GETTING CONNECTED

1
GETTING CONNECTED

• Session III 1115 - 1215
• Dr Deepak B Phatak,
• IIT Bombay

2
MODERN INFORMATION DELIVERY MECHANISMS

• Early Networks
• Modern Network Components
• Emerging Network Scenario

3
EARLY NETWORKS

• Computer to Devices
• RS. 232, Parallel Centronics port
• Computer to Intelligent Devices
• Escape Sequences, Disk Read/Writes
• Computers to Computers

4
LOCAL AREA NETWORKS

• Within A Building, Campus
• Ethernet, Packet Switched Network
• TCP/IP Protocol
• IP Address 144.16.111.248
• Typical LAN 10/100 Mbps
• Network Switches, Hubs
• Nodes Connected Through RJ42

5
WIDE AREA NETWORKS

• Same Principle, Stretched Across cities,
  countries and the globe
• Variety of Media
• Telephone lines (PSTN)
• Microwave, Radio Links
• VSATS

6
MODEMS AND DATA COMMUNICATION

• Modulation Standards (V.32, V.32bis, V.fast)
• Interface Specifications (RS232, V.24, X.21)
• Error Correction (MNP Class 4, V.42)
• Data Compression (MNP Class 5, V.42bis)

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ASYNCHRONOUS DATA TRANSMISSION

• High Overhead (20)
• Slower Speeds
• Simpler Circuitry ? Lower Cost
• Dial-up Lines

8
SYNCHRONOUS DATA TRANSMISSION

• Low Overhead (Much Less Than 20)
• High Speeds
• Complex Circuitry ? Higher Cost
• Leased Lines

9
SATELLITE COMMUNICATIONS

• History
• Sputnik (1957), Explorer (1958), Intelsat,
  Comsat, .... INSAT
• Geo-Stationary Orbit (35,680 km)
• Footprint (30 of Earths Surface)
• Low-Orbit (Iridium, Inmarsat)
• Rotating Antenna, Out Of Range?

10
SATELLITE COMMUNICATIONS

• Frequency Bands (Transponders)
• C Band Clashes With Terrestrial Radio
• Ku Band Affected By Rain (Dampening)

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MODERN NETWORKS

• Content Independent Delivery Mechanism
• Like Postal Service
• Addressing and Connectivity Issues

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MODERN NETWORKS

• Bandwidth needs
• CD audio 706 kbps, Digital Phone 64 kbps
• Motion Video 96 Mbps
• MPEG-2, 6 Mbps

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MODERN NETWORKS

• More Bandwidth Issues
• Bandwidth on Demand
• Virtual Circuits
• Isochronous Network Environment Needed (Low and
  Predictable Node to Node Delays)

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MODERN NETWORKS

• The Glue That Holds Things Together
• Software in Switches, Routers
• Protocol Stacks (Software) Within a Computer

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EMERGING NETWORK SCENARIO

• Indian 64 Kbps, 2 Mbps
• Global T3, E3
• Address Bottleneck, IP-V6
• Frame Relay
• ATM - the Ultimate Winner?

16
LAN-WAN DIVIDE

• Why?
• Functionality Same
• Move Bits From Point A To Point B
• Obvious Differences
• Distance, Ownership
• Speeds (10 - 100 Mbps Vs Kbps)
• Protocols

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LAN-WAN DIVIDE

• LAN Is Shared Media
• WAN Is Point-to-point Link
• No Buffering Needed For LAN
• Memory Needed In WAN Routers!

