Differences between OS1, OS2, & OM1, OM2, OM3, OM4, and OM5 Fiber optic cables used in telecommunication are broadly categorized into two types – Multimode fiber and Single-mode fiber cables. The multimode fiber cable is prefixed with 'OM' and the Single-mode fiber cable is prefixed with 'OS'. In ISO/IEC 11801 and EIA/TIA standards five types of Multimode – OM1, OM2, OM3, OM4 & OM5 and two types of Single-mode – OS1 & OS2 fibers are mentioned. In all the standards the OM/OS system applies to cabled optical fiber, and the cabling standards deal with cable and connecting hardware. ISO/IEC 11801 and 24702 make it clear that the nomenclatures OM1, OM2, OM3, OS1, and OS2 relate to cable transmission performance whereas the BS EN 50173 series makes it even clearer by describing the OM/OS nomenclature as "optical fiber cable categories".
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