Scalable Flow Isolation With Work Conserving Stateless Core Fair Queuing for Deterministic Networking

Abstract

We consider guaranteeing end-to-end (E2E) latency bounds to flows in a network. It is desirable that flows are isolated from other flows. The bursts from other flows or the network utilization level should not affect a flow's latency bound. The fair queuing technique, which includes Packetized Generalized Processor Sharing (PGPS) and Virtual Clock (VC), is based on the concept of ideal packet service completion time called the Finish Time (FT). The fair queuing is known to provide the best flow isolation but suffers from the fact that it has to maintain the flow states. Alternative schemes were suggested, in which the entrance node in a network generates FT for a packet and records it in the packet with other necessary information. Subsequent nodes, based on these records, decide the service eligibility and service order of the packets. A packet is served only when it is eligible, thus the system is non-work conserving. In this paper, a simpler framework for deriving such FTs in core nodes is presented, in which initial FT is updated by adding a delay factor that is a function of parameters of nodes and flow. The proposed scheduler is work conserving and has the property that, for a certain choice of the delay factor, the expression for E2E latency bound can be found. This E2E latency bound function is the same as that of a network with stateful fair queuing schedulers in all the nodes. Moreover, utilizing the fact that the service order of packets passing through the same path can be unaltered in the middle of the path, we also present a FIFO-based architecture whose performance is similar to that of a sorted queue-based architecture. The extensive simulations prove that the proposed framework shows an ideal flow isolation performance over a wide range of delay factor values, with superior scalability.