dmt tones

Hi, My Zyxel router does line quality analysis and I've noticed that my Talktalk connection (very slow and unstable) only uses the first 128 tones (symbols). I tried this router on two other Talktalk lines, one uses only first 128 the other all 256 tones (fast connection). I queried this with Talktalk 2nd. level who said "tones, dunno about them mate" Anyone have any insight into this, it would seem to indicate that my line cannot support higher frquencies to me?

In reply to:

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it would seem to indicate that my line cannot support higher frquencies to me?

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That's right. It's perfectly normal behaviour - high frequencies get attenuated more, and this can make the signal too low to be usable on longer lines.

Thanks cahaddras, that was my assumption BUT (there's always a but). It seems odd to me that tone usage cuts off at 128, there is no bit loading after 128, I live 1.8km from local llu point (2.8km cable length). One of the other sites I tried the router at is a similar distance as is the third site that uses all 256 tones. My question is, is this restricted at the dslam but the isp provider as a global parameter and if so why? (bad cable plant?)

It's not just the line length and attenuation that matter - it's also the noise. The DSLAM doesn't limit the tone range, although I guess it's possible you have an obscure fault of some kind. You would need to post some line stats or DMT tool charts to get a better idea.

Edit - it's possible the modem is accidentally negotiating G.Lite instead of G.DMT, although it shouldn't if it's working correctly. You may be able to disable the G.Lite option if your modem allows this.

Edited by cahaddras (Wed 28-Mar-07 20:16:42)

Here you go,
The poor loading per tone is due to the line now being "capped" @ 512 to increase snr because it keeps dropping. Thats Talktalk "fixing" it.
It has been reported and tested by Openreach as "no fault found" on numerous occaizyxel2602> wan adsl linedata near

noise margin downstream: 18 db
output power upstream: 11 db
attenuation downstream: 48 db
carrier load: number of bits per symbol(tone)
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 02 33 22 24 34 22 32 03 33 01 34 34 44 33 43 33
tone 64- 95: 42 34 32 33 22 43 34 23 24 32 21 10 22 11 22 02
tone 96-127: 22 11 10 11 20 11 10 10 00 00 00 00 00 00 00 00
tone 128-159: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 160-191: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 192-223: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 224-255: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

zyxel2602>

sions.

That's dying out at tone 100, not 128, plus it's dying gradually rather than an abrupt cutoff. It's generally very low, but then that's to be expected with a 512kbps sync.

What was the problem you reported that caused TT to set a 512kbps sync?

The problem reported to Talktalk was loss of sync anything up to 20 times a day (I use Trapmon a free snmp monitor) when allowed to "free run, it connects at 2-3mb/s but upstream snr has always been an issue, at this speed it is gnerally less than 6db (and falling). At this speed the 128 cut off is more pronounced. The router is in adsl2 mode.
Big clue! had the same problem with previous ISP pipex after free upgrade to 1mb/s. The only common kit is the copper (or aluminium) Local Loop, I'm guessing here but (as an ex BT eng with 20+) I think it's a line fault. However "it tests ok". (wet finger??). I've not seen any other reference to "tone capping" but I beleive a global parameter can be set?

Aside from the fact that you've not provided any evidence for 'tone capping', there's no link between this idea and the actual problem of excessive resync.

TT have made a perfectly reasonable change. The line's unstable at 2-3Mbps and OpenReach have reported the line's sound, so they've dropped the speed to a stable one. You're apparently picking up lots of noise which TT are not responsible for solving.

It's a bit late now, but did you try eliminating faults on your extension cabling, bad filters, missing filters, etc? Did you try the modem on the test socket behind the master faceplace?

Line test results are from master socket all internal wiring 'dis'd off. I never suggested there was a link between "tone capping" and excessive resync, I just wondered if any one else had experience of this. Ofcom giudlines disagree, openreach have a responsibility to supply a connection that can sustain a "speed" that you should expect at this distance. Anyway the point of this testing is a)since the copper doesn't terminate on BT kit anymore HOW can they test it? b)In this broadband age continuity is not enough, BT Openreach nead to demonstrate line characteristics to qualify "No Fault Found", they have failed their customer (Talktalk) in not providing this, why do Talktalk not pursue this?

re:...why do Talktalk not pursue this?

Talk Talk are very new to the Broadband market.....and I suspect you've already answered the point yourself.

I queried this with Talktalk 2nd. level who said "tones, dunno about them mate"

Probably don't have much idea about anything to do with broadband.


For what it's worth; my ZyXEL gives the data below

I have a very good line; synch at 8128 with 5.5-6.1 throughput, and 'SamKnows' states;

You are approximately 679 metres from the exchange (straight line distance).


noise margin downstream: 13 db
output power upstream: 19 db
attenuation downstream: 13 db
carrier load: number of bits per symbol(tone)
tone 0- 31: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 32- 63: 00 00 00 00 23 44 56 67 88 89 9a aa ab bb bc cc
tone 64- 95: 0c cc cc cc cc cc cc cc cc cc cc cc cc cc cc cb
tone 96-127: bb bc cc bb bb bb bb bb bb bb bb bb bb bb bb bb
tone 128-159: bb bb bb aa aa aa aa aa aa aa aa aa aa aa aa aa
tone 160-191: aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa aa
tone 192-223: aa aa aa aa aa aa aa aa aa aa aa a9 99 99 99 99
tone 224-255: 99 99 99 99 99 99 99 99 99 99 99 99 99 88 76 43
tone 256-287: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 288-319: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 320-351: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 352-383: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 384-415: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 416-447: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 448-479: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
tone 480-511: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00