Subject: Re: [Ieprep] Multiple instances of EF

From: [email-masked]
Date: Tue, 22 Jul 2003 15:55:47 EDT

In a message dated 7/16/2003 9:51:47 AM Eastern Daylight Time, 
[email-masked] writes:

> Since this came up twice in today's IEPREP meeting, here is the text from
> 3246 (last paragraph of actual text before the author addresses).
> 
>    "It should be noted that it is quite acceptable for a Diffserv domain
>    to provide multiple instances of EF.  Each instance should be
>    characterizable by the equations in Section 2.2 of this
>    specification.  The effect of having multiple instances of EF on the
>    E_a and E_p values of each instance will depend considerably on how
>    the multiple instances are implemented.  For example, in a multi-
>    level priority scheduler, an instance of EF that is not at the
>    highest priority may experience relatively long periods when it
>    receives no service while higher priority instances of EF are served.
>    This would result in relatively large values of E_a and E_p.  By
>    contrast, in a WFQ-like scheduler, each instance of EF would be
>    represented by a queue served at some configured rate and the values
>    of E_a and E_p could be similar to those for a single EF instance."
> 

I think this notion of multiple instances of EF has caused some confusion, 
since RFC 3246 says so little about it. As noted above, with a multilevel 
priority scheduler, an instance of EF (queue) not at the highest priority would not 
comply with the criteria for being called "EF". Therefore, it is not EF.

With a WFQ-like scheduler, each EF queue is guaranteed to be served often 
enough, that is, a certain amount of the output bandwidth is reserved for it and 
its queue size limit must be set based on the amount of bandwidth it gets. It 
seems that this makes all such EF queues equal, but depends on careful 
scheduling of serving the queues so no one gets ignored too long. It also seems to me 
that the next logical step is to use a single queue, but to apply different 
queue thresholds for each of the multiple DSCPs which point to that one queue.

Mike Pierce
Artel

---

From: "Gunn, Janet" <[email-masked]>
Date: Tue, 22 Jul 2003 16:15:02 -0400

Responding in particular to:
" As noted above, with a multilevel priority scheduler, an instance of EF
(queue) not at the highest priority would not comply with the criteria for
being called "EF". Therefore, it is not EF."

Yes it is.  It is just EF with a relatively large  E_a and E_p.  The
definition of EF doesn't say they have to be small, just they have to be
bounds.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Tuesday, July 22, 2003 3:56 PM
To: Gunn, Janet; [email-masked]
Subject: Re: [Ieprep] Multiple instances of EF

I think this notion of multiple instances of EF has caused some confusion,
since RFC 3246 says so little about it. As noted above, with a multilevel
priority scheduler, an instance of EF (queue) not at the highest priority
would not comply with the criteria for being called "EF". Therefore, it is
not EF. 

With a WFQ-like scheduler, each EF queue is guaranteed to be served often
enough, that is, a certain amount of the output bandwidth is reserved for it
and its queue size limit must be set based on the amount of bandwidth it
gets. It seems that this makes all such EF queues equal, but depends on
careful scheduling of serving the queues so no one gets ignored too long. It
also seems to me that the next logical step is to use a single queue, but to
apply different queue thresholds for each of the multiple DSCPs which point
to that one queue. 

Mike Pierce 
Artel 

_______________________________________________
Ieprep mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/ieprep