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Re: [802.3BA] Longer OM3 Reach Objective

Ryan and Others

The standard should not dictate or force an specific implementation in 802.3ba.  Any module which has a gearbox does inherently retiming.
Assuming the MAC ASIC electrical interface has minimum functionally i.e. nxXFI "XLAUI/CAUI it can directly interface to any module with gearbox which
retimes the data without any PMA-PMA device.  But, if the PMD is based on nx10G then you may need retimer and/or equalizer to drive these PMDs. 
If the MAC SerDes has better jitter performance and/or equalizer it may be able to drive all PMDs without any external retimer or PMA-PMA. 

For smaller module form factors like QSFP or CSFP if there is a retiming and/or equalizer it is expected to be external.  Again the PMA-PMA
interface is optional and should not be forced to be in the module unless there is a mux/de-mux in the module, this allow overtime elimination
of this function when the MAC ASIC SerDes performance improves.

The question of limiting and linear PMD is separate from the having an XLAUI/CAUI, having the optional PMA to PMA each PMD
electrical decision can be made standalone without impacting all the pieces of the puzzle.


Ryan Latchman wrote:

Hi Everyone,


I apologize for the late input on this thread, but I feel it is important to highlight that linear and limiting are not the only options here.  A retimed interface has already proven its ability to meet multiple distance objectives (including 300m over OM3), along with having numerous other benefits including having the highest margin of all three interfaces as shown in latchman_01_0108.pdf.


I think that we should avoid dictating specific implementations, and strive for architectural flexibility when writing this standard.  The 10GbE standard did a reasonably good job at this since numerous architectures have evolved over time while maintaining overall standards compliance.  It is however important to establish overall market needs to ensure that the standard appropriately satisfies them.


Best Regards,



From: Ali Ghiasi []
Sent: March 25, 2008 7:09 PM
Subject: Re: [802.3BA] Longer OM3 Reach Objective



I suggest you compare the PHY price premium for linear and limiting SFP+.
No one is proposing LRM like linear interface, we have proposed SLI "simple
linear interface".  Every 8 Gig FC port which supports copper cables will have
a 3 tap DFE, since most SerDes must have at least 1 tap DFE to compensate for
8" of FR4 after the limited receiver going to a 3 tap DFE has not been a burden.

I agree low cost is archived by using a known low cost technology, but lowest cost is
achieved only if your are open minded and you explore the possibilities not limit yourself
to the 20 years interface concept.  1000Base-T is a clear vivid example how complex
DSP was successfully applied to solve a very complex problem, currently at equal power
to the optics but with significantly lower cost than optics.


Jonathan King wrote:

Sure, adding dollars and watts to the link can buy margin, but highest margin does not equate to lowest cost or best suitability for high volume adoption, (otherwise wouldn't we be using trans-oceanic terminal equipment for SR apps. ?)

lowest cost is achieved by choosing known low cost technologies to meet 90+% of the application market and ensuring any application spec doesn't try to squeeze the technology to its limits.



Jonathan King

Finisar Corp

1389 Moffet Park Drive

Sunnyvale, CA 94089


ph: 1 408 400 1057

cell: 1 408 368 3071


cube C127


-----Original Message-----
From: Brad Booth [mailto:bbooth@AMCC.COM]
Sent: Tuesday, March 25, 2008 7:28 AM
Subject: Re: [802.3BA] Longer OM3 Reach Objective


That's definitely one way it can be interpreted.  There is some apples and oranges comparison going on there, and I'm not sure how the VG got added to the 802.3 mix. ;-)


But with optics, I would agree that the tougher choices haven't always been made, even when the writing was on the wall.  The biggest complaint with 10GbE was all the possible port types (thank you WAN interface sublayer).  The 10GBASE-SR PHY is doing well in the market though, and that's partially due to the fact that it is the only 850nm wavelength PHY for that space.  Interestingly enough though, implementations can be achieved with either linear or limiting components.  And, if you put a linear at one end and a limiting at the other, they will communicate. 


That's what I do like about Ali's proposal.  He has shown that it is possible to do 300m of MMF with an linear approach.  That indicates to the task force there is more margin in a linear approach than in a limiting approach; therefore, having more margin to play with, the linear approach with a 100m MMF reach should be able to become the lowest cost solution for the largest volume of the MMF market.  That's a huge benefit.  Rather than trying to pushing the limits and slowing the adoption curve, there is an implementation option which should make 100G MMF up to 100m a fiscally viable option.





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fn:Ali Ghiasi
adr;dom:;;3151 Zanker Road;San Jose;CA;95014
title:Chief Architect