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EVOLUTION OF INTERNET

• ARPANET of 60s
• TCP/IP included in BSD UNIX
• Extensively Used for E-Mail and News Groups
• Reducing Cost of Bandwidth
• Address Bottleneck

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INTERNET GROWTH

• Number of Host Machines
• 1969 4
• 1971 23
• 1977 111
• 1984 1024
• 1987 28174
• 1989 130000

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INTERNET GROWTH

• Number of Host Machines
• 10/1992 1,136,000
• 10/1993 2,056,000
• 01/95 4,852,000
• 01/96 9,472,000
• 01/97 16,146,000

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ARRIVAL OF WWW

• Traditional Network Utilisation
• E-mail, FTP, Telnet / rlogin, Gopher, News Groups
• HTTP and HTML Proposed
• 1989 Tim Berners-Lee at Cern
• Hyper Text Transfer Protocol
• Hyper Text Mark-up Language

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ARRIVAL OF WWW

• Hyper Links Within Documents
• Browser as Front-End
• NCSA Mosaic, 1993
• Marc Andreessen, Netscape, 1994

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GROWTH OF WWW

• Number of Web Sites
• 06/1993 130
• 12/1993 623
• 06/1994 2,738
• 12/1994 10,022
• 06/1995 23,500

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GROWTH OF WWW

• Number of Web Sites
• 01/1996 100,000
• 06/1996 252,000
• 01/1997 646,000
• 06/1997 1,117,000

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DIMENSIONS OF WWW

• Basic Characteristics
• Hyperlinks - Distributed Documents
• URL Uniform Resource Locator
• Multimedia data
• Software Becomes Mobile
• Applets in Java Language

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INTRANET

• A WAY OF CARRYING OUT ALL INTERNAL CORPORATE
  ACTIVITIES USING INTERNET DERIVED TECHNOLOGIES
  WHILE INTERACTING WITH CUSTOMERS ON INTERNET

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CORPORATE ENTITIES NEED

• Distributed Systems with Site Autonomy
• Access to these distributed databases on-line for
  Business
• Security against outsiders trying to access or
  change our corporate Data

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SOMETHING MORE

• Apart from the above, INTRANET ALSO MEANS
• A Common Interface to All End-users of the
  Corporation, Typically Based on a Browser
• Ability to Navigate Through Different Data Bases

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SECURITY IN INTRANET

• IP Network Is Inherently Unsafe.
• IP Addresses Can Be Faked
• Access to Your INTRANET GATEWAY May Permit Access
  to Your Corporate Data!

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FIREWALLS

• What is a Firewall
• System That Acts As a Security Buffer Between
  Your Intranet and The Outside Internet

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PROPERTIES OF FIREWALLS

• Filtering and Screening Capabilities
• Authentication Levels
• Logging and Accounting
• Transparency and Flexibility
• Manageability

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CLIENT-SERVER APPLICATIONS ON INTERNET

• What Is A Socket?
• Analogy With Telephone
• Instrument, Number, Line

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EXAMPLE APPLICATIONS

• From/etc/services on Unix
• Connection Oriented (TCP)
• Mail, Telnet, FTP
• WWW Browser
• Connectionless (UDP)
• SNMP
• NFS

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WEB MODEL

• Hyber-Text Transfer Protocol (HTTP)
• Browser Decides How To Display

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WWW CONTENT

• Static Content
• Text, Data, Pictures, Sound
• Viewer Has No Control
• Dynamic Content
• Interactive Games, Teaching Software, Drawings
• User Interacts/Controls Content

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WWW DIMENSIONS

• How To Get Non-static Information?
• User Chooses Content He Desires To See
• Gives Much More Power To WWW

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UNIFORM RESOURCE LOCATOR

• Name Used For
• http Hypertext (HTML)
• (http//www.cse.iitb.ernet.in)
• ftp FTP
• (ftp//ftp.cc.iitb.ernet.in/pub/unix)
• file Local File
  
• (/usr/pg96/graj/prog.c)
• news News Article
  newsEL8Gur.x4_at_bhishma.cse.iitb.ernet.in
• gopher Gopher
  gopher//gopherr.tc.umn.edu/11/Libraries
• mailto Sending Email
  mailtograp_at_cse.iitb.ernet.in
• telnet Remote Login
  telnet//www.w3.org80
• Browser Hides Different Protocols
• No Need To Learn Mail/ftp/telnet etc.

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WWW CLIENT SOFTWARE

• Browsers
• Netscape, IE, Lynx
• Other
• wget, WWW By Email!

