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An Internet service provider, or ISP, maintains, installs and provides internet connection to residential or commercial areas. Some examples of ISP clients include - homes, coffee shops, hotels, libraries, offices. They usually charge a fee for installing the connection and a monthly fee for maintaining it.
The internet is basically a web of interconnected networks - which are maintained by a huge number of different ISPs. They keep connected around the world by giving their clients access to other ISP networks. This is called peering.
ISPs offer different types of connections such as dial-up, DSL, through optical fiber wires, through a cable television connection, or wireless. Communications satellite connections are used mainly in remote areas. Dial-up is the slowest connection, while a direct fiber-optic connection is usually the fastest.