Internet telephony service provider
ITSPs provide services to end-users directly or as whole-sale suppliers to other ITSPs.
ITSPs use a variety of signaling and multimedia protocols, including the Session Initiation Protocol (SIP), the Media Gateway Control Protocol (MGCP), Megaco, and the H.323 protocol. H.323 is one of the earliest VoIP protocols, but its use is declining and it is rarely used for consumer products.
Retail customers of an ITSP may use traditional analog telephone sets attached to an analog telephony adapter (ATA) to connect to the service provider's network via a local area network, they may use an IP phone, or they may connect a private branch exchange (PBX) system to the service via media gateways.
ITSPs are also known as VSP (Voice Service Provider) or simply VoIP Providers.
Usually, ITSP source for route terminations to different parts of the globe from multiple VoIP providers. ITSP customers can then indirectly choose which VoIP providers they would like to use for their VoIP calls. The ITSP customers do this by specifying the maximum price they are willing to pay per minute for the call and the lowest quality they are willing to tolerate. The ITSP routing software will then search for the wholesale VoIP providers who meet the customers' specification and attempt to route the customer call over the VoIP providers starting with the one with the lowest price. Prices to different part of the world depend on several factors. For example, if the call is going over a white route or a black route, wholesaler's margin, the countries regulation to name a few.
Before 2003, many VoIP services required customers to make and receive phone calls through a personal computer. This is not the case any more though as the smartphone has provided a more natural platform.
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November 1995 Announces Plans to Release First PC-to-Phone Technology