SKYPE P2P Kedar Kulkarni 04/02/09. Goals Study Skype working Study VOIP using P2P Use of P2P for...
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Transcript of SKYPE P2P Kedar Kulkarni 04/02/09. Goals Study Skype working Study VOIP using P2P Use of P2P for...
SKYPE P2PKedar Kulkarni
04/02/09
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