Learn in the textbookInternet Connection Services and Telecommunications Carriers
DefinitionA line carrier (回線事業者) is an operator that sets up and supplies communication line facilities such as optical fiber, telephone lines, and base stations.
ExplanationThe line between a telephone office (the local exchange, 収容局) and a subscriber's home is called the subscriber line (加入者線), and what the line carrier uses for it shapes the character of the service. For example, ADSL runs high-speed digital communication over existing metal (copper) phone lines, while FTTH replaces that line with optical fiber. High-speed lines like these are collectively called broadband lines (ブロードバンド回線).
AnalogyIt resembles a company that builds and maintains roads. Whatever vehicles travel and whatever they carry is a separate matter; it supplies the road itself.
Memory hookIts other name, carrier (キャリア), literally means "something that carries," which ties it to the companies that own the paths data travels on.