NUS.SOC.CS5248Ooi Wei Tsang

Previously, on CS5248..

NUS.SOC.CS5248Ooi Wei Tsang

IP Multicast

NUS.SOC.CS5248Ooi Wei Tsang

New Model: IP Multicast

sender

receivers

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Question 1

Router

G?

should I forward this packet to my

subnet?

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IGMP v2.0

JOIN messageA : “I want to join group G.”

QUERY messageR : “Which group have you joined ?”

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IGMP v2.0

LEAVE message“I want to leave group G”

Group-Specific Query“Anybody else belongs to group G ?”

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Rate Adaptations

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Layered Video

Layer 1 Layer 2 Layer 3

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TCP-Equation

Window size behavior in TCP/IP with constant loss probability T. Ott, J. Kemperman, and M. MathisJune 1997, HPCS 1997

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Heterogeneity

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Internet Heterogeneity

2 Mbps

40kbps

56kbps

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Two Simple Solutions

one stream to fit them all

send multiple streams

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Network

Encoder

Sender

Middlebox

Receiver

Decoder

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Receiver-Driven Layered Multicast

Steve McCanne, Van Jacobson, Martin VetterliSIGCOMM 1996

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Layered Multicast

1 Layer : 1 Multicast Group

Receiver subscribes to as many layers as desired

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RLM Example

S R1

R2

R3R4

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Questions

How many layers are enough?

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Solution: Join Experimenthighest layer = 1join layer 1while no packet loss

highest layer ++join next layer

leave highest layerhighest layer --

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Details

Tjoin

Time between join experiments

Tdetect

Time taken to detect packet loss

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Effects of Tjoin

Need to converge to the right level quickly Tjoin should be small

Repeated failed experiments congest networks Tjoin should be large

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Adapting Tjoin(i)

One Tjoin per layer

if join experiment for layer k fails

Tjoin(k) = Tjoin(k)*2

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Example

1

2

3

4

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Adapting Tdetect

Set Tdetect to large initial value

Estimate Tdetect with mean and deviationMeasure time between join and packet loss occur

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Two Problems

Interference Scalability

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Problem 1: Interference

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Problem 1: Interference

I see, layer 2 is bad for me..

I see, layer 2 is bad for me..

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Problem 2: Scalability

Lots of receivers Lots of experimentsLots of congestions

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Solution: Shared Learning

I am joining

layer 2, do not

disturb!

I am joining

layer 2, do not

disturb!

NUS.SOC.CS5248Ooi Wei Tsang

Solution: Shared Learning

NUS.SOC.CS5248Ooi Wei Tsang

Solution: Shared Learning

I am joining

layer 3, do not

disturb!

I am joining

layer 3, do not

disturb!

NUS.SOC.CS5248Ooi Wei Tsang

Solution: Shared Learning

I see, layer 3 is bad for me..

I see, layer 3 is bad for me..

NUS.SOC.CS5248Ooi Wei Tsang

Solution: Shared Learning

I see, layer 3 is bad for me..

I see, layer 3 is bad for me..

NUS.SOC.CS5248Ooi Wei Tsang

Problem

Reducing interference decrease convergence time

Solution:

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Evaluation

Session Size

Convergence Time (s)

20

100

2 100

40

60

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EvaluationLoss Rate (%)

Session Size

1

100

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Problems with RLM

Not TCP Friendly

Share learning is “clumsy”

Failed join experiments is bad for the network

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Thin Streams: An Architecture for Multicasting Layered Video

L. Wu, R. Sharma., B. SmithNOSSDAV 97

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How bad is failed experiment?

R : sending rate of a layerTj : IGMP join latency

Tl : IGMP leave latency

Tdetect: time before drop

Buffer space at the router =

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How big is IGMP Leave Latency?

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What To Do?

Buffer space at the router = R(Tj + Tl + Tdetect)

Proposal of ThinStreamReduce RReduce Tdetect

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Reducing Tdetect

Detect congestion before it happens

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Calculating A & E

R : bandwidth of one layer I : measurement interval N : number of bytes received in I

G : number of layers joined

A =

E =

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ThinStreams Algorithm

if (E - A > leave_threshold)leave

else if (at least Tjoin since last join)

and (E - A < join_threshold)

join

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Fairness

Improve fairnessleave_threshold as a function of G

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Problems with ThinStreamSmall R

Still not TCP friendly

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TCP-Like Congestion Control for Layered Multicast Data Transfer

L. Vicisano, J. Crowcroft, L. RizzoINFOCOM 98

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The RLC Protocol

1. Try to emulate TCP2. Synchronize join3. “Probe” before join

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Recall TCP’s Behavior

AIMD

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Recall Layered Multicast

1

2

3

4

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1. Emulating TCP

Idea: By finding appropriate Bi and Tjoin(i)

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Idea

12

3

4

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2. Synchronizing Join

Idea: send special packets in data stream to signal join

Distance between synchronization point for layer i is Tjoin(i)

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Sync Point

1

2

3

4

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3. Probe before Join

Emulate joining the next layer

If this causes packet drop, don’t join

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Sender-Based Probing

baselayer

layeri

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Sender-Based Probing

baselayer

layeri

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Problems with RLC

Burst too short

No fine grain increment

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Summary

Receiver Driven Layered Multicast

Lots of ProblemsNo Perfect Solutions