Re: [Bloat] Detecting bufferbloat from outside a node

[Neil Davies <neil.davies@pnsol.com>]

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Hi Jonathan
On 27 Apr 2015, at 16:25, Jonathan Morton <chromatix99@gmail.com> wrote:

> One thing that might help you here is the TCP Timestamps option. The timestamps thus produced are opaque, but you can observe them and measure the time intervals between their production and echo. You should be able to infer something from that, with care.
> 
> To determine the difference between loaded and unloaded states, you may need to observe for an extended period of time. Eventually you'll observe some sort of bulk flow, even if it's just a software update cycle. It's not quite so certain that you'll observe an idle state, but it is sufficient to observe an instance of the link not being completely saturated, which is likely to occur at least occasionally.
> 
> - Jonathan Morton
We looked at using TCP timestamps early on in our work. The problem is that they don't really help extract the fine-grained information needed. The timestamps can move in very large steps, and the accuracy (and precision) can vary widely from implementation to implementation.

The timestamps are there to try and get a gross (if my memory serves me right ~100ms) approximation to the RTT - not good enough for reasoning about TCP based interactive/"real time" apps

Neil

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