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

2. October 2002Bent Thomsen - FIT 2-12 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,..

3. October 2002Bent Thomsen - FIT 2-13 Small Local Networks

4. October 2002Bent Thomsen - FIT 2-14 Local Area Networks

5. October 2002Bent Thomsen - FIT 2-15 Large Local Area Networks

6. October 2002Bent Thomsen - FIT 2-16 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

7. October 2002Bent Thomsen - FIT 2-17 Direct connection

8. October 2002Bent Thomsen - FIT 2-18 Client/Server connection

9. October 2002Bent Thomsen - FIT 2-19 Web based client/server

10. October 2002Bent Thomsen - FIT 2-110 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

11. October 2002Bent Thomsen - FIT 2-111 The Internet is a collection of interconnected networks

12. October 2002Bent Thomsen - FIT 2-112 Connecting to the Internet Through ISP –Modem dialup –Always-on: ADSL, Cable, FWA Direct/Dedicated network –Companies –Universities –(WLAN operators)

13. October 2002Bent Thomsen - FIT 2-113 How to connect to the Internet

14. October 2002Bent Thomsen - FIT 2-114 An Internet Backbone

15. October 2002Bent Thomsen - FIT 2-115 A bigger Internet backbone UUNet/WorldCom

16. October 2002Bent Thomsen - FIT 2-116 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.dkwww.but.auc.dk Looked up via DNS (130.225.56.21)

17. October 2002Bent Thomsen - FIT 2-117 Package switched

18. October 2002Bent Thomsen - FIT 2-118 Routing on the Internet

19. October 2002Bent Thomsen - FIT 2-119 Things that may be in your way Operating system settings Gateways Firewalls Proxy servers Caches Virus filters Spam filters Adult filters

20. October 2002Bent Thomsen - FIT 2-120 Internet Applications Electronic mail (email) Mailing lists Newsgroups File Transfer Chat Instant Messaging World Wide Web

21. October 2002Bent Thomsen - FIT 2-121 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

22. October 2002Bent Thomsen - FIT 2-122 “a consensual hallucination experienced daily by billions of operators in every nation …” Gibson Cyberspace