MaximumPC 2007 01

A

ll this talk of Voice over Internet

Protocol (VoIP), broadband phone, digi-

tal voice, computer telephony, and the like

is enough to leave Ma Bell spinning in her

anti-trustifi ed grave. Although each of these

terms is merely a different way to describe

the technology that makes Internet phone

calls a reality, we can hardly assuage her

concern over the whole concept.

VoIP, as it’s most commonly known,

is here to stay. It’s gaining popularity, it’s

growing more sophisticated, and it most

surely will continue to challenge POTS

(plain old telephone service) in the months

and years ahead.

Just how big has VoIP become in the

overall telephone market? Prominent VoIP

purveyor Skype claims almost 300 million

downloads of its eponymous free software,

and Skype -centric blogs throw around mile-

stones such as a purported recent peak of

8 million concurrent users.

Skype’s much-hyped competitor Vonage

says it reached 2 million paid subscriber

lines in September of 2006. Does this mean

hundreds of millions of people have dumped

their traditional telephone service in favor

of the Internet variety? Not on your life, but

fi gures such as this certainly give Ma and

all her baby Bells pause. The question isn’t

whether VoIP will eventually kill off traditional

telephone technology, but when.

VoIP isn’t merely a new face on ancient

POTS technology; it’s a truly different con-

cept based on the more effi cient commu-

nication protocol upon which the Internet

functions. Comparing the two methods

fundamentally boils down to comparing these

two concepts.

PATH OF LEAST RESISTANCE

When you place any telephone call, you

initiate a series of events that begins with

the digitizing of your speech. Your voice’s

waveforms are captured via an analog-to-

digital conversion process at 8,000 sam-

ples per second; that signal is compressed

and sent on its way. The opposite process

occurs at the receiving end: the digital

sample is converted back into analog. It’s

how that data moves across the Internet

that distinguishes POTS from VoIP.

POTS uses a technique known as cir-

cuit switching. When this type of a call is

placed, a direct path is opened between

the calling and receiving telephones. The

delay you sometimes experience when

placing calls over long distances is sim-

ply the telephone system hunting for that

direct path.

Once established, this two-way cir-

cuit becomes exclusive to that call. Even

though just half the connection is typically

utilized at any one time (because one per-

son is listening while the other is speaking);

and even during periods of silence, when

no one is speaking, the circuit remains

open until one of the parties hangs up and

breaks the connection. Callers on a circuit-

switching network essentially “rent” their

own private data highway for the duration

of their conversation.

Circuit-switching technology is reliable,

virtually error-free, and once the connec-

tion is established, fast. It’s also inef-

fi cient—and that’s not a good thing when

you consider that the standard telephone

system is already taxed to the max.

BREAK IT DOWN

Data moves over the Internet using

packet-switching technology and is much

more effi cient than circuit switching, so it’s

understandable that VoIP would use the

same protocol. Packet switching dynami-

cally allocates bandwidth, so it’s con-

sumed only when it’s needed: If no data is

being sent, because one or neither party

is speaking, no bandwidth is consumed.

When data does need to be transmitted,

the sending computer chops it up into

small chunks known as packets.

Each packet represents less than

100ms of audio content encoded in hun-

dreds or low thousands of bytes. The

packets are then transported via the fast-

est route available at the time. Using pack-

et switching, numerous simultaneous calls

consume less bandwidth than a single call

initiated using circuit switching.

Once these packets arrive on the

Internet, they appear and are treated no

differently than the packets representing

video, photographs, or email zooming

through the Internet’s pipelines—which

White Paper: Voice over Internet Protocol

HOW IT WORKS

Using VoIP technology, you can even call old-fashioned telephones connected to the phone company’s network. Your call will start out as basic

Internet traffi c, and then switch over to the phone company’s network before it reaches your caller.

PHONE

COMPANY

NETWORK

POTS

Plain old telephone

service

Internet-based telephone The VoIP-to-POTS hookup

service has come of

age—it isn’t just for

über-geeks and any more.

BY GORD GOBLE

Regular

phone

Internet phone adapter

Regular

phone

Cell phone

VoIP

phone

VoIP

phone

INTERNET

r & d BREAKING DOWN TECH —PRESENT AND FUTURE

60 MAXIMUMPC JANUARY 2007

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