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RE: [EFM] EFM OAM on Preamble

Title: RE: [EFM] EFM OAM on Preamble


How do you guarantee that the value embedded in the preamble do not contain the SFD pattern and cause a false lock?

Repeaters normally regenerate the preamble and SFD so it would not pass through a new value.  I agree that this will only work for full duplex.


-----Original Message-----
From: Hiroshi Suzuki [mailto:hsuzuki@xxxxxxxxx]
Sent: Wednesday, November 21, 2001 10:41 AM
To: Ben Brown
Cc: 802.3ah
Subject: Re: [EFM] EFM OAM on Preamble

Hi Ben,

Thank you for the question.

Indeed, during my presentation, there was a discussion on Preamble
In the current PCS/RS/GMII clauses of existing 802.3  spec clearly describes
PHY may shrink preamble to only SFD and RS has to accept a frame with any
shrinked preamble.

For these comments, I made it clear that

- OAM on Preamble is applied to Full duplex mode only. Not for half-duplex
/ CSMA-CD mode.
Preamble shrinkage to "any" size  happens only for CSMA-CD mode.
And EFM environments and SP provider circumstances, any half duplex mode
does not make sense
due to distance limitation.  So this assumption is valid, I hope.
Only thing to modify the spec is that we state something like in RS/GMII
clause ( where  OAM handler  locates )
  "Preamble not be shrinked by PHY  in full duplex mode, when OAM is used"

-EFM Cupper P2P, EPON will have PCS change as well as PMD, so we can make
sure preamble transparency in the new spec.

-For P2P GE, there is the following issue, as you anticipate.
( this was not discussed during presentation but
discussed  off-line  during the meeting)
  Since Idle detection is done by every 16bits,  Aligned / Unalined frame
may lose the first byte of Preamble, where
   the second byte  be replaced with /S/.
  We have 2 options for this.
  a) Not to use this byte. This means we  have only 6byte preamble (
including SFD byte.) to carry OAM.
      Since we have 2 reserved byte, still OK with it. This actually was
discussed  off-line last week.
  b) PCS recovers /S/+7byte preamble ( including SFD byte ), when Unaligned
      This is simply done by having additional 3-4 byte FIFO in PCS.
  We will discuss about these options  in detail in Jan meeting.
  Note this  occurs only in GE. Not in 100baseX, 10GE.

-For 802.3ae 10GE, it is clearly stated in the spec, no preamble shrinkage.
  If preamble is shrinked, MAC can discard whole frames.

Hope this helps.



At 09:48 AM 11/20/2001 -0500, Ben Brown wrote:

>I did not attend your presentation entitled "EFM OAM on Preamble"
>but I've seen a copy of your slides. I wonder if this question
>was asked during the presentation and would like to hear your
>How is this protocol handled when preamble bytes are lost?
>Specifically in the case of 1GE when the first byte of
>preamble is discarded around 50% of the time.
>Ben Brown
>Benjamin Brown
>2 Commerce Park West
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