Fwd: RE: [bmwg] BMWG Last Call: draft-ietf-bmwg-igp-dataplane-conv-*** -10
Al Morton <acmorton@att.com> Mon, 10 April 2006 19:43 UTC
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Date: Mon, 10 Apr 2006 15:43:34 -0400
To: bmwg@ietf.org
From: Al Morton <acmorton@att.com>
Subject: Fwd: RE: [bmwg] BMWG Last Call: draft-ietf-bmwg-igp-dataplane-conv-*** -10
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BMWG, I took a last look at the IGP Dataplane drafts today, and had the short exchange with Scott, below. Scott will respond with the proposed resolution for your consideration. I hope this will prompt others to take one last look... Al >Date: Mon, 10 Apr 2006 14:41:04 -0400 >To: sporetsky@reefpoint.com >From: Al Morton <acmorton@att.com> >Subject: RE: [bmwg] BMWG Last Call: draft-ietf-bmwg-igp-dataplane-conv-*** -10 > >Scott, > >I understand that a pre-condition is to (first find and then) offer >the "Throughput" traffic level to the DUT. And also that Throughput >is defined in RFC 2544 only, in fact, the procedure in Sections 23 >and 24 for Trials seem to be the details that encumber the Throughput >benchmark and make it difficult to use when measuring rate-derived >convergence, especially the queue bleeding-off time (2 seconds). > >So, what I thought was used here was a combination of Throughput >and Forwarding Rate benchmarks. > > - Throughput is needed to establish the "maximum" traffic load > and conduct the benchmark test for Convergence Time > (regardless whether Rate-Derived or Loss-Derived CT is measured). > > - Forwarding Rate is needed to characterize the Rate-Derived > Convergence Time, specifically to determine which 100 ms > packet sampling intervals contain the "convergence event instant" > and "convergence recovery instant" as in figure 1 of the terms draft. > >In other words, I think you can read a series of forwarding rate >measurements taken at Throughput level, using 100 ms sampling: > >500 500 500 500 500 500 ... 500 pkt/s > 125 200 > 0 0 0 0 0 0 >and calculate the convergence time of this event to be 9 x 100ms = 900 ms > >I guess that my difficulty is that I cant see how to determine the >"convergence event instant" and "convergence recovery instant" >without making a measurement at egress, and getting a new measurement >every 100ms (which Forwarding Rate can do). > >But as I said, I think a straight Throughput measurement works fine >for Loss-derived convergence time. > >This may be a point that's hard to make by e-mail, >feel free to call me if you want... > >Al > >At 12:35 PM 4/10/2006, sporetsky@reefpoint.com wrote: >>Hi Al, >> >>This work item does not define Forwarding Rate nor Throughput. In order to >>make the Convergence Time measurement it is necessary to provide a known >>Offered Load for which there is no packet loss. >>Throughput is the measurement of this value obtained as specified in RFC >>2544. Given that value as defined and measured in another BMWG document, >>the Loss-Derived Convergence Time can be measured using the IGP Data Plane >>Covergence methodology. Throughput is a better choice than Forwarding Rate >>since it is required that there be no packet loss. >> >>Does this help? >> >>Scott >> >>-----Original Message----- >>From: Al Morton [mailto:acmorton@att.com] >>Sent: Monday, April 10, 2006 12:04 PM >>To: sporetsky@reefpoint.com >>Subject: Re: [bmwg] BMWG Last Call: >>draft-ietf-bmwg-igp-dataplane-conv-***-10 >> >> >>At 11:44 AM 4/3/2006, Al Morton wrote: >> >BMWG: >> > >> >A WG Last Call period for the Internet-Drafts titled: >> >... >> >will be open from 3 April through 10 April 2006. >> >>Scott, (off-list) >> >>I have been reviewing the drafts again, with an eye toward >>filling-out the shepherding form and making a publication request. >>(in fact, the paper copies showed-up this morning, thanks!) >> >>I'm struggling a bit with the change from Forwarding Rate >>to Throughput. At first I was concerned that this might have >>been one of *my* previous comments and I had led you astray! >>But I found that this comment dates back to the WGLC on version 06 >>(July '05), and Timmons made the comment, finding an inconsistency >>between the term and meth drafts. You concluded that the better >>choice was Throughput, and implemented this change in version 09. >> >>Unfortunately, the last time the WG really read the drafts was version 08, >>during the October 2005 WGLC, and I'm a bit concerned that this late >>change might cause some problems in the future. Perhaps you >>can set me straight on this, and put my mind at ease. >> >>Let me briefly describe my concern: >> >>It doesn't seem possible to make the repeated Throughput measurements >>necessary to collect the Rate-Derived Convergence Time. >>You have to >> >> - repeatedly measure packet rate at the egress interfaces to see when the >> rate begins to drop and when it returns to the pre-convergence rate >> (throughput is a measure of offered load, either loss-less or not >> in each successive trial) >> >> - make measurements in very short time intervals, like 100ms >> (Throughput Trials require you to wait 2 seconds afterward >> to bleed the queues, so you only get one Throughput measurement >> per trial, and whether it was a loss-less trial or not) >> >>At the same time, I can see how performing a single Throughput Trial >>allows us to calculate the Loss-derived Convergence time. One simply >>determines the Frame loss count, and relates that count to time. >> >>So help me out, what dots am I failing to connect this morning? >> >>Al _______________________________________________ bmwg mailing list bmwg@ietf.org https://www1.ietf.org/mailman/listinfo/bmwg