[c-nsp] SFP compatibility

[James Jun]

On Thu, Feb 04, 2016 at 09:53:26AM +0100, Juergen Marenda wrote:
> Most SFP's (esp. Older one for "low" speed) are fixed frequency,
> So they will not get in sync.
> 
> An "GIG" SFP syncs at approx. 1.25 GHz and will not operate at FastEthernet
> Speed.
> 
> OK, there _are_ multi-frequency SFP's, 1G SAN+2GSAN +1GE for example,
> but yoru device will not set the Clock to FastEthernet on the normal Gig-SFP


I think it has more to do with whether the router recognizes EEPROM and considers it valid optic to turn on the interface.

For example, it's perfectly fine to bring up OC-3 with 1000Base-LX SFP, as long as SONET card doesn't care about what's coded on the EEPROM,
and the inserted optics is SFP 1.0 (not SFP+) and has greater than 155 +/- Mbps bit rate to clock out.

James