  The analysis of computer and communication networks gives rise to some
interesting inverse problems. This paper is concerned with active network
tomography where the goal is to recover information about quality-of-service
(QoS) parameters at the link level from aggregate data measured on end-to-end
network paths. The estimation and monitoring of QoS parameters, such as loss
rates and delays, are of considerable interest to network engineers and
Internet service providers. The paper provides a review of the inverse problems
and recent research on inference for loss rates and delay distributions. Some
new results on parametric inference for delay distributions are also developed.
In addition, a real application on Internet telephony is discussed.
