Dynamic Coding for TCP Transmission Reliability in Multi-hop Wireless Networks

In lossy environment like wireless networks, random losses are treated by TCP as signals of congestion and TCP cuts down the sending rate, leading to the performance degradation. The practical network coding system TCP/NC can address this problem. TCP/NC masks the random losses by allowing the destination to acknowledge every degree of freedom even though original data is not decoded yet. Consequently, TCP smoothly reacts to random losses without reducing the performance. The sole problem from TCP/NC is that TCP/NC sends redundant traffic every pre-set interval which does not recover random losses in time. We suggest an end-to-end adaptive redundancy control based on re-designing the coding scheme from TCP/NC, called Dynamic Coding (DynCod). Our main idea is how the destination can inform to the source whether the latest data sent from the source is decodable or not and how many packet losses occur via acknowledgement packets. Particularly, we change the principle of the information delivered by TCP ACKs: the destination does not only acknowledge every degree of freedom, but also announces how many unseen packets (>= 0) remain in the coding window. The source can be informed via TCP ACKs and adjust the number of redundant packets accordingly. We have compared the performances of DynCod and TCP/NC using NS-2. The simulation results show that DynCod outperforms the original TCP/NC in terms of throughput and packet delivery time.