NC-LINK TELL YOU 6 THINGS YOU SHOULD KNOW

ABOUT POE FOR IP CAMERA SYSTEM

Since the rapid development of network video

surveillance, technical barriers are getting higher and

higher, manufacturers offer technical support is also

becoming comprehensive and systematic. John Wangis a

sales representative in video surveillance industry for

several years, everyday exchanges ideas with security

integrators. In the exchange of technology, integrators and

installers often feel confused on Power over Ethernet (PoE)

problems, John feel the importance of PoE technology,

herein, John invited a PoE expert to provide

comprehensive information about PoE.

#1 What's Power over Ethernet (PoE)?

PoE stands for Power over Ethernet, it's a technology that

transmits both data and power supply simultaneously to

network devices (such as VoIP phones, Wireless AP,

network camera etc) without changing existing Cat.5 cable

network structure. PoE allows you to supply power to a

networking device using the same cable that transmits the

data, which in turn, greatly reduce the cost of installation

and maintenance.

A complete PoE system includes Power Sourcing

Equipment (PSE) and Powered Device (PD) two parts.

Power Sourcing Equipment (PSE): The equipment

supports PoE function such as PoE switch, PoE injector

(midspan) etc.

Powered Device (PD): IP/network cameras in video

surveillance system.

Note: Currently, PoE technology has two standards

-IEEE802.3AF and 802.3AT

#2 Is PoE technology reliable?

On technical perspective, PoE technology has been

developed for many years, now PoE technology is in

mature stage. However, current video surveillance market

faces cost pressure, the quality of selected PoE switch and

Cat5 cable is too poor, or the project design is

unreasonable, may result in the maintenance workload of

PoE project is huge, so integrators hold the common view

that PoE technology is not stable.

For network video surveillance projects, different from

common network cabling, data transmission is huge,

power consumption is high, additionally requires 24/7

days continuous working, choosing high quality PoE

device and cable can ensure the reliability of system.

#3 What's the advantage of PoE?

1. Simple cabling, reduce installation cost

Centralized power supply, one network cable can transmit

data and power supply, PoE enables network devices no

longer require extra power supply, greatly reduce the

installation cost and time.

2. Safe and convenient

Power Sourcing Equipment only provides power supply to

PoE-enabled devices. For example, PoE switch only

transmit power supply when it detects the connection of

PoE-enabled devices. This can avoid the risk of leakage.

Users can mix use existing non-PoE device and

PoE-enabled devices, both of them can co-exist.

3. Convenient for maintenance

Similar to data transmission, PoE can be managed

through Simple Network Management Protocol (SNMP).

This function can offer shut down at night, remote reset

etc functions.

Simple Network Management Protocol (SNMP) is a

popular protocol for network management. It is used for

collecting information from, and configuring, network

devices, such as servers, printers, hubs, switches, and

routers on an Internet Protocol (IP) network.

#4 Possible problems or disadvantages of PoE?

1. Power insufficient, powered device can't boot: 802.3af

PoE standard maximum output power is below 15.4W, this

is sufficient to provide power supply for most of IP

cameras. However, this output power is not sufficient for

high power consumption devices such as network PTZ

camera.

2. Centralized risk: Generally, a PoE switch connects to

multiple IP cameras, if PoE network switch encounters

any problems, all IP cameras will stop working.

3. High equipment and maintenance cost: Compared to

other power supplying methods, PoE technology increases

maintenance workload, when considering security and

stability, separate power supply is best.

#5 How to select PoE switch?

1. Power consumption of IP camera: PoE network switch

adopts different standards, the output power is also

different. For example, IEEE802.3af can support powered

devices that don't exceed 15.4W. As cable transmission will

consume power, IEEE802.3af can provide power supply to

powered devices that don't exceed 12.95W. According to

IEEE802.3at standard, IEEE802.3at PoE switch can work

with powered devices that don't exceed 25W.

2. Max. support powered devices: PoE switch has an

important parameter - total power. Under IEEE802.3af

standard, If 24CH PoE switch's total power reaches 370W,

then each ports can get sufficient power (370/15.4=24),

but if based on IEE802.3at standard, each port supports

30W, the PoE switch only can provide power supply to 12

ports (370/30=12).

PoE IEEE 802.3af Technical Specification

3. Required quantity of ports, whether having Optical

Fiber port, or network management, bandwidth

(10/100/1000M).

#6 What's the PoE transmission range? advice on selecting

cable?

PoE transmission range is 100 meters, recommend to use

Cat5 Ethernet cable.

You should be cautious when buying the Ethernet cable

from China. PoE IEEE802.3af standard requires PSE

output power is 15.4W, after 100 meters transmission, the

PD can receive 12.95W power, according to 802.3af

standard current value - 350ma to calculate, the resistance

value of 100 meters Ethernet cable should be

(15.4-12.95W)/350ma = 7 Ohm or (15.5-12.95)/350ma =

7.29 Ohm.

Obviously, standard Cat5 cable can meet this requirement.

but there are many non-standard Ethernet network cables

selling in the market, they are produced not strictly in

accordance with the requirements of the standard network

cable. Non-standard network cable utilizes other materials

such as copper clad steel, copper clad aluminum, copper

coated iron, etc. The resistance of these cables is big, not

suitable for POE power supply. POE power supply must

use oxygen-free copper material, namely, the standard

network cable.