Congestion-Aware Path Selection for Tor
Tor, an anonymity network formed by volunteer nodes, uses the estimated bandwidth of the nodes as a central feature of its path selection algorithm. The current load on nodes is not considered in this algorithm, however, and the authors observe that some nodes persist in being under-utilized or congested. This can degrade the network's performance, discourage Tor adoption, and consequently reduce the size of Tor's anonymity set. In an effort to reduce congestion and improve load balancing, they propose a congestion-aware path selection algorithm. Using latency as an indicator of congestion, clients use opportunistic and lightweight active measurements to evaluate the congestion state of nodes, and reject nodes that appear congested.