Summary

Recommendation ITU-T Y.3129 specifies the requirements and framework for deterministic networking with a set of work conserving packet schedulers that guarantees end-to-end latency bounds to flows. The schedulers in core nodes do not need to maintain flow states. Instead, the entrance node of a flow marks an ideal service completion time according to a fluid model, called finish time (FT), of a packet in the packet header. The subsequent core nodes update FT by adding a delay factor, which is a function of the flow and upstream nodes. The packets in the queue of the scheduler are served in the ascending order of FT. This mechanism is called stateless fair queuing. The result is that flows are isolated from each other almost perfectly. The latency bound of a flow depends only on the flow's intrinsic parameters, except the maximum packet length among other flows sharing each output link with the flow.