Tracking down Traffic Dario Bonfiglio Marco Mellia Michela Meo Nicolo Ritacca Dario Rossi Agenda A few words about Skype Known facts Preliminary definitions Investigate Skype Traffic Voice traffic Reaction to network performance degradation Signaling traffic Signaling patterns & peer selection Users behavior Please, see the paper Why Skype ? Skype is very popular More than 100M users, 5% of all VoIP traffic Easy to use, many free services
voice / video / chat / data transfer over IP Understanding Skype is a challenging task Closed design, proprietary solutions Almost everything is encrypted Uses a P2P architecture Skype for Dummies Architecture P2P design Skype for Dummies Architecture P2P design Service traffic Voice calls Video calls Chat Data transmission
Skype for Dummies Architecture P2P design Service traffic Voice calls Video calls Chat Data transmission Skypeout/ Skypein Skype for Dummies Architecture P2P design Service traffic Voice calls Video calls Chat Data
transmission Skypeout/ Skypein Signaling traffic Methodolody Service traffic Small scale active testbed Controlled bandwidth, packet loss voice service, many Codecs, TCP/UDP traffic Signaling traffic Passive measurement technique D.Bonfiglio, M.Mellia, M.Meo, D.Rossi, P.Tofanelli, Revealing Skype Traffic: When Randomness
Adopt black-box Plays witha You, SIGCOMM'07 approach 7000 hosts 1700 peers 300.103 external peers Preliminary Definition Useful information At installation, Skype chooses a port at random The port is never changed (unless forced by the user) All traffic multiplexed over the same socket (UDP preferably) Skype flow A sequence of packets originated from a Skype
peer (and destined to another skype peer) Flow starts when the first packet is observed Skype peer A Skype peer can be identified by its endpoint Consider only peers that were ever a call (IPobserved addr, making UDP port) Flow ends when no packet is observed for a given inactivity timeout (200s) Skype Source Model Skype Message TCP/UDP IP
Service traffic Codec Impact Service Traffic: Normal Condition 250 Smooth Transient 200 Bitrate [kbps] ISAC iLBC iPCM-WB PCM G729 Normal Behavior 150
Aggressiv e Startup 100 50 0 0 10 20 30 Time [s] 40 50 60
200 150 100 50 0 Average Throughput Bandwidth limit Framing Time [s] [Bytes] Skype performs congestion control Skype Message Size Time [s] 0 30 60 90 120 150 180 210 240 270 300
Time [s] Service Traffic: Packet Loss Loss % 60 10 50 8 40 Inter-Pkt 30 Gap [ms] 20 6 4 Aggressively tries to deal with losses 10 2
0 0 Skype performs loss recovery 0 500 Payload [Bytes] 100 200 300 400 500 10 Loss profile
400 8 300 6 200 4 ...by multiplexing old and new voice blocks 100 2 0 0 0 100 200
Time [s] 300 400 500 Service traffic Video Traffic Service Traffic: Video Source 800 B [kb p s ] 600 400 200 [m s ] 0
80 IPG 60 Skype 20 40 Time [s] Video messages multiplexes different sources are Bigger Voice messages 0 are the same L Usual IPG for
Time [s] Back-to-back video pure audio messages Massages => frame [B yte s ] 900 600 300 0 0 10 20 30 Time [s] 40 50 60
Signaling traffic Signaling Traffic: Activity Pattern 1500 1000 Out 500 0 -500 -1000 -1500 In 0 6 12 18 24 Time [Hr] Legend Consider a single client Each dot is a packet Top: outgoing, Bottom: incoming For every new peer,
increment the ID For every old peer, use the previous ID Rather different patterns emerge from the plot Signaling Traffic: Activity Pattern 1500 1000 Out 500 0 -500 -1000 -1500 In 0 6 12 18 24 Time [Hr] Probes Single packet Sent toward unknown
peers Reply possibly follows No further traffic between the same peers pair Majority of the flows Peer discovery is a continuous task Signaling Traffic: Activity Pattern 1500 1000 Out 500 0 Non-Probes Flows longer than one packet Series of single-packet flows Sent toward the same peer Carry most signaling bytes -500 -1000
-1500 In 0 6 12 18 24 Time [Hr] Talk to super peers, notify buddies of status change, Signaling Traffic: All Peers 1500 1000 Out Majority of the flows Non-probes 500 Carry most signaling bytes Signaling bandwidth
0 95% generate <100 bps Only 1% exceeds 1 Kbps -500 Signaling spread -1000 -1500 Probes In 0 6 12 18 24 Time [Hr] 95% of peers contact <40 peers (in 5 min) 1% exceeds >75 (in 5 min) Conclusions User
Service Characterization traffic Active Number testbed of calls per unit of time Call Skype duration implements for different a congestion services control Aggressive Peer Lifetime with losses with bottlenecks Details Conservative are in the paper, not in this talk Future Work Signaling
traffic Extensive measurement in different networks Passive measurement Campus LAN Two ADSL different threads shapes the overlay installation Probes Cellular Network Non-Probes Signaling rate and spread Very limited bitrate Large number contacted peers Signaling Traffic: Peer Selection 0.012 pdf Non-Probe Probe
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