Re: [tcpm] [EXTERNAL] Questions on HyStart++ draft 02

[Junho Choi <[e-mail]>]

Hi Yi,

Thanks. See inline for my following question.

On Wed, Apr 1, 2020 at 5:04 PM Yi Huang <[e-mail]> wrote:

> 1. Section 4.2 -- each round is initialized as
>
>
>
>    lastRoundMinRTT = currentRoundMinRTT
>
>    currentRoundMinRTT = infinity
>
>    rttSampleCount = 0
>
>
>
> In the very beginning of the connection, what is "currentRoundMinRTT" when
>
> there is no previous value?
>
>
>
> I am using current rtt (or initial rtt value) and is it ok?
>
>
>
> [Yi]: In our implementation, lastRoundMinRTT and currentRoundMinRTT are
> initialized to 0xffffffff as sentinel values. We only compare
> lastRoundMinRTT with currentRoundMinRTT when both of them are valid values.
> Using currRTT seems to essentially behave the same as assigning a sentinel
> value.
>

So in the beginning of the connection lastRoundMinRTT is <inf>. When ack is
received currentRoundMinRTT = min_rtt but
lastRoundMinRTT is still <inf>. When the 1st round ends, it looks always
doing nothing because the following if() is always false?

  if (currentRoundMinRTT >= (lastRoundMinRTT + RttThresh))



>
>
> 2. Section 4.2 -- When used with cubic, CA_cwnd() is based on cubic
> algorithm I think.
>
>  This means I need to do cubic variables calculation during slow start
>
>  such as K and W_cubic. When is considered as a start of
>
>  congestion avoidance and what W_max will be?
>
>
>
>  Currently I use a start of limited slow start as a beginning of
> congestion recovery
>
>  and use cwnd at the time for W_max. Is my understanding correct?
>
>
>
> [Yi]: Yes, that’s exactly what we do in Windows.
>

Sound great. Thanks.

Best,

-- 
Junho Choi <junho dot choi at gmail.com>