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Introduction to Networksand
the Internet
Bent Thomsen
Institut for Datalogi
Aalborg Universitet
October 2002 Bent Thomsen - FIT 2-1 2
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, ..
October 2002 Bent Thomsen - FIT 2-1 3
Small Local Networks
October 2002 Bent Thomsen - FIT 2-1 4
Local Area Networks
October 2002 Bent Thomsen - FIT 2-1 5
Large Local Area Networks
October 2002 Bent Thomsen - FIT 2-1 6
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
October 2002 Bent Thomsen - FIT 2-1 7
Direct connection
October 2002 Bent Thomsen - FIT 2-1 8
Client/Server connection
October 2002 Bent Thomsen - FIT 2-1 9
Web based client/server
October 2002 Bent Thomsen - FIT 2-1 10
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
October 2002 Bent Thomsen - FIT 2-1 11
The Internet is a collection of interconnected networks
October 2002 Bent Thomsen - FIT 2-1 12
Connecting to the Internet
• Through ISP– Modem dialup– Always-on: ADSL, Cable, FWA
• Direct/Dedicated network– Companies– Universities– (WLAN operators)
October 2002 Bent Thomsen - FIT 2-1 13
How to connect to the Internet
October 2002 Bent Thomsen - FIT 2-1 15
A bigger Internet backbone UUNet/WorldCom
October 2002 Bent Thomsen - FIT 2-1 16
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)
October 2002 Bent Thomsen - FIT 2-1 17
Package switched
October 2002 Bent Thomsen - FIT 2-1 18
Routing on the Internet
October 2002 Bent Thomsen - FIT 2-1 19
Things that may be in your way
• Operating system settings• Gateways• Firewalls• Proxy servers• Caches• Virus filters• Spam filters• Adult filters
October 2002 Bent Thomsen - FIT 2-1 20
Internet Applications
• Electronic mail (email)
• Mailing lists
• Newsgroups
• File Transfer
• Chat
• Instant Messaging
• World Wide Web
October 2002 Bent Thomsen - FIT 2-1 21
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
October 2002 Bent Thomsen - FIT 2-1 22
“a consensual hallucination experienced daily by billions of operators in every nation …”
Gibson
Cyberspace