Interpreting Tx/Rx rates as found in Client Monitor's Client Info messages

  • 1
  • Question
  • Updated 4 years ago
  • Answered
Hi guys, I need some help in reading the Client Monitor output regarding Tx and Rx rate values.

Basically,
when there is no throughput noted for the client, the Tx rate is
reasonable (e.g. 78 Mbps), and the Rx rate is always indicated with 1
Mbps. As soon as we see traffic flowing through, the Rx rate is
indicated with something reasonable (e.g. 39 Mbps).

See the 2 example messages:

02/06/2014
05:54:10 PM  14109FD432F3                LHE-LR-Farms1-3-S  DETAIL 
(294)Client Info: [Up throughtput: 0 kbps, Down throughtput: 0 kbps, Tx
Rate: 78 mbps, Rx Rate: 1 mbps, RSSI: -71, Noise floor: -92, Client type:6,
Channel: 11, Client health score: 100]

 

02/06/2014
05:54:35 PM  14109FD432F3                LHE-LR-Farms1-3-S  DETAIL 
(319)Client Info: [Up throughtput: 12 kbps, Down throughtput: 11 kbps,
Tx Rate: 78 mbps, Rx Rate: 39 mbps, RSSI: -78, Noise floor: -92, Client type:6,
Channel: 11, Client health score: 100]

Question is: Is this the normal behaviour, and what is the
cause? (E.g. is the client reducing its own Tx rate when no traffic is
generated, or is the AP radio not able to determine the Rx rate when
there is no traffic?)

Or is this a hint that we do have an issue with the wireless transmission path from clients back to the Access Point?


PS: I do know that the RSSI is very low, especially in the 2nd message, giving a SNR of 14...

Photo of Carsten Buchenau

Carsten Buchenau, Champ

  • 356 Posts
  • 117 Reply Likes

Posted 4 years ago

  • 1
Photo of Brian Powers

Brian Powers, Champ

  • 396 Posts
  • 92 Reply Likes
A packet analysis would reveal a lot more information on this matter.  But here is my interpretation of things...

Example 1 - no throughput.  But there are most likely QoS Null Data frames being sent from the client to the AP and being ACK'd by the AP (at the lowest base data rate, possibly 1 Mbps).  No issue here that I'm aware of as I've seen the same things happen when I was in charge of a Meru network.  We had Vocera badges that when idle would have high Tx, but low Rx and the QoS Null Data frame & ACK is what I attested it to as when I would initiate or send a call to said device, the Rx would increase as frames with a true payload were being delivered at a higher data rate.

Example 2 - 12U/11D throughput.  This one is more tricky, but I believe what you are seeing is also normal.  It was always my understanding that the APs have superior hardware in them when compared to the clients.  So the datasheet for the AP121 says that it can Tx @ MCS7 (65 Mbit/s) where as the client might only be able to use MCS4 (39 Mbit/s) at the same RSSI/SNR levels.

Again, my interpretation and I could be WAY off... :)
Photo of Carsten Buchenau

Carsten Buchenau, Champ

  • 356 Posts
  • 117 Reply Likes
Thanks Brian!

Your explanation for Rx=1Mbps sound logical, that would make sense.

The point is that we do have a coverage issue at this location, and I am looking for data to back it up / narrow it down. Next step is to enhance the infrastructure (adding APs, changing AP330 with AP350 to get 360° signal distribution, ...), and it would be good to know what data to compare after the change.

Guess I keep looking at RSSI / SNR values, as well as retry times and loss for radios.
Photo of Carsten Buchenau

Carsten Buchenau, Champ

  • 356 Posts
  • 117 Reply Likes
For the record: We did a proper site survey and re-deployed all existing APs plus added a few more. All good now - so yes, the issues we saw were related to coverage, density and throughput.

A typical scenario where wireless was deployed, once upon a time, for coverage with low or medium throughput demands and 1 or 2 devices per user. Now the demands are for 3 - 5 devices per user, and "Youtube must always work". Suddenly, the installation didn't work anymore, and just adding a few APs here and there wouldn't have solved it.