In my previous post we covered the configuration of some basic layer 3 services for my Ruckus ICX 7150-C12P which is going into my home laboratory. But now we actually want to start plugging things in and turning APs ON! In this post I dig into the details of working with PoE on the ICX Switches.
When I started this post I really thought it would be quite trivial, at best a purely supplemental post. Turns out, I was a little wrong, this really does deserve its place as a standalone post!
A Quick Refresher
Yes, I know, you’ve been working in this field for ages, or are just starting out, and either way, you, like me, think that you know pretty much everything there is to know about boring old PoE. Regardless, let’s revise a little:
Terminology
The PSE is the Power Sourcing Equipment, and is located on the switch ethernet interface / PoE injector “out” interface. The PD is the Powered Device, and is located on the other end of the Cat5e/Cat6 ethernet cable.
Power at the PSE vs Power at the PD
The Ethernet cable is made of copper wires and has a certain resistance and impedance specified by the standard to which it adheres (Cat 6 characteristics here). This means that not all power at the PSE will reach the PD. We must accommodate power losses for up to 100m of cable.
PoE Standards
802.3af allows a maximum of 15.4 Watts at the PSE / 12.95 Watts at the PD. 802.3at allows a maximum of 30 Watts at the PSE / 25.5 Watts at the PD. You may see 60 Watt “Ultra Power PoE” or “PoE++” injectors or similar, these use a modified version of 802.3at but are typically not standardized. Power over HDBaseT (PoH) allows a maximum of 100 Watts at the PSE. PoH enables the PD to detect cable length/resistance and to maximize power draw whilst remaining below the limits of 100 Watts at the PSE. There is also a newer standard called 802.3bt which aims to update the 802.3af/802.3at standards and allow operation with up to 90 Watts of power at the PSE / 71 Watts at the PD. The latest timeline states it will be released as a standard in 2018.
For more on the various PoE standards check out the wikipedia article which is pretty useful!
Which Twisted Pairs Carry Power?
Ethernet cables have 4 twisted-pairs of copper wire. A 100/1000 Ethernet link using 802.3af or 802.3at use only 2 twisted pairs in the Cat5e / Cat6 cable to transfer power and data, and 2 twisted pairs to transfer data only. Originally in the days of 10/100 Ethernet, only 2 twisted pairs were used for data transfer. The decision of which two pairs to use for power transfer depended on the type of device injecting the power. For an end-span device like a PoE Switch, power is transferred on the same pairs used for data transfer (Pins 1, 2, 3 , & 6) called Mode A. For a mid-span device like a PoE injector, power is injected on the unused twisted pairs (pins 4, 5, 7, & 8) called Mode B. When selecting 802.3af/at compatible devices, be aware that they typically only support Mode B operation. 802.3af/at compliant devices however support BOTH Mode A and Mode B. By comparison, PoH and 802.3bt both use 4 twisted pairs to transfer power and data. The 60 Watt “Ultra Power PoE” injectors use all 4 twisted pairs to deliver power and data. You will sometimes see 60 Watt “Ultra Power PoE” injectors or similar, these use all 4 twisted pairs to deliver power and data, but are typically not standardized.
If you want to dig into this specific hole a bit more:
- What is PoE Mode A and Mode B?
- Compatible vs Compliant PoE Devices
- IEEE introduction to PoE 802.3af / 802.3at
What Can I Power with PoE?
All the things that you can power with PoE. And I am sure there is more, just keep looking.
Ruckus ICX7150 PoE Capabilities
First, let’s just talk quickly about the main PoE capabilities of the Ruckus ICX Switching range when it comes
802.3at Power – For Everyone
All Ruckus ICX switches are capable of 802.3at power at the PSE. The number of ports that can handle simultaneous 802.3at power depends on the power budget of the switch. A summary of the limits on these switches (you can check it in the datasheets yourself) is presented in the table below.
| Model | PoE+ Ports | PoH Ports | PoE Power Budget | Simultaneous | ||
| 802.3af Ports | 802.3at Ports | PoH ports | ||||
| ICX7150-C12P | 12 | – | 124 Watts | 8 | 4 | – |
| ICX7150-24P | 24 | – | 370 Watts | 24 | 12 | – |
| ICX7150-48P | 48 | – | 370 Watts | 24 | 12 | – |
| ICX7150-48PF | 48 | – | 740 Watts | 48 | 24 | – |
| ICX7150-48ZP | 32 | 16 | 1480 Watts (2 PSU) | 48 | 48 (2 PSU) |
16 (2 PSU) |
As you can see from the table, the ICX7150-C12P I am using in the lab at least gets me over the hump on 802.3at for up to four APs.
Power by Class
PoE devices are separated into classes by how much power they require. You can configure a port to only support a specific class of power. For instance:
RobLab_7150_C12P_1(config)#inline power ethernet 1/1/12 power-by-class 2
This command limits the port to operating on class 2 only (3.84 to 6.49 Watts at the PD, 7 Watts at the PSE).
