Flow Control Over Wireless Network and Application Layer Implementation
Flow control, including congestion control for data transmission, and rate control for multimedia streaming, is an important issue in information transmission in both wireline and wireless networks. Widely accepted flow control methods in wireline networks are TCP (1) for data, and TCP Friendly Rate Control (TFRC) (2) for multimedia. Kelly (3) (4) has laid down theoretical framework for TCP in wireline networks demonstrating its optimality, fairness, and stability. However, TCP and TFRC both assume that packet loss in wireline networks is primarily due to congestion, and as such, are not applicable to wireless networks in which the bulk of packet loss is due to errors at the physical layer. In this paper we first show flow control in the wireless networks can be formulated as the same concave optimization problem Kelly defined in the wireline networks. TCP and TFRC in the wireless networks pursue the optimal solution using inaccurate feedback. All existing approaches to this TCP/TFRC over wireless problem correct the inaccurate feedback by casting modifications to existing protocols, such as TCP, or infrastructure elements such as routers, thereby making them hard to deploy in practice. In this paper, we formulate the problem as another concave optimization problem with a different utility function, and propose a new class of solutions. Our approach is end-to-end, and achieves reasonable performance by adjusting the number of connections of a user according to a properly selected control law. The control law is based on only one bit of information, which can be reliably measured at the application layer. We show that the control system has a unique stable equilibrium that solves the concave optimization problem, implying scalability and optimality of the solution. We apply our results to design a practical rate control scheme for data transmission over wireless networks, and characterize its performance using NS-2 simulations and actual experiments over Verizon Wireless 1xRTT data network. Analysis and simulation results also indicate our scheme is applicable to both wireline and wireless scenarios.