Re: [bmwg] RFC 2889, Appendix A

["Timmons C. Player" <timmons at monkeyplayground.net>]

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Jerry Perser wrote:
> Comments inline:
> 
>> * The formulas are incomplete.  The TXTIME formulas has no numerator.
>> (I'm guessing this is a known bug)
> 
> Your right.  Somehow a line got deleted and no one noticed. The formula
> should read:
> 
>             [ BURST * (IFG + 64 + 8*LENGTH) ] - IFG
>   TXTIME = ------------------------------------------
>                             SPEED
> 
>> * The included example doesn't agree with the IBG formula
> 

In addition to adding the formula above to the Errata Al mentioned, I'd
like to suggest making the following change as well.  In stead of reading:

   Example:

     LENGTH   = 64  bytes per frame
     LOAD     = 100 % offered load
     BURST    = 24  frames per burst
     SPEED    = 10  Mbits/sec (Ethernet)
     DURATION = 10  seconds test


    IBG       = 1612.8 uS
      TXTIME    = 1603.2 uS
    #OFBURSTS = 3110

I think it should read:

   Example:

     LENGTH   = 64  bytes per frame
     LOAD     = 50 % offered load
     BURST    = 24  frames per burst
     SPEED    = 10  Mbits/sec (Ethernet)
     DURATION = 10  seconds test


    IBG       = 1622.4 uS
    TXTIME    = 1603.2 uS
    #OFBURSTS = 3101



>> Anyway this leads me to the question:  What is the IBG supposed to be?
>>
>> Does the IBG contain the IFG + extra?  Or is the IBG seperate from the
>> IFG?
>>
>> Put another way:  At 100% load is my IBG supposed to equal the IFG? (RFC
>> formula)
>> or does it equal 0? (RFC example)
> 
> RFC 2285, section 3.4.3 does not specify.  
> 
Hmm...  Well, I guess it doesn't really matter so long as the formula
for IBG and TXTIME are consistent.  In any case, the corrected TXTIME
formula and existing IBG formula make it clear that the IBG contains the
IFG since at 100% load, the IBG equals the IFG.

> Try not to use acronyms like PPM.  I was chastised on this reflector several
> years ago by a brilliant programmer for using it.  It made no sense to her
> why I was using Packets Per Minute.  Notice that RFC 2889 no longer uses
> that acronym.
> 
Noted.  Explaining your TLAs (Three Letter Acronyms) is always a good
idea. :)
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