A systems administrator must cable a new 10 Gbit/s backbone link between a top-of-rack switch and an aggregation switch 240 m away. Both switches are already equipped with 10GBASE-SR SFP+ transceiver modules, and the project budget cannot accommodate different optics or mode-conditioning patch cords. Which fiber-optic cable type should the administrator order to meet the IEEE 802.3 distance specification while keeping costs to a minimum?
10GBASE-SR uses an 850 nm VCSEL laser that is specified only for multimode fiber. According to IEEE 802.3, its maximum reach is 300 m over laser-optimized 50/125 µm OM3, 400 m over OM4, 82 m over 50/125 µm OM2, and just 33 m over 62.5/125 µm OM1. It is not specified for single-mode OS2 at all. Because the planned run is 240 m, only OM3 (or the more expensive OM4) will meet the distance requirement with the existing SR optics. Choosing laser-optimized 50/125 µm OM3 therefore satisfies the specification with the least additional cost. OM2, OM1, and OS2 either fall short of the required distance or would need different transceivers to operate.