From: Chris Lewis (chrlewiscsco@gmail.com)
Date: Mon Jan 16 2006 - 00:12:49 GMT-3
It is an order of operation thing within the router that is specific to
FRF.12
Packets larger than the fragment size are first enqueued to a WFQ sub-queue
from which they are fragmented, prior to them going in to the interface high
or low priority queue.
This link has more detail
http://www.cisco.com/en/US/tech/tk543/tk544/technologies_tech_note09186a00800
a4754.shtml
The high priority queue gets packets that are:
1. less than the fragment size AND
2. are packets that were classified as priority in the policy map (have
priority x defined on policy-map for that class)
FRF.11 can avoid fragmentation of voice packets if they are larger than the
fragment size, but the only time I've been able to use that is when the
vpoice was coming in on a voice port and not from a VoIP phone.
Chris
On 1/15/06, Curt Girardin <curt.girardin@chicos.com> wrote:
>
> Team,
>
> My understanding is that with frame-relay, using FRF.12 with either some
> type of LLQ or high priority queue on a subinterface or using the
> *frame-relay ip rtp priority* command under a map-class, that
> frame-relay physical interface will use two queues. One acts as a
> *high* priority queue with strict priority, and the other acts like a
> *normal* queue. Very similar to the Priority Queuing logic, except only
> those two queues.
>
> The packets in the *normal* queue can be fragmented; so that
> delay-sensitive packets in the *high* queue can be interleaved between
> fragments of the bigger packets in the *normal* queue.
>
> That being said, are the packets in the *high* queue subject to
> fragmentation ??? I mean, if these packets in the *high* queue are the
> delay-sensitive important packets, being interleaved between fragments
> of less-important traffic, why bother fragmenting the packets in the
> *high* queue at all? What would be the advantage?
>
> I haven't found any documentation that clearly states that this either
> is or is not the actual behavior. If anyone can point me in the right
> direction, that would be great.
>
> Thanks,
>
> Curt
>
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