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[jon_]

Hi,

I did a search but couldn't find a definitive answer to this, so please don't flame the newbie if it's been answered before!

I've just migrated from ADSL Max to a TT LLU reseller (Xilo). I've been connected a few days, but am obviously looking to get the best I can out of my connection! Xilo are pretty helpful and let you change the SNR margins, as well as turn interleaving on and off, so I have a bit to play with.

Initially I had a 12dB SNR Margin applied:

> adsl status 
  --------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
   Running Mode            : ADSL2+(G.992.5)       State                : SHOWTIME
   DS Actual Rate          : 11640386 bps   US Actual Rate       :   971833 bps
   DS Attainable Rate      : 11888000 bps   US Attainable Rate   :   972000 bps
   DS Path Mode            :        Fast    US Path Mode         :        Fast
   DS Interleave Depth     :        1       US Interleave Depth  :        1
   NE Current Attenuation  :       29 dB    Cur SNR Margin       :       12  dB
   DS actual PSD           :    20. 4 dB    US actual PSD        :    11. 8   dB
   ADSL Firmware Version   : 2471201_A
  -------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :       15 dB    Far SNR Margin       :       12  dB
   CO ITU Version[0]       : 00004946       CO ITU Version[1]    : 0000544e
   DSLAM CHIPSET VENDOR    : < IFTN >
 
(Note no interleaving). I requested a SNR margin of 6dB, which resynced at a much higher speed, 14.8M, and downloads were significantly quicker (1.4M/sec), however the CRC error count went through the roof - approx 10 per second (!!) although the connection seemed reasonably stable.

I got them to turn it down to a 9dB SNR margin, and now I get:

> adsl status
  --------------------------- ATU-R Info (hw: annex A, f/w: annex A) -----------
   Running Mode            : ADSL2+(G.992.5)       State                : SHOWTIME
   DS Actual Rate          : 13112649 bps   US Actual Rate       :  1019968 bps
   DS Attainable Rate      : 13428000 bps   US Attainable Rate   :  1080000 bps
   DS Path Mode            :        Fast    US Path Mode         :        Fast
   DS Interleave Depth     :        1       US Interleave Depth  :        1
   NE Current Attenuation  :       29 dB    Cur SNR Margin       :        9  dB
   DS actual PSD           :    20. 2 dB    US actual PSD        :    11. 9   dB
   ADSL Firmware Version   : 2471201_A
  -------------------------------- ATU-C Info ---------------------------------
   Far Current Attenuation :       15 dB    Far SNR Margin       :       11  dB
   CO ITU Version[0]       : 00004946       CO ITU Version[1]    : 0000544e
   DSLAM CHIPSET VENDOR    : < IFTN >

I don't get an excessive amount of CRC errors anymore and the connection is stable and throughput is good.

I'm currently using a Draytek 2820 which doesn't support SNR tweaks, so I'll likely change to something like a Billion to allow me to do 'local' SNR Margin tweaks.

I suppose my big questions are - based on the stats above, what do you think is a realistic stable connection speed to acheive?

Interleaving is currently off - at 9dB the error count is low, so I don't think many retransmits are going on. If I turn it on, I understand there will be higher latency (which I'm not bothered about as I'm not a gamer) - but how much would it affect throughput? If I had it on, is there a chance that it would allow me to run back on the faster SNR margins as it would mop up the CRC errors?

Thanks

jon

[roseway]

Hi and welcome

We can't really be certain without some indication of how the SNRM varies over time. But it looks as though you could usefully drop the target SNRM to 6 dB and have interleaving switched on to compensate for the errors. Interleaving won't significantly affect your throughput.

I don't know if Routerstats (or Routerstats-Lite) will work with your router, but if it does, then several hours plotting of the SNRM will be very revealing.

[jon_]

Thanks for the reply. I've never noticed the SNRM fluctuating - unscientific I know but every time I have looked at it since I've migrated to ADSL 2+ it's been sat at the target, day or night.

I've enabled syslog output which shows me SNR Margin periodically - I'll leave it going for a while and report back

[jon_]

I went through the syslogs this morning - I would print a fancy graph but excel is playing up!

