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Wireless slow performance issue

singhkulbir29881
Beginner
Beginner

I have Cisco AP 1242. When I started something to download from Internet maximum downloading speed goes upto 16 Mbps even I have 40 Mbps link from ISP. While troubleshooting, I monitored AP fastethernet interface pointing towards WLC and radio interface, and found some error counters were increment while downloading. Following are some outputs:-

AP# show interface Dot1 0

!

 Input queue: 0/1048/75/0 (size/max/drops/flushes); Total output drops: 85
Queueing strategy: fifo
Output queue: 0/30 (size/max)
30 second input rate 8000 bits/sec, 8 packets/sec
30 second output rate 2000 bits/sec, 2 packets/sec
3604753 packets input, 464864218 bytes, 0 no buffer
3959188 packets output, 616251261 bytes, 0 underruns
27719 output errors, 0 collisions, 4 interface resets
0 unknown protocol drops

AP# show interface Fastethernet0
Input queue: 41/1048/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/40 (size/max)
30 second input rate 6000 bits/sec, 8 packets/sec
30 second output rate 22000 bits/sec, 17 packets/sec
7286764 packets input, 656786273 bytes
Received 128810 broadcasts, 0 runts, 0 giants, 0 throttles
2347545 packets output, 424028626 bytes, 0 underruns
0 output errors, 0 collisions, 3 interface resets
11284 unknown protocol drops

Question- Even the fastethernet interface utilization was very low then why packets were buffered in input Queue?

Another "show controller" output has been taken. In Dot 11 statistics section, CRC errors, CTS not received, Retries, Invalid header etc counters were increment while downloading. Following is the output:-

DOT11 Statistics (Cumulative Total/Last 5 Seconds):
RECEIVER                                                 TRANSMITTER
Host Rx K Bytes: 3080236 / 101                Host Tx K Bytes: 505274 / 5216
Unicasts Rx: 16142436 / 1779                   Unicasts Tx: 67365332 / 3560
Unicasts to host: 16142436 / 1779             Unicasts by host: 23527967 / 3534
Broadcasts Rx: 185864473 / 148               Broadcasts Tx: 86691313 / 98
Beacons Rx: 60486095 / 68                       Beacons Tx: 86691311 / 98
Broadcasts to host:92830298 / 74             Broadcasts by host: 2 / 0
Multicasts Rx: 375269 / 0                           Multicasts Tx: 222620 / 0
Multicasts to host: 0 / 0                              Multicasts by host: 222620 / 0
Mgmt Packets Rx: 32422617 / 6                Mgmt Packets Tx: 43480383 / 0
RTS received: 5 / 0                                    RTS transmitted: 2274275 / 86
Duplicate frames: 490387 / 59                  CTS not received: 1058802 / 11
CRC errors: 101210915 / 174                   Unicast Fragments Tx: 66970191 / 3536
WEP errors: 886 / 0                                  Retries: 9272649 / 2071
Buffer full: 0 / 0                                         Packets one retry: 2964819 / 732
Host buffer full: 0 / 0                                 Packets > 1 retry: 2160972 / 499
Header CRC errors: 46091 / 0                 Protocol defers: 13279037 / 431
Invalid header: 1534748 / 22                   Energy detect defers: 15200490 / 14
Length invalid: 0 / 0                                 Jammer detected: 336 / 0
Incomplete fragments: 30 / 0                   Packets aged: 0 / 0
Rx Concats: 0 / 0                                    Tx Concats: 0 / 0

RATE 1.0
Rx Packets: 93405277 / 74 Tx Packets: 51729 / 0
Rx Bytes: 2126460368 / 14960 Tx Bytes: 20010463 / 0
RTS Retries: 151775 / 0 Data Retries: 215567 / 0

RATE 2.0
Rx Packets: 260512 / 0 Tx Packets: 22105 / 0
Rx Bytes: 35130734 / 0 Tx Bytes: 12298677 / 0
RTS Retries: 34439 / 0 Data Retries: 88357 / 0

RATE 5.5
Rx Packets: 484293 / 0 Tx Packets: 183769 / 0
Rx Bytes: 83138985 / 0 Tx Bytes: 224332357 / 0
RTS Retries: 43846 / 0 Data Retries: 168707 / 0

RATE 11.0
Rx Packets: 765181 / 0 Tx Packets: 212643 / 0
Rx Bytes: 87144682 / 0 Tx Bytes: 224945368 / 0
RTS Retries: 55067 / 0 Data Retries: 296399 / 0

