电子商务英文版版课件ch08

Click to edit Master title style,Click to edit Master text styles,Second level,Third level, 2017 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website or school-approved learning management system for classroom use.,#,Click to edit Master title style,Click to edit Master text styles,Second level,Third level, 2017 Cengage Learning. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part, except for use as permitted in a license distributed with a certain product or service or otherwise on a password-protected website or school-approved learning management system for classroom use.,#,Web Server Hardware and Software,CHAPTER 8,.,Learning Objectives,In this chapter, you will learn:,How a Web server performs its basic functions,What operating system and server software is used on Web servers,How to identify and manage e-mail and spam control issues,How commonly used Internet and Web site utility programs work,What hardware online businesses use to power their Web sites,How cloud computing and content delivery networks are providing new Web infrastructure,2,2,Introduction,Case study: Israels Channel 2 News,Produces news content and programming for other Channel 2 shows, Web sites and its mobile device app,Web site and mobile app offer many high-resolution photographs and video chips,Online news organizations face wide variation in user interest levels and need for Internet bandwidth,Breaking news events lead to high demands on the Web site and mobile app and can result in system overload,Peak periods in news business can be unpredictable,As a solution, Channel 2 uses Google Cloud Computing to store content,3,Web Server Basics,Client/server architectures used in LANs, WANs, Web,Server computers have more memory and larger, faster disk drives than the client computers they serve,Web browser: a type of Web client software,Platform neutrality is the ability of a network to connect devices using different operating systems,Critical in rapid spread, widespread Web acceptance,Web,servers main,job to respond to Web,client requests,Main,elements: Hardware, operating system software, and Web server software,4,5,FIGURE 8-1 Platform neutrality of the Web, Cengage Learning 2017,Dynamic Content Generation,Static page is an,unchanging,page retrieved from,stored Web,server file(s),Dynamic page created in response to user request,Customized pages give user an interactive experience,Client-side,scripting,s,oftware,operates on the Web client (browser,) and changes,Web page display in response to a users,actions (JavaScript,or Adobe,Flash),Server-side,scripting program,runs on a Web,server and creates,Web page in response to request for specific information from a Web client,6,Dynamic Content Generation (contd.),S,oftware tools to create dynamic Web pages,Microsoft ASP.NET, Apache Software Foundation Hypertext Preprocessor (PHP) and Adobe ColdFusion,AJAX,(asynchronous JavaScript and XML,) creates,interactive Web sites that look like applications,Ruby,on,Rails, Scala and Python,(scripting language,) are used to accomplish the same objectives,Many Web sites use more than one language and/or development framework to accomplish specific objectives,7,Multiple Meanings of “Server”,Server is any computer providing files or making programs available to other computers connected to it through a network,Server software makes files and programs available,May be part of the operating system (OS) and be referred to as server software (confusing),Some servers connected to Internet via a router,Runs,Web server,software that makes,servers files available to other,computers and called a Web server,E-mail,server: handles incoming and outgoing,e-mail,8,Multiple Meanings of “Server” (contd.),Database server runs database management software,Transaction server runs accounting and inventory management software,“Server,” describes several types of computer hardware and software,Context needed to determine the intended meaning,9,Web Client/Server Architectures,Web browser requests files from Web server and uses the Internet as the transportation medium,Request formatted by browser using HTTP and sent to server computer,Server receives request, retrieves requested Web page file, formats using HTTP, and sends back to client over the Internet,Client Web browser software displays page,Repeating,process of request, response, display,Web page with graphics can be slow because each page element requires separate request and response,10,Web Client/Server Architectures (contd.),Basic model is two-tier client/server architecture,One client and one server computer,Request message is the Web,client message sent to request file(s) from a Web,server that consists of three major parts,Request line contains,command, target resource name, protocol name, version number,Optional request,headers contain,file