RE: [802.3ae] Question on Modal Bandwidth
First a point of clarification. I believe the lowest modal bandwidth at 850
nm is 160 MHz-km, not 140.
The reason that the bandwidth differs between 850 and 1300 nm operation on
62.5 um fibers is that legacy (installed base) 62.5 um fiber (also referred
to as FDDI grade) is optimized for 1300 nm operation, whereas the bandwidth
of legacy 50 um is spread evenly between the two operating windows. There
are two typical grades of minimum overfilled launch bandwidths for legacy
62.5 um specified to support operation at both 850 and 1300 nm: 160/500 and
200/500 MHz-km at 850/1300 nm. Likewise, typical legacy 50 um minimum
overfilled launch bandwidths at 850/1300 nm are 400/400 and 500/500 MHz-km.
All of these grades are reflected in the 10GbE draft.
Fiber systems engineering
> From: Marshall Eisenberg[SMTP:marshall@xxxxxxxxxxxxxx]
> Sent: Wednesday, November 21, 2001 8:10 AM
> To: stds-802-3-hssg@xxxxxxxx
> Subject: [802.3ae] Question on Modal Bandwidth
> In scanning the spec, I found an interesting contradiction.
> The modal bandwidths listed for the 850nm Serial PMD starts at 140 MHz/Km
> (62.5/125 MMF) but the modal bandwidth for the 1310 WWDM (similar fiber)
> starts at 500 MHz/Km. Why such different starting modal bandwidth
> specifications for the same cable type for different PMD specifications?
> Marshall Eisenberg
> Director of Product Marketing
> Foundry Networks Inc.
> 2100 Gold Street
> P.O. Box 649100
> San Jose, CA 95164-9100
> 408.586.1754 direct
> 408.586.1900 fax
> 408.398.0014 cell