Batman-adv high TQ and Low throughput
Recently i have experienced something quite usual to my experience and that was not happening previously in the same scenario where it is happening now.
Here is the example:
2 nodes at with adhoc at 2.4ghz at a distance of 415 meters
one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.
This link was previously providing up to 21 mbit being 17 mbit a the lowest. Batman-adv TQ value was always around 230 being many times above 250.
However this has recently changed the same link with 230~250 TQ and the same txpower is now outputting 1.93 Mbits/sec
I have used iperf for bandwidth tests. Batman-adv version is 2013.4. Although i have considered several types of scenarios that can be causing this issue i have also tested against some which leaves me puzzled in regards to the presented TQ quality and dBm values as the nodes dBm are sometimes bad (ie: -80 ~ -90)
One of the main questions is: shouldn't batman-adv TQ reflect or be influenced by dBm values ? How come with -90 dBm i get batman-adv to show me 230 TQ ?
Also any feedback based on your experience regarding this type of scenario is welcome. This situation happened overnight without any access point new configurations or physical setup changes.
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Quoted 21 lines
Recently i have experienced something quite usual to my experience and that was not happening previously in the same scenario where it is happening now.
Here is the example:
2 nodes at with adhoc at 2.4ghz at a distance of 415 meters
one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.This link was previously providing up to 21 mbit being 17 mbit a the lowest. Batman-adv TQ value was always around 230 being many times above 250.
However this has recently changed the same link with 230~250 TQ and the same txpower is now outputting 1.93 Mbits/sec
I have used iperf for bandwidth tests. Batman-adv version is 2013.4. Although i have considered several types of scenarios that can be causing this issue i have also tested against some which leaves me puzzled in regards to the presented TQ quality and dBm values as the nodes dBm are sometimes bad (ie: -80 ~ -90)
Quoted 3 lines
One of the main questions is: shouldn't batman-adv TQ reflect or be influenced by dBm values ? How come with -90 dBm i get batman-adv to show me 230 TQ ?
The current implementation in batman-adv counts broadcast packets to compute the TQ. Therefore this number reflects (more or less) the transmit success probability on whatever wifi broadcast modulation rate you have configured (default the lowest, e.g. 1M in 2.4 GHz). A common tweak is to set the broadcast rate (also called multicast rate) to something higher, e.g. 18M or 36M, to get a better analysis on these modulation rates. This should also help in your scenario, but might affect the range of your batman-adv network.
Cheers,
Simon
Hi,
I would like to add some additional insights I gained while working on my bachelor thesis (which of course used batman :D ).
The dBm you see is the power at which packets are received (Prx). The value of Prx depends on a lot of factors, primarily distance and interferrence caused by re/deflections [1].
There is a minimum Prx at which the signal must arrive in order for your Wi-Fi module to be able to see it as a proper signal rather than noise. This minimum, combined with (thermal) noise (N) gives you a signal-to-noise ratio, which should at least be about 15 dB (SNR = Prx - N >= 15).
N is usually somewhere around -100 dBm, meaning that a Prx of about -85 dBm is generally the minimum you need for succesful transmissions. Note that these numbers don't take into account any antennae you might be using, these are only really relevant for calculating the Prx. A higher number means the signal is clearer, but that's really all it means.
Because the Prx can only be determined if a packet arrives, the number in itself is meaningless without a time reference, which in turn would only indicate when the last packet was received.
Like Simon said, the transmission quality batman-adv returns is based on the probability of packets arriving properly on the other side of the Wi-Fi link.
Batman-adv uses counters to determine how many packets were lost and as a result gives a more informative view of how well the link behaves. Because the counters are based on packet reception, this means the Prx also has to be above the minimum.
In summary:
high dBm = the things that are received, are received very clearly high TQ = nearly everything you send is received.
High chance of proper reception => less retransmissions => higher throughput => happy you.
[1]: http://en.wikipedia.org/wiki/Path_loss
Signature · 2 lines
Thijs van Veen [email protected]
Quoted 40 lines · Simon Wunderlich
Quoted 21 lines
Recently i have experienced something quite usual to my experience and that was not happening previously in the same scenario where it is happening now.
Here is the example:
2 nodes at with adhoc at 2.4ghz at a distance of 415 meters
one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.This link was previously providing up to 21 mbit being 17 mbit a the lowest. Batman-adv TQ value was always around 230 being many times above 250.
