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Re: more on : IEEE 802.3 Requirements

Hi Lisa,

You may be shorting yourself a bit. Aside from effects such as DMD,
which can drastically reduce maximum link distance, and very poor laser
launch into MMF, a 500 MHz*km fiber should be able to support distances

a) 500 MHz*km/1.5625 MHz = 320 m @ 3.125 GBaud 8B/10B encoded
b) 500 MHz*km/1.25 Mhz = 400 m @ 2.5 GBaud unencoded/scrambled

Note that Baud/2 = max carrier frequency for On-Off-Keying/PAM2

These are conservative estimates since the bandwidth-distance product of
a fiber is generally a conservative estimate of the performance of a

Is there any other effect of mixing more than one wavelength that
reduces the maximum effective link distance your 300 m figure, or am I
just reading too much into your conservative estimate.


Buckman, Lisa wrote:
> Mike,
> Sorry for the confusion.  The WWDM approach that I was referring to is the
> 1310 nm version discussed at the last GbE meeting by Hewlett-Packard Labs.
> At 1300 nm, the MMF will have a bandwidth-distance of 500MHz*km.  The GbE
> spec supports distances of 550 m at 1.25 Gb/s.  I believe the fiber was
> shown to support slightly longer distances, but that 550 m was chosen for
> the standard.  At 2.5 Gb/s per channel, we should be able to reach about
> 300m (approx.).  The actual link length will depend on the encoding scheme
> chosen and the link budget.
> Lisa


Best Regards,

Richard Taborek Sr.    Tel: 650 210 8800 x101 or 408 370 9233       
Principal Architect         Fax: 650 940 1898 or 408 374 3645
Transcendata, Inc.           Email: rtaborek@xxxxxxxxxxxxxxxx 
1029 Corporation Way     
Palo Alto, CA 94303-4305    Alt email: rtaborek@xxxxxxxxxxxxx