Inconsistency of logical and physical topologies for overlay networks and its effect on file transfer delay

In overlay networks consisting of underlying physical nodes and links, data files are transferred by overlay routing managed at application level. The end-to-end filetransfer delay depends on both logical and physical topologies resulting from overlay routing. In this paper, we focus on six types of four-terminal four-router physical network, and investigate the impact of topology inconsistency on the file-transfer delay. The analysis model is based on a two-layer queueing network, taking into account both logical and physical topologies. The model is validated in comparison with ns-2 simulation. Numerical examples show that the end-to-end file-transfer delay is small when both logical and physical topologies are the same. It is also observed that the end-to-end delay significantly depends on the traffic intensity for some logical topologies, regardless of physical topology.