Kitz Forum
Broadband Related => Broadband Technology => Topic started by: audiolab on February 20, 2009, 09:26:19 PM
-
Hey there.
Im connected to my router by cable, i am the only active connection and the router itself is plugged into the main phone line, ive tried changing the faceplate, the micrfilter etc.....getting a little tired of BT's support.
Here are my connection details:
This Test comprises of Best Effort Test: -provides background information.
Your DSL connection rate: 8128 kbps(DOWN-STREAM), 448 kbps(UP-STREAM)
IP profile for your line is - 7150 kbps
Actual IP throughput achieved during the test was - 114 kbps
and the router report:
ADSL line status
Connection information
Line state Connected
Connection time 2 days, 2:16:47
Downstream 8,128 Kbps
Upstream 448 Kbps
ADSL settings
VPI/VCI 0/38
Type PPPoA
Modulation ITU-T G.992.1
Latency type Interleave
Noise margin (Down/Up) 6.4 dB / 29.0 dB
Line attenuation (Down/Up) 26.0 dB / 16.5 dB
Output power (Down/Up) 19.8 dBm / 11.8 dBm
from my understanding this should be a good connection! but i seem to get abismal speeds all the time. that is the 10th or so test ive run and the results have been almost identical.
any advice?
just an observation i could be wrong ,but isnt adslmax with interleave maxed out at 7616?
-
just an observation i could be wrong ,but isnt adslmax with interleave maxed out at 7616?
Not always - especially when the line has a very low attenuation.
-
Not even with low attenuation. My attenuation was 39dB and when I was interleaved I could still connect up to 8128kbps.
I think it all depends whether the modem and DSLAM are both set up to support ANSI T.143 which is like an enhanced version of the standard G.DMT ADSL modulation.
Whether that's to do with the DSLAM / modem chipsets being compatible, or whether it's to do with what mood the BT engineer who configured the DSLAM is in.. who knows - but I don't think it's related to attenuation
-
Interleaving has different levels. Best I ever got on my connection (also with 39dB DS attenuation) was 7616 kbps. Of course this was then, now I don't seem to be able to get a sync rate above 4800. :(
-
Its not reliant on attenuation nor the depth or delay of interleaving.
Its actually to do with something called S=1/2 mode.
Standard ADSL1 architecture has a maximum download speed of 8.128 Mbps due to framing overheads.. or more specifically a limitation of the maximum Reed Solomon (RS) codeword size (http://www.kitz.co.uk/adsl/error_correction.htm#RS).
s=1/2 mode allows 2 RS codewords to be interleaved and mapped to one data frame which in turn greatly increases the maximum acheivable downstream speed up to the limitation of the maximum number of bits that can be carried across the available DMT subchannels (http://www.kitz.co.uk/adsl/adsl_technology.htm#dmt). (num of subchannels x 15 bits per subchannel x 4kbps).
If all DMT subchannels were in use - which theyre not - and if the SNR in each subchannel was good enough to carry 15bits per tone... now we are talking near 16 Mbps.
DMT (in the UK) generally uses downstream tones 33-254 so we now have a maximum download speed of somewhere approaching 13Mbps.
BTW - Are these figures ringing any bells with adsl2 anyone? - ignore adsl2+ since that works by doubling the no of available subchannel frequencies.
So how does this fit in to the question?
If you have a router that supports s=1/2 mode... and the dslam you are on is also configured to supposrt s=1/2 mode (not all are), and if your line is good enough to be able to load sufficient bits per subchannel (http://www.kitz.co.uk/adsl/adsl_technology.htm#bit_loading).... then an interleaved line can over-ride the maximum 'normal' limitation of 7616 for an interleaved line. You wont ever get more than 8128 though, since that will be a hardcoded maximum configuration of BTs dslams.
-
Top class explanation and links as usual! Thank you. :)
-
Since this wasnt relevant really to the OPs original query and has sidetracked a bit from their issue, Ive split this to a separate thread :)