The Internet and Internet Services

By Suresh Chand

 Important Questions

The Internet is a global networks that enables computers of all kinds to directly and transparently communicate and share services

Any two computers, having different software/hardware, can exchange information over the Internet, as long as they obey the technical rules of Internet communication.

The exchange of information occur among connected computers regardless of geographical located.

Download Application: Complete CSIT Notes Application

Internet Timeline/History

Internet started from a prototype research project.

Networking of computers origin at the US Department of Defense Advanced Research Projects Agency (DARPA)


  • ARPA (Advanced Research Project Agency) Sponsored by US Department of Defencedevelop ARPAnet; Internet predecessor.
  • Designed to connect Military research centers
  • Supports Internetworking
  • Overcoming the faults; TCP/IP was developed (set of rules used by a network for communication)


  • US National Science Foundation (NSF) designed a successor to ARPANET, called NSFNET. open for use to all university research groups, libraries and museums.


  • many Internet applications like electronic mail, newsgroups, file transfer facility andremote login were developed.
  • telnet


  • New application World Wide Web (WWW) it changed everything about internet
  • British scientist Tim Berners Lee


Mosaic browser; Netscape navigator(Market Dominant)

Internetworking Protocol

TCP/IP is the communication protocol for the Internet

It specifies how data is exchanged over the internet by providing end-to-end communications that identify how it should be broken into packets, addressed, transmitted, routed and received at the destination.

TCP/IP requires little central management, and it is designed to make networks reliable, with the ability to recover automatically from the failure of any device on the network.

The TCP/IP protocol has two parts: TCP and IP

How TCP/IP Works?

User Loaded Image | CSIT Guide
Step 1:

  • Each packet contains address, sequencing information, and error control information.The address is used to route the packet to its destination.
  • The error control information is used to check that the packet arrived at the destination is the same as that sent from the source

Step 2:

  • Internet Protocol (IP) allows different computers to communicate by creating a network ofnetworks.
  • IP handles the dispatch of packets over the network.
  • It handles the addressing of packets, and ensures that a packet reaches its destination traveling through multiple networks with multiple standards

step 3:

  • TCP sequencing information in the packet is used to reassemble the packets in order, at their destination

User Loaded Image | CSIT Guide

The Internet Architecture/Internet hierarchical

Architecture of Internet is hierarchical in nature

at center: “Backbone” ISPs (e.g., MCI, Sprint, AT&T, Cable and Wireless), national/international coverage

  • treat each other as equals

User Loaded Image | CSIT Guide

“Regional” ISPs: smaller ISPs

  • Connect to one or more Backbone ISPs, possibly other Regional ISPs

User Loaded Image | CSIT Guide

“Tier-3” ISPs and local ISPs

  • last hop (“access”) network (closest to end systems)

User Loaded Image | CSIT Guide

Internet Services

1. Electronic Mail

  • Electronic mail (E-mail) is an electronic message transmitted over a network.
  • E-mail is a text-based mail consisting of lines of text, and can include attachments (audio messages, pictures and documents).
  • Features:
    • Single/Multiple Reception
    • Convenience
    • Faster
    • Record/Reference
    • Attachments of files and documents
    • Unique emai-id enables feature of postal service.(send, reply, forward, store, delete etc)2/25/202014
    • Saves Money & Time
  • E-mail Address
    • Consist Three part
      Parts of Email | CSIT Guide
  • E-mail Message Format
    • consists of two parts-header and body.
  • E-mail Services
    • Application-based e-mail
    • Web-based e-mail
  • How E-mail Works
    • client-server model.
    • E-mail clients
    • E-mail server
    • (POP3), (SMTP) & (IMAP).

How E-mail works | CSIT Guide

Post Office Protocol 3, Simple Mail Transfer Protocol & Internet Message Access Protocol

SMTP (Simple Mail Transfer Protocol)

SMTP (Simple Mail Transfer Protocol) | CSIT Guide

SMTP function is different from the other two.

SMTP mostly used forsending outemail from an email client (e.g. Microsoft Outlook, Thunderbird or Apple Mail) to an email server.

It’s also used forrelayingorforwardingmail messages from one mail server to another.

The ability to relay messages from one server to another is necessary if the sender and recipient have different email service providers.

uses TCP/IP port 25 by default.

POP3 (Post Office Protocol 3)