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Please note: I am not asking for specific product reccomendations.

I am in the process of expanding wired ethernet cabling in a building during a remodel. I currently have about 20 runs of CAT6a to various rooms and plan on another 16 to 20 more runs as more of the structure is remodeled. The actual ports will likely be heavily under-utilized, only 10-20% of these network runs will typically be in-use at any given time. Nevertheless, I still plan on installing many runs for future proofing and to avoid needing small 5 or 8 port switches in rooms.

These runs of cables will terminate at a central location in the basement, and will be connected to 1 or 2 network switches with all runs being connected.

My understanding of 802.3az from reading wikipedia is that the switch is able to turn off ports that are not active and thus save electricity. Since I will have a low utilization of connected ports, on the surface, this seems like it would be a big deal.

What I would like to know is if a switch supporting the IEEE 802.3az / Energy Efficient Ethernet standard would be worth the extra cost (over a less efficient switch) for this scenario. I imagine as technology progresses, all switches will support energy efficient features, but currently for those who are budget constrained, an older model switch is significantly cheaper than newer "green" switches.

migrated from serverfault.com Mar 24 '15 at 0:29

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  • How much power could an unused port really use? – joeqwerty Mar 23 '15 at 19:57
  • Exactly. I don't know. Hence the question on whether it's important to have a switch that does this. – cathode Mar 23 '15 at 19:58
  • While it is a sensible thing to get, I don't see why you expect to pay much more, if anything, for an 802.3az-enabled switch. – Andrew Morton Mar 23 '15 at 19:58
  • Refurbished pricing is significantly different for newer, energy efficient switches (some which may not even be available refurbished) versus slightly older models. Both myself and my company utilize refurb equipment to save on capex. Also, is there a reason why this got downvoted with no explanation? I realize it says "home wiring" but the question easily applies to any structured cabling install. And how often do you have 40+ runs of ethernet cabling in a non-professional setting? – cathode Mar 23 '15 at 20:16
  • There is no general rule for this. To answer this, you need to define following items: 1.) which non-802.3az switch you would use, 2.) which 802.3az switch you would use, 3.) cost of each, 4.) power savings in W/hour from using 802.3az switch 5.) cost savings seen by item #4. Then you should have your answer... – jlehtinen Mar 23 '15 at 20:30
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A copper ethernet link without an established link (at least one end disconneccted) uses near-zero power on any switch, even old ones. There simply isn't a complete circuit to transmit energy.

On standard switches, if a 10/100/1000-based-T copper link is up, it basically runs at full power even if no data is being transmitted because of differential signaling.

So EEE only applies to "connected but idle" links I believe, which is a pretty narrow use case, as in general a modern workstation is always doing something on the network in the background. So EEE may be helpful for connected workstations that have gone to sleep overnight but have Wake-on-LAN or similar functionality keeping the link up, but that's about it.

In short: don't worry about it at all, it should be the last feature you consider in a decision.

  • That makes sense. I've learned never to assume anything about the way engineers would design a product. Thanks. – cathode Mar 23 '15 at 20:41
  • I believe one of the original use cases for EEE was to allow links to be sped up or slowed based on need, but I doubt that saves much power in practice, as it requires both endpoints to support it. Or perhaps you could turn down all but one port of say an 8-port LAG overnight when traffic is low. But again, not much savings. You'd save a lot more juice by turning off idle devices and turn them back on if needed. All of our company's fixed workstations have a (user-abortable) shutdown at 6PM to save power. THis breaks the Ethernet link too as we have wake-on-LAN disabled. – rmalayter Mar 23 '15 at 20:46

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