Overcoming the Challenges of Wireless in the Classroom Patrick Bristow Software Engineer, ConferenceXP External Research & Programs, Microsoft Research Thursday, July 21th, 2005 Tablet PC Workshop
Outline • What is multicast? • Why use multicast over wireless? • Great! What’s the problem? • So what do we do?
What Is Multicast? 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 • Multicast is a type of traffic destined to a group of users (one-to-many type of traffic)
If Multicast Is Not Used … source The Source can’t afford the bandwidth! The same traffic is going over one link multiple times. Thank you Sauleh Eetemadi for the animations!
IP Multicast source Was born with WWW in early 90’s, butdeployment is far behind expectation!
Multicast Over Wireless Wireless is already multicast
Multicast and Unicast Throughput over 802.11b 7.9 Mbps 460 Kbps Data source: Performance of Reliable Transport Protocol over IEEE 802.11 Wireless LAN: Analysis and Enhancement; Haitao Wu, et al; IEEE InfoCom 2002
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.
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
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
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!