Comparison of Time Sensitive Networking (TSN) and TTEthernet

Time-Triggered Ethernet (TTEthernet) is a time-critical network for industrial and avionics applications improved from the Avionics Full Duplex Switched Ethernet (AFDX). It is standardized by SAE AS6802 and satisfies strict timing transmission by use of a mixture infrastructure to support Time-Triggered (TT), Rate-Constraint (RC) and Best-Effort (BE) traffics. The key feature is a time-triggered communication paradigm according to off-line schedule table based on global synchronization. Three integration methods (preemption, timely block and shuffling) are used to resolve conflict when a TT message gets ready and a RC message is already in transmission. Besides several real-time Ethernet solutions, Time Sensitive Networking (TSN) shows great interests and attractions to satisfy the increasing and variable transmission requirements for automotive and aeronautical industry. TSN is comprised of several IEEE standards developed under IEEE 802.1 TSN Task Group, such as 802.1AS, 802.1Qav, 802.1Qat, 802.1BA, 802.1Qbv and 802.1Qbu. On top of SPQ (Static Priority Queuing) scheduling mechanism, with best effort traffics in parallel, TSN introduces guaranteed timing behavior with focus on the transportation for Control Data traffic (CDT) under Time Aware Shaper (TAS) and audio video streams under Credit-Based Shaper (CBS). This paper introduces the basic principles of TSN standard in details, compares it with the properties of the TTEthernet standard. In particular, we first investigate their clock synchronization algorithms and discuss their shaping and scheduling strategies for traffic types with individual timing requirements. Then we show the impact the hard real-time traffic has on soft real-time traffic and give the worst case end-to-end latency calculation. Finally, we determine whether TSN offers flexibility for the requirements of avionic.

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