Understanding Power Over Ethernet

Sa karaniwang network, we normally connect our end devices like pc, printers, scanners to our switches for “data” connection. We connect the LAN cable to its interface card and connect their power to a power outlet. That’s what normal switches do.

Today, meron na tayong mga tinatawag na POE switches which is capable to produce or supply power over its ethernet port.

Pano nangyayari?

Let me explain.

A common/traditional switch for example, will allow our end devices to connect to the network via its ethernet ports. Katulad nga ng nabanggit natin like desktops and printers or CCTVs. Then itong mga CCTV na ito ay naka-connect or nakasak-sak din to its own power supply. Siyempre para gumana.

It looks something like this.

Now, we have new kind of switches where in it can also give or supply power or electrical energy via its ethernet port. Ibig sabihin, it uses its port and the ethernet cables to supply power to the end devices.

Pero siyempre, hindi naman desktop or printer or ibang devices na kailangan ng mataas na voltage or power. Those other network end devices na maliit lamang mag-consume or mag-require ng electrical power like ip phones and ip camera.

As you can see in our sample image, we have an ip phone and an ip camera connected to our switch.

Normally, ang mga ip camera at ip phone ay kailangan ng electrical power. Pero this time, hindi na ito naka-connect sa power outlet dahil ang switch na natin(a poe switch) na ang nagsu-supply ng power sa mga ito. This is how POE works.

Power over Ethernet or PoE technology transfer electrical power, along with data, to remote devices over standard data cables in an Ethernet network (Cat3/Cat5/Cat5e/Cat6 ). 

Ang original na IEEE 802.3af-2003 standard version ng PoE supplies up to 15.4 watts of DC power (minimum 44 VDC and 350 mA) to each device. Pero only 12.95 watts is assured available for the powered device(PD). At ito ang maganda, hindi ito nakaka-epekto sa data and network performance ng ethernet even if 10/100 or 1000 Mbps link.

Here are some of the development of this PoE standards:

• IEEE 802.3af – 15.4 W (12.95 assured power supplied)
• IEEE 802.3at – 30 W of power supplied
• IEEE 802.3bt – 100W of power supplied

Ang galing di ba?

Imagine we can use the port of the switch for a LAN connection and we can also use it for power connection para sa ating mga devices like ip phones and ip cameras. Or even access point.

Benefits of Power Over Ethernet

As we can see, there are a lot of benefits  PoE can provide sa ating network. Imagine, we’re using a single port of the switch both for ethernet connection and power supply(again ha, for certain devices lang – – 12.95 W is only assured as I shared earlier).

Here are some of its benefits.

1. Installation cost savings – Siyempre hindi na natin kailangan mag-install ng mga power outlet for those end devices na kayang i-support ng ating mga PoE switches. 
2. Simplify installation – Isang cable na lang ang ginagamit natin for LAN connection and power
3. Centralized power backup – We only need to power-up the PoE switch and normally we have a backup power for these devices
4. Save power – hindi nito na-aapektuhan ang non-PoE devices

These are just some of the benefits. Astig di ba?

Power Over Ethernet terminologies

1. PSE (Power Source Equipment) 
   This is the PoE capable switch. It’s basically the “source” of the power. Ang isa sa mga Cisco switch models na PoE capable is: Cisco Catalyst 2960-48PST-L 
   
2. PD (Powered Devices)
   Siyempre ito naman yung mga end devices na naka-connect sa ating switch both for ethernet connection and power. Normal PDs are ip phone, ip camera and access points.

Verifying PoE in Cisco switches

As an administrator, meron tayong option to configure the PoE settings sa ating mga PoE capable(or compliant) switches. Pero take note, this is on and set to auto by default.

To verify we can use the command “show power inline” in our PoE capable switch. It will show the available power and the powered devices connected to it(kung meron) at kung ilang watts ang nagagamit nila.

It will look like this:

As you can see, we have 15.4 watts available from each port (Gigabit port). We can say na this Cisco switch is IEEE 802.3af compliant. Makikita rin natin na naka-set sa “auto” ang bawat ports. This means, it will supply the needed power of the device connected to it automatically(max is 15.4 watts). 

Although we can set or configure each port PoE settings based on the needs, normally it is set to auto to let the switch detect how much power is needed by the powered device. In our course, we will have this configure.

For now, this is the fundamentals of our PoE topic.