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

[Aaron]

On Tue, Oct 23, 2012 at 6:59 AM, Phil Mayers <p.mayers at imperial.ac.uk> wrote:
> 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.

The ones that I have seen have a sensor that can tell if the fiber is
plugged in, if there is no fiber in the TX, it shuts off the laser.

>
> 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.
>
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