Last Call Review of draft-ietf-ippm-reporting-metrics-
review-ietf-ippm-reporting-metrics-genart-lc-gurbani-2012-04-11-00

Request Review of draft-ietf-ippm-reporting-metrics
Requested rev. no specific revision (document currently at 09)
Type Last Call Review
Team General Area Review Team (Gen-ART) (genart)
Deadline 2012-04-11
Requested 2012-03-29
Other Reviews Secdir Last Call review of - by Sam Hartman (diff)
Review State Completed
Reviewer Vijay Gurbani
Review review-ietf-ippm-reporting-metrics-genart-lc-gurbani-2012-04-11
Posted at http://www.ietf.org/mail-archive/web/gen-art/current/msg07416.html
Draft last updated 2012-04-11
Review completed: 2012-04-11

Review
review-ietf-ippm-reporting-metrics-genart-lc-gurbani-2012-04-11

I am the assigned Gen-ART reviewer for this draft. For background on
Gen-ART, please see the FAQ at
<

http://wiki.tools.ietf.org/area/gen/trac/wiki/GenArtfaq>.

Please resolve these comments along with any other Last Call comments
you may receive.

Document: draft-ietf-ippm-reporting-metrics-08
Reviewer: Vijay K. Gurbani
Review Date: May-08-2012
IETF LC End Date: April-11-2012
IESG Telechat date: May-10-2012

Summary: This draft is ready as an Informational but has some minor
issues and nits that should be fixed before publication.

Major issues: 0
Minor issues: 6
Nits/editorial comments: 5

Minor issues:
- S3.1: I suspect that the metrics like packet loss and packet delay
 discussed in S3.1 are for hosts on the (I)nternet and not in a
 laboratory setting, yes?  If so, it may be good to state this.

- S4.1: I would mention at the end of the paragraph that you intend
 to fill the gap in RFC2680 by providing a reasonable value for the
 waiting time.

- S4.1.1: In Figure 1, t_0 is probably the delay in the initial
 link before you get to the first router.  If so, please make this
 explicit.

- S4.1.1: Just curious --- you provide a rationale for the choice
 of link delay of 100ms and queue length of 100ms.  But n=5 and L=4
 seem to be magic numbers.  I suspect that the choice of these is
 sound, but a couple of words on why the values of these variables
 are set to the ones shown would be good.

- S5.1.1: In the two bullet items here, you posit that processes
 are spawned when an unexpected condition occurs.  Why should this
 be a process?  Why not a thread?  Or a light-weight process?  Or
 an event loop?  My point is to stay away from well known and
 contextual words that dictate a specific architecture; i.e., the
 receiver spawns processes to handle an event.  Better to be generic,
 something like the following (please modify as you see fit):

 OLD:
  o  Packets that arrive within expected tolerance are handled by
      processes that remove headers, restore smooth delivery timing (as
      in a de-jitter buffer), restore sending order, check for errors in
      payloads, and many other operations.

   o  Packets that do not arrive when expected spawn other processes
      that attempt recovery from the apparent loss, such as
      retransmission requests, loss concealment, or forward error
      correction to replace the missing packet.
  NEW:
  o  Packets that arrive within expected tolerance are handled by
      removing headers, restoring smooth delivery timing (as
      in a de-jitter buffer), restoring sending order, checking for
      errors in payloads, and many other operations.

   o  Packets that do not arrive when expected lead to an attempted
      recovery from the apparent loss, such as retransmission
      requests, loss concealment, or forward error correction to
      replace the missing packet

- S5.1.2: Figure 3 --- if I understand the surrounding text for Figure
 3 correctly, then to show a "small fraction of packets are lost",
 the CDF curve should be asymptotic to the Y-axis and then become
 stable at the Y=1 value (i.e., be asymptotic to it).  We want to
 denote that almost 100% of the packets exhibit a loss close to 0.

Nits:

- S1: While characterizing the main audience, I am not sure what
 "consumer" means --- is it synonymous with "user"?  And if so, I
 think that replacing consumer with user may be better.  If these
 terms are not synonymous, then please provide a definition (even a
 loose one) of what a consumer is.

- S3.1, seems like a grammatical error in the sentence:
 "We have calculated a waiting time above that should be sufficient
 to differentiate between packets that are truly lost or have long
 finite delays under general measurement circumstances, 51 seconds."
 Probably better to rephrase as:
 "We have calculated that under general measurement circumstances,
 51 seconds is an appropriate length of time to differentiate between
 packets that are truly lost from packets that are experiencing
 long finite delays."

- S4.1.1: Right before Figure 1, you define D.  My suggestion would
 be to replace the text:
   "The normal path delay across n hops without encountering a
   loop, D, is"
 with
   "The normal path delay, D, across n hops without encountering a
   loop is"
 Here, "D" is qualifying the delay, not the loop.  So it is best
 close to the word "delay".

- S5.1.2: In Figure 3, I would suggest using "+Inf" instead of
 "+o0" to denote infinity.  It took me a while to figure out that
 the latter is an ASCII approximation to infinity.

- S6.6: In the section heading, I would advise spelling out
 "Avail." completely.  Truncating it as such serves no purpose that
 I could see and simply acts as a detraction.

Thanks!	

- vijay
--
Vijay K. Gurbani, Bell Laboratories, Alcatel-Lucent
1960 Lucent Lane, Rm. 9C-533, Naperville, Illinois 60563 (USA)
Email: vkg at {bell-labs.com,acm.org} / vijay.gurbani at alcatel-lucent.com
Web:   

http://ect.bell-labs.com/who/vkg/