However this has recently changed the same link with 230~250 TQ and the same txpower is now outputting 1.93 Mbits/sec
I have used iperf for bandwidth tests. Batman-adv version is 2013.4. Although i have considered several types of scenarios that can be causing this issue i have also tested against some which leaves me puzzled in regards to the presented TQ quality and dBm values as the nodes dBm are sometimes bad (ie: -80 ~ -90)
Quoted 3 lines
One of the main questions is: shouldn't batman-adv TQ reflect or be influenced by dBm values ? How come with -90 dBm i get batman-adv to show me 230 TQ ?
The current implementation in batman-adv counts broadcast packets to compute
the TQ. Therefore this number reflects (more or less) the transmit success
probability on whatever wifi broadcast modulation rate you have configured
(default the lowest, e.g. 1M in 2.4 GHz). A common tweak is to set the broadcast rate (also called multicast rate) to something higher, e.g. 18M or
36M, to get a better analysis on these modulation rates. This should also help
in your scenario, but might affect the range of your batman-adv network.Cheers,
Simon
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Quoted 1 line · Thijs van Veen
N is usually somewhere around -100 dBm, meaning that a Prx of about -85
unsure about that: it depends on the WiFi-receiver's quality, isn't it?
when i use 'iwinfo' the noise is always '-95', no matter on which location. it seems to come from nl80211_get_noise() but i dont understand it fully.
or do i mix something up? bye, bastian
It depends a bit on the receiver's quality, I've had experiences where the SNR could drop to about 8 and the link would still somewhat work.
The thermal noise is mostly intrinsic to how energy relates at a particle level, this is denoted by the Boltzmann constant (k). Further, it depends on the bandwidth (B) used and temperature (T). Nthermal = B * k * T = 20*10^6 Hz (802.11 channel) * 1.38065*10^-23 J/K
* 300 K (27 Celsius) ~= 8.28 * 10^-11
This gives the noise in Watts, to change it to dBm (which references miliWatts), you take 10*log10( N * 1000 ) ~= -100.
[1] Has a nice table with examples of this noise.
In reality, there's more interference than just from the temperature. It's quite probable your receiver adds another 5 dBm to its reported noise to account for this.
I also recall from my time working on my thesis that receivers/drivers tend to return a static value for noise, rather than actually measure it.
[1]:http://en.wikipedia.org/wiki/Thermal_noise#Noise_power_in_decibels
Signature · 2 lines
Thijs van Veen [email protected]
Quoted 10 lines · Bastian Bittorf
Quoted 1 line · Thijs van Veen
N is usually somewhere around -100 dBm, meaning that a Prx of about -85
unsure about that: it depends on the WiFi-receiver's quality, isn't it?
when i use 'iwinfo' the noise is always '-95', no matter on which location.
it seems to come fromnl80211_get_noise()but i dont understand it fully.or do i mix something up? bye, bastian
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love email againInline reply
Quoted 35 lines · Simon Wunderlich
Quoted 21 lines
Recently i have experienced something quite usual to my experience and that was not happening previously in the same scenario where it is happening now.
Here is the example:
2 nodes at with adhoc at 2.4ghz at a distance of 415 meters
one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.This link was previously providing up to 21 mbit being 17 mbit a the lowest. Batman-adv TQ value was always around 230 being many times above 250.
However this has recently changed the same link with 230~250 TQ and the same txpower is now outputting 1.93 Mbits/sec
I have used iperf for bandwidth tests. Batman-adv version is 2013.4. Although i have considered several types of scenarios that can be causing this issue i have also tested against some which leaves me puzzled in regards to the presented TQ quality and dBm values as the nodes dBm are sometimes bad (ie: -80 ~ -90)
Quoted 3 lines
One of the main questions is: shouldn't batman-adv TQ reflect or be influenced by dBm values ? How come with -90 dBm i get batman-adv to show me 230 TQ ?
The current implementation in batman-adv counts broadcast packets to compute the TQ. Therefore this number reflects (more or less) the transmit success probability on whatever wifi broadcast modulation rate you have configured (default the lowest, e.g. 1M in 2.4 GHz). A common tweak is to set the broadcast rate (also called multicast rate) to something higher, e.g. 18M or 36M, to get a better analysis on these modulation rates. This should also help in your scenario, but might affect the range of your batman-adv network.
Quoted 2 lines
what's the
mcast_ratevalue?
having 230~250 TQ on a -80/-90dBm link seems like you have a very lowmcast_rate.
I did try change the mcast_rate as well as the rate and while at first it did show some gains the same did not maintained after a few days.
dbm levels and throughput have not changed and in fact in a few cases my throughput got worse.
