Internet Services - Introduction to Computing - Lecture Slides, Slides of Introduction to Computing

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CS101 Introduction to Computing

Lecture 30

Internet Services

During the last lecture … (Introduction to the Internet)

• We looked at the role Internet plays in today’s computing
• We reviewed some of the history and evolution of the Internet

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The Internet is unlike

any previous human

invention. It is a

world-wide resource,

accessible to all of

the humankind.

Key Characteristics (1)

Geographic Distribution

Global - reaches around the world

Robust Architecture

Adapts to damage and error

Speed

Data can travels at near ‘ c’ on copper, fiber, airwaves

Internet: Network of Networks

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• A large number of networks, interconnected physically
• Capable of communicating and sharing data with each other
• From the user’s point view, Internet – a collection of interconnected networks – looks like a single, unified network

TCP/IP (2) Transmission Control Protocol/Internet Protocol

• TCP breaks down the message to be sent over the Internet into packets
• IP routes these packets through the Internet to get them to their destination
• When the packets reach the destination computer, TCP reassembles them into the original message

1980's

1983 - The TCP/IP protocols becomes the only set of protocols used on the ARPANET

This sets a standard for all networks, and generates the use of the term Internet as the net of nets

1990's

1993 - CERN releases WWW, developed by Tim Berners-Lee

It uses HTTP and hypertext, revolutionizing the way info is presented & accessed on Internet

Today’s Goal: Internet Services

• To look at several services provided by the Internet
• FTP
• Telnet
• Web
• eMail
• Instant messaging
• VoIP

But first, we need to find out about the addressing scheme used on the Internet

Internet Addressing

• Regular post cannot be delivered unless we write a destination address on the envelope
• Same is true for the Internet
• Regular post can be delivered at the intended address even if the given address is not precise. That is not the case for Internet addressing

IP Address (1)

• A unique identifier for a computer on a TCP/IP network
• Format: four 8-bit numbers separated by periods. Each 8-bit number can be 0 to 255
• Example:
  • 203.215.177.33 (IP address of the VU Web server)

server

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client

Domain Names

• IP addresses are fine for computers, but difficult to recognize and remember for humans
• A domain name is a meaningful, easy-to-remember ‘label’ for an IP address
• Examples:

203.215.177.33 www.vu.edu.pk 216.239.33.101 www.google.com

DNS: Domain Name System (1)

• DNS is the way that Internet domain names are located & translated into IP addresses
• Maintaining a single, central table of domain name/IP address relationships is impractical - Billions of DNS-IP translations take place every day - The DNS-IP tables get updated continuously