Use of attenuator with LRM?

[merlin_le]

Hi,

I am looking at upgrading our network backbone from 1Gb to 10Gb. We have 62.5/125µm multimode fibre already in place, so will be using that. The shortest length between switches is approximately 25 meters, so we will go with LRM optics. I realise Mode Conditioning Patch Cables are required but I've also seen mention that an attenuator may be required over "short distances".

Question:

If I use Mode conditioning Patch Cables is there still the possibility that an attenuator will be requied? If an attenuator is required, what is considered a "short distance" and will I require them for a link of around 25 meters?

Thanks

[Reza Sharifi]

Hi,

Alternator is usually used when the distance is too long.  For 25 meters, you don't need to use LRM, you just need Multimode optics and you already have multimode 62.5 cable in place.  What type of switch or router is going to be connected to this fiber?

For example, Cisco SFP-10G-SR can go up to 26 meter over 62.5 fiber.

Have a look at table-1 in this link:

http://www.cisco.com/en/US/prod/collateral/modules/ps5455/data_sheet_c78-455693.html

HTH

[merlin_le]

Thanks for the reply,

I probably wasnt entirely clear in my description. There are multiple fibre runs, of which the shortest is approximately 25 meters (I am not confident of this estimate so it may well be longer). All other runs are 30+ meters. Hence why i was looking at using LRM.

I think I confused myself on the use of an attenuator. Looking at the 'Use of mode condition patch cables' page (http://www.cisco.com/en/US/prod/collateral/modules/ps5455/product_bulletin_c25-530836.html) only the following note mentions an attenuator, which is not applicable in my case.

Notes for LRM:

1. For customers using OM3 fiber type, MCP should not be used. It is highly recommended to measure the power level before plugging the fiber into the adjacent receiver. When the received power is measured to be above 0.5dBm, a 5-dB attenuator for 1300nm should be used and plugged at the transmitter source of the optical module on each side of the link.

[sajid_m123]

Though, it may not be the solution in your case as you have OM3 installed, however, we never observed any issue in using direct SM fiber with LRM. I know Cisco suggests using MCP cables in such scearios but Sm also worked without any issues.

[Reza Sharifi]

1. For customers using OM3 fiber type, MCP should not be used. It is  highly recommended to measure the power level before plugging the fiber  into the adjacent receiver. When the received power is measured to be  above 0.5dBm, a 5-dB attenuator for 1300nm should be used and plugged at  the transmitter source of the optical module on each side of the link.

OM3 and OM4 work with Multimode over 50/125um and not 62.5

[sajid_m123]

Reza is correct, I did not mean using MCP with OM3 rather using MCP with LRM for a short distance. Reza, Thanks for the correction anyway.