M¨alardalenUniversity School of Innovation Design and Engineering V¨aster˚as,Sweden Thesis for the Degree of Master of Science in Computer Science - Embedded Systems 15.0 credits PERFORMANCE ANALYSIS OF THE PREEMPTION MECHANISM IN TSN Lejla Murselovi´c [email protected] Examiner: Saad Mubeen M¨alardalenUniversity, V¨aster˚as,Sweden Supervisors: Mohammad Ashjaei M¨alardalenUniversity, V¨aster˚as,Sweden June 9, 2020 Lejla Murselovi´c Performance Analysis of the Preemption Mechanism in TSN Abstract Ethernet-based real-time network communication technologies are nowadays a promising communi- cation technology for industrial applications. It offers high bandwidth, scalability and performance compared to the existing real-time networks. Time-Sensitive Networking is an enhancement for the existing Ethernet standards thus offers compatibility, cost efficiency and simplified infrastructure, like previous prioritization and bridging standards. Time-Sensitive Networking is suitable for networks with both time-critical and non-time-critical traffic. The timing requirements of time-critical traffic are undisturbed by the less-critical traffic due to TSN features like the Time-Aware Scheduler. It is a time-triggered scheduling mechanism that guarantees the fulfilment of temporal requirements of highly time-critical traffic. Features like the Credit-Based Shapers and preemption result in a more efficiently utilized network. This thesis focuses on the effects that the preemption mechanism has on network performance. Simulation-based performance analysis of a singe-node and singe-egress port model for different configuration patterns is conducted. The simulation tool used is a custom developed simulator called TSNS. The configuration patterns include having multiple express traffic classes. In a single-egress port model, the most significant performance contributor is the response time and this is one of the simulation measurements obtained from the TSNS network simulator. The comparison between the results of these different network configurations, using realistic traf- fic patterns, provides a quantitative evaluation of the network performance when the network is configured in various ways, including multiple preemption scenarios. i Lejla Murselovi´c Performance Analysis of the Preemption Mechanism in TSN Table of Contents 1. Introduction 1 1.1. Motivation........................................1 1.2. Problem Formulation...................................2 1.3. Thesis outline.......................................2 2. Background 3 2.1. Computer Network....................................3 2.2. Ethernet..........................................3 2.2.1. Shared (broadcast) Ethernet..........................4 2.2.2. Switched Ethernet................................4 2.2.3. Industrial Ethernet................................5 2.3. Time-Sensitive Networks.................................6 2.3.1. IEEE 802.1AS - Timing and Synchronization for Time-Sensitive Applications6 2.3.2. IEEE 802.1Q - VLAN Priority Queuing....................7 2.3.3. IEEE 802.1Qav - Forwarding and Queuing Enhancements for Time-Sensitive Streams...................................... 10 2.3.4. IEEE 802.1Qbv - Enhancements for Scheduled Traffic............ 12 2.3.5. IEEE 802.3br and 802.1Qbu Interspersing Express Traffic (IET) and Frame Preemption.................................... 14 3. Related Work 18 3.1. Performance evaluation of real-time Ethernet Standards............... 18 3.2. Performance analysis of individual TSN standards.................. 18 3.3. Evaluation of TSN with Frame Preemption...................... 18 3.4. Existing network simulators............................... 19 3.5. Discussion......................................... 20 4. Method 20 5. Ethical and Societal Considerations 22 6. Effects of the Preemption Mechanism 23 6.1. Schedulability....................................... 23 6.2. Guard band size..................................... 23 6.3. Preemptable configuration of scheduled traffic..................... 24 6.4. Multiple scheduled traffic classes............................ 25 6.5. Effects on the SR traffic class.............................. 25 6.6. Preemption effects in a multi-SR traffic class configuration.............. 26 6.7. Multiple ST and SR traffic classes........................... 28 6.8. Lower priorities as express................................ 29 7. Time-Sensitive Network Simulator TSNS 31 7.1. Assumptions....................................... 31 7.2. TSNS egress port model design............................. 31 7.2.1. Queuing...................................... 33 7.2.2. Transmission Selection Algorithm........................ 34 7.2.3. Gate mechanism................................. 34 7.2.4. Transmission Selection.............................. 