An experimental study of the skype peer to peer voip system
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An Experimental Study of the Skype Peer-to-Peer VoIP System. Saikat Guha, Cornell University Neil DasWani, Google Ravi Jain, Google IPTPS ’ 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

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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 University

Neil DasWani, Google

Ravi Jain, Google

IPTPS’06

Presenter: Te-Yuan


What do they want to know
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
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
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
Expt. 1: Basic operation

  • To Answer: How do two Skype clients connect 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
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 cont1
Expt. 1: Basic operation – Cont.

  • Level 0: Initiator NAT’ed


Expt 1 basic operation cont2
Expt. 1: Basic operation – Cont.

  • Level 1: Recipient NAT’ed


Expt 1 basic operation cont3
Expt. 1: Basic operation – Cont.

  • Level 2: Both NAT'ed (well-behaved NATs)


Expt 1 basic operation cont4
Expt. 1: Basic operation – Cont.

  • Level 3: Both NAT'ed


Expt 1 basic operation cont5
Expt. 1: Basic operation – Cont.

Level 0

Level 1

Level 2

Level 3


Outline experiments1
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
Expt. 2: Promotion to supernode

  • To Answer: What kind of node will be promote 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 experiments2
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
Expt. 3: Supernode network activity

  • Goal: To observe the network traffic of a Skype supernode

  • Duration: 135 days (Sep. 1, 2005 to Jan. 14, 2006)

  • Data captured: 13GB with ethereal


Expt 4 supernode and client population
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 population1
Expt. 4: Supernode and client population

Connect to a SN

A list of SN

Save the list

Connect to a SN from the list

A list of SN


Expt 4 supernode and client population2
Expt. 4: Supernode and client population

  • Collect client info

    • Collect the number reported by skype client


Expt 5 supernode presence
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
Expt. 5: Supernode presence - Cont

Num. of SuperNode is more Stable

diurnal behaviorof SN

Weekend


Expt 5 supernode presence cont1
Expt. 5: Supernode presence - Cont

  • Geographic Distribution of Active SuperNodes

15-25%

20-25%

45--60%

peak at 11am UTC (Europe mid-day)


Expt 5 supernode presence cont2
Expt. 5: Supernode presence - Cont

  • SuperNode Session Time

Median is 5.5h


Expt 5 supernode presence cont3
Expt. 5: Supernode presence - Cont

  • Fraction of supernodes joining or departing

Node arrival concentrated toward morning

Skype usage is correlated with working hours

Different from P2P file-sharing

Node departureconcentrated toward evening


Expt 5 supernode presence cont4
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
VoIP in Skype: Preliminary Observation

90.4%SN no need to relay VoIP traffic

  • SuperNode Traffic


Voip in skype preliminary observation1
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 observation2
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 observation3
VoIP in Skype: Preliminary Observation

  • File-transfer sizes

File size:

Median: 346kB


Conclusion
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