[Bloat] head drop vs tail drop

Greg White g.white at CableLabs.com
Fri Oct 15 13:09:03 EDT 2021

Be careful with the terminology, since there are two types of head drop:

1) head drop based on sojourn time 
2) head drop based on current queue depth

That paper used type 2. 

In type 1, the drop is based on the queue that existed at the time "this" packet was enqueued (i.e. the packets that arrived *before* this packet), and thus is equivalent* to tail drop.  In type 2,  the drop is based on the queue caused by the packets that arrive *after* this packet.

* modulo the difference in predicted queue delay vs measured queue delay.

Type 2 detects and signals congestion more quickly than tail drop.   Type 1 is the same as tail drop.


On 10/10/21, 12:32 PM, "Bloat on behalf of Dave Taht" <bloat-bounces at lists.bufferbloat.net on behalf of dave.taht at gmail.com> wrote:

    We've never really characterized the differences between head and tail
    drop. A good tidbit went
    by here, where in one experiment 15 v 22 drops were observed.


    Last paper I'm forwarding for the day!

    Fixing Starlink's Latencies: https://www.youtube.com/watch?v=c9gLo6Xrwgw

    Dave Täht CEO, TekLibre, LLC
    Bloat mailing list
    Bloat at lists.bufferbloat.net

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