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WWW and Internet Access

WWW and Internet Access. Yaşar Tonta Hacettepe Üniversitesi Bilgi ve Belge Yönetimi Bölümü DOK 422 : Bilgi Ağları. Kaynak: Bogdan Ghita – http://ted.see.plymouth.ac.uk/bogdan. Session Content. The World Wide Web

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WWW and Internet Access

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  1. WWW and Internet Access Yaşar Tonta Hacettepe Üniversitesi Bilgi ve Belge Yönetimi Bölümü DOK 422: Bilgi Ağları Kaynak: Bogdan Ghita – http://ted.see.plymouth.ac.uk/bogdan

  2. Session Content • The World Wide Web • HTTP (HyperText Transfer Protocol), HTML (HyperText Markup Language), URL (Uniform Resource locator) • Dial-up Internet access • PPP (Point-to-Point Protocol) and SLIP (Serial Line Internet Protocol) • (Why) is my / the Internet slow? • ISPs (Internet Service Providers)

  3. The history of Internet 1969 1999 From: bell-labs.com From: historyoftheinternet.com

  4. The World Wide Web • “The World Wide Web is the universe of network-accessible information, the embodiment of human knowledge” (WWW Consortium - W3C) • The most popular Internet application • Also known as "WWW', "Web" or "W3" • Began as a networked information project at CERN (European Laboratory for Particle Physics) • Developed by Tim Berners-Lee • now Director of the W3C

  5. WWW - Background • Early ‘vision statement’ from Tim Berners-Lee • Merges the techniques of networked information and hypertext to make a global information system. • Represents any information accessible over the network as part of a seamless hypertext information space • Allows information sharing within internationally dispersed teams and dissemination of information by support groups. • Originally aimed at the High Energy Physics community, it has spread to other areas and attracted much interest in user support, resource discovery and collaborative work

  6. What is Hypertext? • Hypertext is text with links • Links can be made within or between documents • Allows reader to escape sequential presentation and pursue threads • Not unique to the web and did not originate with it • Documents can be text, graphics, movies, sound, etc • The term "hypermedia", meaning "multimedia hypertext" is often applied to WWW

  7. HyperText Transfer Protocol (HTTP) • The data transmission protocol used to transfer web resources across the Internet • Format negotiation • A feature of HTTP is that the client sends a list of the representations it understands along with its request (e.g. graphics formats such as GIF and JPEG) • server can then ensure that it replies in a suitable way • allows the web to distance itself from the technical and political battles of the data formats

  8. HTTP (cont.) • HTTP is stateless • Each request is an independent entity that does not depend upon the state left over from any prior request • HTTP is transaction-based • Non-persistent (version 1.0) requires a new, independent connection to the server for every element to be downloaded • inefficient, particularly for low bandwidth scenarios • Persistent (version 1.1) - the requests are pipelined

  9. HyperText Markup Language (HTML) • The basic language used to create / present web documents • Written and stored as plain ASCII text • Based on SGML - Standard Generalised Markup Language • Describes the logical structure of the document instead of its formatting • Allows it to be displayed optimally on different platforms using different fonts and conventions • Uses special ‘tags’ to encode styles and effects • Interpreted by the client / browser to render document in correct format

  10. HTML (cont.) • Has evolved in several versions - current is HTML 4.0 • Also other related WWW markup languages • e.g. VML (Vector ML), WML (Wireless ML), DHTML (Dynamic HTML), ... • The future seems to belong to XML (eXtensible Markup Language) – a better HTML (more tags, more flexible) • WWW also has standards for ‘active’ content • e.g. Java, JavaScript, Active-X • can be embedded within HTML documents

  11. HTML Example - The Markup Q: How to obtain the above? A: Right-click on a web page then select View source

  12. HTML Example - The result

  13. Uniform Resource Locator (URL) 1 2 3 4 1 Transfer protocol used to access site (e.g. HTTP, FTP, TELNET) 2 Address of the host (DNS name or IP address) 3 Directory path of resource 4 Resource name • Each resource on the web has an address e.g. http://ted.see.plym.ac.uk/bogdan/CNET209/default.htm

  14. WWW Client-Server Model • To allow the web to scale, it was designed without any centralised facility • Anyone can publish information, and anyone (authorised) can read it • To publish data you run a server, and to read data you run a client • All the clients and all the servers are connected to each other by the Internet • The WWW protocols and other standard protocols allow all clients to communicate with all servers

  15. Web Browsers • Web browser - client program used to visit web pages • First ever - written by Tim Berners-Lee, CERN (1990) • The first used heavily by public – Mosaic (1993) • Marc Andreessen (undergraduate at the time) and colleagues at the National Center for Supercomputing Applications (NCSA) • Most of that group went on to form Netscape Corporation • The current main competitors: Netscape (Navigator) and Microsoft (Internet Explorer) • Web browser has increasingly become the only network application client you need to use • Migration of applications to web interface

  16. Internet Access methods • It’s all about money - price dependent on • Connectivity method: leased line (always-on) or dial-up) • Speed • Amount of traffic exchanged • Contention rate (number of users vs. connectivity speed to Internet ratio) • Alternatives • Dial-up • ADSL • LAN, ...

