[ntp:questions] Detecting bufferbloat via ntp?

David Malone dwmalone at maths.tcd.ie
Wed Feb 16 14:43:15 UTC 2011


Danny Mayer <mayer at ntp.org> writes:

>> For traditional TCP (single flow), you need bandwidth*latency as
>> sockbuf at both ends plus the same at the bottleneck router. Some
>> of the new TCP congestion control systems can do with less, and
>> still fill the link if they are the only flow.

>Since NTP only uses UDP the packet handling will be different. I'm not
>sure why you are talking about TCP here.

Oh - I though we'd drited onto the topic of how much buffering was
sensible in a network. The bandwidth*latency rule of thumb, which
Terje mentioned, is basically derived from the amount of buffering
required for a TCP flow to fill a link. I agree this has nothing
to do with ntp, except that NTP packets will often share a buffer
with TCP packets.

>It would be more useful to discuss what happens with UDP flows since
>that is what NTP uses.

For ntp, I suspect the required amount of buffering is (number of
peers)*(largest number of packets sent in burst modes), and probably
less in practice?

	David.




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