Processing is shared among multiple small computers known as clients that are connected via a network to a host computer known as a server .
Clients - typically PCs, a type of high-powered small computer built for specialized applications called a workstation , or a network computer.
Server - typically dedicated to a specific type of processing, such as providing files with a file server, responding to database queries with a database server, or handling high-speed processing with an application server.
Because both the client and the server are capable of processing, processing is shared between the two computers depending on the capability of each.
Types of Servers Server Type Purpose File Provides both software and data files to users Database Handles queries to a large database and returns matching records Application Handles high speed processing Web Handles requests for Web pages Mail Sends and receives e-mail for entire organization Fax Sends and receives faxes for entire organization
Client/Server Advantages and Disadvantages Advantages Disadvantages Computing burden can be shared among servers and clients Programming relationship between clients and servers is more complex Servers can be specialized to one particular type of task System upgrades require that all clients and servers be upgraded regardless of location Upgrading system can be done in small steps Loss of client does not stop other clients from accessing server
It is possible to set up a peer-to-peer network, where each computer in the network is on the same level as other computers, and each computer is equally responsible for overseeing the functions of the network.
Any two computers in a peer-to-peer network may communicate directly with one another, or they may communicate through intermediate peer computers.
Peer-to-peer networks may be easier to setup, but are not as efficient as client/server networks.
Comparing Client/Server and Peer-to-Peer Networks
The physical layer sends packets over telephone lines, or other media, using packet switching.
Packet switching - individual packets are routed through the network based on the destination address contained in each packet. With packet switching, the same data path can be shared among many computers in the network, and if a computer on the network is inoperable, the packet finds another way to reach its destination.
A router is a special type of computer that has the sole purpose of accepting packets and determining the best way to send them to the destination computer--that is, the router specializes in switching the packets.
The sequence order allows the receiving computer to reconstruct the message.
Sending Data Between Computers on the Internet
Data Component Media 2 2 Source: Jerry Fitzgerald and Alan Dennis, Business Data Communications and Networking , 8th ed., p. 85, New York: John Wiley, 2005. Media Cost Error Rates Speed Twisted Pair Low Low Low-high Coaxial Cable Moderate Low Low-high Fiber Optics High Very Low High - very High Radio Low Moderate Low Infrared Low Moderate Low Microwave Moderate Low- Moderate Moderate Satellite Moderate Low- Moderate Moderate
Maximum Data Rates Transmission Method Maximum Data Rate Comments Standard telephone service 56 Kbps Available everywhere Digital Subscriber line (DSL) 6 Mbps in; 640 Kbps out Becoming more available. Does not slow down as more people sign up. Cable As high as 55 Mbps but averages between 200 Kbps and 2 Mbps Cable must support two-way communication; available in many locations but slows down as more people use it in a specific location T-1 to T-4 1.544 Mbps - 274 Mbps Leased lines used for commercial telecommunication
Wireless LANs (WLANs) – replaces cabling with wireless transmissions that use radio frequencies to transmit information between individual computers
The individual computers do not communicate directly with each other; instead they communicate with a wireless network hub or router, which is also used to bridge the wireless network to traditional ethernet or provide a shared Internet connection.
Wi-Fi (for Wireless Fidelity) – also called IEEE 802.11b standard, the current popular standard for wireless networking supports data rate of 11 megabits/second, with a typical range through open air of about 220-1100 yards (200-1000 meters).
An e-mail address is composed of two parts: the user name and the server address .
The user name is assigned to a person or organization that is connected to a server, and it is separated from the server address by the at symbol (@).
Server address (a.k.a. domain name) – the IP address of the email host. The right-most part of the address is known as the top level domain .
Server addresses are easy-to-remember versions of the numeric IP addresses.
Top Level Domains Type of Organization Designation Example Commercial company .com www.ebay.com (eBay Auctions) Educational institution .edu www.uga.edu (The University of Georgia) Nonprofit organization .org www.redcross.org (The Red Cross) Network provider .net www.netscape.net (Netscape) Government .gov www.ustreas.gov (U.S. Treasury Department) Military .mil www.usmc.mil (The U.S. Marine Corps) Aerospace organizations* .aero www.ba.aero (British Airways) Businesses* .biz www.webmaster-resource.biz (Webmaster-Resource.biz, an e-commerce company) Cooperatives* .coop www.credit-cooperatif.coop (Crédit Coopératif Group in France) Various* .info www.lanka.info (Information on Sri Lanka) Museums* .museum mhp.moscow.museum (Moscow House of Photography in Russia) Various* .name www.yourname.name Professionals* .pro www.broadway.pro (Broadway theater shows)
Internet Operations Internet Operations Purpose E-mail Asynchronously exchange electronic messages with other Internet users FTP Download files (software, documents, or data) from or upload files to a server located on the Internet Newsgroups Participate in a wide variety of online discussion groups Telnet Work on a computer elsewhere on the Internet Internet Relay Chat Synchronously exchange electronic messages with other Internet users World Wide Web Transfer text, images, video, and sound to your computer; search for information on Internet
The Web is a special type of client/server network. To access the Web, the client computer uses software called a browser that initiates activity by sending a request to a Web server for certain information. The Web server responds by retrieving the information from its disk and then transmitting it to the client.
Browser – application layer software used for sending requests and displaying the results
Hypertext markup language (HTML) - tags in World Wide Web documents that are part of a special publishing language
Documents on the Web are referred to as Web pages, and their location is a Web site .
Web Pages vs. Physical Pages Characteristics Web Page Physical Page Form Electronic Ink on paper Amount of information Can extend beyond single screen Restricted to single piece of paper Types of information Can include text, images, audio, and video information Restricted to text and images Links to other pages Can be linked to other pages through hypertext Can be linked only through a separate index Creation Can be created with HTML and saved to a server Can be created using word processor and printer
Internet Protocols Protocol Purpose http Retrieve Web pages file Retrieve files from local hard disk telnet Log on to a remote computer connected to the Internet ftp Download or upload files from an Internet FTP server mailto Send outgoing e-mail news Display news group
The fastest growing trend in networks is wireless networks, both WANs and LANs.
Primary advantage: devices connected to the network can go virtually anywhere
In the case of wireless WANs, a mobile telephone client is the most popular method of connecting to the Internet and Web.
A number of mobile telephone companies have collaborated to create a special protocol, called Wireless Application Protocol (WAP) , just so their telephones can connect to the Internet.
Short Message Service (SMS ) is a service for sending text messages up to 160 characters long to mobile telephones.
Global System for Mobile communication (GSM) protocol is the most widely used standard mobile telephone protocol in the world, with the exception of the United States where it is gaining ground.
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