1. Overcoming the Challenges of Wireless in the Classroom Patrick Bristow Software Engineer, ConferenceXP External Research & Programs, Microsoft Research Thursday, July 21 th, 2005 Tablet PC Workshop

2. Outline What is multicast? Why use multicast over wireless? Great! What’s the problem? So what do we do?

3. What Is Multicast? Multicast is a type of traffic destined to a group of users (one-to-many type of traffic) What Isn’t Multicast? Unicast traffic is what makes up virtually all internet traffic today; i.e. HTTP goes over TCP, which is a reliable unicast protocol

4. source If Multicast Is Not Used … The Source can’t afford the bandwidth! The same traffic is going over one link multiple times. Thank you Sauleh Eetemadi for the animations!

5. source IP Multicast Was born with WWW in early 90’s, but deployment is far behind expectation!

6. Unicast Over Wireless

7. Multicast Over Wireless Wireless is already multicast

8. Multicast and Unicast Throughput over 802.11b Data source: Performance of Reliable Transport Protocol over IEEE 802.11 Wireless LAN: Analysis and Enhancement; Haitao Wu, et al; IEEE InfoCom 2002 7.9 Mbps 460 Kbps

9. Unicast: It Gets Worse… Wireless MAC contention The ‘x’ factor: TCP contention Wireless signal strength Competing signals / uses Result? It usually takes an act of God to get 20 laptops in the same room to have “usable” wireless.

10. Multicast Is My New Best Friend? Multicast doesn’t guarantee reception Data loss is “bursty” –(Ink packets are lost when slides aren’t) Hardware problems –Intel Centrino issue / PSP –Latest firmware for AP important –Unusual problems seen on ‘g’ networks

11. ConferenceXP “Research platform” / “RDK” –Free download for non-commercial use –Shared Source Two-part strategy: –High-quality A/V conferencing –In-class learning technology platform No perfect solution General upward trend; technology is still early Early adopter: Classroom Presenter

12. Looking Forward Reliable multicast (Wenjun Zeng) CXP 4.0 New wifi technologies Share your experiences: http://www.conferencexp.net/ Message Boards e-Mail Distribution Lists Soon to come: Wiki!