Kitz Forum
Broadband Related => Broadband Technology => Topic started by: Weaver on May 01, 2018, 11:05:03 PM
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I have finally after x years managed to do some very rudimentary checks on the effects of disabling bitswap on my DLink DSL-320B-Z1 modem. (ADSL2)
And the answer - a null result, quite shocking.
with bitswap:
d/s sync | d/s snrm
2745 (?)
2738 1.6 (after a while)
2699 3.0
2723 2.6
without bitswap:
d/s sync | d/s snrm
2674 3.3
2745 3.4
2723 3.4
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Interesting, so ultimately your line(s) may be better off not using bitswap? How are the error counters?
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My circuit was better off without bitswap (significantly less errored seconds) on Netgear DGND3700v2 (on D-Link DSL-2740B no difference) when I had ham band mask. Currently my circuit is better off with bitswap.
https://forum.kitz.co.uk/index.php/topic,20136.0.html
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Have you discovered if the modem supports monitored tones?
I think bitswap without monitored tones is just a downward spiral really. Like a game of musical chairs with an ever decreasing number of tones to fit the same total number of bits into.
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I don't know whether or not these MediaTek/Trendchip devices (DLink DSL-320B-Z1) do support monitored tones. I somehow doubt it, don't know why, but I just imagine they were a low-end product.
The SNRM tends to drop pretty quickly then sometimes stabilises at say 0.8dB. I wonder if that pattern might be an indication of support for monitored tones or lack of it. Perhaps G.DMT or some other kitizens know something about this chipset.
They tend to hold on to sync for a long time these days, but in the past they used to give up and desynchronise after about a week or so. However there is no real pattern even now. It is a long time since I realised that AA was sending them out with the default setting which is bitswap off.
As for error rate, I have not had them running for very long. One of the modems has racked up a lot of HEC errors - about 2% per cell - in a short time. Currently they are all running very fast, with d/s sync rates over 2800 kbps.
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Could someone help me understand
How / whether availability of bitswap might or might not affect determination of sync rate? Or is it just all about reliability?
Speculation: Is it true that bitswap matters less if you have a high target SNRM, in the sense that the link will stay up for ever anyway if that is all that matters, longevity?
I can see that broadcom users can get data for the rate of bitswaps per unit time, iirc. Is that right?
How important is bitswap, in the sense of the feasibility of surviving without it?
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During line activation, every sub-channel calculates the signal-to-noise ratio (SNR) and the number of bits to be transmitted. After the line is activated, the SNR may change because the external environment changes. For example, the SNRs of some sub-channels reduce, whereas the SNRs of some other sub-channels increase. After a long period of time, the line may be disconnected.
The bit exchange function has the following advantages:
Allows sub-channels failing to transmit the specified number of bits to switch some bits to sub-channels with higher SNRs.
Reduces the transmit power of sub-channels with higher SNRs to increase the sending rate and SNRs of sub-channels with lower SNRs.
This reduces the bit error rate without triggering line negotiation.
this is from huawei website
looks like it is better to keep it enabled
https://support.huawei.com/enterprise/en/doc/EDOC1000174046/be8e4aee/vdsl-interface-configuration-commands#adsl_bitswap_vdsl_view
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@Neil Agreed. I always thought it would be madness to turn bitswap off, no? Unless you know something about a bug-ridden implementation thereof perhaps.