COMPUTER NETWORK

INTERNET AND ITS ARCHITECTURE

THE INTERNET

• An internet that spans the world is a computer network that interconnects hundreds of millions of computing devices throughout the world.

Internet Architecture

• Internet service provider(ISP) Tier -1 Tier- 2 Tier-1 and tier-2 ISP’s are network of routers that collectively

provide the internet’s communication infrastructure.• Access ISP : provides connectivity to the internet Traditional telephones Cable connections Wireless DSL

Internet Composition

Internet Addressing

• IP address : pattern of 32 or 128 bits often represented in dotted decimal notation.

eg - 140.201.8.221000110011001011 00001000 00010110

• Mnemonic address(alternative addressijng system more suitable for humans)

Domain namestop-level domains

Internet Software Layers

• Application : constructs message with address.• Transport : chops messages into packets. • Networks : handlesrouting through the internet• Link : handels actual transmission of packets.

Following A Message Through The Internet

Intrenet Protocols – TCP/IP protocol Suite

• Transport layer TCPUDP

• Network layerIP (IPv4 and IPv6)

Choosing between TCP and UDP

Traditional Internet Applications

• Electronic mail (email)Domain mail server collects incoming

mail and transmits outgoing mail.Mail server delivers collected incoming

mail to clients via POP3 or IMAP• File transfer protocol (FTP)• telnet and SSH• WWW (worl wide web)

Email Architecture

• E-mail system consists of two parts1) user agents , which allows peoples to read

and send email2) Message transfer agents, which move the

message from source to destination.

POP3• Starts when the user starts the mail reader• Mail reader calls up the ISP and establishes a TCP connections with

the message transfer agent on port 110; ~ authorization having user logged in by sending its username and password ~ transactions user collecting the e-mail and marking them for

deletion ~update causes the e-mail to be deleted

IMAP

• POP3 works fine for user with one e-mail account with one ISP accessed from one PC

~ if mail was accessed from different locations, user may loose emails , security issues may appear• An alternative final delivery protocol IMAP(internet

message access protocol) ~ instead assuming that all message will be downloaded

and work offline after that IMAP assumes that all email will remain on server indefinite in multiple mailbox

www

• WEB is a collection of web pages ,each page contains links to other pages.

• Hypertext – idea of having one page point to another. It is text, displayed on a computer ,with refrences to other text that the redear can immediately follow.

• Browser – program to view pages

Architectural Overview

HTTP• Hypertext transfer protocol is the transfer protocol used throughout

the world wide web.• It specifies what message clients may send to server and what

responses they get back in return.• Each interaction consists of one ASCII request followed by one RFC

822 MME-like response.• ConnectionsA browser contacts a server by making a TCP connection

on port 80. ~ In http1.0 after a connection was setup,one request

was sent over,one response was sent back,then TCP connection was released.

~ In http1.1 persistent connections are supported.