Greg, One thing to keep in mind is that even though we can measure latency at a precision of 10's or 100's of nanoseconds, does it hurt to round the link delay up to the nearest microsecond? One way to look at this is that by doing such rounding up, we add at most 1 usec worth of additional delay per hop. That was my rationale for thinking it's probably OK to leave the resolution at 1 usec.
I don't have a strong opinion either way. Anoop On Mon, May 24, 2021 at 7:32 PM <[email protected]> wrote: > Dear All, > > thank you for the discussion of my question on the unit of the Maximum > Link Delay parameter. > > Firstly, I am not suggesting it be changed to a nanosecond, but, perhaps, > 10 nanoseconds or 100 nanoseconds. > > To Tony's question, the delay is usually calculated from the timestamps > collected at measurement points (MP). Several formats of a timestamp, but > most protocols I'm familiar with, use 64 bit-long, e.g., NTP or PTP, where > 32 bits represent seconds and 32 bits - a fraction of a second. As you can > see, the nanosecond-level resolution is well within the capability of > protocols like OWAMP/TWAMP/STAMP. As for use cases that may benefit from > higher resolution of the packet delay metric, I can think of URLLC in the > MEC environment. I was told that some applications have an RTT budget of in > the tens microseconds range. > > > Shraddha, you've said > > "The measurement mechanisms and advertisements in ISIS support > micro-second granularity (RFC 8570)." > > Could you direct me to the text in RFC 8570 that defines the measurement > method, protocol that limits the resolution to a microsecond? > > > To Acee, I think that > > "Any measurement of delay would include the both components of delay" > > it depends on where the MP is located (yes, it is another "It depends" > situation). > > > I agree with Anoop that it could be beneficial to have a text in the draft > that explains three types of delays a packet experiences and how the > location of an MP affects the accuracy of the measurement and the metric. > > > Best regards, > > Greg Mirsky > > > Sr. Standardization Expert > 预研标准部/有线研究院/有线产品经营部 Standard Preresearch Dept./Wireline Product R&D > Institute/Wireline Product Operation Division > > > > E: [email protected] > www.zte.com.cn > _______________________________________________ > Lsr mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/lsr >
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