The Cost of Legacy 802.11b Rates
Leaving 1, 2, 5.5 and 11 Mbps enabled on 2.4 GHz costs airtime three ways: slow beacons, one old client that drags everyone down, and protection frames in front of every modern frame. Pick the lowest basic rate and see the cost.
How to use this tool controls and what to look for
Pick the lowest basic rate and see the airtime cost in four places: beacons, slow clients, protection and cell size.
Controls to change
- Lowest basic rate: compare 1, 2, 5.5 and 11 Mbps with 6, 12 and 24 Mbps.
- SSIDs per AP: add SSIDs. Each one sends its own beacons.
- APs heard on the same channel: add the other APs whose beacons use the same airtime.
- Beacon size: change the beacon size in bytes.
- Old 802.11b client sends at: set the old client's rate: 1, 2, 5.5 or 11 Mbps.
- CTS-to-self sent at: set the rate of the protection frame sent before each modern frame: 1, 2 or 11 Mbps.
What to look for
- At 1 Mbps, a few SSIDs and neighbouring APs can fill a large share of every beacon interval with beacons alone.
- One old client at 1 or 2 Mbps takes many times more airtime than a modern client to send the same frame.
- Protection puts a CTS-to-self or RTS/CTS in front of every modern frame, sent at a slow rate.
- Low basic rates make cells bigger, so more APs hear each other and share the channel.
About this tool
1, 2, 5.5 and 11 Mbps are 802.11b data rates from 1999. They only exist on 2.4 GHz, and leaving them enabled costs airtime in three ways: beacons sent slowly, slow clients that hold everyone back, and protection frames in front of every modern frame. Pick the lowest basic rate and see what each option costs.
What you'll learn
- How much airtime beacons use at 1 Mbps compared with 6 or 24 Mbps, especially with several SSIDs
- How one 802.11b client slows every other client down
- What protection frames (RTS/CTS or CTS-to-self) add in front of modern frames
- Why low basic rates also make cells bigger and add interference
Common questions
Should I disable 802.11b rates?
In most networks, yes. Very few devices still need them, and removing 1–11 Mbps saves a lot of airtime on 2.4 GHz.
How much airtime do beacons use at 1 Mbps?
A beacon at 1 Mbps takes about 2–3 ms. With several SSIDs every 102.4 ms that can add up to a large share of the channel before any data is sent.
What basic rate should I use on 2.4 GHz?
Commonly 12 Mbps or higher in dense designs, and at least 6 Mbps elsewhere, once no 802.11b devices need to connect.
Free for private and educational use. This interactive model is a simplified teaching aid and may contain mistakes. It is provided as is, without warranty. Use it to understand the concepts, not as a substitute for a site survey, vendor documentation or professional design advice.