Information Technology Reference
In-Depth Information
of your wiring infrastructure and exhaust your supply of electrical outlets (because each
inline PoE coupler requires a dedicated plug).
Power
Patch
Panel
V
Inline
Coupler
V
Figure 3-3
Design for Power Patch Panels or Inline Couplers
Powering the IP Phone with a Power Brick
Using a power brick to power a device is so simple that it warrants only brief mention.
Thus, the reason for this section is primarily to mention that most Cisco IP Phones do not
ship with power supplies. Cisco assumes most VoIP network deployments use PoE. If you
have to choose between purchasing power bricks and upgrading your switch infrastruc-
ture, it's wise to check the prices of the power bricks. The average Cisco IP Phone power
brick price is between $30-$40 USD. When pricing out a 48-switchport deployment, pur-
chasing power bricks for all the IP phones may very well be in the same price range as up-
grading the switch infrastructure.
Note:
Some devices exceed the power capabilities of the 802.3af PoE standard. For
example, when you add a sidecar module to a Cisco IP Phone (typically to support more
line buttons), PoE connections can no longer support the device. These devices will need a
power brick adapter.
After the IP phone has received power, it must determine its VLAN assignment. Because
of security risks associated with having data and voice devices on the same network,
Cisco recommends isolating IP phones in VLANs dedicated to voice devices. To under-
stand how to implement this recommendation, let's first review a few key VLAN concepts.
VLAN Review
When VLANs were introduced a number of years ago, the concept was so radical and
beneficial that it was immediately adopted into the industry. Nowadays, it is rare to find
any reasonably sized network that is not using VLANs in some way.
