Title: End-to-End Available Bandwidth: Measurement Methodology, Dynamics, and Relation with TCP Throughput
1End-to-End Available Bandwidth Measurement
Methodology, Dynamics, and Relation with TCP
Throughput
- M Jain, C Dovrolis
- Proceedings of ACM SIGCOMM02, 2002
- Presented by Ivan
2Outline
- Introduction
- Self-Loading Periodic Streams
- Measurement Tool Pathload
- Verification And Discussion
- Comment
3Available Bandwidth
- Available bandwidth of the end-to-end path during
a time interval
Determine the end-to-end available bandwidth
Determine the end-to-end available capacity
Figure1. A pipe model with fluid traffic for a
three-hop network path
4Available Bandwidth (cont.)
- The end-to-end avail-bw is defined as the maximum
rate that the path P can provide to a flow,
without reducing the rate of the rest of the
traffic in P. - Narrow Link ? the link with the minimum capacity
- Tight Link ? the link with minimum avail-bw
5Outline
- Introduction
- Self-Loading Periodic Streams
- Measurement Tool Pathload
- Verification And Discussion
- Comment
6Self-Loading Periodic Streams (SLoPS)
- A periodic stream in SLoPS consists of K packets
of size L, sent to the path at a constant rate R. - If the stream rate R is higher than the avail-bw
A, the one-way delays of successive packets at
the receiver show an increasing trend. - Use the increasing delays property in an
iterative algorithm to measure end-to-end
avail-bw.
7Self-Loading Periodic Streams (SLoPS) (cont.)
- Suppose SND sends a periodic stream of K packets
to RCV at a rate R0. Denotes the One-Way Delay
(OWD) DK. - The OWD difference between two successive packets
k and k1 is - ,
- Proposition 1.
- If R0 gt A, then gt 0 for k 1,K-1. Else,
if R0 ? A, 0 for k1,K-1
8An iterative algorithm to measure A
- R(n1) can be computed as follows,
- Rmin and Rmax are lower and upper bounds for the
avail-bw after stream n. - Initially, Rmin0, and Rmax is a sufficiently
high value gt A. - The algorithm terminates when
- Rmax Rmin ? ? (estimation resolution)
9SLoPS with real cross traffic
Grey-Region
10Outline
- Introduction
- Self-Loading Periodic Streams
- Measurement Tool Pathload
- Verification And Discussion
- Comment
11Some issues
- Clock and timing issues
- Not affect ?Measure relative OWD DK
- Stream parameters
- A stream consists of K packets of size L, with
rate R. - Packet inter-spacing T, packet size LRT, stream
duration VKT
12Detecting an increasing OWD trend
- Suppose the OWDs are D1, D2, , DK, partition
into G groups, then compute the median OWD
of each group - Pairwise Comparison Test (PCT)
-
- ,
-
- PCT measures the fraction of consecutive OWD
pairs that are increasing. 0? SPCT ?1. - OWDs indep ? SPCT ?0.5
- Strong increasing trend ? SPCT approaches 1
13Detecting an increasing OWD trend (cont.)
- Pairwise Difference Test (PDT)
-
- PDT quantifies how strong is the start-to-end OWD
variation. -1? SPDT?1. - OWDs indep. ? SPDT ?0
- Strong increasing trend ? SPDT approaches 1
- Default, SPCT gt0.55, SPDT gt0.4 ? Increasing
14Fleets of Streams
Limit the average pathload rate to less than 10
of R
Total Duration N(V?)
- To determine whether RgtA, it sends a fleet of N
streams. - The average pathload rate during a fleet of R ?
15Grey-Region
- Using a fraction f of N streams to determine
type-I (increasing) or type-N (non-increasing) - Grey-region ( )
- Less than Nf streams are increasing trend
- Less than Nf streams are non-increasing trend
- Grey-region upper bound ? Gmax
- Grey-region lower bound ? Gmin
- Default f is set to 70
16Rate Adjustment Algorithm
Increasing trend ( R(n) gt A ) Rmax
R(n) R(n1) (Gmax Rmax)/2 Non-increasing
trend ( R(n) lt A ) Rmin R(n) R(n1) (Gmax
Rmin)/2 Grey region R(n) gt Gmax Gmax
R(n) R(n1) (Gmax Rmax )/2 Grey region
R(n) lt Gmin Gmin R(n) R(n1) (Gmin Rmin
)/2
Grey region
Terminate if Rmax Rmin lt ? (estimation
resolution)
or Gmax Gmin lt ? (grey-region resolution)
More detail in Pathload a measurement tool for
end-to-end available bandwidth
17Measurement Latency
- Default K100, L800B, T100µsec, a stream
carries 80,000 bytes and lasts for 10msec - If A ? 100Mbps and ? 100ms, pathload takes less
than 15 sec to produce a final estimate - The latency increases as the avail-bw or
grey-region increase, and it also depends on ?
?
18Outline
- Introduction
- Self-Loading Periodic Streams
- Measurement Tool Pathload
- Verification And Discussion
- Comment
19Accuracy Results
MRTG range is 6Mbps
MRTG range is 1.5Mbps
Fall within the MRTG range in 10 out of the 12
runs
Fall within the MRTG range in 9 out of the 12 runs
20Variability and Load conditions
- Relative variation
- The variability of the avail-bw increases
significantly as the utilization u of the tight
link increases
21The Effect of the Stream Length Fleet Length
Fig13. The effect of N on the variability
of the avail-bw.
Fig12. The effect of K on the variability
of the avail-bw.
Fleet duration increases ?Variability of the
avail-bw increases, Variation across
different pathload runs decreases
Stream duration increases ?Variability of the
avail-bw decreases
22Is Pathload Intrusive?
Avail-bw measurements
RTT measurements
Do not show a measurable decrease when pathload
runs.
23TCP vs. Available Bandwidth
RTT measurements
Avail-bw and TCP Throughput
- TCP connection manages to saturate the path
- Shorter TCP connections expect a significant
variability in their throughput - TCP connection will grab part of the throughput
of other TCP connections
24Outline
- Introduction
- Self-Loading Periodic Streams
- Measurement Tool Pathload
- Verification And Discussion
- Comment
25Comment
- Pathload is the first generation tool using the
SLoPS method to measure the avail-bw - IGI pathChirp are the modified ones
- The similar measurement accuracy
- With less bw-usage overhead
- With less measurement latency
26Pathload vs. pathChirp
From the pathChirp Efficient Available
Bandwidth Estimation for Network Paths