Impact Of Precedence Enabled Per Hop Behaviors on TCP Flows

In the Department of Defense´s (DoD) Global Information Grid (GIG) transport network, packet handling must provide preferential transport to high Precedence traffic under all networking conditions, specifically conditions of resource scarcity, e.g., network overload conditions, while simultaneously satisfying packet scheduling required to meet application Quality of Service (QoS) needs. Our approach to this duality is to enhance Active Queue Management (AQM) techniques to provide Precedence and Preemption (P&P) capabilities and rely upon standard, well studied QoS Per Hop Behavior (PHB), e.g., Weighted Round Robin, Class-Based Fair Queuing, etc., for handling QoS requirements. In this way, when operating under engineered loads, the well known scheduling algorithms support high quality QoS for applications. Under network congestion situations, the enhanced AQM layer provides the necessary P&P preferential packet handling favoring high Precedence-Level (P-L) information. Our scheme allows low order queues (within the context of QoS handling) to plead up to the next higher order queue for help in alleviating queue congestion under periods of communication link overload. We refer to our scheme as the Cross Queue-AQM (CQ-ACM) Scheme. Our scheme can be extended to higher numbers of queues and any type of scheduler in a straightforward manner. Through extensive simulation studies and analytical modeling, we investigate the performance of our CQ-AQM scheme under heavy traffic limits, where Preemption is required. The performance metrics of interest to our analysis are packet delay, packet loss and throughput as a function of the packet QoS class and P&P level.