From: sabrina pittarel (sabri_esame@yahoo.com)
Date: Mon Oct 02 2006 - 02:15:54 ART
Mmmmh,
I like when this happens, one start confused, and he ends up more
confused that before.
I went to that link after Scott reply and from there to
another one:
http://www.cisco.com/en/US/products/sw/iosswrel/ps1834/products_feature_guide
09186a0080080122.html
But I guess I have misread it. It seemed to me it was
saying (see below) that packets in the priority queue was passing thru
unfragmented, but it is instead saying that *small* packets are not
fragmented. Still voice can get accellerated transmission thru the LLQ, but
yet fragmentation is required...
Frame Relay Fragmentation
The purpose of
Frame Relay fragmentation (FRF.12) is to support voice and data packets on
lower-speed links without causing excessive delay to the voice packets. Large
data packets are fragmented and interleaved with the voice packets.
When
FRF.12 is configured with low latency queueing, small packets classified for
the PQ pass through unfragmented onto both the low latency queueing PQ and the
high priority interface queue. Large packets destined for PQ are shaped and
fragmented when dequeued.
Use the frame-relay fragment and service-policy
map-class configuration commands to enable low latency queueing with FRF.12 .
Sabrina
----- Original Message ----
From: Petr Lapukhov
<petr@internetworkexpert.com>
To: Scott Morris <swm@emanon.com>
Cc: sabrina
pittarel <sabri_esame@yahoo.com>; ccielab@groupstudy.com
Sent: Sunday, October
1, 2006 9:31:41 PM
Subject: Re: Q. on frame relay fragmentation
Let's talk a
little bit more about FRF.12, leaving VoFR stuff aside :)
To start with,
there are two ways of configuring FRF.12 - per VC and at
interface level.
In both cases, important moment is that fragmentation occurs after dequeueing
(but _before_ intereaving). And fragmentation decision is based solely on
packet *size*, nothing else. (At least, on hardware platforms commonly
encountered in CCIE lab, check out Chris Lewis' reply a bit later)
Now, there
is no way to _conditionally_ avoid packet fragmentation with FRF.12,
even by
putting them into any kind of priority queue. This has been discussed
a few
times, just a couple of references:
http://www.groupstudy.com/archives/ccielab/200605/msg01632.html
http://www.groupstudy.com/archives/ccielab/200605/msg01675.html
To finish,
let's just add that whole idea of fragmentation is connected to the
concept
of "interleaving" queue. With per-VC this is dual-FIFO at interface level.
With interface level fragmentation it's unclear, but Cisco says it works :)
HTH
PS
There is also exist "voice-adaptive" fragmentation, that turns on
FRF.12,
based on packets presense in priority queue. But it still uses packet
size
for fragmentation decision.
2006/10/2, Scott Morris <swm@emanon.com>:
That depends on what you do with them. FRF11 is designed for VoFR, and will
not fragment any VoFR frames. FRF12 is more generic in nature, and makes no
specific delineation for voice or other packet types (IP is IP).
However,
if you have voice in a priority (LLQ) queue on the interface,
anything in the
priority queue will bypass the entire fragmentation scheme
and is therefore
unaffected. There are some previous posts regarding this
if you want to
search the archives for a little more detail that may be
slipping my mind at
the moment.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service
Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP -
Curriculum Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
_____
From: sabrina pittarel
[mailto:sabri_esame@yahoo.com]
Sent: Sunday, October 01, 2006 3:37 PM
To:
Scott Morris; ccielab@groupstudy.com
Subject: Re: Q. on frame relay
fragmentation
I see...
are then voice packets automatically excluded from
fragmentation or should I
manually set the fragment size to be bigger then the
voice packets...is the
this behavior different for different types of
fragmentation (FRF.12 FRF.11
or cisco)?
Sabrina
----- Original Message ----
From: Scott Morris <swm@emanon.com >
To: sabrina pittarel
<sabri_esame@yahoo.com>; ccielab@groupstudy.com
Sent: Sunday, October 1, 2006
11:23:10 AM
Subject: RE: Q. on frame relay fragmentation
Because it will
introduce extra latency into the mix, and voice traffic is
latency-sensitive.
So you don't want to have choppy voice.
That and voice packets are typically
small enough that it makes little sense
to fragment them. Fragmentation is
done to make all things play better with
each other on slower speed links.
And since voice (or SNA or some other
stuff) is generally the reason for
fragmentation, it wouldn't serve much
purpose to fragment that traffic as
well.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
#4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPExpert VP - Curriculum
Development
IPExpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From:
nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
sabrina
pittarel
Sent: Sunday, October 01, 2006 2:17 PM
To: ccielab@groupstudy.com
Subject: Q. on frame relay fragmentation
Hi,
I was reading about frame relay
fragmentation and everywhere in the
documentation I read that voice packets
should not be fragmented...
Why is
that?
Sabrina
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