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The point of VoIP is to enable voice to pass over an IP network. Voice signals from the microphone are converted into a digital stream and split into small packets of information using the Internet Protocol (IP). At the receiving end, the IP packets are reassembled into a digital stream and converted back to an analogue signal for a loudspeaker.
The conversion from analogue to digital is performed either by a phone handset, such as a Polycom IP501, or by a ‘softphone’, which uses a microphone and headset plugged into a PC.
Call quality is an important consideration for any business telephony application, and the point to remember about VoIP is that aside from the choice of a quality handset or soft-phone with adequate PC resources, speech quality is dependant on the attributes of the network that transports the VoIP packets.
Speech happens in real time, so its critical that the stream of IP packets across the network are delivered within tightly defined parameters, key ones being delay, jitter and packet loss.
VoIP on the public Internet
If VoIP is used on the public Internet, speech quality is a random quantity; excellent at times, but verging on the un-usable at others. The reason is the lack of guarantees on delivery time, routes taken or congestion encountered en-route. VoIP over the public Internet has applications in business for internal calls and as an ad-hoc solution, but it is not suited for customer calls or any usage where speech quality matters.
VoIP on a Private Internet
VoIP that uses a Private Internet, for example an MPLS IP VPN with private ADSL or dedicated high speed links, can meet the performance guarantees required for business class call quality (previously referred to as Toll Quality). The network is architected for resilience end-to-end and can be fine-tuned to ensure that each voice packet is forwarded with the highest priority over the fastest routes.
In the domestic environment, VoIP is taken to mean voice over the public Internet, and the main attraction is toll-bypass (free calls) and the ability to call home from a wireless access point.
In a business environment, VoIP is taken to mean voice over a Private Internet, and the main attraction is the cost savings of IP convergence on a single infrastructure, together with the business benefits of Unified Communications, such as Presence.
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