it – som værktøj bent thomsen institut for datalogi aalborg universitet
TRANSCRIPT
IT – som værktøj
Bent Thomsen
Institut for Datalogi
Aalborg Universitet
September 2003 Bent Thomsen - FIT 1-1 2
Opgaver og øvelser fra sidst
• Web search
• Instant messaging
• Unix – X-win32 version 5.2.2
• LaTeX – brug Unix maskinen dolomit
Introduction to Networksand
the Internet
Bent Thomsen
Institut for Datalogi
Aalborg Universitet
September 2003 Bent Thomsen - FIT 1-1 4
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, ..
September 2003 Bent Thomsen - FIT 1-1 5
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