Kitz ADSL Broadband Information
adsl spacer  
Support this site
Home Broadband ISPs Tech Routers Wiki Forum
 
     
   Compare ISP   Rate your ISP
   Glossary   Glossary
 
Please login or register.

Login with username, password and session length
Advanced search  

News:

Pages: [1] 2 3 ... 5

Author Topic: Output power (dBm)  (Read 46520 times)

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Output power (dBm)
« on: April 26, 2012, 10:37:31 PM »

Hi,

I was just curious about Output power (dBm), can this alter on different profile snr settings for example if im on a 9snr profile and my dBm is 9, if i was to change to a 12snr profile would my dBm raise, drop, or stay the same because snr doesnt effect it?
Logged

burakkucat

  • Respected
  • Senior Kitizen
  • *
  • Posts: 38300
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Output power (dBm)
« Reply #1 on: April 27, 2012, 01:26:37 AM »

I would expect the output power to remain virtually the same.
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33881
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Output power (dBm)
« Reply #2 on: April 27, 2012, 10:19:49 AM »

Output power isnt related to any of the DLM profile settings and is independent.
Theres several different PSD masks in use which can affect the output power but this is more to do with line length/quality.
Output power can vary slightly depending upon the line conditions ie it can wap up a bit if the line is struggling, or reduce if the line is syncing at a rate much lower than its capable of.  It can do this on the fly without resyncs being needed.
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Re: Output power (dBm)
« Reply #3 on: May 01, 2012, 11:42:48 AM »

Cheers for the input guys. I was wondering also is there a tool i could use to monitor the dBm, apart from obviously checking my router stats?
Logged

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Re: Output power (dBm)
« Reply #4 on: May 01, 2012, 11:45:32 AM »

Cheers for the input guys. I was wondering also is there a tool i could use to monitor the dBm, apart from obviously checking my router stats?
Even better is there a tool i can use to override the dBM and change the value?
Logged

BritBrat

  • Kitizen
  • ****
  • Posts: 1359
Re: Output power (dBm)
« Reply #5 on: May 01, 2012, 12:03:09 PM »

Cheers for the input guys. I was wondering also is there a tool i could use to monitor the dBm, apart from obviously checking my router stats?

Are we talking about wireless?

If so you can see strength using inSSIDer 2.0 and that of your neighbours.

YOU CAN
– Inspect your Wi-Fi and surrounding networks
– Scan and filter hundreds of nearby access points
– Troubleshoot competing access points and clogged Wi-Fi channels
– Highlight access points for areas with high Wi-Fi concentration
– Track the strength of received signals in dBm over time
– Sort results by MAC Address, SSID, Channel, RSSI, Time Last Seen
– Export Wi-Fi and GPS data to a KML file in Google Earth

As for tweeking the strength there are legal limits.


« Last Edit: May 01, 2012, 12:08:13 PM by BritBrat »
Logged

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33881
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Output power (dBm)
« Reply #6 on: May 01, 2012, 12:39:31 PM »

Even better is there a tool i can use to override the dBM and change the value?

If you mean between the router and MSAN - not that Im aware of.
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Re: Output power (dBm)
« Reply #7 on: May 01, 2012, 12:56:42 PM »

Even better is there a tool i can use to override the dBM and change the value?

If you mean between the router and MSAN - not that Im aware of.
Yea thats what i meant.
Logged

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Re: Output power (dBm)
« Reply #8 on: May 03, 2012, 06:46:40 PM »

Hi guys,

I have some more questions about dBm  ;D.
So i read on this site that the average for an ASDL2+ line is about 18-19, so then does it not depend on the length of the line?
I was wondering also is there some kind of formula for which u could use to work out what sort of value of output power dBm you should be getting close to?

 :-\
Logged

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33881
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Output power (dBm)
« Reply #9 on: May 03, 2012, 07:00:39 PM »

On adsl2+ the vast majority of lines will be running to their maximum capability... hence the 19dB average.

ie a long line at full power may only get say 4Mbps..  but a shortish line needs that same amount of power to get say 24Mbps.

Its only really when you see a line not syncing at its full capability would you expect to see anything less (although there are some routers that mis-report and a known issue with some Sky lines)

Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

kezzaman

  • Reg Member
  • ***
  • Posts: 139
Re: Output power (dBm)
« Reply #10 on: May 03, 2012, 07:41:02 PM »

On adsl2+ the vast majority of lines will be running to their maximum capability... hence the 19dB average.

ie a long line at full power may only get say 4Mbps..  but a shortish line needs that same amount of power to get say 24Mbps.

Its only really when you see a line not syncing at its full capability would you expect to see anything less (although there are some routers that mis-report and a known issue with some Sky lines)

I see... I was worried my dB was to low at 9dBm, but my sync speeds are what they should be, so i guess no problems there.
Logged

burakkucat

  • Respected
  • Senior Kitizen
  • *
  • Posts: 38300
  • Over the Rainbow Bridge
    • The ELRepo Project
Re: Output power (dBm)
« Reply #11 on: May 03, 2012, 09:05:39 PM »

The transmitting device only needs to use sufficient power for the receiving device to obtain a clear signal. There is a dialogue between the two ends: "Eh? What? Speak up, I can't hear you!" . . . "Stop shouting, I'm not that deaf, you know" . . . etc, etc.

