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Client occationally drop from 200Mbps to 40Mbps on 5Ghz 40Mhz VHT

A customer of mine have reported odd performance issues running with IAP-305 or IAP-315 on 5Ghz, 40Mhz VHT channels.

 

In an attempt to reproduce the problem I've deployed a single IAP-315 connected to a 2530-24G-PoEP switch. Connected to the switch is a wired desktop running Linux and iperf3 in server mode.

 

The IAP broadcasts a single SSID "MathiasPSK" on 5GHz, 40MHz and VHT enabled, and there are no other 5GHz APs or devices in the neighbourhood:

 

a8:bd:27:c0:44:fc# show ap spectrum channel-details

Channel Summary Table
---------------------
Channel  Quality(%)  Utilization(%)  WiFi(%)  Bluetooth(%)  Microwave(%)  Cordless Phone(%)  Total nonwifi(%)  KnownAPs  UnknownAPs  Noise Floor(dBm)  MaxAPSignal(dBm)  Max AP SSID  Max AP BSSID  MaxInterference(dBm)  SNIR(dB)
-------  ----------  --------------  -------  ------------  ------------  -----------------  ----------------  --------  ----------  ----------------  ----------------  -----------  ------------  --------------------  --------
52+      100         0               0        0             0             0                  0                 1         0           -94               -                 -            -             -                     0

While only having a single laptop or two connected, I can both send and receive 200+ Mbps from my laptop "IT-089":

 

C:\Users\mathias.sundman\Downloads\iperf-3.1.3-win64>iperf3 -c 192.168.88.99
Connecting to host 192.168.88.99, port 5201
[  4] local 192.168.88.60 port 50537 connected to 192.168.88.99 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  25.5 MBytes   213 Mbits/sec
[  4]   1.00-2.00   sec  22.6 MBytes   190 Mbits/sec
[  4]   2.00-3.01   sec  24.6 MBytes   205 Mbits/sec
[  4]   3.01-4.00   sec  24.2 MBytes   204 Mbits/sec


C:\Users\mathias.sundman\Downloads\iperf-3.1.3-win64>iperf3 -c 192.168.88.99 -R
Connecting to host 192.168.88.99, port 5201
Reverse mode, remote host 192.168.88.99 is sending
[  4] local 192.168.88.60 port 49826 connected to 192.168.88.99 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  27.3 MBytes   229 Mbits/sec
[  4]   1.00-2.00   sec  29.4 MBytes   247 Mbits/sec
[  4]   2.00-3.00   sec  29.7 MBytes   249 Mbits/sec
[  4]   3.00-4.00   sec  29.3 MBytes   246 Mbits/sec

The client-table while everything is good looks like this:

a8:bd:27:c0:44:fc# show clients

Client List
-----------
Name             IP Address     MAC Address        OS       ESSID       Access Point       Channel  Type  Role        IPv6 Address               Signal    Speed (mbps)
----             ----------     -----------        --       -----       ------------       -------  ----  ----        ------------               ------    ------------
IT-089           192.168.88.60  a4:34:d9:63:f9:0c  Windows  MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  fe80::7455:924e:6276:4868  62(good)  400(good)
Mathiass-MBP     192.168.88.80  f4:0f:24:19:b0:f9  Win XP   MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  --                         47(good)  600(good)

