COMMUNICATION
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.
● Texting - provides very efficient direct text communication between individuals using short electronic messages.
● Video Conferencing - provides a very-low-cost alternative to long-distance telephone calls using electronic voice and video delivery.
● Electronic commerce - buying and selling goods electronically.
In this Blog, we will focus on the communication systems that support these and many other applications. Connectivity, the wireless revolution, and communication systems are key concepts and technologies for the 21st century,
CONNECTIVITY
Connectivity is a concept related to using computer networks to link people and resources. For example, connectivity means that you can connect your personal computer to other computer and information sources almost anywhere. With this connection, you are linked to the world of larger computers and the Internet. This includes hundreds of thousands of web servers and their extensive information resources. Thus, being able to efficiently and effectively use computers becomes a matter of knowing not only about connectivity through networks to personal computers but also about larger computer systems and their information resources.
THE WIRELESS REVOLUTION
The single most dramatic change in connectivity and communications in the past decade has been the widespread use of mobile devices like smartphones and tablets with wireless Internet connectivity. Students, parents, teachers, businesspeople, and others routinely talk and communicate with these devices. It is estimated that over 1.5 billion smartphones are in use worldwide. This wireless technology allows individuals to stay connected with one another from almost anywhere at any time.
So what's the revolution? While wireless technology was originally used primarily for voice communications, today's mobile computers support email, web access, social networking, and a variety of Internet applications. In addition, wireless technology allows a wide variety of nearby devices to communicate with one another without any physical connection. Wireless communications allows you to share a high-speed printer, share data files, and collaborate on working documents with a nearby co-worker without having your computers connected by cables or telephone. High-speed Internet wireless technology allows individuals to connect to the Internet and share information from almost anywhere in the world. But is it a revolution? Most experts say yes and that the revolution is just beginning.
COMMUNICATION SYSTEMS
Communication systems are electronic systems that transmit data from one location to another. Whether wired or wireless, every communication system has 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.
● Connection devices. These devices act as an interface between the sending and receiving devices and the communication channel. They convert outgoing messages into packets 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.
● Communication channel. This is the actual connecting or transmission medium that carries the message. This medium can be a physical wire or cable, or it can be wireless.
For example, if you wanted to send an e-mail to a 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 be described in the data transmission specifications. After your message traveled across the channel, the receiver's modem, a connection device, would reformat it so that it could be displayed on your friend's computer, the receiving device. (Note: This example presents the basic 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.)
Questions :
Define computer communications and connectivity.
What is the wireless revolution?
Describe the four elements of every communication 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 a wire or cable. The other category is wireless.
PHYSICAL CONNECTIONS
Physical connections use a solid medium to connect sending and receiving devices. These connections include twisted-pair, coaxial, and fiber optic cables.
● Twisted-pair cable consists of pairs of copper wire that are twisted together. Both standard telephone lines and Ethernet cables use twisted pair. Ethernet cables are often used in networks and to connect a variety of components to the system unit.
● 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 glass.The data transmission speeds of fiber optic cables are incredible; recently speeds of petabit per second were measured (a petabit is 1 million 1 gigabits). Compared to coaxial cable, it is lighter, faster, and more reliable at transmitting data, Fiber optic cable is rapidly replacing twisted-pair cable telephone lines,
WIRELESS CONNECTIONS
Wireless connections do not use a solid substance to connect sending and receiving devices. Rather, they move data through the air.
Most wireless connections use radio waves to communicate. For example. smartphones and many other Internet-enabled devices use radio waves to place telephone calls and to connect to the Internet. Primary technologies used for wireless connections are Bluetooth, Wi-Fi, microwave, WiMax, cellular, and satellite connections.
● Bluetooth is a short-range radio communication standard that transmits data over short distances of up to approximately 33 feet. Bluetooth is widely used for wireless headsets, printer connections, and handheld devices.
● Wi-Fi (wireless fidelity) high-frequency radio signals to transmit data. A number of standards for Wi-Fi exist, and each can send and receive data at different speed.Most home and business wireless networks use Wi-Fi.
● Microwave communication uses high-frequency radio waves.It is sometimes referred to as line-of-sight communication because microwaves can only 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.
● WiMax (Worldwide Interoperability for Microwave Access) is a new standard that extends the range of Wi-Fi networks using microwave connections. WiMax is commonly used by universities and others to extend the capability of existing Wi-Fi networks.
● Cellular communication uses multiple antenna (cell towers) to send and receive data within relatively small geographic regions (cells). Most cell phones and mobile devices use cellular networks.
● Satellite communication uses satellites 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 communication system, Satellites orbit at a precise point and speed above the earth. They can amplify and relay microwave signals from one transmitter on the ground to another. Satellites can be used to send and receive large volumes of data. Uplink is a term relating to sending data to a satellite. Downlink refers to receiving data from a 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 communications is for global positioning. A network of satellites owned and managed by the Department of Defense 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 many 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. Most of today's smartphones and tablets use GPS technology for handheld navigation.
Questions
What are communication channels?
List the three physical connections.
Define Bluetooth, wi-fi, microwave communication and WiMax.
What are cellular and satellite communications? GPS? Infrared?
