1 LYU0502 P2P Digital TV Recorder Supervisor: Professor Michael R. Lyu Prepared by:Ho Tsz Wing, Andy Lau Wai Shun, Jack.

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LYU0502LYU0502P2P Digital TV RecorderP2P Digital TV Recorder

Supervisor: Professor Michael R. Lyu

Prepared by:Ho Tsz Wing, AndyLau Wai Shun, Jack

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Outline• Motivation• Objective• Development Platform • Approach• Performance Enhancement• Erasure Code Analysis • Future Work• Conclusion• Q&A

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Motivation• Watching TV is a major entertainment activi

ty for people• People often miss their favorite program be

cause they have to work overtime or go out to travel

• People need to schedule the recording of the programs

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Objective• Allow people view to back previous TV

program without doing scheduling themselves

• Let the user view the program on demand

• Increase the availability of the TV program

• Achieve load balancing among the participating peers

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Develop Platform• Windows XP Media Center Edition• First released in Aug. 2003• Capable of watching DVD, recording TV, list

ening to music and sharing digital photos• Media Center Edition 2005 SDK – Click-To-R

ecord Feature• Enables applications to programmatically sche

dule the recording of TV programs• Supported in Visual C#.Net

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Windows XP Media Center Edition• Need an Electronic Program Guide (EPG) in

order to schedule the recording• Use TVxb to convert the schedule obtained fro

m webpage to an XML format• Use Quickguide to convert the XML schema to

the EPG

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Approach• Interface of the application

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Approach• There are different types of peer-to-peer fil

e sharing architectures according to their “degree of centralization”• Hybrid decentralized architectures (Napster)• Purely decentralized P2P architectures (Gnutell

a)• Partially centralized systems (KaZaA)

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Approach• In this term, we choose to implement

our system using the hybrid decentralized architectures

• There is a centralized server maintaining the list of online peers and the directories of the shared files

• The server is also responsible to schedule the recording to the online peers in a fair and efficient way

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Approach• On the other hand, the peers are

responsible to handle the scheduling request made by the server

• Also, they need to serve the downloading request from other peers

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Approach• Reasons to choose the hybrid

decentralized architectures• It is simpler to implement• It serves as a model for us to investigate

the feasibility of the project and measure the performance of the system under different peers behavior

• After implementing our system using the hybrid decentralized architectures, it is relatively easier for us to deploy it to the purely decentralized P2P architectures

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Approach• Component of the server

• p2p.mdb – database which maintains the peer table and share table

• Login.asp – make entries in the peer table and share table when a user login

• Search.asp – search the file requested by the user and generate suitable response

• Userlist.asp – return the list which contains the information of the currently logged-in peers

• Updateshare.asp – update the share table after a user recorded or downloaded a program

• Xml.asp – return the schedule of all the channels in a particular date

• Logout.asp - delete entries in the peer table and share table when the user logout

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Approach• The client side application

Start

Login to the system through login.asp

Listen to incoming connection

Upload requestRecording request

Upload the requestedfile to the peers

Schedule the recordingUsing click-to-record

feature

Download request

Search peers usingsearch.asp

Connect to the peersand start downloading

No

YesYes

Logout the system through logout.asp

Stop

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Approach

Alice Bob

Suppose Alice wants to see the program “ The Apprentice (III) “She will send a query to the serverThe server will reply to Alice with the list of peers

(Bob) that have a copy of “The Apprentice (III) “

She will then make a direct connection to Bob to get the file

The Apprentice (III)

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Performance enhancement• How to schedule the recording tasks to

the peers effectively?• How to increase the availability of the

video files? • How to improve the performance of

retrieving the video files from peers?

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Scheduling policies• Policies:

• Do scheduling 15 minutes before the program start

• Select the peers randomly• N peers will be scheduled• In this project, N is assigned to be 2

• Assumptions:• The selected peers will not leave manually• The peer who gets the whole video file has

the responsibility to do the encoding process

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Scheduling policies• The server side application

Start

Obtain the schedule of allchannel at 5:40 am everyday

Schedule the recording ofall program

Send the xml recordingrequest to the selected peers

Get 2 randomly selectedpeers from userlist.asp

15 minutes before thestart of a program

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Scheduling policies

Alice Bob

15 minutes before the program starts, the server will randomly send it’s schedule to any two of the online peers

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Availability enhancement• Whole file replication (WFR)

