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Foreign Battery ADSL

Well, ever since I started this site, Ive noticed that my DSL2 connection has not been that flash, and Ive been experiencing speed/dropout issues. The way I noticed this was that the Cisco 877 was not able to remain synced for more than 1-2 days without dropouts. Upon further investigation I discovered that the modem was receiving a large amount of HEC/CRC errors, around 2000+ each day. However the line seemed to work fine on a Billion 7300, with a Standard profile set on the DSLAM end, but this was still reporting a very high amount of errors. Also the SNR margin was not consistent and would fluctuate wildly from 10dB right down to -2dB. It was worse during nights etc.

So now im expecting anyday now for the Telco to come and fix this issue, as it appears its being caused from one of the poles in the street.

So what is this “Foreign Battery” issue? Well I managed find a few answers..

“Foreign battery will affect your ADSL sync. From my understanding foreign battery is unwanted voltage getting onto the line from somewhere. Which means the there is more voltage on the line than is normal, which in turn will give noise and interference on the line and cause issues with devices.”

“The high frequency of ADSL will often get through a poor or open circuit joint but low voltage VF (voice) signals will not. ADSL will work over most types of faulty lines surprisingly well, except for a Foreign Battery fault where your line is crossed with the battery side of another line, quite low voltages will kill ADSL but may not even be noticed on the phone.”

So if you are having these types of issues yourself, it could be a “Foreign Battery” fault!



  1. Marcus
    Marcus March 3, 2009


    Thanks for the great write up on your connection issues. I’ve been having similar issues with our Cisco 877. I am working my way through your suggestions (modem firmware etc). Have you solved the issue?


  2. aLcAtRoN
    aLcAtRoN March 3, 2009

    Hi Marcus,

    Ive just had the telco come out today, and fix up some of the wiring around in the street, there were some issues. Ive just plugged in the Cisco 877 to see how it will go from now on. I have a billion 7300 and found it more stable compared to the Cisco, when I had the fault on my line. I found the billion is less sensitive to noise fluctuations etc compared to Cisco.

    At the moment Im running on IOS c870-advsecurityk9-mz.124-15.T6.bin, with DSL Firmware AMR-3.0.043.bin.

    The one thing I would definitely change on a Cisco 877 is the default DSL controller firmware, the later firmwares have fixes and support more dslam types. Also Ive noticed downstream attenuation can drop (which is a good thing), and line sync speed is improved.

    What kind of issues are you having exactly?

    You can always change profile settings at DSLAM end to improve stability (you ask isp or online toolbox), or you can use the dsl noise margin command on the modem for stability, or you can try the various firmware/ios to see how it goes.
    Also I would definitely recommend having a central splitter installed, for optimum performance.


  3. Marcus
    Marcus March 3, 2009


    Thanks for the update.

    We have a Internode ADSL2+ connection on a Telstra DSLAM. We are about 4km from the exchange and get about 8000/800kbps. We’ve have been having stability problems lately with tens of drop outs per hour and sync dropping down to <500kbps interspersed with 12+hrs of perfect connection. Since I saw you posts last night I’ve been logging the SNR margin and the downstream is fluctuating from 2 to 12dB over a few minutes

  4. Marcus
    Marcus March 3, 2009

    oops.. hit the submit button…

    The cisco 877 is the only device on the line (No PSTN phones etc). I’ll try and obtain that firmware tomorrow. You mentioned having compatibility issues with different IOS version and different firmware version. Do you have a link to that info or was it by trial and error?

    Telstra has been on site to ‘fix’ the problem four times now over the last three months. I’m waiting to hear back from Internode what the next step is. We have tried a whole collection of ADSL modems and even purchased the 877 trying to get this issue sorted.

    Again thanks for your posts, especially the SNMP details – that info got me recording the SNR, Attenuation etc details.



  5. aLcAtRoN
    aLcAtRoN March 3, 2009

    It was only trial and error, you can keep the same IOS version but I would upgrade the dsl controller firmware. I think default is AMR-3.0.014.bin, however there are many others after this revision, which you can try. Id recommend trying: 3.0.43 & 4.0.15.

    I am personally 4.9km from exchange, here are my stats from the Cisco 877 after 5hours 45minutes uptime..

    Noise Margin: 6.5 dB 9.0 dB
    Output Power: 18.5 dBm 12.0 dBm
    Attenuation: 55.5 dB 28.0 dB
    Init FW: init_AMR-3.0.043.bin
    Operation FW: AMR-3.0.043.bin
    FW Source: external
    FW Version: 3.0.43

    DS Channel1 DS Channel0 US Channel1 US Channel0
    Speed (kbps): 0 3161 0 1021
    Cells: 0 25938480 0 49878561
    Reed-Solomon EC: 0 22851 0 0
    CRC Errors: 0 732 0 0
    Header Errors: 0 620 0 0
    Total BER: 0E-0 4702E-9
    Leakage Average BER: 0E-0 3092E-9
    Interleave Delay: 0 19 0 6

    As you can see, in the last 5 hours or so I have received 732 CRC and 620 header errors.

    Try looking at your 877s sync stats by “sh dsl int” to give more info about the connection, and errors its receiving etc.

    Ive also noticed the 877s attenuation reading is a bit higher compared to when I have a billion modem on the line. Cisco 55.5dB where billion is 52dB. I even then tried a speedtouch 546 and that recorded 49dB. Then I tried a billion 7402 and that recorded 39db! No idea how its all different, even though the sync speeds remained about the same. (Billion 7300 had the highest line sync)

    In my case I still think the 700+ CRC errors in last 5 hours is quite a bit, thats even after the tech left and fixed whatever needed fixing in the street. He mentioned because im so far out from the exchange, there is about 5 or more different Gauge cables I go through which can impact on the connection, however nothing can be done about it 🙁

    Another suggestion I have is try a “Broadcom Chipset” modem on the line and see how that goes. Broadcom chipsets are known to work well on long distance lines. Modems such as the Netgear DG834, SpeedTouch 546, Dynalink RTA1320 all have broadcom chipsets.

    Hope this helps.

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