Re: [tcpm] I-D Action: draft-ietf-tcpm-cubic-00.txt

["Scheffenegger, Richard" <[e-mail]>]

Hi Michael,

the critique around the "inverse" beta is also something that I found. It should be straightforward to fix the text and formulas in order to use a more standard use of the parameter "beta".

Making this consistent with other TCP documents is valuable IMHO.

Best regards,
  Richard



> -----Original Message-----
> From: tcpm [mailto:[e-mail]] On Behalf Of Michael Welzl
> Sent: Dienstag, 30. Juni 2015 11:54
> To: Zimmermann, Alexander
> Cc: [e-mail] Extensions
> Subject: Re: [tcpm] I-D Action: draft-ietf-tcpm-cubic-00.txt
> 
> Hi,
> 
> A detail:
> 
> the beta factor (for multiplication when there is congestion) is 0.7, not
> 0.8, since Linux kernel 2.6.25 from 2008.
> The draft talks about beta as a (1-beta) multiplication factor - so,
> accordingly, to capture the current implementation state, in section 3.5:
> 
> ***
> When a packet loss occurs, CUBIC reduces its window size by a factor
>    of beta.  Parameter beta SHOULD be set to 0.2.
> ***
> 
> should be:
> 
> ***
> When a packet loss occurs, CUBIC reduces its window size by a factor
>    of beta.  Parameter beta SHOULD be set to 0.3.
> ***
> 
> 
> Side note: personally I find this use of beta confusing - "reduce by ..."
> indicates subtraction to me, and I'm not sure if "reduce by a factor of"
> is easily parsed by everyone as "multiplied by (1- ...)". Just like the
> code, I would therefore rather write:
> 
> ***
> When a packet loss occurs, CUBIC reduces its window size by multiplying it
> with a factor
>    of beta.  The parameter beta SHOULD be set to 0.7.
> ***
> 
> ... and change (1-beta) to beta below. But that's just a matter of
> style/taste I guess.
> 
> Cheers,
> Michael
> 
> 
> 
> > On 19. jun. 2015, at 09.12, Zimmermann, Alexander
> <[e-mail]> wrote:
> >
> > This is just a resubmission of draft-zimmermann-tcpm-cubic-01 as WG
> item.
> > Received feedback will be addressed in upcoming versions
> >
> > Alex
> >
> >> Am 18.06.2015 um 21:24 schrieb [e-mail]:
> >>
> >>
> >> A New Internet-Draft is available from the on-line Internet-Drafts
> directories.
> >> This draft is a work item of the TCP Maintenance and Minor Extensions
> Working Group of the IETF.
> >>
> >>       Title           : CUBIC for Fast Long-Distance Networks
> >>       Authors         : Injong Rhee
> >>                         Lisong Xu
> >>                         Sangtae Ha
> >>                         Alexander Zimmermann
> >>                         Lars Eggert
> >>                         Richard Scheffenegger
> >> 	Filename        : draft-ietf-tcpm-cubic-00.txt
> >> 	Pages           : 14
> >> 	Date            : 2015-06-18
> >>
> >> Abstract:
> >>  CUBIC is an extension to the current TCP standards.  The protocol
> >> differs from the current TCP standards only in the congestion window
> >> adjustment function in the sender side.  In particular, it uses a
> >> cubic function instead of a linear window increase of the current TCP
> >> standards to improve scalability and stability under fast and long
> >> distance networks.  BIC-TCP, a predecessor of CUBIC, has been a
> >> default TCP adopted by Linux since year 2005 and has already been
> >> deployed globally and in use for several years by the Internet
> >> community at large.  CUBIC is using a similar window growth function
> >> as BIC-TCP and is designed to be less aggressive and fairer to TCP in
> >> bandwidth usage than BIC-TCP while maintaining the strengths of BIC-
> >> TCP such as stability, window scalability and RTT fairness.  Through
> >> extensive testing in various Internet scenarios, we believe that
> >> CUBIC is safe for deployment and testing in the global Internet.  The
> >> intent of this document is to provide the protocol specification of
> >> CUBIC for a third party implementation and solicit the community
> >> feedback through experimentation on the performance of CUBIC.
> >>
> >>
> >> The IETF datatracker status page for this draft is:
> >> https://datatracker.ietf.org/doc/draft-ietf-tcpm-cubic/
> >>
> >> There's also a htmlized version available at:
> >> https://tools.ietf.org/html/draft-ietf-tcpm-cubic-00
> >>
> >>
> >> Please note that it may take a couple of minutes from the time of
> >> submission until the htmlized version and diff are available at
> tools.ietf.org.
> >>
> >> Internet-Drafts are also available by anonymous FTP at:
> >> ftp://ftp.ietf.org/internet-drafts/
> >>
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> >
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