getting connected session iii 11:15 - 12:15 dr deepak b phatak, iit bombay
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TRANSCRIPT
Dr. Phatak, IIT Bombay
Getting Connected 2
MODERN INFORMATION DELIVERY MECHANISMS
Early Networks Modern Network Components Emerging Network Scenario
Dr. Phatak, IIT Bombay
Getting Connected 3
EARLY NETWORKS
Computer to Devices
– RS. 232, Parallel Centronics port Computer to Intelligent Devices
– Escape Sequences, Disk Read/Writes Computers to Computers
Dr. Phatak, IIT Bombay
Getting Connected 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
Dr. Phatak, IIT Bombay
Getting Connected 5
WIDE AREA NETWORKS
Same Principle, Stretched Across cities, countries and the globe
Variety of Media– Telephone lines (PSTN)
– Microwave, Radio Links
– VSATS
Dr. Phatak, IIT Bombay
Getting Connected 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)
Dr. Phatak, IIT Bombay
Getting Connected 7
ASYNCHRONOUS DATA TRANSMISSION
High Overhead (20%) Slower Speeds Simpler Circuitry Lower Cost Dial-up Lines
Dr. Phatak, IIT Bombay
Getting Connected 8
SYNCHRONOUS DATA TRANSMISSION
Low Overhead (Much Less Than 20%)
High Speeds Complex Circuitry Higher Cost Leased Lines
Dr. Phatak, IIT Bombay
Getting Connected 9
SATELLITE COMMUNICATIONS
History Sputnik (1957), Explorer (1958),
Intelsat, Comsat, .... INSAT Geo-Stationary Orbit (35,680 km) Footprint (30% of Earth’s Surface) Low-Orbit (Iridium, Inmarsat) Rotating Antenna, Out Of Range?
Dr. Phatak, IIT Bombay
Getting Connected 10
SATELLITE COMMUNICATIONS
Frequency Bands (Transponders) C Band Clashes With Terrestrial
Radio Ku Band Affected By Rain
(Dampening)
Dr. Phatak, IIT Bombay
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MODERN NETWORKS
Content Independent Delivery Mechanism– Like Postal Service
Addressing and Connectivity Issues
Dr. Phatak, IIT Bombay
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MODERN NETWORKS
Bandwidth needs– CD audio 706 kbps, Digital Phone 64
kbps
– Motion Video 96 Mbps
– MPEG-2, 6 Mbps
Dr. Phatak, IIT Bombay
Getting Connected 13
MODERN NETWORKS
More Bandwidth Issues– Bandwidth on Demand
– Virtual Circuits
– Isochronous Network Environment Needed (Low and Predictable Node to Node Delays)
Dr. Phatak, IIT Bombay
Getting Connected 14
MODERN NETWORKS
The Glue That Holds Things Together– Software in Switches, Routers
– Protocol Stacks (Software) Within a Computer
Dr. Phatak, IIT Bombay
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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?
Dr. Phatak, IIT Bombay
Getting Connected 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
Dr. Phatak, IIT Bombay
Getting Connected 17
LAN-WAN DIVIDE
LAN Is Shared Media WAN Is Point-to-point Link No Buffering Needed For LAN Memory Needed In WAN Routers!
Dr. Phatak, IIT Bombay
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EVOLUTION OF INTERNET
ARPANET of 60’s TCP/IP included in BSD UNIX Extensively Used for E-Mail and
News Groups Reducing Cost of Bandwidth Address Bottleneck
Dr. Phatak, IIT Bombay
Getting Connected 19
INTERNET GROWTH
Number of Host Machines– 1969 4
– 1971 23
– 1977 111
– 1984 1024
– 1987 28174
– 1989 130000
Dr. Phatak, IIT Bombay
Getting Connected 20
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
Dr. Phatak, IIT Bombay
Getting Connected 21
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
Dr. Phatak, IIT Bombay
Getting Connected 22
ARRIVAL OF WWW
Hyper Links Within Documents Browser as Front-End
– NCSA Mosaic, 1993
– Marc Andreessen, Netscape, 1994
Dr. Phatak, IIT Bombay
Getting Connected 23
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
Dr. Phatak, IIT Bombay
Getting Connected 24
GROWTH OF WWW
Number of Web Sites– 01/1996 100,000
– 06/1996 252,000
– 01/1997 646,000
– 06/1997 1,117,000
Dr. Phatak, IIT Bombay
Getting Connected 25
DIMENSIONS OF WWW
Basic Characteristics– Hyperlinks - Distributed Documents
– URL : Uniform Resource Locator
– Multimedia data Software Becomes Mobile
– “Applets” in Java Language
Dr. Phatak, IIT Bombay
Getting Connected 26
INTRANET
A WAY OF CARRYING OUT ALL INTERNAL CORPORATE ACTIVITIES USING INTERNET DERIVED TECHNOLOGIES WHILE INTERACTING WITH CUSTOMERS ON INTERNET
Dr. Phatak, IIT Bombay
Getting Connected 27
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
Dr. Phatak, IIT Bombay
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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
Dr. Phatak, IIT Bombay
Getting Connected 29
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!
