What is the maximum number of devices 802.11n WLAN card can serve?

Question

I have found device called Dell Edge Gateway 5100 which has Wireless 802.11n LAN Card.

I have found out some specs for this devise:

1. Maximum Data Rate - 600 Mbps
2. Modulation - DSSS or CCK or OFDM
3. RF Band - 2.4 GHz or 5 GHz
4. Number of Spatial Streams - 1, 2, 3, or 4
5. Channel Width 2 - 20 MHz or 40 MHz

How can I know maximum number of connected devices it can serve?

Answer 1

That is impossible to tell.

In theory there is no a 2007 device upper limit. (Thank you Spiff for correcting me.)

In practice bandwidth saturation and CPU power available to the gateway will at some point make the device too congested to serve more clients. (Or make connections already established unstable.)
Where this limit exactly lays... It totally depends on the combination of clients, gateway configuration, bandwidth and latency requirements of the clients, even on the amount of interference/data-loss caused by other users of the same radio-frequencies.

What is acceptable to operate 100 low-bandwidth devices (like Internet Of Things stuff) might be completely insufficient for 5 high-throughput clients (like HD media streaming devices or full-HD CCTV cameras) or for just one PC with a 1000 torrent downloads running.
It all depends.

Answer 2

The 802.11 protocol has a hard limit of 2007 associated clients per AP (per BSSID, per band), because of limited number of Association IDs (AIDs) that can be represented in the combination Duration/ID field in the 802.11 header. That Dell box you linked to appears to have a single radio, and unless it can be configured to support multiple BSSIDs (that is, act as multiple virtual APs), it probably has a hard limit of 2007 simultaneously associated clients.

Even boxes that allow you to configure multiple BSSIDs don't usually let you set the same [E]SSID for more than one BSSID, so it's typical to have a hard limit of 2007 simultaneously associated clients per SSID per AP.

And of course, even if all your 2007 clients could do the same 600 Mbps 4 spatial stream 802.11n that that Dell box can do (which is pretty rare; the vast majority of 802.11n clients can only do 300 Mbps or less), and even if they were all packed in close enough to maintain that rate, if they were all trying to move traffic at the same time, they'd each get less than 300 kbps, which is a pretty crappy rate. So your practical limits are much lower than the protocol hard limit of 2007.

In the past, I've seen 802.11n AP radio hardware that only had hardware support for 50 or 64 client WPA/WPA2 keys. Beyond that, any additional clients had to have their WPA/WPA2 encryption done in software, with a significant performance penalty. This is just one example of a class of implementation-specific practical limits or hard limits that may exist in any given 802.11 AP.