high profile+modem sync lower OR low profile+modem sync max?

high profile+modem sync lower OR low profile+modem sync max?
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bjlockie @ 4th Nov 01:54AM:
high profile+modem sync lower OR low profile+modem sync max?

Which is better a higher profile and let the modem sync as best it can or a lower profile that the modem can definitely sync to?
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Bicephale @ 4th Nov 02:24AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Personally i much prefer to get the highest possible profile
for my phone-line as i can tweak (lower) the BitRates from
my end if necessary. It helps to stress it a little when one
tries to conduct tests/comparisons, that's where the best
possible profile proves most handy for me...

bjlockie @ 4th Nov 11:59AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

I went from dry to wet and they put me on the 5M/800K profile.
I was on the 3M/512K profile.

I was syncing at 3008/512.
Now I sync at 3552/768.
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Guspaz @ 4th Nov 03:51PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

With no tweaking, lower profile. With tweaking, higher profile.

Left by itself (untweaked), an ADSL modem syncing as fast as it can will produce incredibly high amounts of errors. For one thing, ADSL1 doesn't have any provisions to deal with changing line conditions (what ADSL2 handles via SRA).
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bjlockie @ 4th Nov 04:11PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by Guspaz :

an ADSL modem syncing as fast as it can will produce incredibly high amounts of errors.

Would these packets be resent.
Would it be slower to resend packets as opposed to slower error-free speed?
What would the break even speed be?

Are more errors/resyncs harder on my modem?
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dslrocker3 @ 4th Nov 04:18PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by bjlockie :

said by Guspaz :

an ADSL modem syncing as fast as it can will produce incredibly high amounts of errors.

Would these packets be resent.
Would it be slower to resend packets as opposed to slower error-free speed?
What would the break even speed be?

Are more errors/resyncs harder on my modem?

Packets being resent does cause a slowdown but the net result really depends on the amount and the fequency of the errors. there's no one answer. It's possible to be synced higher be get slower throughput over a measured period of time. The opposite is also possible.
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An_Onymous @ 4th Nov 04:20PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

There is no harder or easier for the modem hardware to send data.

You can work out the math yourself based on how much higher a sync rate you can get vs % of resend.
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dslrocker3 @ 4th Nov 04:31PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by An_Onymous :

There is no harder or easier for the modem hardware to send data.

You can work out the math yourself based on how much higher a sync rate you can get vs % of resend.

True, but that can only be averaged because noise and errors that cause retransmissions do not always occur at a constant rate.
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bjlockie @ 4th Nov 04:43PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by An_Onymous :

There is no harder or easier for the modem hardware to send data.

What about if the modem resyncs often?
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An_Onymous @ 4th Nov 04:45PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

You do realize that WITHOUT SNR number on a per band basis and the bit loading, there are insufficient info to calculate.

You question is weakly thought out and does not deserve any analysis. You deserve the generalized answer for the break even point which is "If your error rate is EQUAL to the increase in data rate"
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Bicephale @ 4th Nov 05:00PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Hi DSLRocker,

Does this illustrate your point accurately?

From the ground up!, Bicephale, 2008-Sep-27

Guspaz @ 4th Nov 06:12PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Dropped/missing packets are *not* resent, as it is not the transport layer that handles this. Higher layer protocols such as TCP that offer reliability services may attempt to resend packets (causing huge drops in throughput for a short period of time), others such as UDP do not.

There is no hard threshold at which point errors become excessive. If I had to make up a number, I'd say that Bicephale's numbers, which are coming out to roughly once per minute, are relatively close to the border of acceptable. If you go one more order of magnitude down (about once every sixth of a minute) then you're starting to see pretty serious impacts on performance.
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Bicephale @ 4th Nov 06:29PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Once per minute?

Don't you mean once per second?

