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Hi fellow 802.3an members, Being a layman, it was hard for me to keep up with the giddy pace of progress at the last meeting in San Antonio. As a result, I decided to air my ignorance in the relatively slow pace of email reflector. The use of email reflector is also motivated by my wish to resolve my confusions long before the next meeting. Given the urgency for progress, I do not with to take up valuable meeting time. One of the questions I attempted to raise on the floor is the system models and methods that were used to calculate the power back off numbers. I was assured by the experts that my concerns were completely irrelevant to the discussion, or it was vender depended and beyond the scope of the standardization process. However, that failed to dispel my confusion. And hence, I am here to seek some clarification, without contradicting any of the experts. The confusion I have with the power back off numbers is as follows. I have done a simple calculation for best achievable SNR for class E cables using the models defined in draft D1.1. The system model I used includes background noise (-150 dBm/Hz), flat transmit (-81 dBm/Hz), and ANEXT using the PSANEXT model from D1.1. AFEXT, and residue Echo, NEXT, and FEXT are ignored for simplicity. Using the model, I calculated the best achievable SNR as a function of length of the class E cable. The insertion loss and the ANEXT are changed according to the length. Please see the attached file (power point) for details. According to my calculation, the optimal SNR does not increase significantly with the decrease in cable length. In fact, my calculation shows the opposite: the SNR is less for lower cable length. Given the numbers there are two possibilities: 1. I have made serious mistakes in my calculations, and the numbers are useless. In that case my apology to all. 2. My calculations have some merit, and in that case I would like to know how on Class E cable we are going to have any power back off, let alone 10 to 16 dB? I would appreciate any engineering feedback on this, from power back off experts and non-experts alike. I would like to add that in this mail my comments are limited to Class E cable. Also the addition of AFEXT, and residue Echo, NEXT, and FEXT will change the achievable SNR, but would not improve it. Thank you. -bijit P.S. Please see the attached file (ppt) for simulation details.