Download errors - How many become significant?

[#1]

I had a problem which I raised with "Help and support" and which, I think, has now been overcome.  However I should be grateful for any expert advice from those present.
I am about 2 miles from my exchange, so I expect rather slow access but, for some time, I had no problems with a 2000 kbps connection and since being on BBMax my IP profile remained fairly steady at 2000 to 2500 with typical download speeds of 1800 kbps.  This continued until a month ago when my IP profile started to fluctuate and, for a while, went down to 750.  When it went down to 250 I raised a query and PN Help and support reset this for me.
I normally connect via an extension but, for the test period, transferred to a direct connection to the main socket and, after the reset, my IP profile had gone up to 2500 to 3000 kbps with download speeds of about 2000 kbps and I returned to my extension connection again.
Now here comes the query:
On checking my D-Link DSL-320T Ethernet modem stats I find that it reports a few download errors even when it was connected to the main socket and I am wondering whether too many download errors will cause my IP profile to be reset to a lower value again.  The number of errors seem to be about two or three in every 100 Mb downloaded but I don't know how many can be reasonably expected.  The number of errors seem to be much the same whether I am connected to the main socket or the extension so I doubt that the original problem was  caused by the extension.  Everything seems to be reasonably stable again with my IP profile remaining between 2000 and 2500 and my download speed being between 1800 and 2000 kbps but is the problem likely to occur again if these download errors continue?

[#2]

That speed is much slower than it should be.
What is:-
Your Sync rate
Your Download attenuation (in dB)
Your noise margin

[#3]

Also see http://community.plus.net/forum/index.php/topic,66937.0.html and the link it has to the 'Community Support' forum, there seems to be a spat of increases in IP profiles at the moment. Not sure we know why this is happening just now. The theory is it is related to work done by BT preparing for 21CN/WBC being enabled. no real proof though.
SW.

[#4]

I disagree.
On the evening (between 10 pm and midnight) my noise margin increased by two steps from 6dB to 9dB to 12dB.
My broadband noise margin is stable for periods of months.
The very next day, BT announced that the upgrade to 21CN WBC status was "complete".
Plusnet had to request BT to reset my noise margin.

[#5]

So you do or do not think it is due to the 21CN/WBC work?
SW.

[#6]

Obviously its not down to synchronicity.
There is a causal relationship.

[#7]

Quote from: axisofevil

That speed is much slower than it should be .What is:- Your Sync rate Your Download attenuation (in dB) Your noise margin

I'm not sure what you mean by "slower than it should be".  Possibly I misinformed you regarding my distance from the exchange.  A while ago, when broadband first came in I was informed by BT that I could not have it on my line because I was too far from the exchange and the attenuation would be too great.  A few months later they changed their mind and informed me that it would be possible for me to get broadband but that I couldn't expect speeds greater than 2000 kbps.  I started using it at that speed. and later, when I was switched from a fixed 2000 kbps connection to ADSL-MAX I found that my download speed remained much the same and it has never been much greater.  I was and still am satisfied with that speed as long as my IP profile remains stable as it did for many months.
Typical results from the BT speed test were:
    IP profile for your line is - 2500 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  2816 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 2250 kbps
and
  IP profile for your line is - 2500 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  2976 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 2094 kbps
However from March onwards my IP profile started to fluctuate wildly and I got results like:
IP profile for your line is - 750 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  864 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 676 kbps
and even
IP profile for your line is - 135 kbps
    DSL connection rate: 448 kbps(UP-STREAM)  2944 kbps(DOWN-STREAM)
    Actual IP throughput achieved during the test was - 81 kbps
It was then that I got PN to look into it and I 'm now back to results like:
Your DSL connection rate: 2944 kbps(DOWN-STREAM),  448 kbps(UP-STREAM)
    IP profile for your line is - 3000 kbps
    Actual IP throughput achieved during the test was - 2394 kbps
and
Your DSL connection rate: 2880 kbps(DOWN-STREAM),  448 kbps(UP-STREAM)
    IP profile for your line is - 2000 kbps
    Actual IP throughput achieved during the test was - 1718 kbps
Information given by my D-Link Ethernet modem now gives me:
                            Downstream              Upstream
SNR Margin            7  dB                          16  dB
Line Attenuation    56 dB                          31 dB
Data Rate                3104 kbps                448 kbps
This seem satisfactory to me but what I was concerned about was this information given by the modem:
ADSL Traffic Statistics display Receive and Transmit packets passing through the DSL-320T.
Transmit
  Tx PDU's 13880 
  Tx Total Bytes 3861766 
  Tx Total Error Counts  0 


