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Marek – This may be a requirement that directly effects the directions we take in the standard, and I think, perhaps you misunderstand me. I am very much for vendor differentiation, and am neither looking for overly tight objectives (e.g., 100nsec), but rather, understanding how they are relative to say 1000BASE-T. I would think that because of the environment and energy efficiency desires the latency would be larger than 1000BASE-T (bigger than, for example, 84 + 244 bit times, or 328nsec, for TX_EN to get to the receiver, excluding prop delay). The MAC/PAUSE control limit isn’t too much bigger, with a pause quantum, 512 bit times, being 0.512 microseconds. In the end, I believe that latency will get specified, as it does in all IEEE PHYs, but, the question remains whether it is loose enough that it is a “don’t care” for the objectives. Thomas Hogemuller’s presentation (http://grouper.ieee.org/groups/802/3/RTPGE/public/may12/hogenmuller_01_0512.pdf) discussed drivers assistance cases, which I wouldn’t expect to be microsecond latencies, but might be hundreds of microseconds or single-digit milliseconds. I recall, but couldn’t find, someone mentioning engine management. If we get machine-to-machine control going on these networks it is really short. As I know Mike and Brad are aware, but others may not be, one path to energy efficiency (particularly in .3az) comes from being able to hold up and gather traffic. This will happen in any system that I can envision which provides for reduced power modes (because reduced power modes necessarily reduce the links’ performance, otherwise they would just be normal operation at a lower power, and not a mode at all). Because of the EMC environment, I’m inclined to think latency will be a key parameter, and will be greater than 1000BASE-T. The question for our friends in the automotive space is, how much do you think is too much for your applications? - if it isn’t too tight, e.g., hundreds of microseconds, it probably isn’t an issue requiring an objective. If it is, however, tens or single-digit microseconds, then we may need it worded into the energy efficiency objective, and possibly as its own objective, as it might have wider impacts. I would agree with Marek, however, that requirements under a microsecond will have substantial impact on complexity. I really just wanted to put the request out there for the users to weigh in. -george From: Mike Bennett [mailto:mjb@xxxxxx] Hi George,
-- Michael J. Bennett Energy Sciences Network Lawrence Berkeley National Laboratory (510) 486-7913 |