INFORMATION AND COMMUNICATION ENGINEERS We

use the network configuration shown in Figure 1 with IMT-2000 support [7] to investigate the TCP performance. Parameters are summarized in Table 1. Here, the bandwidth of the downlink is 384kbps for best effort service in the first deployment in Japan. In this configuration, since the major application of the current Internet is to download the Web documents from the fixed server to the wireless terminal, we assume that TCP segments are transmitted towards the wireless terminal from the wired terminal, and ACK segments are in the reverse direction. We consider that packet loss is mainly caused by the transmission error on the wireless link, and the packet loss due to buffer overflow is assumed to be negligible. 3. Performance Comparison for TCP on Wireless Cellular Network In this section, we first describe major schemes of improving for TCP throughput on wireless cellular network, and then evaluate TCP throughput for major schemes. TCP provides reliable end-to-end data communication using the following two main congestion control mechanisms. The one is Fast Retransmit and Fast Recovery mechanisms, which throttle the congestion window size to half, if the TCP sender detects triple duplicate ACKs continuously. The other is a retransmission timeout mechanism, which draws back the congestion window size to 1 MSS (Maximum Segment Size), if the ACK for the TCP segment is not received before retransmission timeout timer expiration. Those congestion control mechanisms perform well on wired links since the most of packet losses occurs due to congestion. However, on wireless links, it does not because the packet loss may occur due to transmission errors and TCP cannot distinguish the packet loss due to congestion and transmission errors. Therefore, it is well known that the packet losses due to transmission errors cause unexpected degradation of TCP throughput in a wireless cellular network environment. Many approaches have been proposed to improve TCP throughput in the wireless cellular network. These are summarized in the IETF (Interne