A customer wants to set up a site-to-site replication using Fibre Channel to a Site...

https://en.wikipedia.org/wiki/Fibre_Channel

https://www.techtarget.com/searchnetworking/tutorial/Network-cable-history-and-fundamentals-Cabling-tips-for-network-professionals-lesson-1

https://fibrechannel.org/wp-content/uploads/2016/04/Fibre_Channel_Connectivity_White_Paper_04-06-16.pdf

This is because single-mode fiber optic cable has a small core diameter that allows only one mode of light to propagate. This reduces signal attenuation and enables longer transmission distances than multimode fiber optic cable, which has a larger core diameter that allows multiple modes of light to propagate. Single-mode fiber optic cable can support distances up to 40 kilometers for Fibre Channel applications.