ADSL Sync Speed - Interesting Findings

If you're on o2 provided over BT's network, then it takes 3 days for the IP profile to raise.

If you're on o2 LLU then they don't have IP profiles. The speed matches the sync rate straight away. However the throughput you see isn't quite as high as the sync rate. For example I'm currently syncing at 18,652kbps which right now is giving me 1930KB/sec download speeds - this equates to 16mbit of throughput.
 
Sync speed - IP Profile

from 6240Kbps 5.5Mbps
from 6816Kbps 6Mbps

So it seems you'd need to connect at 6.8~ to get a higher profile than 5.5mb
 
On the subject of interesting ADSL sync speed findings... here's one I've just discovered:

I told my ISP to disable interleaving on my ADSL2+ line. I had expected it to get a little faster but actually the opposite happened. When it was disabled it went from 14.8Mbit to just 12.1Mbit. However the DSLAM increased the SNR Margin from 12dB to 15dB - presumably to reduce the likelihood of CRC errors. I asked my ISP to forcefully reduce the SNRM to 12dB but they declined.

Instead they put me back onto Interleaving (and the higher sync rate) but configured it so that it does not cause much increased latency. Apparently Interleaving on ADSL2+ has lots of configuration options that can be tweaked.

I have inspected my router and it is reporting that the Interleaving adds just 4ms on the downstream and 2ms on the upstream. The parity word size is 6 bytes.

The FEC is catching a fair few errors as well, at about a 95% success rate. Which is better than dropping the packet entirely and resulting a CRC error.

For the cost of just a couple milliseconds I think I'll leave it how it is now.

I've since done some reading up on the subject and it turns out that ADSL2+ actually *requires* Interleaving and FEC. To run it on fast path mode is both standards uncompliant and is vendor-specific depending upon the DSLAM! However, as said before, there are a lot of configuration options for Interleaving/FEC on ADSL2+... So, if you wanted, you could reduce the parity word size and interleaving depth to their smallest values and therefore pretty much remove the overhead if you wanted.
 
The interleave depth was configurable on ADSL as well, just most ISPs couldn't be bothered doing anything about it.

Where did you find that interleaving is required on ADSL2+? There's nothing in the ITU G.922.5 docs saying that interleaving is mandatory....
 
I read it on Google somewhere. Might have been a dslreports thread, can't remember exactly.

I think what it was trying to say is that "fast path" mode is deprecated and that if you wish to "disable" interleaving and FEC then you should set the DSLAM to use the smallest values that it supports.
 
I don't think so. To be honest it seems pretty clear to me now that a lot of the advancement in ADSL2+ comes from the interleaving and FEC. That's why my sync rate dropped by almost 3Mbit when I had those features disabled on my line.

I suppose it's slightly analogous to disabling Superfetch on Windows Vista :p

Or for a automotive anology... a bit like removing a turbocharger from your engine even though it was designed to have one.
 
No, the extra speed in ADSL2+ comes from doubling the downstream frequency range, giving you double the number of bits over ADSL2 (you go from 12Mbps to 24Mbps). G.DMT ADSL does 12Mbps too, the main difference between ADSL and ADSL2 being the extra power-saving features, SRA, easier bonding, better diagnostics et al.

In your case, the reduction in sync rate came about because of the 3dB increase in SNR margin. If the ISP (or wholesale provider) had dealt with that, odds are you'd have been in exactly the same position with interleaving off as on.

Edit: Using your Superfetch analogy, it would mean you take a performance hit disabling it, but see no performance improvement from "fetching more" (i.e. having more precached in RAM). That isn't remotely logical.
 
Disabling interleaving on my line put my sync rate up from approx 17mbit at the time to 19mbit. With Be you can disable and enable interleaving yourself from their control panel and I consistently get a higher sync rate with it disabled.

It depends on the line.
 
Right, something to add to the mix. I lost sync. tonight whilst I was on the phone.

Does this help point to anything at all?

DSL Connection

Link Information

Uptime: 0 days, 0:14:17
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 880 / 6,479
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 12.0 / 19.0
Line Attenuation (Up/Down) [dB]: 25.5 / 47.0
SN Margin (Up/Down) [dB]: 6.5 / 7.5
Vendor ID (Local/Remote): TMMB / BDCM
Loss of Framing (Local/Remote): 12 / 0
Loss of Signal (Local/Remote): 2 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 25 / 0
FEC Errors (Up/Down): 283 / 7,426
CRC Errors (Up/Down): 283 / 423
HEC Errors (Up/Down): 54,486 / 420
Click to expand...
 
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Have you got a new phone yet to try?
Can`t see in this thread that you have bought/borrowed one to rule out the telephone you are using :)
 
no not yet. Will get one though. Is it possible the phone can cause sync loss?

EDIT - I note it drops out as soon as I pick up my phone to dial out. I rarely use the house phone so I expect it has been like this for some time.
 
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Finally got round to testing with a different phone and... perfect!

Sync'ing at almost 7mb, pretty much my limit (& the speed o2 predicted) and no drop outs etc.



The DECT phone is only a month old so do I return it for a different model? Or will all DECT phones cause this issue? Do you think this phone is a one-off or the model itself at fault?

Link Information


Uptime: 0 days, 0:10:33

DSL Type: G.992.5 annex A

Bandwidth (Up/Down) [kbps/kbps]: 1,213 / 6,837

Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00

Output Power (Up/Down) [dBm]: 12.0 / 18.5

Line Attenuation (Up/Down) [dB]: 25.0 / 47.5

SN Margin (Up/Down) [dB]: 6.5 / 7.0

Vendor ID (Local/Remote): TMMB / BDCM

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): 3 / 971

CRC Errors (Up/Down): 3 / 1

HEC Errors (Up/Down): 102,109 / 0
 
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Nothing at all unfortunately. The factors that determine attenuation are things you have no real control over - like line length, the material your line is made of and so on.

You've got a pretty good sync rate for a fairly high attenuation :)
 
Thats tosh, I have a 45 att and have a 10MB sync rate which holds very stable.

I would phone up and try the 3dB profile over a 24h period, the worst that can happen is your line is unstable at that snr and you have to phone up for it to be put back, its worth a try IMO.
 
It's not tosh, you just have a very good line :) Attenuation isn't the only factor that determines a line's quality.
 
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