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SFP high power alarm

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marcuk at me

Aug 21, 2012, 3:13 AM

Post #1 of 11 (2140 views)
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SFP high power alarm

10 GIG cisco compatible SFP in a 3750-X switch.
we started to see this error message after a fibre break and repair:

%SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm;
Operating value: 0.6 dBm, Threshold value: 0.0 dBm

Cant see how the TX power can go high? any ideas? Interface is up and
working ok.

--
Marc

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z at amused

Aug 21, 2012, 3:37 AM

Post #2 of 11 (2114 views)
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Re: SFP high power alarm [In reply to]

Marc,

Perhaps it was right on the limit of max receive threshold and they
repaired a splice that was dodgy to start with increasing the signal.

Patrick

Tue, Aug 21, 2012 at 11:13:48AM +0100, marc williams wrote:

> 10 GIG cisco compatible SFP in a 3750-X switch.
> we started to see this error message after a fibre break and repair:
>
> %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm;
> Operating value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Cant see how the TX power can go high? any ideas? Interface is up and
> working ok.
>
> --
> Marc
>
> _______________________________________________
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p.mayers at imperial

Aug 21, 2012, 3:40 AM

Post #3 of 11 (2117 views)
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Re: SFP high power alarm [In reply to]

On 21/08/12 11:13, marc williams wrote:
> 10 GIG cisco compatible SFP in a 3750-X switch.
> we started to see this error message after a fibre break and repair:
>
> %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm; Operating
> value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Cant see how the TX power can go high? any ideas? Interface is up and
> working ok.

Lasers vary, between units and over time. And laser power sensors have
limited precision.

What type of SFP is it?
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john at citylinkfiber

Aug 21, 2012, 5:26 AM

Post #4 of 11 (2119 views)
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Re: SFP high power alarm [In reply to]

Put a real optical power meter on the fibers and adjust with pads as
needed to get your levels within specs.

On 8/21/12 4:37 AM, "Patrick Cole" <z [at] amused> wrote:

>Marc,
>
>Perhaps it was right on the limit of max receive threshold and they
>repaired a splice that was dodgy to start with increasing the signal.
>
>Patrick
>
>
>Tue, Aug 21, 2012 at 11:13:48AM +0100, marc williams wrote:
>
>
>> 10 GIG cisco compatible SFP in a 3750-X switch.
>> we started to see this error message after a fibre break and repair:
>>
>> %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm;
>> Operating value: 0.6 dBm, Threshold value: 0.0 dBm
>>
>> Cant see how the TX power can go high? any ideas? Interface is up and
>> working ok.
>>
>> --
>> Marc
>>
>> _______________________________________________
>> cisco-nsp mailing list cisco-nsp [at] puck
>> https://puck.nether.net/mailman/listinfo/cisco-nsp
>> archive at http://puck.nether.net/pipermail/cisco-nsp/
>>
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wayne at tuckerlabs

Aug 21, 2012, 6:13 AM

Post #5 of 11 (2115 views)
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Re: SFP high power alarm [In reply to]

On Tue, Aug 21, 2012 at 3:13 AM, marc williams <marcuk [at] me> wrote:
> 10 GIG cisco compatible SFP in a 3750-X switch.
> we started to see this error message after a fibre break and repair:
>
> %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm; Operating
> value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Cant see how the TX power can go high? any ideas? Interface is up and
> working ok.

Too much signal can cause receiver saturation, which in turn leads to
errors on the interface. If you aren't seeing errors then you're
probably OK, but I always prefer to attenuate the signal so the errors
go away.

You can buy attenuators in various sizes, or you can fashion a
temporary one by wrapping the receive fiber around a pencil (the small
radius attenuates the signal).

Is this a long haul optic (10GBASE-ER, ZR, etc.)?

:w
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peter at rathlev

Aug 21, 2012, 7:47 AM

Post #6 of 11 (2111 views)
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Re: SFP high power alarm [In reply to]

On Tue, 2012-08-21 at 06:13 -0700, Wayne Tucker wrote:
> On Tue, Aug 21, 2012 at 3:13 AM, marc williams <marcuk [at] me> wrote:
> > %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm; Operating
> > value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Too much signal can cause receiver saturation, which in turn leads to
> errors on the interface. If you aren't seeing errors then you're
> probably OK, but I always prefer to attenuate the signal so the errors
> go away.

Maybe I misunderstand the DOM parameter, but would attenuation have an
influence on what the TX power is according to the transceiver itself?

To me it sounds like a faulty transceiver, though an optical power meter
could qualify that a bit.

Not really related but we have previously had a few transceivers logging
"Voltage low alarm; Operating value: 0.00V". We ignore these since they
work fine and since 0.00V sounds more like a measuring bug than actual
low voltage.

--
Peter

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gert at greenie

Aug 21, 2012, 9:05 AM

Post #7 of 11 (2113 views)
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Re: SFP high power alarm [In reply to]

Hi,

On Tue, Aug 21, 2012 at 12:26:50PM +0000, John Brown wrote:
> Put a real optical power meter on the fibers and adjust with pads as
> needed to get your levels within specs.

