Lecture Notes: Power Over Ethernet (PoE)

Introduction to PoE

• Definition: Power over Ethernet (PoE) allows a single cable to provide both data connection and electrical power to devices.
• Example: An IP phone requires both a power connection and an internet connection, both of which can be accomplished via PoE.

History and Origin

• Cisco's Contribution: Cisco invented the concept, originally naming it "Cisco Inline Power" in 2000.
• First Standard: In 2003, IEEE ratified the first PoE standard, 802.3af, allowing 15.4 watts of power.

Technical Explanation

• PoE Components:
  • PSE (Power Sourcing Equipment): The device providing power, like a switch.
  • PD (Powered Device): The device receiving power, like an IP phone.
• Initial PoE Method: Utilized unused wires in Ethernet cables for transmitting power.

Evolution of PoE Standards

• 802.3af (Type 1 PoE): 15.4 Watts, supports various equipment beyond Cisco.
• 802.3at (PoE Plus, Type 2 PoE): Introduced in 2009, providing 30 Watts.
• Cisco UPOE and 802.3bt (Type 3 and 4 PoE):
  • Introduced more power, 60 Watts for Type 3, and 90 Watts for Type 4.
  • Type 4 PoE can power larger devices like small computers, LED lighting, and HVAC systems.

Why PoE is Important

• Convenience: Reduces the need for separate power and data cables, easing installation and reducing costs.
• Flexibility: Allows easy relocation of devices without electricians.

Types of PoE

• Active PoE: Negotiates the power needs with the device, ensures appropriate power supply.
• Passive PoE: Always delivers power, lacks negotiation, may not be safe for all devices.

Protocols for Power Negotiation

• CDP (Cisco Discovery Protocol): Cisco's proprietary protocol for power negotiation.
• LLDP (Link Layer Discovery Protocol): Industry-standard protocol used for power negotiation.

Practical Application and Example

• Cisco CLI Demonstration: Example with Cisco switch CLI showcasing how devices are powered and managed.
• Real-world Implications: Challenges such as managing power limits on switches with many ports.

Hands-On Experience

• Cisco Packet Tracer: Used for simulating PoE installations and testing configurations.
• Real-world Devices: Demonstrated with Cisco phones and access points.

Important Considerations

• Power Management: Understanding available power and managing it across devices and ports is crucial.
• Technical Standards: Remember the key standards (802.3af, 802.3at, 802.3bt) and their capabilities.

Conclusion

• Future of PoE: PoE technology continues to evolve, expanding into more areas like computing and building infrastructure.
• Resources: Recommendation to use Boson software for further study and exam preparation.

Bonus Question and Summary

• Practice Exam: A question from Boson's practice exams summarized the implications of power limits on devices.
• Key Insight: Understanding the error state when a device draws more power than allocated.