IT

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IT som værktøj

• Bent Thomsen
• Institut for Datalogi
• Aalborg Universitet

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Opgaver og øvelser fra sidst

• Web search
• Instant messaging
• Unix X-win32 version 5.2.2
• LaTeX brug Unix maskinen dolomit

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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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Cyberspace
a consensual hallucination experienced daily by
billions of operators in every nation Gibson