An End-to-End Adaptation Protocol for Layered Video
Multicast Using Optimal Rate Allocation
Jiangchuan Liu, Member, IEEE, Bo Li, Senior Member, IEEE, and Ya-Qin Zhang, Fellow, IEEE
IEEE TRANSACTIONS ON MULTIMEDIA, VOL. 6, NO. 1, FEBRUARY 2004
Content
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Paper Overivew
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Related Works
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TCP-Friendliness
Layered Video Multicast
Rate Adaptation & Allocation
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Objective
Key Issues
Motivation of Paper
Sender-side functionality
Receiver-side functionality
Simulation Result
Paper Overview
Objectives
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Problem :
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Multicasting 시, coarse-grained layer subscription levels과
heterogeneous한 환경의 수신자가 요구하는 rate 간의 불일치
(mismatches)
To solve this problem
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Sender-side : support to dynamic and fine-grained layer rate allocation
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Rate allocation/layer 을 하기 위한 지표(기준)를 확립해야 한다.

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Application-aware Fairness index
Works 1 : 저자는 rate allocation에 대해, multicast session을 받는 모든 수신자의 expected
fairness index를 maximization 하자는 목표를 가지고 optimization problem을 formulate 한다.
Works 2 : 효과적인 scalable solution HALM(Hybirid Adaptation Layered Multicast)을 제시한다
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HALM Profit
It can be seamlessly integrated into an end-to-end adaption protocol.
This protocol takes advantage of the emerging fine-grained layered coding(2004년도) and is fully compatiable
with the best-effort internet infra-.
Key Issues
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Two key issues.
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Dynamic allocation layer rate allocation can be an
effective.
Practical complement : receiver-driven adaptation.
Question…
 What are the proper criteria for optimal allocation?
 How to derive an efficient algorithm for the optimal
allocation?
 How to design an integrated adaptation protocol
using the optimal allocation?
Motivation of this paper(3/3)

Real-time video transmission has to adapt to dynamic
network conditions
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For Adaptation :
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In traditional Unicast : usually done by the sender, which collects the
receiver’s status via a feedback alg. and adjusts its transmission rate
In Multicast : single rate를 가지기 때문에 다양한 환경의
users(required BW가 다 틀리기 때문)을 만족시켜줄 수 없다.
이 결과로 multicast에 fair distribution을 위해 multi-rate
multicast 방식이 제안됨.

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Fair distribution은 각 receiver는 하나의 세션 내에서 required BW
가 서로 틀림에도 불구하고, 자신의 capacity에 적합한 rate로 비디
오를 받는다.
이와 같이 주어진 multicast session 의 member와 관련되어 fairness
를 높이는 목적을 가지는 fair distribution 방식을 intra-session
fairness 라 부른다.
Motivation of this paper(2/3)
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A commonly used multi-rate multicast approach is
cumulative layered transmission :
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raw video  layered encoding : transmission (base,
Enhancement layer).
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As an example, layers can be mapped to different IP multicast groups
disadavantage:

실제적으로 layered encoder가 지원하는 layer는 개수의 제한이 있
고, receiver들의 다양한 환경에서 오는 required BW에 대한
control은 몇 개의 layer로써 control 하기는 힘들다.

또한 이런 점은 remarkable fairness degradation을 가져온다.
Motivation of this paper(3/3)
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To mitigate this problem,
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one possible solution is the use of fine-grained sender adaptation as a
complement, i,e., dynamically allocating the layer rates.
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First, the source coder should have the ability to control the layer rate.
Second, the sender should know the global state of the receivers.
Related Works
H.264/AVC Extension

FGS functionality has been removed from the SVC
specification that is still under development (SVC
amendment will be finalized by the next(Geneva) JVT
meeting beginning of July 07)
Related Works
TCP-Friendliness

TCP는real-time video delivery protocol로 사용하긴 힘
들다.
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Why? Because these applications usually require a smoothed
transmission rate and stringent restrictions on end-to-end
delay.
대부분의 internet traffic은 TCP인데 video streaming
protocols은 혼잡상황에 민감한 TCP flows를 많은 영
향을 끼치지 않는 한도 내에서 video traffic을 보장하기
위해 몇 가지 rate control algorithm이 필요하다.
Related Works
Design of TCP-Friendliness
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
Note that, short-term adaptation results in bandwidth
oscillations, which is not desirable for video transmission.
Thus our objective is to provide an adaptive protocol that
will not starve background TCP traffic and, meanwhile, try
to achieve a long-term fair share as close as possible.
Related Works
Layered Video Multicast

Receiver-driven Layered Multicast (RLM) is a pure end-toend adaptation protocol
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It sends each video layer over a separate multicast group.
A receiver periodically joins a higher layer’s group to explore
the available bandwidth.
Congestion detected : join-experiment
Shared learning mechanism : suppress to join experiment by
other receivers
Rate Adaptation & Allocation
Hybrid Adaptation Protocol For Layered
Multicast(HALM) Sender Functionality(1/2)
Layered Video
Layered
Encoder
Layer l
Enhancement
Layer
Base layer
bl
…
…
Layer 3
b3
Layer 2
b2
Layer 1
b1
cl
l denote the rate vector of the
cumulative layers,
l  (c1 , c2 ,..., cl )
discrete set offers all possible video rates that
a receiver in the session could receive
c2
c1
The layer rates are given by
bi , i =1, 2, 3, ... , l.
Let c j denote the cumulative layer
rate up to layer , that is,
the maximum rate delivered to
a receiver with an expected bandwidth r
thus will be
(r, l )  max{c : c  r , c  l )
Sender Report(SR) :
< SSRC, Stime,  l ,Response Reqeust >
i
Receiver 2
Receiver 3
SR
l
c j   bi , j  1, 2,..., l
Receiver 1
TSR s
Receiver 4
Expected BW :
The sender will adaptively allocate the layer rates
based on the distribution of the receivers’ expected bandwidths.
Hybrid Adaptation Protocol For Layered
Multicast(HALM) Sender Funtionality(2/2)


