1000BASE-LX/LH GLC-LH-SM= appropriate F/O cable

[herdin.maritz]

Dear All,

Currently i'm using 1000BASE-LX/LH GLC-LH-SM= [ 1000BASE-LX/LH long-wavelength/long haul; without DOM ] with WS-C2960G-24TC-L and i plan to use Multimode 62.5-micron diameter MMF F/O cable with 100 meter length.

According to Cisco reference as attached, MCP (mode-conditioning patch cord) is required if distances greater than 984.25 feet (300 meters), my understanding is MCP is not required since distance in my case is less than that.

but there is one statement in this document is that make me doubt is “We do not recommend using the WS-G5486 or GLC-LH-SM and MMF with no patch cord for very short link distance (tens of meters). The result could be an elevated bit error rate (BER).”

In what case MCP is required ?

Please advise what is the appropriate cable should we use ? and what is the minimum distance of 1000BASE-LX/LH GLC-LH-SM= if we are using this transceiver with MMF without any MCP ?

Thank you in advance for your assistance.

Best regards,

Herdin Maritz

[Tom Randstrom]

I would recommend using the latest documents for directions on using MCPs. 

The current SFP data sheet and installation document indicates that MCPs (CAB-GELX-625= for 62.5um or similar from an alternative vendor) are required in all installations using MMF (no link length dependent).

SFP Data Sheet

http://www.cisco.com/en/US/prod/collateral/modules/ps5455/ps6577/product_data_sheet0900aecd8033f885.html

SFP Installation Document

http://www.cisco.com/en/US/docs/interfaces_modules/transceiver_modules/installation/note/78_15160.html

Mode Conditioning Patch Cables Document

http://www.cisco.com/en/US/prod/collateral/modules/ps5455/product_bulletin_c25-530836.html

The IEEE 802.3 specs outline the use of MCPs for MMF links. 

"To ensure that the specifications of Table 38–7 are met with MMF links, the 1000BASE-LX transmitter output

shall be coupled through a single-mode fiber offset-launch mode-conditioning patch cord, as defined in

38.11.4."

The statement regarding short link distances is typically for lab environments where the equipment is being tested with only short interconnect jumpers. Seeing your link is 100m, this is irrelevant.

You could save some money by using lower cost 1000Base-SX SFPs without MCP cables on your 100m 62.5um fiber links (I understand there may be other reasons for using the LX modules).   

I hope this helps!

Tom

[herdin.maritz]

Thank you for your suggestion Tom,

Kindly please advise me for the following queries,

Does MCP still required if i change my MMF F/O cable with 100meter SMF one ?

Does MCP is still required if my MMF F/O type is OM3 ?

and refer to Cisco product bulletin, 5-dB attenuator for 1300nm can also be used if we reluctant to use MCP. Please advise if we can implement this way without any MCP with multimode 62.5-micron diameter MMF F/O cable.

Thank you & best regards,

herdin maritz

[Tom Randstrom]

Herdin,

If you use SMF with 1000Base-LX, then no MCP is required. 

If you use OM3 or OM4 MMF with 1000Base-LX, then no MCP is required. 

Regarding the use of a 5dB attenuators instead of the MCPs ... I could not say whether it will work or not.  The statements in the Cisco Bulletin are not clear as to what "short reaches" of fiber optic cable is. The only way to confirm proper operation would be to insert the 5dB attenuators in your network and monitor its operation.  Just based on the Cisco's wording, this configuration is not something they recommend (especially if you have other options available, like SMF or OM3/4 MMF).

I hope this helps!

Tom