Explicit congestion indication for TCP over wireless networks

Abstract

Transmission control protocol (TCP), the widely used transport protocol in the Internet, assumes that packet losses are because of congestion. Wireless networks have higher error rates than wired networks; TCP misinterprets the error losses as congestion and wrongly invokes congestion control algorithms. In the proposed scheme, we show that by using congestion indication feedback from the network, performance of TCP can be improved in network paths containing wireless links. The routers in the network detect congestion and set a congestion indication bit on packets flowing in the forward direction. The congestion indication is communicated back to the users through the transport-level acknowledgement. When the sender encounters a packet loss, explicit congestion indication feedback received for the packets sent before and after the packet dropped are used to identify the state of the network at the time of drop. If the network is identified as not congested when the packet was lost and the recent congestion indication feedback is also low, then the packet is considered to be lost because of transmission error. We compared our scheme against TCP-Reno which assumes that all packet losses are because of congestion. Under low congestion in the network, our scheme can lead to significant throughput improvement.