ProbeCast: MANET admission control via probing

An inelastic flow is a flow with inelastic rate: i.e., the rate is fixed, it cannot be dynamically adjusted to traffic and load condition as in elastic flows like TCP. Real time, interactive sessions and video/audio streaming are typical examples of inelastic flows. Reliable support of inelastic flows in wireless ad hoc networks is extremely challenging because flows and routes dynamically change and flows compete for the shared wireless channel. Bandwidth must be reserved for inelastic flows at session set up time. To avoid repeated attempts to set up reservations in a volatile" network and prevent serious network capacity degradation due to call set up over- head, a Call Admission Control strategy robust to mobility must be developed. In this paper we propose ProbeCast, a probe based call admission control scheme with QoS guaran- tees for inelastic flows. ProbCast was designed for multicast streams but can also work, by default, for unicast. In Probe- Cast, a path (or a tree) is probed for capacity availability. If an intermediate link along the probed path fails to meet the QoS requirement, the flow is pushed back" via backpres- sure upstream to the source. The backpressure principle is simple; however its implementation requires some care to avoid unfairness and eventually capture by one of the flows sharing a congested bottleneck. We show that proportional fairness among inelastic contenders will prevent capture. To achieve this, we have developed the Neighborhood Proportional Drop (N-PROD) scheme. N-PROD guarantees the same proportional drop rate among allows competing in the same contention domain. We demonstrate the efficacy and robustness of ProbeCast for unicast as well as multicast scenarios using the Qualnet simulation platform. © 2008 ACM.