[mrtg] Re: Utilization graph uncertainty

[Bill Wichers]

At 05:37 PM 2/11/2004 -0500, Soden, David wrote:
>As I understand it, the T1 provides symmetric communications, meaning
>that any one of the 24 channels in the circuit can be sending or
>receiving, but not both, at any given point in time.  So, if we were
>only using 50% of the T1 to receive data, it is possible for the other
>50% of available bandwidth to be utilized for sending data.  If we are
>using 100% of the bandwidth for sending data there are no pathways left
>for receiving.

T1 is full duplex -- you can be sending *and* receiving on ALL 24 channels 
ALL the time if you want. Most customers don't actually do this however -- 
at least not very often, since end users are typically either downloading a 
big file or uploading a big file but not at the same time. In MRTG you 
would see both the IN and OUT traffic levels at near 100% for such a 
scenario, with the total traffic if you were to sum the IN and OUT being a 
bit less than 3.072 Mb/s since router traffic counters don't seem to 
include low-level packet overhead IMHO. You would set maxbytes to the total 
traffic possible in EITHER direction at any given time though.

Looking at your screenshot, your graph looks correct for a T1 link. Your 
peaks are both under the 192 kB/s maximum for the line.

Remember that T1s were originally designed for voice phone service and it 
is possible to both talk and hear at the same time on a phone :-)

>So with that said, I'm still left uncertain how the combined total was
>over 100%.

The combined total isn't over 100%. You have the full capacity of the T1 
circuit available in both directions at all times since it is a full-duplex 
circuit.

To my knowledge, all digital telecom circuits in current use are full duplex.

         -Bill


*****************************
Waveform Technology
UNIX Systems Administrator

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