I tried with 36000 as well as 6000
I am now believing 2 possible scenarios:
1: Software/driver problems or bug
a) big or weak support that only came into effect after playing wit firmware settings. (re-flashing the routers without new or the same firmware should clear this doubt)
2: Interference caused by:
a) weather conditions that have changed since the nodes lost huge performance levels.
b) Although i am able to have the local community cooperation by having them changing their home routers to non overlapping frequencies i wonder how much of it can be caused by the network nodes and their co-existent channels. Then again this does nto explain why the loss of performance did not happened right away after the network upgrade.
However all these possibilities do not answer the fact that these nodes worked flawlessly for some time and one day overnight the problem happened.
c) deliberate interference caused by some possible competitor. although i cannot be sure at this moment; i see it as the biggest possibility.
In the past this has led me to look for this:
https://lists.openwrt.org/pipermail/openwrt-users/2013-April/002420.html
which keeps me thinking about Wi-Spy + Chanalyzer or equivalent if any.
Which i am currently, once again very included to do and suggestions/alternatives are welcome as well as wanted.
Hello Ben
Last night i decreased all the network access points to 17 dBm thinking if my problem is due too much noise from co-existent channels from same network nodes and unless i my conclusion is wrong i do not think the Ap's cause problems to each other because after the decrease in txpower; not only batman-adv TQ got lower as well as dBm and throughput. In other words there was no improvement and this is not the first time i try the sort of test.
Today i reverted to normal higher values and things improved but still far from whet they were when the nodes were upgraded.
I will describe the situation i have with 2 of the 3 access points. They all run ath9k on one radio with vap interfaces.
AP (A) uses a 15 dbi omni Atheros AR9132 rev 2
AP (B) uses a 8 dbi omni Atheros AR7240 rev 2
Distance from each other is about 100 metres.
Right now AP A is at 20 dbm and AP B at 19 dBm
From AP (B) to AP (A) i get:
Station AP (B) (on adhoc0)
inactive time: 20 ms rx bytes: 1087140 rx packets: 9708 tx bytes: 906 tx packets: 7 tx retries: 14 tx failed: 2 signal: -49 [-49, -58] dBm signal avg: -49 [-49, -58] dBm tx bitrate: 2.0 MBit/s rx bitrate: 1.0 MBit/s authorized: yes authenticated: yes preamble: long WMM/WME: yes MFP: no TDLS peer: no
Batman-adv TQ at 91 and with a hop in the middle. Without the hop batman-adv does not even see AP (A). The hop has a penalty of 150.
iperf reports:
0.0-10.3 sec 7.38 MBytes 6.02 Mbits/sec
However batman-adv chooses another gateway which is further away but doe not have a hop and gets less throughput
and continues to
inactive time: 30 ms rx bytes: 4320939 rx packets: 40264 tx bytes: 2561 tx packets: 18 tx retries: 55 tx failed: 9 signal: -59 [-59, -68] dBm signal avg: -58 [-59, -67] dBm tx bitrate: 2.0 MBit/s rx bitrate: 1.0 MBit/s
From AP (A) to AP (B)
Station AP (A) (on adhoc0)
inactive time: 1110 ms rx bytes: 106752 rx packets: 629 tx bytes: 1753 tx packets: 13 tx retries: 70 tx failed: 5 signal: -91 [-94, -111, -93] dBm signal avg: -89 [-93, -107, -91] dBm tx bitrate: 6.5 MBit/s MCS 0 rx bitrate: 6.0 MBit/s authorized: yes authenticated: yes preamble: long WMM/WME: yes MFP: no TDLS peer: no
Batman-adv TQ at 101 with the same hop in the middle iperf reports 7.38 MBytes 6.11 Mbits/sec
And this is somewhat an okay scenario since this link was at 17 dBm from AP (B) providing 15 mbit and with a TQ of 250 average.
Usually i get tx and rx bitrate around 1mbit from AP (A) side.
There is a huge discrepancy here with link quality and how batman-adv is doing the choice as well as signal and signal average.
Before Both sides were around -50 dBm in average but now AP (A) is always around -80 and worse.
Notice that these results are only possible due to the existence of a middle node that was setup as a backup.
Without the middle node AP (A) does not see AP (B).
