Transcript Get|Post
GETTING CONNECTED Session III 11:15 - 12:15 Dr Deepak B Phatak, IIT Bombay MODERN INFORMATION DELIVERY MECHANISMS Early Networks Modern Network Components Emerging Network Scenario Dr. Phatak, IIT Bombay Getting Connected 2 EARLY NETWORKS Computer – to Devices RS. 232, Parallel Centronics port Computer – to Intelligent Devices Escape Sequences, Disk Read/Writes Computers Dr. Phatak, IIT Bombay to Computers Getting Connected 3 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 4 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 5 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 6 ASYNCHRONOUS DATA TRANSMISSION High Overhead (20%) Slower Speeds Simpler Circuitry Lower Cost Dial-up Lines Dr. Phatak, IIT Bombay Getting Connected 7 SYNCHRONOUS DATA TRANSMISSION Low Overhead (Much Less Than 20%) High Speeds Complex Circuitry Higher Cost Leased Lines Dr. Phatak, IIT Bombay Getting Connected 8 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 9 SATELLITE COMMUNICATIONS Frequency Bands (Transponders) C Band Clashes With Terrestrial Radio Ku Band Affected By Rain (Dampening) Dr. Phatak, IIT Bombay Getting Connected 10 MODERN NETWORKS Content Independent Delivery Mechanism – Like Postal Service Addressing Dr. Phatak, IIT Bombay and Connectivity Issues Getting Connected 11 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 12 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 13 MODERN NETWORKS The Glue That Holds Things Together – – Software in Switches, Routers Protocol Stacks (Software) Within a Computer Dr. Phatak, IIT Bombay Getting Connected 14 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 15 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 16 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 Getting Connected 17 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 18 INTERNET GROWTH Number – 1969 – 1971 – 1977 – 1984 – 1987 – 1989 Dr. Phatak, IIT Bombay of Host Machines 4 23 111 1024 28174 130000 Getting Connected 19 INTERNET GROWTH Number of Host Machines – 10/1992 – 10/1993 – 01/95 – 01/96 – 01/97 Dr. Phatak, IIT Bombay 1,136,000 2,056,000 4,852,000 9,472,000 16,146,000 Getting Connected 20 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 21 ARRIVAL OF WWW Hyper Links Within Documents Browser as Front-End – NCSA Mosaic, 1993 – Marc Andreessen, Netscape, 1994 Dr. Phatak, IIT Bombay Getting Connected 22 GROWTH OF WWW Number of Web Sites – 06/1993 – 12/1993 – 06/1994 – 12/1994 – 06/1995 Dr. Phatak, IIT Bombay 130 623 2,738 10,022 23,500 Getting Connected 23 GROWTH OF WWW Number of Web Sites – 01/1996 – 06/1996 – 01/1997 – 06/1997 Dr. Phatak, IIT Bombay 100,000 252,000 646,000 1,117,000 Getting Connected 24 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 25 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 26 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 Getting Connected 27 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 28 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 29 FIREWALLS What is a Firewall: – System That Acts As a Security Buffer Between Your Intranet and The Outside Internet Dr. Phatak, IIT Bombay Getting Connected 30 PROPERTIES OF FIREWALLS Filtering and Screening Capabilities Authentication Levels Logging and Accounting Transparency and Flexibility Manageability Dr. Phatak, IIT Bombay Getting Connected 31 APPLICATIONS ON INTERNET What Is A Socket? Analogy With Telephone Instrument, Number, Line Dr. Phatak, IIT Bombay Getting Connected 32 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 33 WEB MODEL Hyber-Text Transfer Protocol (HTTP) Browser Decides How To Display Dr. Phatak, IIT Bombay Getting Connected 34 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 35 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 36 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) Dr. Phatak, IIT Bombay Getting Connected 37 WWW CLIENT SOFTWARE Browsers – Netscape, IE, Lynx Other – wget, WWW By Email! Dr. Phatak, IIT Bombay Getting Connected 38 BROWSERS Features Supported – Multimedia, Frames – Styles Sheets – Java Applets – Javascript – Secure Transactions Dr. Phatak, IIT Bombay Getting Connected 39 BROWSERS Performance Availability Cost Open Source Model! In The Future: Browser Is Everything! Dr. Phatak, IIT Bombay Getting Connected 40 POPULAR BROWSERS NCSA Mosaic Arena/Amaya (W3C) Red Baron (RedHat) Lynx Internet Explorer Netscape Navigator/Communicator Dr. Phatak, IIT Bombay Getting Connected 41 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 42 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 43 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 44 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 45 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 46 HTTP REQUEST HEADERS If-Modified-Since Pragma: “no-cache” User-Agent: Mozilla (Netscape), Lynx, ... Dr. Phatak, IIT Bombay Getting Connected 47 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 48 WEB SERVER SOFTWARE Cern httpd [European Laboratory For Particle Physics (CERN)] NCSA HTTPd Microsoft IIS Netscape Server Dr. Phatak, IIT Bombay Getting Connected 49 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 50 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 51 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 52 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 53 TWO WAYS TO RECEIVE DATA FROM FORMS Syntax: Form Action=“URL of Script” Method=[Get|Post]] Dr. Phatak, IIT Bombay Getting Connected 54 GET The URLencoded Data Is Made Available To The Script In The Environment Variable QUERY STRING Dr. Phatak, IIT Bombay Getting Connected 55 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. Dr. Phatak, IIT Bombay Getting Connected 56 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 Dr. Phatak, IIT Bombay Getting Connected 57