Ethernet Switch Manages Power Over Ethernet Resources

Testing systems in the lab is often a challenge since I do not always have the latest and greatest tools. One technology I have been wanting to do more with is Power over Ethernet (PoE). This allows an Ethernet switch to provide power to devices thereby eliminating the power brick often found alongside access points and IP telephones.

I have been using Supermicro's (Super Micro Computer) SSE-G2252P Gigabit Ethernet, layer 2, non-blocking switch (Fig. 1). The smart, 1U switch has 48 regular ports with PoE support plus four SFP ports. I'll get to the more detailed specs and web-based management later.


Figure 1. Supermicro's SSE-G2252P Gigabit Ethernet switch has 48 ports that support Power over Ethernet plus 4 SFP ports.

The first PoE standard was IEEE 802.3af-2003. It defined support of up to 15.4W. This was in the form of 44 V DC at 350 mA. Devices should only count on 12.95W due to cable losses.

PoE plus (PoE+) is the newer IEEE 802.3at-2009 standard. It ups the limit to 25.5W on two wire pairs (1/2 and 3/6). Some switch vendors provide more power but use a non-standard 4 pair connections

Supermicro's switch provides fine tuned power distribution via its web-based interface (Fig. 2). It can provide up to 30W per port but the total amount of power is limited to 400W. This means it can deliver 8.5W to all ports at the same time or 15.4W to just over half. There is independent circuit overload per port. There is a status LED per port for PoE.


Figure 2. Supermicro's Power over Ethernet management screen shows the priority groups as well as the consumption on a per port basis.

Supermicro also provides class-based priority allocation so high priority devices can be guaranteed power. Allocations can also be scheduled. This can be handy if some devices are going to be use during a specific time perioid. The web interface also provides information on consumption allowing a network manager to see how the network is operating.

One reason I wanted to check out the switch was to use devices other than the usual PoE devices like access points and IP telephones. For example, I have three Ethernet-based debug modules for ZigBee development. This is very handy because these ZigBee platforms can be plugged into any handy Ethernet socket and be powered directly from the Ethernet cable.

Some development kits also take advantage of PoE. These are typically platforms targeting applications like access points and IP telephones but other devices such as wireless gateways and IP cameras are in the mix. In this case, Supermicro's switch comes in handy because developers can now test their designs. It can be used to provide different power levels.

A lab can provide more detailed tracking but this can be a challenge if the number of devices increases past one. Likewise, putting devices in diverse locations. This might be a challenge in the lab with conventional equipment. Distributing test equipment to remote locations can be taxing as well.

Of course, the SSE-G2252P is first and foremost a gigabit Ethernet switch. The SSE-G2252 is the same switch but without PoE support (see SSE-G2252-G2252P specifications).

The switches support up to 256 VLANs in addition to Jumbe Frame support up to 9 Kbytes. They also have quality of service (QoS) support with 4 queues per port with strict and deficit weighted round robin priority scheduling. The QoS support also handles traffic shaping and ingress/egress metering.

I started with the command line interface that is available via a dedicated serial port. I set a fixed IP address although network managers may want to handle this via DHCP and the MAC address. I also checked out the web-based (Fig. 3) and SNMP-based management. The web-based interface includes context sensitive, online help. The online interface was easy to use but the PDF manual is still handy for finding some configuration details.


Figure 3. Supermicro's web-based interface allows network managers to configure the system as well as monitor system operation like CPU Load.

Overall Supermicro's SSE-G2252P Gigabit Ethernet switch has proven to be very flexible. I only use half a dozen PoE devices right now but I expect more to start cropping up now that I have a way to deliver power. My prior PoE box had only 8 ports, no management support, and limited power output. The SSE-G2252P targets the enterprise space and does a good job from both a switch standpoint as well as a power distribution standpoint.

TAGS: Ethernet
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