TCP over Load-Reactive Links

Emerging network technologies offer new design choices for performing traffic engineering and management, while introducing challenges for existing protocol control mechanisms. There is a tension between new hop-by-hop capabilities and existing end-to-end mechanisms. In this paper we examine one such capability, the Load-Reactive Link (LRL), which has capacity that can be automatically varied in response to the offered load. Before such adaptive links can be considered for deployment, it is essential to understand the behavior of widely deployed end-to-end protocols, in particular TCP. We study the behavior of TCP flows over a particular type of LRL that uses a hysteresis control mechanism for capacity allocation that reacts to current traffic loads. Our results indicate that reasonable performance for a single TCP flow can be achieved with careful choice of control parameters. We also show that poor choice of control parameters make it difficult or impossible for TCP to function. Preliminary simulations have been done with multiple TCP flows, but further investigation is needed to understand the behavior of the aggregation of a large number of flows.