RATE 6.0
Rx Packets: 378998 / 0 Tx Packets: 148977 / 0
Rx Bytes: 23148640 / 0 Tx Bytes: 143801572 / 0
RTS Retries: 37528 / 0 Data Retries: 182116 / 0

RATE 9.0
Rx Packets: 67255 / 0 Tx Packets: 156533 / 0
Rx Bytes: 42341496 / 0 Tx Bytes: 156315093 / 0
RTS Retries: 30721 / 0 Data Retries: 169733 / 0

RATE 12.0
Rx Packets: 250570 / 0 Tx Packets: 573978 / 5
Rx Bytes: 84769975 / 0 Tx Bytes: 655506995 / 7540
RTS Retries: 74659 / 2 Data Retries: 612798 / 31

RATE 18.0
Rx Packets: 1092528 / 0 Tx Packets: 930207 / 43
Rx Bytes: 258436745 / 0 Tx Bytes: 1134151231 / 64844
RTS Retries: 97805 / 3 Data Retries: 1484102 / 203

RATE 24.0
Rx Packets: 1510941 / 3 Tx Packets: 2307663 / 120
Rx Bytes: 443365624 / 144 Tx Bytes: 2896935713 / 180960
RTS Retries: 2 / 0 Data Retries: 1535184 / 388

RATE 36.0
Rx Packets: 2057633 / 2 Tx Packets: 7214023 / 280
Rx Bytes: 820644775 / 96 Tx Bytes: 1126230387 / 422240
RTS Retries: 7 / 0 Data Retries: 1806433 / 604

RATE 48.0
Rx Packets: 2135521 / 527 Tx Packets: 5614880 / 2645
Rx Bytes: 614911862 / 25394 Tx Bytes: 2931077826 / 3980065
RTS Retries: 0 / 0 Data Retries: 1375588 / 706

RATE 54.0
Rx Packets: 6564025 / 1247 Tx Packets: 6064532 / 441
Rx Bytes: 666253762 / 63282 Tx Bytes: 3434959023 / 646344
RTS Retries: 0 / 0 Data Retries: 811816 / 134

Anybody have any idea? Are these counters causing WiFi slowness performance issue? Please reply.

5 Replies 5

Leo Laohoo
VIP Community Legend VIP Community Legend
VIP Community Legend

Anybody have any idea? Are these counters causing WiFi slowness performance issue?

Disable the 802.11b radio and see if the performance improves.

Hi Leo Laohoo,

Access point have two radio interfaces 

AP# sh int dot11Radio0
Dot11Radio0 is up, line protocol is up
Hardware is 802.11G Radio,

!

AP# sh int dot11Radio 1
Dot11Radio1 is up, line protocol is up
Hardware is 802.11A Radio,

As the output says the interfaces are 802.11G & 802.11A, which radio you are talking about to disable? 

Hello,

Disabling the 802.11b rates will increase the overall performance of the network. To do this you have to disable the following rates: 1, 2, 5.5 and 11. These are on the 2.4 GHz band, so the change has to be done on radio 0.

In addition, I want to make sure you are not comparing wireless rates to wired speeds. You mentioned that you have a 40 Mbps connection from your ISP but this does not mean that you will have that rate on wireless since these are two different technologies.

Wireless uses the air as its medium and has to share it with all clients which means that the available "speed" will be devided between all the clients. Also, WiFi transmissions are half-duplex; every radio can only receive or transmit a frame, cannot do both at the same time. Today's technology allows to have transmissions and receptions at the same time but with different streams (and other technical stuff) but at the end of the day it continues to be half duplex.

So, depending on the air quality, quantity of clients, configuration, clients drivers etc you will see a reduction on your performance and cannot be compared to wired.

If you want a more accurate test for wireless only you can use iperf:

https://supportforums.cisco.com/document/12068771/iperf-test-measuring-throughputspeed-wlan-client

I hope this information helps

Marco Gonzalez

Hello Marco Gonzalez,

Thanks for reply. I understand what you want to say but even if a single client is associated, throughput is same (means 16Mbps)

What does these counter ( CRC errors, CTS not received, Retries, Invalid header etc) increment means?

What are the possible reasons for these counters increment?

Disable radio interface Dot110.

What does these counter ( CRC errors, CTS not received, Retries, Invalid header etc) increment means?

Wireless transmission always operate in half duplex:  One talks and everyone else waits for their turn.  CRC, CTS, etc ... these errors will always increment when the wireless environment is either noisy or too much co-channel interference.

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