[xrblock] Fw: Ralph Droms' Discuss on draft-ietf-xrblock-rtcp-xr-summary-stat-08:(with DISCUSS)
Qin Wu <bill.wu@huawei.com> Wed, 20 February 2013 08:42 UTC
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From: Qin Wu <bill.wu@huawei.com>
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Date: Wed, 20 Feb 2013 16:42:05 +0800
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Subject: [xrblock] Fw: Ralph Droms' Discuss on draft-ietf-xrblock-rtcp-xr-summary-stat-08:(with DISCUSS)
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Hi, One issue raised in IESG review is about how to represent burst loss rate using 16-bit and how to report total loss or burst lost rate of 1.0. In the current version -v08, we take OPTION1. However Option1 introduces expensive multiply/divide operations by using 2^15-1 as multiplier, Option 2 and Option 3 are proposed to avoid such expensive multiply/divide operations, i.e., using 2^15 or 2^16 as mutiplier and therefore only shift is needed. However Option 3 just use 65535/65536 to approximate burst loss rate of 1.0 and can not be used to represent burst loss rate of 1.0. Option 2 allow maximum value of 32768 and can use 32368/32368 to represent total loss. Based on this discusion, I think we should go with Option 2. Please speak if you disagree or have other ways to address this. Thanks. Regards! -Qin ----- Original Message ----- From: "Barry Leiba" <barryleiba@computer.org> To: "Qin Wu" <bill.wu@huawei.com> Cc: "Ralph Droms" <rdroms.ietf@gmail.com>; "The IESG" <iesg@ietf.org>; <xrblock-chairs@tools.ietf.org>; <draft-ietf-xrblock-rtcp-xr-summary-stat@tools.ietf.org> Sent: Wednesday, February 20, 2013 1:12 AM Subject: Re: Ralph Droms' Discuss on draft-ietf-xrblock-rtcp-xr-summary-stat-08:(with DISCUSS) > draft-ietf-xrblock-rtcp-xr-summary-stat-08 > > I've been thinking more about Ralph's and my DISCUSSes, and I see that > there've been three suggested resolutions; I want to be sure we're all > clear about what we're using and what the consequences of the change > are. > > There have been three suggestions: one that just fixes the text and > leaves alone the algorithms for filling in the fields; one that > changes the algorithms to multiplying by 32768 instead of 32767; and > one that changes the algorithms to multiplying by 65536 instead of > 32767. Here are the proposed texts: > > > OPTION 1 (fix text only): > > NEW > The fraction of packets lost during bursts since the beginning of > reception, expressed as a fixed point number with the binary point > immediately to the right of the leftmost bit. This value is > calculated by dividing Packets Lost in Bursts by Total Packets > Expected in Bursts, multiplying the result of the division by > 32767 (0x7FFF), and keeping only the integer part. The maximum > value is thus 7FFF. Representing this as a formula: > > integer-part( (Packets Lost in Bursts / Total Packets Expected in > Bursts) * 0x7FFF ) > > If the measurement is unavailable, the value 0x8000 MUST be > reported. > END > > > OPTION 2 (fix text and multiply by 32768): > > NEW > The fraction of packets lost during bursts since the beginning of > reception, expressed as a fixed point number with the binary point > immediately to the right of the leftmost bit. This value is > calculated by dividing Packets Lost in Bursts by Total Packets > Expected in Bursts, multiplying the result of the division by > 32768 (0x8000), and keeping only the integer part. The maximum > value is thus 0x8000. Representing this as a formula: > > integer-part( (Packets Lost in Bursts / Total Packets Expected in > Bursts) * 0x8000 ) > > If the measurement is unavailable, the value 0xFFFF MUST be > reported. > END > > > OPTION 3 (fix text and multiply by 65536): > > NEW > The fraction of packets lost during bursts since the beginning of > reception, expressed as a fixed point number with the binary point > at the left edge of the field. This value is calculated by > dividing Packets Lost in Bursts by Total Packets Expected in > Bursts, multiplying the result of the division by 65536 (0x10000), > limiting the maximum value to 65535 (to avoid overflow), > and keeping only the integer part. The maximum value is thus > 0xFFFF. > > integer-part( min(Packets Lost in Bursts / Total Packets Expected > in Bursts) * 0x10000 ) > > This field MUST be populated and MUST be set to zero if no packets > have been received. > END > > > Notes: > > For option 1, this is just clarifying the text and not changing the > algorithm, so there will be no effect on implementations, and the > working group has already agreed to the algorithm. On the other hand, > the bit about the binary point isn't really correct because of the odd > multiplier. > > For option 2, the change in the multiplier makes the binary point > accurate. Because it's a change in the algorithm, it will make > existing implementations slightly wrong and will require the working > group to approve the change. The degree of "wrong" is so small as to > not really be significant, but the value for "unavailable" changes. > > For option 3, the change in the multiplier makes the binary point > accurate except in the case of total packet loss, and there's another > bit of granularity in the value. Because it's a change in the > algorithm, it will make existing implementations slightly wrong and > will require the working group to approve the change. The degree of > "wrong" is significant and the value for "unavailable" changes and is > no longer distinguishable from "no packet loss". > > Do I have the proposed text options correct? > Which option are we going with (any of the three are OK with me)? > Has the working group been consulted, and does it approve? > > Barry