Download PowerPoint

Experiences with Multimedia
Streaming over 2.5G and 3G
Networks
J. Chesterfield, R. Chakravorty, J.
Crowcroft, P. Rodriguez, S. Banerjee
Presented by Denny Iskandar
1. Introduction
• What?
– Evaluates performance of multimedia
streaming over wireless network.
• Why?
– 2.5G and 3G technologies are being deployed
everywhere (Europe, America, and Asia)
– Popularity of multimedia applications such as
videoconferencing, Voice over IP, and
audio/video broadcasting
1. Introduction
• Scope of experiment
– Measurements from real networks:
• The effect of heterogeneity of network is captured
by comparison across different network
technologies: (GSM), GPRS, and UMTS.
• Describes the importance of cooperation between
network and application using an application called
vorbistreamer.
Roadmap
1.
2.
3.
4.
Introduction
Network measurements
Application measurements
Conclusions
Application layer
Presentation layer
Session layer
Transport layer
Network layer
Data link layer
Physical layer
2. Network Measurements
• Multimedia traffic characterization
– Assume layered organization of media
– Bandwidth used ranges between a minimum
and a maximum target rate.
2. Network Measurements
2.1 Propagation delay and jitter
Figure taken from paper.
2. Network Measurements
2.1 Propagation delay and jitter
The figure is only an
approximation.
2. Network Measurements
2.1 Propagation delay and jitter
– Compare with ITU recommendation for voice
communications: RTT ≤ 500 ms
Mean
Variance
GSM
1460 ms
GPRS
220 ms
UMTS
30 ms
Not
80-500 ms 20-300 ms
mentioned
Note: For GPRS, disabling ARQ reduces jitter at the
cost of higher packet loss rate (around 3%).
2. Network Measurements
2.2 Capacity variation
Figure taken from paper.
2. Network Measurements
2.2 Capacity variation
Figure taken from paper.
2. Network Measurements
2.3 Summary
– Propagation delay and delay jitter are reduced
as link capacity increases.
– GPRS should disable ARQ for multimedia
application.
– Sub-packet error detection [1] improves
performance.
[1] J. Chesterfield, R. Chakravorty, S. Banerjee, P. Rodriguez and
I. Pratt. Transport Level Optimisations for Interactive Media
Streaming Over Wide-Area Wireless Networks. In WiOpt ’04,
2004.
3. Application Measurements
• Use Vorbis codec
– A layered codec, encodes data into a base
layer and enhancement layers
Figure taken from paper.
3. Application Measurements
• Design of vorbistreamer
– Implements IP-based data striping; this is
used to aggregate channel bandwidth.
– Uses RTP as transport protocol.
– Supports interactivity constraints from fully
interactive communication to one-way
streaming.
– Uses Vorbis codec.
3. Application Measurements
• Encoding techniques
– For multimedia application, reliability is
disabled
– Needs to add redundancy to multimedia data
to facilitate receiver-based repairs
– Also involves interleaving of encoding blocks
to reduce the effect of error burst
3. Application Measurements
3.1 Intra-packet redundancy (UEP)
Vorbis frame
Header
Base layer
frame1
RLC packets
EL1
EL2
...
n-2 frames
ELn
FEC1
FEC2
FEC blocks
3. Application Measurements
• Things to note:
– This “bucketing” is done at application layer,
the actual RLC packetization is done at link
layer.
– Multiple layers in one packet to minimize
header overhead.
3. Application Measurements
3.2 Inter-packet redundancy
• Cross-packet coding
– Sends parity data in separate packets than
the original data.
original data
parity data
d
The greater d is:
• The more effective recovery
• The greater recovery delay
3. Application Measurements
3.2 Inter-packet redundancy
• Cross-channel coding
– From tests, it is more likely that error occurs to
A and B than to B and C
A
B
C
channel 1
channel 2
3. Application Measurements
3.3 Interleaving
• Intra-packet: change the order of frames in
the same packet
• Inter-packet: change the order of packets
in the same channel
• Inter-channel:
channel 1
7
5
3
1
channel 2
8
6
4
2
3. Application Measurements
3.4 Comparison
Tables taken from paper.
4. Conclusions
• The need for cooperation between
network and application.
• Encoding and organization of multimedia
data is important.
• Benefits from aggregating independent
channels.
• Benefits from sub-packet error detection.
5. Related works
[1]
[2]
J. Chesterfield, R. Chakravorty, S. Banerjee, P.
Rodriguez and I. Pratt. Transport Level Optimisations
for Interactive Media Streaming Over Wide-Area
Wireless Networks. In WiOpt’04: Modelling and
Optimization in Mobile, Ad Hoc and Wireless
Networks, 2004.
R. Chakravorty, J. Chesterfield, P. Rodriguez and S.
Banerjee. Measurement Approaches to Evaluate
Performance Optimizations for Wide-Area Wireless
Networks. In Passive and Active Network
Measurement (PAM 2004) 5th International Workshop,
2004.