# [Cake] A few puzzling Cake results

Luca Muscariello luca.muscariello at gmail.com
Tue Apr 17 09:47:40 EDT 2018

```It is more complex than that. The general formula is the max-min fair-rate.
The formula Toke has provided works only if you have one single sparse flow
s and all the others are bottlenecked at this link.
I.e. the experiment he has reported.

If you have N_s sparse flows and each consumers  R_s,i  and N_b
bottlenecked flows the max-min fair-rate is
(R - sum_i R_s,i) / N_b

The simplest way to compute max-min fair-rates is using the water filling
procedure (starting for low rate upwards) which
sets the threshold to determine if a given flow is in N_s or N_b.

BTW, this is well known literature. Search max-min rates calculations.

On Tue, Apr 17, 2018 at 2:22 PM, Toke Høiland-Jørgensen <toke at toke.dk>
wrote:

> Y via Cake <cake at lists.bufferbloat.net> writes:
>
> > From: Y <intruder_tkyf at yahoo.fr>
> > Subject: Re: [Cake] A few puzzling Cake results
> > To: cake at lists.bufferbloat.net
> > Date: Tue, 17 Apr 2018 21:05:12 +0900
> >
> > Hi.
> >
> > Any certain fomula of fq_codel flow number?
>
> Well, given N active bulk flows with packet size L, and assuming the
> quantum Q=L (which is the default for FQ-CoDel at full-size 1500-byte
> packets), the maximum rate for a sparse flow, R_s, is bounded by
>
> R_s < R / ((L/L_s)(N+1))
>
> Where R is the link rate and L_s is the packet size of the sparse flow.
> This assumes that the sparse flow has constant spacing between its
> packets, which is often the case for a VoIP flow...
>
> -Toke
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