Advantages: 1) Multiple access of the video files

2) No decoding neededDisadvantages: 1) Storage overhead is large

2) Replication time is long

• Erasure Code replication (ECR)Advantages: 1) Multiple access of the video files

2) Storage overhead is smallDisadvantages: 1) Encoding and decoding time

2) Difficult to implement

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TVBNews.dvr-ms

Whole File Replication• Do replication on the whole file• Redistribute the file to other peers

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• Replication factor r• Peers availability P• Total Number of Peers N• Availability

• Independent of N• When P 1, A(w) 1• When r , A(w) 1

Whole File Replication

rPwA 11)(

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Erasure Code - BackgroundMessage n blocks

Encoding (to m blocks, where m > n)

Decoding (Requires any n blocks)

Message n blocks

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Erasure Code - Implementation• Divide the video file into n fragments• Code these n fragments in m (m>n)• Any n (unique) fragments are able to

reconstruct the video files• Send the fragments to random peers

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TVBNews.dvr-ms

Erasure Code• Do encoding on the whole file • Redistribute part of file to other peers

4

3 2

1

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Erasure Code - Analysis• Replication factor r• Divide the video file into n fragments• Code these n fragments in m (m>n)• Stretch factor s = m/n• Any n (unique) fragments are able to

reconstruct the video files

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Comparison – WFR Vs. ECR•Whole File Replciation - Availability

irir

i

r

i

rrrr

r

rr

C

CCwA

1

11)(

1

11

1

•Erasure Code Replciation - Availability

rm

ni

irmirm

i

rmrmrmrm

n

nrmnrm

n

C

CCSA

1

1...1

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Availability Analysis - µ = 0.1

Peer Availability (=0.1)

0

0.2

0.4

0.6

0.8

1

0 5 10 15 20

A(w)

A(E)

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0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20

A(w)

A(E)

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0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20

A(w)

A(E)

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0.96

0.97

0.98

0.99

1

1.01

1.02

0 5 10 15 20

A(w)

A(E)

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Availability Analysis - Conclusion• If the storage is not limited, ECRperforms better than WFR in most cases.

• When peer availability large than 0.5, the performance of WFR tends to ECR if the replication factor increases.

• However, the storage is limited in real world

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Storage Analysis - µ = 0.7


0.90

0.92

0.94

0.96

0.98

1.00

2 3 4 5 6 7 8

A(w)

A(E)

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Storage Analysis - Conclusion• If the peers availability is high, ECR is more storage-effective than WFR.

Adopted from : Replication Strategies for Highly Available Peer to Peer Networks,Ranjita Bhagwan et. al,

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Block Size Analysis – r = 2• If the storage is limited, the performance

of erasure code replication will highly depends on the peer availability

Adopted from : Erasure Code Replication Revisited,W.K. Lin, D.M. Chiu, Y.B. Lee

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Future Work• Implement the system in Server-less way• Design a algorithm for placing the

encoded check blocks • Investigate the relationships between

popularity and download frequency of a TV program (Dynamic replication factor)

• Implement choking algorithm to encourage users to share their own contents.

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Conclusion• We have implemented the P2P system

in the Server-Client model.• The availability of the TV Programs are

enhanced by using Erasure Code Replication.

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~ END ~~ END ~

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Q&A SessionQ&A SessionThank you very muchThank you very much

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Backup SlideBackup Slide

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Replication factor (r) File Availability (A)

5 0.40951

10 0.65132

15 0.79411

20 0.878423

Erasure Code Replication

r No of data block Total No of block Availability

5 4 20 0.13295

10 4 40 0.57687

15 4 60 0.86260

20 4 80 0.96469

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5 0.83193

10 0.97175

15 0.99525

20 0.99920



5 4 20 0.89291

10 4 40 0.99940

15 4 60 0.99999

20 4 80 0.99999

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5 0.968750

10 0.999023

15 0.999969

20 0.999999



5 4 20 0.998712

10 4 40 0.999999

15 4 60 0.999999

20 4 80 0.999999

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2 0.910000

4 0.991900

6 0.999271

8 0.999934


r No of data block Total No of Block Availability

2 4 8 0.942032

3 4 12 0.998308

4 4 16 0.999966

5 4 20 0.999999

1 LYU0502 P2P Digital TV Recorder Supervisor: Professor Michael R. Lyu Prepared by:Ho Tsz Wing, Andy Lau Wai Shun, Jack.

Documents

peer table

share table

previous tv program

list of online peers

different peers behaviorafter

different types of peer

favorite program

user logoutapproachthe