Optical Module Link Training via Out-of-Band Clock Synchronization
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Solution Overview
Problem
Existing link training methods for optical modules and host devices face interoperability issues and race conditions due to unsynchronized clock timings and untrained links, particularly when auto-negotiation is not performed, leading to prolonged timeouts and inefficient synchronization.
Innovation Solution
Implementing out-of-band based independent link training, where in-band transmission and reception links are trained independently using out-of-band signals, with IDLE signals transmitted until response is received, and clock synchronization is achieved through separate out-of-band channels, decoupling the training process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional in-band link training is used, then link training can be performed using existing communication channels, but race conditions and synchronization issues occur due to unsynchronized clock timings
Solution Approach 1:
An out-of-band communication channel is introduced as an intermediary to carry training signals separately from the in-band data communication channel. This mediator allows independent control and synchronization of clock timings without interference from data traffic, resolving the race condition problem while maintaining link training functionality.
Solution Approach 2:
The link training process is segmented into separate in-band and out-of-band channels. The out-of-band channel handles synchronization and training signals independently, while the in-band channel handles data communication. This segmentation allows each channel to be optimized for its specific function without causing interference or race conditions.
2Productivity
If auto-negotiation is not performed, then link training speed is improved, but interoperability issues and prolonged timeouts occur
Solution Approach 1:
Clock synchronization and basic parameter alignment are performed as preliminary actions through the out-of-band channel before initiating fast link training. This preliminary setup ensures both ends are ready for rapid training without requiring time-consuming auto-negotiation, achieving both speed and reliability.
Solution Approach 2:
The out-of-band channel serves as a mediator that enables rapid parameter exchange and synchronization without the need for iterative auto-negotiation protocols. This intermediary provides reliable interoperability assurance through dedicated synchronization mechanisms while maintaining high training speed.
3Loss of time
If in-band transmission and reception links are trained simultaneously, then training completion time is reduced, but race conditions occur due to untrained links and unsynchronized clocks
Solution Approach 1:
Clock synchronization is performed as a preliminary action through the out-of-band channel before simultaneous in-band link training begins. This preliminary clock alignment eliminates race conditions while allowing both transmission and reception links to be trained simultaneously, achieving fast and stable training.
Solution Approach 2:
The out-of-band communication channel acts as a mediator that coordinates the simultaneous training of in-band links by providing synchronized clock references and control signals. This intermediary enables parallel training operations without race conditions by ensuring both ends are synchronized throughout the process.
Data Source
AI summary
A first optical module includes an optical transceiver and a chip. The optical transceiver, subsequent to completion of link training of an in-band transmission link between the first optical module and a host device, waits for a second optical module to come up including transmitting a first awake signal from the first optical module to the second optical module, and receives a second awake signal from the second optical module when the second optical module is up. The chip i) based on a first out-of-band signal transmitted via an out-of-band link, performs the link training of the in-band transmission link independently of an in-band reception link between the first optical module and the host device, and ii) based on the second awake signal and a second out-of-band signal transmitted via the out-of-band link, performs link training of the in-band reception link independent of the in-band transmission link.