type information client accepts,Optional entity,body is used to pass,bulk information to server,11,12,FIGURE 8-2 Message flows in a two-tier client/server network, Cengage Learning 2017,Web Client/Server Architectures (contd.),Server receiving request message executes command included in message,Retrieves Web page file from disk and creates a response message to send back to client,Identical in structure to request message (slightly different function),Response header line indicates server HTTP version, response status, status information explanation,Response header field returns information describing servers attributes,Entity body returns HTML page requested by the client machine,13,Web Client/Server Architectures (contd.),Three-tier architecture allows additional processing before server responds to clients request,Often includes databases and related software applications that supply information to the Web server,Web server uses software applications output when responding to client requests,N,-tier,architectures have more than three tiers,Track customer purchases stored in shopping carts,Look up sales tax,rates, ;keep,track of customer,preferences, update,in-stock inventory databases,Keep product catalog current,14,15,FIGURE 8-3 Message flows in a three-tier client/server network, Cengage Learning 2017,Operating Systems for Web Servers,Operating system tasks include running programs, allocating computer resources to programs, and proving input and output services,Required for a computer to run programs,Larger system responsibilities include tracking multiple users, ensuring no interference,Web server operating systems software run on Microsoft Windows Server products, Linux or UNIX-based operating systems,16,Operating Systems for Web Servers (contd.),Some companies consider Microsoft operating system simpler to use than UNIX based systems,Some concerns about security weaknesses caused by tight integration of Microsoft products,Linux is open-source, fast, efficient, easy to install,Can be downloaded free from the Web but most companies buy it through a commercial distributor for the additional utilities and support,Mandriva, Red Hat, SuSE Linux,Enterprise,Oracle sells Web server hardware with its UNIX-based operating system Solaris,17,Web Server Software,Commonly used programs are Apache HTTP Server and Microsoft Internet Information Server (IIS),Some businesses, such as Google, wrote their own,Apache dominant Web server software since 1996,Free and user-supported with other services available,Microsoft IIS bundled with Microsoft Windows Server OS and runs only on Windows systems,Used on many intranets, and small and large sites that have adopted Microsoft products as standard,ISS is free but OS it comes with can be expensive,18,19,FIGURE 8-4 Percent of active Web sites that use major Web server software products,Electronic Mail (E-Mail) and E-Mail Benefits and Drawback,E-mail used to gather information, execute transactions and perform electronic commerce tasks,Reason people originally attracted to the Internet,Conveys messages in,seconds with attachments often the most,important message part,Most popular form of business,communication,Drawbacks include the time spent answering e-mails,Burdensome and can take 2 hours per day,Email attachments can be or contain a computer virus,Most frustrating and expensive problem is spam,20,Spam and Solutions to the Spam Problem,In 2009, the peak year for spam, one 24-hour period showed 220 billion spam e-mail messages sent,S,pam growth has leveled off and legal and technical solutions will continue to reduce it,Benefits reaped by spammers still make it attractive,Reducing spam approaches require passing laws and technical changes in Internet mail-handling systems,Approaches under existing laws and technologies require cooperation by organizations,Some tactics can be taken by individual e-mail users,21,22,FIGURE 8-5 Spam as a proportion of all business e-mail,Individual User Antispam Tactics,Using a complex e-mail address reduces the chance that a spammer can automatically generate it,Downside is that a complex address can be hard to remember,Control e-mail address exposure,Spammer software robots search for e-mail addresses on discussion boards, in chat rooms, other online sources that use email,Use multiple e-mail addresses,Switch to another if spammers use one,Use filtering techniques based on contents,23,Basic Content Filtering,Content-filtering techniques differ in terms of content elements examined, spam indications and how strictly message classification rules applied,Basic content filters examine e-mail headers,Client-level filtering: individual users computers,Server-level filtering: mail server computers,Black list spam,filter looks,for known spammers in incoming messages From addresses,White,list spam,filter looks,for