The Skype Network Ordinary Host (OH) A Skype client Super node (SN) A Skype client
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Telephony Protocol Salman Abdul Baset and Henning Schulzrinne Internet Real-Time Lab, Columbia University http:// www.cs.columbia.edu/~salman/skype / The Skype Network Ordinary Host (OH) • A Skype client Super node (SN) • A Skype client • Has public IP address, ‘sufficient’ bandwidth, CPU and memory Bootstrap super nodes (maintained by Skype) • Used when running Skype for the first time • A total of seven nodes hard-coded in Skype executable Login server • Stores Skype id’s, passwords and buddy lists • Used at login for authentication • Version 1.4: 212.72.49.141 and 195.215.8.141 The Skype Components Port • No default listening port. Randomly chooses a port upon installation. Host cache (HC) • IP address and port number of online Skype nodes • Maximum size: 200 entries Codecs (GlobalIPSound) • Wideband codecs (50-8,000 Hz) • iLBC (packet size: 20 and 30 ms bitrate: 15.2 kb/s and 13.3 kb/s) • iSAC (packet size: 30-60 ms bitrate: 10-32 kb/s) • G.729 for SkypeOut? Skype login server M essage exchange w ith the login serverduring login ordinary host(SC ) supernode (SN ) neighborrelationships in the Skype netw ork SkypeIn / SkypeO ut servers IN TER N ET A (public IP) B (public IP) IN TER N ET A (private IP) B (public IP) port-restricted N AT IN TER N ET A (private IP) B (private IP) port-restricted N AT U D P-blocking firew all port-restricted N AT U DP-blocking firewall Experimental Setup Public NAT Firewall Login 10 KB (3-7 secs) 11 KB (3-7 secs) 7 KB (30-35 secs) Search 1-2 KB (3-4 secs) 1-2 KB (5-6 secs) 5-7 KB (10-15 secs) Call establishm ent 6 KB 8 KB 8 KB Skype Functions Summary Super Nodes 8,153 login attempts over four days 35% hostnames had a ‘.edu’ suffix • 102 universities • 894 unique SNs Unique SN IP distribution: US 83.7%, Asia 8.9%, Europe 7.1% Top 20 nodes received 43.8% of the total connections Total successful calls 8,882 % of successful calls between Relay distributio n 8:00am and 7:59pm EST 8:00pm and 7:59am EST Global 44.66% (3,985) 55.34% (4,937) Asia 3.3% (131) 7.9% (392) Australia 0.05% (2) 0.2% (10) Europe 42.9% (1,709) 38.51% (1,901) North America 52.42% (2,089) 52.17% (2,576) South 0.14% (54) 1.18% (58) Skype Relay Experiments Jan 20 th to Feb 5 th 2006. . Caller and callee machines in IRT lab 8,822 successful call attempts and 4,904 unique relay IP addresses 60% of the calls routed through caller SN Relay nodes in 51 countries Internet C allerSkype C allee Skype NAT NAT Applicati on version Memory usage before call (caller, callee) Memory usage after call (caller, callee) Process priority before call Process priority during call Mouth- to-ear latency Skype 1.4.0.84 19 MB, 19 MB 21 MB, 27 MB Normal High 96ms MSN 7.5 25 MB, 22 MB 34 MB, 31 MB Normal Normal 184ms Yahoo 7.0 beta 38 MB, 34 MB 43 MB, 42 MB Normal Normal 152ms Skype, MSN, Yahoo and Google Talk TCP TCP Caller(NAT+firewall) SN 713B 3464B Relay M edia:TCP Caller M edia:TCP Relay Callee TCP Caller N1, N2, N3 TCP TCP Callee TCP 19B 19B 19B 19B Callerand callee on the average exchange 3 m sg/s overTCP w ith N 1, N 2 and N 3 aftercallhasbeen established. TCP TCP Caller 124B 45B Callee (NAT+firew all) TCP TCP 51B 117B (7) (8) (4) (4) (4) (3) Call Establishment
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The Skype Components Port No default listening port. Randomly chooses a port upon installation. Host cache (HC) IP address and port number of online Skype nodes Maximum size: 200 entries Codecs (GlobalIPSound) Wideband codecs (50-8,000 Hz) - PowerPoint PPT Presentation
Transcript of The Skype Network Ordinary Host (OH) A Skype client Super node (SN) A Skype client
An Analysis of the Skype Peer-to-Peer Internet Telephony Protocol
Salman Abdul Baset and Henning Schulzrinne Internet Real-Time Lab, Columbia University
http://www.cs.columbia.edu/~salman/skype/
The Skype Network Ordinary Host (OH)
• A Skype client Super node (SN)
• A Skype client • Has public IP address, ‘sufficient’ bandwidth, CPU and memory
Bootstrap super nodes (maintained by Skype)• Used when running Skype for the first time• A total of seven nodes hard-coded in Skype executable
Login server• Stores Skype id’s, passwords and buddy lists• Used at login for authentication• Version 1.4: 212.72.49.141 and 195.215.8.141
The Skype Components Port
• No default listening port. Randomly chooses a port upon installation.
