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[802.3_10SPE] PLCA and burst mode

Dear CG-colleagues,


I first of all have to apologize that I cannot be in Bangkok. I nevertheless wish you all a successful meeting. Concerning 10BASE-T1S I would like to make some very general requirements, which I hope can help to clarify our standpoint to some of the items discussed.


1.       PLCA in general

As we reiterated various times, low relative costs was an important driver for supporting the 10BASE-T1S development. This lead to the requirement to support a multidrop architecture, so that the number of PHYs in the system can be reduced. IEEE inherently supports CSMA/CD for such a structure. However, CSMA/CD is not usable in the car for reasons of being totally undeterministic. Maximum latency is one of the most important quality criteria that need to be met. Multidrop with PLCA allows to design our systems to such a criteria. I.e. PLCA is essential. Without it, we will not be able to use the multidrop mode and without the multidrop mode 10BASE-T1S will not be competitive. From my understanding the effort to implement PLCA is way below the effort of an additional PHY. I therefore cannot share the statement that it makes 10BASE-T1S too expensive.

2.       PLCA burst mode

Various options have been discussed to add some more capability with the PLCA for QoS purposes. The proposed optional burst mode seems to meet the target with the lowest additional effort. I hope it can be adopted. To add feature that imitate some of the CAN behavior, I find critical. CAN is again undeterministic. In order to make sure that low priority packets on CAN are not dropped, we allow to load the CAN only to a very low level (i.e. 30-50%). Anything like this would be totally counterproductive for 10BASE-T1S with PLCA. I know that many system designers in the car industry still think CAN and that such a feature could make migration to Ethernet easier for them. Overall, it would be totally counterproductive to everythink we want to achieve with Ethernet.


Kind regards,



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