Information Technology Reference
In-Depth Information
IOS devices can be configured for NTP using commands, such as the following:
■
clock timezone:
Sets the time zone on IOS devices
■
ntp server:
Configures an IOS device to synchronize its software clock to the specified NTP server
Inline Power: Cisco and 802.3af
Cisco IP phones can be supplied with power in a number of ways, including using
An external power supply unit (a power “brick”):
An external power supply unit provides power directly to a phone from
an electrical socket.
■
Power over Ethernet (PoE) from a switch:
Switches can use PoE to supply power over an Ethernet cable to connected
devices such as IP phones.
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A midspan power injector/inline power patch panel:
A midspan power injector is a device that sits between a switch and
an IP phone and supplies power to the connected phone. An inline power patch panel is a patch panel that sits between a
switch and multiple IP phones and supplies power to those phones.
■
Many Cisco switches can send power over Ethernet cables to connected devices such as Cisco IP phones. There are two methods of
supplying PoE: using a Cisco proprietary method and using the IEEE 802.3af standard. Both the Cisco proprietary method and IEEE
802.3af provide power to connected devices over switch port pins 1, 2, 3, and 6.
Cisco proprietary and IEEE 802.3af methods involve detecting connected devices that require power in slightly different ways. When
using the Cisco proprietary method, a switch sends a Fast Link Pulse (FLP) to the connected device, and the connected device loops
the FLP back to the switch, thereby indicating that it requires power. When using IEEE 802.3af, on the other hand, the switch applies
a voltage (-2.8 to -10 V), and if a resistance of 25K ohm is detected, it supplies power to the connected device.
When using midspan power injectors/inline power patch panels, power is sent to the connected device or devices using pins 4, 5, 6,
and 7.
PoE can be configured on IOS switches that support it using the
power inline
command.
