Media Streaming Performance in a Portable Wireless Classroom Network

Presenter: Jean CaoSupervisor: Carey WilliamsonTRLabs & Dept. of Computer Science UoCApril 14, 2005

Motivations Media Traffic Characterization Classroom Measurements Extended Experiments:

Capacity Bottleneck The “Bad Apple” Phenomenon

Conclusions Current and Future Work

Outline

MotivationsOn-Line

Education

A French Cinematography

Class Test

Feasible?

Performance Issues?

Note: Citation numbers are referred to the corresponding references of the paper.

Server

ClientClient

Client

Sniffer

Protocol Efficiency?

WirelessLAN

PortableWireless ClassroomNetwork [7, 8, 11]

Multimedia Streaming [1, 2, 3, 4]

MotivationsOn-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?

WirelessLAN

PortableWireless Classroom

Network [7, 8, 11]

Multimedia Streaming [1, 2, 3, 4]

Server

ClientClient

Client

MotivationsOn-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?

WirelessLAN

PortableWireless Classroom

Network [7, 8, 11]

Server

ClientClient

Client

Multimedia Streaming [1, 2, 3, 4]

MotivationsOn-Line

Education

Feasible?

Performance Issues?

Note: Citation numbers are referred to the corresponding references of the paper.

Sniffer

Protocol Efficiency?

WirelessLAN

PortableWireless Classroom

Network [7, 8, 11]

Server

ClientClient

Client

Multimedia Streaming [1, 2, 3, 4]

A French Cinematography

Class Test

MotivationsOn-Line

Education

Note: Citation numbers are referred to the corresponding references of the paper.

Sniffer

WirelessLAN

PortableWireless ClassroomNetwork [7, 8, 11]

Server

ClientClient

Client

Multimedia Streaming [1, 2, 3, 4]

A French Cinematography

Class Test

Feasible?

Performance Issues?Protocol Efficiency?

MotivationsOn-Line

Education

Note: Citation numbers are referred to the corresponding references of the paper.

WirelessLAN

PortableWireless ClassroomNetwork [7, 8, 11]

Server

ClientClient

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-4 Audio @ 128 kbps

and 43 fps Video @ 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 Rate @ coarse-grain time scale

Variable Bit Rate @ 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

Time

Additional Experiments

8 clients saturate the network; and the 9th client degrades the performance of all clients equally.

Bottleneck – the wireless channel

The Bad Apple Phenomenon

Server

Client 1 Client 2 Client 3

The Bad Apple Phenomenon

Server

Client 1 Client 2 Client 3

X

The Bad Apple Phenomenon

Server

Client 1 Client 2 Client 3

X

The Bad Apple Phenomenon

Server

Client 1 Client 2 Client 3

X

One Bad Apple Spoils

the Batch!

The Bad Apple Phenomenon

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

The Bad Apple Phenomenon

Scenario Normal 4 Clients

1 Bad, Retry = 16

1 Bad, Retry = 1

Video rate (fps) 29.96 29.69 29.77Audio rate (fps) 43.09 41.84 42.90Avg skipped video frames (per client statistics)

0(0/0/0/0)

36(37/34/27/46)

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)

2.5 14.5 5.75

Playback Stats at Clients

Conclusions

Portable Wireless Classroom Network is a promising technology for education

Currently, 802.11b 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?