Improving end-to-end performance of TCP using link-layer retransmissions over mobile internetworks

TCP does not perform well in networks with high packet error rates, such as those with wireless links, since TCP assumes network congestion to be the major cause for packet losses. Wireless losses make TCP unnecessarily initiate its congestion control mechanism which results in poor performance in the form of low throughput and high interactive delay. We investigate, through computer simulations, the end-to-end effects of link-layer retransmissions on TCP Reno over a low-data-rate wireless link. Our results show that, by using the more effective selective-reject ARQ at the link layer, the problem of competitive retransmissions between TCP and link layer is much less serious than previously reported. We show that a non-sequencing link layer in combination with fragmentations of datagrams at the base stations and mobile hosts can be employed without significantly degrading TCP performance. We propose link-layer modifications for best-effort retransmissions to reduce possible adverse effect of link-layer resets on TCP.