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Network Characteristics

Network Characteristics. USC Database Laboratory. Types of Measurement. Active Send active probes and take measurements. Adds to the network traffic. Passive Passive techniques examine the flow in the network and do not add traffic to the network. Parameters to be Estimated.

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Network Characteristics

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  1. Network Characteristics USC Database Laboratory

  2. Types of Measurement • Active • Send active probes and take measurements. • Adds to the network traffic. • Passive • Passive techniques examine the flow in the network and do not add traffic to the network.

  3. Parameters to be Estimated • Available Bandwidth • Latency – RTT/2 • Loss rate • Response Time out

  4. Bandwidth • Actual Bandwidth. • Available Bandwidth. • Bottleneck Bandwidth

  5. Loss Rate • Depends on the no of retransmissions done by TCP.

  6. Response Timeout • Starts with some initial value ( 3 sec) • RTO = SRTT + 2 * MDEV • MDEV is the average absolute error -- the "mean deviation" -- of SRTT • SRTT is the"Smoothed Round Trip Time." It is obtained by the formula:  SRTT(n+1) = alpha*SRTT(n) + (1 - alpha)RTT(n) • where alpha is a constant between 0.8 and 0.9, and RTT(n) is the nth RTT measurement

  7. Tools • Iperf – lossrate, available bandwidth • Pathload – available bandwidth • Ping – lossrate, RTT • Netstat – tcp statistics • Pchar – bandwidth, lossrate (long time)

  8. Available Bandwidth Estimation • Most of the tools focus on capacity rather than available bandwidth. • Done using Pathload • Explanation of pathload follows -

  9. pathload • C, End to End Capacity – Max rate that the path can provide to a flow when there is no traffic on the path. • A , Available Bandwidth - Max rate that the path can provide to a flow without reducing the traffic on the path.

  10. pathload • Two network hosts – SND and RCV. • ti - SND timestamps packet prior to transmission • ai – Arrival of ith packet at RCV. • Di – OWD – ai – ti • The offsets between the clocks at RCV and SND are ignored because relative magnitudes of OWD are considered.

  11. pathload • R = L/T • R is the transmission rate of the stream • L is the size of each packet • T is the packet transmission period. • Stream consists of K packets.

  12. pathload • If R > A then, The relative OWDs {D1, D2, …Dk} are expected to have an increasing trend. • On the other hand if R<A The relative OWDs {D1, D2, …Dk} are expected to have a non - increasing trend.

  13. pathload • RCV can infer if R>A based on self loading effect of periodic stream (SLoPS) • The two endpoints have to cooperate so that the stream rate converges iteratively to A. • If R(n) > A SND sends at rate R(n+1) < R(n) • Else if R(n) < A SND the rate is R(n+1) > R(n) • There is an algorithm to estimate R(n+1)

  14. pathload • Fleet of streams • Pathload does not esimate if R>A only based on a single stream • Instead it send N streams • Reason – Check for N independent measurements to verify increasing trend. • In pathload N= 12.

  15. pathload • Detection of Increasing trend- Divide {D1, D2, ..Dn) into L=sqrt(K) groups. Let m(D1)…m(Dl) be median OWD. • Pairwise Comparison test – Spct = Sum of [ I(m(Dk) > m(Dk-1)) ] / L-1 for k ranging from 2 to L. 0<=Spct<=1 Spct > 0.66 then increasing trend, Spct < 0.54 decreasing trend.

  16. pathload • Pairwise Difference Test – x = Sum of [m(Dk) – m(D(k-1))] for k = 2 to L. Spdt = (Dl – D1)/x -1<= Spdt < = 1 If Spdt > 0.55, increasing trend if Spdt < 0.45 , non increasing trend

  17. pathload • Stream is of • Type-I – one metric reports increasing, while the other is either “increasing” or “ambiguous” • Type-N – one metric reports non increasing, while the other is either “non increasing” or “ambiguous” • Stream discarded – when both ambiguous or one increasing and other is non increasing

  18. pathload • If a large fraction of the N streams f showz increasing trend then we infer R>A. • In pathload f = 70%.

  19. pathload • Termination – 1. When Rmax – Rmin <= w Rmax = highest rate less than bandwidth. Rmin = lowest rate greater than bandwidth. 2. Rmax – Gmax < = x And Gmin - Rmin <= x Gmin = lowest range that has been shown in grey area Gmax = highest range that has been shown in grey area

  20. pathload • Final output Rmax and Rmin

  21. Results • Receiver csed1.usc.edu starts measurements on sender csed10.usc.edu at Mon Sep 30 19:31:40 2002 • Requested bandwidth resolution :: 0.50 • Minimum packet spacing :: 100 usec • Receiving Fleet 0 • Fleet Parameter :: R=72.74Mbps, L=881B, K=100packets, T=100usec • Lossrate per stream :: :0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0 • Fleet Parameter(act):: R=72.74Mbps, L=881B, K=100packets, T=100usec • CS @ sender :: [0][0][0][0][0][0][0][0][0][0][0][0] • Discard[ 0] :: [0][0][0][0][0][0][0][0][0][0][0][0] • Trend per stream[12]:: IIIIIIIIIIII • Aggregate trend :: INCREASING • Rmax :: 72.74Mbps

  22. Results • Receiving Fleet 1 • Fleet Parameter :: R=36.37Mbps, L=427B, K=100packets, T=100usec • Lossrate per stream :: :0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0:0.0 • Fleet Parameter(act):: R=36.37Mbps, L=427B, K=100packets, T=100usec • CS @ sender :: [0][0][0][0][0][0][0][0][0][0][0][0] • Discard[ 0] :: [0][0][0][0][0][0][0][0][0][0][0][0] • Trend per stream[12]:: NNNNNUNUNNNN • Aggregate trend :: NO TREND • Rmin :: 36.37Mbps

  23. Issues-Suggestions • Lossrate • RTO • Estimation time

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