Achieving Fair Throughput for TCP Flows in Multi-hop Wireless Backhaul Networks

The use of multihop wireless networks based on the 802.11 technology has been growing. The primary advantages of this approach are mature technology and ease of deployment. However, the fairness property provided by the 802.11 DCF (distributed coordination function) in a single hop environment has been shown to be non-existent in a multihop environment. For example, in the multihop wireless backhaul network, nodes that are more hops away from the gateway are starved by nodes that are closer to the gateway. This paper focuses on the fairness study when TCP flows are carried over wireless backhaul networks. By not modifying lower layer protocols, this work identifies TCP parameters that impact throughput fairness and proposes adjusting those parameters to reduce frame collisions and improve throughput fairness. With the aid of simple mathematical formulations and ns2 simulations, this study finds that the frame transmissions from each node can be effectively controlled by properly controlling the delayed ACK timer and using a suitable advertised window. For chain topology with long hops, the fairness index of our proposed method outperforms basic 802.11 DCF by over 90 percent. The proposed methods are simple and easy to deploy.