Experiments with Pathload

Problem
Two bandwidth metrics that are commonly associated with a path are the capacity and the available bandwidth (avail-bw).

The capacity is the maximum throughput that the path can provide to an application when there is no competing traffic load (cross traffic). The avail-bw, on the other hand, is the maximum throughput that the path can provide to an application, given the path's current cross traffic load.

Measuring the avail-bw is of great importance for predicting the end-to-end performance of applications, for dynamic path selection and traffic engineering, and for selecting between a number of differentiated classes of service.

We have developed an avail-bw estimation tool called Pathload. The basic idea in Pathload is that the one-way delays of a periodic packet stream show increasing trend when the stream rate is larger than the avail-bw. The measurement algorithm is iterative and it requires the cooperation of both the sender and the receiver.

The tool is available at:

Here is what you need to do.

1. Read the following paper on avail-bw estimation and Pathload.
   • M.Jain, C.Dovrolis, ``End-to-End Available Bandwidth: Measurement methodology, Dynamics, and Relation with TCP Throughput'', in ACM SIGCOMM 2002.

2. Download and install Pathload at two Unix machines. NOTE: It is important that one of these machines is outside the GAtech campus. For example, you can use your undergraduate school account, if you still have one.

3. Run Pathload about 70 times, uniformly distributed over the time period of one week. Repeat these experiments and analysis for both paths (i.e., both from A to B and from B to A). We would normally expect maximum avail-bw at very early morning hours, and minimum avail-bw in the afternoon or evening. Do you observe such a correlation between the measured avail-bw and the time-of-day?

4. Analyze the variability of the avail-bw in both paths, computing the CDF of the "relative variation index" (defined in the previous paper). Is there a correlation between the variability of the avail-bw and the actual avail-bw magnitude?

Background

Deliverables

• Write a 5-10 page report showing your measurement methodology and summary of results.

Evaluation
Based on the report turned in to the sponsor of the project by the due date.