Research On TCP Congestion Control In Wireless Networks

With the development of wireless communication technology, the future wireless networks will develop into an all IP mobile Internet which can provide access for customers at any time and anywhere, and the wireless network and wired network will also convergent seamlessly. Due to the unique characteristics of wireless communication, technologies from the wired network face great challenges in application, especially for TCP technologies in transport layer.This paper mainly conducts research on protocols in transport layer, and the main contents include:The current development situation and trend is introduced. The characteristics of wireless networks are discussed in detail and the application limitations of TCP protocol from wired networks in wireless networks are pointed out. The state of art research of TCP protocols in both wireless cell networks and Ad Hoc networks is summarized.The framework and layered architecture of TCP/IP protocol are described in detail. The operation mechanism of TCP which includes the establishment and removal of TCP sessions and the state transformation model described in finite state machine is analyzed. In the light of congestion control technique of TCP, the principles and characteristics of the key mechanisms which include slide window, self clocking, additive increase and multiplicative decrease, management of retransmission timeout are analyzed.Various TCP versions are studied. Based on the NS2 software, simulation of the congestion control technique of different TCP versions on the context of single packet loss and multiple packets losses is conducted and the micro mechanism is analyze in detail. Meanwhile, the macro throughput was analyzed on the context of packet losses caused by congestion, random loss and hybrid losses. The results show that SACK has a unique advantage in dealing with multiple packets losses in a single window and have a promoting application prospective in wireless networks. Based on the Markov error model, the performance of TCP protocol in wireless local network and wireless cell network was studied, the variation of throughput and congestion window with packet losses of different TCP versions in wireless networks are compared.The mechanism and principle of Snoop protocol is introduced in detail. Configurated with Snoop protocol, the performance of TCP protocol is studied in wireless cell networks. The result shows that the Snoop agent in the base station can sense the packet losses in the lower layer well and conduct local retransmission which resolve the problem of wireless packet drops in a certain extent and improve the network throughput of wireless networks in a large extent.