A reconfigurable protocol setting to improve TCP over wireless

Wireless access to the Internet requires that information integrity be preserved while transmitting data over the radio channel. Automatic repeat request (ARQ) schemes and transport control protocol (TCP) are often used as error-control techniques at the link layer and at the transport layer, respectively. In this paper, we study the interactions between an ARQ protocol and TCP when the last hop of the connection path is wireless. Link layer retransmissions are used to hide losses over the wireless link to TCP and to avoid that TCP interprets these losses as signs of network congestion. By adapting the protocol parameter setting at the link and transport layers to the time-varying characteristics of the wireless channel, we obtain a reliable communication link in spite of disadvantageous radio channel conditions. The number of retransmissions of the ARQ scheme and the TCP segment size can be set to proper values that, given certain propagation conditions, enable the desired quality of service (QoS) at the transport layer. In order to derive the protocol parameter setting fulfilling the QoS requirements, we develop detailed models of the ARQ protocol and TCP by using standard Markovian techniques. Through these models, the impact of the link layer functions on the TCP performance is evaluated in the presence of different wireless environments.