A Method for P2P Streaming System Join Latency Reduction Using Preferred Peer Lists

A Method for P2P Streaming System A Method for P2P Streaming System Join Latency Reduction Join Latency Reduction

Using Preferred Peer ListsUsing Preferred Peer Lists

A Method for P2P Streaming System A Method for P2P Streaming System Join Latency Reduction Join Latency Reduction

Using Preferred Peer ListsUsing Preferred Peer Lists

Jeonghun NohJeonghun NohSachin Deshpande*Sachin Deshpande*

Information Systems LaboratoryInformation Systems LaboratoryStanford UniversityStanford University

* Sharp Laboratories of America* Sharp Laboratories of America

22J. Noh : A Method For Join Latency Reduction Of Using PPL Jan. 10 2008

Toward Low Latency P2P Video StreamingToward Low Latency P2P Video Streaming

• Real-time video streaming is time-sensitive.– Users prefer quick video play-back.– Channel surfing benefits from a short join latency.

• Join latency in P2P systems– During join procedure, new peers connect to peers

in the system to receive video.– Existing P2P networks: new peers blindly probe

for parents at random.

GOAL: Design a P2P network that provides a small join latency


OverviewOverview

• Preferred Peers List System– Overview– Preferred Peer Cache/List– Parent switching– Soft Handover

• Experimental Results• Conclusions


Overview: Preferred Peer List SystemOverview: Preferred Peer List System

• Preferred Peer Cache (PPC)– Caches information about available peers (preferred peers) in the

overlay.– Maintained by the source peer

• Preferred peers have a high probability of being available to other peers

• Using PPC for peer recommendations– New incoming peers contact the source peer. – The source peer sends a Preferred Peer List (PPL) containing

preferred peers.– The new peers directly contact the preferred peers to connect to.


Partial Learning of the OverlayPartial Learning of the Overlay• Source peer partially learns about the

overlay from the peer’s join / leave reports

X

S

PX

Y

PY

JOIN Report LEAVE Report


Using the Knowledge about the OverlayUsing the Knowledge about the Overlay

• A list of peers, PPL, is created when a recommendation is requested from new peers.

• Among the most recently updated peers, peers recommended less often are chosen.

PPC (at the source)

Peer address | Use-count | Update time (in secs)

Selected peers

3 0 24.0

12 2 23.0

7 3 20.0


Join Join PProcedure Using PPLrocedure Using PPLInitial join request• Contact video source• Receive number of trees, video rate• Receive flat list, preferred peer list (PPL)

Use probe replies; if preferred peer attempt fails.• Selects best parent from probe replies• Parent selection factor

– Available bandwidth– Minimize tree height

… …Video stream

Direct connection and peer probe• Contact preferred peers on PPL• Probe peers on flat list


Parent SwitchingParent Switching• Preferred peer recommendations do not

guarantee the best parents• One method to choose better parents

– Utilize collected probe replies– Perform the probe-based join process


Distribution Tree at time 71sDistribution Tree at time 71s

: peer that left the session

: video source

: peer in the session

No Parent Switch

Average Tree Height : 3.76Average PSNR : 39.71dB


: peer that left the session

: video source

: peer in the session

Parent Switch

Distribution Tree at time 71sDistribution Tree at time 71s

Average Tree Height : 2.67Average PSNR : 40.13dB


Soft HandoverSoft Handover• Parent switching may cause video discontinuity.• Using Soft Handover

– Keep old and new parents simultaneously so that both parents forward video packets.

– As soon as duplicate packets are detected, send leave message to old parent.


Experimental SetupExperimental Setup• Network simulation in ns-2

– 75 / 300 active peers – Random peer arrival/departure

average: ON (90 sec) / OFF (10 sec)– Peer uplink: typical access bandwidth / uniform bandwidth

• Video streaming– Mother & Daughter sequence encoded with H.264/AVC @ 281

Kb/s (CIF quality)– 15-minute live multicast

• System constructs 4 complimentary multicast trees.


Distribution of Join LatencyDistribution of Join Latency

First tree join time Full connection time

• Comparison of join time distribution– PPL system versus a probe-based system– Influence of peer uplink bandwidth: heterogeneous / uniform

distributions


Effects of Parent SwitchingEffects of Parent Switching

• Simulation setup: 500 secs, uniform bandwidth distribution for peer uplink

• PSNR averaged over 10 simulations and 75 peers

Probe-based

PPLPPL with

Parent Switch

PSNR (dB) 40.67 40.33 40.85

Average play-out latency (sec) 1.97 1.40 1.38


Effects of Soft HandoverEffects of Soft Handover

• Observations(+) Up to 55% of redundant packet forwarding is reduced(-) Slight PSNR drop may occur

Ignorant Handover

Soft Handover

Number of duplicate packets 7,677 3,448

Average video quality (dB) 39.89 39.72


ConclusionsConclusions

• PPC keeps partial information about the P2P overlay system.

• Preferred peers are selected from incomplete PPC.

• One step closer to low-latency P2P video streaming:– New peers can join faster.– By switching parent after PPL-based direct attach, overlay

quality is improved.– By Soft Handover, up to 55% of redundant video packet

transmission can be avoided.

Documents

A Method for P2P Streaming System Join Latency Reduction Using Preferred Peer Lists