BW-meter

Measurement tools for the capacity and load of Internet paths.

Background

The performance of network connections is based on their bandwidth, since more bandwidth normally means higher end-to-end throughput and better quality-of-service for the applications. Recently, the issue of bandwidth monitoring has become of major importance. Users need to check whether they get the access bandwidth that they expect or pay for, and whether the network `clouds' that they use are sufficiently provisioned. Network managers also need bandwidth monitoring tools in order to plan their capacity upgrades, and to detect congested or underutilized links.

Two bandwidth metrics that are commonly associated with a path are the capacity and the available bandwidth. The capacity is the maximum throughput that the path can provide to an application when there is no competing traffic load (cross traffic). The available bandwidth, on the other hand, is the maximum throughput that the path can provide to an application, given the path's current cross traffic load. Our main objective is to develop methodologies and tools that can accurately measure these two bandwidth metrics. Measuring the capacity is crucial for `debugging', calibrating, and managing a path. Measuring the available bandwidth, on the other hand, 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. Additional constraints about these measurement methodologies are that they should not have a negative impact on the normal network traffic (i.e., non-intrusive methods), they can be performed in real-time, and they should not require information from the path routers.



Figure 1
TOP: The capacity of a path is determined by the link with the minimum capacity (narrow link). In this example, the capacity is C=C1.
DOWN: The available bandwidth of a path is determined by the link with the minimum unused capacity (tight link). In this example, the available bandwidth is the part of the tight link that is shown as A.