Can't believe this is correct - Zen ADSL

Hello! If Zen is not a 'BT Wholesale' provider then I apologise for the wrong forum.

I've been struggling to get a stable line with Zen on a BT landline. Finally we had an approx. 7 day period when packet loss was low and no resyncs. So then what happens? The BT DSLAM 'decided' to drop my target SNR down to 3db to get better speed. [censored]!

A full day of horrid-ness ensued (see ping monitor here http://www.thinkbroadband.com/ping/share/eb6c00a5762... - note, speed was probably not 7.7 at this time).

Some interference on my line clearly requires 6 to 9db of SNR on the downstream side and when I can maintain that (with a resulting sync rate in the 8000 range) things are not too bad.

So I email Zen to ask what the heck is going on and they say, paraphrasing, "BT's DLM saw that my line was stable for a while and decided to try 3db margins again!".

This is like having my line managed by a 10-year old boy who just wants a little more speed. We already requested a change from 3db target on downstream to 6db a month earlier.

Zen says that there is nothing they can do about it as the system is automated. This means my line will go from working fine to unbearable every couple of weeks I guess!

I really can't believe this is correct. Some lines need 6db, some need 9db, maybe some work fine at 3db -- not mine. It is ridiculous for DLM to keep trying 3db and wrecking my line. Any advice?

BT's DLM can be annoying, no doubt about it.

You can either try and get a router which supports force syncing at a particular speed / target SNR value or move to a provider (probably LLU) where this kind of thing can be hard set by the ISP. The old Draytek routers (ADSL1 generation) did have a feature where you could configure them to sync no faster than a given speed, for exactly this reason, but I only ever saw this feature on ADSL1 provisioned lines and hardware, not on ADSL2+.

AAISP do offer connectivity via the TalkTalk backhaul network so you could always move to them. It will be AAISP supplying the service (which is very decent by the way) but through TalkTalk LLU, meaning they are more than likely able to fixate your line's SNR. You'll never have to deal with TalkTalk directly either (probably a good thing).

Finally, is the connection ADSL1 or ADSL2/+ ? If ADSL2+, you could try dropping the router down to only negotiating on ADSL2 or just ADSL1 (if that's supported) and see if that helps. Also you've not disclosed the length of your line or your current sync speed, which may help clarify why this issue is occurring (I'm guessing it's long, due to the high variance in noise on the line).

Edited by mixt (Thu 10-Apr-14 14:42:21)

Some interference on my line clearly requires 6 to 9db of SNR on the downstream side and when I can maintain that (with a resulting sync rate in the 8000 range) things are not too bad.

Been there, done that ,got the T shirt !
In my case the S'N margin had been jacked up to 15 dB due to interference, and when I reduced the interference it didn't go down till Zen noticed in the course of another query and got it reduced - Bingo ! Now running about 2.5* the "estimate"

To be honest, DLM is unlikely to have dropped you to a 3db target if the line wasn't super stable for a good length of time.

If you think 6db is required, Zen can request BT Wholesale pin the SNR to this.

What kit are you using, some types of router, most notably Cisco's, will through a hissy fit with a 3db margin.

Thanks for your replies -- nice to know I'm not the only one who has suffered, but it sure seems backward. Does BT do this to their own customers also? I suppose so.

I did ask Zen about ensuring my line was never targeted below 6db -- I think really 9 would be better which they tech support guy said was the target after the 3db nightmare ended. What terminology should I use to try to get my desired SNR 'Pinned' as Zarjaz put it?

I'm using a cheap 'router', the Thompson/Technicolor TG582n, but just as a modem, my pfSense virtual machine is doing the PPPoE connection and routing to my home network.

As I am away from home for a bit I can't give up-to-date line specs, but some I captured earlier are:

Link Information

Uptime:
4 days, 6:28:27

DSL Type:
ITU-T G.992.5

Bandwidth (Up/Down) [kbps/kbps]:
1.187 / 9.383

Data Transferred (Sent/Received) [MB/GB]:
994,16 / 1,99

Output Power (Up/Down) [dBm]:
12,3 / 0,0

Line Attenuation (Up/Down) [dB]:
16,9 / 37,0

SN Margin (Up/Down) [dB]:
5,9 / 3,1

System Vendor ID (Local/Remote):
TMMB / ----

Chipset Vendor ID (Local/Remote):
BDCM / IFTN

Loss of Framing (Local/Remote):
9 / 0

Loss of Signal (Local/Remote):
34 / 0

Loss of Power (Local/Remote):
0 / 0

Loss of Link (Remote):
-

Error Seconds (Local/Remote):
8.644 / 0

FEC Errors (Up/Down):
363 / 231.286.707

CRC Errors (Up/Down):
72 / 330.981

HEC Errors (Up/Down):
70 / 7.831.906

37db of attenuation doesn't seem bad at all, so I'm not sure what the deal is really. Zen have offered to get BT to repair the line if I go through the preliminary troubleshooting steps. I should of course do those things but haven't had a chance to do them yet.

Thanks again...

Some alternative router firmware can add/subtract a percentage from the target SNR. I used to use the DGTeam firmware on an old, ex-Sky Netgear. Because the line was super-quiet, I was able to eke an extra one or two dB out of it, despite Be's insistence that they couldn't reduce the target below 3dB..