

Connection devices: We have seen that connection devices act as the interface between the sending and receiving devices and the communication channel. A great deal of computer communication takes place over telephone lines. Telephones send and receive analog signals which are continuous electronic waves. Computers, on the other hand, send and receive digital signals which are binary signals.

Modems: The word “modem” stands for modulator-demodulator. “Modulation” is the process of converting digital signals to analog form. “Demodulation” is the process of converting analog signals to digital form. The modem thus enables digital microcomputers to communicate across analog telephone lines.

The speed at which modems transfer data is called “transfer rate”. This is typically measured in “bits per second (bps)”. The various units to measure transfer speed are shown in the displayed chart.

There are four basic types of modems: external, internal, PC Card and wireless.

The “external modem” stands outside the computer and 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-sized expansion board that is inserted into portable computers. A telephone cable connects the modem to the telephone wall jack.

A “wireless modem” may be internal, external or a PC Card. Unlike other modems, it does not use cables. It sends and receives signals through the air.

Connection Service: Standard telephone lines and conventional modems provide a “dial-up service” which is quite slow. Large corporations lease special high-speed lines from telephone companies which provide very high capacity. These lines are known as T1, T2, T3 and T4 lines and do not require conventional modems.

While special high-speed lines are very expensive, there are other affordable connections which provide significantly higher capacity than a dial-up service. These include DSL, cable modems, satellite and cellular services.

“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.

“Cable modems” use existing telephone cables to provide high-speed connections.

Satellite/air connection services use satellites and the air to send data to users at faster rates than dial-up connections.

“Cellular services” are used by mobile devices and laptops. These devices use “3G cellular networks” to download data from the Internet.

Let us compare typical user connection costs and speeds.

Data Transmission: Several factors such as bandwidth and protocols affect how data is transmitted.

Bandwidth: This is a measurement of the width or capacity of the communication channel. It indicates the volume of information that can move across the communication channel in a given time. Audio and video files require a wider bandwidth than text documents to be transmitted. There are three categories of bandwidth.

“Voiceband” is used for standard telephone communication. Microcomputers with standard modems and dial-up service use this bandwidth. This is also known as low bandwidth.

“Medium band” is the bandwidth used in special leased lines to connect minicomputers and mainframes as well as to transmit data over long distances.

“Broadband” is the bandwidth used for high capacity transmissions. Specialized high-speed devices and microcomputers with DSL, cable and satellite connections use this bandwidth.

hese act as the interface between the sending and receiving devices and the communication channel. They convert messages into packets that can travel across the communication channel.

4) Data transmission specifications: These are procedures that coordinate the sending and receiving devices by defining the way in which the messages will be sent across the communication channel.

For example, when you send an e-mail, your computer would be the “sending device”. Your modem would be the “connection device” which would modify the message so that it could travel efficiently across the “communication channel” which is the telephone line. How the message is modified and sent would be described in the “data transmission specifications”. At the receiving end, another modem modifies it once again so that it can be displayed on the “receiving device” which would be another computer.

Communication Channels: You know that communication channels are an essential element of every communication system. There are two categories of communication channels. One category connects sending and receiving devices by providing a physical connection such as a wire or cable. The other category is wireless.

“Physical Connections” use a solid medium to connect sending and receiving devices. They include telephone lines, coaxial cable and fiber-optic cable.

Telephone lines 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.

Coaxial cable is a high-frequency transmission cable and consists of a single solid-copper core. 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 glass. Compared to coaxial cable, fiber-optic cable is lighter and more reliable at transmitting data as compared to coaxial cable.

Wireless Connections: Wireless connections use air to connect sending and receiving devices. They do not use any solid substances like wires and cables. Primary technologies used for wireless connections are infrared, broadcast radio, microwave and satellite.

“Infrared” uses infrared light waves to communicate over short distances. Since the light waves travel in a straight line, sending and receiving devices must be in clear view of one another. One of the most common applications is to transfer data from a portable device such as a notebook computer or PDA to a desktop computer.

