Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02

[Shraddha Hegde <[e-mail]>]

Snipped …


>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?



Pls refer RFC 8570 sec 4.1. The link delay is encoded in microseconds

“   Delay:  This 24-bit field carries the average link delay over a
      configurable interval in microseconds, encoded as an integer
      value.  When set to the maximum value 16,777,215
      (16.777215 seconds), then the delay is at least that value and may
      be larger.
“

Exact same text can be found in OSPF RFC 7471 sec 4.1.5 as well.



Rgds

Shraddha





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Subject: Re: [Lsr] LSR WG Adoption Poll for "Flexible Algorithms: Bandwidth, Delay, Metrics and Constraints" - draft-hegde-lsr-flex-algo-bw-con-02

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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


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