Digital Voice
is Nothing New
Would you believe that digital
telephony is nearly 50 years old?
It seems like VoIP telephone systems are
a relatively new technology without the hundred years of experience
that built the solid, dependable public switched telephone system.
Would you be shocked to learn that digital telephony has been
part of telephone technology for nearly 50 years? Would you also
be surprised to learn that most phone calls you make today are
at least partially digital? Digital voice is not only a proven
technology, it offers quality advantages over old fashioned analog
telephone.
The Story Behind the Digital Telephone
Revolution
When Alexander Graham Bell yelled for Mr. Watson, his invention
was pure analog technology. A vibrating microphone converted
speech pressure to electricity which then vibrated an earpiece
in the next room. That principle was used in every phone and
phone line for decades. So, why change it?
For one thing, analog technology can consume
a lot of wires... one pair for each conversation. Analog multiplexing
electronics can shift frequencies to stack many conversations
on a pair of wires, but it's complicated and gets out of alignment.
Analog signals also pick up noise every time they are amplified.
Anyone who remembers the poor quality of long distance and international
calls thirty years ago knows that they sounded nothing like the
"next door" quality you experience today.
By the 1950's, digital technology had advanced
to a point where phone companies began to use it to transport
calls between phone company offices. The T1 digital line carries
up to 24 conversations and a T3 digital line carries up to 672
simultaneous phone calls. That's quite a savings in wire. Moreover,
as long as the digital signals are automatically regenerated
when they get weak, no noise is added to the signal. What comes
out is exactly the same as what went in.
Today nearly every long distance call and
many local and regional calls have been converted to and from
the digital domain without your being aware. What you do notice
is the quiet background and clear voice quality even on international
calls. The person you are talking to in the next state may just
as easily be down the street. That's the value of digital transmission.
How It Works
Your regular phone is connected to the telephone office or your
company's PBX system by a pair of copper wires. At that point,
an analog to digital converter called a CODEC (coder / decoder)
converts it to a digital signal that is a set of numbers rather
than varying voltages and currents. Another device called a multiplexer
combines your call with others into a single bit stream that
is loaded onto a digital trunk line. At the other end, the process
is reversed and the digital voice is converted back to analog
and sent to the receiving party's phone. Unless you are aware
of the inner workings, the conversion processes are transparent
and you can't really tell if the phone call was sent by analog
or digital means.
How Does This Relate to VoIP?
In a VoIP telephone system, the phone call is converted to digital
much earlier in the process. If you have an IP telephone, the
circuitry to convert between analog and digital in built right
into the phone. Only the handset itself is analog. The line that
connects the telephone to the phone network is actually a digital
network line. Everything between phones happens in the digital
domain.
The other difference is one of technique.
In the T1 digital system, each phone call is assigned to one
of 23 or 24 channels that the line can handle. If no one is speaking,
the channel is still tied up. If only a few calls are taking
place, the other channels are idling empty but you still have
to pay for them.
In VoIP, the digital voice is sent out
as a series of packets that share a common network line with
other VoIP phones and computers. The phone generates packets
only when a conversation takes place. Otherwise, packets from
other sources are free to use the bandwidth available in the
network. It's a more efficient system and gives you the ability
to converge voice and data into a single network.
What About Quality?
The legacy digital phone system called TDM for Time Division
Multiplexing was designed to mimic the characteristics of the
analog phone standards. Quality is assured.
VoIP phone systems can sound just a good
as the best analog or other digital phone. TDM phones use a conversion
process that generates 64K bits per second. VoIP also has this
standard available. However, you may wish to opt for a slightly
reduced quality standard that generates 8K bits per second. This
standard lets 8 phone conversations use the same bandwidth as
1 conversation of the highest voice quality.
There are also lower quality coding standards
that offer even higher bandwidth efficiency, but at noticeably
poorer voice quality. If your only experience with VoIP phone
calls has been with earlier PC based phones on dial-up Internet,
you might be inclined to think of VoIP as a poor quality medium.
However, with high quality phones on a properly designed enterprise
network, VoIP can sound as good and maybe even better than some
analog systems.
Need More Help?
For assistance with your particular enterprise network and telephony
issues, please use our Enterprise VoIP inquiry form. A member
of our technical sales team will be in touch quickly. There is
no cost or obligation for this service.
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