TCP fairness in ethernet PON

Abstract

In this paper, we are interested in the TCP fairness problem in EPON due to the interaction between the bandwidth allocation scheme and TCP behavior. We have shown that conventional bandwidth allocation schemes cannot guarantee the fairness between TCP connections in the different ONUs, in which there are different number of TCPs through simple analysis and simulations. From our observation that it is hard to solve this problem using only the bandwidth allocation scheme, we proposed a novel control-theoretic explicit window adaptation algorithm using the cycle time. The proposed algorithm explicitly controls an window to maintain a target cycle time and modifies receiver`s advertised window in acknowledgment packets. We select an optimal target cycle time value to maximize utilization on condition that the mean packet delay in EPON is smaller than whatever we decide. Therefore, each TCP connection achieves the fairness in MAX-MIN sense, and moreover, the mean packet delay is bounded to the value we want. Through simulations under various scenarios, we verify that proposed algorithm gives significant improvements in not only the fairness but also delay, jitter and packet loss compared to the conventional schemes.