SKYPE P2PKedar Kulkarni04/02/09

Goals Study Skype working Study VOIP using P2P Use of P2P for VOIP Analyze effects of Churn Data for future P2P VOIP systems

Skype Communication system VOIP IM File Transfer Video User Search Paid services

Skype P2P Not much known Similar to Kazaa Hierarchical P2P Supernodes/nodes Login Server

Basic Operation Control Traffic / Media Traffic Nodes connect to supernodes Behind NAT and Firewalls Host Cache Supernode promotion Supernode Relay Robust Encryption

Skype User Search Uses Global Index technology Skype always could find an Online User Search query sent to SN

SN returns 8 IPs of possible matches if not found SN sends 24 next. And so on.

For SC behind NAT, SN will process the query

Login Server is the fall back option.

Skype Calls To call, callee should be in

the friends list If not, first search is done. Public SCs

Caller establishes TCP connection with Callee

Caller behind NAT Signaling information

exchanged with SN first Media flow between Caller

and callee

Calls Caller and Callee behind NAT

Signaling information exchanged with SN Media flow through relay

Experiments Supernode network activity

Observed a supernode for 135 days with 13GB of total data.

Supernode and client population Obtained SN info from host cache 250K total SNs found

Supernode Presence Observed which SNs were online by sending

ping msgs 6000 random SNs at 30 min interval

Characterization Diurnal Behavior Stable, than skype users clients

Characterization Fraction of

supernodes joining or departing the network

Log log plot of the complimentary CDF of supernode session times.

Characterization

Semi log plot of CDF of bandwidth used by the supernode

Geographic distribution of supernodes

Comparison with other IMs

Skype Supernode Map

US: 83.7%, Asia8.9%, Europe 7.1%

Conclusion Diurnal, work-week behavior. Similar to web browsing Stability of SNs mitigates churn SNs use little bandwidth, occasionally

relay media and file transfer Best Mouth to ear latency

Papers An Experimental Study of the Skype Peer

-to-Peer VoIP System S. Guha, Neil Daswani, and Ravi Jain

An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol. S.A.Baset and H.G. Schulzrine