From: eicc tester (reto_ccie@yahoo.com)
Date: Thu Aug 30 2007 - 20:13:38 ART
Oopss!
sorry is Tc.
committed rate measurement interval (Tc)The time interval during which the user can send only Bc-committed amount of data and Be-excess amount of data. In general, the duration of Tc is proportional to the burstiness of the traffic. Tc is computed (from the subscription parameters of CIR and Bc) with the formula Tc = Bc w CIR. Tc is not a periodic time interval. Instead, it is used only to measure incoming data, during which it acts like a sliding window. Incoming data triggers the Tc interval, which continues until it completes its commuted duration. See also committed information rate (CIR) and committed burst size (Bc) above.
Wink <dwinkworth@wi.rr.com> wrote:
Eric:
What is TS? Do you mean Tc?
----- Original Message -----
From: "eicc tester"
To: "Scott Smith" ; "groupstudy"
Sent: Thursday, August 30, 2007 10:35 AM
Subject: Re: frame-relay traffic shaping, fragmentation, port speed
> Hi,
>
> The issue with fragmentation is related with the TS , the time that you
> use for shaping, in order to keep the CIR rate in the TS. The
> fragmentation have to be small enough in order to fill completely between
> the TS time-space.
>
> For example a 512K CIR using a TS of 10 ms, implied a BC of 5120 bits,
> which correspond with a maximum of 640 bytes fragment. You transmit rate
> are T1 , then you are able to transmit 5120 bits in less of 10 ms (aprox
> 4ms) the rest 6 ms are idle (no transmit) for that pvc.
>
> The fragmentation to 640 is used to cut big data packet (1500 bytes) in
> fragments in order to match the shapping. voice packet with less of 640
> will not be fragmented.
>
> reto
>
>
>
> Scott Smith wrote:
> I'm hoping someone can shed some light on why my thinking is wrong on
> this.
>
> Config example: 2 512k PVCs on a T1 port. Each PVC is shaped via FRTS
> to 512k with no burst and the physical interface can run at T1 speed.
>
> Cisco says "you do not need fragmentation because the port speed is
> T1, irregardless of the shaping."
>
> I know all the in and outs of fragmentation/interleaving,
> serialization delay, etc and how this impacts voice traffic. Where
> I've got a problem is the seeming disregard for the amount of traffic
> that will actually pass through the interface. T1 port or not a single
> PVC cannot send more than 512k since it is shaped to that rate.
> Granted, once the traffic passes through shaper and its time to place
> the bits on the wire it'll be serialized at T1 rate (512k of traffic
> will be serialized at T1 rate) . Since a single PVC can only place
> 512k on the T1 port how is it that we completely ignore this fact when
> deciding to frag or not frag? It seems to me, in this case, the port
> speed is irrelevant because we can only send at 512k... OK, I could go
> on and on but I'll spare you all :-)
>
> So, obviously I'm wrong and or confused... lord knows it isn't the
> first time and will not be the last but I'd really like to know why my
> logic is flawed. Thus far no one who says I'm confused (including
> Cisco) has been able to explain why.
>
> TIA!
>
> --
> Scott
> CCIE #17040 (R&S)
>
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