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Week 1 – Internet Technology &Web DevelopmentSlides were modified from Ch1&2, Connolly, R. and Hoar, R. (2018).Fundamentals of Web Development. 2nd ed.USA: Pearson Education.How the Web WorksInternet ProtocolsA Layered ArchitectureTCP/IP.These protocols have been implemented in every operatingsystem, and make fast web development possible.Networking is it’s own entire discipline.Web developer needs general awareness of what the suite ofInternet protocols doesInternet ProtocolsA Layered ArchitectureInternet Protocols• Responsible for• physical transmission of data across media (both wired andwireless) and• Establishing logical links.It handles issues like packet creation, transmission,reception, error detection, collisions, line sharing, andmore.Much more to learn in Networking courses outside ofweb development.Link LayerInternet ProtocolsThe Internet layer provides “best effort”communication.Makes use of IP addressesInternet LayerInternet ProtocolsInternet Layer (IP)Internet Protocols• Ensures transmissions arrive in order and without errorTransport Layer (TCP)Internet ProtocolsThere are many application layer protocols. Web developersshould be aware of :• HTTP. The Hypertext Transfer Protocol is used for webcommunication.• SSH. The Secure Shell Protocol allows remote commandline connections to servers.• FTP. The File Transfer Protocol is used for transferring filesbetween computers.• POP/IMAP/SMTP. Email-related protocols for transferringand storing email.• DNS. The Domain Name System protocol used forresolving domain names to IP addresses.Application LayerWhere Is the Internet?From the Computer to the Local ProviderOur main experience of the hardware component of the Internet is that whichwe experience in our homes.Where Is the Internet?RoutersThe wireless router is perhaps the most visiblemanifestation of the Internet in one’s home, in that itis a device we typically need to purchase and install.Routers are in fact one of the most important andubiquitous hardware devices that makes the Internetwork.At its simplest, a router is a hardware device thatforwards data packets from one network to anothernetwork.Where Is the Internet?(Simplified) Routing TablesWhere Is the Internet?Out of the HouseOnce we leave the confines of our own homes, thehardware of the Internet becomes much murkier.In the illustration, the various neighborhoodbroadband cables (which are typically using copper,aluminum, or other metals) are aggregated andconnected to fiber optic cable via fiber connectionboxes.Where Is the Internet?To the ProviderThese fiber optic cables eventually make their way toan ISP’s head-end, which is a facility that may containa cable modem termination system (CMTS) or adigital subscriber line access multiplexer (DSLAM) in aDSL-based system.Where Is the Internet?From the Local Provider to the Ocean’s EdgeEventually your ISP has to pass on your requests for Internet packets toother networks.This intermediate step typically involves one or more regional networkhubs.Your ISP may have a large national network with optical fiber connectingmost of the main cities in the country.Some countries have multiple national or regional networks, each withtheir own optical network.Where Is the Internet?From the Local Provider to the Ocean’s Edge –IXP and Data CentersWhere Is the Internet?Across the Oceans – undersea fiber optic linesEventually, international Internet communication will need to travel underwater.The amount of undersea fiber optic cable is quite staggering and is growingyearly.But why noton air viaSatellites?Domain Name SystemName LevelsDomain Name SystemName LevelsDomain Name SystemName LevelsDomain Name System• Generic top-level domain (gTLD)• Unrestricted. TLDs include .com, .net, .org, and .info.• Sponsored. TLDs including .gov, .mil, .edu, and others.• New TLDs.• Country code top-level domain (ccTLD)• TLDs include .us , .ca , .uk , and .au.• Internationalized Domain Names• arpaTypes of Top Level DomainsDomain Name SystemName RegistrationDomain Name SystemAddress ResolutionDefinitions and HistoryThe Internet and WWW are different (but related) thingsDefinitions and History1. URLS2. HTTP3. SERVERS4. BROWSERS5. HTMLThe Birth of the Web (1990)Definitions and HistoryAdvantages:• Accessible from any Internet-enabled computer.• Usable with different operating systems and browserapplications.• Easier to roll out program updates• Fewer security concerns about local• Storage.Web Applications in Comparison to Desktop ApplicationsDefinitions and HistoryDisadvantages:• Requirement to have an active Internet connection• Security concerns about sensitive private data beingtransmitted over the• Internet.