This is what my modem/router reports --

Quote
Current Output Power:    18.6 dBm (Downstream) 12.5 dBm (Upstream)

The DS output power is the level that the DSLAM/MSAN is transmitting to my modem/router (the value is only known by the DSLAM/MSAN and is sent in a data packet so that the modem/router can display it), the US output power is the level that my modem/router is transmitting to the DSLAM/MSAN.
« Last Edit: May 03, 2012, 09:13:00 PM by burakkucat »
Logged
:cat:  100% Linux and, previously, Unix. Co-founder of the ELRepo Project.

Please consider making a donation to support the running of this site.

kitz

  • Administrator
  • Senior Kitizen
  • *
  • Posts: 33881
  • Trinity: Most guys do.
    • http://www.kitz.co.uk
Re: Output power (dBm)
« Reply #12 on: May 03, 2012, 09:13:29 PM »

Quote
I see... I was worried my dB was to low at 9dBm,

Is that adsl1? 
IIRC my output power when on adsl1 was somewhere in the region 10dBm as this line is/was capable of 24Mbps and therefore didnt need to be at full power to be able to sync at 8128kbps.

Otherwise it may be a router misreport - there are a few that do.   
As B*cat say the main thing is that you have enough power to sync at the anticipated speed.
Logged
Please do not PM me with queries for broadband help as I may not be able to respond.
-----
How to get your router line stats :: ADSL Exchange Checker

c6em

  • Reg Member
  • ***
  • Posts: 504
Re: Output power (dBm)
« Reply #13 on: May 03, 2012, 09:24:26 PM »

From what I've seen on the old ADSL1/ADSLmax on 20CN....short lines have reduced power and long lines increased power.  I've only seen two power settings quoted in forums from the router stats provided.

My interpretation of this was that BTOR did not want to use full power on short lines as
a) they did not need it to function fully and
b) excess power on the lines means increased cross talk between the cable pairs with other broadband customers. 

So to ensure that the ADSL signal actually got to the end of those customers on very long lines it was essential to cut back the power for those on short lines as at full power the cross talk from the short lines would swamp the signal for those on the long ones.

Many routers seem not to report the downstream signal power on ADSL2+, it seems to be a bug in the software somewhere either in the router or the MSAN/DSLAM is not reporting it to the router (mine included) so there does not seem to be the availability of output power figures  in router stats as there was on ADSLmax.
Logged

asbokid

  • Kitizen
  • ****
  • Posts: 1286
    • Hacking the 2Wire
Re: Output power (dBm)
« Reply #14 on: May 03, 2012, 09:41:01 PM »

More expert advice as ever from the Tzarina of Kitz  :)

If you take a look-see at the ITU-T specs G.992.3 [1]... described within are the parameters used to determine the output power for each subcarrier or tone.

The output power for a tone should never fall outside the bounds of the spectral shaping mask (which is in place to reduce crosstalk amongst the pairs in a cable bundle).   That mask which restrains output power is defined as a mathematical function - the transmitter spectral shaping function (tss).

The modem at each end of the transmission line can only control the output power levels used for the subcarriers in its own upstream bands.  Neither the DSLAM nor the CPE modem has control over the TX power levels used by the Far End.  So that means that our CPE modems can only control the upstream power output levels.

There is a fine tune gain control that is applied by the modem's transmitter for each subcarrier.  The gain for an individual tone can be tweaked by +/- 1dBm (as a linear equivalent).

However, the output power can never, or should never, be tweaked to exceed the bounds of the power spectral density (PSD) mask for the bandplan.

In theory it's possible to retrieve the 'gains table' from a Broadcom chipset modem.  That table contains those fine tune gain levels that are being applied to each subcarrier.

Here are all the diagnostic data tonemaps used by the Broadcom 6348/6358 chipset modems. The gains table is stored as an array of shorts (16-bit integers).  The full source code for the Broadcom kernel driver is here [2]

Code: [Select]
/* ADSL diag data */

short snr[kAdslMibMaxToneNum];
short showtimeMargin[kAdslMibMaxToneNum];
uchar bitAlloc[kAdslMibMaxToneNum];
short gain[kAdslMibMaxToneNum];
ComplexShort chanCharLin[kAdslMibMaxToneNum];
short chanCharLog[kAdslMibMaxToneNum];
short quietLineNoise[kAdslMibMaxToneNum];


The xdsl diagnostic tool in the firmware of most Broadcom modems (known variously as the xdslcmd, adslctl or adslcfg tool) is not equipped to get the gains table data from the kernel driver.  However, it is probably still possible to retrieve that data by hook or by crook.

One quirk of the Broadcom chipsets relates to output power.  With the BCM6368 - the latest xDSL Broadcom chipset - the aggregate output power for the downstream bands often drops momentarily to zero for no obvious reason, before returning to a sane value of 19dBm or thereabouts.

Incidentally, you have very tasty looking limbs, kezzaman.  Do you strictly need them all?!

cheers, a

[1] http://www.analytic.ru/articles/lib26.pdf
[2] https://forum.openwrt.org/viewtopic.php?pid=120035
« Last Edit: May 03, 2012, 09:43:33 PM by asbokid »
Logged
Pages: [1] 2 3 ... 5
 

anything