1. Medium access in “new” contexts: Are we reinventing the wheel? Koushik Kar ECSE Department Rensselaer Polytechnic Institute, Troy, NY (koushik@ecse.rpi.edu)

2. Koushik Kar In a way, not much! Most of the “new” protocols are largely based on protocols proposed long time back (like Aloha, CSMA, Token passing, Reservation-based etc.) Some are minor tweaks, even repetitions We don’t have time to read others’ work! We identify a problem with a protocol, and try to fix it by proposing another (which has problems of its own) No clear notion of how far we are from the “optimum” MAC: Are we saying anything new?

3. Koushik Kar So should give up on MAC research? Not quite. We are realizing that the well known protocols do not work well in many emerging scenarios (multi-hop networks, long delays, high mobility, large number of channels etc.) Models used in our analysis and simulations are often too simplistic Often not tied up with physical layer realities Perfect scheduling can have unrealistically high complexity/communication complexity We have to settle with suboptimal low coordination scheduling, which is still efficient

4. Koushik Kar How is the ongoing MAC research useful? We are really putting to test existing MAC protocols in extreme environments (large multi-hop networks, long delays, high mobility, large number of channels etc.), which they were not originally designed for A small tweak can make a huge difference of properties (both in terms of analysis and actual performance) Providing fresh insights to MAC design, and prompting us to revisit the original design as well Possibly lead to better integration of MAC with physical layer properties

5. Koushik Kar Different emerging scenarios can be viewed as imposing different types/degrees of constraints on control communication/complexity/delay tolerance Analyze performance/properties of existing protocols under arbitrary topologies, large delays etc. Optimize the attainable throughput/fairness subject to protocol or other realistic complexity/communication constraints New directions in MAC analysis and optimization

6. Koushik Kar Some sample research questions Throughput/fairness properties of CSMA/CA, and optimization of Aloha-like (“no carrier sensing”) and CSMA based random access schemes Analysis and optimization of low-coordination maximal scheduling Access control and power allocation for throughput maximization in a WiMAX-like multichannel system under limited channel state feedback

7. Koushik Kar Summary I believe that new application scenarios are indeed imposing fresh challenges to MAC design Provides justification for looking at MAC performance in arbitrary topologies, limited feedback and long delays From a theory perspective, we need fundamental bounds on the achievable throughput under limited feedback/ communication/complexity and delay Finally, we need to translate these results into efficient protocols under the given scenarios, and compare existing protocol performance against these benchmarks