Skype Relay Calls Skype Relay Calls Measurements and Experiments Wookyun Kho Salman Abdul Baset Henning 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.A 2.B 3.C 4.D 5.E 6.… TCP connection Background SN ASN BSN CSN E SC 1SC 2 Media SN D SC = Skype Client SN = Super Node NAT

Experimental Setup SC 1SC 2 SC 1SC 2 SC 1SC 2 Internet Unrestricted NATed Direct-blocked 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 Calls Experimental SetupsTotal UnrestrictedNATDirect-blocked HC deleteNot deleteHC deleteNot delete Call trials8674,6495,65815,77411,68038,628 Succ calls ,5672,5868,59717,962 Succ rate100%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 suffix vs. % RNs Domain name suffix vs. % RCs

Relay Distribution (3/3) Organization AS #% of RNs% Succ CallsMedian RTT (ms) Cable Vision RR-NYC Rogers SBC Comcast AOL Comcast Columbia Univ Cox Comcast 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 = 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