A Two-Level Quality of Service Scheme for Collision based Mobile Ad Hoc Networks

When fielding a hard real time application in a mobile ad hoc network, it is necessary to give priority to its traffic over traffic fulfilling other purposes. For example, in the U.S. Army´s One Tactical Engagement Simulation System (OneTESS), engagement (shot) simulation must meet hard real time deadlines, whereas data collection and control messaging can be delivered on a best-effort basis. However, since collision-based mobile ad hoc networks lack centralized control, there is currently no way for a node waiting to send a high priority packet to get preferential access to the medium over nodes having lower priority traffic. The present paper describes a QoS scheme, QoS-MAC, for collision based MANETs that operates by enforcing a mandatory preemption period after each transmission for low priority traffic; high priority traffic can seize the medium whenever the channel is free, while low priority traffic must wait out the preemption period after each transmission. We combine this with intra-node queue prioritization and low-priority packet cancellation to obtain a two level QoS scheme. In addition to describing the approach, we discuss a substantial study of it in the context of MANET applications within the OneTESS system.