35 7.2.5. Preemption mechanism............................. 35 7.3. TSNS model....................................... 36 ii Lejla Murselovi´c Performance Analysis of the Preemption Mechanism in TSN 8. Evaluation 39 8.1. Scenario 1: Single-simulation - Offline generated message set - Per-message results 40 8.1.1. Results...................................... 41 8.1.2. Discussion..................................... 42 8.1.3. Conclusion - Scenario 1............................. 42 8.2. Scenario 2 - Express ST and multiple express SR traffic............... 42 8.2.1. Results...................................... 43 8.2.2. Conclusion - Scenario 2............................. 44 8.3. Scenario 3 - No ST traffic class............................. 45 8.3.1. Results...................................... 46 8.3.2. Discussion..................................... 47 8.3.3. Conclusion - Scenario 3............................. 47 8.4. Scenario 4 - Express ST and various single express SR - express ST and express LP - High number of traffic classes.............................. 48 8.4.1. Results...................................... 48 8.4.2. Discussion..................................... 49 8.4.3. Conclusion - Scenario 4............................. 50 9. Conclusions 51 9.1. Future work........................................ 51 10.Acknowledgments 52 References 55 iii Lejla Murselovi´c Performance Analysis of the Preemption Mechanism in TSN List of Figures 1 The evolution of Ethernet in the 20th century.....................3 2 Master-slave architecture for time synchronisation in IEEE Std 802.1AS [1]....7 3 Insertion of IEEE 802.1Q Tag in the Ethernet frame.................7 4 Software Architecture of the Bridge with Strict Priority Selection..........9 5 Credit-Based Shaper Algorithm operations in different conditions.......... 11 6 Software Architecture of the Bridge with the Credit-Based Shaper Algorithm... 11 7 Time-triggered scheduled traffic transmission..................... 12 8 Operation examples of the CBS with TAS....................... 13 9 Software Architecture of the Bridge with Time-Aware Scheduler.......... 14 10 Preemptable MAC (pMAC) and express MAC (eMAC) scheme [2]......... 15 11 Preemption Mechanism Trace Example........................ 16 12 Hold and Release mechanism enabled vs. disabled.................. 17 13 Research framework [3].................................. 20 14 Preemption configuration causing ST traffic latency................. 24 15 Credit behaviour of express Class A .......................... 26 16 Example trace with no express frames......................... 27 17 Example trace with only Class A - express....................... 27 18 Example trace with only Class B - express....................... 28 19 Example trace with both Class A and B - express................... 28 20 Response time of LP traffic in express vs. preemptable configuration........ 30 21 TSNS Switch model................................... 32 22 Defined TSNS structures................................. 33 23 Overall software architecture design of the simulator................. 33 24 Credit flow diagram................................... 34 25 TS flow diagram..................................... 36 26 Preemption flow diagram................................ 37 27 TSNS model design.................................... 37 28 Scenario 3- Bar-graph representation of response time per-class........... 47 29 Scenario 4 - Plot of results - Average response time per traffic class......... 49 30 Scenario 4B - Plot of results - Maximum response time per traffic class....... 50 iv Lejla Murselovi´c Performance Analysis of the Preemption Mechanism in TSN 1. Introduction In traditional communication networks there in no common time-base concept and as a result, these networks can not provide synchronization nor precision timing. Reliable delivery of data is more important than the time window in which these are delivered so there is no need for timing constraints. Soft requirements can not be used in real-time embedded systems that are specified by strong constraints concerning timing. A set of standards is developed defining mechanisms that consider time constraints, for data transmission over deterministic Ethernet networks, called Time-Sensitive Networking (TSN) [4]. TSN is an extension of conventional switched Ethernet network protocols with several additional fea- tures, such as hard real-time guarantee on time-critical traffic and preemption support. The primary standard is IEEE 802.1Q-20181 and there are several amendments on enhancing various mechanisms, such as IEEE 802.1Qav2, IEEE 802.1Qbu3 and IEEE 802.1Qbv4. The key components of a TSN network that enable real-time capability in Ethernet-based machine-to-machine communication are time synchronization, scheduling