From: Petr Lapukhov (petrsoft@gmail.com)
Date: Tue May 30 2006 - 15:28:35 ART
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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