As I said, the ISP doesn't have any responsibility to resolve noise issues unless these are being caused by a fault with the cable itself. There is no 'expected' speed for ADSL - if the line happens to be picking up lots of noise because of the local environment then there's nothing anybody can do about it. In any case very many noise issues are caused by the customer's own wiring, which is solely the customer's responsibility.

More generally, you've gone for a cheap broadband provider and so you really cannot expect for them to provide anything but the most basic service.

thanks for that gipsydog, I guess what I'm really asking here is is this "tone capping" which has an abrupt cut off @ 128+ a fault or a restriction by my ISP does anyone else with routers capable of tone analysis experience these problems?

Perhaps your modem negotiated G992.4, aka ADSL2 Lite? As with ADSL Lite, this only uses 128 tones. I've never personally heard of this happening, but I imagine that on an ADSL2 system like TT-LLU it may occur in the same way that occasionally you see fallback to G.Lite on ADSL1.

Thats exactly how the connection behaves, like g.dmt(lite) my Zymon software monitors my router which will not connect as g.dmt(lite) it will only connect as G.DMT or multimode (adsl2). Because the drop in tone usage is "vertical" ie no 128+ tones in use (but reasonable usage up to 128) at all I,m thinking this is either deliberate (ISP setting) or there is a filter of some description on the line. Since I have seen this on another talktalk llu line (and another which uses all 256 tones) on three different exchanges I'm very baffled. I'm wondering if I have a faulty microfilter somewhere (could be any one of them?)

The Zyxel certainly supports G.992.4, but it sounds as though you have no way of controlling or even showing whether it chooses G.992.3 (full ADSL2) or G.992.4 (lite ADSL2). I guess it's possible that TalkTalk have made a mistake configuring their DSLAMs to only support G.992.4 for some lines, but I still think it's far more likely that the router is getting confused by line conditions during mode selection, especially as you're reporting bad noise problems anyway. As you've seen the problem on two lines you may have a router with faulty auto-sense that's prone to selecting G.992.4 when it shouldn't.

All I can suggest is that (a) you try the usual methods of tracking down noise problems, the first of which is to try the test socket on your master to eliminate internal wiring entirely, and/or (b) you try a different router. Problem is, whilst your line is fixed at 512kbps you can't easily tell whether this helps, so I think you first need to get TalkTalk to put the cap back up to 8Mbps.

My Zyxel 2602hw-61 is controllable either thru telnet or "zyxmon" application, however after a lengthy chat with talktalk 2nd level who did understand this time, the problem has been isolated to faulty microfilters, it seems that my filters (purchased from ebuyer) all block tones from about 550khz upwards! they have now been replaced with a bt active filtered faceplate and I now get 4mb+ and a full pattern of tones. The reason this has been difficult to isolate has been multiple faulty filters which has disconnected individually before but not all at once, any guy's thanks for the interest, happy surfing (I know I am)

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my filters (purchased from ebuyer) all block tones from about 550khz upwards

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If that was the case then they would not be ADSL filters at all, as these just provide low-pass filtering for the phone socket. The modem socket is just wired straight through to the line.

Far more likely that they were just sub-standard. They were letting interference through or abnormally loading the line, confusing the modem.