FIFOn

FIFOn stands for First-In-First-Out Overlay Network, a theoretical model in distributed systems and network theory. It describes a messaging layer that preserves the relative order of messages across multiple nodes while enabling parallel processing to improve throughput. In FIFOn, each message carries a global sequence number and a per-path label. Routers forward messages using a framing that ensures in-order delivery to sinks, using buffers and backpressure to prevent overflow. The model separates logical ordering from physical transmission, allowing concurrent paths to carry different segments of the same logical stream without violating overall sequencing.

Variants of FIFOn explore different scheduling policies, such as strict FIFO, windowed FIFO with reordering allowances, and deferred ordering where final assembly occurs at the destination. Network simulators use FIFOn to study latency, jitter, and throughput under varying load and failure scenarios. It is often discussed as a teaching tool to illustrate the trade-offs between strict order and parallelism in distributed queues. In practice, FIFOn-like mechanisms appear in streaming platforms and event-driven architectures, though real systems typically implement specialized protocols rather than a formal FIFOn model.

Historically, FIFOn has no standard specification; it is used mainly in theoretical literature and classroom examples. Criticism centers on the added complexity and potential latency from maintaining global order, especially in high-throughput networks. Supporters argue that it clarifies the limits of scalability for ordered delivery and provides a framework for evaluating alternative designs. See also FIFO, queueing theory, ordered delivery.