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Wael- This is, in fact a quite old issue that has been settled long ago (back in the days of CSMA/CD) The answer becomes more obvious when you look at older networks, i.e. networks that do not have 2 synchronously connected PMDs In these older networks there is some bit loss upon reception due to the start-up characteristics of the analog front ends (these go away in synchronous PHYs since the signaling layer is lit all of the time). The GAP spec applies to the transmit side at the MDI. What resultant gap you may get at the decoding point on the receive side may be quite different. This shows up in Annex B of the standard, particularly in the 3rd column of the table. I believe it is also discussed extensively in the "Network Systems Tutorial" The relevance of this has sort of re-emerged with EEE since we are moving away from an "always on" signaling layer to conserve energy. It shows up differently at the higher speeds though. Since we want EEE to work across a significant variety of PHYs and speeds a fixed (small) number from a higher layer won't work very well, thus we effectively have a separate "Light Up" command and a parameter for the particular PHY. All of this is due to the divisions made to the standard in 1980 that were done for implementation reasons rather than architectural ones. The divisions of functionality that we attribute to "layering" were heavily biased by other considerations long ago. At that point, the divisions were not actually MAC, PHY and PMD but rather nMOS LSI (the Intel 82586), integrated bipolar analog SSI+ (which turned out to be a terrific problem for Intel, they got scooped by the SEEQ 8023) and discrete component transceivers (displaced by the BICC hybrid technology implementation). I don't know whether or not I will actually be able to attend the Maintenance Meeting given my new duties as Chair of the ES-ECSG. I hope this will give you enough meat to resolve the request. David and Pat are both highly knowledgeable in the area. I hope this helps, Geoff On 11/12/09 9:15 AM, Wael Diab wrote:
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