Download speed lower than Line speed

[#1]

Morning all
Can anyone explain why I am only getting a download speed of 4.5Mb when my line speed is showing as 5.4Mb?
Plusnet Line Speed:
Estimated line speed:
    There's no speed estimate currently held on your account.
Current line speed:
    5.4 Mb
BT Speed checker:
Best Effort Test:  -provides background information.
Download  Speed
4.45 Mbps

0 Mbps 7.15 Mbps
Max Achievable Speed
Download speed achieved during the test was - 4.45 Mbps
For your connection, the acceptable range of speeds  is 2 Mbps-7.15 Mbps.
IP Profile for your line is - 5.48 Mbps
2. Upstream Test:  -provides background information.
Upload Speed
0.74 Mbps

0 Mbps 0.83 Mbps
Max Achievable Speed
Upload speed  achieved during the test was - 0.74Mbps
Additional Information:
Upstream Rate IP profile on your line is - 0.83 Mbps
Router Stats:
Mode: ADSL_G.dmt
Traffic Type: ATM
Status: Up
Link Power State: L0

Downstream Upstream
Line Coding(Trellis): On On
SNR Margin (1 dB): 4.6 10.0
Attenuation (1 dB): 48.5 30.5
Output Power (1 dBm): 19.9 12.3
Attainable Rate (Kbps): 6304 1032

Path 0 Path 1
Downstream Upstream Downstream Upstream
Rate (Kbps): 6208 864 0 0

K (number of bytes in DMT frame): 195 28 0 0
R (number of check bytes in RS code word): 16 16 0 0
S (RS code word size in DMT frame): 1.00 8.00 0.0 0.0
D (interleaver depth): 32 4 0 0
Delay (msec): 8.00 8.00 0.0 0.0
INP (DMT symbol): 1.21 0.09 0.0 0.0

Super Frames: 4972461 4972461 0 0
Super Frame Errors: 671 38 0 0
RS Words: 338127314 42310577 0 0
RS Correctable Errors: 874178 371 0 0
RS Uncorrectable Errors: 6891 0 0 0

HEC Errors: 6614 35 0 0
OCD Errors: 0 0 0 0
LCD Errors: 0 0 0 0
Total Cells: 1237666718 0 0 0
Data Cells: 70318818 0 0 0
Bit Errors: 0 0 0 0

Total ES: 417 0
Total SES: 1 0
Total UAS: 42 42
I had two disconnects night before last which did reduce the line speed but did a graceful resync yesterday which restored my normal level - as shown in the stats. I've been getting a download of around 5 to 5.25 Mb since the middle of November, despite a less than ideal line - previous topic http://community.plus.net/forum/index.php/topic,145602.0.html has some background if anyone is interested.
Do I need to raise a fault with Plusnet or is there a chance that a member of the CRT on the Forum could help?

[#2]

Caerefail,
The figures are interesting in a number of aspects.
First some guidance.  The SYNCH speed is the raw bit rate of the line.  The DATA rate is limited by the line's profile (IP) rate, reported on the PlusNet portal as "Current Speed".  For CN21 services the profile is 88.2% of the synch rate; for 20CN services the profile is 'banded' depending on the synch rate - see http://www.plus.net/support/broadband/speed_guide/broadband_terminology.shtml#ipProfile
Reading here - http://community.plus.net/forum/index.php/topic,145602.msg1283251.html#msg1283251 - suggests that you are on 21CN, albeit with ADSL1 modulation.  I am surprised at the suggestion that your line is too long for ADSL2 - 48.5dB suggests a length of about 3.5km.  My ADSL2 attenuation (always a bit higher than that for ADSL1) 50dB delivers a steady 5.4Mbps SYNCH speed at 3dB.  If I were in your shoes I'd be pushing for a try with ADSL2, given the comment here - http://community.plus.net/forum/index.php/topic,145602.msg1284065.html#msg1284065 - ADSL2 error management is better than ADSL1.
The DS SNRM is between two standard settings - are you still using the Billion and have you forced a SNRM adjustment?  In the other thread, you've hinted that you have REIN/SHINE, in such circumstances if you force the SNRM down to get a better synch speed (as it appears you have - 6208kbps is somewhat higher than would be expected on a 48.5dB line at 6dB) then you can expect to see higher levels of transmission errors requiring retransmission to successfully transfer the data.  Consequently the measured DATA speed will be markedly less than the MAXIMUM potential data speed suggested by the profile figure.
If you really wan to see this line perform better, I suggest that you request a change to ADSL2, investigate the possibility of REIN/SHINE and undo the manipulation of the SNRM and allow the DLM to manage the issues on the line.
I do not recall seeing much (if any) CRT touch on the other threads (see also http://community.plus.net/forum/index.php/topic,143479.msg1265871.html#msg1265871). ; Looking back through all of your threads (would be useful if they were merged) you've had higher synch speeds than you have now - even higher still than expected.  Given your perception of disconnections, I wonder if there is now merit in using the BB fault reporter - see link below.
@CRT,
A VR plot and  CLT report would be useful please.

