On the expected file download time of the random time-based switching algorithm in P2P networks

The expected file download time of the random time-based switching algorithm for peer selection and file downloading in a peer-to-peer (P2P) network is still unknown. The main contribution of this paper is to analyze the expected file download time of the time-based switching algorithm for file sharing in P2P networks when the service capacity of a source peer is totally correlated over time, namely, the service capacities of a source peer in different time slots are a fixed value. A recurrence relation is developed to characterize the expected file download time of the time-based switching algorithm. It is proved that for two or more heterogeneous source peers and sufficiently large file size, the expected file download time of the timebased switching algorithm is less than and can be arbitrarily less than the expected download time of the chunk-based switching algorithm and the expected download time of the permanent connection algorithm. It is shown that the expected file download time of the time-based switching algorithm is in the range of the file size divided by the harmonic mean of service capacities and the file size divided by the arithmetic mean of service capacities. Numerical examples and data are presented to demonstrate our analytical results.