"Slow" speed on WiFi - EAP

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"Slow" speed on WiFi - EAP

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"Slow" speed on WiFi - EAP
"Slow" speed on WiFi - EAP
2020-11-16 14:16:17 - last edited 2020-11-16 18:50:56
Model: EAP245  
Hardware Version: V3
Firmware Version: 2.21

Hello gents, there is something that I don't understand regarding the speed of the access point EAP245 at 2.4GHz.

 

It should be 450 Mbps on 2.4G and 1300 Mbps on 5G. But this test is just for the 2.4.

 

My test setup is simple, 2 PC connected to the same EAP in a room with no obstacle and distance of 3 meters from the PCs to the EAP. No other devices connected to the EAP.

Signal strenght is -35dBm.

Both PCs are equipped with an "ac Wireless Adapter" so both capable to handle - one is Intel(R) Wireless-AC 9260 160MHz and the other one is Intel(R) Dual Band Wireless-AC 3165.

 

Then I transfer a 1GB zip file from one PC to the other. Even if this is less or no relevant, both PC are settled with Fixed IP and are both in the same subnet (192.168.0.20 and 192.168.0.23).

 

Channel width is left at 20/40MHz.

 

The starting situation (before file transfer) is the following:

 

First question, why I see a 14% usage in Rx/Tx ? The 2 PC are yes connected but if I check their activity speed is very low: one pc 2.5Kb/s and the other 0 Kb/s. Don't think this can occupy 14% of the channel.

Then there is some interference that I suppose is band occupied because presence of others SSID in the environment.

 

In any case let's say that the starting point is with 18% of occupied channel, but we still have a 72% free that in my poor knowledge means 72% of 450mbps = 324mbps.

 

Now I start the file transfer but at best I obtain 3.2 MB/s (often going down at 1 or 2mbps) - approx 35mbps let's say that is much less than the 324 mbps, I understand that 450mbps is just ideal but 35mbps it's very distant.

If you see during the transfer the channel utilization goes up to 83% + interference is 94%.

83% of 450mbps means to me 374mbps.

It doesn't matter if I transfer from PC1 to PC2 or viceversa.

Also there are almost no errors or dropped frames.

 

Can you explain this and what is wrong in my reasoning ?

 

 

 

 

 

 

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Re:"Slow" speed on WiFi - EAP-Solution
2020-11-16 16:52:23 - last edited 2020-11-16 18:50:56

Hi @Xstreem,

 

I'm not sure I understand why you are testing the 2.4GHz radio if your PC's have 802.11ac adapters (which support 5.8GHz), but be that as it may:

 

it's important to understand that the "speeds" which are used for Wireless performance marketing are almost completely made up.  (-:  Not really, but these speeds NEVER apply in real world situations.

 

The first questions to ask yourself are:

1) what is the network technology?  n, ac, or ax?

2) what is the bandwidth of the wifi connection?  20MHz, 40MHz, 80MHz?

3) how many Tx and Rx chains are supported by my wifi network card?  Is this the same for both radios or does one radios?  How many Tx & Rx chains are supported by my Access point.

 

So, in your example, you have 2.4GHz 802.11n, 20/40, with unkoen Tx? and Rx? chains

 

Generally speaking 40MHz channels on 2.4GHz is not generally available / recommended.  Most of the time the 2.4GHz spectrum is too crowded.  Just because you request 20/40 in most cases it will just be 20MHz.  Similarly, many laptops only have 1x1 radios/antennas.  Some have 2x2.  A few very high end laptops have 3x3, but this is very rare.

 

The marketing speeds listed for Access points give a fictious best case scenario (note that I'm using rough numbers to make a point, the actual details of the negotiated link rates are somewhat more complicated)

 

For example AC1750 -- This is never possible, as you cannot "carrier aggregate" across the 2.4GHz and 5.8Ghz radios (unlike what can be done with modern cellular phones)

 

For the 2.4GHz radio, the marketing "speed" is listed as 450 Mbit/sec 

 

This assumes the following:


1) 3x3 chain radios on the client and the AP (the EAP245 has 3, but your clients most likely do not).  Most Wifi devices are only 1x1.  Maybe 30-40% are 2x2.  Less than 5% are 3x3.  

2) The 150 Mbit/sec per chain, assumes 40MHz.  Which, like I said, is typically only 20Mhz.  So this brings us down to ~75 Mbit/sec per chain.

3) Finally, the "air link rate" that is reported for your wifi device's connection is not the actual throughput you can expect to get.  Typically, the "goodput" or application level throughput is roughly 50-60% of the air link rate due to overhead, noise, frame headers, collissions, retransmitted frames, etc.

 

So, if, at the end of the day, you're getting ~40-50Mbit/sec through a 2.4GHz link, you're actually doing pretty good.

