Media Streaming Performance in a Portable Wireless Classroom Network Presenter: Jean Cao Supervisor: Carey Williamson TRLabs & Dept. of Computer Science UoC April 14, 2005

 Motivations  Media Traffic Characterization  Classroom Measurements  Extended Experiments: Capacity Bottleneck The “Bad Apple” Phenomenon  Conclusions  Current and Future Work Outline

Motivations On-Line Education A French Cinematography Class Test Feasible? Performance Issues? Note: Citation numbers are referred to the corresponding references of the paper. Server Client Sniffer Protocol Efficiency? Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Multimedia Streaming [1, 2, 3, 4]

Motivations On-Line Education A French Cinematography Class Test Feasible? Performance Issues? Note: Citation numbers are referred to the corresponding references of the paper. Sniffer Protocol Efficiency? Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Multimedia Streaming [1, 2, 3, 4] Server Client

Motivations On-Line Education A French Cinematography Class Test Feasible? Performance Issues? Note: Citation numbers are referred to the corresponding references of the paper. Sniffer Protocol Efficiency? Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Server Client Multimedia Streaming [1, 2, 3, 4]

Motivations On-Line Education Feasible? Performance Issues? Note: Citation numbers are referred to the corresponding references of the paper. Sniffer Protocol Efficiency? Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Server Client Multimedia Streaming [1, 2, 3, 4] A French Cinematography Class Test

Motivations On-Line Education Note: Citation numbers are referred to the corresponding references of the paper. Sniffer Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Server Client Multimedia Streaming [1, 2, 3, 4] A French Cinematography Class Test Feasible? Performance Issues? Protocol Efficiency?

Motivations On-Line Education Note: Citation numbers are referred to the corresponding references of the paper. Wireless LAN Portable Wireless Classroom Network [7, 8, 11] Server Client Multimedia Streaming [1, 2, 3, 4] A French Cinematography Class Test Feasible? Performance Issues? Protocol Efficiency? Sniffer

Media Traffic Characteristics  Digitized 8 min clip from movie “Au Revoir Les Enfants (1998)”  Converted to MPEG kbps and 43 fps 400 kbps and 30 fps  Total 14,854 video frames Mean frame size 1,641 bytes 90% frames are [1 KB, 2 KB] 1.4% > 4 KB

Media Traffic Characteristics  Video Source Traffic Profile at Different Granularities: (a) 1 second(b) 3 seconds(c) 30 seconds(d) 1 minute Constant Bit coarse-grain time scale Variable Bit finer-grain time scale

Classroom Measurements  French cinematography class  System setup IEEE802.11b Ad Hoc Network (11Mbps theoretical bandwidth) 8 laptops as Clients (mpeg4player) 1 laptop as Server (Apache http server and Darwin Streaming server) 1 laptop as channel monitor (Sniffer software)  Procedure: Watch the 8 minute movie clip Complete the Web based multiple-choice quiz Review 2 short movie clips while answering questions

Classroom Measurements  Results Conducted successfully Feedbacks from students are positive

Classroom Measurements  Observations 469,778 packets tx over the channel 99.3% of UDP and 0.7% of TCP 0.025% CRC errors 0.43% MAC retransmissions First 200 seconds: TCP (RTSP) UDP (RTP) data packets After 10 minutes: TCP (HTTP) Heaviest demand from multimedia streaming Max throughput is about 4.6 Mbps (vs. 5-6 Mbps effective BW of 11b) TCP (RTSP) UDP (RTP) TCP (HTTP) UDP (RTP) 4.6 Mbps Time

Additional Experiments  8 clients saturate the network; and the 9 th client degrades the performance of all clients equally.  Bottleneck – the wireless channel

The Bad Apple Phenomenon Server Client 1Client 2Client 3

The Bad Apple Phenomenon Server Client 1Client 2Client 3 X

The Bad Apple Phenomenon Server Client 1Client 2Client 3 X

The Bad Apple Phenomenon Server Client 1Client 2Client 3 X One Bad Apple Spoils the Batch!

The Bad Apple Phenomenon

Server Wireless Network Interface Queue Wireless Channel MAC Protocol Client 1 Client 2 Client 3 Drop X

The Bad Apple Phenomenon

ScenarioNormal 4 Clients 1 Bad, Retry = 16 1 Bad, Retry = 1 Video rate (fps) Audio rate (fps) Avg skipped video frames (per client statistics) 0(0/0/0/0)0(0/0/0/0) 36 (37/34/27/46) 2(0/0/0/7)2(0/0/0/7) Avg dropped packets (per client statistics) 0 (0/0/0/2) 330 ( 309 / 320 / 294 / 399 ) 80 ( 80 / 77 / 83 / 729 ) Avg lateness (sec) Playback Stats at Clients

Conclusions  Portable Wireless Classroom Network is a promising technology for education  Currently, b network can support limited number of streaming clients, and the bottleneck is at the wireless channel  When system is overloaded, degrading performance for all clients  The “bad apple” phenomenon can seriously degrade multimedia delivery in wireless environments; can a security problem

Current and Future Work  More elegant solutions to the “bad apple” problem Adaptive MDMI (Multiplicative Decrease and Multiplicative Increase) algorithm Multi-Channel Multi-Rate algorithm  QoS support in Wireless LAN -- keep “bad apple” problem in mind

QUESTIONS?