Link Layer Preemption for Low Latency Automotive Networks
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Solution Overview
Problem
Current MAC sublayer standards, such as IEEE 802.1 and IEEE 802.3, experience unacceptable delays when high-priority frames are held back by lower priority frames, especially with larger 'jumbo' frames, which is critical in applications like automotive networking where such delays can interfere with critical systems.
Innovation Solution
Implementing preemption at the MAC sublayer to allow high-priority frames to interrupt lower priority frames, with techniques like fragmentation and modified CRC fields to manage and reassemble frames efficiently, minimizing changes to existing standards and devices.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If lower priority frames are transmitted completely before high priority frames, then transmission order is maintained, but high priority frame delay increases
Solution Approach 1:
The patent divides a lower priority frame into multiple segments, allowing a high priority frame to be inserted between segments. This segmentation enables preemption of high priority frames without requiring complete transmission of lower priority frames, thereby reducing high priority frame delay while maintaining manageable MAC sublayer complexity through structured frame division and reassembly mechanisms
Solution Approach 2:
The patent transmits the initial segment of a lower priority frame before preempting with a high priority frame. This preliminary transmission of the first segment reduces the waiting time for high priority frames while ensuring that some data progress is made on lower priority traffic, balancing both requirements through advance partial transmission
2Loss of time
If high priority frames interrupt lower priority frames, then high priority frame delay is reduced, but frame transmission completeness is compromised
Solution Approach 1:
By segmenting frames and implementing reassembly protocols at the receiver, the patent ensures that interrupted transmissions can be completed by sending remaining segments after the high priority frame. This maintains transmission completeness while enabling preemption, as the segmented structure allows for orderly resumption without data loss
Solution Approach 2:
The patent employs acknowledgment and reassembly confirmation mechanisms where the receiver signals when frames or segments are successfully received and reassembled. This feedback loop ensures transmission completeness by allowing retransmission of any lost or interrupted segments, thereby maintaining reliability even when preemption occurs
3Productivity
If frame preemption is implemented at MAC sublayer, then network responsiveness is improved, but compatibility with existing standards decreases
Solution Approach 1:
The patent designs the preemption mechanism to operate within the existing IEEE 802.1 and IEEE 802.3 MAC sublayer frameworks, making the MAC sublayer multi-functional by supporting both traditional priority queuing and the new preemption capability. This universal approach allows the system to maintain compatibility with existing standards while adding enhanced responsiveness functionality
Solution Approach 2:
The patent introduces preemption parameters such as preemption thresholds, segment size configurations, and priority levels that can be adjusted to balance responsiveness and compatibility. By making these parameters configurable, the system can adapt to different network requirements and maintain compatibility with various existing standards implementations while enabling improved network responsiveness where needed
Data Source
AI summary
Disclosed are various embodiments for frame preemption and fragmentation at the media access control (MAC) sublayer of the link layer or the MAC merge sublayer of the link layer. Traffic classes may be organized into preemptive traffic classes and non-preemptive traffic classes. Preemptable frames may be fragmented when a preemptive frame is to be transmitted. The fragmentation may be indicated through modification of the value of cyclic redundancy check (CRC) field in a predetermined way, through addition of a fragmentation trailer, and/or through other approaches.