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Author Topic: Modem Advice  (Read 4421 times)

drew01829

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Modem Advice
« on: January 03, 2007, 10:14:03 AM »

I have been engaged in a long running discussion with BT about the performance of ADSL2+ since upgrading to BT Total Broadband back in September last year.  To keep things brief, they have investigated, sent an engineer to my house and rewired my phone extensions, given me a beta release of the next version of BT Homehub firmware, but they seem unable to deliver a steady and reliable high speed connection.

The Homehub connects, typically with a  downstream speed of approx 5Mbits/s.  Over a period of 24 hours or so it degrades, typically settling at around 2Mbits/s.  Because of the bRAS profile, I end up with a service significantly worse than my original 2Mbits/s fixed broadband service.  I live 2.29km from the exchange and below is the adsl line status report soon after restarting the homehub.

Would another modem provide a more stable and ultimately higher speed connection.  I've heard positive things about the Netgear DG834N and bigsyd seems to be having a reasonable amount of success with his us robotics modem on broadly similar line status.  There are a couple of specific questions.

1) Is G.DMT different from G.992.1 Annex A or am I comparing apples with oranges?
2) The FEC error count is astronomical?  Is there anything I can do to reduce this?

Thanks for any insight anybody can provide.

Uptime:   0 days, 1:44:44
Modulation:   G.992.1 annex A
Bandwidth (Up/Down) [kbps/kbps]:   448 / 5,248
Data Transferred (Sent/Received) [MB/MB]:   2.62 / 14.01
Output Power (Up/Down) [dBm]:   11.5 / 19.5
Line Attenuation (Up/Down) [dB]:   20.0 / 37.0
SN Margin (Up/Down) [dB]:   22.0 / 6.5
Vendor ID (Local/Remote):   TMMB / ALCB
Loss of Framing (Local/Remote):   0 / 0
Loss of Signal (Local/Remote):   0 / 0
Loss of Power (Local/Remote):   0 / 0
Loss of Link (Remote):   0
Error Seconds (Local/Remote):   0 / 0
FEC Errors (Up/Down):   0 / 227,476
CRC Errors (Up/Down):   0 / 6,194
HEC Errors (Up/Down):   0 / 4,118
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roseway

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Re: Modem Advice
« Reply #1 on: January 03, 2007, 10:53:58 AM »

Hi drew01829, welcome to the forum.

Are you really on ADSL2+ via BT? I don't know much about ADSL2+, but your figures look like normal ADSL Max to me.

G.DMT and G.992.1 are the same thing, and apply to ADSL Max up to 8Mbps. For ADSL2+ the modulation type is G.992.5, and many modems/routers won't have support for this.

If I assume (maybe wrongly) that you're on Max then your figures are not brilliant for your attenuation, but they're OK. Does the router re-sync as the speed deteriorates, or is it just the download speed which suffers? If the latter, then the router isn't the problem; it's probably down to congestion in your local exchange or something similar. In that case, a different router won't make any difference. But if the router does re-sync at progressively lower speeds, then something like the DG834 might give better results.

One thing which you might do to get better performance is to fit a filtered master socket faceplate. See http://www.kitz.co.uk/adsl/lowSNR.htm for more info.

Eric
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drew01829

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Re: Modem Advice
« Reply #2 on: January 03, 2007, 11:22:36 AM »

Many thanks Eric. 

You are correct in your assumption - I am not on ADSL2+.  Sorry for the confusion.

The router does progressively resync at lower and lower speeds over time, so maybe I will try an alternative router/modem.  I already have the filtered faceplate fitted - that was one of the things that BT did to try and resolve the problems.

Since I am ony 2.29km from the exchange, its a bit disappointing that I can't get a more reliable and faster connection.  Its clearly not practical for BT to lay a new line to my house - its just a shame that they are not more up front about the potential issues that can adversely affect the theoretical line throughput prior to signing up for the service.

Thanks again

Andrew
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roseway

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Re: Modem Advice
« Reply #3 on: January 03, 2007, 11:53:32 AM »

One thing I forgot to mention is about the FEC errors. If interleaving has been applied to your connection, as it probably has in the circumstances, then large numbers of FEC errors are quite normal. FEC is forward error correction, and it's a means by which extra data is transmitted to enable the router to correct errors without having to request retransmission of the data. So the figures represent success of the FEC process, not failures.

It does look as though your best option is to try a different router, but there's no guarantee of course. There may be some serious interference sources affecting your line. With a filtered faceplate there's not much more you can do at home to improve matters, and a different router might just get you a result.

Eric
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kitz

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Re: Modem Advice
« Reply #4 on: January 03, 2007, 12:10:13 PM »

Sorry..  I started to type this quite a while ago then got distracted by a phone call before managing to hit the "post" button.  :(

Some of the stuff has already been covered  (Warning - 2 new replies have been posted. You may wish to review your post)
.. but going to post it anyhow.    ::)

---------------


>> Are you really on ADSL2+ via BT?

Thats one of the first things that entered my head..  afaik BTb arent using adsl2+ yet on any of the exchanges other than the 21C network ones (cardiff).

448 / 5,248 looks like Maxdsl to me therefore unless you are on adsl2+, modulation would be G.DMT. However it would appear that the HH sets G.992.1 annex A by default.

Ive also just noticed that the remote vendor ID is ALCB - which is Alcatel. If so then its probably an older type dslam rather than a MSAN. afaik the MSANs that BTw use are either Juniper or Marconi.
Dont quote me on that though because its not always a sure fire method of getting the dslam from the remote linecard chipset.


Yes the FEC errors are high..  but this can be fairly typical if your line has interleaving applied and means that Interleaving is correcting any errors on your line.  Therefore would depend on how much data you have transfered since the router has been up.

As roseway says.. those stats are OK.. but could be better

I'd try testing from the socket behind the master phone socket to see if that improves anything.. in which case an NTE5 adsl filtered faceplate would be beneficial.  [No longer applicable]

Im also not a big fan of the HH, since it doesnt quite seem to perform as well on max as some other routers, but a faceplate is a lot cheaper and also quite often one of the best performance fixes you can make.

« Last Edit: January 03, 2007, 12:13:09 PM by kitz »
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