80211b legacy devices impact on 802.11AC environment

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I have a healthcare client that is a high care facility currently running 802.11N AP's soon to be replaced with 802.11ac's

They are about to retire their existing cable based Nursecall System with a 3rd party product that only operates on 802.11b. At present all devices (Laptops, Tablets, Vocera Badges) connected to the AP's are 802.11n capable so transaition to the higher rate AP's wasnt going to be an issue.

What is the impact of having legacy devices running 802.11b when all others run at higher rates? The WIreless LAN has run flawlessly for 5 years since installed, and my concern comes from my limited understanding of what I saw with a Ruckus deployment at an equivalent site where the Ruckus units would ramp down to accomodate the 802.11b devices then after a period ramp back up to 802.11n. This lag time affected other services on the site such as Telehealth Video Conferencing (*where a patient was engaged in a consult with a GP or specialist Dr via viedo link attached to the Wifi)

Is there a deadline for 802.11b to be EOL by the IEEE or Wifi Alliance? SHould I be concerned?

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Ask Itee

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Posted 12 months ago

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Darrel Rhodes, Employee

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Much of what you ask is dictated either by the IEEE802.11 standard and/or the laws of physics.

In a 'standard' Wi-Fi network, when an 802.11b client joins, ALL devices are effectively limited to 802.11b speeds (max 11Mbps).

However Ruckus introduced a technology called "Airtime Fairness" that mitigates much of the negative impact of an 802.11b client joining.  Please see:  https://support.ruckuswireless.com/articles/000002008

I would recommend connecting the 802.11b devices on a separate WLAN. This won't prevent the speed impact issues described in the above article, however it will allow you to manage the network settings for the legacy devices.  E.g. https://support.ruckuswireless.com/articles/000009669

Personally, I don't believe the IEEE or Wi-Fi alliance will EoL the 802.11b protocol as there are still a lot of devices in use that require it.  However it would certainly be best to retire the legacy devices as soon as possible to allow your network to achieve the best performance.

I hope that helps.

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Ask Itee

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Thanks Darrel, you've confirmed my suspicisions and ensured I am on the right track with the Ruckus sites I support.

The product is a Nursecall System called Alexys here in Australia and they are still producing a product that runs in the 802.11b.  I've been suspicious of vendors who have a "reluctance" to move with the times seeing it as an indicator that the product development has stalled or the vendor simply cant keep up with developments in new tech.

Sadly the Board of Dir's for the client made the call on the vendor without much consultation, so were stuck with it.  Perhaps its a little paranoia on my side too given the Wireless environment has been issue free for 5 years with every piece working nicely and logs being a very very boring read :)
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Robert Lowe

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"At present all devices (Laptops, Tablets, Vocera Badges) connected to the AP's are 802.11n capable so transaition to the higher rate AP's wasnt going to be an issue."

Think you need to dig deeper to work out what will be affected. Are the SSID's for Tablets, Laptops & Vocera badges configured to use 2.4 & 5GHz or just one? For example, the Vocera badges will most likely only be configured to use 1 band. 

Once you know what devices are using what band, then you will be in a better place to scope the extent of the impact. To be clear though, the presence of 802.11b capable clients on your network will degrade the 2.4GHz performance.
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Ask Itee

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HI Robert thanks for the comment.  Our badges use both bands and we had ensured that all devices at or under 802.11b were retired. See my comment to Darrel above.
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John D, AlphaDog

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802.11b on 2.4GHz forces the network to use the older DSSS modulation scheme on 2.4GHz for management frames / beacons as well, which can reduce your 2.4GHz network capacity.

However, since you have 802.11b devices, I don't think there's a lot you can do about that. Management frames should be a small fraction of total airtime consumption (SmartZone has some health graphs you can use to check how much time is used by management frames)

Other than that, as Darrel said, (ignoring 802.11ac and 802.11ax improvements), WiFi is a single duplex medium. At any point in time, your AP is listening or talking to 1 client at a time. For each client (and for each packet), the transmitter tries to pick the best transmission speed to the client. So talking to a slow 802.11b client doesn't mean it can't talk to a quicker 802.11n client at 802.11n speeds.... But it does mean that communicating the same information to an 802.11b client takes longer than doing that with an 802.11n client.

With that said, Ruckus has Airtime Fairness which tries to make sure that all clients fairly share downlink airtime, which in effect means that 802.11b clients see less throughput when they are sharing airtime with 802.11n clients, but that allows your 802.11n clients to see higher throughput without the channel being hogged by slower clients.
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Ask Itee

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Thanks for your response John.  It came as  quite a surprise to find out at the pre-project meeting that the gear remains on 802.11b.

Wish me luck everyone.