RE: [EFM] EFM OAM on Preamble
Hi Ed,
At 03:44 PM 11/21/2001 -0800, Ed Boyd wrote:
>Hiroshi,
>
>How do you guarantee that the value embedded in the preamble do not
>contain the SFD pattern and cause a false lock?
-RS with OAM handler actually overwrites SFD with CRC at TX side.
At RX side, RS-OAM only looks at SOP pattern to find a frame.
When passing frames to MAC, RS converts OAM preamble back to normal
preamble with SFD.
Therefore SFD pattern in OAM preamble is acceptable.
>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.
-802.3 Repeater is defined only for the half-duplex mode. so not applicable
for preamble OAM.
( But If 802.3 had defined full-duplex repeater ( 1port to 1port )
we would have suggested this new device to support OAM
in the same way as SONET re-generator : Ethernet re-generator...)
Hope it makes sense to you.
Happy Thanks-giving !!
Hiroshi
>Thanks,
>Ed...
>
>-----Original Message-----
>From: Hiroshi Suzuki [<mailto:hsuzuki@xxxxxxxxx>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
>transparency.
>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
>case.
> 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.
>
>Thanks!
>
>Hiroshi
>
>At 09:48 AM 11/20/2001 -0500, Ben Brown wrote:
>
> >Hiroshi,
> >
> >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
> >response:
> >
> >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.
> >
> >Thanks,
> >Ben Brown
> >
> >--
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