Packet Drops and Low Bandwidth

[KedaiMimih]

In our company we use WLC Type Cisco Catalyst 9800-L Wireless with Software Vesi 17.6.4, and for AP type AIR-AP2802I
Configuration QoS 15Mbps per Client, not per SSID
The problem is that when there are more than 50 clients connecting to the AP, there is a decrease in speed and it drops a lot

Number of Client Connects:

50-70 Clients : 1Mbps (Not Normal)
10-40 Clinet : 10Mbps (Normal)
Link: https://www.speedtest.net/

from the AP Type Air Ap2802i database, support clinet connections for up to 200 clients,
why when connecting 50-70 there is a lot of speed drop?

[Leo Laohoo]

What kind of wireless clients are they, laptops, tablets, smartphones? 

[KedaiMimih]

 laptops and smartphones

[Leo Laohoo]

Is this happening to all the APs or just one or a few APs?

What radios are the wireless clients connected to when they are slow?

10 Mbps is unacceptably slow.

[KedaiMimih]

Is this happening to all the APs or just one or a few APs?

> Yes All APs, when the number of clients reaches 50 clients and above

What radios are the wireless clients connected to when they are slow?

> 2.4Ghz and 5Ghz

10 Mbps is unacceptably slow?
> 10 Mbps in our opinion is normal, not too slow, because we use QoS 15Mbps per User

[Leo Laohoo]

Take the QoS off (for testing) and see the speed increases for everyone.

[KedaiMimih]

We have tried broadcasting 2 SSIDs in 1 APs

.:Setup:.
AP-1
- SSID A (QoS 15Mbps)
- SSID B (No QoS)
- 20 Mhz

.:Test results:.
AP-1
- SSID A (67 Client) Speedtest = 0.47Mbps
- SSID B (1 Client, My Laptop) = 25 Mbps

Why is it that for SSID A, with 67 Clients you only get 0.47Mbps, whereas in QoS we setup it with 15Mbps Per-User not Per-SSID
Is there something wrong with the configuration or is it really the technology from Cisco, "the more clients that connect, the throughput will go down"

[Leo Laohoo · Accepted solution]

I think the QoS is wrong.  I think everyone, on SSID A, is sharing 10 Mbps.  Everyone.

[KedaiMimih]

how to check, this qos is for share or per-user,
show what can bring up the configuration?

[KedaiMimih · Accepted solution]

Yes,
It turns out there was something wrong with the QoS that we implemented,
there are 2 QoS in 1 Policy Profile, after we removed one (QoS SSID), Bandwidth returned to normal,

Thank you All

[JPavonM]

As @Leo Laohoo has recommended above, take the QoS off.

Firstly rate limiting modern clients is not a cbest practice as they would take much more time to transmit when they are rate limited as they will need to stop transmission, and contend for a new time slot to transmit, so impacting the Quality of Experience (QoE) of the users. That is more noticiable when there are more stations connected, and especially if they need to transmit too much stuff.

Lastly, having 50 active users connected to the same AP's radio could impact performance even with no rate-limit active. As more clients do use the same RF medium (same channel) they need to contend for a time slot to transmit. More clients implies more collisions when trying to get access into the medium so an increase on the binary exponential backoff timer from 7 to 15, then to 31, then to 63,...  and so on until 1023. On a congested scenario were 50 stations want to transmit, it is likely that the backoff timer will rise to 63 so impacting performance.

See this excellent blog post from Andrew von Nagy that explains this on deep (https://revolutionwifi.blogspot.com/2010/08/wireless-qos-part-5-contention-window.html)

[KedaiMimih]

Below are the QoS and Policy settings, for SSID A

[Leo Laohoo]

QoS SSID Policy means apply the QoS to the entire SSID.  The more people joins the SSID, the slower it gets. 

QoS Client Policy means apply the QoS for every client. 

Screenshot shows QoS is enabled on both so the SSID gets 10 Mbps and each client gets 10 Mbps.  Since the SSID gets 10 Mbps, this gets triggered FIRST.  QoS Client Policy does not get triggered because none of them will ever get near 10 Mbps.

[Rich R]

> Configuration QoS 15Mbps per Client, not per SSID
Not according the screenshots you provided!

Like Leo said you have applied the QoS to the SSID so as he said "everyone, on SSID A, is sharing" that 15Mbps rate limit so no surprise they're getting a dreadful service!

If you want client rate limits then leave the QoS on the client but remove it from the SSID.