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Time-Triggered Ethernet

Aerospace Standard
AS6802
Reaffirmed

Published November 09, 2016 by SAE International in United States

Sector:

Aerospace

Issuing Committee:

AS-2D2 Deterministic Ethernet and Unified Networking

Language: English

Scope

The Time-Triggered Ethernet (SAE AS6802) standard defines a fault-tolerant synchronization strategy for building and maintaining synchronized time in a distributed system of end systems and switches (we use the term end system for “data terminal equipment” (DTE) as specified in IEEE 802.3), which can be used to support communication among these components for traffic, which may have different levels of time criticality. In particular, the standard defines algorithms for clock synchronization, clique detection, startup, and restart. These algorithms have been designed to allow scalable fault-tolerance and provide self-stabilization mechanisms.

Time-Triggered Ethernet supports the design of communication systems with mixed time criticality in which several applications of mixed time criticality share a single physical network. In particular, an Ethernet network can be used to transfer frames in a time-triggered mode (synchronous communication) and non-time-triggered modes (asynchronous communication as for example Ethernet frames transmitted according to the best-effort strategy). The Time-Triggered Ethernet synchronization strategy inherently compensates for latency and jitter resulting from this integration and ensures high-quality synchronization despite increased network latency and jitter. Synchronized time provides the foundation for partitioning and isolation of critical applications from the less critical or non-critical ones.

End systems exchange application data with each other by transmitting standard Ethernet frames. The points in time when end systems dispatch these frames can be coupled to the synchronized time. The transfer of these frames is then called time-triggered transfer, because the trigger for frame dispatch is derived from time. Time-Triggered Ethernet formally defines the relationship between the synchronized time and the time-triggered transfer.

Time-Triggered Ethernet covers only the network aspects for mixed time-criticality systems¹. Time-Triggered Ethernet does not address how to integrate mixed time-criticality applications within a single node. Hence, partitioning strategies for shared resources other than the network, e.g., memory partitioning, are not discussed in Time-Triggered Ethernet. Furthermore, the fault-tolerance strategies discussed in AS6802 also address only the networking aspects. Time-Triggered Ethernet does not specify or recommend any complete system architecture for highly reliable systems.

Rationale

AS6802 has been reaffirmed to comply with the SAE five-year review policy.

Data Sets - Support Documents

Title	Description	Download
Unnamed Dataset 1
TABLE 1	COMPRESSION OF COLDSTART FRAMES
TABLE 2	PCF PAYLOAD
TABLE X.1	SM_INTEGRATE STATE TRANSITION SUMMARY
TABLE X.2	SM_UNSYNC STATE TRANSITION SUMMARY
TABLE X.3	SM_FLOOD STATE TRANSITION SUMMARY
TABLE X.4	SM_WAIT_4_CYCLE_START_CS STATE TRANSITION SUMMARY
TABLE X.5	SM_TENTATIVE_SYNC STATE TRANSITION SUMMARY
TABLE X.6	SM_SYNC STATE TRANSITION SUMMARY
TABLE X.7	SM_STABLE STATE TRANSITION SUMMARY
TABLE X.8	SM_WAIT_4_CYCLE_START STATE TRANSITION SUMMARY
TABLE X.10	SC_SYNC STATE TRANSITION SUMMARY
TABLE X.11	SC_STABLE STATE TRANSITION SUMMARY
TABLE X.12	CM_INTEGRATE STATE TRANSITION SUMMARY
TABLE X.13	CM_WAIT_4_CYCLE_START STATE TRANSITION SUMMARY
TABLE X.14	CM_UNSYNC STATE TRANSITION SUMMARY
TABLE X.15	CM_TENTATIVE_SYNC STATE TRANSITION SUMMARY
TABLE X.16	CM_SYNC STATE TRANSITION SUMMARY
TABLE X.17	CM_STABLE STATE TRANSITION SUMMARY
TABLE X.18	CM_INTEGRATE STATE TRANSITION SUMMARY
TABLE X.19	CM_UNSYNC STATE TRANSITION SUMMARY
TABLE X.21	CM_WAIT_4_IN STATE TRANSITION SUMMARY
TABLE X.22	CM_SYNC STATE TRANSITION SUMMARY
TABLE X.23	CM_STABLE STATE TRANSITION SUMMARY
TABLE 3	SM THRESHOLD ASSIGNMENTS FOR THE TWO FAULT-TOLERANT HIGH-INTEGRITY SM CONFIGURATION
TABLE 4	SM THRESHOLD ASSIGNMENTS FOR THE FAULT-TOLERANT STANDARD-INTEGRITY SM CONFIGURATION
TABLE 5	CM THRESHOLD ASSIGNMENTS FOR THE TWO FAULT-TOLERANT HIGH-INTEGRITY SM/CM CONFIGURATION
TABLE 6	CM THRESHOLD ASSIGNMENTS FOR THE TWO FAULT-TOLERANT HIGH-INTEGRITY SM/CM CONFIGURATION

Reference

Number	Title
ARINC653	This document is not part of the subscrption.
ARNIC664	This document is not part of the subscrption.
IEEE1588	This document is not part of the subscrption.
IEEESTD802.3	This document is not part of the subscrption.

Aerospace Standard	TTP Communication Protocol
Aerospace Standard	Handbook of System Data Communications
Journal Article	Multiplex Communication Protocol for Switch/Sensor/Actuator Network: “CXPI”

	2023-02-14	\|	AS6802A
	2016-11-09	\|	AS6802

Citation
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Time-Triggered Ethernet

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