good sender From addresses in incoming messages,High false positives,rate,24,Challenge-Response Content Filtering,Compares all incoming messages to a white list,If sender is not on the white list, automated e-mail response sent (challenge),Challenge asks sender to reply to e-mail (response),Reply must contain response to a challenge presented in the e-mail,Designed so human can respond easily,More information,Carnegie Mellon University CAPTCHA Project site,Drawback is potential,abuse,25,26,FIGURE 8-6 Example of a challenge that uses distorted letters and numbers, Cengage Learning 2017,Advanced,Content Filtering,Looks for spam indicators in entire e-mail message,Indicator identified: messages spam “score” raised,Indicator types are words, word pairs, certain HTML codes, information about where word occurs,Spammers stop including defined indicators,Bayesian revision statistical technique uses additional knowledge to revise earlier probability estimates,Nave Bayesian filter software allows users to review messages and indicate if message is spam (not spam),Software gradually learns,to identify spam and is correct about 95% of the time after training,27,Legal,Solutions,January 2004: U.S. CAN-SPAM law went into effect,Spam decreased first two months, but returned to previous levels after no threat of federal prosecution,Prohibits misleading e-mail message,address,header information,deceptive subject headers and transfer of email addresses,Some spammers,have been,prosecuted, fined and,received jail,time,Many use servers outside U.S. (jurisdiction issues),Legal,solutions have had only limited success,Expensive to prosecute spammers,28,Technical,Solutions,Internet design did not include mechanisms ensuring e-mail sender identity would be know to recipient,Internets communication protocol designed to be a polite set of rules where a sending computer waits for acknowledgement that message was received,Originating computer will slow if acknowledgement is delayed (must continue to scan for it) and will not send more messages until acknowledgment received,Defending (receiving) company must,develop way to identify computers sending,spam and delay acknowledgement,29,Technical,Solutions (contd.),Computer being spammed can also launch a return attack called teergrubing (“tar pit”),Send e-mail messages back to suspected spamming computer with the objective of setting a trap that drags down its ability to send spam,Concern,is that counterattack might violate laws,Ultimate spam solution could come from new e-mail protocols providing absolute verification of e-mail message source,Currently most effective solutions have been coordinated efforts to identify and block spammers,30,Web Site Utility Programs,TCP/IP supports utility programs (tools),Run on Web server or client computers,E-mail:,e,arliest Internet utility program,Most important utility,Key element in electronic commerce strategies,31,Tracert and Other Route-Tracing Programs,Tracert (TRACE RouTe) sends data packets to every computer on path between one computer and another and clocks packets round-trip times,Provides indication of time message needs to travel from one computer to another and back,Ensures remote computer online and pinpoints data traffic congestion,Calculates and displays the number of hops between computers and time to traverse entire one-way path,32,33,FIGURE 8-7,Tracing a path between two computers on the Internet, Cengage Learning 2017,Telnet and FTP Utilities andIndexing and Searching Utility Programs,Telnet program allows a person using one computer to access files and run programs on a second computer connected to the Internet,File Transfer Protocol (FTP) is the part of the TCP/IP rules that defines formats used to transfer files between TCP/IP connected computers,Search engines and indexing programs are important elements of many Web servers,When a browser requests a Web site search, engine compares index terms to the requesters search terms to find matching documents,34,Data Analysis Software,Web servers capture visitor information and places it into a Web log file (grows quickly),Third-party Web log file analysis programs summarize information in the file,Query log file and return gross summary information or accumulating details,Popular Web log file analysis programs,Adobe Analytics, Google Analytics, WebTrends,35,Link-Checking Utilities,Dead link displays an error message rather than Web page when clicked,Sites with many dead links are said to have link rot,Link checker utility examines each site page and reports URLs that no longer exists,Identifies orphan files which are files on Web server not linked to a page,Also includes script checking and HTML,validation,Adobe Dreamweaver includes link-checking program,Free standing link-checking programs include Elsop LinkScan and LinxCop,36,Remote Server