We assume a rate vector is different from the one in the
previous control period (in case they are the same, the
sender can offset the current vector by a small value).
Hence, the change of the rate vector can serve as an
implicit synchronization signal to trigger the receivers’
joining/leaving actions.
Hybrid Adaptation Protocol For Layered
Multicast(HALM) Receiver Functionality(1/3)

To be friendly to TCP, a receiver directly uses a TCP
throughput function to calculate its expected bandwidth.
s : packet size
RTT : round-trip time
RTO : retransmit timeout value
p : steady state loss event rate

Main operation of receiver’s
Hybrid Adaptation Protocol For Layered
Multicast(HALM) Receiver Functionality(2/3)
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Advantages
 First, it is TCP-friendly


because the rate is equivalent to or less than the long-term throughput of a
TCP connection running over the same path.
Second, it is scalable
 because the receivers’ joining/leaving actions are synchronized

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cf) RLM : shared learning
Finally, it is very robust

because the implicit signal will be detected even if some SR
packets are lost.
Hybrid Adaptation Protocol For Layered
Multicast(HALM) Receiver Functionality(2/3)

Configuration of Loss event parameter
Receiver 1
Receiver 2
Receiver 3
SR
TSR s
Receiver 4
persistent congestion
RR
- Response Report(RR) = <SSRC, expected bandwidth>
- RR serves as a request for RTT estimation
TRR s
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In highly dynamic network environment
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network load change during the interval  persistent
congestion
To avoid persistent congestion, if the loss rate p exceeds
a threshold, a receiver has the flexibility to leave
the highest layer being subscribed.
Sender-based Dynamic Rate Allocation(1/3)
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Optimization Criteria for Heterogeneous Receivers
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
Total Throughput ???
Fairness Index ???

with a cumulative subscription policy
 the subscription level of a receiver relies on its expected
bandwidth and the set of cumulative layer rates.

Fairness Index for a receiver with expected
bandwidth as follows:
This definition can be used to access the satisfaction of a receiver
when there is a performance loss incurred by a mismatch
between the discrete set of the possible receiving rates and the
expected bandwidth.
Sender-based Dynamic Rate Allocation(2/3)

Nonlinearity can be characterized by a utility function
we define an Application-aware Fairness Index

For a multicast session, our objective is to maximize the
expected fairness index
, for all the receivers in the
session by choosing an optimal layer rate vector.
where L is the maximum number of layers that the sender can manage.
Sender-based Dynamic Rate Allocation(3/3)

The complexity of this optimization problem can be
further reduced by considering some characteristics of a
practical layered coder.

Assume there are M operational points the set of operational
rates is given by  ={R , R ,...., R : R  R }
1
2
M
i 1
i
RM
…
QP value = { x,y.z ….} :
a finite set of admissible quantizers
RM
…
R3
R3
R2
R2
R1
R1
…
Optimal Allocation Algorithms(1/3)

Assume ,
the expected fairness index
can be calculated as follows:
Receiver
Layer l-1
Sender
Layer l
Layer l-1
Subscription level of receiver’s
Optimal Allocation Algorithms(2/3)


Let
: the maximum expected fairness index when cl is set to
the mth operational point, Rm
Recurrence relation
Rl
R2
R1
Optimal Allocation Algorithms(3/3)

according to the definition of
and the recurrence
relation, the following inequation holds for all
nonnegative
and nondecreasing
>= 0
Parameter Measurements and Local
Coordination

Estimation of Round-Trip Time(1/2)
 Obtaining an accurate and stable measurement of the

round-trip time is of primary importance for HALM
To find the “true RTT”, we must use a feedback loop

Feedback mechanism


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Many receiver’s & high frequency(BW??) : cause implosion at the sender
Many receiver’s & low frequency(BW??) : inaccurate conclusions.
Using two mechanism
Closed-loop RTT
the sender does not give a response to
each request but uses a batch process.
Open-loop RTT
The open-loop estimation method tracks
the one-way trip time from the sender
to the receiver and transforms it to an
estimate of RTT.
Parameter Measurements and Local
Coordination

Estimation of Round-Trip Time(2/2)

Timing diagram for closed-loop and open-loop RTT
estimations
where t0 and t’ are the current local time and the local time that the
request was initiated, respectively.
Note that an RTT estimate  can be expressed as
is the one-way trip time from the sender to the receiver and
is the time from the receiver to the sender.
Simulation Result(1/3)

Simulation Topology & Distribution of cumulative layer
rate without joining and leaving.
Simulation Time: 1000 sec (long-term : steady-state)
HALM init cumulative layer rates = { 256, 512, 1024 kbps}
Simulation Result(2/2)

Bandwidth distribution
between HALM and
TCP at different switches.
Simulation Result(3/3)
DISTRIBUTION OF THE RECEIVED BANDWIDTHS (Kbps).
THE RATIO IS OBTAINED BY DIVIDING THE LAYERED STREAM
BANDWIDTH BY THE TCP BANDWIDTH
LMSA(Layered Multicast Static Allocation) – U (Uniform Distribution)
: { 200, 1100, 2000 kbps}
Distribution of cumulative layer rates with
dynamic joining and leaving
LMSA – E (Exponential)
: { 256, 512, 1024 kbps}