10GBase-SR and Fiber Cable Plants

I’ve been in the Technology field for quite a few years now. I originally worked on Token Ring and FDDI and 10Base5 and 10Base2 networks. I’m sure a few folks will remember the 5-4-3 repeater rule. Over the years I’ve also worked on ATM, 10Mbps (10BaseFL, 10BaseT, 10Base5, 10Base2), 100Mbps (100BaseT, 100BaseFX) and Gigabit (1000BaseSX, 1000BaseLX, 1000BaseXD) networks.

As we’ve migrated to newer technologies the demand on the fiber cabling plant has been significant. At 10Mbps using 10BaseFL transceivers it was possible to reach distances of 2km over 62.5/125 µm multi-mode fiber optic cabling. At 100Mbps using 100BaseFX transceivers it was possible to reach distances of 400m over 62.5/125 µm multi-mode fiber optic cabling. At 1000Mbps using 1000BaseSX transceivers it was possible to reach distances of 220m over 62.5/125 µm multi-mode fiber optic cabling. At 10Gbps using 10GBase-SR transcievers it is possible to reach distances of 26m over 62.5/125 µm multi-mode fiber optic cabling. While all these numbers change depending on the fiber cable ( 62.5 µm OM1, 50 µm multimode fiber OM2, 50 µm 2000Mhz fiber OM3, or 9 µm single mode fiber) and the trascievers you can see that as the speed has increased the maximum possible distance has come down.

A few years ago I was asked to help an organization that was having issues lighting a new 1000Mbps link between two campus buildings. They already had multiple ATM OC-3 interfaces between the two buildings and were trying to upgrade from ATM LAN to a Gigabit LAN trying to use the existing fiber that had installed about 5 years earlier. Unfortunately they had only installed multi-mode fiber and while the ATM OC-3 interface could drive a distance of 2000 meters the 1000BaseSX and 1000BaseLX interfaces they were trying to use would only work for distances of 220m and 550m respectively. As luck would have it they were out around 850m.

The point of this article is simple… don’t forget about the fiber cable plant when deciding to upgrade your Local Area or Metro Area Network.

While I’ve kept things really simple above there are a lot of different classes of fiber optic cabling today. There is multimode fiber and single mode fiber. There is 62.5 µm multimode (OM1) and 50 µm multimode fiber (OM2) and newer laser optimized (2000Mhz) 50 µm multimode fiber (OM3) . The distances you can traverse with any of these can vary greatly so it’s important that you check with the hardware manufacturer to make sure your going to be within spec.

Cheers!

References;

http://en.wikipedia.org/wiki/Multi-mode_optical_fiber