How to increase wifi upload speed

[daniel.tanch]

Hi,

I am currently using WLC 9800 with AP 9120. When I upload a file via ftp to a server using 1 laptop, the upload speed was around 60MB/s. But when I am using 2 laptops to upload to the same server, the upload speed was shared. Laptop A got around 35MB/s and laptop B get around 20MB/s, is there a way to increase the upload speed for both laptops to achieve the speed of 60MB/s? 

From my understanding MU-MIMO only work for download and not upload. Do correct me if I am wrong. I had also increase the channel width to 80MHz. 

[Rasika Nayanajith]

What is laptop capability? Does that support 11ax? How many spatial streams it supports? The below page may find useful to find its capability.

https://clients.mikealbano.com/ 

Since you get 60MB/s which translates into 480Mbps (60x8), if that is the throughput you get with a single client, that may be the total throughput AP can offer based on client's capability. When you adding multiple devices, then throughput will reduce further, when many clients in the cell, then many overheads for inter-operability (an increase of control  & management frames). Therefore two client throughput is less than single client throughput in the cell.

9120 support UL & DL MU-MIMO, however, to get the benefit, your client should support it. Pls check client capability as it is the limiting factor here.

HTH

Rasika

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[daniel.tanch]

Hi Rasika,

The laptop is using 802.11ac 2x2 with WLAN channel bandwidth at 80MHz for 5GHz. Both the laptop are of the same spec. Between the AP was place less then a meter away from the laptop. 

Why the throughput is reduce when more clients are added? Is there any docu? Is there a way to increase the throughput for both the clients? 

For 9120, is UP MU-MIMO supported if client is using 802.11ac and not on 802.11ax? 

https://www.cisco.com/c/en/us/solutions/collateral/enterprise-networks/802-11ac-solution/q-and-a-c67-734152.html

Q. Will MU-MIMO work in the downstream direction only?
A. The 802.11ac standard defines only downlink (DL) MU-MIMO, which is for the access point sending to multiple clients concurrently. The uplink version, with multiple clients coordinating to transmit separate packets to the access point at the same time, was considered for 802.11ac but was deemed too difficult to address in a reasonable time. Certainly most traffic flows in the downlink direction, so DL-MU-MIMO helps with the most pressing problem.
Uplink (UL) MU-MIMO, however, is a key feature planned by the 802.11ax High Efficiency WLAN working group in the IEEE, which is defining the next-generation 802.11 Wi-Fi specification, with a proposed target of mid-2019/2020 for a finalized standard.

[patoberli]

One simple word, overhead.
Wireless is a shared medium, similar to a hub. So if you have two (or more) active clients, you start to get a lot of "pause" frames. The more clients, the worse it gets.
This was somewhat reduced by MU-MIMO (with capable APs AND clients) in 802.11ac Wave2 and is now being vastly improved on 802.11ax (again, clients also need to be 802.11ax and support it). You still get a performance hit, but with many simultaneously clients, the hit should be considerably lower than what it was before (I'm still awaiting real world benchmarks to show this), in theory.

[Rasika Nayanajith · Accepted solution]

"Why the throughput is reduce when more clients are added? Is there any docu? Is there a way to increase the throughput for both the clients? "

For wireless to work, there are 3 types of frames exchanges involve

1. Management frames
- Beacon, Probe Req/Resp, Association Req/Resp, Reassociation Req/Res, Authentication Req/Res

Typically beacon frames are chatty, each AP generates one frame in 100ms for each SSID on it. When you add more client they generate more mgt frames,

2. Control frames

- Act, Block Ack, RTS/CTS

Typically these frames to avoid collisions in wireless communication, carry no user data.

3. Data frames 

This is the only type of frame to carry user data. 

Now if you want to achieve the highest throughput, then you can have a 1 client (that match AP data rate capability) & 1 AP. In that way you minimize contention (as no other clients to compete for medium access).

When you add more Clints to the cell, then they have to coordinate medium access with a random backoff, also more clients will generate more control/management frames, so reduce airtime for data frames. In that way, when you add more client, overall throughput will reduce compared to the best-case scenario

HTH

Rasika

[Scott Fella · Accepted solution]

I think what you show is what you will achieve with the clients you have. If you have ax client devices, then your throughput would be different. Even if you set you channel width to 80mhz, does your clients support 80mhz, if not, they will utilize only 40mhz. Keep in mind that capabilities have to be on both the wireless system and the client device(s).

[daniel.tanch]

Hi Scott,

Yes, I am showing what the clients had achieved. Currently the clients are using 802.11ac and it able to supported 80MHz channel width at 5GHz. 

Am I right to say these:

• if the clients is using 802.11ac and not 802.11ax then the UL MU-MIMO does not applied to them? Thus the UL throughput is shared between the clients? 
• inorder to increase the UL throughput, I had to increase the channel width to 160MHz with a client supporting it? Assuming it using 802.11ac
• else had the client supporting 802.11ax since the AP 9120 supported 802.11ax

[Scott Fella]

You are right with your assumptions. Keep in mind, throughput also have other variables like noise, utilization, and how manufacturers implement their features. You probably will not see those types of numbers in a real world production.

[daniel.tanch]

Hi Scott and Rasika,

Thanks for your help and advice.