[c-nsp] Optics warnings - SR /LH Modules SFP+

[Nick Hilliard]

On 21/07/2015 10:22, Nick Cutting wrote:
> There are connected in a 40 Gig port channel, using 10GBase-SR modules
> and 3 metre and 5 metre cables. They have wildly different power values,
> and Te5/1 filling up syslog with THRESHOLD error messages.  It is using
> the same Cable type (OM3 I think) as the other 3 links - does this mean
> the SFP is faulty?

Assuming that each port is connected to the same port on the other chassis,
you have -2.1dBm transmit and -0.7dBm receive.  I.e. the transceivers are
reporting that more light is being received than transmitted.  This means
that either the transmitter on one side or the receiver on the other is
faulty.  You can check this by replacing transceivers and seeing what happens.

This is also happening to a smaller degree on te6/2.

On the other transceivers, you would normally expect the difference between
tx on one side and rx on the other to be roughly the same to within 0.25 dB.

> The second issue is with a link to an upstream ISP that has contacted me
> regarding errors on their side that the RX is also too high on a
> 1000BaseLH module.  Are there minimum distances for these modules as
> they are expected for longer distances?  I am using the same cables on
> this link, it's about 3 metres into the ME3400 as in the SR modules.

Link errors shouldn't be happening on MMF due to high light levels.  More
likely to be a loose coupler or faulty transceiver or something.

> Also - does anyone know why the sh int transceiver command is not
> available for this module?

Because: Cisco.

Retrieving transceiver values on IOS is full of fail.  Sometimes you can
have multiple different commands on the same chassis, depending on what
sort of line cards are installed.

> What kind of cables would you typically use for each of these modules?
> Is this a faulty module - or do I need use different cables i.e.
> different types of OM3. Can anyone point me towards a comprehensive
> Module -> cabling guide ?

If you're going to use multi-mode cabling:

- you will do yourself a favour to throw away any 62.5/125 (OM1) cabling,
including structured cabling.  It's rubbish.

- OM2 is the CAT5 of multimode, i.e. fine for plenty of short haul
applications.  In situations where it's not fine, you should install single
mode instead.

- OM3 is a waste of admin/time/resources.  Use single mode instead.

- all data cross-connects outside a cage/rack should be done over single
mode.  Multimode is just not worth it for this.

Nick