We have two categories OS1 & OS2. Both are SMF (Single-mode Fibres); however, their characteristics, performance and application are quite different. In today's modern-day WAN-based network, only the OS2 type of Fibre is used in the manufacture of these cables. However, on internal short links applications, it is acceptable to use OS1 fibres. The single most significant difference is the increased attenuation with OS1, hence the shorter links. You would not introduce OS1 Fibre into an OS2 WAN network. So it is essential to plan out your network and clearly understand fibre types and applications.
