Which QoS queuing method transmits packets strictly in the order they arrive?

FIFO (First-In, First-Out) queuing transmits packets in the exact order they are received, without any special treatment based on packet type or priority. It's the default queuing mechanism on most interfaces. Custom queuing allows administrators to define multiple queues and assign a byte count to each, ensuring a certain amount of bandwidth for specific traffic types, but it doesn't strictly process in arrival order. Weighted Fair Queuing (WFQ) provides fair bandwidth allocation to different flows by ensuring no single flow starves, but it also reorders packets based on flow. Priority queuing always transmits packets from the highest priority queue first, regardless of when they arrived in lower priority queues, thus not preserving arrival order.