[#3]

Townman,
I think that the line was put on ADSL1 because the original BT speed forecast was 2 to 2.5Mb and Plusnet say that if the forecast is under 4 they'll opt for ADSL1 even if ADSL2 is available. I'm pretty sure that the exchange is 21CN.
I'm currently using the 2704N Plusnet router as before moving to Plusnet I was only getting 2Mb at best and I wasn't sure that the Billion router was reliable. I have to say that the 2704N hangs onto the line very well - I've seen the SNRM down to 0.7dB at night and the line has still held! So no tweaks on my part on the SNRM. The line is quite stable during daylight hours but between about 8pm and 6 am it does suffer from interference as well as some SHINE - irregular and external to the property  DLM is free to do its best (or worst!)
I was really wondering why, given that the IP Profile is 5.48 Mbps and the Plusnet line speed matches this, I was only getting 4.5Mb download - I've had this profile and line speed regularly since mid-November and usually get around 5+ Mb download. Guess it is time to complete the fault reporter - I'll try to set up the Billion router, see how that behaves tonight and post the results up here for info' and then complete the Broadband Troubleshooter. Fingers crossed it doesn't completely mess things up.
Funny thing is - once I'd have been more than happy with 4.5Mb, but after getting 5+Mb for a number of weeks, I want to keep it 

[#4]

Sometimes what happens is that the Plusnet profile updates, as shown by the Plusnet Current Line Speed, but your PPP session does not get disconnected automatically (usually this does happen, or at least it should), so the new profile doesn't actually start being used. If that happens, all you need to do is log in to the router, click a Disconnect button for the PPP or Internet connection, then click Connect after.

[#5]

Good one ejs!
@Caerfail - I think the 'debate' to take back to PlusNet is "The decision basis for setting this line to ADSL1 has been refuted - can you please re-provision it as ADSL2/2+?".

[#6]

@ ejs - Arrgh! Why didn't I think of that? I'm sure you've told me this before as well  Thanks - speed now back to 'normal'
@ Townman Thanks for your suggestions. Any advice on the best way to ask Plusnet to re-provision the line as ASDL2/2+? I won't bother messing with the Billion router now.

[#7]

Usually CRT would pick up request here, however they are a bit thin on the ground at the moment 

[#8]

Perhaps they're busy 

[#9]

Has dropping the PPP session sorted the throughput speed?

[#10]

Quote from: Caerefail

Thanks - speed now back to 'normal'

[#11]

Oops.
@Caerefail
Have you treated yourself to that UPS yet?
Edit: btw, what time of day was it you did the graceful resync?

[#12]

@ AO - not yet  - perhaps Father Christmas will be nice!
Graceful resync was at 7.30 am yesterday, PPP reconnect was 3.00 pm this afternoon. I try to do any graceful resyncs either around 7 am or 5 pm - the SNRM seems to be around the best level then to maximise speed and hang onto the line overnight. If I do it in the middle of the day the speed is better but the SNRM drops too low at night to keep the connection.

[#13]

Timing of the resync is just as I recall.
So with that latest one in mind, it shows that the current error rate won't be contributing to any real noticeable drop in throughput, as your last test shows your speeds are back to normal even though I missed the comment
I do hope Father Christmas is nice for you, apart from relieving you of any mains dips dropping sync, the filtering in most of these units may help suppress some of that SHINE you periodically observed if it's still there. But at least with the SNRM/Sync combination you usually manage to achieve the night time holds on.
If Father Christmas is kind, it'll be interesting to see how you get on, and if things turn out to be even more stable, it might then be worth considering having a play with the Billion - first with no tweaks and some monitoring with RSL as you did before moving to Plusnet, and if all that looks good, consider a tweak. The limiting factors will be the size of any remaining SHINE coupled with how low your SNRM is dipping at night and the other being the error count

[#14]

@AO Thanks for your guidance. Yes, I’ve been thinking of resurrecting the Billion router - if only to do some more monitoring to see if any pattern to the SHINE has appeared - and, indeed, if it's still there. Will have to wait until after Christmas though!

[#15]

Quote from: Anotherone

Oops.

It happens, sometime even the best of us miss a bit of someone's post - so don't beat yourself up - forgive yourself instead!