Post on 09-Feb-2016
description
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?