Receive
  Rx PDU's 19660 
  Rx Total Bytes 22545731 
  Rx Total Error Counts 1
 
Note that these data are lost when the modem is rebooted (which was done recently) so that the Rx Total Bytes is small (22545731) and  only one error occurred but I find that when Rx Total Bytes reaches a value in the order of 100,000,000 (100 Mb) there may be some 4 or 5 errors reported and I was wondering if this is too great.

[#8]

You are on a long line so some errors are to be expected, especially the higher your sync rate gets.
Those error figures are well below what would be considered a problem so unless they get into the 100s you can ignore them.

[#9]

Line Attenuation    56 dB - and two miles from the exchange?
There is something wrong here.
Unless the actual line length is very much longer than this you should get a much higher sync rate.

[#10]

With respect, I think 'axisofevil' is misled here. In my own experience at a line attenuation of 56 dB you can't realistically expect better than 1M speeds, so if you are getting upwards of 2M you are very lucky indeed. 2 miles is 3.2 km, which is perfectly realistic for that attenuation.
Regarding error rates, my modem (a Speedtouch) distinguishes three different types:
1. FEC. Forward Error Correction. These are the errors detected and automatically corrected. You can have thousands per second and see no impact on performance.
2. CRC. Cyclic Redundancy Check. These are the ones to watch out for as they represent a need to resend the errored packet. During a noisy period I get thousands per second, but then my line is almost unusable. At good times they can range from 0 to a few tens or so per second.
3. HEC. Header Error Correction. I don't get many of these and I'm not sure whether they represent a need to resend the packet or not.
Obviously, it's not the total number of errors that is important but how many you get per second. You expect the numbers to get higher the longer the modem has been connected. (I find it doesn't depend on how much data has been transferred.)
It looks like your modem is reporting CRC errors. In any case, your number is very low indeed.
Anyway, that's my experience - someone with a noisy but mostly usable line.

[#11]

Quote from: axisofevil

There is a causal relationship.

Although I very much suspect you are right, on a sample size of one or just a few, it is difficult to be sure.
SW.

[#12]

Many thanks to all who replied.  So it seems that the error notifications are well within expected limits and I'll just have to wait to see if my IP profile remains steady or starts fluctuating wildly again.

[#13]

With all due respect to an earlier poster, if you have a line attenuation of 56dB then the (cable) distance from the exchange should be around 4km and unless you have bad noise problems you should be able to get sync speeds approaching 3.4M.
The OP's stats from his D-Link modem look reasonable to me. The trick is to re-sync when your noise margins are highest, usually daylight am.
With regard to errors, this from a BT Broadband engineer -
For a 5 min period - errored seconds <15 , crc & hec errors <60-100 are ok. Interleaved service crc & hec errors up to 1000 are ok, fec & rs errors up to 11000- 14500 are ok.
With regard to the OP's distance from the exchange, if the cable length is around 2 miles then there is something amiss. I am 3km from my exchange and my attenuation is 43dB.
Below are my stats from a few moments ago.
I did post similar stats in another thread, but no-one spotted anything. If you do and wish to comment please do so here and not in this thread mucking up the OP.
Statistics Downstream Upstream  
Line Rate 7648 Kbps 448 Kbps  
Noise Margin 6.7 dB 22.0 dB  
Line Attenuation 43.0 dB 22.0 dB  
Output Power 19.8 dBm 12.3 dBm
BML, keep an eye on your router stats and report back any significant variability.
Regards.

[#14]

According to the AA, I am 1.37 miles from the exchange (by road) and since the bulk of this distance is along a dual carriageway, I would guess it is similar to my line length.
This is also roughly the same distance that the crow would fly - although we don't seem to get crows in London.
I get a constant 26dB attenuation. - and a sync rate of around 7800kbps.
A 56dB attenuation would correspond to 3+ miles.