An Implementation and Experimental Study of the Variable-Structure Congestion Control Protocol (VCP)

The Variable-structure Congestion control Protocol (VCP) has been proposed as an alternative approach to the eXplicit Control Protocol (XCP). In our earlier work, we reported the NS2 simulation results of cross-layer profiling studies of VCP, XCP, and TCP+REM in encrypted wireless networks. Our studies utilized finite-state Markov chains to model bit error characteristics of wireless links and applied per packet link layer FEC codes in order to compensate for such errors. Our simulation results showed that VCP takes a significant step toward addressing the tradeoff between the performance and practicality of implementation. In this paper, we report the results of our implementation of VCP in the Linux kernel. Our implementation of VCP consists of a number of Linux Loadable Kernel Modules (LKMs) associated with transmitting, intermediate, and receiving nodes. Our implementation allows for the co-existence of VCP with standard transport protocols such as TCP and UDP. Utilizing an experimental wired testbed capable of realistically emulating the fading characteristics of wireless links, we profile the performance of the Linux implementation of VCP. Based on our profiling results in the Linux kernel, we observe (1) the need for protecting protocol's metadata as well as data against bit errors, and (ii) that VCP represents a high performing yet practical congestion control protocol for encrypted wireless networks.