Catch up on stories from the past week (and beyond) at the Slashdot story archive

 


Forgot your password?
Close
typodupeerror
×
Wireless Networking Hardware

Concerns Over Increased 802.11n Power Usage 72

Posted by CmdrTaco from the omg-my-battery-broke dept.
alphadogg writes "Next-generation 802.11n systems promise to considerably improve WLAN performance. But the processing required for the boost sucks up more power than the older 802.11a/b/g networks. Still, many enterprise-class Wi-Fi vendors claim to deliver full 802.11n capabilities without enterprise customers having to touch their power infrastructures. So what gives?"
This discussion has been archived. No new comments can be posted.

Concerns Over Increased 802.11n Power Usage More

Concerns Over Increased 802.11n Power Usage

Comments Filter:
  • I just skimmed the article, but the power issues seemed to be at the switch. Are they saying that the remote clients aren't affected? I'd be more concerned about sucking even MORE power out of laptops and PDAs than out of an outlet.

    • Re:What about the remote clients? (Score:5, Informative)

      by maird ( 699535 ) on Monday January 28, 2008 @12:00PM (#22209430) Homepage

      Maybe skimming TFA wasn't the best basis for comment. The article mentions no power issue at the client. It's basically saying that:

      • The problem applies to 802.11n wireless access points powered via Ethernet (PoE)
      • The 802.3af PoE standard only permits about 12.95W of power at the cable end where power is required
      • 802.11n devices in current production typically require up to 18W
      • 18 > 12.95
      • Therefore, such 802.11n access points cannot operate at full power (probably limiting their transmit power)
      • Therefore, such 802.11n access points cannot transmit with the same range as a fully powered version
      • Clients are unaffected and can transmit at full power and full range (maybe the AP can't reach them to reply though)
      • The 802.3at PoE standard (when available) will provide up to 30W for devices
      • Likely has nothing to do with transmit power. The devices, I believe, run at 100mW for 2.4Ghz, 250mW for 5Ghz. I don't think they're upping the power any here because of the FCC.
        • The point is that if the CPU and baseband are consuming too much power, an AP can reduce its transmit power to compensate.

          • Re: (Score:3, Funny)

            by dgatwood ( 11270 )

            Uh, no it can't. 18W - 100mW is 17.9W. Even if you cut the transmit power to zero, you're still not going to be able to cut 6W. That's like trying to empty a bathtub with a single bucket without making multiple trips....

            • trying to empty a bathtub with a single bucket without making multiple trips...
              Trivially done.
              Freeze the tub, balance the ice block precariously on the bucket, imply a threat to let it land on pedantic person trotting out something as archaic as math get in the way of your argument.
              It's really not so much what you say as how you say it.
              Body language, man: body language.
    • With only a 5 watt difference would it be possible to use some form of power injector with old systems rather than buy all new PoE switches after 802.3at is released?
      • It is, but then you have an additional mess at the switch location. What is more likely to happen is that those APs using PoE will not be upgraded to .11n until such time as the switches off of which they feed are upgraded. However, this may, in some circumstances, require that power in the room be upgraded, especially if PoE is used on a wide scale.

  • What Gives? Simple. (Score:5, Interesting)

    by TheRaven64 ( 641858 ) on Monday January 28, 2008 @11:52AM (#22209312) Journal
    Enterprise hardware does not use general-purpose CPUs, it uses special-purpose ASICs. These are lower power than general purpose hardware. They are fab'd using a newer process than the older ones, and so use less power per transistor than the old chips. Less power per transistor means more transistors (which means more processing power) per watt. If you rolled out 802.11g infrastructure four years ago, you can now fit around three to four times as many transistors on the same area of silicon as was possible when you deployed your current infrastructure.

    • Re:What Gives? Simple. (Score:5, Informative)

      by seanadams.com ( 463190 ) * on Monday January 28, 2008 @12:58PM (#22210004) Homepage
      Enterprise hardware does not use general-purpose CPUs, it uses special-purpose ASICs

      Actually they don't - take a look in a high-end AP some time. "Enterprise" wireless systems use the same, or often older generation, of wireless technology that is in consumer access points. Competition in the consumer AP market is what drives all the incredible price/performance in wireless technology, and I assure you nobody is going to spend the tens of millions to do a custom spin of one of those chipsets for the relatively small high-end market. Those products sell on branding, special software features, and support contracts, not silicon performance. And as far as the CPU/memory etc, these are going to be much LESS specialized in a high-end system than in a consumer AP. Low-cost APs use highly integrated ARM or MIPs-based SOCs that are designed for sub $20 BOM cost. A higher-end system, however, is not bound by BOM costs and might have four times the memory and a more general purpose processor capable of running more software.

