> On 5 Jun, 2018, at 9:34 pm, Sebastian Moeller <[email protected]> wrote:
> 
> The rationale for that decision still is valid, at low bandwidth every 
> opportunity to send a packet matters…

Yes, which is why the DRR++ algorithm is used to carefully choose which flow to 
send a packet from.

> …and every packet being transferred will increase the queued packets delay by 
> its serialization delay.

This is trivially true, but has no effect whatsoever on inter-flow induced 
latency, only intra-flow delay, which is already managed adequately well by an 
ECN-aware sender.

May I remind you that Cake never drops the last packet in a flow subqueue due 
to AQM action, but may still apply an ECN mark to it.  That's because dropping 
a tail packet carries a risk of incurring an RTO before retransmission occurs, 
rather than "only" an RTT delay.  Both RTO and RTT are always greater than the 
serialisation delay of a single packet.

Which is why ECN remains valuable even on very low-bandwidth links.

 - Jonathan Morton

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