Dr. Phatak, IIT Bombay
Getting Connected 30
FIREWALLS
What is a Firewall:
– System That Acts As a Security Buffer Between Your Intranet and The Outside Internet
Dr. Phatak, IIT Bombay
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PROPERTIES OF FIREWALLS
Filtering and Screening Capabilities Authentication Levels Logging and Accounting Transparency and Flexibility Manageability
Dr. Phatak, IIT Bombay
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CLIENT-SERVER APPLICATIONS ON INTERNET
What Is A Socket? Analogy With Telephone Instrument, Number, Line
Dr. Phatak, IIT Bombay
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EXAMPLE APPLICATIONS
From/etc/services on Unix Connection Oriented (TCP)
– Mail, Telnet, FTP
– WWW Browser Connectionless (UDP)
– SNMP
– NFS
Dr. Phatak, IIT Bombay
Getting Connected 34
WEB MODEL
Hyber-Text Transfer Protocol (HTTP)
Browser Decides How To Display
Dr. Phatak, IIT Bombay
Getting Connected 35
WWW CONTENT
Static Content– Text, Data, Pictures, Sound
– Viewer Has No Control Dynamic Content
– Interactive Games, Teaching Software, Drawings
– User Interacts/Controls Content
Dr. Phatak, IIT Bombay
Getting Connected 36
WWW DIMENSIONS
How To Get Non-static Information?
User Chooses Content He Desires To See
Gives Much More Power To WWW
Dr. Phatak, IIT Bombay
Getting Connected 37
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 news:[email protected] gopher Gopher gopher://gopherr.tc.umn.edu/11/Libraries mailto Sending Email mailto:[email protected] telnet Remote Login telnet://www.w3.org:80 Browser Hides Different Protocols No Need To Learn Mail/ftp/telnet etc.
Dr. Phatak, IIT Bombay
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WWW CLIENT SOFTWARE
Browsers– Netscape, IE, Lynx
Other– wget, WWW By Email!
Dr. Phatak, IIT Bombay
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BROWSERS
Features Supported – Multimedia, Frames
– Styles Sheets
– Java Applets
– Javascript
– Secure Transactions
Dr. Phatak, IIT Bombay
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BROWSERS
Performance Availability Cost Open Source Model! In The Future: Browser Is
Everything!
Dr. Phatak, IIT Bombay
Getting Connected 41
POPULAR BROWSERS
NCSA Mosaic Arena/Amaya (W3C) Red Baron (RedHat) Lynx Internet Explorer Netscape Navigator/Communicator
Dr. Phatak, IIT Bombay
Getting Connected 42
HTML TAGS
<HTML> ... </HTML> Declares The Web Page To Be Written
In HTML <HEAD> ... </HEAD> Delimits The Page’s Head <B> ... </B>, <I> ... </I> Set ... In Boldface, In Italics
Dr. Phatak, IIT Bombay
Getting Connected 43
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
Dr. Phatak, IIT Bombay
Getting Connected 44
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
Dr. Phatak, IIT Bombay
Getting Connected 45
HTTP REQUEST HEADERS
HTTP REQUEST HEADERSAccept Which MIME Types The Client Will Accept
Accept-Encoding, Accept-Language Compress, gzip
Authorization Username And Password
Dr. Phatak, IIT Bombay
Getting Connected 46
HTTP REQUEST HEADERS
Content-length: Specify How Many Bytes It Is Sending via POST
Content-type: Application From: User’s Email Address
(Privacy!)
Dr. Phatak, IIT Bombay
Getting Connected 47
HTTP REQUEST HEADERS
If-Modified-Since Pragma: “no-cache” User-Agent: Mozilla (Netscape),
Lynx, ...
Dr. Phatak, IIT Bombay
Getting Connected 48
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
Dr. Phatak, IIT Bombay
Getting Connected 49
WEB SERVER SOFTWARE
Cern httpd [European Laboratory For Particle Physics (CERN)]
NCSA HTTPd Microsoft IIS Netscape Server
Dr. Phatak, IIT Bombay
Getting Connected 50
WEB SERVER SOFTWARE
Apache– King Of All Web Server
– 53% In Jan 1999
– Descended From NCSA httpd
– www.apache.org
– Open Source Model
Dr. Phatak, IIT Bombay
Getting Connected 51
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
Dr. Phatak, IIT Bombay
Getting Connected 52
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
Dr. Phatak, IIT Bombay
Getting Connected 53
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
Dr. Phatak, IIT Bombay
Getting Connected 54
TWO WAYS TO RECEIVE DATA FROM FORMS
Syntax: Form Action=“URL of Script”
Method=[Get|Post]]
Dr. Phatak, IIT Bombay
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GET
The URLencoded Data Is Made Available To The Script In The Environment Variable QUERY STRING
Dr. Phatak, IIT Bombay
Getting Connected 56
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.