a8:bd:27:c0:44:fc# show ap debug client-table

Client Table
------------
MAC                ESSID       BSSID              Assoc_State  HT_State    AID  PS_State    UAPSD            Tx_Pkts  Rx_Pkts  PS_Qlen  Tx_Retries  Tx_Rate  Rx_Rate  Last_ACK_SNR  Last_Rx_SNR  TX_Chains  Tx_Timestamp              Rx_Timestamp              MFP Status (C,R)  Idle time  Client health (C/R)  Tx_Bytes   Rx_Bytes
---                -----       -----              -----------  --------    ---  --------    -----            -------  -------  -------  ----------  -------  -------  ------------  -----------  ---------  ------------              ------------              ----------------  ---------  -------------------  --------   --------
f4:0f:24:19:b0:f9  MathiasPSK  a8:bd:27:84:4f:d0  Associated   AWvSsEeBbM  0x1  Power-save  (0,0,0,0,N/A,0)  243115   205125   0        23          600      48       48            51           4[0xf]     Thu Apr 13 22:03:43 2017  Thu Apr 13 22:03:43 2017  (0,0)             29         100/93               480550541  529986917
a4:34:d9:63:f9:0c  MathiasPSK  a8:bd:27:84:4f:d0  Associated   AWvSsEBbM   0x2  Awake       (0,0,0,0,N/A,0)  39       219      0        0           400      400      67            55           4[0xf]     Thu Apr 13 22:04:06 2017  Thu Apr 13 22:04:06 2017  (0,0)             6          100/93               15574      25012

A little later, most likely after I had joined also my iPhone to the network, my laptop "IT-089" suddenly can only transmit about 40Mbps. It can still receive +200M though:

 

C:\Users\mathias.sundman\Downloads\iperf-3.1.3-win64>iperf3 -c 192.168.88.99
Connecting to host 192.168.88.99, port 5201
[  4] local 192.168.88.60 port 50684 connected to 192.168.88.99 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  4.88 MBytes  40.8 Mbits/sec
[  4]   1.00-2.00   sec  5.12 MBytes  43.0 Mbits/sec
[  4]   2.00-3.00   sec  5.12 MBytes  43.0 Mbits/sec
[  4]   3.00-4.00   sec  5.12 MBytes  43.0 Mbits/sec

C:\Users\mathias.sundman\Downloads\iperf-3.1.3-win64>iperf3 -c 192.168.88.99 -R
Connecting to host 192.168.88.99, port 5201
Reverse mode, remote host 192.168.88.99 is sending
[  4] local 192.168.88.60 port 50754 connected to 192.168.88.99 port 5201
[ ID] Interval           Transfer     Bandwidth
[  4]   0.00-1.00   sec  24.0 MBytes   201 Mbits/sec
[  4]   1.00-2.00   sec  25.5 MBytes   214 Mbits/sec
[  4]   2.00-3.00   sec  25.3 MBytes   213 Mbits/sec
[  4]   3.00-4.00   sec  24.9 MBytes   208 Mbits/sec

Examining the client-table again still says that IT-089 has a Tx_Rate and Rx_Rate of 400:

 

a8:bd:27:c0:44:fc# show clients

Client List
-----------
Name             IP Address     MAC Address        OS       ESSID       Access Point       Channel  Type  Role        IPv6 Address               Signal    Speed (mbps)
----             ----------     -----------        --       -----       ------------       -------  ----  ----        ------------               ------    ------------
Mathiass-iPhone  192.168.88.77  b4:8b:19:db:38:b1           MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  --                         56(good)  360(good)
SELT-0046        192.168.88.59  e8:b1:fc:08:39:41  Win 7    MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  fe80::a06e:2ac6:fdaa:9aec  56(good)  400(good)
IT-089           192.168.88.60  a4:34:d9:63:f9:0c  Windows  MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  fe80::7455:924e:6276:4868  62(good)  400(good)
Mathiass-MBP     192.168.88.80  f4:0f:24:19:b0:f9  Win XP   MathiasPSK  a8:bd:27:c0:44:fc  52+      AC    MathiasPSK  --                         47(good)  600(good)
Number of Clients   :4
Info timestamp      :6737


a8:bd:27:c0:44:fc# show ap association

The phy column shows client's operational capabilities for current association

Flags: A: Active, B: Band Steerable, H: Hotspot(802.11u) client, K: 802.11K client, M: Mu beam formee, R: 802.11R client, W: WMM client, w: 802.11w client V: 802.11v BSS trans capable

PHY Details: HT   : High throughput;      20: 20MHz;  40: 40MHz; t: turbo-rates (256-QAM)
             VHT  : Very High throughput; 80: 80MHz; 160: 160MHz; 80p80: 80MHz + 80MHz
             <n>ss: <n> spatial streams

