TSN-MCU integration: who will wait until 2020?

September 28, 2016 // By Julien Happich
During the Ethernet & IP @ Automotive Technology Day organized in Paris by the IEEE Standards Association, Time-Sensitive Networks (TSN) were all the rage.

A work in progress at the IEEE standards association, TSN features represent a set of extensions to be added to existing 802.1 and 802.3 Ethernet standards in order to ensure a deterministic performance of the network. The so-called automotive Ethernet that all car OEMs are longing for will be in fact a TSN-enabled implementation of 802.3 Ethernet, with new PHY standards 100BASE-T1 and gigabit PHY allowing the use of a light unshielded twisted pair of copper wires for the automotive Ethernet backbone.

The TSN features undergoing a standardization process include, Timing and Synchronization, Frame Pre-emption, Scheduled Traffic, enhancements to the Stream Reservation Protocol (SRP), Per-Stream Filtering and Policing, and Frame Replication and Elimination for Reliability.

Timing and Synchronization (IEEE P802.1AS-REV) is a revision of the existing Audio-Visual Bridging (AVB) standard to add support for multiple time domains.

Frame Pre-emption (IEEE P802.3br) allows critical data packets to have priority over non-critical data packets by breaking-up the interfering frames into smaller “fragments” should there be data in transit. This means the critical data doesn't have to wait until the full frame of non-critical data has been transmitted, ensuring a faster routing.

The Scheduled Traffic (IEEE 802.1Qbv) option divides Ethernet traffic into different classes each with reserved access to the network at specific times, creating class-specific protected “channels”.

The SRP enhancements & performance improvements under TSN option IEEE 802.1Qcc add a User Network Interface (UNI) allowing for a remote centralized network configuration.

The Per-Stream Filtering and Policing option (IEEE 802.1Qci), also known as ingress policing, is used to prevent traffic overload conditions (that could be due to software bugs on endpoints or switches) from affecting the receiving node or port. Ingress policing could also be used against hostile devices or attacks.

The TSN option IEEE P802.1CB described as "Frame Replication and Elimination for Reliability" is to enforce robust and reliable communication regardless of link failures, cable breakage and other faults. This option ensures that duplicate copies of critical traffic are sent across disjoint paths in the network, only keeping whatever packet reaches its destination first for a seamless redundancy.

Eventually, once stabilized, these new deterministic features would turn Ethernet as a viable option to replace all existing legacy networks in the car, such as CAN, LIN, MOST and FlexRay, becoming the car's core network backbone.

In the exhibition hall, several companies were demonstrating TSN-ready automotive Ethernet, typically showing real-time control tasks running across an Ethernet network, unfazed by other non-critical data (such as synchronized streams of passenger entertainment audio and video or an end-node going wrong) competing for bandwidth.