Subject: Liaison statement regarding "Network performance measurement for periodic streams"

From: Grotefeld Glenn-cecl03 <[email-masked]>
Date: Thu, 11 May 2000 10:37:08 -0500

To:  ippm working group
From: Glenn Grotefeld, Motorola, Inc.
co-author, Network performance measurement for periodic streams 

The following is the text of a "liaison" sent from a North American
Standards Development Organization (SDO), Committee T1A1.3, regarding
version -00 of the Internet-Draft.  Since version -01 was posted on 04 May,
some of the comments have been superseded. Within the text is a
point-by-point response to the liaison that will be sent back to T1A1.3 by
separate note.  As always, questions/comments/clarifications that advance
work on the Internet-Draft are welcome.

DISCLOSURE: Aside from being a co-author of this draft, I am also vice-chair
of T1A1.2, which works in parallel with T1A1.3, the working group providing
this liaison.

*******************  LIAISON/RESPONSE START *******************

To:		Will Leland and Matt Zekaukas - IPPM Co-Chairs
Subject:	T1A1 Comments on Network Performance Measurement with
Periodic Streams (draft 00)

Will and Matt,

At its April meeting, Working Group T1A1.3 reviewed the Internet draft
"Network Performance Measurement with Periodic Streams (draft 00)" currently
under development in the IPPM Working Group.   T1A1.3 supports the
development of this Internet draft and others like it.   Such cooperative
work with tight linkages between the definitions of the relevant T1 and
ITU-T standards and actual IETF metrics to assess performance enhances the
usefulness of both outputs.   Specific comments on draft-00 follow.

1. The Results/Statistics section (4.9) appears consistent with the packet
transfer outcomes defined in ITU-T/Rec. Y.1540 (ex I.380).  It is likely
that ITU-T and T1A1 will reference the approved version of this draft as a
method of measurement in future standards, such as Draft Rec. Y.1541.

GG: Noted.  I.380 (not checked in its successor, Y.1540) makes a number of
references to RFC 2330, the framework document for this Internet-Draft.  I
support the effort to "harmonize" these documents where appropriate. 

2. T1A1.3 believes that there is a need to handle step delay changes during
a delay measurement.   This could be handled by using small test intervals,
or sliding window evaluation.

GG: Noted. Proposed text would be most useful.

3. The example definition of delay Jitter in section 4.2.4 needs
clarification.  It was noted that the Jitter measurement is suitable in this
document, since its scope is end-to-end measurement.   T1A1.3 noted that
evaluating delay variation at intermediate points (between domains, or with
hybrid networks) may require the set of 1-way packet transfer delays as a
basis.   This would be a useful extension of the current draft.

GG:  There are significantly different schools of thought between the
authors regarding "jitter" within the scope of this Internet-Draft.  In
fact, in the -01 version of the document, the term jitter has been replaced
with Successive Delay Variation (Consecutive Delay Variation was considered
as a title, but not used to prevent confusion with CDV as used in ATM
circles).  You can expect to see much more debate on "jitter" as this
document progresses.

GG:I also refer you to the end of section 3.5 of the document: "It is also
possible to have intermediate measurement points between MP(Src) and
MP(Dst), but that is beyond the scope of this document."

4. The Tcon parameter in section 4.2.1 needs clarification.   It does not
seem to be used or defined elsewhere in the draft.   Specific code to
implement the metric may be helpful in this regard.

GG: Noted.  I think you will find version -01 clarifies the use of "Tcons".

5. Although the scope of this document is end-end IP transport of periodic
packet streams, the measurements should be applicable in the evaluation of
the entire IP portion of a hybrid PSTN-IP network.   This application of the
metric would be useful to T1A1.3 in its ongoing work.

GG:  Noted.

6. The current metric, focused on delay, is very close to the alternate
definition of IP Packet delay variation in Appendix II (II.3) of Y.1540 (ex
I.380).   With a little work it appears that this single metric could be
modified to provide a metric for this version of IP packet delay variation.

GG:  This author would dispute that this Internet-Draft is "focused on
delay".  Delay is ONE OF a number of measurable parameters of interest.
This Internet-Draft also is concerned about duplicate packets, which was not
covered in I.380.

GG: The jitter (version -00) or Successive Delay Variation (version -01) is
very close to the definition of IP packet delay variation in Y.1540.

GG:  FINAL NOTE: Again, this author STRONGLY ENCOURAGES all interested
parties in T1A1.3 to join the ippm e-mail list and express their views to
the entire working group.  In this author's view, there are no planned
changes to version -01 based on this liaison.

*******************  LIAISON/RESPONSE STOP *******************

Glenn Grotefeld

Motorola, Inc.
[email-masked]
US  847 576-5992
      847 538-7455  FAX