Intelligent Star Coupler for Time-Triggered Ethernet Jitter Control
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Solution Overview
Problem
Existing Ethernet protocols lack good real-time properties, such as minimal jitter, which is crucial for precise clock synchronization and control engineering in distributed real-time systems.
Innovation Solution
A communication method that distinguishes between conventional Ethernet messages (ET) and time-triggered Ethernet messages (TT), where TT messages are transported with a priori known constant delay time, and in case of conflicts, ET messages are aborted to ensure TT messages are transmitted with minimal jitter, using intelligent star couplers to manage communication channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional Ethernet protocol is used for message transmission, then cost is reduced and compatibility is improved, but real-time properties and jitter performance deteriorate
Solution Approach 1:
The Ethernet message stream is segmented into two distinct types: event-triggered messages (ET) and time-triggered messages (TT). This segmentation allows the system to apply different handling mechanisms to different message types, with TT messages receiving priority treatment to ensure real-time properties while ET messages maintain standard Ethernet behavior
Solution Approach 2:
An intelligent star coupler is introduced as an intermediary device in the Ethernet network. This mediator intercepts messages, identifies TT messages based on their type field, and applies special handling (constant delay time insertion, pre-emptive transmission) to ensure real-time performance without requiring changes to standard Ethernet protocols or controllers
2Reliability
If priority-based message handling is implemented, then real-time properties improve, but message transmission delay increases due to waiting for lower priority messages
Solution Approach 1:
The system performs preliminary identification of TT messages at the star coupler before transmission conflicts occur. By pre-marking TT messages and pre-configuring the star coupler to prioritize them, the system prevents time conflicts rather than resolving them after they arise, eliminating the need to wait for lower priority ET messages to complete
Solution Approach 2:
Constant delay time is inserted in advance into TT messages before they enter the transmission medium. This preliminary action ensures that TT messages are transmitted in predetermined time slots with guaranteed timing, preventing conflicts with ET messages and eliminating the need to wait for their completion
3Measurement precision
If constant delay time is guaranteed for TT messages, then clock synchronization precision improves, but ET message transmission reliability deteriorates due to aborts
Solution Approach 1:
The system converts the potential harm of ET message aborts into a benefit by implementing a retransmission mechanism. When a TT message requires pre-emptive transmission, the conflicting ET message is aborted but automatically retransmitted later, ensuring eventual delivery while allowing TT messages to maintain their constant delay time guarantee for clock synchronization
Data Source
AI summary
A communication method for transmitting Ethernet messages in a distributed real-time system in which a plurality of network node computers, e.g. four network node computers (111, 112, 113, 114), each comprising at least one communication controller (121, 122, 123, 124), are linked via a communication system comprising one or more communication channels (109), one or more intelligent star couplers (101, 102) being disposed in each communication channel. According to the invention, a distinction is made between conventional Ethernet messages (ET messages) and time-triggered Ethernet messages (TT messages), the TT messages being transported with an a priori known constant delay time (Δ) between transmitter and receiver, and, when there is a time conflict between ET and TT messages, the transport of the ET message that is in conflict being delayed or aborted in order to be able to transport the TT message with the constant delay time (Δ). Furthermore, the invention relates to a corresponding communication system and a star coupler for such a communication system.