Subject: [xrblock] open issue: which discard type is used in Burst/Gap Discard Summary Statistics Block

From: Qin Wu <[email-masked]>
Date: Thu, 19 Jul 2012 14:52:13 +0800

Hi,all:
In the draft-zorn-xrblock-rtcp-xr-al-stat-06 
(http://tools.ietf.org/html/draft-zorn-xrblock-rtcp-xr-al-stat-06),
one issue I like to raise is which discard type is used to calculate 
Gap discard rate metric in the Burst/Gap Discard Summary Statistics Block
The Gap discad rate is calculated based on the following formulation:

      (number of packets discarded - Packets Discarded in Bursts) /
      (Packets Expected - Total Packets expected in Bursts)

"number of packets discarded" is obtained from the RTCP XR
  Discard Block (i.e., draft-ietf-xrblock-rtcp-xr-discard). However Discard
count block now support 4 types of discards:

"
         00: Report packet discarded or being thrown away before playout
         due to packets duplication.

         01: Report packet discarded due to too early to be played out.

         10: Report packet discarded due to too late to be played out.

         11: Report the total number of discarded packets due to both
         early and late to be played out.

"
So which discard type is used to calculate the Gap discard rate.
As we discussed Discards draft during WGLC, Varun raised one issue is whether Burst Gap drafts need to synchronize with
Discard draft regarding discard type. I clarified with no and proposed the following change:
OLD Text:
 "
    Gap Discard Rate: 16 bits

       The fraction of packets discarded during gaps 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 the difference between number of packets discarded and
       Packets Discarded in Bursts by the difference between Packets

       Expected and Total Packets expected in Bursts as follows:

       (number of packets discarded - Packets Discarded in Bursts) /
       (Packets Expected - Total Packets expected in Bursts)

       where "number of packets discarded" is obtained from the RTCP XR
       Discard Block [DISCARD] and Packets Expected is calculated as the
       difference between "extended last sequence number" and "extended
       first sequence number" (Interval or Cumulative) provided in the
       Measurement Information block [MEASIDENT]."

  NEW TEXT:
 "
    Gap Discard Rate: 16 bits

       The fraction of packets discarded during gaps 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 the difference between number of packets discarded and
       Packets Discarded in Bursts by the difference between Packets

       Expected and Total Packets expected in Bursts as follows:

       (number of packets discarded - Packets Discarded in Bursts) /
       (Packets Expected - Total Packets expected in Bursts)

       where "number of packets discarded" is obtained from the RTCP XR
       Discard Block [DISCARD] with "Discard Type" field set to 2     
      (i.e.,packets are discarded due to both early to be played out and late to be played out.)      
       and Packets Expected is calculated as the
       difference between "extended last sequence number" and "extended
       first sequence number" (Interval or Cumulative) provided in the
       Measurement Information block [MEASIDENT]."
"
Varun has already confirmed the proposed change address his comment.
Now after WGLC of discard draft, we have already changed the order of Discard type. So I like to additional change to 
my proposal metioned above.

 NEW TEXT:
 "
    Gap Discard Rate: 16 bits

       The fraction of packets discarded during gaps 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 the difference between number of packets discarded and
       Packets Discarded in Bursts by the difference between Packets

       Expected and Total Packets expected in Bursts as follows:

       (number of packets discarded - Packets Discarded in Bursts) /
       (Packets Expected - Total Packets expected in Bursts)

       where "number of packets discarded" is obtained from the RTCP XR
       Discard Block [DISCARD] with "Discard Type" field set to 3     
      (i.e.,the total number of discarded packets due to both
         early and late to be played out..)      
       and Packets Expected is calculated as the
       difference between "extended last sequence number" and "extended
       first sequence number" (Interval or Cumulative) provided in the
       Measurement Information block [MEASIDENT]."
"

Regards!
-Qin