A Novel Per-Hop Per-Flow Flow Control Scheme-Shie-Yuan Wang

Abstract

Performing flow control inside a network can effectively avoid packet loss due to buffer overflow in switches. IEEE 802.1Qbb Priority-based Flow Control (PFC) exercises a scheme to achieve this goal. But it still suffers from several serious problems such as congestion spreading, deadlock, and packet loss.

In this work, we propose a Per-hop per-Flow Flow Control scheme (PFFC) to avoid all of these problems. We design, implement, and evaluate the performance of PFFC in P4 hardware switches. Experimental results show that

PFFC outperforms PFC in many aspects including avoiding congestion spreading, deadlock, and packet loss
The bandwidth overhead of PFFC is only slightly higher than that of PFC.

Design and Implementation

Our design and implementation including 3 main mechanisms: (1) Per-flow buffer usage accounting, (2) Per-flow control frames generation and (3) Per-flow control frames reaction

Per-flow Buffer Usage Accounting

Fig. 1 illustrates the process of per-flow buffer usage accounting. When a packet enter IMAP (Ingress Match Action Pipeline), the FBU (Per-flow Buffer Usage) and PBU (Packet Buffer Usage) counters are incremented by the packet size respectively. When a packet is cloned in EMAP (Egress Match Action Pipeline), PFFC recirculate (re-enter IMAP) the cloned packet for decrement the FBU and PBU counters.

Fig. 1: The per-flow buffer usage accounting in PFFC

Per-flow Control Frames Generation

If the FBU or PBU counter triggers the given threshold Xoff / Xon , a PAUSE/RESUME frame and a MIGRATE/MIGRATE-BACK frame will be generated and sent to upstream.

Per-flow Control Frames Reaction

As shown in Fig. 2, if a flow is not paused, we direct its packet the DEQ (Default Egress Queue). When the node receives PAUSE frame, it pauses a PEQ (Paused Egress Queue). The MIGRATE frame directs the flow which is to be paused to a PEQ. When the node receives RESUME frame, it resumes a PEQ, The MIGRATE-BACK frame redirect the paused flow to DEQ.

Fig. 2: The DEQ and PEQs in an output port in PFFC

Contributions

PFFC avoids many serious problems in PFC such as congestion spreading, deadlock and packet loss.
In addition, the average flow completion time of mice flows in PFFC is shorter than that in PFC.
The bandwidth overhead of PFFC is only slightly higher than that of PFC.
PFFC is a good candidate scheme to be used for losses networks.

Publication: S.Y. Wang, Y.R. Chen, H.C. Hsieh, R.S. Lai, and Y.B. Lin, “A Flow Control Scheme based on Per Hop and Per Flow in Commodity Switches for Lossless Networks,” IEEE Access, Volume 9, pages 156013-166029, 2021. (Digital Object Identifier: 10.1109/ACCESS.2021.3129595)