by Steve Greechie
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VoIP service is technical stuff and the vocabulary can be confusing. Before talking with a potential VoIP provider, a potential buyer should understand the basics.
VoIP
First problem: Voice over Internet Protocol is a misnomer. A more precise term is IP Telephony, or IPTeL. The technology can transport other things besides voice over the system: video, text, and other real-time media can be delivered over IP networks as well. Other terms for VoIP include broadband telephony and voice over broadband.
VoIP is replacing the traditional telephone system, the public switched telephone network (PSTN).
Sampling and Compressing in VoIP Systems
As a transmitter of voice, a VoIP system takes samples of the voice or other sounds--thousands each second--and delivers them to another computer where the voice can be heard.
For efficiency, a computer may compress the sound samples. The algorithm needed to do this is called compressor/de-compressor, or CODEC. Using a CODEC decreases the bandwidth needed for the delivery. There are CODEC's for all sorts of applications, such as film and music. A VoIP CODEC optimizes voice transmission by deleting data in frequencies the voice doesn't use. For this reason, music doesn't transmit well over VoIP.
Making Bundles of VoIP Data
After sampling and compressing sound, a VoIP phone system bundles the samples into larger packages. This process is called packetization. These IP packets most commonly contain 10-to-20 milliseconds of speech.
Of course, there is an agreed format for the data packets--the payload format.
Data Loss in VoIP
IP Packets sometimes get lot in transmission over a VoIP service. CODEC's compensate for this using a process call packet-loss concealment which fills in the gaps between the transmitted packets. Another method to reduce packet loss is redundancy, in which a CODEC sends a packet multiple times.
A third response to packet loss is forward-error correction (FEC). FEC compensates for lost data by transmitting some data in adjoining packets, so that the lost data can be identified.
Data Delay in VoIP Services
Sometimes data packets are delayed in transmission, so that they're useless, too old to use. They're ignored, and the system compensates.
Fortunately, delay is generally constant--n better systems, less than half a second. However, variation in delay, the jitters, can be a problem, and VoIP systems address it with jitter buffer algorithms. An adaptive jitter buffer can queue up sound packets to accommodate late data and reduce the delay.
Devices for VoIP Telephone Systems
VoIP phone service is usually thought of as a computer-to-computer protocol. However, a VoIP system can be used on a range of hardware. IP phones replace traditional telephones and can look like them. Gateway devices interface between VoIP and traditional PSTN networks. One type of gateway is the analog terminal adapter, also called analog telephone adapter or ATA. It allows traditional phones to use VoIP.
VoIP Bottom Line for Enterprise
The businessperson should remember the bottom line: VoIP phone service is important because it reduces communications costs. Using a broadband connection for transmitting many types of media is convergence, and it's the goal of business VoIP.
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About the Author
Steve Greechie (MBA, MSLIS, MA) is a freelance business writer in New York City. He's published extensively in a range of publications, including The Boston Business Journal, Information Outlook, Online, Architectural Record and The Journal of Business and Finance Librarianship. He contributed to The Core Business Web, which The American Library Association named The Best Business Reference Book of 2003. His internet copy appears widely.
