Investigating interactions between ARQ mechanisms and TCP over wireless links

In this paper we investigate interactions between TCP and wireless ARQ mechanisms. The aim is to understand what is the best conguration of the wireless link protocol in order to guarantee TCP performance, seemingly a controversial issue. Interactions between TCP and different link layer mechanisms are evaluated by means of an analytic model, that reproduces a generic selective repeat ARQ protocol (widely used in the current wireless environments) and the TCP behavior in a wired-cum-wireless network scenario. A numerical investigation is carried out in a specic case study (TCP over 3G radio access) by means of simulations collected with a very detailed UMTS-TDD simulator based on ns. Our main nding is that fully reliable ARQ protocols are the best choices from the TCP perspective; in fact, whereas a residual packet loss left over by not fully reliable ARQ protocols may not degrade appreciably TCP throughput performance as long as it is a fraction of the overall end-to-end TCP packet loss, no apparent performance advantages (e.g. energy savings) come from limiting the number