Re: [Bloat] Detecting bufferbloat from outside a node

[David Lang <david@lang.hm>]

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On Mon, 4 May 2015, Neil Davies wrote:

> Jonathan
>
> We see the problem as the difference between averages and instantaneous.
>
> Network media is never “average” used - it is either “in-use” or “idle” - what 
> we were seeing (and it was not an ISP but the core of a public service network 
> here in the UK) was that delay can be “high” even when the loading is “low” 
> (in the particular 5minute period the actual offered traffic was <0.01% of the 
> capacity) - it was that the path under examination happened to be the 
> constraining factor for a bulk transfer - the induced delay was high enough to 
> place at risk other real-time applications (as defined by the public service 
> network’s users).

If you are doing a single bulk data transfer through a link and are at a small 
percentage of the capacity but yet experiencing long delays, then something is 
wrong.

either you have a small window size so that you aren't actually using the full 
capacity of the link, you are in the ramp-up time, or you have something 
dropping packets preventing you from getting up to full speed. But all of this 
should be affecting the sending machine and the speed that it is generating 
packets.

the device should not be buffering anything noticable if it's at such a small 
percentage of utilization. check to see if there is QoS configuration on the 
system that may be slowing down this traffic (and therefor causing it to queue 
up)

David Lang