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Introduction to Networks
and
the Internet
Bent Thomsen
Institut for Datalogi
Aalborg Universitet
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
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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
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Operating system settings
Gateways
Firewalls
Proxy servers
Caches
Virus filters
Spam filters
Adult filters
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Internet Applications
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Electronic mail (email)
Mailing lists
Newsgroups
File Transfer
Chat
Instant Messaging
World Wide Web
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The World Wide Web
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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
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