Introduction to Networks and the Internet Bent Thomsen Institut for Datalogi Aalborg Universitet

Introduction to Networksand

the Internet

Bent Thomsen

Institut for Datalogi

Aalborg Universitet

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What is a network

• Carrier of data between connected computers• What does a network consist of?

– End hosts connected to the network– Physical links that carry data

• Ethernet, FDDI, ATM, …

– Routers/switches– Protocols

• TCP/IP, HTTP, FTP, SMTP, …

– Applications that communicate with each other• Printing, email, file transfer, web browsers, ..

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Small Local Networks

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Local Area Networks

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Large Local Area Networks

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Client/Server networking

• Access large data sets and huge computing resources from desktop machines

• Separate data processing from presentation• Facilitate several views on raw data • Split workload between machines across a

network – Do some processing locally and some on a server

– Middleware and distributed objects

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Direct connection

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Client/Server connection

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Web based client/server

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The Internet

• A set of connected networks– All use the same network protocol (IP)

• Most common protocol used is TCP/IP– Connection oriented– Reliable, in-order byte-stream

• Application protocols on top of TCP/IP– SMTP– HTTP– FTP

• UDP is another protocol– Used for streaming video and audio– Some peer-to-peer applications

Protocols define format,order of messages and actions taken on messages

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The Internet is a collection of interconnected networks

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Connecting to the Internet

• Through ISP– Modem dialup– Always-on: ADSL, Cable, FWA

• Direct/Dedicated network– Companies– Universities– (WLAN operators)

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How to connect to the Internet

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An Internet Backbone

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A bigger Internet backbone UUNet/WorldCom

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Some Internet basics

• Each computer on the internet has a unique address – the IP address– 123.225.409.109– Most end-user computers are allocated an IP

address when they connect – DHCP– IP addresses can be given a name

• E.g www.but.auc.dk

• Looked up via DNS (130.225.56.21)

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Package switched

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Routing on the Internet

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Things that may be in your way

• Operating system settings• Gateways• Firewalls• Proxy servers• Caches• Virus filters• Spam filters• Adult filters

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Internet Applications

• Electronic mail (email)

• Mailing lists

• Newsgroups

• File Transfer

• Chat

• Instant Messaging

• World Wide Web

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The World Wide Web

• 1991 The web (HTML/HTTP) - 1 web server

• 1993 The Mosaic Browser - 186 web servers

• 1994 Netscape – over 42000 web servers

• 1995 Internet Explorer - over 200000 web servers

• 1995 Java

• 1996 Browser wars – over 1 million web servers

• 1997 IE4

• 1998 XML and WAP – over 5 million web servers

• 1999 IE5

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“a consensual hallucination experienced daily by billions of operators in every nation …”

Gibson

Cyberspace