Understanding HTTP traffic performance in TDMA mesh networks

TDMA based wireless mesh networks have gained prominence as some of the recent standards such as WiMAX, 801.11s have proposed the use of TDMA based MAC protocol for mesh networks. But as of yet there have been no attempts to study the performance of HTTP based web browsing traffic in TDMA mesh networks. HTTP web browsing traffic has different characteristics compared with other types of traffic. In particular, as HTTP traffic consists of large number of small sized file transfers (median file size is 10KB), it can impose high scheduling overhead. As we highlight, HTTP traffic requires that RTT (round trip time) be small and also it requires that large sized flows be allocated higher share of bandwidth. Given these characteristics of HTTP traffic, it is not clear what protocol design for TDMA mesh networks performs best. In this work we have studied the comparison of four different TDMA MAC protocols for HTTP web browsing traffic. Two of these protocols follow distributed scheduling, one centralized and the other naive static fixed schedule approach. Comparison of the different protocols enables us to understand as to how the different scheduling mechanisms used by the different protocols affect the HTTP traffic performance. A particularly crucial aspect that our results point out is that the performance of the two distributed protocols specified by the recent WiMAX and 802.11s standard is poor in comparison with the naive static approach for some commonly arising conditions. This implies that there is need for further improvement of these standard protocols. Specifically we observed that the two distributed protocols perform well under high load and single channel operation. But, in comparison with the static approach, their performance is quite poor in presence of wireless packet loss or co-existing large sized HTTP file downloads. Likewise we observed that none of the protocols perform well under all the dimensions that we have considered implying a need to devise a better protocol that can efficiently support HTTP traffic. We believe that our results lay foundation for further efficient protocol design, for TDMA mesh networks.