Per-Flow Throughput of a FIFO Buffer

FIFO buffers are widely employed in networking devices to store packets prior to transmission. Their impact on aggregate traffic has been extensively studied and is well documented in the literature. In contrast, significantly less attention has been allocated to the impact of FIFO buffers on individual flows contributing to the aggregate traffic. In this paper, the throughput of each flow traversing a FIFO buffer supplied with complex traffic composed of numerous flows, potentially exhibiting heterogeneous statistical properties, is investigated. A full queuing model of a FIFO buffer fed by many flows with different characteristics is considered first. This model is very precise with respect to each flow, but cannot be solved in practice. Then, a simplification of the full model based on a limiting theorem is proposed. For the simplified model, exact formulae for throughput and loss ratio of each participating flow are derived. In numerical examples, the throughput of flows of diverse types in scenarios with various buffer sizes, buffer loads, and transmission time distributions is calculated. It is also examined, how these factors influence per-flow throughput. Finally, it is demonstrated that in typical scenarios, the results of the simplified model differ by only a few percent from those obtained through simulations of the full, precise model.