getting connected session iii 11:15 - 12:15 dr deepak b phatak, iit bombay

GETTING CONNECTED

Session III 11:15 - 12:15

Dr Deepak B Phatak,

IIT Bombay

Dr. Phatak, IIT Bombay

Getting Connected 2

MODERN INFORMATION DELIVERY MECHANISMS

Early Networks Modern Network Components Emerging Network Scenario


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


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


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


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)


Getting Connected 7

ASYNCHRONOUS DATA TRANSMISSION

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


Getting Connected 8

SYNCHRONOUS DATA TRANSMISSION

Low Overhead (Much Less Than 20%)

High Speeds Complex Circuitry Higher Cost Leased Lines


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?


Getting Connected 10

SATELLITE COMMUNICATIONS

Frequency Bands (Transponders) C Band Clashes With Terrestrial

Radio Ku Band Affected By Rain

(Dampening)



MODERN NETWORKS

Content Independent Delivery Mechanism– Like Postal Service

Addressing and Connectivity Issues



MODERN NETWORKS

Bandwidth needs– CD audio 706 kbps, Digital Phone 64

kbps

– Motion Video 96 Mbps

– MPEG-2, 6 Mbps



MODERN NETWORKS

More Bandwidth Issues– Bandwidth on Demand

– Virtual Circuits

– Isochronous Network Environment Needed (Low and Predictable Node to Node Delays)



MODERN NETWORKS

The Glue That Holds Things Together– Software in Switches, Routers

– Protocol Stacks (Software) Within a Computer



EMERGING NETWORK SCENARIO

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



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



LAN-WAN DIVIDE

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



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



INTERNET GROWTH

Number of Host Machines– 1969 4

– 1971 23

– 1977 111

– 1984 1024

– 1987 28174

– 1989 130000



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



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



ARRIVAL OF WWW

Hyper Links Within Documents Browser as Front-End

– NCSA Mosaic, 1993

– Marc Andreessen, Netscape, 1994



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



GROWTH OF WWW

Number of Web Sites– 01/1996 100,000

– 06/1996 252,000

– 01/1997 646,000

– 06/1997 1,117,000



DIMENSIONS OF WWW

Basic Characteristics– Hyperlinks - Distributed Documents

– URL : Uniform Resource Locator

– Multimedia data Software Becomes Mobile

– “Applets” in Java Language



INTRANET

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



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



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



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!



FIREWALLS

What is a Firewall:

– System That Acts As a Security Buffer Between Your Intranet and The Outside Internet



PROPERTIES OF FIREWALLS

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



CLIENT-SERVER APPLICATIONS ON INTERNET

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



EXAMPLE APPLICATIONS

From/etc/services on Unix Connection Oriented (TCP)

– Mail, Telnet, FTP

– WWW Browser Connectionless (UDP)

– SNMP

– NFS



WEB MODEL

Hyber-Text Transfer Protocol (HTTP)

Browser Decides How To Display



WWW CONTENT

Static Content– Text, Data, Pictures, Sound

– Viewer Has No Control Dynamic Content

– Interactive Games, Teaching Software, Drawings

– User Interacts/Controls Content



WWW DIMENSIONS

How To Get Non-static Information?

User Chooses Content He Desires To See

Gives Much More Power To WWW



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.



WWW CLIENT SOFTWARE

Browsers– Netscape, IE, Lynx

Other– wget, WWW By Email!



BROWSERS

Features Supported – Multimedia, Frames

– Styles Sheets

– Java Applets

– Javascript

– Secure Transactions



BROWSERS

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

Everything!



POPULAR BROWSERS

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



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



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



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



HTTP REQUEST HEADERS

HTTP REQUEST HEADERSAccept Which MIME Types The Client Will Accept

Accept-Encoding, Accept-Language Compress, gzip

Authorization Username And Password




Content-length: Specify How Many Bytes It Is Sending via POST

Content-type: Application From: User’s Email Address

(Privacy!)




If-Modified-Since Pragma: “no-cache” User-Agent: Mozilla (Netscape),

Lynx, ...



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



WEB SERVER SOFTWARE

Cern httpd [European Laboratory For Particle Physics (CERN)]

NCSA HTTPd Microsoft IIS Netscape Server



WEB SERVER SOFTWARE

Apache– King Of All Web Server

– 53% In Jan 1999

– Descended From NCSA httpd

– www.apache.org

– Open Source Model



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



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



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



TWO WAYS TO RECEIVE DATA FROM FORMS

Syntax: Form Action=“URL of Script”

Method=[Get|Post]]



GET

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



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.



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

getting connected session iii 11:15 - 12:15 dr deepak b phatak, iit bombay

Documents

u typical lan

mbps u global

terrestrial radio u

postal service u

pointtopoint link u

hubs u nodes

campus u ethernet

mbps u network switches