What type of SFP modules are needed for this link?

Unanswered Question
Mar 13th, 2007

I have a client that Single mode fiber running from point A to point B, and Multi mode Fiber running from point B to point C. They want to run a Gibabit network from point A to point C. If we connect the two fiber runs with a Single Mode to Multi Mode converter, what type of SFP modules will we need on each side? Will we need a 1000Base-LX module on the single mode side and a 1000Base-SX module on the Multi mode side? Is this possible?

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sbilgi Mon, 03/19/2007 - 11:30

The Cisco SFPs are supported across a variety of Cisco switches, routers, and optical transport devices.

Refer to Cisco 100-Megabit Ethernet SFP Modules Compatibility Matrix for more details.

http://www.cisco.com/en/US/products/hw/modules/ps5455/products_device_support_table09186a0080380847.html

Refer to the SFP modules section of the Catalyst 3560 Switch Hardware Installation Guide: Product Overview for more information on the SFP modules supported in the Cisco Catalyst 3560 switch.

http://www.cisco.com/en/US/products/hw/switches/ps5528/prod_installation_guides_list.html

konigl Fri, 03/23/2007 - 22:35

John,

To answer your question simply: yes, it's possible. Now for the details...

A 1000Base-LX/LH module at point A should be good enough to drive Gigabit Ethernet 10km over SMF to point B. (I've done it a little further than that, but Cisco only supports it out to 10km.)

The Gigabit Ethernet media converter you use at point B has to have similar transmit and receive optical characteristics to Cisco's LX/LH module. The 1000Base-LX specification only requires support for operation out to 5km over SMF; Cisco and other manufacturers have used higher-grade optical components to extend the signal reliably to 10km. That's why Cisco adds the /LH to the product description (for "Long Haul"). If your media converter only supports 1000Base-LX, it may not be able to reach back to point A.

The specifics you need to worry about are TX wavelength (1300 to 1310nm); TX optical power between -9.5dBm (min.) to -3dBm (max.); and RX optical sensitivity between -19dBm (min.) to -3dBm (max.) for GBICs, or -20dBm (min.) to -3dBm (max.) for SFPs.

Working it back from point C to point B is the tricky part. Whether you can do Gigabit Ethernet over that multimode fiber cable or not depends on distance and the modal bandwidth of the fiber cable. The 1000Base-SX module can do 220m to 275m over older 62.5/125 micron MMF; or 500m to 550m over 50/125 micron MMF. Some modern versions of 50/125 MMF have been optimized to be able to carry Gigabit Ethernet up to 2km, but unless you know you have this fiber I wouldn't count on it.

If you have old 62.5/125 MMF and the distance is between 275m and 550m, Gigabit Ethernet is still an option from point C back to point B: you can use 1000Base-LX/LH modules and special mode-conditioning launch cables. But your media converter back at point B would have to be LX-to-LX rather than LX-to-SX. The only manufacturer I know who makes an LX-to-LX for this type of application is Transition Networks, with their SFMFF1424-220.

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