Subject: question on draft-ietf-tewg-measure-04.txt

From: Jing Shen <[email-masked]>
Date: Sun, 12 Jan 2003 14:46:01 +0800

Hi,

in sec10.1, there is a "Delay Variation" measured at Interface, 
to my understanding IPDV is a type of measurement at e2e level or link
level. Why does the draft propose that? and how to measure it?

I'm not clear what's the relationship between "throughput" and "goodput"
used in the draft. If they all refer to the amount  of traffic
successfully
delivered,  do we need to measure network traffic sent by source nodes?

And, what about the measurement precision? I means should the accuracy
of measurement be discussed? 

regards

-- 
Jing Shen

State Key Lab of CAD&CG
ZheJiang University(YuQuan)
HangZhou, Z.J. 310027
P.R.China

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From: "Dr. Richard W. Tibbs" <[email-masked]>
Date: Mon, 13 Jan 2003 14:56:42 -0500

Greetings, and thanks for your question. Apologies if you get this twice.

A one-point delay is sometimes desirable in several situations.
First, ITU Y.1540 states in appendix II:
<quote>
II.4 Guidance on Applying the Different Parameters
Guidance that serves the practical side of measurement is as follows:
- When synchronized clocks are not possible (or temporarily unavailable)
in measurement devices,
1. 1-point Packet Delay Variation (PDV) is a possible substitute for
1-way delay range/histogram, applicable for measurements on packet
streams with periodic sending times (once the reference arrival time is
appropriately set).
2. IPPM Inter-packet delay variation is applicable to all traffic flow
types.
</quote>
Second,
when flows must be regulated to ensure QoS, as for example in RSVP, a
similar reference arrival time exists based on the negotiated traffic
envelope parameters, e.g.,
1/peak_rate or 1/mean_rate, etc.
Our draft is intended as a framework document, and we wish to be quite
general in our definitions, so that subsequent drafts may focus on such
areas for TE measurement.

Hope this helps.

Yours truly,
Dr. Richard W. Tibbs.
Radford University
Dept. of Information Technology