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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, .. October 2002 Bent Thomsen - FIT 2-1 2 Small Local Networks October 2002 Bent Thomsen - FIT 2-1 3 Local Area Networks October 2002 Bent Thomsen - FIT 2-1 4 Large Local Area Networks October 2002 Bent Thomsen - FIT 2-1 5 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 6 Direct connection October 2002 Bent Thomsen - FIT 2-1 7 Client/Server connection October 2002 Bent Thomsen - FIT 2-1 8 Web based client/server October 2002 Bent Thomsen - FIT 2-1 9 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 October 2002 Bent Thomsen - FIT 2-1 Protocols define format, order of messages and actions taken on messages 10 The Internet is a collection of interconnected networks October 2002 Bent Thomsen - FIT 2-1 11 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 12 How to connect to the Internet October 2002 Bent Thomsen - FIT 2-1 13 An Internet Backbone October 2002 Bent Thomsen - FIT 2-1 14 A bigger Internet backbone UUNet/WorldCom October 2002 Bent Thomsen - FIT 2-1 15 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 16 Package switched October 2002 Bent Thomsen - FIT 2-1 17 Routing on the Internet October 2002 Bent Thomsen - FIT 2-1 18 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 19 Internet Applications • • • • • • • Electronic mail (email) Mailing lists Newsgroups File Transfer Chat Instant Messaging World Wide Web October 2002 Bent Thomsen - FIT 2-1 20 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 21 Cyberspace “a consensual hallucination experienced daily by billions of operators in every nation …” Gibson October 2002 Bent Thomsen - FIT 2-1 22