Hi,
I'm not sure how to calculate it for 4 seconds, but
all the documentation and examples I've seen explain
Bc (Commited burst) as bc = 1/8 / line access rate,
where 1/8 is the time period for a one second period
which is a common time period from my understanding.
Example:
line access rate: 64k
CIR Contracted: 32k
bc (1/8 / line access rate) = 8000
be (excess burst) = 0 (recommended)
According to what I read, there are 8 intervals
(transmission periods) in this one second period.
Interval 1: bc + be (be is only sent on 1st interval)
Interval 2-8: bc only
So, using a bc of 8000 and be of 0, 8000 * 8 = 64000
which is the line speed.
If you make bc 4000 and be 32000 then you will be
sending 32000 commited burst and 32000 excess on first
interval of cycle, for total of 64000.
In cisco terms (Frame Relay traffic shaping)
cir = line access rate
mincir = contracted CIR with provider
bc = commited burst
be = excess burst
I hope this helps and is accurate.
--- Fred Danson <[EMAIL PROTECTED]> wrote:
> Hey guys, I just got a quick question about Frame
> Relay.
>
> I've been reading the BCRAN book published by
> Sybex, and I'm finding
> the frame relay chapter a bit confusing. A few
> paragraphs from the Sybex
> book state the following:
> "Committed burst size and excess burst size are
> the two types of burst
> sizes. Each of these sizes is measured over a
> specific time interval called
> the committed rate measurement interval. Committed
> burst size is the maximum
> amount of data that the network can guarantee will
> be delivered during the
> committed time interval. The excess burst size is
> the amount of traffic
> which the user may exceed the committed burst size.
> For example, take a user who buys a Frame Relay
> circuit with the
> following characteristics: 1544Kbs access rate, 256K
> CIR, 4 second committed
> time interval.
> The user is guaranteed a CIR of 256Kbps over a
> four-second period. The
> user could transmit 256Kbps for four seconds, and
> the network would ensure
> delivery. The user could alternately send 1024Kbps
> for one second,
> representing the committed burst. However for the
> remaining three seconds,
> there would be no guarantee of delivery for the
> excess burst traffic."
>
> When the author says "The user could
> alternately send 1024Kbps for one
> second, representing the committed burst.", is he
> defining the committed
> burst as any speed above the CIR that does not
> exceed the total amount of
> information (256Kbps * 4 second interval = 1024K,
> total info) allowed to be
> sent during the time interval ? I always thought of
> the committed burst rate
> as a rate of information agreed upon with the Telco.
> For example, I thought
> you could get a CIR of 256Kbps and a burst up to
> 512Kbps, or a CIR of
> 256Kbps with a burst up to 1.544 Mbps.
> Could anyone do me the favor of defining
> committed burst rate and
> excess burst rate, and while you're at it
> differentiate between the two? :)
>
> Thanks,
> Fred Danson
>
>
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