High-Density WLAN Tuning¶
Default WLAN settings assume a handful of clients per AP. Put several hundred devices across a dozen or more APs and the limiting resource stops being bandwidth and becomes airtime — a single half-duplex medium per channel, shared by every device that can hear it. Adding more APs does not add airtime; it adds contention unless the channel plan and the per-WLAN settings are tuned for it.
Everything below is about spending less airtime on overhead so more is left for user traffic. Settings are named as they appear in Ruckus Unleashed; the same options exist under different labels on ZoneDirector and SmartZone.
Broadcast & Multicast — the Big One¶
Every broadcast frame is transmitted at the lowest basic rate so that all clients can hear it. At 1 Mbps, one ARP broadcast occupies roughly as much airtime as several hundred data frames at modern rates.
Now put 1,000 devices on a flat subnet, all doing ARP, mDNS, SSDP, NetBIOS and DHCP, and the channel fills with discovery chatter before a single user loads a page. Broadcast traffic scales with the size of the broadcast domain, not with how busy the users are.
Four settings, all per-WLAN in Unleashed:
| Setting | What it does |
|---|---|
| Directed Multicast | Converts multicast to unicast for known clients, so it goes out at full rate instead of the basic rate |
| Proxy ARP | The AP answers ARP on behalf of its clients from its own table, so ARP requests stop being flooded over the air |
| Drop / filter broadcast-multicast | Kills mDNS, SSDP and Bonjour discovery traffic — no client on a public network needs to discover anyone else's printer or Chromecast |
| Client isolation | Isolate clients from each other and from other hosts on the subnet, with the gateway MAC allowlisted. Halves the broadcast problem, and is a security requirement for public WiFi anyway |
Pair this with a smaller broadcast domain — split clients across several VLANs rather than one flat subnet (VLANs, Add a User VLAN, Wireless VLAN Build). The two together are the single biggest lever available.
Data Rates¶
Disable the 802.11b rates entirely — Ruckus has an OFDM-only toggle that does this, and it only affects 2.4 GHz. Then raise the BSS minimum rate and management Tx rate to 12 or 24 Mbps.
Three things happen at once:
- Beacons and broadcasts stop costing 12–24× the airtime they need to
- The effective cell shrinks, so clients roam instead of clinging to a distant AP at 1 Mbps
- One ancient device can no longer drag a whole cell down by transmitting slowly
Cell size is a feature here, not a loss. Dense deployment means small cells and more of them.
SSID Count¶
Each SSID is a separate BSS beaconing roughly ten times a second, per radio, per AP. That cost is paid whether or not anyone is connected:
| SSIDs | Beacons/sec across 20 dual-band APs |
|---|---|
| 1 | 400 |
| 2 | 800 |
| 4 | 1,600 |
One SSID is ideal, two is the practical maximum — typically a public one and a crew one. If segmentation beyond that is needed, do it with dynamic VLAN assignment on a single SSID rather than more SSIDs.
Channels¶
Turn 2.4 GHz off on most APs. There are only three non-overlapping channels, and with 20 APs there is no plan that avoids them interfering with each other. Leave it enabled on a handful for legacy devices and run everything else on 5 GHz.
On 5 GHz use 20 MHz, or 40 at the widest. 80 MHz feels fast in a demo and is wrong here — it collapses the channel count, so APs start sharing channels and contending with each other. More narrow channels beats fewer wide ones every time in density.
Usable 5 GHz channels (UK/ETSI, indicative):
| Width | Total channels | Without DFS |
|---|---|---|
| 20 MHz | 19 | 4 |
| 40 MHz | 9 | 2 |
| 80 MHz | 4 | 1 |
DFS is the judgement call. It roughly doubles the usable channel count, but a radar hit forces an AP off its channel mid-event. Near an airport, marine radar or a weather station, plan on it happening.
Steering & Fairness¶
| Setting | Purpose |
|---|---|
| Band Balancing | Pushes dual-band clients to 5 GHz, using a target ratio rather than a hard block |
| Load Balancing | Spreads clients across APs, so an AP at a natural gathering point doesn't take 200 associations |
| Airtime Fairness / Airtime Decongestion | Stops slow clients consuming disproportionate airtime |
| Max clients per WLAN | Cap around 75–100 per AP so the balancing has teeth |
| Transient Client Management | Stops passers-by outside the venue associating briefly, consuming a lease and airtime |
Roaming¶
- 802.11k and 802.11v (neighbour reports, BSS transition) are safe and help clients make sensible roaming decisions
- 802.11r is faster but historically breaks older clients. On a public network full of unknown devices, leave it off — or test it hard first
Rate Limiting¶
Per-client caps, in both directions. On a shared circuit, a handful of devices doing cloud backup or software updates will otherwise take the lot. Something like 5 Mbps down / 2 Mbps up per client is generous for browsing and social use, and protects everyone else.
What to Monitor¶
Channel utilisation is the number that matters. Under about 60% and things feel fine; above 80% it does not matter how many APs are deployed.
| Metric | Reading it |
|---|---|
| Channel utilisation | The headline number — under ~60% healthy, over 80% saturated |
| Per-AP client count | Identifies hot spots the balancing hasn't caught |
| Retry rate | A rising rate points at co-channel interference |
Unleashed shows all three. Also set a shorter client idle timeout so ghost devices release their DHCP leases, which ties back to having enough addressing headroom in the first place.