Internet Service Provider(ISP)

Internet Service Provider (ISP) also called as Internet Access Provider (IAP) is the company that provides its customers access to the internet. It provides services to users to communicate with each other globally. Further more many ISPs also provide related Internet services like email, Web hosting and access to software tools.

The largest National and Regional ISPs include:
AT & T WorldNet
IBM Global Network
MCI
Netcom
UUNet
PSINetRegional Providers includes:
New England's NEARNet
Samfrancisco Bay area BARNet.

ISP Connects by using data transmission technology appropriate for delivering Internet protocol datagram such as Dial up, DSL, Cable Modem, Wireless or Dedicated high-speed Interconnects.
For users and small business, most popular options includes Dial up, DSL( typically ADSL), Broadband wireless, Cable Modem, Fiber to the Premises (FTTH) & Integrated Services Digital Network(ISDN). For the medium & Large Business that demands large requirements, the options includes DSL(often SHDSL/ADSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN(BRI or PRI), ATM, Satellite Internet Access & Synchronous Optical Networking(SONET).
Recently Wireless Internet Service Providers (WISP) have emerged that offer Internet access through wireless LAN or Wireless Broadband Networks.
Some Companies also offer free ISP service to those who need Internet connectivity occasionally. These free offerings feature limited connect time and are often bundled with some other product or service.

Source: https://en.wikipedia.org/wiki/Internet_service_provider