最後更新: 2018-12-18

介紹

 

POE: A single cable to provide both data connection and electric power to devices (802.3)

PoE 一共有兩種制式, 分別是

• PoE   (Type 1) [802.3af]     # 舊
• PoE+ (Type 2) [802.3at]    # 新

某些 switch 會同時支援這兩種制式

縮寫

• PD: powered device (AP, Cam ...)
• PSE: power sourcing equipment (PoE 火牛)

目錄

• Classification
• 802.3af (POE)
• Passive PoE
• 802.3at (PoE+)
• Hardware

 

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Classification

 

# class from 0-4 based on how much power they require.

Classification follows the signature detection stage, and is an optional process.  

If a PD displays a classification signature, it lets the PSE know how much power it requires to operate, as one of three power classes.

Class 1    

Max device power: 3.84W

Class 2

Max device power: 6.49W

Class 3

Max device power: 12.95W

Class 0

devices have not received a proper class designation from the manufacturer

If a PD does not display a signature, it is class 0 and must be allocated the maximum 12.95 watts

even if the Class 0 device actually uses very little power.

 

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802.3af (POE)

 

Operates at a voltage range of 44-57V and supplies a current of 10-350mA.

Maximum power delivered by PSE: 15.40 W

Power available at PD: 12.95 W

 

Three power class levels (1-3) negotiated by signature

mode A & mode B

POE treats each pair as a single conductor (+/-)

 * 用 2 pairs 供電

mode A

它是用 data pin 供電供 Data

原理

Power is transmitted on the data conductors by applying a common voltage to each pair

Pin

Pin 1,2  # DC +
Pin 3,6  # DC -

 

mode B

Pin

Pin 4(Blue solid)         # DC +
Pin 5(White/blue stripe)  # DC +
Pin 7(White/brown stripe) # DC −
Pin 8(Brown solid)        # DC −

好處: 易 troubleshooting, 因為 power 與 data pin 係分開的

 

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Passive PoE

 

In passive PoE, no negotiation takes place between the two devices,

but instead the known cable layout is used from Standard 802.3af, mode B.

 * The power is "always on", so it's possible to burn out devices if they're not prepared for electrified Ethernet wires

Data + Power => Ingector --- Cable(1,2,3,6 || [+]4,5 [-]7,8) ---> Splitter => Data + Power

Active PoE

Refers to any type of PoE that negotiates the correct voltage between the switch and the PoE-powered device.

Detection:

PoE negotiation is comprised of three stages: discovery, classification and operation.

discovery phase

PSE leaves the Ethernet port unpowered and periodically checks with small voltage

classification

• Hardware-based classification
• Software-based LLDP classification

Hardware-based

PSE sends a single voltage impulse to the PD, reads the current value on the wire,
 checks what PoE class this current value corresponds to, and provides power accordingly.

• Class 0: 0~4 mA
• Class 1: 9~12 mA
• Class 2: 17~20 mA
• Class 3: 26~30 mA

operation

PD receives sufficient power from PSE

 

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802.3at (PoE+)

 

Four power class levels (1-4) negotiated by signature

Supply Voltage: 50V ~ 57V

Supply current: 10-600mA

Maximum power delivered by PSE: 30.0 W

Power available at PD: 25.50 W

 

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802.3bt (PoE++) [4PPoE]

 

 

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Hardware

 

Switch: TL-SF1005LP

• 802.3af
• 5-Port 10/100Mbps(PoE Port x 4)
• Priority Mode (on/off)
  (ensures high priority of ports 1–2 to guarantee the quality of sensitive application)
• 15.4 W on each PoE port. The total 41 W PoE power budget
• Extend mode (on/off)
   * the PoE transmission distance reaches up to 250 m
   * Extended is 10 Mbps/port
• Intelligent Power Management
   * When total power consumption exceeds 41 W,
      the intelligent power management will cut the lower priority port power.
   * PoE Max LED

Switch: TL-SF1005P V2

• 802.3af/at
• 5-Port 10/100Mbps(PoE+ ports x 4)
• 30 W for each PoE port (The total 67 W)
• Priority Mode
• Extend Mode