4.2.1 Types of VoIP

VoIP services differ depending on whether:

The service provides a competitive alternative to conventional telephone services,
A conventional telephone can transmit and receive calls,
Subscribers need to acquire and install additional equipment on their premises,
Traffic routes into or from the PSTN, and
Users pay for service.

This section describes three broad categories of VoIP service: Internet telephony via computer; Internet telephony that is partially accessible from and to the PSTN; and Internet telephony that is fully accessible from and to the PSTN.

Internet Telephony via Computer

Internet telephony via computer offers a variety of voice communications services. These include:

Person to person voice calls,
Electronic commerce Internet sites that offer a “push to talk” icon that provides an opportunity to talk to a customer service representative,
Video games that enable players to talk to other players.

Computer-to-computer Internet telephony services, such as Skype and Pulver.com require users to download software. Users can then set up free voice conversations with other subscribers through the Internet. Calls are routed using a peer-to-peer arrangement that uses the computer of any logged on subscriber as an intermediary for routing traffic on to the intended call recipient.

An end-to-end Internet telephony connection via computer requires that parties have personal computers equipped with:

Compatible software,
A sound card or similar device, and
Access to the Internet.

Figure 1: Internet Telephony via Computer

Figure 1: Internet Telephony via Computer

Source: ITU

Internet telephony via personal computer has several drawbacks:

Typically, calls do not access the PSTN (unless one of the computers accesses the Internet via a modem and conventional dial-up telephone line),
Subscribers must log onto the service in order to make and receive calls,
The service does not provide caller identification and location information needed in emergencies,
Finally, the service does not offer the same sound quality and reliability as conventional circuit switched telephony.

For these reasons, most countries treat Internet telephony via computer as an unregulated information service, largely free of traditional telephone carrier responsibilities.

Internet Telephony Partially Accessible from and to the PSTN

This category of VoIP calls includes:

Long distance telephone calls originated by subscribers of incumbent carriers, and by users of calling cards who call from payphones and mobile phones. In both cases calls originate and terminate over the PSTN, but transit the Internet for all or a portion of the long haul,
Internal corporate VoIP traffic that originates and terminates over an enterprise network. Some enterprise networks can route traffic into the PSTN,
VoIP services that enable customers to make calls over the Internet. Such calls typically originate over a broadband Internet link and terminate at the call recipient’s end without ever traversing the PSTN (see Internet Telephony via Computer). However, these services can also deliver traffic to non-subscribers over the PSTN and a normal telephone handset (see Figure 2).

Figure 2: Internet Telephony Partially Accessible from and to the PSTN

Figure 2: Internet Telephony Partially Accessible from and to the PSTN

Source: ITU

The Internet and conventional circuit switched telephone numbering systems use different addressing systems. Thus VoIP services in this category must provide call processing software that can “map” Internet Protocol addresses to call recipients with conventional telephone numbers. The software routes the call as far as possible through Internet networks, to a “gateway” or “point of presence” as close as possible to the intended call recipient. At that point, the service converts the call to telephony traffic and hands it off to a conventional telephone network.

To access this category of VoIP services, users need:

A subscription to a VoIP service,
Broadband Internet access,
A modem, and
An Analog Terminal Adapter, to configure VoIP onto the user’s DSL or cable modem link. This device converts the call signal from analog to digital (and vice versa).

The ability of subscribers to access service from conventional telephones, or alternatively to call conventional telephone numbers, makes this form of Internet telephony more attractive to customers (and therefore more commercially attractive) than Internet telephony via computer.

Internet Telephony Fully Accessible from and to the PSTN

Many telephone companies already use Internet carriage to handle long distance calls (see Figure 3). The customer making the call may not even be aware of this.

Most current VoIP services do not use the PSTN for both call origination and termination. In the future, almost all VoIP services will require a broadband, digital Internet access link. Telephone companies and cable television companies will replace copper networks with optical fibre. This will enable voice services to ride over a ubiquitous broadband digital network as a software application.

Figure 3: VoIP Fully Accessible from and to the PSTN