• Concerns over the storage, licensing, and use of uploaded data.• Problems with certain websites not having an identicalappearance across all• browsers.• Restrictions on access to operating system resources• Clients or their IT staff may have additional plugins added• to their browsersWeb Applications in Comparison to Desktop ApplicationsDefinitions and HistoryStatic Websites versus Dynamic WebsitesDefinitions and HistoryStatic Websites versus Dynamic WebsitesDefinitions and HistoryStatic Websites versus Dynamic WebsitesUniform Resource LocatorsOverviewUniform Resource LocatorsPreviously, we listed several application layer protocols onthe TCP/IP stack. FTP, SSH, HTTP, POP, IMAP, DNS, …Requesting• ftp://example.com/abc.txt sends out an FTP requeston port 21, while• http://example.com/abc.txt transmits an HTTP requeston port 80.ProtocolUniform Resource Locators• The domain identifies the server from which we arerequesting resources.• Since the DNS system is case insensitive, this part of theURL is case insensitive.• Alternatively, an IP address can be used for the domainDomainUniform Resource Locators• The optional port attribute allows us to specifyconnections to ports other than the defaults• Add a colon after the domain, then specify an integer portnumber.PortUniform Resource LocatorsFamiliar concept to anyone who has ever used a computerfile system.The root of a web server corresponds to a folder somewhereon that server.• On many Linux servers that path is /var/www/html/• On Windows IIS machines it is often /inetpub/wwwroot/The path is optional. However, when requesting a folder orthe top-level page, the web server will decide which file tosend you.PathUniform Resource LocatorsQuery StringHypertext Transfer ProtocolHeadersHypertext Transfer Protocol• Request headers include data about the client machine.• Response headers have information about the serveranswering the request and the data being sentHeadersHypertext Transfer ProtocolRequest MethodsHypertext Transfer Protocol• 2## codes are for successful responses,• 3## are for redirection-related responses,• 4## codes are client errors,• 5## codes are server errors.Response CodesHypertext Transfer Protocol200: OK301: Moved Permanently304: Not Modified307: Temporary redirect400: Bad Request401: Unauthorized404: Not found414: Request URI too long500: Internal server error(Some) Response CodesWeb BrowsersFetching a Web PageWeb Browsers• Interpreting the entire HTML markup together with theimage and other assets into a grid of pixels for displaywithin the browser window is called rendering thewebpage.• Implemented differently for each browser (Firefox,Chrome, Safari, Explorer, and Opera)Browser RenderingWeb Browsers• search engine integration,• URL autocompletion,• Form autocompletion,• cloud caching of user history/bookmarks,• phishing website detection,• secure connection visualization,and much moreBrowser FeaturesWeb Servers• A web server is nothing more than a computer thatresponds to HTTP requests.• Real-world web servers are often more powerful thanyour own desktop computer• Webservers must choose an application stack to run awebsite. This application stack will include an• operating system,• web server software,• a database,• and a scripting language for dynamic requestsOperating SystemsWeb ServersWe will rely on the LAMP software stack ,which refers to• L inux operating system,• A pache web server,• M ySQL database, and• P HP scripting languageOther stacks include WAMP, WISA, MEAN, …Application StacksWeb Servers• MySQL• PostgreSQL• Sqlite• Oracle• IBM DB2• Microsoft SQL Server• MongoDBDatabase SoftwareWeb Servers• PHP• ASP.NET• Python• Node.js• …Scripting SoftwareWeb DevelopmentThe Client-Server ModelThe Request-Response LoopThe Client-Server ModelThe Peer-to-Peer AlternativeThe Client-Server Model• Web Servers• Application Servers• Database Servers• Mail Servers• Media Servers• Authentication Servers• …Server TypesThe Client-Server ModelReal-World Server Installations – Server FarmThe Client-Server ModelReal-World Server Installations – Data CenterWorking in Web DevelopmentRoles and SkillsWorking in Web Development• Hardware Architect/Network Architect/Systems Engineer• System Administrator• Database Administrator/Data Architect• Security Specialist/Consultant/Expert• Developer/Programmer• Front-End Developer/UX DeveloperRoles and SkillsWorking in Web Development• Software Engineer• UX Designer/UI Designer/Information Architect• Tester/Quality Assurance• SEO Specialist• Content Strategists/Marketing Technologist• Project Manager/Product Manager• Business Analyst• Nontechnical RolesRoles and Skills (II)Working in Web DevelopmentTypes of Web Development CompaniesQuestions?
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