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BROWSERS

• Features Supported
• Multimedia, Frames
• Styles Sheets
• Java Applets
• Javascript
• Secure Transactions

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BROWSERS

• Performance
• Availability
• Cost
• Open Source Model!
• In The Future Browser Is Everything!

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POPULAR BROWSERS

• NCSA Mosaic
• Arena/Amaya (W3C)
• Red Baron (RedHat)
• Lynx
• Internet Explorer
• Netscape Navigator/Communicator

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HTML TAGS

• ltHTMLgt ... lt/HTMLgt
• Declares The Web Page To Be Written In HTML
• ltHEADgt ... lt/HEADgt
• Delimits The Pages Head
• ltBgt ... lt/Bgt, ltIgt ... lt/Igt
• Set ... In Boldface, In Italics

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HTTP

• Hyper Text Transfer Protocol
• RFC 1945 By T. Berners-Lee, R. Fielding, H.
  Nielsen, Hypertext Transfer Protocol -
  HTTP/1.0, 05/17/1996
• Fielding, et. al., RFC 2068 HTTP/1.1 January 1997

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HTTP REQUESTS

• GET Fetches The Specified Document
• POST Sends User-specified Data To A Script And
  Returns The Results
• HEAD Requests Header Information About The
  Specified Document
• PUT Places A Document On The Server
• DELETE Deletes A Document On The Server

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HTTP REQUEST HEADERS

• HTTP REQUEST HEADERSAccept Which MIME Types The
  Client Will Accept
• Accept-Encoding, Accept-Language Compress, gzip
• Authorization Username And Password

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HTTP REQUEST HEADERS

• Content-length Specify How Many Bytes It Is
  Sending via POST
• Content-type Application
• From Users Email Address (Privacy!)

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HTTP REQUEST HEADERS

• If-Modified-Since
• Pragma no-cache
• User-Agent Mozilla (Netscape), Lynx, ...

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HTTP RESPONSE HEADERS

• Date The Current Date
• Last-Modified The Last Time The Requested
  Document Was Modified
• Expires The Date Which The Requested Document
  Expires

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WEB SERVER SOFTWARE

• Cern httpd European Laboratory For Particle
  Physics (CERN)
• NCSA HTTPd
• Microsoft IIS
• Netscape Server

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WEB SERVER SOFTWARE

• Apache
• King Of All Web Server
• 53 In Jan 1999
• Descended From NCSA httpd
• www.apache.org
• Open Source Model

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STEPS IN ONLINE FORM PROCESSING

• Have The User Fill Out An HTML Form
• Have The Browser Pass The Info To A CGI Script
• Have The Script Process The Info And Send An
  Acknowledgement To The User

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HOW TO MAKE AN ONLINE FORM

• Use Various HTML Form Elements To Get The Desired
  Info In A Convenient Manner
• Specify The Script Which Is To Process The
  Filled-in Info And Also The Method By Which To
  Send The Info

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STRUCTURE OF FORM ELEMENTS

• Textarea
• Menus
• Element With INPUT Tag
• Commonality In All These Elements
• Note That Each Element Has Basically a NAME And
  When The User Interacts With It Gets Some VALUE

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TWO WAYS TO RECEIVE DATA FROM FORMS

• Syntax Form ActionURL of Script
• MethodGetPost

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GET

• The URLencoded Data Is Made Available To The
  Script In The Environment Variable QUERY STRING

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POST

• In This, The URLencoded Data Is Passed Onto The
  STDIN. So The Script Has To Read STDIN. The
  Number Of Bytes To Be Read Is Given By the
  Content-Length Environment Variable.
• The CGI Interface Accepts A Couple Of Lines Of
  Info That Tell The Browser What It Should Be
  Doing.

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GIVING INFO TO THE BROWSER

• After Giving This Type Info, Send A Blank Line To
  Let The Browser Know That You Are Now Going To
  Send The Actual Info. To Be Displayed