|
On 2/14/17 10:06 PM, Greg Mirsky wrote:
Well, no - that was point in the text from my review of -12 that caused me to make comment in the first place. What does "precise accuracy" even _MEAN_? You're waving your hands with words that don't help the reader guess what you mean at the moment. The subsequent email exchange said the important part was that you measure _precisely_ (in that the measurements are always taken the same way), but accuracy isn't that important (you've (and here by "you" I mean the set of people that have responded to the review") told me it's not important whether the reading is taken at the beginning of the bit-stream, the end, or several 1000 nanoseconds after the last bit came off the physical media as long as it's done the same way for each packet). The fact that you're carrying a measurement that can talk about times smaller than the interarrival time for individual bits for some real world line speeds says that different implementations taking the measurement different ways is going to result in different residence time measurements, even if the residence time was really identical. You've told me that's not important to the protocol using the measurement as long as the an individual implementation doesn't introduce something that will look to the using protocol like jitter that's not really there. The text does not say that to an implementer right now. To restate that long paragraph with maybe a longer one, assume a simplified world where everything is perfectly constant. Packets are all flowing at the same size and same rate. For reference, I assert that the time between the first bit of a packet entering the system taking the measurement and the first bit of that packet leaving the system is exactly T (every time). You are telling me that if the system returns cT for some constant T other than 1 (and not necessarily close to 1), everything is fine. You're also telling me that if you replace the system with another that preserves T, but measures differently so that it returns c'T where c' != c, everything is fine. The important part to you is that c and c' don't change for their respective systems. (That surprises me, I can see how the way the clocks are going to use this will do the right thing, but I can't help but think someone later will look at the difference between the two systems and say something is wrong with one of them). What you've told me is not fine is that if you drop i a third system that also preserves T but reports aT where a _varies_ over some range. Have I heard you correctly?
|