Robust transport protocol for dynamic high-speed networks: enhancing the XCP approach

Transport protocols have the difficult task of providing reliability and fair sharing of the bandwidth to end-users. In this paper, we focus on very dynamic high-speed networks where the available best-effort bandwidth for regulated traffics can vary over time. Foreseen problems introduced by such highly dynamic environments are inefficiency due to convergence time and high amount of packet losses due to dramatic reductions of the available bandwidth. Therefore end-to-end solutions show their limitations for exploiting the current very high-speed infrastructures. XCP is a promising approach as the evolution of the sender congestion window size is dictated by the routers. However, as the XCP sender relies on the returned ACKs to adapt its congestion window size, XCP performances can be affected if many losses occur on the reverse path. This paper proposes to calculate the congestion window size at the receiver side and to overcome the problem of ACK losses. The result is a more robust XCP transport protocol, capable of achieving a high level of performance in very dynamic high-speed networks, thus able to function in a broader range of network conditions.