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4 Δεκ 2013 (πριν από 3 χρόνια και 14 μέρες)

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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

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


䱯睥爠䍯Ct



Dial
-
up Lines

Dr. Phatak, IIT Bombay

Getting Connected

8

SYNCHRONOUS DATA
TRANSMISSION


Low Overhead (Much Less Than
20%)


High Speeds


Complex Circuitry


䡩杨敲⁃潳


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


K
u
Band Affected By Rain
(Dampening)

Dr. Phatak, IIT Bombay

Getting Connected

11







MODERN NETWORKS


Content Independent Delivery
Mechanism


Like Postal Service


Addressing and Connectivity Issues

Dr. Phatak, IIT Bombay

Getting Connected

12







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

Getting Connected

15







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

Getting Connected

18

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

Getting Connected

28

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

Getting Connected

31

PROPERTIES OF
FIREWALLS


Filtering and Screening Capabilities


Authentication Levels


Logging and Accounting


Transparency and Flexibility


Manageability

Dr. Phatak, IIT Bombay

Getting Connected

32

CLIENT
-
SERVER
APPLICATIONS ON
INTERNET


What Is A Socket?


Analogy With Telephone


Instrument, Number, Line

Dr. Phatak, IIT Bombay

Getting Connected

33

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:EL8Gur.x4@bhishma.cse.iitb.
ernet.in


gopher Gopher
gopher://gopherr.tc.umn.edu/11/Lib
raries


mailto Sending Email
mailto:grap@cse.iitb.ernet.in


telnet Remote Login
telnet://www.w3.org:80


Browser Hides Different Protocols


No Need To Learn Mail/ftp/telnet
etc.

Dr. Phatak, IIT Bombay

Getting Connected

38

WWW CLIENT SOFTWARE


Browsers


Netscape, IE, Lynx


Other



wget, WWW By Email!

Dr. Phatak, IIT Bombay

Getting Connected

39

BROWSERS


Features Supported


Multimedia, Frames


Styles Sheets


Java Applets


Javascript


Secure Transactions

Dr. Phatak, IIT Bombay

Getting Connected

40

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

Getting Connected

55

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.

Dr. Phatak, IIT Bombay

Getting Connected

57

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