Power Adjust Class
You can also adjust the amount of power being fed to devices that belong to a certain class. For instance, consider a batch of access points that should work in class 0 (0 to 12.95 Watts), but for some reason end up drawing just a bit more than that at boot up or some other scenario. In these cases often a switch will simply shut the port down! Well you can work around that with this command, shown in the example below:
RobLab_7150_C12P_1(config)#inline power adjust class 0
delta delta power to be allocated over the LLDP request for the PD class
minimum Minimum power to be allocated for the PD class
RobLab_7150_C12P_1(config)#inline power adjust class 0 delta 1000
RobLab_7150_C12P_1(config)#inline power adjust class 0 minimum 16400
Power Limiting
In some scenarios you may have to budget your power quite carefully. The last thing you want is someone plugging in a new PoE+ or PoH capable device and exceeding the PoE power budget of the switch. To protect yourself against this possibility, you can set power limits on specific PoE interfaces of the switch. Limiting the maximum power budget on specific interfaces will prove useful in scenarios where you are using equipment that is capable of running on multiple PoE standards like the Ruckus R720 / R710 / R610 APs. Below is a table of recommended PoE power limits for different Ruckus AP models that I have gathered from the product data sheets. In my home laboratory, I know that the maximum power draw for the mesh AP into my home network should be no more than 15.4 watts at the switch.
| Ruckus AP Model | 802.3af PoE (15.4 Watts) | 802.3at PoE+ (30 Watts) | PoH Power (< 90 Watts) |
| H510 | PoE Output 4 Watts Peak 9.2 Watts (no PoE out) Typical 7.3 Watts |
Recommended PoE Output 12.95 Watts |
– |
| R310 | Recommended Peak 11 Watts Typical 7.8 Watts |
– | – |
| R510 | Recommended Peak 12.6 Watts Typical 7.5 Watts |
– | – |
| R610 | 2 Chain Transmit (2.4 & 5 GHz) 3 Chain Receive 18dBm / chain (2.4 & 5GHz) USB Disabled Secondary Ethernet Disabled |
Recommended Peak 18.8 Watts Typical 10.4 Watts |
– |
| R710 | 2 chain Transmit (2.4GHz only) 4 chain Receive 16dBm/Chain (2.4GHz Only) USB Disabled Secondary Ethernet Disabled |
Recommended |
– |
| R720 | 1 Chain Transmit (2.4 & 5GHz) 4 Chain Receive 18dBm/chain 2.4GHz 20dBm/chain 5GHz USB Disabled Secondary Ethernet Disabled |
4 Chain Transmit 4 Chain Receive 18dBm/chain 2.4GHz 20dBm/chain 5GHz USB Disabled Secondary Ethernet Disabled |
Recommended |
| T300 | Recommended Peak 11 Watts Typical 7.5 Watts |
– | – |
| T610 |
2 Chain Transmit |
Recommended Peak 25 Watts (With USB) Typical 10.4 Watts (No USB) |
– |
| T710 | – | Recommended Peak 25 Watts Typical 10.4 Watts (PoE Output Disabled) |
802.3at PoE Output enabled. Peak 60 Watts. |
Power Prioritization
Another tool in your arsenal is power prioritization. This is especially useful if you are running 2 PSUs in a switch and need to plan for a failure of one of the PSU’s. Or what about if you are uncertain of the power requirements of the PoE devices that will be connected? When the power budget of the switch is exceeded, what do you keep running and what do you kill? In my laboratory environment, I want to make sure that the mesh AP into the home network stays up in case anything maxes out the power budget of the switch. Priority levels can be set between 1 (highest) and 3 (lowest), all interfaces are set to priority 3 by default.
Decoupled PoE & Data Link Operations
Heads up WLAN people, this one is for you! There are some scenarios where editing an Ethernet interface’s settings can cause power delivery on those interfaces to be affected. Scenarios include adding / removing a PSE port from a LAG, adding / removing a tagged PSE port from a VLAN or VLAN group, or enabling / disabling the Ethernet port. In these scenarios, you may want the data link to go up and down, but not the power!
OverDrive
This a VERY cool feature. Overdrive allows Class 0 & Class 4 powered devices to negotiate for more than 30 Watts using LLDP on a normal PoE+ port! For example, a Ruckus R720 requires about 35 Watts (Peak) to enable all of its features. The Overdrive feature allows a powered device (like an AP) to request more than 30 Watts from a standard 802.3at, PoE+ capable PSE, up to the maximum rated power for the PSE. This feature is available on the PoE+ ports of the switches in the below table:
| Switch Model | Max PSE Power (PoE+) |
| ICX 7150-48ZP | 47 Watts |
| ICX7450-24P | 42 Watts |
| ICX7450-32ZP | 35 Watts |
| ICX7450-48P | 35 Watts |
Notes:
- PoE overdrive was only introduced in 08.0.61, make sure to update your PoE firmware on the switch to ensure this feature works!
- PoE Overdrive is only supported on PoE+ / PoH capable Ports.
- Maximum power output is limited by the hardware limitation of the PSE on the switch port.
- Overdrive is only valid on Ports that use 2 pairs for power, or on 4-pair ports configured for 2-pair operation. i.e Overdrive is supported by default on PoE+ ports, but you will need to configure any PoH ports to use only 2 twisted pairs for power and data.
Inline Power on Secondary LAG Ports
You can also configure the switch to deliver power over multiple interfaces that make up a LAG. For example you can add several ethernet interfaces to a LAG and supply power over one, two or every one of them. This is a useful feature if you require redundant power to some device or perhaps a large amount of power delivered, for example a 200 Watt digital signage display?
—
Thats all for now!
(PS: have fun reading the command guide!)