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WWW and Internet Access

Yaşar TontaHacettepe Üniversitesi

Bilgi ve Belge Yönetimi Bölümü DOK 422: Bilgi Ağları

Kaynak: Bogdan Ghita – http://ted.see.plymouth.ac.uk/bogdan

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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)

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The history of Internet

1969

From: historyoftheinternet.com1999From: bell-labs.com

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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

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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

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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

CNET209/left_border.htm

CNET209/CNET_209_handouts.htm

CNET209/CNET_209_links.htm

CNET209/Contact.htm

CNET209/left_border.htm

http://t.extreme-dm.com

Default.htm

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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

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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

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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

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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

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HTML Example - The Markup

Q: How to obtain the above? Q: How to obtain the above?

A: Right-click on a web page then select A: Right-click on a web page then select View sourceView source

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HTML Example - The result

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Uniform Resource Locator (URL)

• Each resource on the web has an address

e.g. http://ted.see.plym.ac.uk/bogdan/CNET209/default.htm

2 Address of the host (DNS name or IP address)2 Address of the host (DNS name or IP address)3 Directory path of resource3 Directory path of resource4 Resource name4 Resource name

1 Transfer protocol used to access site (e.g. HTTP, FTP, TELNET)1 Transfer protocol used to access site (e.g. HTTP, FTP, TELNET)

11 22 33 44

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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

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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

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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, ...

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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

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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

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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

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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

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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!

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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)

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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

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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?

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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

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“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

texttext imageimage audioaudio videovideo

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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