Hardware Autopsy
means the packets could arrive at their
destination in a disorganized jumble.
To account for this, each packet con-
tains a header in addition to its digitized-
voice payload. The header is less than 100
bytes of data that describes where the
packet originated, where it’s going, and
how and where it should appear in relation
to the other packets arriving from the same
origin. The receiving device reads these
headers, organizes the packets into the
appropriate order, and converts the digital
payload back into an analog audio signal.
There are downsides to VoIP—it’s not
the ultimate panacea for those whose jobs
or lifestyles entail frequent telephone use.
VoIP is less impervious to service interrup-
tions than the conventional phone system,
for example. Because your VoIP hardware
depends on electrical power from utility
companies, its vulnerable to power out-
ages (conventional copper-wire phone lines
carry a small amount of electricity that’s
independent of the power grid). Packet loss
and latency can also effect VoIP quality and
reliability. Lastly, not all VoIP services offer
E911 service (an FCC-mandated means of
connecting to the 911 emergency-response
system); and those that do can’t connect
you to a 911 operator if your power is out
during an emergency.SERVICE PROVIDERS
There are a number of ways to jump on
the VoIP bandwagon, but peer-to-peer is
the easiest and least expensive. Based on
the same principles as P2P fi le-sharing
apps, P2P VoIP asks only that you have
a broadband Internet connection and a
mic-equipped headset. Skype , the most
celebrated P2P VoIP solution, permits free
computer-to-computer calling between
Skype users anywhere in the world. Skype
charges by the minute for calls made to
traditional landline phones or cell phones.
The company also earns revenue from
value-added products and services,
including voice mail, hardware sales, and
incoming calls originating on landlines.
Vonage is the leading commercial VoIP
service provider and relies on your conven-
tional phone, which you plug into an ana-
log phone adapter. The only freebies you’ll
fi nd here are calls from one Vonage mem-
ber to another, although both members
must fi rst sign up for one of the company’s
paid services. But if you have typical call-
ing habits, you might fi nd Vonage to be
a cost-effective alternative to traditional
phone service; moreover, you get to keep
your current telephone number—some-
thing Skype can’t yet offer.JANUARY 2007 MAXIMUMPC 61
White Paper: Voice over Internet Protocol
LOGIC BOARD: This printed circuit board con-
tains the sensors for all of the pad’s digital buttons,
twin analog triggers, and twin analog thumbsticks.
The circuit board houses an intricate network of
printed wires that connect to contact terminals,
where button presses are registered.Xbox 360
Gamepad for Windows
There’s a bunch of circuits, analog and digital controls, and even a couple of motors under
the hood of the Xbox 360 gamepad. We put one under the knife to show you how it all works.Gamepad for WindowsGamepad for Windows
LOGIC BOARD: This printed circuit board con-
tains the sensors for all of the pad’s digital buttons,
twin analog triggers, and twin analog thumbsticks.
The circuit board houses an intricate network of
printed wires that connect to contact terminals,the hood of the Xbox 360 gamepad. We put one under the knife to show you how it all works.
r & d BREAKING DOWN TECH —PRESENT AND FUTURE
60 MAXIMUMPC JANUARY 2007
FORCE-FEEDBACK MOTORS: The 360 case houses twin motors in the handles
that deliver the “rumble” effect you feel in supported games. Each motor vibrates a
crescent-shaped weight with variable frequency, replicating the recoil of a shotgun
blast in Doom 3 or a bone-crushing tackle in Madden 2007.ANALOG
THUMBSTICKS:
The 360 pad has
two analog thumb-
sticks that are
extremely sensitive
and can provide
very subtle input
data. The sticks
are analog rather
than digital because
this allows the pad
to transmit small
changes in each
stick’s position to
the PC more accu-
rately. The same
goes for the twin
analog triggers on
the other side of the
pad (not shown). An
onboard chip trans-
lates the analog
input data to digital
before it is trans-
mitted to the PC,
off-loading work
from the host CPU
and providing more
precise in-game
controls.BUTTON SENSORS: These serve as the contact
points for the pad’s four top-mounted buttons and
eight-way directional pad. Pressing any of the but-
tons, or the d-pad, essentially completes an electri-
cal circuit which the host PC then recognizes as the
appropriate in-game command: fire, duck, punch,
etc. How long you hold down each button can
provide different input feedback. For example, tap
the “x” button and you’ll lob a soft pass in Madden ;
hold it down to fire a bullet pass.