Peer to Peer WorkshopUnderstanding Peer Abandonment in

BitTorrent networks

Introduction to BitTorrent

Introduction to BitTorrent

BitTorrent – Overview

Understanding Peer Abandonment

Abandonment – departure of a peer before completing the file download

Swarm size & Torrent

Size

Peer’s DL & Completion

rate

Challenges

Identify peer abandonment• How can we be sure that the peer has actually left?

Collect abandonment parameters• How can we know what’s the peer’s DL and completion

rate at abandonment?

Collect ‘enough’ information• How to collect enough information about abandonments

in the swarm for statistical purposes?

The BitTorrent Protocol

•Identify each other

Handshake•The pieces I hold

Bitfield

•I have a certain piece

Have

•I’m still here

Keep Alive

•An ID of the torrent

Info Hash•The client

stopped / completed

Stopped / Completed

Peer to Peer Peer to Tracker

Tracker to Peer

•A subset of peers from the swarm

Peers

What to do?

Client Tracker

Peer abandonment

An educated guess Using stopped event

Abandonment parameters

Conclude from events

Not in the protocol

Enough information

Connect to many peers

Who’ll use our tracker?

TIMCrawler ClientTorrent Impatience Monitor

Identify peer abandonment• Continuously try to reconnect to known non-seeders peers• ‘Play by the rules’

Collect abandonment parameters• Determine peer’s DL rate using the ‘Have’ frequency• Never become a seeder (to assure ‘Have’ msgs are sent)

Collect ‘enough’ information• Each test is a 24h run in a single swarm• Connect to many peers• Collect all data to a DB and analyze later

Results – Swarm size

up to 100 100-1000 1000 and over0%

2%

4%

6%

8%

10%

12%

14%1244 peers

3328 peers

16450 peers

Abandonment rate by number of seeders(total of 21022 peers)

Number of seeders

Aver

age

aban

donm

ent r

ate

Results – File size

<800MB 800MB-2GB >2GB4.8%

5.0%

5.2%

5.4%

5.6%

5.8%

6.0%

6.2%

5918 peers

8664 peers

6440 peers

Abandonment rate by file size(total of 21022 peers)

Torrent size

Aver

age

aban

donm

ent r

ate

Results – Completion rate

0-20 20-40 40-60 60-80 80-100

020406080

100120140160180200

Number of abandoners by completion rate(total of 536 peers)

Completion of torrent (%)

Num

ber o

f aba

ndon

ers

Results – Download rate0 10 20 30 40 50 60 70 80 90 100

110

120

130

140

150

160

170

180

190

200

210

220

230

240

250

260

270

290

05

101520253035404550

Number of abandoners by download rate (total of 277 peers)

Estimated download rate (kB/s)

Num

ber o

f aba

ndon

ers

Conclusions

•Higher abandonment rate on small swarms

Swarm size

•Does not seem to affect abandonment

File size

•Most abandoners departure at the very beginningCompletion

rate

•Significant impact of DL rate on abandonmentDownload

rate