Effect of channel variation in IP/cdma2000 interconnection performance

In order to support high data rate requirements and effectively manage scarce wireless resources, additional bandwidth channels are quite frequently allocated and taken away from mobile stations in 3G wireless data networks. A TCP sender connected to the mobile, on seeing ACKs coming at a faster pace after additional bandwidth allocation, turns overtly optimistic and injects data into the network in a more bursty manner that might be excessive for an intermediate router, thereby leading to loss of multiple packets and subsequent prolonged recovery and periods of underutilization. We characterize this problem using an analytical model for losses based on a continuous flow approximation as well as an extensive simulation setup. We also illustrate how bandwidth oscillations create more severe congestion than an increase in the number of users to the extent that even the RED algorithm is unable to check the sharp growth of queues. As a result, multiple packets are lost in a droptail fashion. We further demonstrate the dependence of congestion due to bandwidth allocation on the time during which mobiles' rates are increased and observe the degradation in performance for typical load scenarios.