Subject: [Diffserv] Definition of "E", draft-charny-ef-definition-01.txt

From: "John Dullaert" <[email-masked]>
Date: Fri, 26 Jan 2001 11:03:02 -0500

Good Morning All,

As the replacement for RFC 2598, I have been analyzing subject draft in
order to be able to explain it in my thesis.  I have noted a possible
discrepancy with the meaning of the "E" term for which I am seeking
clarification.

In the first part of the document, I am interpreting "E" to be the
device induced delay.  In other words, if there are no EF packets in the
device when the jth one arrives, and no other EF packets arrive before
that packet departs the device, "E" would need to be greater than or
equal to d(j) - a(j) - L(j)/R if the device is to conform.  Therefore,
"E" accounts for all delays induced within the device, including but not
limited to IP processing and queuing/scheduling.

The apparent discrepancy arises in para 3 where "E" is shown to be
definable for particular scheduler mechanisms, apparently ignoring all
other sources of latency within the device.  If this was the intent,
then perhaps a disclaimer needs to be added to this para indicating that
the definition is satisfied in the following cases if one assumes that
all other sources of delay within the device are negligible.  Appendices
B and D address the issue by mentioning negligible internal delay, but
not every reader will necessarily look at the appendices, so I suggest
that it should be clear in the body of the main document as well.
Appendix C reintroduces the discrepancy and although the disclaimer
could probably be inferred from appendix B, it should likely be restated
at the beginning of the section.

One other point is the fact that in the last para of D.2 "DEF_2" is
referred to even though it has not yet been stated.

Respectfully,

jcd

---

From: Anna Charny <[email-masked]>
Date: Fri, 26 Jan 2001 11:32:17 -0500

John,

You are quite correct that the value of E depends not only on the output 
scheduler, but on the entire device.  The examples given in the draft are 
for the ideal output-buffered device model, much in the same way as the 
implementation examples in the original RFC 2598 were given just for the 
output scheduler.

However, we are indeed planning to put in some text explaining that E in 
fact is a function not only of the output scheduler, but of the entire 
device architecture.

Thanks,
Anna

>referred to even though it has not yet been stated.

---------------------------------------
Anna Charny
Cisco Systems, Inc
300 Apollo Drive
Chelmsford, MA  01824
Tel. (978)-244-8172
Fax (978)-244-8126

_______________________________________________
diffserv mailing list
[email-masked]
http://www1.ietf.org/mailman/listinfo/diffserv
Archive: http://www2.ietf.org/mail-archive/working-groups/diffserv/current/maillist.html