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An Internet service provider (ISP, also called Internet access provider, or IAP) is a company that offers its customers access to the Internet. The ISP connects to its customers using a data transmission technology appropriate for delivering Internet Protocol datagrams, such as dial-up, DSL, cable modemor dedicated high-speed interconnects.

ISPs may provide Internet e-mail accounts to userswhich allow them to communicate with one another by sending and receiving electronic messages through their ISPs' servers. (As part of their e-mail service, ISPs usually offer the user an e-mail client software package, developed either internally or through an outside contract arrangement.) ISPs may provide other services such as remotely storing data files on behalf of their customers, as well asother services unique to each particular ISP.

End-User-to-ISP Connection

ISPs employ a range of technologies to enable consumers to connect to their network.

For users and small businesses, the most popular options include dial-up, DSL (typically Asymmetric Digital Subscriber Line, ADSL), broadband wireless,cable modem, fiber to the premises (FTTH), and Integrated Services DigitalNetwork (ISDN) (typically basic rate interface).

For customers with more demanding requirements, such as medium-to-large businesses, or other ISPs, DSL (often SHDSL or ADSL), Ethernet, Metro Ethernet, Gigabit Ethernet, Frame Relay, ISDN (BRI or PRI), ATM, satellite Internet access and synchronous optical networking (SONET) are more likely to be used.

Typical home user connection
▪ Dial-up
▪ DSL▪ Broadband wireless access
▪ Cable Internet
▪ FTTH
▪ ISDN
▪ Wi-Fi
Typical business type connection
▪ DSL
▪ SHDSL
▪ Ethernet technologies
[edit]Locality
When using a dial-up or ISDN connection method, the ISP cannot determine the caller's physical location to more detail than using the number transmitted using an appropriate form of Caller ID; it is entirely possible to e.g.connect to an ISP located in Mexico from the USA. Other means of connection such ascable or DSL require a fixed registered connection node, usually associated at the ISP with a physical address.

ISP Interconnection

Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access. An upstream ISP usually has a larger network than the contracting ISPand/or is able to provide the contracting ISP with access to parts of the Internet the contracting ISP by itself has no access to.

In the simplest case, a single connection is established to an upstream ISP and is used to transmit data to or from areas of the Internet beyond the home network; this mode of interconnection is often cascaded multiple times until reaching a Tier 1 carrier. In reality,the situation is often more complex. ISPs with more than one point of presence (PoP) may have separate connections to an upstream ISP at multiple PoPs, or they may be customers of multiple upstream ISPs and may have connections to each one of them at one or more point of presence.

Peering
Main article: Peering

ISPs may engage in peering, where multiple ISPs interconnect at peeringpoints or Internet exchange points (IXs), allowing routing of data between each network, without charging one another for the data transmitted—data that would otherwise have passed through a third upstream ISP, incurring charges from the upstream ISP.

ISPs requiring no upstream and having only customers (end customers and/or peer ISPs) are called Tier 1 ISPs.

Network hardware, software andspecifications, as well as the expertise of network management personnel are important in ensuring that data follows the most efficient route, and upstream connections work reliably. A tradeoff between cost and efficiency is possible.

Virtual ISP

Main article: VISP

A Virtual ISP (VISP) is an operation which purchases services from another ISP (sometimes called a "wholesale ISP" in this...