Why I'm getting only half of TX/RX rate

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Why I'm getting only half of TX/RX rate

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Why I'm getting only half of TX/RX rate
Why I'm getting only half of TX/RX rate
2020-03-30 14:03:32 - last edited 2020-04-01 07:35:54
Model: CPE520  
Hardware Version:
Firmware Version:

 

I have 100mbps internet connection. but I noticed that I can only receive half of given TX/RX, is there a configuration I missed? or it really worked that way? 
also noticed that same with link speed.

I have old TP link router that is capable of 45mbps, in link speed it says 30 mbps, in speedtest I'm getting 15mbps only. 

what's the reason with "half" actual speed.? 

thanks in advance

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Re:Why I'm getting only half of TX/RX rate-Solution
2020-03-31 12:42:47 - last edited 2020-04-01 07:35:54

@NAJIV, you compare Ethernet bandwidth with WiFi rate (apples, oranges).

 

WiFi rate is the throughput over a half-duplex, shared medium. This is the amount of WiFi frames being received or transmitted, including protocol overhead.

 

Ethernet bandwidth is the throughput (also called »goodput«) over a full-duplex medium such as an Ethernet cable, excluding protocol overhead.

 

For 802.11b, goodput can be as low as roughly 50% of the throughput. For g/n, loss of bandwidth due to protocol overhead is nearly 30%.

 

So let's do the math: A N300 AP such as a CPE can transmit wireless frames at 300 Mbps WiFi rate, but only in one direction at a given time:

 

 

When we assume 802.11n-only mode and 40 MHz channel width, data throughput (the goodput of TCP/IP-encapsulated data) is about 210 Mbps (300 Mbps - 90 Mbps = 210 Mbps). However, this is half-duplex which means it's the throughput in one direction only:

 

Now, when sending and receiving, the direction of WiFi frames travelling through the air changes on a half-duplex medium:

 

 

On the full-duplex Ethernet interface (WLAN7 is an Ethernet interface), data flows bidirectional, which means a 100 Mbps interface can transmit data at 200 Mbps, that's 100 Mbps in sending direction and 100 Mbps in receiving direction simultaneously. That's why you see a much lower goodput in speed tests compared to the WiFi rate / the Ethernet throughput:

 

 

 

Additional notes:

  1. WiFi rate negotiated between sender and receiver always changes between 6 Mbps and max. rate at 802.11n due to signal quality, interferences, idle time etc.
  2. Speed always remains the same for EM waves: they are travelling at nearly speed of light. Only the amount of data transmitted over EM waves is different (that's bandwidth, throughput).

 

So, to get best goodput use:

  • 802.11n-only mode between two CPEs,
  • 40 MHz channel width for CPE510, 20 Mhz for CPE210 (depending on how overcrowded your area is, you can also try 40 MHz channel width),
  • MAXtream TDMA disabled,
  • exact distance setting (real distance + 0.1km or »Auto« to let the CPE determine best setting),
  • properly aligned antennas.

 

 

 

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Re:Why I'm getting only half of TX/RX rate-Solution
2020-03-31 12:42:47 - last edited 2020-04-01 07:35:54

@NAJIV, you compare Ethernet bandwidth with WiFi rate (apples, oranges).

 

WiFi rate is the throughput over a half-duplex, shared medium. This is the amount of WiFi frames being received or transmitted, including protocol overhead.

 

Ethernet bandwidth is the throughput (also called »goodput«) over a full-duplex medium such as an Ethernet cable, excluding protocol overhead.

 

For 802.11b, goodput can be as low as roughly 50% of the throughput. For g/n, loss of bandwidth due to protocol overhead is nearly 30%.

 

So let's do the math: A N300 AP such as a CPE can transmit wireless frames at 300 Mbps WiFi rate, but only in one direction at a given time:

 

 

When we assume 802.11n-only mode and 40 MHz channel width, data throughput (the goodput of TCP/IP-encapsulated data) is about 210 Mbps (300 Mbps - 90 Mbps = 210 Mbps). However, this is half-duplex which means it's the throughput in one direction only:

 

Now, when sending and receiving, the direction of WiFi frames travelling through the air changes on a half-duplex medium:

 

 

On the full-duplex Ethernet interface (WLAN7 is an Ethernet interface), data flows bidirectional, which means a 100 Mbps interface can transmit data at 200 Mbps, that's 100 Mbps in sending direction and 100 Mbps in receiving direction simultaneously. That's why you see a much lower goodput in speed tests compared to the WiFi rate / the Ethernet throughput:

 

 

 

Additional notes:

  1. WiFi rate negotiated between sender and receiver always changes between 6 Mbps and max. rate at 802.11n due to signal quality, interferences, idle time etc.
  2. Speed always remains the same for EM waves: they are travelling at nearly speed of light. Only the amount of data transmitted over EM waves is different (that's bandwidth, throughput).

 

So, to get best goodput use:

  • 802.11n-only mode between two CPEs,
  • 40 MHz channel width for CPE510, 20 Mhz for CPE210 (depending on how overcrowded your area is, you can also try 40 MHz channel width),
  • MAXtream TDMA disabled,
  • exact distance setting (real distance + 0.1km or »Auto« to let the CPE determine best setting),
  • properly aligned antennas.

 

 

 

༺ 0100 1101 0010 10ཏ1 0010 0110 1010 1110 ༻
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Re:Why I'm getting only half of TX/RX rate
2020-04-04 19:04:49

Thank you for such a wealth of information. I have been looking for an answer to this question for a long time.

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