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Month: February 2009

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!

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Cisco IOS Feature Navigator

So you got your cisco device, but what if you want to quickly find the right IOS, and other software releases for features you want to run on your network. There are many different versions of the cisco IOS for each device. I came accross this handy cisco website which you can use to research software releases by searching by image name, platform, product code etc. Once you select what you want, it will give you more information about the particular IOS for your device, and what it can run.

So checkout:

http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp

I believe it will come in quite handy!

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Some more Cisco 877 Tips…

Need to know what your dsl sync stats are and more details about the link?

cisco877>sh dsl int

Or as in my case improving the attenuation on the upstream by 3dB..we can modify the gain tx-offset value to 3

Enter exec mode:

cisco877#conf t
cisco877(config)#int atm0
cisco877(config-if)#dsl gain-setting tx-offset 3

To show ppooe uptime on the session:

Look at the active time column

cisco877#sh caller

To show logs on the modem to see activity:

cisco877#sh log

Need to troubleshoot pppoe events, atm, errors, and see more detail, simply issue..

cisco877#debug pppoe events
cisco877#debug pppoe errors
cisco877#debug atm events
cisco877#debug atm errors

These details will then be logged into the log file as above. To remove the debugging simply issue the no statement at the front.

If you have any more tips,hints, recommendations, please comment below 🙂

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