Association Table
-----------------
Name               bssid              mac                auth  assoc  aid  l-int  essid       vlan-id  tunnel-id  phy              assoc. time  num assoc  Flags  DataReady
----               -----              ---                ----  -----  ---  -----  -----       -------  ---------  ---              -----------  ---------  -----  ---------
a8:bd:27:c0:44:fc  a8:bd:27:84:4f:d0  b4:8b:19:db:38:b1  y     y      4    20     MathiasPSK  1        0x0        a-VHT-40sgi-2ss  1m:53s       1          WV     Yes (Implicit)
a8:bd:27:c0:44:fc  a8:bd:27:84:4f:d0  e8:b1:fc:08:39:41  y     y      3    250    MathiasPSK  1        0x0        a-VHT-40sgi-2ss  23s          1          W      Yes (Implicit)
a8:bd:27:c0:44:fc  a8:bd:27:84:4f:d0  a4:34:d9:63:f9:0c  y     y      2    250    MathiasPSK  1        0x0        a-VHT-40sgi-2ss  14s          1          W      Yes (Implicit)
a8:bd:27:c0:44:fc  a8:bd:27:84:4f:d0  f4:0f:24:19:b0:f9  y     y      1    10     MathiasPSK  1        0x0        a-VHT-40sgi-3ss  53m:54s      1          W      Yes (Implicit)
Num Clients:4
a8:bd:27:c0:44:fc# show ap debug client-table

Client Table
------------
MAC                ESSID       BSSID              Assoc_State  HT_State    AID  PS_State    UAPSD            Tx_Pkts  Rx_Pkts  PS_Qlen  Tx_Retries  Tx_Rate  Rx_Rate  Last_ACK_SNR  Last_Rx_SNR  TX_Chains  Tx_Timestamp              Rx_Timestamp              MFP Status (C,R)  Idle time  Client health (C/R)  Tx_Bytes   Rx_Bytes
---                -----       -----              -----------  --------    ---  --------    -----            -------  -------  -------  ----------  -------  -------  ------------  -----------  ---------  ------------              ------------              ----------------  ---------  -------------------  --------   --------
f4:0f:24:19:b0:f9  MathiasPSK  a8:bd:27:84:4f:d0  Associated   AWvSsEeBbM  0x1  Power-save  (0,0,0,0,N/A,0)  245028   209414   0        26          600      540      48            47           4[0xf]     Thu Apr 13 22:29:57 2017  Thu Apr 13 22:29:57 2017  (0,0)             7          97/94                481564301  530766840
b4:8b:19:db:38:b1  MathiasPSK  a8:bd:27:84:4f:d0  Associated   AWvSsEe     0x4  Power-save  (0,0,0,0,N/A,0)  26       347      0        0           360      360      57            56           4[0xf]     Thu Apr 13 22:29:58 2017  Thu Apr 13 22:29:58 2017  (0,0)             6          100/94               4622       3713
e8:b1:fc:08:39:41  MathiasPSK  a8:bd:27:84:4f:d0  Associated   WvSsEbM     0x3  Awake       (1,1,1,1,2,0)    66       140      0        0           400      270      61            56           4[0xf]     Thu Apr 13 22:29:59 2017  Thu Apr 13 22:30:02 2017  (0,0)             2          100/94               21497      55268
a4:34:d9:63:f9:0c  MathiasPSK  a8:bd:27:84:4f:d0  Associated   AWvSsEBbM   0x2  Awake       (0,0,0,0,N/A,0)  10813    37469    0        231         400      400      77            63           4[0xf]     Thu Apr 13 22:30:02 2017  Thu Apr 13 22:30:03 2017  (0,0)             1          90/94                1692430    56257386

How can I further diagnose what is capping the traffic?

 

PS: During the day while troublshooting this behaviour in the customers network the problem moved between different clients (HP Latops, Lenovo laptops, Linux Laptops, Windows 10 laptops) and sometimes it was TX that was capped and sometimes it was RX.

 

Why?? I could understand it in a heavily used network, but we're talking about an isolated network without disturbance or any other client taking up the bandwidth...

 

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