The Necessity of Combining ELN and SACK to Improve TCP Performance over Heterogeneous Networks

TCP suffers severe performance degradation over heterogeneous networks due to its inadaptability to the characteristics of the wireless link. Techniques such as explicit loss notification (ELN) and selective acknowledgement (SACK) have been proposed to mitigate such link-related degradations. In this paper, we demonstrate the inadequacy of using ELN or SACK alone and the necessity of combining them. It will be shown that the combination of ELN and SACK is not a simple superposition of two mechanisms, but rather is an organic integration with positive interactions on each other. Simulation results show that, by combining ELN and SACK, TCP achieves considerably higher throughput than using any one mechanism separately.