CONNECTION DEVICES
At one time nearly all computer communication used telephone lines. However, Because the telephone was originally designed for voice transmission, telephones typically send and receive analog signals, which are continuous electronic waves. Computers, in contrast, send and receive digital signals.These represent the presence or absence of an electronic pulse-the on / off binary signal.
MODEMS
The word modem is short for modulator-demodulator. Modulation is the name of the process of converting from digital to analog. Demodulation is the process of converting from analog to digital. The modem enables digital personal computers to communicate across different media, including telephone wires, cable lines,and radio waves.
The speed with which modems transmit data varies. The speed, called transfer rate, is typically measured in millions of bits (megabits) per second (Mbps).The higher the speed, the faster you can send and receive information. For example, to download a complete full-length motion picture (700 MB) on a 1.5-Mbps modem would take about 1 hour. Using a 10.0-Mbps modem would take about 9 minutes.
There are three commonly used types of modems: DSL.Cable, and wireless.
● A DSL (digital subscriber line) modem uses standard phone lines to create a high-speed connection directly to your phone company's offices. These devices are usually external and connect to the system unit using either a USB or an Ethernet port
● A cable modem uses the same coaxial cable television. Like a DSL modem, a cable modem high-speed connections using the system unit's Ethernet port
● A wireless modem is also known as a WWAN (wireless wide area network) modem. Almost all computers today have built-in wireless modem. For those that do not wireless adapter cards are available that plug into USB or special card ports
CONNECTION SERVICE
For years, large corporations have been leasing special high-speed lines from telephone companies. Originally, these were copper lines, known as TI lines, that could be combined to form higher capacity options known as T3 or DS3 lines. These lines have largely been replaced by faster optical carrier (OC) lines.
While the special high-speed lines are too costly for most individuals, Internet service providers do provide affordable connections For years, individuals relied on dial-up services using existing telephones and telephone modems to connect to the Internet. This type of service replaced by higher speed connection services including DSL, cable, satellite, and cellular services.
● Digital subscriber line (DSL) service is provided by telephone companies using existing telephone lines to provide high-speed connections. ADSL ( asymmetric digital subscriber line) is one of the most widely used types of DSL. DSL is much faster than dial-up.
● Cable service is provided by cable television companies using their existing television cables. These connections are usually faster than DSL.
● Fiber Optic service (FiOS) is showing up in some areas, but it is a new technology and not widely available. Current providers of FiOS include Google and Verizon with speeds faster than cable or DSL connections.
● Satellite connection services use satellites to provide wireless connections.While slower than DSL and cable modem, satellite connections are available almost anywhere using a satellite-receiving disk.
● Cellular service providers, including Verizon, AT&T, Sprint, and T-Mobile, support voice and data transmission to wireless devices using cellular networks. These networks have gone through different generations.
First-generation mobile telecommunications (1G) started in the 1980s using analog radio signals to provide analog voice transmission service.
Second-generation mobile telecommunications ( 2G ) started in the 1990s using digital radio signals.
Third-generation mobile telecommunications (3G) started in the 2000s and provided services capable of effective connectivity to the Internet marking the beginning of smartphones
Fourth-generation mobile telecommunications (4G) has begun to replace 3G networks in some areas with providers using LTE (Long Term Evolution) connections to provide faster transmission speeds. While a user's experience with 4G will depend on several factors, including carrier, geography, and proximity to cell towers, 4G technologies can provide speeds up to 10 times faster than 3G.
Questions
What is the function of a modem?
Compare the three types of modems.
What is a connection service?
Compare the five high-speed connection services.
Describe the four generations of mobile communications.
DATA TRANSMISSION
Several factors affect how data is transmitted. These factors include bandwidth 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. For example, to transmit text documents, a slow bandwidth would be acceptable. However, to effectively transmit video and audio, a wider bandwidth is required. There are four categories of bandwidth.
● Voiceband, also known as low bandwidth, is used for standard telephone communication. Personal computers with telephone modems and dial-up service use this bandwidth. While effective for transmitting text documents, it is too slow for many types of transmission, including high-quality audio and video.
● Medium band is used in special leased lines to connect midrange computers and mainframe as well as to transmit data over long distances. This bandwidth is capable of very high-speed data transfer.
● Broadband is widely used for DSL, cable, and satellite connections to the Internet. Several users can simultaneously use a single broadband connection for high-speed data transfer.
● Baseband is widely used to connect individual computers that are located close to one another. Like broadband, it is able to support high-speed transmission Unlike broadband, however, baseband can only carry a single signal at a time.
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.
https, or hypertext transfer protocol secure, is widely used to protect the transfer of sensitive information. Another widely used Internet protocol is TCP/IP (transmission control protocol/Internet protocol). The essential features of this protocol involve (1) identifying sending and receiving devices and (2) breaking information into small parts, or packets, for transmission across the Internet.
● Identification: Every computer on the Internet has a unique numeric address called an IP address (Internet protocol address). Similar to the way a postal service uses addresses to deliver mail, the Internet uses IP addresses to deliver e-mail and to locate websites. 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.mhhe.com, a DNS converts this to an IP address before a connection can be made.
● Packetization: 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.
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