      Routers and switches are a different story, and those DO use ASICs and FPGAs. The high-end models of these have to deliver a totally different hardware feature set than consumer equipment, and unlike wireless technology, the bleeding edge tends to be developed for the highest priced products before trickling down.

      • Re: (Score:2)

        by afidel ( 530433 )
        Actually you're wrong. Cisco makes their own ASICs for their AP's, or at least they did in late 90's early 2000's when I supported their wireless division (formerly Aironet Communications). They were making enough cards and AP's that it was deemed worth it to spin their own chips. The biggest reason is they could do crypto at full wire speed in an AP that was powered by PoE, something that their competitors couldn't do at the time. I don't know if they've gotten away from ASICS as process improvements have

        • Re: (Score:1, Troll)

          by seanadams.com ( 463190 ) *
          Actually you're wrong. Cisco makes their own ASICs for their AP's, or at least they did in late 90's early 2000's when I supported their wireless division

          You're saying I'm wrong but admitting that your information is ten years out of date. A LOT has happened since then. The whole industry has consolidated and everything is now driven by the consumer AP market. Encryption is now done in hardware even in the cheapest g/n chipsets. These is NO reason to do custom silicon to support any of the features offered

          • Re: (Score:3, Informative)

            by afidel ( 530433 )
            Actually my informations is only 5 years out of date and from a quick Google search the 1300 series AP which is their next to newest offering is also ASIC based, so I wouldn't consider it so out of date =) They considered the stuff they could build into the ASIC to be a competitive advantage and knew that they could be to market with a new product months before the major chip houses would have even engineering samples. To be more on-topic their 1250AP which is 802.11n draft 2 compliant is only supported wit

            • Re: (Score:1)

              by Cramer ( 69040 )
              FPGA != ASIC I've taken a lot of cisco gear apart; very few have had real, custom logic in them. (and that was very expensive gear.) Bugs in ASICs are very difficult and expensive to fix. FPGAs are simple to reprogram; that's why they show up in everything.

              • Re: (Score:1)

                by afidel ( 530433 )
                No, these were ASIC's. I know because they talked about cost to have a mask made and the minimum units expected in order to justify doing one.

          • Re: (Score:1)

            by Cramer ( 69040 )

            Encryption is now done in hardware even in the cheapest g/n chipsets
            Negative. WEP is done in hardware. WPA/WPA2 are done in software in every router I've looked at -- based on broadcom, atheros, ralink, and intel chips. Most of the broadcom cpus have a crypto processor in them, however no linux based firmware uses it. (the vxworks based ones might, but I've disassembled them to see.)
          • Cisco ceased being relevant a LONG time ago for most people. They still have their place in the ultra-high-end optical market, but most offices are best served by a bunch of big dumb switches and PC-based routers.
  • 802.11n causes cancer.

  • Not a significant usage of power (Score:4, Insightful)

    by Kohath ( 38547 ) on Monday January 28, 2008 @12:01PM (#22209438)
    It's like 8 watts instead of 3 watts (not exact numbers). It's not a significant amount of power. That's why you don't need to upgrade your infrastructure.

    I'm not sure how a silly article like this gets published. If it was tons of power, how could they make 802.11n adapters for laptops?

    • Re:Not a significant usage of power (Score:5, Informative)

      by evilviper ( 135110 ) on Monday January 28, 2008 @12:33PM (#22209678) Journal

      It's like 8 watts instead of 3 watts

      From TFA: "some 802.11n Draft 2.0-based access points consume up to 18 watts."

      That's why you don't need to upgrade your infrastructure.

      From TFA: "802.3af power-over-Ethernet (PoE) switches and power injectors supply about 15 watts of power at the switch port."

      No go sit in the corner and think about what you've done...

      • Re: (Score:2)

        by Kohath ( 38547 )
        Yes, I went back and read the article. There's really no need to use 18 Watts for 802.11n, especially on a continuous basis. Twelve should be a lot more than enough.

        Even so, a device that needs 18 watts at peak and an average of about 6 can easily be made to work when only 12 watts are available continuously.
        • So is power drain based on distance from the emitter? Say I'm right next to it, do I consume less power then somebody several floors away?

        • Re: (Score:1)

          by ArAgost ( 853804 )

          Twelve should be a lot more than enough.
          So you're basically saying that 12 W should be enough for everybody?

    • Tons of Power?? (Score:1, Funny)

      by Anonymous Coward
      Does this mean I will have to upgrade the strap on my laptop bag? Will this help me lose weight? I better join a Gym and get in shape before I upgrade. This tech stuff is really difficult.

    • Re: (Score:2)

      by Bretai ( 2646 )
      If it was tons of power, how could they make 802.11n adapters for laptops?

