GBIC - LH

[ptorrico]

Wich is the longest distance to work with GBIC - LH over multimode fiber.

Pablo

[konigl]

Pablo,

The standard supports 1000BASE-LX over multimode fiber out to 550 meters. Whether you can push the optical signal beyond that distance depends on exactly what kind of fiber you have, and how well it was installed. Also limiting the distance you can go is the minimum optical power budget of the 1000BASE-LX/LH GBIC, which is 9.5dB

To achieve distances beyond 250m to 300m, a special patch cable is required at each end of the link. Known as a mode-conditioning patch cord, it has a small section of single-mode fiber on one of the two strands; the single-mode fiber part attaches to the TX port of an LX GBIC. About halfway down the patch cable that single-mode fiber is spliced into a multimode fiber strand, at an offset so the centers do NOT line up. The fiber coming from the RX port is totally multimode. These mode-conditioning patch cords, sometimes referred to as launch cables, are used to connect your LH GBIC to the long run of multimode fiber.

Here are some useful links:

Cisco GBICs

http://www.cisco.com/en/US/partner/products/hw/modules/ps872/products_data_sheet09186a008014cb5e.html

Mode-Conditioning Patch Cord Installation Note

http://www.cisco.com/en/US/partner/products/hw/switches/ps679/products_installation_and_configuration_guide09186a008007d1cb.html

Hope this helps.

[konigl]

Here are the links again, if you don't have a CCO login account:

Cisco GBICs

http://www.cisco.com/en/US/products/hw/modules/ps872/products_data_sheet09186a008014cb5e.html

Mode-Conditioning Patch Cord Installation Note

http://www.cisco.com/en/US/products/hw/switches/ps679/products_installation_and_configuration_guide09186a008007d1cb.html

[ptorrico]

Thanks for your comments,

Well I have the conditioning cable on both sides, my distance is 900 m and I have link, however there is no trunk.

If I have link, the trunk should be able?

Pablo

[konigl]

I have had LX/LH GBICs show me a link LED over extra-long single-mode fiber spans, but not work reliably. ZX GBICs and in-line attenuators fixed those problems, but won't fix yours since they're not intended for use on multimode fiber.

Since the other switch is only 900m away, can you bring it back so you can run some tests with both units in the same room? You can use a known good regular patch cable, either multimode or single-mode, to connect the two LX GBICs. If you get your trunk to work in the same room, but it doesn't work across the long multimode run, then the fiber's most likely the problem. If the trunk doesn't work when the switches are in the same room, then it's either a config problem or equipment problem. Fix it, and try it again across the fiber.

I have a customer whose campus network was built years ago with underground multimode fiber only. Found that Gigabit Ethernet could not be run over it using SX or LX GBICs because the runs were too long. (I know they were longer than 550m and under 2km; but I don't recall the exact distances now, and they don't have their scan results available.) This customer went with 4x100-megabit full duplex Fast EtherChannel instead, using media converters, because 100BASE-FX is rated to 2km over multimode.

Do you have access to any optical test equipment, to check the dB loss end-to-end at the 1300nm wavelength? How many strands of multimode fiber do you have available between the two locations? Is the fiber aerial or underground? What's the feasibility of pulling some new single-mode fiber along the same path as the multimode? Do you have line-of-sight between the two locations, such that you could consider a wireless solution instead (microwave or free space optics)?

Hope this helps.