...as there are 86400 seconds per day?...
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anon @ 5th Nov 02:13AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

ADSL2 added SRA, but I can probably guarantee its not enabled on your line or your modem. Most modems (even new VDSL2 BCM6368 cpe) still have SRA disabled by default, on the Speedtouch's its only enabled in the 7.x firmwares.

Since Bell hasn't learned the virtues of INP (apparently they like CRC/CV errors?), I highly doubt they have SRA enabled either. Even on ALU ADSL2+ dslams, support for SRA on ADSL2/ADSL2+ has only been present on FG 3.6 and newer.
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Guspaz @ 5th Nov 01:08AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Hrrm, yes, I messed up the math. Once per second is an excessive error rate. It won't have much impact on games or VoIP (they're designed to tolerate much higher packetloss than that), but TCP will croak.

The reason that you're probably not having much trouble is that noise tends to be bursty; there isn't a one-to-one correlation between dropped ATM cells (48 byte payload) and TCP/IP packets (1500 bytes).

For example, if you lost 31 consecutive ATM cells, you would only lose 1-2 full-sized TCP/IP packets.
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Bicephale @ 5th Nov 01:57AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

Yes, it seems noise rarely flows as steadily as tap water!

TilhasBB @ 5th Nov 02:31AM:
Re: high profile+modem sync lower OR low profile+modem sync max?

What modem do you have?

have you tried cleaning up your line or connect directly to demarc point? maybe you can push a stable 4 meg profile.
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bjlockie @ 5th Nov 01:43PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by bjlockie :

Which is better a higher profile and let the modem sync as best it can or a lower profile that the modem can definitely sync to?

I have a 2wire.
I'm in apartment and Bell said I couldn't get above the 512 they first put me on.
After some haggling with TSI, they agreed to ask for highspeed and if it was stable at 1+, they would pay the speed change (I was stable at 3008/512 :-)).
I recently moved from dry to wet and Bell put me on the 5M profile.
My syncs and noise margins over 36 hours:
3552/768 -2/6.0
3456/768 6.0/5.0
3616/768 -1/6.0
2848/768 8.0/6.0
3136/768 7.0/5.0
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dslrocker3 @ 5th Nov 01:50PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by bjlockie :

My syncs and noise margins over 36 hours:
3552/768 -2/6.0
3456/768 6.0/5.0
3616/768 -1/6.0
2848/768 8.0/6.0
3136/768 7.0/5.0

I would try to check all of your wiring if possible. If that was my line, the differences/intability would be too great for my liking. My opiion would be that with those numbers, I believe you should be set to 2496/640 or 2496/800.
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bjlockie @ 5th Nov 03:41PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by dslrocker3 :

I would try to check all of your wiring if possible. If that was my line, the differences/instability would be too great for my liking. My opiion would be that with those numbers, I believe you should be set to 2496/640 or 2496/800.

Why choose a slower profile instead of letting the modem handle it?
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Guspaz @ 5th Nov 03:54PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by bjlockie :

Why choose a slower profile instead of letting the modem handle it?

Please read the thread.
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dslrocker3 @ 5th Nov 04:30PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

said by bjlockie :

Why choose a slower profile instead of letting the modem handle it?

Having the profile set too high can causes higher amounts of CRC errors that canl actually making your internet experience slower. Also, if the modem is always connecting at the absolute maximum, the connection can momentarily stop working any time that line conditions get worse.
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STN @ 5th Nov 05:39PM:
Re: high profile+modem sync lower OR low profile+modem sync max?

I think a good answer for this is sometimes a modem can have "eyes bigger than it's stomach". When it trains you may not have your transient noise occurring, which could be causing you errors at different times. So at times a modem can sync at a rate that is ok momentarily, but will not be stable long term. It will try and max out the line to the target SNR (6? 10?) and will leave little room for error when the noise rears it's ugly head.

If you instead you pick a slower profile you will enforce a higher SNR, even if the modem could train higher, and this would give you a more stable line as the noise comes and goes.
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