1. Motivation and Tools NETD411 – Computer Technology and Architecture

2. Contents Historic Motivation 1 Explosive Growth 2 Internet 3 Complexity 4 Abstractions and Concepts 5

3. Historic Motivation Early computers were expensive –Large footprint –Centralized Programs took a long time to run Couldn't afford to put computers everywhere

4. ARPA Advanced Research Projects Agency initiated project to connect researchers with computers Adopted new technology: –Packet switching –Internetworking Resulted in system for remote access to expensive resources

5. Packet switching Data transmitted in small, independent pieces –Source divides outgoing messages into packets –Destination recovers original data Each packet travels independently –Includes enough information for delivery –May follow different paths –Can be retransmitted if lost

6. Growth since 1981

7. Probing the Internet Two tools: –ping - sends message that is echoed by remote computer –traceroute - reports path to remote computer

8. ping Sends packet to remote computer Remote computer replies with echo packet Local computer reports receipt of reply

9. ping (Example) Can arrange to send multiple packets Reports round trip time

10. ping (Example)

11. traceroute Sends series of packets along path to destination –Each successive packet identifies next router along path –Uses expanding ring search Reports list of packets

12. traceroute (Example)

14. THANK YOU End of Presentation