I am inclined to think about a driver issue that got into play after i played with some configurations. I see this as a possibility for the tp-link routers i have in the mesh as the dlinks seem to perform better.
and continues to
inactive time: 1730 ms rx bytes: 186480 rx packets: 1303 tx bytes: 2381 tx packets: 17 tx retries: 92 tx failed: 8
Some more info bellow from AP (A)
Wireless kernel debug
Reset:
Baseband Hang: 0
Baseband Watchdog: 0
Fatal HW Error: 0
TX HW error: 0
TX Path Hang: 0
PLL RX Hang: 0
MCI Reset: 0Ani:
ANI: ENABLED
ANI RESET: 175
SPUR UP: 37
SPUR DOWN: 37 OFDM WS-DET ON: 0
OFDM WS-DET OFF: 0
MRC-CCK ON: 0
MRC-CCK OFF: 0
FIR-STEP UP: 27
FIR-STEP DOWN: 49
INV LISTENTIME: 0
OFDM ERRORS: 192247
CCK ERRORS: 200380Interrupt:
RX: 2352822
RXEOL: 0
RXORN: 0
TX: 498420
TXURN: 0
MIB: 0
RXPHY: 0
RXKCM: 0
SWBA: 2634014
BMISS: 0
BNR: 0
CST: 788
GTT: 34321
TIM: 0
CABEND: 0
DTIMSYNC: 0
DTIM: 0
TSFOOR: 0
MCI: 0
GENTIMER: 0
TOTAL: 5313102
SYNC_CAUSE stats:
Sync-All: 5165669
RTC-IRQ: 2863390
MAC-IRQ: 4227348
EEPROM-Illegal-Access: 2837451
APB-Timeout: 57826
PCI-Mode-Conflict: 57422
HOST1-Fatal: 43642
HOST1-Perr: 66006
TRCV-FIFO-Perr: 92477
RADM-CPL-EP: 58826
RADM-CPL-DLLP-Abort: 60567
RADM-CPL-TLP-Abort: 51149
RADM-CPL-ECRC-Err: 54651
RADM-CPL-Timeout: 89152
Local-Bus-Timeout: 69195
PM-Access: 80875
MAC-Awake: 104915
MAC-Asleep: 137511
MAC-Sleep-Access: 761892Dma:
Raw DMA Debug values:
0: 88888888 1: 00000000 2: 12249249 3: 00000000
4: 00000000 5: 00000000 6: 001d264c 7: 000281c0
Num QCU: chain_st fsp_ok fsp_st DCU: chain_st
0 0 1 1 0 1 0 1 1 0 2 0 1 1 0 3 0 1 1 0 4 0 1 1 0 5 0 1 1 0 6 0 1 1 0 7 0 1 1 0 8 0 0 1 0 9 0 0 1 0
qcu_stitch state: 0 qcu_fetch state: 0 qcu_complete state: 0 dcu_complete state: 0 dcu_arb state: 0 dcu_fp state: 0 chan_idle_dur: 147 chan_idle_dur_valid: 1 txfifo_valid_0: 0 txfifo_valid_1: 0 txfifo_dcu_num_0: 9 txfifo_dcu_num_1: 14 pcu observe: 0x2890 AR_CR: 0x4
Xmit:
BE BK VI VO
MPDUs Queued: 5747 0 0 7405 MPDUs Completed: 137383 0 0 4183 MPDUs XRetried: 7730 0 0 3222 Aggregates: 17209 0 0 0 AMPDUs Queued HW: 0 0 0 0 AMPDUs Queued SW: 308165 0 0 0 AMPDUs Completed: 168767 0 0 0 AMPDUs Retried: 12546 0 0 0 AMPDUs XRetried: 32 0 0 0 TXERR Filtered: 3 0 0 0 FIFO Underrun: 0 0 0 0 TXOP Exceeded: 0 0 0 0 TXTIMER Expiry: 0 0 0 0 DESC CFG Error: 0 0 0 0 DATA Underrun: 0 0 0 0 DELIM Underrun: 0 0 0 0 TX-Pkts-All: 313912 0 0 7405 TX-Bytes-All: 161389767 0 0 233291 HW-put-tx-buf: 12 0 0 146 HW-tx-start: 262235 0 0 7405 HW-tx-proc-desc: 262416 0 0 7405 TX-Failed: 0 0 0 0
Queues:
(VO): qnum: 0 qdepth: 0 ampdu-depth: 0 pending: 0 stopped: 0 (VI): qnum: 1 qdepth: 0 ampdu-depth: 0 pending: 0 stopped: 0 (BE): qnum: 2 qdepth: 0 ampdu-depth: 0 pending: 0 stopped: 0 (BK): qnum: 3 qdepth: 0 ampdu-depth: 0 pending: 0 stopped: 0 (CAB): qnum: 8 qdepth: 0 ampdu-depth: 0 pending: 0 stopped: 0
Quoted 149 lines · Ben West
What does "iw wlan0 station dump" have to say? In particular, what is the ratio of TX packets to TX retries (or failures)?
