Proportional rate reduction for ns-3 TCP

The implementation of Transmission Control Protocol (TCP) in the Linux kernel has kept pace with its ongoing research. However, it is not the case with the implementations of TCP in network simulators. This limitation has been a major hindrance in thoroughly evaluating the performance of new TCP extensions, since carrying out real-time experimental evaluations is a non-trivial task. Recently, there have been significant efforts to align the TCP implementation in ns-3 to that of Linux. Nonetheless, there still exist several features that the implementation of TCP in ns-3 lacks. In this work, the TCP implementation in ns-3 has been extended to support Proportional Rate Reduction (PRR) algorithm. PRR is a de facto loss recovery algorithm used since Linux kernel 3.2. This paper describes the implementation and validation of PRR algorithm in ns-3 and also highlights the need to modularize the implementation of loss recovery algorithms in ns-3.