Ethernet In-Vehicle Network Start-Up Triggering Mechanism
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Solution Overview
Problem
The IEEE 802.1 Qbv standard does not provide a solution for determining when bridges/switches and devices should start transmitting time-aware shaper (TAS) frames, leading to unpredictable latency and jitter in Ethernet-based in-vehicle networks, which are critical for deterministic traffic scheduling.
Innovation Solution
A method and system that utilize a trigger node to send trigger messages with a timestamp field, informing devices when to send their first scheduled frame and bridges when to forward it, ensuring a guard band is established to prevent interference, and an enhanced mechanism to handle conflicts between multiple frame sources.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If guard band is used to prevent interference between scheduled and non-scheduled traffic, then transmission reliability is improved, but transmission latency increases
Solution Approach 1:
The trigger message mechanism performs preliminary action by notifying the sending device of the exact transmission start time before the scheduled traffic begins. This allows the device to prepare and transmit the first scheduled frame precisely at the designated time, minimizing the guard band duration while ensuring no interference with non-scheduled traffic.
Solution Approach 2:
The trigger message acts as a feedback mechanism from the bridge to the sending device, providing precise timing information about when the guard band ends and scheduled traffic should begin. This feedback enables the sending device to synchronize its transmission perfectly, reducing unnecessary latency while maintaining reliability.
2Manufacturing precision
If deterministic scheduling of TAS frames is implemented, then transmission precision is improved, but system complexity increases
Solution Approach 1:
The trigger message serves as an intermediary that carries timing information from the bridge to the sending device. This intermediary simplifies the system by providing a clear, standardized mechanism for synchronization, avoiding the need for complex distributed scheduling algorithms at each device.
Solution Approach 2:
The sending device uses the timing information from the trigger message to autonomously determine when to transmit its first scheduled frame. The device self-adjusts its transmission timing based on the received trigger message, eliminating the need for complex centralized control or intricate coordination protocols.
3Productivity
If multiple devices send TAS frames simultaneously, then network utilization is improved, but transmission reliability deteriorates due to conflicts
Solution Approach 1:
The bridge acts as an intermediary that receives trigger message requests from multiple sending devices and assigns distinct transmission times to each. This intermediary coordination prevents conflicts by ensuring that first scheduled frames from different devices are transmitted at different times, maintaining reliability while allowing high network utilization through parallel scheduled traffic.
Data Source
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AI summary
To implement the restraints suggested by IEEE 802.1 Qbv in an Ethernet-based in-vehicle network (100), wherein the network (100) comprises at least one device (1) configured for sending TAS-based frames (F1, F2, F3, F4) and at least one bridge (2, 3, 4, 5) configured for transmitting TAS-based frames (F1, F2, F3, F4), and wherein the at least one device (1) and the at least one bridge (2, 3, 4, 5) use a guard band (16) for determining, when a TAS-based frame (F1, F2, F3, F4) has to be sent or transmitted, it is suggested to - transmit a trigger message to the device (1), wherein the trigger message defines the time (t21) at which the device (1) has to start sending its first scheduled frame (F1); - adjust the guard band (16) of the device (1) with respect to the transmitted time (t21); - transmit a trigger message to at least one bridge (2, 3, 4, 5) in the network (100), wherein the trigger message (32) defines the time (t22, t23, t24, t25; t26) at which the bridge (2, 3, 4, 5) will receive the first scheduled frame (F1) from the device (1); and - adjust the guard band (16) of the bridge (2, 3, 4, 5) with respect to the transmitted time (t22, t23, t24, t25; t26).