Research On TT Flow Scheduling Exceptions And Frame Filtering Mechanisms In Time-Sensitive Networking

Time-Sensitive Networking(TSN)is an Ethernet-based real-time communication technology drawing plenty of attention recently.It is capable of transmitting all kinds of flows requiring different qualities of service and then providing underlying supports for the Industrial Internet.In TSN,Time-Triggered(TT)flows usually carry the critical data in industrial manufacturing and therefore require superb performances in latency,jitter,packet loss ratio,etc.To enhance the security and robustness of TT communication in TSN,this thesis concentrates on TT flow scheduling exceptions and frame filtering mechanisms and achieves the following contributions:1.For frame disordering,this thesis conducts cause analyses and simulations and proves the sequences of TT frames are unpredictable in cell switching and then lead to forwarding scheduling exceptions.Therefore,a configurable shaping mechanism FOS for deterministic frame sequences is proposed.FOS locates between switch fabric and egress queues and is capable of adjusting the entering sequences of TT frames to egress queues according to a configurable TCAM which records the expected sequence.To TSN controllers,FOS provides northbound interfaces for frame sequence configurations.The theoretical analyses and simulations demonstrate FOS is able to guarantee the frame sequences without requiring unreasonable extra latency.2.After analyzing several cases,this thesis notices the root cause of exception diffusion in TT communication is that an unexpected frame has a chance to preempt the forwarding slots of normal frames and then derives more exceptions.Therefore,an approach to prevent the diffusion is to keep unexpected frames out of egress queues.The OMNeT++simulations support the existence of the exception diffusion effect and show that a small number of original exceptions may lead to a burst of derived exceptions.So,a functional frame filtering mechanism is required for TSN to enhance its robustness.Although the IEEE 802.1Qci standard has proposed an ingress frame filter PSFP,the randomness of frame sequences places restrictions on the receiving window configurations in PSFP.The configurations enable a surfeit of TT frames to be injected into TSN switches.For the above security loophole in PSFP,a CAM-based ingress frame filter TSN-Defender is proposed.TSN-Defender is able to count the arrived frames of each flow in each window and then drop the redundant frames by comparing the count value with the maximum amount.This thesis conducts OMNeT++simulations for PSFP and verifies the loophole,then implements TSN-Defender on a Tofino P4 switch and accomplishes its functionality examination.