From: Ralph (Mandela@myrealbox.com)
Date: Tue Nov 01 2005 - 01:23:32 GMT-3
Dave,
The CiscoPress Book "IP Quality of Service" by Srinivas Vegesna, Has a good explanation and case study on frame-relay fragmentation. IMHO, I think this book does a good job explaining a lot of QoS topics.
Ralph
-----Original Message-----
From: "Schulz, Dave" <DSchulz@dpsciences.com>
To: "Ralph" <Mandela@myrealbox.com>
Date: Mon, 31 Oct 2005 21:59:53 -0500
Subject: RE: Re: Frame-Relay fragmentation
Thanks for the great info, Ralph. Do you have any recommendations on
the technical details of fragmentation. The doc CD is somewhat limited
on this subject. Yes, fragmentation is fair game. Even though voice is
not a part of the R&S exam, surely having the router/switch prepared for
this, would be a viable test option.
Dave Schulz,
Email: dschulz@dpsciences.com
-----Original Message-----
From: Ralph [mailto:Mandela@myrealbox.com]
Sent: Monday, October 31, 2005 7:36 PM
Cc: Schulz, Dave; ccielab@groupstudy.com
Subject: Re: Re: Frame-Relay fragmentation
Dave:
Using a Tc of 10ms is good for voice latency. Calculate the fragment
size from the Bc value. If its greater than the average size of VOIP
packets, VOIP should be transmitted unfragmented.
HTH
Ralph
-----Original Message-----
From: "Ralph" <Mandela@myrealbox.com>
To: DSchulz@dpsciences.com
Date: Mon, 31 Oct 2005 18:48:24 -0500
Subject: Re: Frame-Relay fragmentation
Hello Dave:
FRF.12 does not discriminate betweeen voice and data. Particularly if
it's VOIP (layer 3)and fragmentation being layer 2. If the fragment size
is less than the average size of the VOIP packets they will all be
fragmented. If the VOIP packets are less than the fragment size, just
like any other type packet, they will be transmitted without being
fragmented.
On the other hand, FRF.11C does discriminate between voice and data. It
does not fragment voice packets regardless of what fragmentation size is
configured. But if I can recollect properly, FRF.11C is used only on
DLCIs configured for VoFR, (layer 2). However, this form of
fragmentation is not recommended for VOIP.
As for the configuration of FRF.12, all you really need is the map-class
frame-relay fragment command. It's also commonly used with the map-class
frame-relay fair queue command; Probably can also be used with the
map-class priority-group command - not very certain. After all
fragmentation actually occurs at the TxQ.
With Voice not being tested anymore in the Lab, do you think frame relay
fragmentation is still something to be concerned with?
HTH
Ralph.
-----Original Message-----
From: "Schulz, Dave" <DSchulz@dpsciences.com>
To: <ccielab@groupstudy.com>
Date: Mon, 31 Oct 2005 17:04:56 -0500
Subject: Frame-Relay fragmentation
I was working through the doc CD, where it stated something about the
FRF.12 inherently allows all voice traffic to pass-through unfragmented,
while fragmenting the data packets to the specific length. So, can I
assume that if a lab states to fragment all packets above 53 bytes (the
default), and allow voice to be unfragmented....then you may simply
configure "frame-relay fragment" command under the specific frame
map-class or interface, along with the frame-relay traffic-shaping
interface command?
I almost want to believe that priority queuing is needed, but am
confused on which way to go here (sometimes we make things more
complicated then they really are). Thoughts?
Dave Schulz,
Email: dschulz@dpsciences.com <mailto:dschulz@dpsciences.com >
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