[c-nsp] forced up/up on a fiber link

[Phil Mayers]

On 23/10/12 10:20, Damian Holdcroft wrote:
> I remember reading something, somewhere, about the lasers sending pulses
> for link detection. I don't seem to be able to find anything on fibre link
> detection at the moment though. Does anybody know anything about it?

I don't think this happens on normal links. As has been said, SX and LX 
optics do indeed "fire into the air". "Link up" is a different matter; 
this usually is based on light detection and autoneg.

Some high-power equipment has "eye protection". I've never entirely 
figured out how this works, but it cuts off the laser when the fibre 
goes down.

I've also seen some WDM equipment which only engages TX if RX is 
receiving light. That's a pain, because if you forget about it and set 
this at both ends, links will never recover ;o)

>
> It would be interesting to see if the hw-module command actually engaged
> the optics. I wouldn't have thought so. Bit of a bugger you can only
> simulate entire linecards!

"no shut" engages the optics.

>
> I'll be trying the mobile phone camera next opportunity. Thanks!

Handy hint: if you have a phone with both back- and front-facing 
cameras, the back-facing camera may have an infrared filter so can't see 
LX, but the front-facing cameras tend to be cheaper and lack the filter 
(true on my HTC, for example). This can be useful.