Power over Ethernet (PoE) and Network Connectivity

Introduction to PoE

• Power over Ethernet (PoE) allows power to be supplied over the same cable used for data transmission.
• Simplifies installation by eliminating the need for separate power cables.

PoE Power Sources

• End Span: Power is supplied directly by a PoE switch.
• Mid Span: A separate device (injector) provides power between a non-PoE switch and the PoE device.

PoE Standards

1. Original PoE

   • 15.4 watts of DC power output.
   • 350 milliamp maximum current.
   • Suitable for small devices like simple telephones or small access points.

2. PoE+ (Plus)

   • 25.5 watts DC power.
   • 600 milliamp maximum current.
   • Used for larger devices like bigger telephones and cameras.

3. PoE++ (Plus Plus)

   • Supports up to 51 watts at 600 milliamps, or 71.3 watts at 960 milliamps.
   • Suitable for large devices like laptops or advanced cameras (pan, tilt, zoom).
   • Supports higher Ethernet standards (2.5Gbps, 5Gbps, 10Gbps).

Compatibility Considerations

• Ensure device compatibility with PoE standards supported by the switch.
• Check switch specifications for PoE support across interfaces (e.g., PoE, PoE+, PoE++ support).
• Calculate maximum PoE power load to ensure it does not exceed switch capacity.

Transceivers and Network Connections

• Importance of using the correct transceiver for specific connections.
• Fiber transceivers must match the fiber type (e.g., 850nm, 1310nm).
• Mismatched transceivers lead to signal loss, errors, or reduced network efficiency.
• Transceiver markings are small and may require removal for inspection.

Signal and Power Budgeting

• Power Budget Calculation

  • Measure transmitted power in decibels per milliwatt (dBm).
  • Consider media length and connection loss.
  • Calculate expected signal loss and subtract from transmitted power.

• Sensitivity Levels

  • Devices have sensitivity levels that indicate the minimum signal needed for proper reception.
  • Sensitivity is expressed as a negative dBm value (e.g., −17 dBm).

Evaluating Signal Strength

• Compare received power to sensitivity levels to ensure sufficient signal strength.
• If received power is greater than sensitivity, signal is strong enough.
• Example: If the power budget results in −17 dBm or higher, the signal is adequate.
• A power budget resulting in −20 dBm indicates insufficient signal strength.

Conclusion

• Proper PoE implementation and transceiver use are crucial for network efficiency.
• Correct calculations and compatibility checks prevent connectivity issues.