Narendran Thangarajan,

Final Year CSE, SSNCE.

What makes a computer network Uses Explain how TCP/IP model evolved

◦ TCP/IP Model Network Access Layer

Internet Layer

Transport Layer

Application Layer

Sockets What happens when we open a website Various fields of research

Two computers connected with a cable

More than two computers connected using an internetworking device

Resource Sharing ◦ Hardware (Processor, Storage, Printers) ◦ Software (Google Docs)

Information Sharing ◦ Access required information anywhere (Files, DB) ◦ Search for Information (Google!)

Communication ◦ eMail and Chat ◦ Forums

Remote Computing Distributed Processing

◦ Grid Computing ◦ Hadoop

Two Sub-layers ◦ Physical Layer ◦ Data Link Layer

Physical Layer ◦ Consists of the basic networking hardware

transmission technologies ◦ Defines how raw bits are transmitted between

computers. ◦ Eg: Ethernet, SONET, USB, Wifi, WiMAX, Bluetooth, IRDA

Data Link Layer ◦ Provides a unique address to each computer.

(MAC Address)

Two major divisions ◦ Wired

Ethernet Physical Cables – Coaxial, UTP

SONET – Synchronous Optical Networking

USB

◦ Wireless

IEEE 802.11 – Popularly called “Wifi”

WiMAX

Bluetooth

IRDA

Infrastructure WLAN Access point bridges the wired network and the wireless network

Adhoc Wireless Networks Decentralized – Does not depend upon preexisting infrastructure

Once physically connected to the network, our computer is identified to the other systems using a hardware address called MAC Address

MAC Address is unique

48-bit address burnt into the NIC of every machine

Hub (Layer 1) Transmits the incoming data to all the nodes attached to it

Switch (Layer 2) Transmits the incoming data to the receiver alone

There must be atleast one switch that knows the location of all the systems in the network.

Any solutions?

Group a set of computers under a single IP network address.

There are many IP host addresses under a single network address. ◦ Eg: Network Address = 10.0.0.0

Host addresses = 10.0.0.1, 10.0.0.2,10.0.0.254

Each group is called a LAN (Local Area Network) and systems are connected using a Switch.

Routers make the Internet Layer of the TCP/IP stack.

Using the IP Address we can find a computer uniquely.

But communications take place between specific processes running on different computers

PORT NUMBERS to the rescue!

Port numbers is a number given to a software-construct and a logical endpoint (not a hardware component). Eg: HTTP – 8080, MySQL - 3306

IP Address Unique computer Port number Unique process

(IP Address : Port Number) Unique process in a given computer. The endpoint for any communication ie. A socket.

Eg: www.facebook.com would be running on 40.0.0.10:8080. 8080 is the port number since it’s a website.

Client Server Applications

Network

A client, A server, and network

Client Server

Client machine Server machine

The Web Service is provided by the server and the clients use these services

This is where sockets come in !!

Sockets

Introduced in BSD 4.1 UNIX 1981.

Sockets are the endpoints of any communication over the internet.

Sockets are identified by socket addresses.

Socket Address = IP Address + Port Number

Why IP Address + Port number?

• IP Address is of the form 10.0.0.1 • Port Number can be anything from 0 to 65,535.

IP Address – Choose network

Destination Socket = 10.0.0.2 : 80

10.0.0.0

20.0.0.0

30.0.0.0

40.0.0.0

IP Address -> MAC Address – Locate the specific system

Destination Socket = 10.0.0.2 : 80

10.0.0.1

10.0.0.2

Port Number – Process specific

Port 10000

Port 11000

Port 120000

Understanding Ports

Transport Layer

Port 1 10000

Port 2 11000

Port 3 12000

Port 4 13000

Gmail OutLook Express

YM AVG

Update

Port num 10000

Data “Hi!”

Packet

Network layer

What happens when you type

www.facebook.com?

Browser looks up IP Address

Browser DNS Cache OS Cache Router Cache ISP DNS Cache Recursive search After all this we get an IP address! The IP Address of

the actual web server where the files of facebook.com are stored.

Browser sends a HTTP request to the webserver

Browser cache?! – Not possible. Facebook is dynamic

GET http://facebook.com/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xaml+xml, [...] User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; [...] Accept-Encoding: gzip, deflate Connection: Keep-Alive Host: facebook.com Cookie: datr=1265876274-[...]; locale=en_US; lsd=WW[...]; c_user=2101[...]

Get the response from facebook.com server

Facebook sends back a permanently moved 301 to redirect the browser to www.facebook.com

HTTP/1.1 301 Moved Permanently Cache-Control: private, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Expires: Sat, 01 Jan 2000 00:00:00 GMT Location: http://www.facebook.com/ P3P: CP="DSP LAW" Pragma: no-cache Set-Cookie: made_write_conn=deleted; expires=Thu, 12-Feb-2009 05:09:50 GMT; path=/; domain=.facebook.com; httponly Content-Type: text/html; charset=utf-8 X-Cnection: close Date: Fri, 12 Feb 2010 05:09:51 GMT Content-Length: 0

Browser takes the redirection

Browser gets the actual IP address and makes a HTTP request to that address.

GET http://www.facebook.com/ HTTP/1.1 Accept: application/x-ms-application, image/jpeg, application/xaml+xml, [...] Accept-Language: en-US User-Agent: Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 6.1; WOW64; [...] Accept-Encoding: gzip, deflate Connection: Keep-Alive Cookie: lsd=XW[...]; c_user=21[...]; x-referer=[...] Host: www.facebook.com

Facebook.com server handles the request

First the web server handles the request.

Then the Request Handler (PHP, Perl, Java, etc.) takes the required data from the request and prepares the output.

Facebook.com sends the requested web page

HTTP/1.1 200 OK Cache-Control: private, no-store, no-cache, must-revalidate, post-check=0, pre-check=0 Expires: Sat, 01 Jan 2000 00:00:00 GMT P3P: CP="DSP LAW" Pragma: no-cache Content-Encoding: gzip Content-Type: text/html; charset=utf-8 X-Cnection: close Transfer-Encoding: chunked Date: Fri, 12 Feb 2010 09:05:55 GMT (Compressed data)2b3��������T�n�@����[...]

Actual data (after decompression)

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en" id="facebook" class=" no_js"> <head> <meta http-equiv="Content-type" content="text/html; charset=utf-8" /> <meta http-equiv="Content-language" content="en" /> ...

End of story