      A couple of points:

      1) Laptop clients are single-radios, not the two radios that the dual-band access points have.

      2) All the other components that the access point needs to have is already powered by the laptop, e.g. cpu, memory, ethernet switch. The client, being just one radio, can draw less than 2 W during continuous 11n transmit.

      Bonus point: The client can also sleep the radio when not in use. The AP has to stay awake and beaconing

    • Re: (Score:1)

      by Cramer ( 69040 )

      If it was tons of power, how could they make 802.11n adapters for laptops
      Simple... laptops don't run their wireless adapters anywhere near max-power. And they don't run them continuously. (unless you've intentionally disabled power management.)

  • My first thought was not for the infrastructure (the Access Points in a hundred conference rooms and spaced over all the cubicle farms). It was for the laptops. Not having one of the newest sexy 11n devices in my laptop, I wondered if MacOSX or Windows managed to drop the speed for battery operation vs tethered DC power operation.

    But the article IS about the corporate fixed infrastructure, right? Are we talking 5% increase of power for something that is already only 1% of the facility power costs? Wo

    • Re: (Score:3, Informative)

      by Sancho ( 17056 )
      The summary sucked, but this is clearly about Power over Ethernet, for which that 5% can be quite significant.

    • Re: (Score:3, Informative)

      by Firethorn ( 177587 )
      I bet most of the energy is in the form of heat from the individual DC converters plugged in to long extension cords laid along the drop ceiling to the nearest electric column.

      And you'd be incorrect. Most corporate infrastructures that heavily/professionally deploy wireless is going to due it via PoE - putting in a PoE switch or injector is much cheaper than wiring dozens or hundreds of new power jacks up in ceilings and such. With PoE all you need to do is run a ethernet cable over to the AP to provide b

      • Re: (Score:2)

        by Bretai ( 2646 )
        With N you're possibly doubling the number of radios to four.

        Ouch, that's embarrassing. Maybe you should've prefaced your comments with, "I'm only guessing here, but..."

        Still two radios for simultaneous 11n in 2.4 GHz and 5 Ghz. Noise floor is likewise not the problem you think it is. Instead, we have channel bonding, which means that you're transmitting across a broader spectrum, and multiple transmit chains (MIMO) means that your transmits are less efficient, even at the same power level as non-11n.

        BTW, I
        • Still two radios for simultaneous 11n in 2.4 GHz and 5 Ghz.

          CURRENT enterprise level APs have dual radios in them. They're capable of running 802.11a & g networks simultaneously at full speed.

          Hmmm... Research shows that while 802.11n pretty much specifies multiple antennas, it doesn't state multiple radios. From my earlier readings this wasn't made clear.

          Instead, we have channel bonding, which means that you're transmitting across a broader spectrum, and multiple transmit chains (MIMO) means that your
    • Eh, I upgraded the wireless card in my work laptop from an 802.11g Intel Proset Wireless to a Dell Wireless 802.11n card. I noticed no difference on battery life, no matter if I am connected to a B, G or N network. I notice no difference in speed between running on Battery and DC - I average 130 Mbps connection on my home N network (I thought it was supposed to do 300, but not really complaining, its much faster than what I had before, and I only have 100Mbps on the ethernet anyways. So at least on the adap

  • Summary is misleading (Score:5, Informative)

    by russotto ( 537200 ) on Monday January 28, 2008 @12:05PM (#22209478) Journal
    First of all, this has little to do with what is usually considered power infrastructure. This has to do with power-over-ethernet. It appears some dual band 802.11n radios require more power than one particular specification (802.3af) allows. Solution? Don't use 802.3af, or, don't use the radios which require too much power. Not really a big deal. I expect that manufacturers will bring the power requirements down to allowable levels over time.

    • Re: (Score:3, Insightful)

      by hawks5999 ( 588198 )
      This could end up being good for the ratification of 802.11n. The spec that gets its power usage down to meet the 802.3af power first, wins.
      • There aren't competing 802.11n specs. Also, adding new requirements at this point is unlikely to speed the completion of the standard.
    • Or, since you can have multiple clients connecting at 108Mbs through the wireless, you just hook up two 15W PoE cables to the access point, to provide more "backend" bandwidth and power.

  • Wrong assumptions (Score:5, Interesting)

    by Casandro ( 751346 ) on Monday January 28, 2008 @12:10PM (#22209528)
    Essentially just because vendor A has devices which consume "up to 18 watts" it doesn't mean that nobody can build devices which take less than 13 Watts.

    That's just 5 watts difference. You could probably achieve this by switching to higher efficiency components. Or you could store some energy for the short bursts of transmission, getting a steady power of 13 watts.

    Keep in mind that most vendors probably still have the very first itteration of hardware. It will significantly improve over the next years anyhow.
    • You could probably achieve this by switching to higher efficiency components.

