From: Ryan B (ryanb@pobox.com)
Date: Fri Feb 21 2003 - 02:35:53 GMT-3
I'd like to re-itterate that the assumption here is no "real time traffic"
such as VoIP. When VoIP comes into the picture things change in that the
minCIR and CIR values end up both being set to the contracted rate and Bc is
set to CIR/100 making Tc 10ms rather then 125ms. Also, even in a non VoIP
situation Cisco recommends setting the CIR above the contracted CIR but
bellow the line access rate, so setting CIR to 64k would be questionable.
Also, some providers don't let you send over the contracted rate, so watch
out.
As far as FR to ATM goes...
If you don't know the SCR in CPS you need to convert...
x * (1/8) * (1/53) = CPS --- Where x = SCR in bps
eg for 1.544mb SCR:
1544000 * (1/8) * (1/53) = ~3641 CPS
Now, to get the FR CIR you use the following equation:
CPS = CIR/8 * (6/250) -- Where 250 is the average packet size and used as
an overhead factor.
So to solve for our SCR of 3641 CPS...
3641 * 8 * (250/6) = 1213666 bits/sec CIR on the frame-relay side.
Since I generally just leave Be the default of zero I don't know how to do
that calculation off the top of my head. I know, I know... I've failed you,
but surely someone else on the list can pick up where I left off...
Ryan Benigno, CCIE #5847
----- Original Message -----
From: "OhioHondo" <ohiohondo@columbus.rr.com>
To: "balaji.balakrishnan" <balaji.balakrishnan@swift.com>;
<ccielab@groupstudy.com>
Sent: Thursday, February 20, 2003 5:51 PM
Subject: RE: Framerelay /ATM traffic shaping
> The URL below is the best simple explanation I have found. Watch the wrap.
>
http://www.cisco.com/en/US/tech/tk713/tk237/technologies_configuration_examp
> le09186a00800942f8.shtml
>
> I'll attempt to summarize with the assumption that there is no Real Time
> traffic:
> The setting of the FRTS parameters totally depends on the situation. One
> situation is where you have 2 sites with a pvc between them --- lets say
> with a contracted 32K CIR. The sites need FRTS if the signalling rate at
the
> sites is different. So let's assume the HUB site has a signalling rate of
> 192K and the SPOKE site has a signalling rate of 64K.
>
> CIR for the pvc at both sites is set to the maximum possible sustainable
> rate between the sites --- that would be 64K which is the lowest
signalling
> rate between the sites.
>
> minCIR is set to the actual CIR of the PVC.
>
> Bc is set to 1/8 of the CIR. This means Tc is 125 milliseconds. Tc=Bc/CIR.
> What this means is that transmission is divvied up into 8 time slots each
> with 125 milliseconds. The 64Kbps CIR that we desire is divvied up into
> eight 8Kbps blocks. (64K/8=8K)
>
> Be will be set differently at each site. What you want is the highest
> possible burst rate. The burst only occurs in the first of the 8 time
> intervals. The calculation for highest possible burst rate is:
>
> SR/8-Bc=Highest possible Be. (Where SR= Signalling Rate)
>
> For the SPOKE router this is 64K/8-8K=0=Be
>
> For the HUB router this is 192K/8-8K=16K=Be
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> balaji.balakrishnan
> Sent: Thursday, February 20, 2003 5:39 PM
> To: ccielab@groupstudy.com
> Subject: Framerelay /ATM traffic shaping
>
>
> Hi group,
>
> I t is always confusing ( atleast for me ) to define and relate frame
relay
> traffic shaping parameters minCIR, CIR,Bc,Be and EIR
> with reference to an practical example. For example, if I say a customer
> frame-relay connection is configured for minCIR =64k,
> CIR=128k and Bc=32k , Can someone explain what does it mean and how you
> derive the remaining parameters Be,Be and EIR.
> Also , in case of Framerelay to ATM internetworking, how these values maps
> to ATM PCR,SCR and MBS.
>
> Rdgs,
> Bala.
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