[Cerowrt-devel] [Bloat] DOCSIS 3+ recommendation?
michawe at ifi.uio.no
Fri Mar 20 16:59:37 EDT 2015
> On 20. mar. 2015, at 17.31, Jonathan Morton <chromatix99 at gmail.com> wrote:
>> On 20 Mar, 2015, at 16:54, Michael Welzl <michawe at ifi.uio.no> wrote:
>> I'd like people to understand that packet loss often also comes with delay - for having to retransmit.
> Or, turning it upside down, it’s always a win to drop packets (in the service of signalling congestion) if the induced delay exceeds the inherent RTT.
Actually, no: as I said, the delay caused by a dropped packet can be more than 1 RTT - even much more under some circumstances. Consider this quote from the intro of https://tools.ietf.org/html/draft-dukkipati-tcpm-tcp-loss-probe-01 :
To get a sense of just how long the RTOs are in relation to
connection RTTs, following is the distribution of RTO/RTT values on
Google Web servers. [percentile, RTO/RTT]: [50th percentile, 4.3];
[75th percentile, 11.3]; [90th percentile, 28.9]; [95th percentile,
53.9]; [99th percentile, 214].
That would be for the unfortunate case where you drop a packet at the end of a burst and you don't have TLP or anything, and only an RTO helps...
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