 

For example, on a 802.11ac 5.8Ghz 80MHz 2x2 link, with perfect signal, your air link rate will be 866 Mbit/sec. One can expect to get at most ~400-500 Mbit/sec out of this in terms of application level (e.g. file transfer) throughput.  Even though the AP can "theoretically" do 1200 Mbit/sec.

 

I should also add, that because both your file "server" and file "client" are wireless, in the example you gave, they are both actively completing for time on the AP during this test.  So there is some additional overhead taking place reducing speeds a bit farther, still.

 

Did that answer your question?

 

-Jonathan

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Re:"Slow" speed on WiFi - EAP-Solution
2020-11-16 17:00:01 - last edited 2020-11-16 18:50:58

@Xstreem 

 

This is a really nice whitepaper that describes things a bit more accurately than I could:

 

https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-3600-series/white-paper-c11-713103.pdf

 

This one is good, too:

https://www.intel.com/content/www/us/en/support/articles/000005725/network-and-i-o/wireless.html

 

 

-Jonathan

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Re:"Slow" speed on WiFi - EAP-Solution
2020-11-16 16:52:23 - last edited 2020-11-16 18:50:56

Hi @Xstreem,

 

I'm not sure I understand why you are testing the 2.4GHz radio if your PC's have 802.11ac adapters (which support 5.8GHz), but be that as it may:

 

it's important to understand that the "speeds" which are used for Wireless performance marketing are almost completely made up.  (-:  Not really, but these speeds NEVER apply in real world situations.

 

The first questions to ask yourself are:

1) what is the network technology?  n, ac, or ax?

2) what is the bandwidth of the wifi connection?  20MHz, 40MHz, 80MHz?

3) how many Tx and Rx chains are supported by my wifi network card?  Is this the same for both radios or does one radios?  How many Tx & Rx chains are supported by my Access point.

 

So, in your example, you have 2.4GHz 802.11n, 20/40, with unkoen Tx? and Rx? chains

 

Generally speaking 40MHz channels on 2.4GHz is not generally available / recommended.  Most of the time the 2.4GHz spectrum is too crowded.  Just because you request 20/40 in most cases it will just be 20MHz.  Similarly, many laptops only have 1x1 radios/antennas.  Some have 2x2.  A few very high end laptops have 3x3, but this is very rare.

 

The marketing speeds listed for Access points give a fictious best case scenario (note that I'm using rough numbers to make a point, the actual details of the negotiated link rates are somewhat more complicated)

 

For example AC1750 -- This is never possible, as you cannot "carrier aggregate" across the 2.4GHz and 5.8Ghz radios (unlike what can be done with modern cellular phones)

 

For the 2.4GHz radio, the marketing "speed" is listed as 450 Mbit/sec 

 

This assumes the following:


1) 3x3 chain radios on the client and the AP (the EAP245 has 3, but your clients most likely do not).  Most Wifi devices are only 1x1.  Maybe 30-40% are 2x2.  Less than 5% are 3x3.  

2) The 150 Mbit/sec per chain, assumes 40MHz.  Which, like I said, is typically only 20Mhz.  So this brings us down to ~75 Mbit/sec per chain.

3) Finally, the "air link rate" that is reported for your wifi device's connection is not the actual throughput you can expect to get.  Typically, the "goodput" or application level throughput is roughly 50-60% of the air link rate due to overhead, noise, frame headers, collissions, retransmitted frames, etc.

 

So, if, at the end of the day, you're getting ~40-50Mbit/sec through a 2.4GHz link, you're actually doing pretty good.

 

For example, on a 802.11ac 5.8Ghz 80MHz 2x2 link, with perfect signal, your air link rate will be 866 Mbit/sec. One can expect to get at most ~400-500 Mbit/sec out of this in terms of application level (e.g. file transfer) throughput.  Even though the AP can "theoretically" do 1200 Mbit/sec.

 

I should also add, that because both your file "server" and file "client" are wireless, in the example you gave, they are both actively completing for time on the AP during this test.  So there is some additional overhead taking place reducing speeds a bit farther, still.

 

Did that answer your question?

 

-Jonathan

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Re:"Slow" speed on WiFi - EAP-Solution
2020-11-16 17:00:01 - last edited 2020-11-16 18:50:58

@Xstreem 

 

This is a really nice whitepaper that describes things a bit more accurately than I could:

 

https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-3600-series/white-paper-c11-713103.pdf

 

This one is good, too:

https://www.intel.com/content/www/us/en/support/articles/000005725/network-and-i-o/wireless.html

 

 

-Jonathan

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Re:"Slow" speed on WiFi - EAP
2020-11-16 18:50:49

@JSchnee21 Thank you very much John, your answer and the Intel link gave me all the explanations. Thanks again.

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Re:"Slow" speed on WiFi - EAP
2020-11-16 19:01:03
Awesome! My pleasure.
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