Peer-to-Peer Streaming

NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)

Peer-to-Peer Streaming


Peer-to-Peer StreamingA type of application-level

multicastBut packets are forwarded by end-

host (not proxies)


Peer-to-Peer StreamingALM with end-hosts as forwarders

S

Video Server

End Host

Overlay Links


Issues with P2P StreamingDepends on peers to forward

packets, but peers can fail/leave anytime

S


CoopNetResilient Peer-to-Peer Streaming, V. Padmanabhan et. al.ICNP 2003


IdeaSplit video into k “parts”, send one

part along one tree


“Smart” SplittingA node may be able to reconstruct

partial data with a subset of the parts

More parts, better quality

“Multiple Description Coding”


Simple Example (Video)Divide into two descriptions

1. Even frames 2. Odd frames

“Multiple State Encoding”

Does not scale to a large number of descriptions


Layered CodingLayer 1 Layer 2 Layer 3


Layered CodingOne layer one description?

But there are dependencies between the descriptions


Multiple Description Coding

D1

D3

D2

L1

L1

L1

L2.1

L2.2

L2.1XORL2.2

L3.1

L3.2

L3.3


Multiple Description CodingD1 L1 L2.1

L1 L2.3

L1 L2.1

L1 L2.3

D2

D3

D4

L3.1

L3.2

L3.3

XOR

L2.2

L2.4

L2.2

L2.4

L2.3

L2.4

L2.1

L2.2


How to Build Tree?Send one description along one

tree only

A node is internal node in at most one tree, and is leaf node in the rest of the trees


Example

R

31

42 65

R

42

31 65


Tree MaintenanceThe source of video maintains all

states.

Isn’t this a centralized design that is not robust?


Node JoinBecomes internal node in a tree

with least number of internal nodes.

Becomes leaf node in the rest of the trees.


To join as internal nodePick highest internal node with

enough bandwidth as parent.

If cannot find, pick internal node with leaf node as child, preempt the leaf node.


To join as leaf nodePick highest internal node with

enough bandwidth as parent.

If cannot find, migrate an internal node from another tree.


Network EfficiencyWhen choosing parents, breaks

ties by choosing closer node as parents.


Effects of Number of Trees


Effects of Number of Trees


MDC versus FEC


Summary of CoopNetRobustness through redundancy in

coding network paths


Issues with P2P StreamingNot all peers are happy to

contribute resources — selfish peers exist.

S


Deter Selfish PeersAdd a constraint:

A peer can only receive at most as much as it is willing to send

S/R >= 1


Practical Issues

Asymmetric Links

Differentdownlinkcapacity


DagsterContributor Aware P2P Streaming in Heterogeneous EnvironmentMMCN 2005


Goals Robustness wrt transient peers Deter selfish users without

restricting S:R ratioHeterogeneous receivers


Issue 1Heterogeneous receivers

Solution: Transcoding


Transcoding

S

C

B

A

D

E

F


Issue 2 Improve Robustness

Solution: Distributed Streaming


Distributed Streaming

S

C

B

A

D

E

F


Multiple State Encoding

S

C

B

A

D

E

F

1,2,3,4..

1,2,3,4..

1,3,5..

2,4,6..

2,4,6..


Issue 3Provide incentives without

constraining S:R ratio? Solution: give peers that pledge

more contributions some benefits “contributor-aware”


Providing Incentives Idea: allow a peer to preempt

another peer with smaller contributions

Benefits Lower rejection rate Closer to source


DAG Construction


Example

S

B

A0:30

15:5

15:5


Example

S

B

A0:30

15:5

15:5


Example

S

B

A0:30

15:5

15:5C

15:15


Example: Preemption

S

C

A0:30

15:5

15:15B

15:5


Example: Rejection

S

B

A0:30

15:5

15:5D

15:6


Preemption RulesA can preempt B if

A is willing to donate more than B B can find new parents after

preemption


Example

S

B

A0:30

15:5

15:5E

10:5


Example

S

B

A0:30

15:5

15:5E

10:5


Example

S

B

A0:30

15:5

15:5H

2:1

F2:1

G

10:5


Example: 2 Preemptions

S

B

A0:30

15:5

15:5H

2:1

F2:1

G

10:5


DetailsCentralized control at the server to

prevent illegal preemption


Details Minimize number of descendents

affected when preempting peers

Find a subset of children to preempt, such that number of descendents affected is minimized, and preempted bandwidth is enough for the new node.

KNAPSACK problem!


DetailsPrefer parents who are closer to

the source and have large contributions

NUS.SOC.CS5248-2015Roger Zimmermann (based in parton slides by Ooi Wei Tsang)

DetailsPeers can cheat by pledging more

contributions than they are capable of.

We can only do our best to detect such cheaters :-(


Evaluations


Simulation SetupHost characteristics based on

study of Gnutella and Napster by Saroiu et. al.

Number of Peers

Reje

ctio

n Ra

te Best Fit (no Preemption)

Contributor-Aware (with Preemption)

Non Contributor Aware (with Preemption)


Number of Peers

Aver

age

Leve

l

Contributor Aware

Non-Contributor Aware


Level

Aver

age

Don

ated

Ba

ndw

idth

Contributor Aware

Non-contributor Aware


Requested Bandwidth

Don

ated

Ban

dwid

th

Admitted

Rejected


Number of ParentsDagster limits maximum number

of parents a node can have.How many is ideal?


Number of Peers

Reje

ctio

n Ra

te

P = 1

P > 1


Number of Peers

Aver

age

Leve

l

P = 2

P = 1


Robustness with PTypical frame-rate 24-30 fps. If P = 3, and one parent fails, then

clients can expect to receive 16-20 fps.

Remaining Tasks17 November 2015 (end of day):

Project reports and software due. In-class presentation on 17 & 18

November

Room and schedule will be announced shortly.


Documents

Peer-to-Peer Streaming