      But wouldn't corporate APs, already restricted to PoE, already be using low power devices? I don't think that they wouldn't keep power usage down if they could for the PoE if it was a trivial process.

      Still, I agree that power demands will probably come down with time.

  • 802.11n has MIMO = more power used, Duh! (Score:3, Informative)

    by Zymergy ( 803632 ) * on Monday January 28, 2008 @12:53PM (#22209944)
    Multiple radios in simultaneous operation (Read: MIMO) plus the circuits to coordinate and control the radios and it has *double the bandwidth* (in the physical layer) = more power use by the 802.11n device. Duh! (Also notice there are more and larger antennas?) http://en.wikipedia.org/wiki/IEEE_802.11n [wikipedia.org]

    If the big deal in the article is over PoE powered 802.11n solutions, just exceed the power spec at the power injector and use 24 Gauge CAT6 UTP (or larger Gauge CAT6 for longer runs) for your PoE runs to lower electrical resistance.
    I have installed PoE devices that have their own proprietary power injectors that exceed the PoE power standard. The problem is where people use long runs of super cheap CAT5 and lots of punch-downs and they expect also their large switch with PoE injection to provide PoE to whatever is connected. There is a reason that the manufacturers' of powered by PoE devices do provide their own wall-wart PoE injectors...
  • "Still, many enterprise-class Wi-Fi vendors claim to deliver full 802.11n capabilities without enterprise customers having to touch their power infrastructures. So what gives?"

    Unless you're running at near maximum electrical load, a few extra watts is not going to set transformers afire and melt power lines. If you were in Cuba, with its infamously collapsing electrical grid, I could see this happening, but there are no enterprises in Cuba to begin with, so it's not a relevant scenario.

    It also might he

  • Duty cycle is key (Score:2, Insightful)

    by sylvandb ( 308927 )
    Just because a given access point will use "up to 18watts" does not mean it will always use 18watts. As long as the average power consumption is under what the supply can deliver, all can be well. Several possibilities exist.

    Best case is that the supply can deliver short term bursts of power sufficient to meet the demand. This is realistic in most scenarios today, as supplies are typically rated by long-term average power. For example, the 20amp breaker on your typical home circuit will easily supply a

    • Re: (Score:2)

      by Firehed ( 942385 )
      You can't compare a breaker box to PoE. Just like fuses, breakers can be designed to either trip immediately or to allow a quick surge for high startup power items. While PoE is probably reasonably flexible, solid-state electronics like wireless access poitns don't have a surge of power during startup to get the motors cranking. Power draw may fluctuate depending on usage, but expect a relatively constant power requirement. A battery/capacitor based solution would in theory work fine, though of course w

      • Power draw may fluctuate depending on usage, but expect a relatively constant power requirement.
        Yes, of course. Because we all know there is no difference between max and min power consumption on a processor or a complete system, even a laptop, so why should there be a difference between max and min consumption on an access point which really is a complete computer system with processor, storage, memory and I/O?

        sdb
      • I'm not sure about the specifics of CAT5/6, but I do know that some electronic transmission media need to be DC balanced. If you have these large spikes, you'll have to compensate somehow, which can double the power draw that it actually needs - I think. I'm no expert on transmission media or engineering these devices, so don't take this as gospel by any means. If this is the case, you could probably rig up an overflow battery or something. You would still see some conversion inefficiencies though, the amou
  • Looks like I will need to find a ZPM to power the thing and the ZPM is where they get you.

  • I know Cisco's 802.11n AP's use 18 watts. This is the brand most used in the enterprise. They can get it down to 802.3af by using only the 2.4ghz radio. But when using the 2,4ghz and 5ghz radio in the AP simultaneously you need power injectors, power to the AP, or new switches.
  • There is several ways vendors are getting around the power issue with .11n, by only having one antenna or by doing some software trickery where instead of getting 15.4 watts over every interface you lower the power to a couple and redistribute that power to get it to 18watts , (I know Cisco is doing this on their 3750-E switches and have been told they plan on it on their 4500E switches). Since most companies don't put 30 access points on one switch anyway (would be bad if that switch went out!) that probab
  • Cisco has new Premium PoE blades for the 4500 E-Series chassis that provide up to 30W of power per port. As for other comments already posted, it has nothing to do with how much power the ASIC or general purpose chips in the AP's consume, that is minimal at best, and you are not going to get your power savings there. The additional requirements are for powering the additional radios in the AP's, and pumping out that power over the air. There's basically no getting around that. Some vendors say they can,
  • Siemens just announced 802.11n which does user only 12.6W

Slashdot Top Deals

Mausoleum: The final and funniest folly of the rich. -- Ambrose Bierce

Close