On TCP Simulation Fidelity in ns-2

The Network Simulator version 2, also known as ns-2, is a widely used platform for network and protocol performance evaluation. Over the years it has benefited from numerous studies in improving its simulation fidelity. Nevertheless, this study discovered that ns-2's TCP simulation accuracy could be impaired substantially in cases where the first-hop link is the bottleneck. This is common in many applications where the client host uploads data to Internet servers as the uplink, e.g., wireless and mobile networks, may have far lower bandwidth than the Internet core. This work investigated this performance anomaly by dissecting and comparing ns-2's implementation against Linux implementation; and by developing extensions to ns-2 to resolve the anomaly as well as five additional updates to bring its implementation to match recent Linux implementations. Extensive verifications against experiments conducted in a physical testbed confirmed the accuracy of the extended ns-2, offering a renewed and accurate simulator for mobile and wireless networking.