Specifications

6
dedicated wire for each call. For the
period of time you were on the phone
you “owned” a copper wire connection
between your phone and the other party.
In today’s PSTN, all calls are digitized
and can be combined with thousands of
others running over fiber optic cable
between central stations. However, the
connection between the two phones
must remain open for the length of
the call.
When computer data is transmitted
over phone lines or cable, it is also in
digital form. However, the data is sent
in packets and does not require a
dedicated pathway to reach its
destination. In fact, when a computer
sends a stream of data packets, they
may all arrive at their destination after
traveling different routes. There are
thousands of possible paths between any
origin and any destination. In addition,
packets from other origins can use any
time spaces between your packets. This
is a more efficient system, as a circuit
does not need to be kept open. This
system is referred to as packet switching.
So if your e-mail is being chopped
up into small packets, how does the
system know what to do with them?
Each packet contains an address that
tells the router what its final destination
is. The sending computer sends the
packet off to a router and then goes on
to its next operation. The router selects
a path to another router and sends the
packet off. This process continues to
the destination computer. At the
destination, the receiving computer
assembles the packets based on the
information contained in each packet.
So what does this have to do with
Internet phones? Very simple. VoIP
uses the packet switching technology
to transmit your call. The digitization
of your voice occurs either through your
sound card or a device known as an
analog telephone adapter (ATA). There
are also Internet phones that connect
directly to a network router and handle
the conversion process. The voice
packets that result from these various
adapters are routed over the Internet in
the same way as data packets. When
you make a phone call, there is always
dead space when no one is talking. With
the packet system, other data packets
from other sources are being transmitted
over the Internet, making maximum use
of its capacity.
In the early days of VoIP, sound
quality was poor, and the method of
operation more like using a walkie-
talkie. Today’s equipment is vastly
improved. Sound quality on many VoIP
systems is the equivalent of that found
in the PSTN. Depending on the system
you are using, you can dial any number,
and your call will be routed over the
Internet. In such a system, you and the
party you called won’t see any
difference in operation or sound from
that of the PSTN.
So why would you be interested in
using an Internet phone instead of your
current local/long distance PSTN
service? One big factor for many people
is cost. The cost of Internet service
ranges from free to $25/month (more in
some cases) for unlimited calls. In
addition, many of the VoIP services
offer features that cost you extra through
your local phone company. It is not
unusual for a VoIP provider to include
Caller ID, Call waiting, Call transfer,
call forwarding, voicemail, and three
way calling as part of the basic price.
Now let’s look at some of the
providers and their services. Skype
<
http://www.skype.com> offers a free