Improving TCP Performance over 3G Links with an ACK Rate Control Algorithm

When TCP is carried over 3G cellular links, the characteristics of wireless channel and error recovery mechanisms cause overbuffering and buffer overflow at the RLC layer, degrading end-to-end performance. We propose and evaluate an algorithm that improves TCP goodput while reducing the delay. This algorithm is implemented at the RLC layer of the network side and consists of adjusting the inder-departure time of the acknowledgements (ACK) in the uplink direction, according to the congestion state of the downlink buffer. Our proposal does not require changes in the end user's protocol stack nor in 3GPP specifications. Additionally, it does not break TCP end-to- end semantics. In this paper we also address the parameter setting of the protocol, highlighting the importance of the radio bearer bandwidth in this aspect. We illustrate how automatic reconfiguration of ACK rate control parameters avoids the degradation caused by abrupt changes in the radio bearer rate.