Improving TCP Performance in High Bandwidth High RTT Links Using Layered Congestion Control

In this paper, we propose Layered TCP (LTCP for short), a simple layering technique for the congestion window response of TCP to make it more scalable in highspeed, high RTT networks. LTCP is a two dimensional congestion control framework the macroscopic control uses the concept of layering to quickly and efficiently make use of the available bandwidth whereas microscopic control extends the existing AIMD algorithms of TCP to determine the per-ack behavior. We provide the general intuition and framework for the LTCP protocol modifications in this paper. Then, using a simple design, we illustrate the effectiveness of using layering for improving the efficiency, without sacrificing the convergence properties of TCP. We assess the RTT unfairness with the chosen design and show that by using a simple RTT compensation factor, the RTT unfairness can be assured to be no worse than that of unmodified TCP. Evaluation of the specified design is based on analyses and ns-2 based simulations. We show that LTCP has promising convergence properties, is about an order of magnitude faster than TCP in utilizing high bandwidth links, employs few parameters and is easy to understand. The choice of parameters can be influenced to reduce the RTT unfairness, compared to TCP or other highspeed solutions. The flexible framework opens a whole class of design options for improving the performance of TCP in highspeed networks.