Network Characteristics

USC Database Laboratory

Types of MeasurementTypes of Measurement

ActiveSend active probes and take measurements.Adds to the network traffic.

PassivePassive techniques examine the flow in the network and do not add traffic to the network.

Parameters to be Estimated

Parameters to be Estimated

Available BandwidthLatency – RTT/2Loss rateResponse Time out

BandwidthBandwidth

Actual Bandwidth.Available Bandwidth.Bottleneck Bandwidth

Loss RateLoss Rate

Depends on the no of retransmissions done by TCP.

Response TimeoutResponse TimeoutStarts 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

ToolsTools

Iperf – lossrate, available bandwidthPathload – available bandwidthPing – lossrate, RTTNetstat – tcp statisticsPchar – bandwidth, lossrate (long time)

Available Bandwidth Estimation

Available Bandwidth Estimation

Most of the tools focus on capacity rather than available bandwidth.

Done using PathloadExplanation of pathload follows -

pathloadpathload

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.

pathloadpathload

Two network hosts – SND and RCV.ti - SND timestamps packet prior to transmissionai – Arrival of ith packet at RCV.Di – OWD – ai – tiThe offsets between the clocks at RCV and SND

are ignored because relative magnitudes of OWD are considered.

pathloadpathload

R = L/TR is the transmission rate of the streamL is the size of each packetT is the packet transmission period.Stream consists of K packets.

pathloadpathload

If R > A then, The relative OWDs {D1, D2, …Dk} are expected to

have an increasing trend.On the other hand if R<AThe relative OWDs {D1, D2, …Dk} are expected to

have a non - increasing trend.

pathloadpathload

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)

pathloadpathload

Fleet of streamsPathload does not esimate if R>A only based on

a single streamInstead it send N streamsReason – Check for N independent

measurements to verify increasing trend.In pathload N= 12.

pathloadpathload

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<=1Spct > 0.66 then increasing trend, Spct < 0.54

decreasing trend.

pathloadpathload

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

pathloadpathload

Stream is ofType-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

pathloadpathload

If a large fraction of the N streams f showz increasing trend then we infer R>A.

In pathload f = 70%.

pathloadpathload

Termination – 1. When Rmax – Rmin <= wRmax = highest rate less than bandwidth.Rmin = lowest rate greater than bandwidth.2. Rmax – Gmax < = xAnd Gmin - Rmin <= xGmin = lowest range that has been shown in grey areaGmax = highest range that has been shown in grey area

pathloadpathload

Final outputRmax and Rmin

ResultsResults

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

ResultsResults

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

Issues-SuggestionsIssues-Suggestions

LossrateRTOEstimation time