From: Schulz, Dave (DSchulz@dpsciences.com)
Date: Tue May 30 2006 - 16:48:55 ART
Petr - On your first statement about doing the interleaving at the
hardware queue level.... I may have this wrong, but I thought that you
cannot do any fragmentation, classification or whatever AFTER the packet
has gone to the Tx-Ring. Any clarification is appreciated.
Dave Schulz,
Email: dschulz@dpsciences.com <mailto:dschulz@dpsciences.com%20>
________________________________
From: Petr Lapukhov [mailto:petrsoft@gmail.com]
Sent: Tuesday, May 30, 2006 2:29 PM
To: Schulz, Dave
Cc: Cisco certification
Subject: Re: Frame-Relay Fragmentation at Interface Level
Dave,
hardware queue is always FIFO, no matter what. Now the real problem
is to interleave the small packets and fragments of large ones in that
queue.
FRTS does that by the virtue of Dual FIFO at interface level. That is,
this priority queue is used to do LFI. Fragmentation is peformed before
Dual FIFO, small packets go high, fragments go low, and then
interleaving
takes place.
So the question is how that thing could be done without Dual FIFO :)
It seems to work somehow with fragmentation at interface level.
Petr
2006/5/30, Schulz, Dave <DSchulz@dpsciences.com>:
Great subject for discussion, Petr! I believe that the order of
operation needs to be classification, before fragmentation. And, any
scheduling or queueing (FIFO) needs to be done at the software level.
Please someone correct me if I am wrong, but the hardware queue
(TX-Ring) will only do FIFO once any packets are in that queue....you
cannot (or, would not want to) manipulate them. HTH.
Dave Schulz,
Email: dschulz@dpsciences.com
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Petr Lapukhov
Sent: Tuesday, May 30, 2006 1:00 PM
To: Cisco certification
Subject: Frame-Relay Fragmentation at Interface Level
Hello group,
The question I have may sound boring, but I think it would be really
useful
to investigate
that matter :))) Not to mention that it touches some deep QoS topics.
To start with, let's recall FRF.12 with FRTS legacy. The main idea is to
enable fragmentation AND
interleaving. Interleaving is performed by the Dual FIFO queue at
interface
level, where "small"
packets go to high priority queue, and "large", fragmented packets are
directed to low priority queue.
This is the way how interleaving works in that case. Small packets get
BETWEEN fragments of large
ones.
An important thing to remember, is that packets are *first* dequeued
from
*PVC-level* queue
(which is WFQ by default, when FRF.12 is turned on). Next, packets are
compressed, and then
fragmented. Therefore, fragmentation occurs AFTER per-VC dequeueing.
Note, that fragmentation decision is based solely on *packet size*, you
voice (small) packets may
be fragmented as well :)
Now, we have that new FRF.12 at interface level (12.2(13)T):
http://www.cisco.com/univercd/cc/td/doc/product/software/ios124/124cg/hw
an_c/ch05/hfrfrint.htm
What's happening here? As far as I get it, fragmentation should occur
AFTER
interface level queue is
processed, and packets are compressed (payload/RTP). The question is -
how
does INTERLEAVING
happen in that case? There is NO Dual FIFO that may help here (At least
I
did not find it with show
commands :))
DocCD vaguely mentions that interleaving happens only when LLQ is
configured
at interface level.
But that means packets should be enqueued AFTER fragmentation? Is that
possible to classify
fragmented data?
This is my doubt. Investigating a bit, I found, reading W. Odom's "CCIE
R&S
Certification Guide
2006" that Dual FIFO still exist "between" software and hardware queue.
But
how could one verify
that? :)
Hope I don't not bother you too much :)
Petr
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