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Author Topic: Issue with any New Modem/ Router with Broadcomm Chipset.  (Read 2136 times)

ardsar

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Issue with any New Modem/ Router with Broadcomm Chipset.
« on: June 27, 2016, 08:40:29 AM »

Guys,

It would appear that i have an issue using any new device based on Broadcomm. I first noticed and reported it when using the Netgear D7000. However, i have exactly the same problem with the new Billion 8900AX-2400 and now the BT Smart Hub.

In summary the issue is with decreasing S/N over time due to bins being permanently marked as unusable.

See my post in this thread.

http://forum.kitz.co.uk/index.php/topic,15601.msg294650.html#msg294650

Netgear concluded that it was a broadcom issue and there was nothing they could do. Having had this on the billion and now the BT Smart hub, i believe them.

It is usual for my S/N to vary by around 1 dB at night due to external "interference". This can be seen in the tone graphs -ie S/N is reduced at certain bins and hence swapped out. With the HG612, billion 8800AXL the same thing happened, but the bins were re-allocated when the S/N recovered.

I have an open fault with BT as a line test showed an issue that has now been fixed. I have kept the issue  open and have the option of having an engineer visit. However, im not sure if this would be worthwhile.

I've attached a graph of S/N performance between the Billion 8800 and Netgear D7000 as an example. The start and end of the graph is with the billion, the middle part is with the D7000. The peaks in the middle are due to a reboot to recover the S/N.

With the BT Smart Hub, i started with a S/N of 7.8 dB, three days later i'm at 5.4dB

« Last Edit: June 27, 2016, 08:57:43 AM by ardsar »
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PhilipD

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #1 on: June 27, 2016, 10:54:58 AM »

Hi

Bins once marked as unusable are never available again until a resync, it was always like this with ADSL and I presume VDSL is no different.  What is happening sounds quite normal and is intended behaviour.

Once those troublesome bins are turned off, you may have an overall lower SNR, but overall the bins are more robust as the troublesome ones have gone.  Remember it is a signal to noise margin, the reason we sync with a margin (typically 6db) is to allow headroom for things like bit swapping and bins that get turned off as well as periods where there is more noise than at other times.

It might be your line is more prone to bursts of noise than other lines so you see the effects more of bit swapping and bins being shut down than maybe other people do, but that is how it works.  My line typically syncs with 8.5db margin (max 80 sync) but now after 30 days it is down to 7db, but that will come back after a resync.

You don't have a problem. :)

Regards

Phil



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ardsar

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #2 on: June 27, 2016, 11:07:25 AM »

Thanks for your reply, but clearly broadcom has changed something as the older devices including the HG612 and 8800AXL do not do this on my line.
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PhilipD

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #3 on: June 27, 2016, 11:38:54 AM »

Hi

It might simply be the reporting was broken on older firmware's and so bins taken out of action were not reflected in any of the statistics.  It's not unusual to see different reporting behaviours/bugs between different Broadcom firmwares, or Broadcom have simply changed some parameters so newer chipsets/firmwares work differently, or perhaps bitswapping is disabled on the other devices.

Is your line actually performing any differently to the HG612/8800AXL, or is it only reported stats that are the different?

Regards

Phil
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ardsar

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #4 on: June 27, 2016, 11:58:13 AM »

I dont know as i am unable to see any detailed router stats. My concern is as the S/N reduces, the error rate may increase. My line is already banded at 22.4M.
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PhilipD

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #5 on: June 27, 2016, 01:20:51 PM »

Hi

You face a similar issue to all of us, SNR only seems to decrease for one reason or another, often it will come back after a resync and those bins turned off are temporarily back on, other times it is due to a new disturber and crosstalk provides a permanent and sometimes drastic reduction.  Unfortunately this is the technology and limitations of using telephone cable only designed for voice calls.

Regards

Phil

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ejs

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Re: Issue with any New Modem/ Router with Broadcomm Chipset.
« Reply #6 on: June 27, 2016, 03:42:40 PM »

Also, on ADSL, some devices (generally newer ones) certainly can and do re-allocate bits to bins that previously got swapped down to zero bits.
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