Subject: Re: [Tsvwg] Q. about "Limited Transmit" algorithm

From: Mark Allman <[email-masked]>
Date: Tue, 29 Aug 2000 09:42:16 -0400

> In my understanding, transmission of a new segment was already
> permited by RFC2581, though in a small cwnd...

That is not the *intent* of RFC 2581.  There may have been some loss
between the intent and the text, but I think it is fairly clear.

> Isn't it true that the receipt of a DUPACK turn down the amount of
> outstanding data (FlightSize) ??? 

No.  FlightSize is defined in RFC 2581 as:

    FLIGHT SIZE:  The amount of data that has been sent but not yet
    acknowledged.

A duplicate ACK (by definition) does not acknowledge new data and
therefore cannot decrease the FlightSize.

As you mention, duplicate ACKs are used during fast recovery as an
indication that something has left the network.  But, this algorithm
is the exception, not the rule.  In fast recovery we are not limited
by the FlightSize, but rather governed by an artificially infated
cwnd, which is based on duplicate ACKs.

I hope that clarifies things.

allman

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From: Rogerio de Carvalho Andrade <[email-masked]>
Date: Tue, 29 Aug 2000 18:21:20 -0300

Thanks, Allman. Your explanation was absolutely clear.

RFC 2581 (as well as RFC 2582) does not explicitly say it but it
can easily inferred (mostly in the outlined definition of Flight
Size).

I've got confused by that other discussion in the end2end-interest
list, where Andrei Gurtov guessed wrong the Linux 2.3x behavior, at
the transmission of a new segment in response to a partial ACK (or
either a DUPACK). Differently to in your recent draft, we were already
in the Fast Recovery algorithm, that time. In FR, DUPACKs and partial
ACKs can trigger a new segment transmission (if cwnd and rwnd permit).

As I could understand, "Limited Transmit" algorithm, proposed in your
draft, aims to permit a new segment sending BEFORE enter in FR, isn't it?
Specifically, your goal is to make it possible to enter in FR, if I'm not
wrong...

Cheers,
Rogerio.

-- 
Rogerio de Carvalho Andrade
Analista de Suporte - Embrapa - DIN
 mailto:[email-masked]
Mestrando em Ciencia da Computacao - UFPE - DI
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