A Sync-less time-divided MAC protocol for mobile ad-hoc networks

Approaches to Medium Access Control (MAC) in mobile ad hoc networks (MANETs) can be broadly classified into TDMA and CSMA/CA. In principle, TDMA offers superior performance as well as better capacity guarantees compared to CSMA/CA. In practice, however, the need to provide network-wide synchronization without centralized control, and to accommodate mobility makes TDMA very hard to design and implement. Consequently, CSMA/CA variants are generally preferred. While the proliferation of real-time multimedia applications demands a protocol with TDMA-like features, the problem of doing so in a practically viable manner remains unsolved. We present SITA (Sync-less Impromptu Time-Divided Access), a MAC protocol for real-time applications over MANETs. SITA combines the advantages of TDMA with the simplicity and robustness of CSMA/CA. SITA provides on (traffic) demand, reserved access to the channel and automatic admission control, while it does not require slot synchronization. The main idea behind SITA is to set up an impromptu, loose, conflict free schedule relative to an initial control exchange. We study the performance of SITA when implemented as an overlay over 802.11 in the ns-2 simulator. Our results show that, with real-time like traffic, SITA provides significant improvement in the end-to-end throughput, by as much as 300%, and on order of magnitude or more decrease in the end-to-end delay and jitter when compared with the vanilla 802.11.