Host cache (HC)• IP address and port number of online Skype nodes• Maximum size: 200 entries
Codecs (GlobalIPSound)• Wideband codecs (50-8,000 Hz)• iLBC (packet size: 20 and 30 ms bitrate: 15.2 kb/s and 13.3 kb/s)• iSAC (packet size: 30-60 ms bitrate: 10-32 kb/s)• G.729 for SkypeOut?
Skype login server
Message exchange with the login server during login
ordinary host (SC)
super node (SN)
neighbor relationships in the Skype network
SkypeIn / SkypeOut
servers
INTERNET
A (public IP) B (public IP)
INTERNET
A (private IP)
B (public IP)port-restricted NAT
INTERNET
A (private IP) B (private IP)port-restricted NATUDP-blocking firewall
port-restricted NATUDP-blocking firewall
Experimental Setup
Public NAT Firewall
Login 10 KB(3-7 secs)
11 KB(3-7 secs)
7 KB(30-35
secs)
Search 1-2 KB(3-4 secs)
1-2 KB(5-6 secs)
5-7 KB(10-15
secs)
Call establishment
6 KB 8 KB 8 KB
Skype Functions Summary
Super Nodes 8,153 login attempts over four days 35% hostnames had a ‘.edu’ suffix
• 102 universities• 894 unique SNs
Unique SN IP distribution: US 83.7%, Asia 8.9%, Europe 7.1%Top 20 nodes received 43.8% of the total connections
Total successful calls 8,882
% of successful calls between
Relay distribution
8:00am and 7:59pm EST
8:00pm and 7:59am EST
Global 44.66% (3,985) 55.34% (4,937)
Asia 3.3% (131) 7.9% (392)
Australia 0.05% (2) 0.2% (10)
Europe 42.9% (1,709) 38.51% (1,901)
North America
52.42% (2,089) 52.17% (2,576)
South America
0.14% (54) 1.18% (58)
Skype Relay Experiments Jan 20th to Feb 5th 2006..
Caller and callee machines in IRT lab 8,822 successful call attempts and 4,904 unique relay IP
addresses 60% of the calls routed through caller SN Relay nodes in 51 countriesInternet
Caller Skype Callee Skype
NAT NAT
Application version
Memory usage before call (caller, callee)
Memory usage after call (caller, callee)
Process priority before call
Process priority during call
Mouth-to-ear latency
Skype 1.4.0.84 19 MB, 19 MB 21 MB, 27 MB Normal High 96ms
MSN 7.5 25 MB, 22 MB 34 MB, 31 MB Normal Normal 184ms
Yahoo 7.0 beta 38 MB, 34 MB 43 MB, 42 MB Normal Normal 152ms
GTalk 1.0.0.80 9 MB, 9 MB 13 MB, 13 MB Normal Normal 109ms
Skype, MSN, Yahoo and Google Talk
TCPTCP
Caller (NAT+firewall) SN713B
3464B
Relay
Media:TCPCaller
Media:TCPRelay Callee
TCPCaller N1, N2, N3
TCPTCP
Callee
TCP
19B19B
19B19B
Caller and callee on the average exchange 3 msg/s over TCP with N1, N2 and N3 after call has been established.
TCPTCP
Caller124B45B
Callee (NAT+firewall)TCPTCP
51B117B
(7)(8)
(4)(4)
(4)(3)
Call Establishment
