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) 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