A Semi-TCP's Implementation With No Modification To Original TCP's Installation

Wireless multi-hop networks are a special network which is acentric, self-organizing and self-healing. Congestion control plays an important role in such kind of networks. The traditional TCP congestion control mechanism is based on the returning ACK packets, which seriously suffers from performance degradation in some cases,especially in the wireless multi-hop networks, where original TCP often misjudge the congestion status in such kind of networks with a slow reaction to it. Therefore, a semi-TCP protocol based on MAC cross-layer design was proposed. Semi-TCP moves down the congestion control function to that data link layer, which provides a hop-by-hop congestion control through a slight modification to the existing MAC protocol. Considering that TCP is widely used and tremendous applications have been implemented on the top of the original TCP.In this paper, we discuss a semi-TCP's implementation with no modification to original TCP's installation in order to improve congestion control performance without changing original TCP framework. The main contributions of this paper include: (i) a virtual TCP layer (called VTCP) proposed to keep the original TCP installation intact, (ii) a logical channel between VTCP layer and MAC layer designed to deliver cross-layer information, and (iii) a virtual ACK rate adjustment mechanism for the conversion between MAC-ACK and virtual TCP-ACK in order to stimulate the adjustment of TCP congestion window. A NS2 simulation study shows that this semi-TCP implementation can perform better in the high bit error or mobile scenarios in comparison with TCP Newreno, TCP-AP and ADTCP.