Re: [bmwg] Martin Duke's Discuss on draft-ietf-bmwg-b2b-frame-03: (with DISCUSS and COMMENT)
"Scott O. Bradner" <sob@sobco.com> Tue, 15 December 2020 14:06 UTC
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From: "Scott O. Bradner" <sob@sobco.com>
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Date: Tue, 15 Dec 2020 09:06:06 -0500
Cc: Martin Duke <martin.h.duke@gmail.com>, The IESG <iesg@ietf.org>, "draft-ietf-bmwg-b2b-frame@ietf.org" <draft-ietf-bmwg-b2b-frame@ietf.org>, "bmwg-chairs@ietf.org" <bmwg-chairs@ietf.org>, "bmwg@ietf.org" <bmwg@ietf.org>
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To: "MORTON, ALFRED C (AL)" <acm@research.att.com>
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Subject: Re: [bmwg] Martin Duke's Discuss on draft-ietf-bmwg-b2b-frame-03: (with DISCUSS and COMMENT)
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I basically understood that but it seemed to me that using a fixed (2 second) extra time, which is unrelated to whatever time that the burst might have taken to be sent seemed risky since I could imagine cases where the play out speed was less than the receive speed but if you are convinced that the 2 seconds extra time would cover all possible cases the go to it Scott > On Dec 14, 2020, at 7:24 PM, MORTON, ALFRED C (AL) <acm@research.att.com> wrote: > > Hi Scott, thanks for helping with this discussion. > > I'm trying to formulate adaptive extra time based on the time it takes to *receive* the burst, with the additional "at least 2 seconds" waiting time to be sure we received all the packets that might arrive. Let me try drawing the timeline that's in my mind, and I'll use a buffer-bloat case example of a 1 second buffer (which dominates all other buffers in the DUT). > > One of the key contributions of this memo is recognizing that the buffer is being emptied while the burst of back-to-back frames is simultaneously trying to fill the buffer. > > Assume that the RFC 2544 Throughput is only half of the back-to-back frame rate for the frame size used. > > From the draft: > 4. A helpful concept is the buffer filling rate, which is the > difference between the Max Theoretical Frame Rate (ingress) and > the Measured Throughput (HeaderProc on egress). If the actual > buffer size in frames was known, the time to fill the buffer > during a measurement can be calculated using the filling rate as > a check on measurements. However, the Buffer in the model > represents many buffers of different sizes in the DUT data path. > > So (danger: calculating while typing and drawing!), a 1 second burst of B2B frames only raises the occupation buffer to 50%, and another second of transmission is needed before reaching 100% occupation. > > Trial > Time, sec: 0 1 2 3 4 5 6 > > Sender: |==========|==========| > Receiver: |= = = = = |= = = = = |= = = = = |= = = = =| > Waiting Time | | | > Trial > Ends > > In the ideal example timeline above, the back-to-back burst stopped exactly when the buffer reached capacity, so there is no loss. The buffer fill rate is half the back-to-back rate. Also, it takes 2 seconds to deplete the buffer and for frames to stop arriving at the receiver. Only then do we start the 2 second waiting time to ensure no more frames will arrive! > > While we're here, let's look at a calculation from the memo: > > Corrected DUT Buffer Time = > / \ > Implied DUT |Implied DUT Measured Throughput | > = Buffer Time - |Buffer Time * -------------------------- | > | Max Theoretical Frame Rate | > \ / > = 2 - [ 2 * 0.5 ] seconds > = 1 second > > and we avoid the error of calculating buffer time based on the sender's burst duration alone. > > hope this helps, > Al > > >> -----Original Message----- >> From: Scott O. Bradner [mailto:sob@sobco.com] >> Sent: Saturday, December 12, 2020 5:18 PM >> To: MORTON, ALFRED C (AL) <acm@research.att.com> >> Cc: Martin Duke <martin.h.duke@gmail.com>; The IESG <iesg@ietf.org>; >> draft-ietf-bmwg-b2b-frame@ietf.org; bmwg-chairs@ietf.org; bmwg@ietf.org >> Subject: Re: [bmwg] Martin Duke's Discuss on draft-ietf-bmwg-b2b-frame-03: >> (with DISCUSS and COMMENT) >> >> this would seem to work if 2 seconds is significantly longer than it takes >> to send the burst - but if it takes 2 second to send the burst >> then 2 seconds extra buffer could easily lose packets - seems to me that >> he extra time should be related to the time it takes to send the burst >> >> e.g 50% of the burst time but not less than 2 seconds >> >> Scott >> >> >>> On Dec 12, 2020, at 10:18 AM, MORTON, ALFRED C (AL) >> <acm@research.att.com> wrote: >>> >>> Hi Martin, thanks for your review and comment, >>> please see my reply, [acm] below, >>> Al >>> >>>> -----Original Message----- >>> ... >>>> >>>> ---------------------------------------------------------------------- >>>> DISCUSS: >>>> ---------------------------------------------------------------------- >>>> >>>> Thank you for engaging with the TSVART review. Despite the wordsmithing >> that >>>> has gone on, I am not sure that we have captured the correct text. >>>> >>>> The proposed change is: >>>>> I clarified: >>>>> The duration of the trial MUST include at least 2 seconds in addition >> to the time >>>>> required to send and receive each burst of frames, to ensure that DUT >> buffers to deplete. >>>>> and I'll add: >>>>> The upper search limit for the time to send each burst MUST be >> configurable as >>>>> high as 30 seconds (buffer time results >>>>> reported at the configured upper limit are likely invalid, and the >> test MUST >>>>> be repeated with a higher search limit). >>>> >>>> But IIUC it's the additional time that needs to scale up. >>> [acm] >>> >>> In the revised text where David and I reached agreement, we identified 3 >> time components of the trial duration, making the duration variable: no >> longer static and at "at least 2 seconds". >>> >>> 1. the time to send the burst of frames (at the back-to-back rate), >> determined by the search algorithm >>> 2. the time to receive the transferred burst of frames (at the RFC2544 >> Throughput rate), possibly truncated by buffer overflow, but certainly >> including the latency of the DUT with or without buffer-bloat >>> 3. at least 2 seconds in addition to the time to receive the burst (2.), >> to ensure that DUT buffers have depleted. >>> >>> So, both components 1. and 2. are variables, and the burst receive time >> component (2.) compensates for large buffers, non-back-to-back burst >> egress, and anything else that contributes to DUT latency. The final "at >> least 2 seconds" is simply about making sure the trial is really over >> before moving on in an automated test - we won't make an error if frames >> trickle-out very late for some unfortunate reason. >>> >>>> A layman's reading of >>>> the document, IMO, suggests that the burst length has a binary search >> but the 2 >>>> seconds of waiting can be fixed. >>> [acm] >>> Yes, that's right, plus all the other factors above. >>> >>> So, let's try this, but I'm trying not to extend or complicate the >> buffer time << 2 seconds testing for the sake of the buffer-bloat case: >>> >>> -=-=-=-=-=-=- >>> >>> The duration of the trial includes three REQUIRED components: >>> >>> 1. the time to send the burst of frames (at the back-to-back rate), >> determined by the search algorithm >>> 2. the time to receive the transferred burst of frames (at the RFC2544 >> Throughput rate), possibly truncated by buffer overflow, and certainly >> including the latency of the DUT >>> 3. at least 2 seconds not overlapping the time to receive the burst >> (2.), to ensure that DUT buffers have depleted. >>> >>> The upper search limit for the time to send each burst MUST be >> configurable as high as 30 seconds (buffer time results reported at or >> near the configured upper limit are likely invalid, and the test MUST be >> repeated with a higher search limit). >>> >>> -=-=-=-=-=-=-=-=- >>> >>> Does that wording do it? >>> >>>> >>>> ---------------------------------------------------------------------- >>>> COMMENT: >>>> ---------------------------------------------------------------------- >>>> >>>> Other than that, this a well-written document. Thanks! >>> [acm] >>> Thank you! >>> >>>> >>>> >>> >>> _______________________________________________ >>> bmwg mailing list >>> bmwg@ietf.org >>> >> https://urldefense.com/v3/__https://www.ietf.org/mailman/listinfo/bmwg__;! >> !BhdT!1uRJDJBUadSunB4ZCkgOTzg3ZssPtiufcyrsTcxEc1F67df5q4YNUa9IYHacnsA$ >
- [bmwg] Martin Duke's Discuss on draft-ietf-bmwg-b… Martin Duke via Datatracker
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… MORTON, ALFRED C (AL)
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… Scott O. Bradner
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… MORTON, ALFRED C (AL)
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… Scott O. Bradner
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… MORTON, ALFRED C (AL)
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… Scott O. Bradner
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… MORTON, ALFRED C (AL)
- Re: [bmwg] Martin Duke's Discuss on draft-ietf-bm… Martin Duke