Information Technology Reference
In-Depth Information
reconfiguration of the voice network. In addition, when combined with a VPN con-
figuration, users can take IP phones home with them and retain their work extension.
IP SoftPhones:
SoftPhones represent an ideal example of the possibilities when
combining voice and data networks. Users can now plug a headset into their laptop or
desktop and allow it to act as their phone. SoftPhones are becoming increasingly
more integrated with other applications such as e-mail contact lists, instant messen-
ger, and video telephony.
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Unified e-mail, voicemail, fax:
All messaging can be sent to a user's e-mail inbox.
This allows users to get all messages in one place and easily reply, forward, or archive
messages.
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Increased productivity:
VoIP extensions can forward to ring multiple devices be-
fore forwarding to voicemail. This eliminates the “phone tag” game.
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Feature-rich communications:
Because voice, data, and video networks have com-
bined, users can initiate phone calls that communicate with or invoke other applica-
tions from the voice or data network to add additional benefits to a VoIP call. For
example, calls flowing into a call center can automatically pull up customer records
based on caller ID information or trigger a video stream for one or more of the callers.
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Open, compatible standards:
In the same way that you can network Apple, Dell,
and IBM PCs together, you can now connect devices from different telephony ven-
dors together. Although this benefit has yet to be fully realized, this will allow busi-
nesses to choose the best equipment for their network, regardless of the
manufacturer.
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The Process of Converting Voice to Packets
Long ago, Dr. Harry Nyquist (and many others) created a process that allows equipment to
convert analog signals (flowing waveforms) into digital format (1s and 0s). It is important
to understand this process, because it will guide your configuration of VoIP audio sample
sizes, Digital Signal Processor (DSP) resources, and codecs.
The origin of the digital conversion process (which fed many of the developments dis-
cussed earlier) takes us back to the 1920s, a far throw from our VoIP world. The Bell Sys-
tems Corporation tried to find a way to deploy more voice circuits with less wire, because
analog voice technology required one pair of wires for each voice line. For organizations
that required many voice circuits, this meant running bundles of cable. After plenty of re-
search, Nyquist found that he could accurately reconstruct audio streams by taking sam-
ples that numbered twice the highest audio frequency used in the audio.
Here is how it breaks down. Audio frequencies vary based on the volume, pitch, and so on
that comprise the sound. Here are a few key facts:
The average human ear is able to hear frequencies from 20-20,000 Hz.
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Human speech uses frequencies from 200-9,000 Hz.
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Telephone channels typically transmit frequencies from 300-3,400 Hz.
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The Nyquist theorem is able to reproduce frequencies from 300-4,000 Hz.
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