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Re: [802.3BA] Discussion on 40G for => 10 km SMF

Hi Mikael,
Operationally, we have a simplex interface. There is no internal redundancy, no logic that lets you operate in any kind of reduced bandwidth "limping" mode.  There is no per-wavelength replacable unit. An optical failure is no different from an electronics failure. If you lose one laser, you are just as dead as if you have a stuck bit on one of your four virtual lanes (which could happen just as easily if the interface were serial) and you can't frame all of the virtual lanes and put the signal back together. You don't need to even know which of four lasers failed, because the repair action is the same in any case.

The serial technology being proposed does not extend to colored interfaces in the same way we saw at 1G and 10G. In the first place, it is 1310nm and for DWDM you would need 1550nm. At 1550nm, you couldn't get the reach you want for 40G without dispersion compensation (at 1310nm you are at the zero dispersion point in the fiber). The EML and NRZ modulation format are not what you would want at 40G because customers want 50GHz spacing between wavelengths. The technology you would want for a DWDM solution shares very little with what is being proposed for 40GbE serial, and choosing serial would do almost nothing to reduce the cost of that application.

So I don't think these are the aspects that should drive the decision. The issues are cost and time to market, and on that basis, I think the clear choice is 4x10 CWDM.

-----Original Message-----
From: Mikael Abrahamsson [mailto:swmike@xxxxxxxxx] 
Sent: Friday, August 08, 2008 12:03 PM
To: STDS-802-3-HSSG@xxxxxxxxxxxxxxxxx
Subject: Re: [802.3BA] Discussion on 40G for => 10 km SMF

On Fri, 8 Aug 2008, Jesse Simsarian wrote:

> 1. Operationally, 4 x 10G and 40G serial are equivalent.  If anyone is 
> voting for serial because of operational concerns, please bring this 
> out on the reflector.

I have two questions (trying to determine operational impact for me as an

In a 4x10G module, if one laser or receiver breaks, what happens then? 
Will the port shut down the same way it would with a 40G serial?

Also, future adhoc standard for 40G serial CWDM optics (ie someone developing 40G serial CWDM-band colored optics the same way that has happened on 1G and 10GE) speaks in favour of serial instead of 4x10G, or am I mistaken?

Mikael Abrahamsson    email: swmike@xxxxxxxxx