First, here is the link to the latest VSG that is referred to in this discussion.
Then, my observation is that the difference between the older VRF and the newer VSG is that the power difference between 2.4 and 5GHz (and now also 6GHz) has changed from 6dB to 'at least 6dB'. That 6dB comes from the free-path-loss that on the higher 5GHz frequency is about 6dB higher (more loss) than on 2.4GHz, and by putting 6dB more transmit power, you compensate for that. One important reason for that is that coverage on 5GHz should be at least as good as on 2.4 to prevent clients picking the 2.4 band because it has a stronger signal. Then my personal view is that this matches what is in the newer VSG, and the stronger the signal (within the limits of co-channel-interference), on 5GHz the better. Because the stronger the signal (without CCI), the better SNR, and the higher MCS, thus better performance. Not sure if this matches the official Aruba standpoint or explanation, but the logic sounds for me.
Then one 'urban myth' about 'power inbalance' between AP and client (again, how I understood it from people that I respect for their knowledge). First of all, the transmit and receive MCS can be different to and from the client. Because most traffic is (in general) from the AP to the client, having the best SNR, thus MCS, provides the best performance overall. The responses back from the client to the AP are smaller frames like acknowledgements. The the power inbalance suggests that the client does not have enough power to reach the AP. If that would be the case, the connection would not come up, and the client would get to a closer AP where it has better signal, so the AP where you would fear the power-inbalance would not be used anyway. Also remember that the MCS from the client to the AP is independent from the transmit power of the AP, so with lower AP transmit power, that AP would not be reachable either in that case. That means that only in coverage designs, the uplink power from client to AP would play a role, in capacity designs, that uplink power is a 'constant' and the MCS to the AP would not change. The MCS from AP to client could benefit from a better SNR, so higher transmit power from the AP with the remark that cells should not become to large and should not significantly overlap.
Once more, this is my personal view based on discussions I had with people I respect for their knowledge and experience in the field, and it matches the change in guidance in the latest VSG. I'll try to find the author of the guide and check if my explanation is correct.
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Herman Robers
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Original Message:
Sent: Jul 08, 2023 09:22 PM
From: cdelarosa
Subject: Transmit power recommendation
So anyone from Aruba can answer this? I would really want to know why did you guys change the parameters
Original Message:
Sent: Jun 27, 2023 04:29 PM
From: mkk
Subject: Transmit power recommendation
Good question, i personally prefer the old documentation.
- 6dBm between 2.4GHz and 5Ghz is to equal the cellsize of both bands.
- Transmitted tx power should be matched to the max transmit power of your mobile devices, usually 15dBm.
- Each 3dBm is a doubling or halving the transmit power.
I'm also curious why the values in the new documentation deviate so much.
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Marcel Koedijk | MVP Expert 2023 | ACEP | ACMP | ACCP | ACDP | Ekahau ECSE | Not an HPE Employee | Opinions are my own
Original Message:
Sent: Jun 26, 2023 06:31 PM
From: cdelarosa
Subject: Transmit power recommendation
I was reading the VSG and i read something that got my attention
Before it was this
Why the change?
Another question i have
If i got a AP that its transmit power its like 20dBm and and i have a device that its transmit max transmit power its 15dBm it wouldnt gave it issues if the AP set at 20 dBm?
Maybe i got lost in the when reading the guide or im just misunderstanding the concepts
Can anyone help me?
Thanks