To summarize, the SNRM was 9dB until about 6pm last night, then dropped to 8dB after dark, and spent all night hovering somewhere between 8dB and 9dB until this morning when it stabilised at 9 again... Sync speeds, everything else all stayed the same (with no retrains or drops).

[jon_]

I asked for Interleaving to be turned on - the change went through this morning, and now my connection is sat at 14387435 downstream, which is quicker than it was before, with the same target SNRM (9dB). So I've gained a meg by turning interleaving on...

Unfortunately I'm checking remotely as I'm away all week so can't see easily what the throughput is compared, but it looks like I'll get even more if I can get the connection stable at 6dB or less (time to order a new router!)

[burakkucat]

Ideally you should consider a SNRM graph over a period of a few days, with the target SNRM set at X dB.

If there is variation in the SNRM over an average 24 hour period, then the ideal target SNRM to have configured is that which will result in a SNRM of 3 dB at the time when the SNRM reaches its minimum.

If the CP/ISP is unable to configure the target SNRM to a value in 1 dB steps, the next best thing would be to have the target SNRM configured to the nearest 3 dB increment above the desired value. Then with a modem/router which uses a Broadcom chipset, the DS target SNRM could be "tweaked down" as appropriate.

[babis3g]

I can see there an Infineon dslam ... once you have the 2820 (it works really good with IFTN), if i was you i would get a cheap infineon modem and connect it front of the 2820 at its wan 2

I don't think getting the billion will give you better results even if is tweaked ... fully tweaked will give you what an un tweaked  infineon modem but the infineon will have less errors because is matching the dslam

When i was at TT with the same attenuator 29 & snr 9 with fastpath (kentish town exchange -London) i got this results
d link 2680 (trendchip) 15000-16000 (supplied by TT)
draytek 2830 (same chip as the 2820) 14-15000 but with modem code 2471201 which is giving little higher speed
asus n55U ralink 12000 (fully tweaked 16000 but lots of errors - very unstable)
billion 7800, 12000 (un tweaked)... did not tried to tweaked it but my guess is the same result as the asus

the modems below can not be tweaked but it will give you optimum result for your line with less errors

Draytek 2700VG (but only g wifi)
belkin F5D8633-4
Belkin F5D8636-4 v1


There is also the netgear dgn3500 which is Lantiq, is not same as the 3 IFTN modems i am aware but close to infineon like the 2820 to give you an idea but with this the SNR can be tweaked as you wish, only if you use amod (3rd part) firmware, but not ipv6

My advise is to keep the 2820 with the modem code 2471201 and don't get the expensive billion ..., if you want to get another modem as alternative to work good, get one of 4 i mentioned and set it with the 2820

EDIT
i am down in Greece for little time and can post further test ... the dslam here is Broadcom

[babis3g]

did not edit this time but i making a new post ... if you planning getting compatible modem in the future, do & your own search for the following (apart the ones mentioned at my previous post)

Linksys AG241
Linksys RTP300 and WRTP54G
Linksys AG310
Linksys WAG54GP

and some infineon/danube which i think are tweakable
FRITZ!Box 7112
FRITZ!Box 7320
FRITZ!Box 7330

[pcourtney]

don't forget the Draytek Vigor 120 modem ( Infineon chipset ) and works amazingly well with TalkTalk LLU

http://www.draytek.co.uk/products/business/vigor-120

NB  the 120 is a bit special in that it only does PPPoA to PPPoE and nothing else !

[babis3g]

the old/first 120 (v1) it is infineon ... the 120 v2 is not, is the same (ADI analog devices) as the 2820,2830,2850 (the separate build in vdsl of the 2850 is metanoia)

[burakkucat]

The company that we knew as Infineon (with regards to modem/router chipsets) now trades, following its sale, under the Lantiq name.

[jon_]

Hi,

Thanks for the replies everyone... The connection seems to be pretty stable at 6dB SNRM now, even though I have a feeling that Fastpath seems to be back - the modem is reporting fastpath, and the CRC errors are back - but Xilo tell me interleaving is 100% enabled...

I'll probably stick with the Draytek for a while and see how it goes - a new billion is a fair wodge of cash for something that's not really going to gain me a lot, and the Draytek has been 100% stable for the couple of years that I've been using it, which means more than a few extra K of speed to be honest!

Thanks

Jon