[mrtg] Re: Bandwidth Calculation

[Dana Hudes]

I don't see why you would want to sum ifInOctets and ifOutOctets together.
It doesn't tell you anything really useful. A serial port running a synchronous circuit
has two symmetric half-duplex channels. You can't use bandwidth from one for the other on the
telco side (yes, we all know about Asymmetric DSL but there again its fixed bandwidth per channel).

Fundamentally the synchronous serial port just has receive and transmit pins (along with misc. control pins)
and under normal circumstance clock comes from your CSU/DSU the port is slaved to it and bits come whenever
(based on the clock, its a synchronous circuit).

When you purchase bandwidth from the telco, you get a pair of channels each of which has that bandwidth.
For example if you purchase 896Kbit/sec on an E1, 14 TDM channels for receive and a separate 14 TDM channels for transmit are both provisioned, as a pair.

If you would like to see % utilization of the bandwidth on your port, 
(ifInOctets*8)/ifSpeed *100
(ifOutOctets*8)/ifSpeed *100
are the two things to put on your MRTG graph.
This assumes you have set ifSpeed to a sensible value in bits/second.
Since you have to configure it, you are perfectly welcome to set it in octets/second and save multiplying by 8 all the time.

----- Original Message ----- 
From: "Eric Lim Choon Keat - CSSG" <limck at csam.com.my>
To: <mrtg at list.ee.ethz.ch>
Sent: Tuesday, March 26, 2002 5:32 AM
Subject: [mrtg] Bandwidth Calculation


> 
> 
> Dear MRTG user,
> 
> i have been using the MRTG for quite some time
> some question are currently confusing myself
> 
> i understand that if we would like to get the bandwidth of the serial port
> we need to put in the cfg file as
> ((ifinoctec + ifoutoctec)*8 / ifspeed)  x 100 %
> correct me if i'm wrong
> 
> with this formula, is it mean that
> the leased line is only providing half duplex circuit ?
> if it is full duplex, the formula would be 2 x ifspeed ?
> 
> under what condition should we make use of ifhcoctec ?
> 
> 
> 
> THANKS & REGARDS
> ==============================================
> Eric Lim 
> 
> 
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