VoIP converts voice into data and sends the voice packets over the network. These packets get mixed with other voice and data packets and are reassembled into voice by an endpoint device (telephone). The result is a telephone call. In theory, the quality is as good as or better than that of the traditional public switched telephone network (PSTN).
VoIP systems work by using standard protocols to communicate. The major protocols to consider in a business communications system will be largely invisible to the users, and most likely result in the same application and quality. The thing to keep in mind with standards is what protocol will provide the richest application and the most interoperability. SIP (Session Initialization Protocol) is the most promising standard.
A VoIP system consists of several components. There are the endpoints, also known as telephones. These can be either an IP telephone or a soft-phone residing on a PC. The role of an IP telephone is identical to that of a traditional telephone. An IP telephone connects directly to a LAN instead of a traditional telephone connection. The soft-phone is a program that runs on your PC and performs all of the same functions of a telephone using your multimedia speakers and microphone plus video in some instances. In a VoIP system, the endpoints are very intelligent.
To control routing calls to and from endpoints there is an IP PBX. This performs similar functions to a PBX/Key System. The IP PBX is the server that all of the endpoints are logged in to. When a smart endpoint wants to make a call, they tell the IP PBX who they want to call. The IP PBX checks to see if the endpoint is available. If it is logged in and the called party will accept the call, then the call is put through. Most of the features in an IP PBX reside in the endpoint as opposed to a traditional PBX where the features are in the central control unit.
When an IP endpoint requires connection to a phone number on the PSTN a gateway is required. The endpoint tells the IP PBX that it wants to make a call to a specific number. The call is then routed to a gateway device where the number gets dialed into the PSTN and the call progresses as a normal telephone call.
A traditional PBX/Key System that supports VoIP is referred to as a converged system. This means that the PBX supports traditional telephones, IP endpoints, VoIP access to another PBX, remote offsite endpoints or all of the above.
Another VoIP system configuration is an infrastructure based system. This is identical to the above converged system but does not support traditional telephones. All of the control for the infrastructure based system resides on a blade in the router and in the IP telephones.
Most business solutions will require connection to the PSTN for the majority of their telephone calls. To connect to the PSTN from your PBX, there is nothing to do since PSTN lines are already connected. To connect to the PSTN from a LAN based VoIP solution, you must install a gateway. A gateway converts LAN based VoIP packets to traditional telephone transmission and provide a connection to the PSTN. Some solutions come bundled with gateway functionality; some require purchasing the gateway plus an IP PBX.
The equipment for VoIP varies depending on the application. The exact list of equipment depends on the specific requirements of your business. VoIP over the LAN often requires some infrastructure changes and adds traffic to the LAN. Extending VoIP calls outside of the LAN to remote users over the Internet or WAN links require additional bandwidth planning.
Considerations are efficiency, cost, reliability and quality. If you already have a good PBX and you just need to ad a few remote users, you can most likely get away with a pretty low cost solution. If you intend to network together many different locations to function as one system over a WAN, there are several solutions that may meet your needs in a broad range of prices. If you are installing a brand new solution in a new location, you have yet more options.
Most applications being installed brand new (Greenfield) may find introducing the infrastructure based pure LAN solution as the best route. Installing a pure LAN solution saves the additional cost of wiring for the PBX system. There are a wide range of available solutions. Some all in one solutions are available on the market from reliable equipment manufacturers. This would be a small VoIP appliance that provides gateway functionality for multiple trunk lines, support for IP telephones, a typical PBX feature set, Voice Messaging, web administration and remote user support for a very reasonable price.
Since traditional PBX equipment is designed to provide 99.999% reliable performance, replacing it with a new complete VoIP LAN based architecture may be a shock to your wallet. Many manufacturers of PBX equipment have enhancements available to provide all of the VoIP features you may require, at a fraction of the cost of a total replacement. Remember that PBX and data gear have a life of about 7.5 years. Replacing the PBX and retaining the digital telephones may provide a viable option to have a complete VoIP solution with all of the features and then some. Seven years from now, the solutions may be entirely different.