multiQ is a passive capacity measurement tool suitable for large-scale studies of Internet path characteristics. It is the first passive tool that discovers the capacity of multiple congested links along a path from a single flow trace, and the first tool that effectively extracts capacity information from ack-only traces. It uses equally-spaced mode gaps in TCP flows' packet interarrival time distributions to detect multiple bottleneck capacities in their relative order.We validate multiQ in depth using the RON overlay network, which provides more than 400 heterogeneous, well-understood Internet paths. We compare multiQ with two other capacity measurement tools (Nettimer and Pathrate) in the first large-scale wide-area evaluation of capacity measurement techniques, and find that multiQ is highly accurate; for instance, though multiQ is passive, it achieves the same accuracy as Pathrate, which is active.

Early simulation experience with wireless ad hoc networks suggests that their capacity can be surprisingly low, due to the requirement that nodes forward each others' packets. The achievable capacity depends on network size, traffic patterns, and detailed local radio interactions. This paper examines these factors alone and in combination, using simulation and analysis from first principles. Our results include both specific constants and general scaling relationships helpful in understanding the limitations of wireless ad hoc networks.