Sunday, April 1, 2012

Chapter 7 - Telecommunications, the Internet, and Wireless Technology

Over the past couple of decades communication has evolved from postage and telephone to connecting with each other instantaneously.  In the past businesses have used basically two types of networks—telephone networks and computer networks.  Now these two networks are merging into one Internet-based technology network. 

A simple computer network consists of two or more computers, a network operating system residing on a dedicated server computer, wiring connecting the devices, network interface cards (NICs), switches, and a router.  A network operating system (NOS) directs and manages communications on the network and coordinates network resources.  A server computer is a computer on a network that performs important network functions for client computers.  Network interface cards are cards in a computer that enable it to connect to the network.  A router is a communications processor used to move packets of data through different networks making sure it reaches the correct address.  By linking many small local area networks to other local area networks and to business-wide corporate networks, a network infrastructure for a large corporation is formed.

Contemporary networks and the Internet are shaped on three main technologies:  client/server computing, packet switching, and TCP/IT and connectivity.  Client/server computing is a distributed computing model where some of the processing power is located within small, inexpensive client computers.  Packet switching is where data is grouped into small packets, which are transmitted independently over various communications channels and reassembled at their final destination.  Transmission Control Protocol/Internet Protocol (TCP/IP) transmits data among different types of computers over long distances.  A protocol is a set of rules and procedures governing transmission of information between two points in a network.  TCP establishes a connection between the computers, sequences the transfer of packets, and acknowledges the packets sent.  IP is responsible for the delivery of packets and includes the dissembling and reassembling of packets during transmission.

Two ways to communicate a message in a network are by analog signal or digital signal.  An analog signal is characterized by a continuous waveform that passes through a communications medium and has been used for voice communication, e.g., telephone handset, speaker on computer, iPod earphone.  A digital signal is a discrete, binary waveform that communicates information as strings of two discrete states—one bit and zero bits.  A modem converts digital signals from a computer into analog signals that can be sent over and/or received from telephone lines, cable lines, or wireless media that use analog signals.

One way to classify networks is according to their geographic range.  Local Area Networks (LANs) are designed to connect personal computers and other digital devices that are within close range of each other.  They are also able to link long-distance networks using the Internet.  LANs are sometimes described by their topologies (the way their components are connected together).  A star topology is where all devices on the network connect to a single hub.  A bus topology is where one station transmits signals, which travel in both directions along a single transmission segment.  A ring topology connects network components in a closed loop.  Another type of network based on geographic range is a wide area network (WAN).  These networks span over a larger geographical range.  The Internet is the most useful WAN.  WANs connect computers through public networks or through leased lines or satellites.  A metropolitan area network (MAN) spans over an area between a LAN and a WAN. 

Networks use different types of physical transmission media.  Twisted wire consists of strands of copper wire twisted in pairs.  It is an older type of transmission medium.  Coaxial cable consists of thickly insulated copper wire than can transmit a larger volume of data than twisted wire.  It is used today for longer runs in large buildings.  Fiber-optic cable consists of bound strands of clear glass fiber.  It is much faster, lighter, and more durable than wire media, and it is well suited for systems that transfer large volumes of data.  Wireless transmission media is based on radio signals of various frequencies.  Three types are microwave, cellular, and Wi-Fi.

The Internet is a worldwide network of networks.  It is based on the TCP/IP networking protocol.  Each computer is assigned an Internet Protocol (IP) address indicating a unique computer location on the Internet.  The Domain Name System (DNS) converts domain names to IP addresses.  The domain name is the English-like name that corresponds to the unique IP address number.  Worldwide Internet policies are established by a number of professional organizations and government bodies, including the Internet Architecture Board (IAB), which helps define the overall structure of the Internet; the Internet Corporation for Assigned Names and Numbers (ICANN), which assigns IP addresses; and the World Wide Web Consortium (W3C), which sets Hypertext Markup Language and other programming standards for the web.  These organizations help to keep the Internet operating as efficient as possible.

The Internet is based on client/server technology.  Individuals using the Internet control what they do through client applications on their computer.  In turn the client uses the Internet to request information from a particular Web server on a distant computer, and the server sends the requested information back to the client over the Internet.  Client programs include PCs and other computers, cell phones, and small handheld digital devices.  Services used to connect a client computer to the Internet include email, electronic discussion groups, chatting and instant messaging, Telnet, File Transfer Protocol (FTP), and the Web.  One or more software programs implement each of these services.  Voice transmission and corporate networking and virtual private networks are other platforms used by the Internet. 

The Web is the most used Internet service with universally accepted standards for storing, retrieving, formatting, and displaying information using a client/server architecture.  A Web site is a collection of Web pages linked to a home page.  Hypertext Markup Language (HTML) is a page description language that describes how data should be presented in the form of Web pages.  Hypertext Transfer Protocol (HTTP) is the communications standard used to transfer pages on the Web that defines how messages are formatted and transmitted.  A uniform resource locator (URL) tells the browser software exactly where to look for a specific address on the Internet.  A Web server is software that locates the Web pages requested by a user on the computer where they are stored and delivers them to the user’s computer. 

Search engines are used to find useful information on the Web nearly instantly.  The top three are Google, Yahoo, and Bing.  In addition to search engines, shopping bots are used to search for and find information.  They use intelligent agent software for searching the Internet for shopping information.

Web 2.0 is a second-generation interactive Internet-based service that allows people to collaborate, share information, and create new services and content online.  It has four defining features, which include interactivity, real-time user control, social participation (sharing), and user-generated content.  Technologies and services behind these features are cloud computing, software mashups and widgets, blogs, RSS, wikis, and social networks.  Web 3.0 is a future version of the Web where all digital information is woven together with intelligent search capabilities.  This is also known as the Semantic Web.

Cell phones, laptops, and small handheld devices have evolved into portable computing platforms.  In the United States the major computing standard for digital cellular service is the Code Division Multiple Access (CDMA).  3G and 4G are cellular networks that allow high-speed, high-bandwidth, digital packet-switched transmission.  Standards for wireless computer networks, such as Bluetooth and Wi-Fi, allow computer users to have access to the Internet without being connected with a wire or cable.

In addition to the wireless systems, radio frequency identification systems and wireless sensor networks are having a major impact.  Radio frequency identification (RFID) systems allow for tracking the movement of goods by using tiny tags with embedded microchips containing data about an item and its location to transmit radio signals over a short distance for processing.  Wireless sensor networks (WSNs) are networks of interconnected wireless devices that are embedded into the physical environment to provide measurements of many points over large spaces.

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