On the flow fairness of aggregate queues

This paper presents S-SFQ which is a single queue design and implementation of the well-known Start-time Fair Queueing (SFQ). This aggregate queue orders packets based on their timestamps rather than order of arrivals. Through simulation, we show the performance gains of S-SFQ over other default single-queue schemes such as RED and FIFO in terms of link utilization and flow fairness. When sources implement end-to-end (e2e) congestion control, S-SFQ can fairly approximate the fairness, both simple and weighted, of per flow queues. In addition, we discuss in detail the adverse effect of packet loss synchronization problem common in such aggregate queues. The qualities of aggregate queue based router scheme may easily and single-handedly be taken away by this problem. Loss synchronization may surface during overloaded (rather than early) drops when the buffer becomes full (e.g., FIFO) or certain (upper) buffer thresholds are exceeded (e.g., RED).