Time-Sensitive Networking (TSN), as an enhancement based on Ethernet, can ensure deterministic traffic transmission with low delays and minimal jitters. However, TSN switches have only eight priority queues inherited from Ethernet at each egress port, which limits the flexibility and efficiency of traffic scheduling, as well as the support for developing traffic management mechanisms. Although per-flow queues boost scheduling and Quality of Service (QoS), static per-flow hardware queues in switches are considered unpractical due to resource limits. In this article, we leverage the limitation of buffer size on the number of concurrent flows in shared buffer TSN switches to design Dynamic Per-Flow Queues (DFQ). DFQ only maintains a fixed number of virtual queues determined by the buffer size and dynamically manages the mapping between virtual queues and active flows to provide the capability of per-flow queuing. By constructing Flow Mapping Table (FMT) with content-addressable memory (or hash bucket), DFQ can quickly match, create, and recycle queues to multiplex limited switch resource. We prototype DFQ on an FPGA switch and evaluate its performance in different scenarios. Experimental results show that DFQ can decrease the overhead of per-flow isolation with minimal impact on delay and throughput, indicating that DFQ is an effective per-flow queues solution.

Dynamic Per-Flow Queues (DFQ) extend queues from per-class to per-flow in Time-Sensitive Networking (TSN) switches that overcome large resource consumption by dynamically mapping a fixed number of physical queues to active flows. It can implement per-flow queuing with much less on-chip resource. Compared to brute-force hardware queues, DFQ prototyped on an FPGA, can effectively manage more per-flow queues, allowing for improved priority scheduling with minimal throughput and latency impact.

Time-sensitive networking (TSN) provides determin-istic time-sensitive transmission services for critical data at the link layer. Cyclic Queuing and Forwarding (CQF) defined by IEEE 802.1Qch is used for critical data transmission. However, unexpected data errors may occur due to transient faults like electromagnetic interference. At present, the solution to such faults defined in the IEEE TSN standards is to transmit multiple data copies on redundant paths, which introduces network resources wastage. Compared to redundant transmission, retransmission can reduce resource waste, but may violate the deterministic transmission guarantee in TSN. To tackle with this issue, we propose a time-redundant fault-tolerant mechanism for CQF, called fault-tolerant CQF (FT-CQF). On the basis of standard CQF, FT-CQF occupies an additional queue to cache copies of Time- Trigger (TT) flows and reserves time slots to forward them. According to the returned CRC-related messages, FT-CQF will decide whether to forward these copies. Non- Ttflows can also be transmitted during this time when copies are not required to be forwarded. We implement FT-CQF in OMNeT++, and verify the performance of FT-CQF in typical network scenarios. The extensive simulation experiments show that FT-CQF is effective in terms of fault-tolerant effects, consumed resources, delay, and jitter.