====== CCNA - PoE ======

===== TL;DR =====
PoE lets you send both **data and power** over a single Ethernet cable.
Commonly used for access points, IP cameras and VoIP phones.

===== Key takeaways =====
  * 2 types of PoE : **Active** and **Passive**
  * Active = smart. It negotiates power safely
  * Passive = dumb. It just sends the power
  * Easy, cheap and fast deployment
  * Switch -> **PSE** //(**P**ower **S**ourcing **E**quipment)//
  * **PD** -> //**P**owered **D**evice//
  * 802.3at = very common

===== Standards =====
First big standard was 802.3af (15.4 watts per port). That's **Type 1 PoE**.

A very common standard is **802.3at** aka **PoE+** (30 watts per port). That's **Type 2 PoE**.

Later, Cisco introduced UPOE (Type 3, up to 60 watts per port) then IEEE standardized higher-power PoE with 802.3bt (Type 4, up to 90 watts).

Most of the time, these standards are backward compatible.

===== Active PoE =====
The PSE and the PD talk to each other to negotiate the necessary power.
The negotiation may use protocols such as:
  * CDP //(**C**isco **D**iscovery **P**rotocol)//
  * LLDP //(**L**ink **L**ayer **D**iscovery **P**rotocol)//

===== Useful links =====
  * [[ccna:ethernet|Ethernet]]
  * [[ccna:osi-tcpip|OSI - TCP/IP]]