Performance Analysis and Improvements of TCP Downstream in an Heterogeneous Network

In an infrastructure network based on IEEE 802.11a/b/g wireless LAN, heterogeneous hosts such as desktop PCs and PDAs can be connected to it. We measured a performance of data transmission between these heterogeneous hosts. When a PDA as a mobile host is used for downloading data from its stationary server, i.e., a desktop PC, a PC and a PDA acts as a fast sender and a slow receiver, respectively, due to substantial differences in their computational capabilities. Our experimental results show that the transmission time during downstream is slower than that during upstream by 20% at maximum. To mitigate this, we present two distinct approaches. First, by increasing the size of a receive buffer for a PDA the congestion window size of TCP becomes more stable. Second, a pre-determined delay between packets to be transmitted at the sender should be given. From the performance point of view a method of buffer sizing is preferred rather than that of adjusting the inter-packet delay. However, such a delay reduces the number of erroneous packets remarkably.