Active Probing Testbed
Active probing consists of sending out probe packets into a network from a sender to a receiver. From the variations in transfer delay, network parameters and conditions can be inferred. An example is the measurement of bottleneck bandwidth: the smallest bandwidth of any link along the path. Another is the measurement of available bandwidth: the actual bandwidth available to an end-to-end connection. A key goal of active probing based network measurement is to be able to obtain accurate, reliable estimates using only a small number of probes, using probing streams of low average rate.
The basic components of an active probing experiment are set out in the figure below:
This slide presentation provides an introduction to active probing with an emphasis on timing and infrastructure issues (accompanying notes will be provided soon).
The testbed consists of a number of sender and receiver stations, switches and hubs, and Ethernet traffic monitors performing high precision timestamping. The timestamping infrastructure includes a GPS synchronised hardware solution, as well as state of the art software based precision packet monitoring and sending developed in CUBIN. The testbed is currently being used in conjunction with similarly equipped external nodes in laboratories in New Zealand, Hungary and elsewhere to perform active probing measurements of the Internet. These measurements verify and inspire active probing analysis work, also under in progress in CUBIN.
Further details of active probing, and the measurement infrastructure, are available on Attila Pásztor's homepage. The current administrator for the testbed is Darryl Veitch. The reader may also be interested in looking at the publications that have come out of work using the testbed, and the probers that made it possible.
A software package for accurate active probing, including a TSC based software clock and accurate active UDP senders under Linux and RealTime Linux, and a probing simulator, is available for use by colleagues. A new user and trouble shooting guide for the use of the software will appear off the software page soon.
The active probing experiments in CUBIN are made possible under a contract with Ericsson Australia.