Two congestion control schemes designed specifically to handle changes in the datalink interface of a mobile host are presented. The future mobile environment is expected to involve multimode connectivity to the Internet and dynamic switching of the connection mode depending on network conditions. The conventional Transmission Control Protocol (TCP), however, is unable to maintain stable and efficient throughput across such interface changes. The two main issues are the handling of the change in host Internet Protocol (IP) address, and the reliability and continuity of TCP flow when the datalink interface changes. Although existing architectures addressing the first issue have already been proposed, the problem of congestion control remains. In this paper, considering a large change in bandwidth when the datalink interface changes, two new schemes to address these issues are proposed. The first scheme, Immediate Expiration of Timeout Timer, detects interface changes and begins retransmission immediately without waiting for a retransmission timeout as in existing architectures. The second scheme, Bandwidth-Aware Slow Start Threshold, detects the interface change and estimates the new bandwidth so as to set an appropriate slow start threshold for retransmission. Through simulations, the proposed schemes are demonstrated to provide marked improvements in performance over existing architectures.

The call processing capacity of a base station in CDMA cellular network can be changeable due to the additive loads from handoff, paging and location registration as well as call setup/release. In general, the load box test is widely used for measuring the call processing capacity of a exchange in the fixed network. But, it is difficult to estimate the processing capacity accurately because system load includes hand-off, paging in a mobile network. In this paper, we propose a new methodology for the calculation of call processing capacity to investigate the effect of traffic parameters on the system capacity, through the traffic modeling of call flow in base station. This result shows that the traffic load of hand-off limits the system capacity largely and is more severe than has been expected. Regression analysis will be also derived for the investigation of unit load and linear relation between CPU load and traffic load. This analysis using the field data from an operating site indicates that the call processing capacity in the wireless network must be specified with the rates of hand-off, paging and location registration, in contrast with the fixed network.

In this paper, we present an exact analysis and an efficient matrix-analytic procedure to numerically evaluate the performance of cellular mobile networks with hand-off. In high-capacity micro-cell cellular radio communication networks, a cell boundary crossed by moving users can generate many hand-off attempts. This paper considers such a priority scheme that some channels and buffers are reserved for hand-off calls to reduce the forced termination of calls in progress. Performance characteristics we obtained include blocking probability, channel utilization, average queue length and average waiting time for hand-off calls. Using the matrix-analytic solution for the stationary state probability distribution, we also derive the probability distribution of the waiting time of a hand-off call. Numerical results show how priority can be provided to hand-off calls according to the number of reserved channels and buffer size. They also clarify the effect of the hand-off priority scheme on the standard deviation of waiting time of a hand-off call.