[tsvwg] Re: New Version Notification for draft-tahiliani-tsvwg-fq-pie-00.txt

[Sebastian Moeller <[e-mail]>]

Hi Mohit,

Thanks for your response.


> On 15. Mar 2025, at 17:31, Mohit P. Tahiliani <tahiliani=[e-mail]> wrote:
> 
> Hi Sebastian,
> 
> Thanks for the email.
> 
> I have replied inline below:
> 
> On Tue, Mar 11, 2025 at 11:50 PM Sebastian Moeller <moeller0=[e-mail]> wrote:
> Hi Mohit,
> 
> 
> thanks. I like this, short and sweet. I do have a question though (probably easy to answer) abgout the following section:
> 
> Thank you for the feedback and the question.
>  Lastly, if an incoming packet arrives when the total number of enqueued packets has already saturated the queue capacity, FQ-PIE drops the packet without further processing. In contrast, FQ-CoDel identifies the queue with the largest current byte count (i.e., a "fat flow") when the queue capacity is saturated and drops half of the packets from this queue (up to a maximum of 64 packets, as specified in Section 4.1 of [RFC8290]). FQ-PIE does not adopt this approach for the reasons explained below.
> 
> One thing that fq_codel but als DualQ seem to do on overload is take a big shovel instead of a scalpel. So while I have no idea which packets to drop, maybe doing a bit more than "close the queue for new comers" might be in order. Especially since together with ECN there is the potential for an unresponsive flow to fill the queue without feeling the "pain" for doing so? Yes, mischievous adversarial traffic might not be a target to optimize for, but I wonder how the drop only on enqueue can ever be safe with ECN?
> 
> I believe the enhancement outlined in Section 5.1 of RFC 8033 (https://datatracker.ietf.org/doc/html/rfc8033#section-5.1) may address this situation. It states that "if the calculated drop probability exceeds mark_ecnth, PIE reverts to packet-dropping for ECN-capable packets. The variable mark_ecnth SHOULD be set to 0.1 (10%)". Both the Linux and ns-3 implementations of PIE currently follow this approach.

[SM] Thanks that addresses my ECN overload concern. Not a big fan of "action at enqueue" but that is inherited from rfc8033 PIE, so is not something to be held against fq-pie, let alone your draft. 

> 
> Let me know your thoughts.

[SM] I would like to ask the WG to adopt this...

> 
> Thanks and Regards,
> Mohit P. Tahiliani