I've generally seen 10% TX retries, compared to total TX packets, to be quite ideal. A substantially higher percentage of TX retries, especially if over 100%, usually indicates a problem with noise or interference.
On Wed, Apr 30, 2014 at 6:57 PM, cmsv <[email protected] <mailto:[email protected]>> wrote:
inline reply
On 04/24/2014 05:27 AM, Nicolás Echániz wrote:
> El 24/04/14 05:34, cmsv escribió:
>> Recently i have experienced something quite usual to my experience and
>> that was not happening previously in the same scenario where it is >> happening now.
>>
>> Here is the example:
>> 2 nodes at with adhoc at 2.4ghz at a distance of 415 meters >> one uses an omni 15 dbi antenna at 18dbi and another 24 dbi grid at 16 dbi.
>>
>> This link was previously providing up to 21 mbit being 17 mbit a the >> lowest. Batman-adv TQ value was always around 230 being many times above
>> 250.
>>
>> However this has recently changed the same link with 230~250 TQ and the
>> same txpower is now outputting 1.93 Mbits/sec
>>
>> I have used iperf for bandwidth tests. Batman-adv version is 2013.4. >> Although i have considered several types of scenarios that can be >> causing this issue i have also tested against some which leaves me >> puzzled in regards to the presented TQ quality and dBm values as the >> nodes dBm are sometimes bad (ie: -80 ~ -90)
>>
>> One of the main questions is: shouldn't batman-adv TQ reflect or be >> influenced by dBm values ? How come with -90 dBm i get batman-adv to >> show me 230 TQ ?
>>
>> Also any feedback based on your experience regarding this type of >> scenario is welcome. This situation happened overnight without any >> access point new configurations or physical setup changes.> what's the
mcast_ratevalue?
>
> having 230~250 TQ on a -80/-90dBm link seems like you have a very low >mcast_rate.I have always used the driver default setup to decide the bitrate and that worked up to a certain moment. Specifying it did not do much better but today i found this message
ath: phy0: unsupported hw bitrate detected
0x1fusing 1 MbitCurrently:
wireless.@wifi-iface[0].mcast_rate=6000and i tested with up to 36000
But i have also gotten the unsupported hw bitrate message without setting
mcast_rateiwinfo reports:
Tx-Power: 19 dBm Link Quality: 36/70
Signal: -74 dBm Noise: -95 dBm Bit Rate: 29.7 MBit/s
Encryption: WPA PSK (CCMP)
Type: nl80211 HW Mode(s): 802.11bgn
Hardware: unknown [Generic MAC80211] TX power offset: unknown Frequency offset: unknown Supports VAPs: yesiw reports:
Frequencies:
* 2412 MHz [1] (20.0 dBm)
* 2417 MHz [2] (20.0 dBm)
* 2422 MHz [3] (20.0 dBm)
* 2427 MHz [4] (20.0 dBm)
* 2432 MHz [5] (20.0 dBm)
* 2437 MHz [6] (20.0 dBm)
* 2442 MHz [7] (20.0 dBm)
* 2447 MHz [8] (20.0 dBm)
* 2452 MHz [9] (20.0 dBm)
* 2457 MHz [10] (20.0 dBm)
* 2462 MHz [11] (20.0 dBm)
* 2467 MHz [12] (20.0 dBm)
* 2472 MHz [13] (20.0 dBm)
* 2484 MHz [14] (disabled)And o notice that i am at the moment unable to set 20dBm unless i re-flash the device.
wireless.radio0.htmode=HT20
Bitrates (non-HT):
* 1.0 Mbps
* 2.0 Mbps (short preamble supported)
* 5.5 Mbps (short preamble supported)
* 11.0 Mbps (short preamble supported)
* 6.0 Mbps
* 9.0 Mbps
* 12.0 Mbps
* 18.0 Mbps
* 24.0 Mbps
* 36.0 Mbps
* 48.0 Mbps
* 54.0 MbpsI also tested while removing HT functionality but without better results
Horst shows;
91% usage for 1M rate
3.4% usage for 6M rate
4% usage for 36M rateanother node shows me :
ath: phy0: unsupported hw bitrate detected0x33using 1 MbitChips in at the moment in use: Atheros AR9130 rev 2 and Atheros AR9132 rev 2
So far it looks like a i have a bug according to atheros mailing lists
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https://lists.openwrt.org/cgi-bin/mailman/listinfo/openwrt-usersSignature · 4 lines
Ben West http://gowasabi.net [email protected] <mailto:[email protected]> 314-246-9434