ISP Interconnection
Just as their customers pay them for Internet access, ISPs themselves pay upstream ISPs for Internet access.
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.
[edit] Peering
Main article: Peering
ISPs may engage in peering, where multiple ISPs interconnect at peering points 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 and specifications, 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.
[edit] Virtual ISP
A Virtual ISP (vISP) is an operation which purchases services from another ISP (sometimes called a "wholesale ISP" in this context[1][2]) which allow the vISP's customers to access the Internet via one or more points of presence (PoPs) owned and operated by the wholesale ISP.
There are various models for the delivery of this type of service. The vISP can provide network (internet) access to end users via access nodes owned by the wholesale ISP (e.g. dial-up modem PoPs or DSLAMs installed in telephone exchanges), routing network traffic itself to its destination.
[citation needed] In another model, the vISP does not route any end user traffic, and needs only to provide AAA (Authentication, Authorization and Accounting) functions, and may additionally provide "value-add" services like email or web hosting using its own facilities.[citation needed]
The service provided by a wholesale ISP in a vISP model is distinct from that of an upstream ISP, in that a vISP in most cases only provides a means of connection for the customer with an actual backbone/upstream ISP handling the routing and transmission of data, while a wholesale ISP handles both in one case; they may however be one and the same company or strongly affiliated, with the vISP being the customer front-end, while the actual backbone provider is a subsidiary or affiliation.
A vISP can also refer to a completely automated white label service offered to anyone at no cost or for a minimal set-up fee. The actual ISP providing the service generates revenue from customers using the service, and may also share a percentage of that revenue with the owner of the vISP.
[citation needed] All technical aspects are dealt with by the ISP providing the infrastructure, thus leaving the owner of the vISP operation with the task of promoting the service. This sort of service is however declining due to the popularity of unmetered internet access also known as flatrate.[citation needed]
[edit] Free ISP
Free ISPs are Internet Service Providers (ISPs) which provide service free of charge. Many free ISPs display advertisements while the user is connected; like commercial television, in a sense they are selling the users' attention to the advertiser.
Other free ISPs, often called freenets, are run on a nonprofit basis, usually with volunteer staff. There are also free shell providers and free web hosts.