That's *RX* power. Not TX power. TX power is something that is measured
inside the SFP - an the question "how can TX power go high" is a valid
one.

gert
--
USENET is *not* the non-clickable part of WWW!
//www.muc.de/~gert/
Gert Doering - Munich, Germany gert [at] greenie
fax: +49-89-35655025 gert [at] net

cnsp at marenda

Aug 21, 2012, 9:10 AM

Post #8 of 11 (2113 views)
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Re: SFP high power alarm [In reply to]

On Tue, Aug 21, 2012 at 06:05:32PM +0200, Gert Doering wrote:
> Hi,
>
> On Tue, Aug 21, 2012 at 12:26:50PM +0000, John Brown wrote:
> > Put a real optical power meter on the fibers and adjust with pads as
> > needed to get your levels within specs.
>
> That's *RX* power. Not TX power. TX power is something that is measured
> inside the SFP - an the question "how can TX power go high" is a valid
> one.

From an X2-Datasheet:

VII. DOM Parameters

Values Parameter min. max. Unit

Transponder Temperature Monitor Accuracy 1) -5 +5 �C
Laser Bias Current Monitor Accuracy 2) -10 +10 %
Transmit Power Monitor Accuracy 3) -3 +3 dB
Receive Power Monitor Accuracy 3) -3 +3 dB

1) 0 to 70�C case temperature.
2) 0 to 12.5 mA.
3) -8.2 dBm to +0.5 dBm

... so that may be just a measurement error.

An other SFP+ shows +-2dB TX or RX Power Monitor Accurancy,
and +-10% TX BIAS Accurancy.

Did not find an explanation of how optical modules
determine optical output power, some kind of
handshake with the remote side , increasing output power
so that the remote side _sees_ sufficient light?

But *cleaning* the fibers and plugs is a very good idea(TM),
with (too much) power the reciever gets blind;
somtimes the dirt beetween fiber-fiber ore fiber-optics
get grilled/emailed onto the glas.

--
Juergen

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wayne at tuckerlabs

Aug 21, 2012, 9:14 AM

Post #9 of 11 (2112 views)
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Re: SFP high power alarm [In reply to]

On Tue, Aug 21, 2012 at 7:47 AM, Peter Rathlev <peter [at] rathlev> wrote:
> On Tue, 2012-08-21 at 06:13 -0700, Wayne Tucker wrote:
>> On Tue, Aug 21, 2012 at 3:13 AM, marc williams <marcuk [at] me> wrote:
>> > %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm; Operating
>> > value: 0.6 dBm, Threshold value: 0.0 dBm
>>
>> Too much signal can cause receiver saturation, which in turn leads to
>> errors on the interface. If you aren't seeing errors then you're
>> probably OK, but I always prefer to attenuate the signal so the errors
>> go away.
>
> Maybe I misunderstand the DOM parameter, but would attenuation have an
> influence on what the TX power is according to the transceiver itself?

Good point - I missed that detail.

> To me it sounds like a faulty transceiver, though an optical power meter
> could qualify that a bit.
>
> Not really related but we have previously had a few transceivers logging
> "Voltage low alarm; Operating value: 0.00V". We ignore these since they
> work fine and since 0.00V sounds more like a measuring bug than actual
> low voltage.

The OP mentioned that it's "Cisco compatible" - maybe it's not 100%
compatible or was programmed for a different type of device (I've seen
quirks when SFPs get mixed up, though they're usually more extreme).

:w
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andrew.koch at gawul

Aug 21, 2012, 10:12 AM

Post #10 of 11 (2113 views)
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Re: SFP high power alarm [In reply to]

On Tue, Aug 21, 2012 at 5:13 AM, marc williams <marcuk [at] me> wrote:
> 10 GIG cisco compatible SFP in a 3750-X switch.
> we started to see this error message after a fibre break and repair:
>
> %SFF8472-5-THRESHOLD_VIOLATION: Te4/1/2: Tx power high alarm; Operating
> value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Cant see how the TX power can go high? any ideas? Interface is up and
> working ok.

The transceiver may be reporting reflected signal. Any splice will
have some reflection, a poor splice may cause high reflected power
back into the transmitter and potentially cause damage.

This is also true for connectors - they will cause reflection of the
signal. This is why APC (angle polished connectors) are used in
high-power environments.

You will want to check your fibers for reflection. An OTDR read-out
from before and after the splice event would be optimal.

HTH,
Andy
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steve.wilcox at ixreach

Aug 21, 2012, 12:54 PM

Post #11 of 11 (2108 views)
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Re: SFP high power alarm [In reply to]

Hi Marc,
as Gert says they vary over time so this has occurred because either its
putting out more power or the sensor has it wrong. You should test it with
a light meter. It may go faulty, this could be a sign its on its way out.

So, its probably not going to do any damage to a receiving optic, max rx on
an LR SR1 type is 0.5 and you're going to lose something in any cabling
(you might want to check the specs on the actual optics you have tho in
case this is different).

The alarm on the tx tho means the optic is working outside its design spec.
There's a good chance its pulling more power from the switch and thats its
hotter than it should be. Probably not an issue, but you wouldnt want an
entire chassis full of hot optics either..

My advice would be to replace it, hardware alarms do not bode well for the
device's future.

Steve

On 21 August 2012 11:13, marc williams <marcuk [at] me> wrote:

> 10 GIG cisco compatible SFP in a 3750-X switch.
> we started to see this error message after a fibre break and repair:
>
> %SFF8472-5-THRESHOLD_**VIOLATION: Te4/1/2: Tx power high alarm; Operating
> value: 0.6 dBm, Threshold value: 0.0 dBm
>
> Cant see how the TX power can go high? any ideas? Interface is up and
> working ok.
>
> --
> Marc
>
> ______________________________**_________________
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>
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