  17. Dial-Up (Internet) Access • The ‘Ideal’ access - dedicated connection • Leased line between a subscriber and a provider • Dial-up - the affordable choice • “Refers to connecting a device to a network via a modem and a public telephone network” (webopedia.com) • Aside from contention rate, access depends on the number of modems used - modems vs. users ratio • Most used protocols – SLIP and PPP • SLIP (Serial Line Internet Protocol) • PPP (Point to Point Protocol) • Common core, but with a few differences

  18. SLIP / PPP • SLIP/PPP provides the ability to transport TCP/IP traffic over serial lines (such as dial-up telephone lines) between two computers • Both computers run TCP/IP based network software • Equipment: modem + phone line • It is a form of direct Internet connection as your computer has • A communications link to the internet, even if it is via a service provider • Networking software that can communicate using TCP/IP protocols with other computers on the Internet • An identifiable address (IP address) at which it can be contacted by other computers on the Internet

  19. SLIP / PPP Differences • PPP is a newer, better designed protocol • Multi-Protocols • SLIP can only transport TCP/IP traffic • PPP is a multi-protocol transport mechanism • Configuration Negotiation • SLIP requires to know your IP address (assigned by the ISP) and the IP address of the system to be connect to • Difficult if IP addresses are dynamically assigned • PPP addresses this problem by negotiating configuration parameters at the start of the connection

  20. SLIP / PPP Differences (cont.) • Automatic Login • Most SLIP software can dial-up and automatically login • …but it depends on the ISP’s system standard prompts • e.g. "login:" to get userid and "password:" to get password • If these are non-standard, you need to write a script to automate the login process or login manually • PPP provides PAP (Password Authentication Protocol) and CHAP (Challenge-Handshake Authentication Protocol) • Both provide the means to automatically send your login userid/password information to the remote system

  21. ADSL • ADSL - Asymmetric Digital Subscriber Line • Why asymmetric? • Uses the telephone lines as transport medium • improvement in the “local loop” (the cable between the phone exchange and the home socket) usage • Speeds (depend also on physical factors) - asymmetric • Downstream - up to 9 Mb/s • Upstream – up to 1.5Mb/s • Requires specific modem, but works on a normal telephone line • The phone can work in parallel with the ADSL connection • It is the dial-up of tomorrow…but much faster and always-on!

  22. Is it over for dialup? • U.S. 2001 statistics – home connectivity • Dialup – 80% • Cable modem – 12.9% • DSL – 6.6% • Other – 0.5% • Not everybody needs 10x bandwidth! – U.S. 2001 application usage • E-mail – 45.2% • Information search – 36.2% • News, weather, sports – 33.3% • Product / service purchase – 21.0% • Employment search – 7.5% • Phone calls – 2.8% (Source: U.S. Dept. of Commerce and U.S. Census Bureau - 2001)

  23. Internet Service Providers (ISPs) • A company that provides access to the Internet • Has infrastructure for: connectivity (computers, routers), access (modems, phone lines), and technical support • Selection issues : cost, PoP(s), contention • Cost - taxes are moving towards the cost of the phone call • Point of Presence (PoP) - A local computer/network owned and operated by an ISP – used to dial into to get onto the Internet • Good user-to-modem ratio in each POP (minimise occasions when users get an engaged tone) – minimum approx. 12:1 • Good contention rate – between 1:20 and 1:50

  24. Other ISP selection issues • Personal Homepage • Does the ISP allow you to set up your own WWW page on their server? How much space do you have allocated? • Shell Access • Does the ISP give you access to a Unix-type login shell account on one / more of their servers? (good for nerds!) • POP3 Mail Server • Lets you pick up mail from the ISP's server so that you can read (and write) them on your own PC • Your mails are first received by the ISP and stored on their servers - how much server space is allocated?

  25. The World Wide Wait? • Factors affecting Internet / WWW performance • Modem speed • Choice of ISP (and their facilities / capacity) • Response times of remote sites • Power outages / server downtime • Time of day and site location • General Internet characteristic of 'best effort' transfer • Hardware of the computer - less of an issue lately • The Internet will NOT be faster or enhanced if you have a faster machine (unless you have a very fast / demanding connection) • 486s or an old Pentiums are VERY slow machines

  26. “My Internet is slow” - Why? • Is it? • Congestion - the main factor to affect performance • Queuing - increases the delay • The output rates and router speed are not limitless • Loss - requires retransmission • The queues have limited sizes • ‘The Internet’ is faster! • But the information content changes text image audio video

  27. Summary • WWW - the universe of information • HTTP - the protocol that makes it work • HTML - the language used to produce it • URL - the addressing system behind it • WWW - is it slow or are we demanding? • Dial-up - the current solution to connect • PPP vs. SLIP - PPP is the winner • ADSL – the future (?) • ISP - the bridge between user and the Internet

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