“Broadcast radio” uses radio signals to communicate with wireless devices. Cellular telephones and many Web-enabled devices use broadcast radio to place telephone calls and to connect to the Internet. Some users connect their notebook or handheld computers to a cellular telephone to access the Web. Most Web-enabled devices follow a standard known as “Wi-Fi (i.e. wireless fidelity)”.

“Microwave” communication uses high-frequency radio waves. Microwaves travel in a straight line and therefore can be transmitted across relatively short distances. Microwave is a good medium for sending data between buildings in a city or a large college campus. For longer distances, the waves are relayed by microwave stations with microwave dishes or antennas. “Bluetooth” is a short-range wireless standard that uses microwaves.

“Bluetooth” is the name of a new technology that promises to change the way we use machines. We see a large number of cables in our offices, homes and everywhere else. We often have a hard time trying to figure out which cable needs to go where. Bluetooth is essentially a cable-replacement technology which tries to solve this problem.

Conceived initially by Ericsson, Bluetooth is a small, cheap radio chip to be plugged into computers, printers, mobile phones, etc. It creates a wireless personal area network (PAN) and provides a way to connect and exchange information between two devices over distances of about 30 feet. It aims to simplify data synchronization between Internet devices and other computers.

“Satellite” communication uses satellites orbiting above the earth as microwave relay stations. Satellites can amplify and relay microwave signals from one transmitter on the ground to another. They can be used to send and receive large volumes of data.

The “Global Positioning System (GPS)” is a network of 24 satellites developed by the United States Department of Defense which continually sends location information to the earth. GPS devices use that information to determine the geographical location of the device. GPS devices provide navigational support in some automobiles. They are sometimes mounted with a monitor to display maps and with speakers to provide spoken directions to the driver.

Let us look at a summary of communication channels.

Connection devices: We have seen that connection devices act as the interface between the sending and receiving devices and the communication channel. A great deal of computer communication takes place over telephone lines. Telephones send and receive analog signals which are continuous electronic waves. Computers, on the other hand, send and receive digital signals which are binary signals.

Modems: The word “modem” stands for modulator-demodulator. “Modulation” is the process of converting digital signals to analog form. “Demodulation” is the process of converting analog signals to digital form. The modem thus enables digital microcomputers to communicate across analog telephone lines.

The speed at which modems transfer data is called “transfer rate”. This is typically measured in “bits per second (bps)”. The various units to measure transfer speed are shown in the displayed chart.

There are four basic types of modems: external, internal, PC Card and wireless.

The “external modem” stands outside the computer and 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-sized expansion board that is inserted into portable computers. A telephone cable connects the modem to the telephone wall jack.

A “wireless modem” may be internal, external or a PC Card. Unlike other modems, it does not use cables. It sends and receives signals through the air.

Connection Service: Standard telephone lines and conventional modems provide a “dial-up service” which is quite slow. Large corporations lease special high-speed lines from telephone companies which provide very high capacity. These lines are known as T1, T2, T3 and T4 lines and do not require conventional modems.

While special high-speed lines are very expensive, there are other affordable connections which provide significantly higher capacity than a dial-up service. These include DSL, cable modems, satellite and cellular services.

“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.

“Cable modems” use existing telephone cables to provide high-speed connections.

Satellite/air connection services use satellites and the air to send data to users at faster rates than dial-up connections.

“Cellular services” are used by mobile devices and laptops. These devices use “3G cellular networks” to download data from the Internet.

Let us compare typical user connection costs and speeds.

Data Transmission: Several factors such as bandwidth and protocols affect how data is transmitted.

Bandwidth: This is a measurement of the width or capacity of the communication channel. It indicates the volume of information that can move across the communication channel in a given time. Audio and video files require a wider bandwidth than text documents to be transmitted. There are three categories of bandwidth.

“Voiceband” is used for standard telephone communication. Microcomputers with standard modems and dial-up service use this bandwidth. This is also known as low bandwidth.

“Medium band” is the bandwidth used in special leased lines to connect minicomputers and mainframes as well as to transmit data over long distances.

“Broadband” is the bandwidth used for high capacity transmissions. Specialized high-speed devices and microcomputers with DSL, cable and satellite connections use this bandwidth.