On Thu, 15 Feb 2024 09:17:48 +0100 Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> wrote: > On Wed, Feb 14, 2024 at 06:41:54PM +0100, Andrew Lunn wrote: > > > Alternative A and B Overview > > > ---------------------------- > > > > > > - **Alternative A:** Utilizes the data-carrying pairs for power > > > transmission in 10/100BaseT networks. The power delivery's polarity in > > > this alternative can vary based on the MDI (Medium Dependent Interface) > > > or MDI-X (Medium Dependent Interface Crossover) configuration. > > > > > > - **Alternative B:** Delivers power over the spare pairs not used for > > > data in 10/100BaseT networks. Unlike Alternative A, Alternative B's > > > method separates power from data lines within the cable. Though it is > > > less influenced by data transmission direction, Alternative B includes > > > two configurations with different polarities, known as variant X and > > > variant S, to accommodate different network requirements and device > > > specifications. > > > > Thanks for this documentation. > > > > It might be worth pointing out that RJ-45 supports up to 4 > > pairs. However, 10/100BaseT only makes use of two pairs for data > > transfer from the four. 1000BaseT and above make use of all four pairs > > for data transfer. If you don't know this, it is not so obvious what > > 'data-carrying pairs' and 'spare pairs' mean. > > @Kory, can you please update it. > > > And what happens for 1000BaseT when all four pairs are in use? > > Hm.. good question. I didn't found the answer in the spec. By combining all > puzzle parts I assume, different Alternative configurations are designed > to handle conflict between "PSE Physical Layer classification" and PHY > autoneg. Oleksij how did you get the definition of Alternative A uses the "data-carrying" pairs for power transmission and Alternative B Delivers power over the "spare pairs"? On my understanding of the 2022 standard the definition is: - Alternative A is for pinout conductors 1, 2, 3 and 6 - Alternative B is for pinout conductors 4, 5, 7, 8. Then indeed if we are in 10/100BaseT Alternative A are "data-carrying pairs" and Alternative B are "spare pairs" but that's not the case on 1000BaseT. You can see it in the figures in the paragraph 145.2.3. Regards, -- Köry Maincent, Bootlin Embedded Linux and kernel engineering https://bootlin.com
