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Skype Relay CallsSkype Relay CallsMeasurements and Experiments
Wookyun KhoSalman Abdul BasetHenning Schulzrinne
Contents
• Background• Experimental Setup• Results and Discussion
– Factors impacting Skype relay calls– Characterizations of Skype relay nodes
• Conclusion and Future Work
Skype Network
Relay Node (RN)
TCP connection
Host cache (HC)1.A2.B3.C4.D5.E6.…
TCP connection
Background
SN ASN B
SN C
SN E
SC 1 SC 2Media
Media Media
SN DSC = Skype ClientSN = Super Node
NATNAT
Experimental Setup
SC 1 SC 2
SC 1 SC 2
SC 1 SC 2
Internet
Internet
Internet
Unrestricted
NATed
Direct-blocked
NAT NAT
Block SC 2
Results and Discussion
• Factors Impacting Skype Relay Calls– Internet connectivity, host cache.
• Characterizations of Skype Relay Nodes– Relay distribution (geographical, ISP, AS)– Round trip time (RTT)– Call distribution over relay nodes– Uptime of relay nodes
Factors Impacting Skype Relay CallsExperimental Setups Total
Unrestricted NAT Direct-blocked
HC delete Not delete HC delete Not delete
Call trials 867 4,649 5,658 15,774 11,680 38,628
Succ calls 867 339 5,567 2,586 8,597 17,962
Succ rate 100% 7.3% 98.4% 16.4% 73.6% 46.5%100% 98.4% 73.6%7.3% 98.4% 73.6%16.4%
# Possible Failure Reasons of Skype Relay Calls a) The stale information about the IP address and port number of the callee and its SN in the cache of other Skype nodes. b) The inability of Skype to find a relay at the time of call establishment.
Relay Distribution (1/3)
Geographical distribution
Relay Distribution (2/3)
Domain name suffixvs. % RNs
Domain name suffixvs. % RCs
Relay Distribution (3/3)Organization AS # % of RNs % Succ Calls Median RTT
(ms)
Cable Vision 6128 9.2 6.1 15.3
RR-NYC 12271 7.3 5.9 16.4
Rogers 812 4.5 2.5 52.1
SBC 7132 4.4 2.5 46.6
Comcast 7015 4.4 3.6 16.2
AOL 1668 3.9 3.4 95.6
Comcast 33287 3.7 2.8 30.1
Columbia Univ. 14 3.1 17.4 0.28
Cox 22773 2.9 1.7 65.6
Comcast 33657 2.6 2.0 34.5
Top Ten ASes
Round Trip Time (RTT)
Total Average : 52.2ms Median : 43.6ms
Partial Median NAT : 95.6ms Direct-blocked : 13.3ms
Call Distribution Over Relays (1/2)
Through RNs in US - NAT : 81.2% - Direct-blocked : 92.4%
Uptime of Relays
Uptime Maximum : 42.5 days Median : 3.5 hrs
Downtime Maximum : 63.5 days Median : 2 hrs
Median lifetime cycle 3.5 + 2 = 5.5 hrs
Median uptime probability 63.6%
Conclusions and Future Work
• The success rate of Skype relay calls depends on:– The network conditions– The presence of a host cache– Caching of callee reachable address by super nodes
• Skype’s relay selection mechanism can further be improved.– The median one-way network latency for relay calls in a
NAT setup is 95.7ms.
Q&A
