June 2005
Intermediate to advanced
502 pages
21h 48m
English
Content preview from Switching to VoIP
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Disaster Survivability
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313
Unlike analog phones on the PSTN, VoIP systems don’t get their
power from the PSTN. VoIP systems will fail during power outages
unless they have adequate backup power.
Multiphase power
Most small offices and residences receive their AC power in the form of a single 120/
240-volt connection. This connection feeds a circuit-breaker block that distributes
individually limited power circuits throughout the premises. When the power fails at
the breaker block, the power fails for the entire premises.
But when power is delivered in multiphase, it can create redundancy. Multi-phase
power means that the same connection to the electric company can deliver two or
three AC supplies to the subscriber’s premises. The supplies are connected to sec-
tions of the breaker block or to different breaker blocks. So, when a single phase
fails, the other phases are still intact, and equipment on the failed phase can be
moved to them. This won’t eliminate all failures, but it can protect you against cer-
tain kinds of failures that occur within the electric company’s facilities.
Uninterruptible power supplies
In order to survive a power failure, all of your network equipment must remain run-
ning—switches in phone closets, servers at the data center, and IP phones them-
selves. This ...
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.