Transcript Receiver Capability Heterogeneity in the Internet

Receiver Capability
Heterogeneity in the
Internet
Agenda
Introduction
 Some proposed approaches
 Performance comparison
 Summary
 Discussion

Introduction

Evolution of VoD systems
rental  Video over Internet
 Unicast  Multicast
 Video
4 data streams
1 data stream
VS
3 data streams
1 data stream
Introduction

Problem created by receiver capability
heterogeneity
1 Mbps
3 Mbps
Introduction

Trivial solutions, we either
 1.
leave video stream rate at 3 Mbps
 Unable to provide real-time streaming
 2.
reduce video stream rate to 1 Mbps
 Video quality degradation
Other Approaches
Replicated stream approach
 Layering approaches

 Cumulative
layering approach
 Non-cumulative layering approach
Replicated Stream Approach

Aggregate server bandwidth: 4 Mbps
Group of clients (CA) –
downlink: 1 Mbps
Sender
Group of clients (CB) –
downlink: 3 Mbps
Full quality stream (3 Mbps)
Low quality stream (1 Mbps)
Layering Approaches

Cumulative layering
 Base
layer + enhancement layers
 Cumulative decoding
 E.g. MPEG-2 and H.263 standards


Spatial scalability, temporal scalability, data partitioning and
SNR scalability
Non-cumulative layering
 Independently
decodable video layers
 E.g. Multiple Description Coding (MDC)
Layering Approaches

Aggregate server bandwidth: 3 Mbps
Group of clients (CA) –
downlink: 1 Mbps
Sender
Group of clients (CB) –
downlink: 3 Mbps
Enhancement layer (2 Mbps)
Base layer (1 Mbps)
Comparison between the Two
Approaches

Common argument:
 Stream
replication wastes server bandwidth
by stream duplication

However, no quantitative and systematic
comparison has been given
Some Counterarguments

Kim and Ammar [1] take into account of
 Layering
overhead
 Protocol complexity
for fair comparison
[1] T. Kim, M. H. Ammar , "A comparison of layering and stream replication video multicast schemes", Proc.
NOSSDAV‘ 01, Port Jefferson, NY, June 25-26, 2001.
Layering Overhead

Information theory states: For the same
source and same distortion,
(1)layered encoding requires at least as much
data rate as a non-layered encoding
(2)equality requires a strict Markov condition to
apply to the source
Layering Overhead

Protocol and packetization overhead
 Source
of overhead: start codes, GOP
information, picture header, macroblock
header etc.
 More severe at low data rates
 According to literature, overhead can be as
much as 20% ~ 30%
Layering Overhead - Example

Aggregate server bandwidth: 3 Mbps
Group of clients (CA) –
downlink: 1 Mbps
Sender
Group of clients (CB) –
downlink: 3 Mbps
Enhancement layer (2 Mbps)
Base layer (1 Mbps)

Take into account the overhead (e.g. 20%),
data rate contributing to video data:
 CA 
0.83 Mbps
 CB  2.5 Mbps
Video Quality Degradation

Layered (2 layers with different quantizer scales)
vs non-layered
Protocol Complexity

In layering protocols, number of channel
subscriptions >= 1, which incurs
 More
join / leave group messages
 Better synchronization capability
Summary
Three basic approaches to Internet
heterogeneity problem
 Superiority not always goes to layered
multicast protocol

Discussion

Possible applications in multicast VoD
systems
 Fast-forward
(FF) VCR operations
 Normal playback resumption after VCR
operations
Q&A

Thank you