An Experimental Study of the Skype Peer-to-Peer VoIP System

An Experimental Study of the Skype Peer-to-Peer VoIP System

Saikat Guha, Cornell UniversityNeil DasWani, GoogleRavi Jain, GoogleIPTPS’06

Presenter: Te-Yuan

What do they want to know?

What makes Skype so successful? Compare with

File-sharing P2P network By Observing Skype’s

User behavior Node Session Time

Overlay Network Traffic SuperNode overlay network Overall utilization & resource consumption

Skype Three Services

two-way audio streams & conference call up to 4 users

Instant Message file-transfer

Structure Alike KaZaA

– SuperNode-based Ordinary Node (ON) Super Node (SN)

Outline - Experiments

Expt. 1: Basic operation Expt. 2: Promotion to supernode Expt. 3: Supernode network activity Expt. 4: Supernode and client population Expt. 5: Supernode presence

Expt. 1: Basic operation To Answer: How do two Skype clients co

nnect to each other? Normally,

ON send control traffic through SN-p2p Including

Availability information Instant messages Request for VoIP & File-transfer

What if ON is behind NAT/Firewall?

Expt. 1: Basic operation – Cont. NAT Traversal in Skype:

Level 0: Initiator NAT’ed Level 1: Recipient NAT'ed Level 2: Both NAT'ed (well-behaved NATs) Level 3: Both NAT'ed

Expt. 1: Basic operation – Cont. Level 0: Initiator NAT’ed

Expt. 1: Basic operation – Cont. Level 1: Recipient NAT’ed

Expt. 1: Basic operation – Cont. Level 2: Both NAT'ed (well-behaved NAT

s)

Expt. 1: Basic operation – Cont. Level 3: Both NAT'ed

Expt. 1: Basic operation – Cont.

Level 0

Level 1

Level 2

Level 3

Outline - Experiments

Expt. 1: Basic operation Expt. 2: Promotion to supernode Expt. 3: Supernode network activity Expt. 4: Supernode and client population Expt. 5: Supernode presence

Expt. 2: Promotion to supernode To Answer: What kind of node will be pro

mote to SN? Setup several Skype clients

One behind a saturated network uplink One behind a NAT One with a 10 Mbps connection & public IP

Key to be SN plenty of spare bandwidth publicly reachable

Outline - Experiments

Expt. 1: Basic operation Expt. 2: Promotion to supernode Expt. 3: Supernode network activity Expt. 4: Supernode and client population Expt. 5: Supernode presence

Expt. 3: Supernode network activity Goal: To observe the network traffic of a

Skype supernode Duration: 135 days (Sep. 1, 2005 to Jan. 1

4, 2006) Data captured: 13GB with ethereal

Expt. 4: Supernode and client population Goal: Collect SN & client IP/port Duration:2005/7/25 – 2005/10/12 Result:

Crawl 150K SN Collect 250K SN info

Expt. 4: Supernode and client population

A list of SN

Connect to a SN

Save the list

Connect to a SN from the list

A list of SN

Expt. 4: Supernode and client population Collect client info

Collect the number reported by skype client

Expt. 5: Supernode presence Goal: how many SN online at a give time Flow

Randomly Select 6000 SN - from the list collected by expt.

4 Send “application-layer Ping” Repeat every 30 mins for a month

Expt. 5: Supernode presence - Cont

Num. of SuperNode is more Stable

diurnal behavior of SNWeekend

Expt. 5: Supernode presence - Cont Geographic Distribution of Active SuperNodes

45--60%

peak at 11am UTC

(Europe mid-day)

20-25%

15-25%

Expt. 5: Supernode presence - Cont SuperNode Session Time

Median is 5.5h

Expt. 5: Supernode presence - Cont Fraction of supernodes joining or departing

Node arrival concentrated toward morning

Node departureconcentrated toward evening

Skype usage is correlated with working hours

Different from P2P file-sharing

Expt. 5: Supernode presence - Cont Node Arrival dependent

on Time Not Poisson or Uniform

process Poisson process with

varying hourly rate

Node arrival concentrated toward morning

Node departureconcentrated toward evening

VoIP in Skype: Preliminary Observation SuperNode Traffic

90.4%SN no need to relay VoIP traffic

VoIP in Skype: Preliminary Observation VoIP Relayed Session Arrival Behavior

Inter arrival time of Relayed VoIP/File sessions may be Poisson

VoIP in Skype: Preliminary Observation VoIP Session Length Behavior Skype:

Median: 2m50s

Average: 12m53s

Longest: 3h 26s

Traditional:

Average: 3m

Fraudulent:

Average: 9m

VoIP in Skype: Preliminary Observation File-transfer sizes

File size:

Median: 346kB

Conclusion First measurement study of Skype VoIP system Skype differs significantly from file-sharing P2P User Behavior

Diurnal & Work-week Calls are significantly longer File transferred are significantly smaller

SuperNode of Skype Consume little bandwidth Relatively stable