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Community Member

what is neg 30" error on fibre optic

Hi all,

at our office location we have telco tec came and he tested the fibre from demarc to our device and reported this

error  neg 30" error, he told us to check our equipment.

my question is what is neg 30" error,.He told us it is extremely low loss.

when we do the ping from our device across the teclo circuit we see packet loss.

thanks

mahesh

2 ACCEPTED SOLUTIONS

Accepted Solutions

Re: what is neg 30" error on fibre optic

You have not provided us any information regarding the network or equipment you are using or where this neg 30 error is being reported.

My guess is the technician tested the level of light at your equipment and measured -30dBmv.  Most optical transceivers, GBICs/SFPs, have a minimum optical input level of between -17 and -29dBmv, depending on the type (SX, LX, ZX, WDM).  So, -30dB receive level would cause errors on your link.

Check the routing of the fiber to see if there are any tight bends or kinks.  Also, make sure the connectors are clean.

Let us know what you find.

Tom

Cisco Employee

Re: what is neg 30" error on fibre optic

It sounds like you may have an issue with excessive span loss.  If this was previously working fine and has degraded the

issue may be due to dirty or damaged fiber.

Your best bet is to get a light meter and start at the far end and check your power levels.  If you know your launch/TX power on the far end, you can calculate your span loss at your near end receiver and compare it to what the actual span loss should be.

Does the problem occur in the opposite direction or is the issue only affecting one direction.

Once you know what type of GBIC or SFP you are using on the far end you can determine what power level it should be launching at and compare that to a light meter reading.

One more thing to try is to roll the fibers on each end so that your TX->RX is swapped on both ends.  If the problem goes to the other side then you definately have a fiber issue.  If after rolling the fiber on both ends the problem remains, the issue is most likely going to be a bad GBIC or SFP, most likely being that far end one since you are receiving a low power on this near end.

Aaron Reed

Carrier Escalation - Cisco Optical TAC

7 REPLIES

Re: what is neg 30" error on fibre optic

You have not provided us any information regarding the network or equipment you are using or where this neg 30 error is being reported.

My guess is the technician tested the level of light at your equipment and measured -30dBmv.  Most optical transceivers, GBICs/SFPs, have a minimum optical input level of between -17 and -29dBmv, depending on the type (SX, LX, ZX, WDM).  So, -30dB receive level would cause errors on your link.

Check the routing of the fiber to see if there are any tight bends or kinks.  Also, make sure the connectors are clean.

Let us know what you find.

Tom

Community Member

Re: what is neg 30" error on fibre optic

Hi,

Thanks for reply .

Here is GBIC type  1000-LX/LH
Module is 1000BaseX Ethernet        WS-X6516A-GBIC .

We checked the fibre it is fine also we had tech from fibre company  coming at site.No issues with fibre.

also we open the tac case with cisco and as per them we need to try and  replace the gbic first .

Re: what is neg 30" error on fibre optic

Just curious, are you leasing dark fiber between two of your buildings or are you connecting your building to the telco?  Is the network operating on singlemode fiber or multimode (OM-1, OM-2, OM-3) fiber?

Good luck!

Community Member

Re: what is neg 30" error on fibre optic

Hi

Thanks for   reply.

how we can check if it is single mode or multimode?

yes we are connecting to telco and we only have layer 2 connection with telco.

mahesh

Re: what is neg 30" error on fibre optic

To determine the type of fiber (MMF or SMF), it is best to look at the printing on fiber cable's jacket or to ask the telco supplying the circuit.  It is difficult to look at the fiber and determine its size and type.

What type of demarc is the telco providing in your facility... do they have a switch installed or just some type of Ethernet demarc box in your building?

Cisco Employee

Re: what is neg 30" error on fibre optic

It sounds like you may have an issue with excessive span loss.  If this was previously working fine and has degraded the

issue may be due to dirty or damaged fiber.

Your best bet is to get a light meter and start at the far end and check your power levels.  If you know your launch/TX power on the far end, you can calculate your span loss at your near end receiver and compare it to what the actual span loss should be.

Does the problem occur in the opposite direction or is the issue only affecting one direction.

Once you know what type of GBIC or SFP you are using on the far end you can determine what power level it should be launching at and compare that to a light meter reading.

One more thing to try is to roll the fibers on each end so that your TX->RX is swapped on both ends.  If the problem goes to the other side then you definately have a fiber issue.  If after rolling the fiber on both ends the problem remains, the issue is most likely going to be a bad GBIC or SFP, most likely being that far end one since you are receiving a low power on this near end.

Aaron Reed

Carrier Escalation - Cisco Optical TAC

Community Member

Re: what is neg 30" error on fibre optic

hi all,

thanks for the reply.

issue was fixed when we replace the gbic.

cables were good.

replacing gbic fixed the issue

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