Administration,Web site administrator controls Web site from any Internet connected computers,Monitor server activity and manipulate server from wherever administrator happens to be,LabTech Software includes remote administration, link-checking, HTML troubleshooting, site-monitoring and other utility programs,Useful in managing the operations on the Web,37,Web Server Hardware,Wide variety of computer brands, types, sizes used by organizations to host online operations,S,mall companies run Web sites on desktop PCs,Most online business operations are operated on computers designed for site hosting,Businesses select specific hardware and software elements based on sites functionality, expected visitors, number and size of pages and graphics,38,Server Computers,Generally have more memory, larger (faster) hard disk drives and faster processors than typical desktop computers,Many,Web server computers use multiple,processors,Most companies spend $2,000-$50,000 on an individual Web server with large organizations spending millions on server hardware,May be housed in freestanding cases but most are installed in equipment racks,Blade,servers are servers-on-a-card,Small in size: 300 installed in single 6-foot rack,39,40,FIGURE,8-8 Rack-mounted blade servers,Web Servers and Green Computing,Significant electrical power needs for operating servers and cooling the room where servers housed,Green computing is efforts to reduce environmental impact of large computing installations,Novel approaches using natural cooling,Google server facility in Finland,Facebook server in Lulea, Sweden,Other companies: Hewlett-Packard, FedEx, Harris Corporation,41,Web Server Performance Evaluation,Benchmarking is testing to compare hardware and software performance and includes many elements,Hardware, operating system software, server software, connection speed, user capacity, type of Web pages delivered and connection bandwidth,U,sers server can handle important, hard to measure,Throughput is the number of HTTP requests hardware and software process in a unit of time,Response time is time server requires to process one,request,Independent testing and benchmarks available,42,Web Server Hardware Architectures,Electronic commerce Web sites use tiered architecture to divide work of serving Web pages,May use more than one computer within each tier,Server farms are large collections of servers lined up row after row,Centralized architecture uses a few expensive, fast computers and more sensitive to technical problems,Requires adequate backup plans,43,Web Server Hardware Architectures (contd.),Distributed architecture (decentralized architecture) uses many less-powerful, less-expensive computers,Spreads risk over large number of servers,Requires additional hubs or switches to connect servers to each and the Internet,Requires cost of load balancing to assign the workload efficiently,44,45,FIGURE,8-9,Centralized and decentralized Web site architectures, Cengage Learning 2017,Load-Balancing Systems,Load-balancing switch is network hardware that monitors server workloads and assigns incoming Web traffic to the server with most available capacity,Simple load-balancing system traffic enters through sites router and encounters load-balancing switch which directs traffic to best Web server,More complex load-balancing,systems incoming,Web traffic,directed to,groups of dedicated Web servers,Groups organized by specific,functions,Cost of load-balancing,systems range from about $2,000 (simple) to $,15,000,-,$,40,000 (complex),46,47,FIGURE,8-10,Basic load-balancing system, Cengage Learning 2017,48,FIGURE,8-11,Complex load,balancing system, Cengage Learning 2017,Cloud Computing,To reduce costs and effort many businesses are outsourcing entire networks using cloud computing,A,llows multiple organizations to share a network of servers and software giving businesses access to computers, storage and backup at lower cost,Sometimes called infrastructure as a service (IaaS) or platform as a service (PaaS),Resources can be allocated dynamically as needed,Some larger firms use hybrid cloud computing,Move large-volume, routine work to cloud provider and maintain more sensitive data and processes internally,49,50,FIGURE 8-12 Cloud computing provider global market share, 2015, Cengage Learning 2015,Content Delivery Networks,Latency occurs when a transmission delay is caused by network inability to handle full traffic load,Problem for businesses that rely on Internet to deliver large audio and video files to customers,To prevent latency, online businesses have turned to content delivery networks,Service that stores large file contents on multiple servers throughout the Internet for a fee,Large file requests routed to nearest server with a stored copy of the file,51,52,FIGURE,8-13 Growth of Internet traffic, actual and projected,