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Why do wireless APs constantly transmit (e.g., with a beacon interval of 10×/sec.), even when no devices are connected to them? Doesn't that just cause needless RFI? Is it really necessary to constantly be sending beacon frames? Is there a way to disable this? (I don't think hiding SSID disables sending beacons.)

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  • @JesseP. It would remember the AP and transmit to it awake it. – Geremia Sep 13 '19 at 19:42
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    The most basic reason: the 802.11 spec says so. The logic behind it is so clients (associated or not) can tell the BSSID (station) is still there. Too many missed beacons and the station is marked as down (may be off, or just out of range.) Messing with the default beacon interval can lead to all manner of weird problems. – Ricky Sep 16 '19 at 22:51
  • @RickyBeam Long beacon intervals can be a good thing, though; cf. this. – Geremia Sep 17 '19 at 0:04
  • @Geremia, long beacon intervals can be very bad though, since there are quite a few client devices that don't respond well to long beacon intervals (especially consumer devices). The "article" you link does not contain nearly enough information nor any truly valid reason to change the beacon interval. Frankly, there is so little gain from doing so and there are quite a few far more effective adjustments that can be made to a wireless configuration with fewer potential risks than tuning the beacon interval. – YLearn Sep 17 '19 at 7:12
  • @YLearn "there are quite a few far more effective adjustments" Such as? And "far more effective" for what? – Geremia Sep 17 '19 at 17:20
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Why do wireless APs constantly transmit (e.g., with a beacon interval of 10×/sec.), even when no devices are connected to them?

Just because an AP doesn't have any client devices associated to them, doesn't mean there are no client devices that would be "interested" in associating to them. In particular, this is useful in deployments that have multiple APs as this helps to provide information to clients so they can make decisions about roaming.

Additionally, beacon frames perform a number of different functions in addition to discovery. They serve as a timing source, provide other information to 802.11 devices, allow for power saving features in client devices, etc.

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A beacon is required in order for clients to know when a particular AP/SSID is nearby and ready for connections. Without that, the client would never know there's available WiFi nearby, regardless of possibly having previously connected to said SSID. You can disable a beacon by disabling/deleting the associated SSID, or you can simply adjust the beacon rate so it's not 10x/second or whatever yours is set to.

You can read more about the beacon frame and its purpose here

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  • An AP can lack an SSID? – Geremia Sep 13 '19 at 20:50
  • Yeah. They lack SSIDs when they're first unpacked (when they're new) most of the time. – Jesse P. Sep 13 '19 at 21:38
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    Technically, yes, an AP needs at least one SSID. But it doesn't have to include it in the beacon. (i.e. "hidden" SSID) If it doesn't have an SSID, nothing can connect to it, and thus its radio should be silent. – Ricky Sep 16 '19 at 22:53
  • @RickyBeam Wrong. Cisco AiroNet APs, for example, do not have any SSIDs configured on them out of the box. Many other APs are the same way. The only APs I've ever seen that come WITH an SSID out of the box have been consumer-grade routers with WiFi built in or wireless bridges. – Jesse P. Sep 16 '19 at 23:01
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    "radios are disabled" "You must create an SSID before you can enable the access point radio interfaces" Without an SSID, it's not a usable, beaconing, AP. – Ricky Sep 16 '19 at 23:14

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