IMC 2004 Network Radar
Network Radar :Tomography from Round Trip Time Measurements
Yolanda Tsang1,2, Mehmet Yildiz2,Paul Barford3, Robert Nowak1,2
1. ECE, Rice University2. ECE, University of Wisconsin - Madison3. CS, University of Wisconsin - Madison
IMC 2004 Network Radar
sender
receivers
NormalAbnormal
Unicast Network Tomography
IMC 2004 Network Radar
sender
receivers
NormalAbnormal
Unicast Network Tomography
From edge-based traffic measurements,infer internal link-level loss rates and delay statistics.
IMC 2004 Network Radar
Packet Pair Approach
Correlations in closely (time) spaced packetpairs allow us to resolve link-level performance
(2)packet (1)packet (2)packet (1)packet
measurement packet pair
cross-traffic
IMC 2004 Network Radar
Measure end-to-end delays of packet-pairs
0
1
2 3
Packets experience identical delays on link 1
Delay Variance Tomography
IMC 2004 Network Radar
sender
receivers
Basic Idea
IMC 2004 Network Radar
Round Trip Time (RTT)
Message ‘Echo’
Time
RTT
IMC 2004 Network Radar
TCP Three-way Handshake
SYN-ACK Generation delay
SYN
RST
RTT
TransmissionPropagationQueuing
SYN-ACK
Time
Sender Receiver
SYN: SynchronizeSYN-ACK: SYN Acknowledgement
RST: Reset
IMC 2004 Network Radar
Network Radar
Send closely time-spaced packets to two different receivers
0
21
SYN
SYN-ACK
IMC 2004 Network Radar
Example (Delay Variance Estimation)
Assumptions:•Independent delay measurements•Identical delays on shared links
Measurements:
where and
IMC 2004 Network Radar
Example (Continue)
Denote as an unbiasedestimator of the variance of theshared link
IMC 2004 Network Radar
Emulation Test-Bed Experiment
Sender
Receiver 1
Receiver 2
xT: Cross Traffic generatorR: Router (Cisco 3600 series)S: Packet Sniffer
Wisconsin Advanced Internet Laboratory
IMC 2004 Network Radar
ResultsEs
timat
es
True Values
IMC 2004 Network Radar
Localization
321
IMC 2004 Network Radar
Future Work & Challenges• Future Work
– Validate software in the real Internet– Improve time-stamping mechanism in hardware– Develop publicly available Network Radar tool– Infer topology from radar measurements
• Challenges– “Signal” to “Noise”– Back-to-back packet generation– Accurate + precise time-stamping
IMC 2004 Network Radar
Thank you!
Questions?
