Minimizing delay in loss-tolerant MAC layer multicast

Many real-time applications require one to many (multicast) communication. Real time applications can gracefully accommodate some loss but require low delay. We minimize the delay in real-time MAC layer multicast by exploiting the broadcast nature of wireless medium and limited loss tolerance of the applications. We show that multiple transmissions of a packet at the MAC layer significantly reduces the delay than that when only one transmission is allowed. But each additional transmission consumes additional power and increases network load. Therefore, our goal is to design a policy that judiciously uses the limited transmission opportunities so as to deliver each packet in minimum possible time to the required number of group members. We show that the problem is an instance of the stochastic shortest path problem, and using this formulation obtain a computationally simple, closed form transmission strategy in important special cases. Numerical computations show that only a small number of transmissions, if used judiciously, are sufficient to minimize the delay subject to loss constraint.