Traditional telephones were powered through the same cable that carried the voice transmission. Simply plug the phone into the RJ11 jack and the LCD and lights worked and you could make and receive phone calls.

IP telephones operate on the data network. Ethernet data networks were not originally designed to power local devices. The computer was plugged into the power outlet in the wall and the data connection was a separate cable that was connected to the computer room.

As always, industry created new technologies to deal with this new paradigm. There are three options for powering an IP telephone:

1. Power the phone locally using a local power supply (derisively referred to as a wall wart).
   
   Pros: It's a simple cost-effective solution.
   
   Cons: Requires two connections for each phone and increases clutter.
   The local power supply is another point of failure.
   No centralized battery backup for phones.
   
   
2. Replace the existing ethernet switches with new Power Over Ethernet (POE) switches, which deliver power to the phone through the existing ethernet cable.
   
   Pros: Clean installation.
   Battery backup can be provided to all phones from centralized location.
   POE switches have QOS software built-in, prioritizing voice transmissions.
   
   Cons: Not practical if existing switches are a relatively recent investment.
   Can be expensive if IT requires managed switches.
   
   
3. Install devices called power injectors that utilize existing ethernet switches and "add" power to the station cables, thus accomplishing POE.
   
   Pros: Power over Ethernet or PoE technology describes the system to transmit electrical power, along with data, to remote devices over standard twisted pair cable in an Ethernet network. This technology is useful for powering IP telephones, wireless LAN access points, and webcams and other appliances where it would be inconvenient or infeasible to sup ply power separately.