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[Pockets]

I'm on a Sky ADSL broadband line. Since I prefer to use my own router, I tried and failed to get a Billion 8800NL working in half-bridge' mode,
http://forum.kitz.co.uk/index.php/topic,18685.0.html

I'm now trying to use a Draytek Vigor 130 as a modem.
I set up the Vigor 130 with a PPPoA to PPPoE conversion which talks to the router quite happily. The router now handles the Sky authenticaion.

However, there is one thing which I can't figure out. Although the Draytek is working nicely, the speeds I am getting are (approx)
0.8 Mbps up
15.0 Mbps down
(that's in the router's info page - the speedtest results are proportionately a bit less than that. 

Compare with the Bilion, which gave
0.8 Mbps up
16.4 Mbps down.

As far as I know, the PPPoA to PPPoE bridge conversion does come with a small overhead. But I didn't expect it to slow the download speed by nearly 10%. Also, when the Draytek is in bridge mode, I don't know whether the figures it gives reflect the connection speed pre-conversion or post-conversion.

Anyway, as far as I know, these are the things you might try to tweak to improve the download speed on the Draytek:
- Modulation method
- SNR Margin
- DLM reset triggered by broadband provider
- Anything else?

- I experimented a bit with the Modulation method, without success.
- The Draytek reports an SNR margin of 3 and Loop Attenuation of 22. As far as I know, it can't really go any lower than that. Besides, the Bilion reported SNR down (which I presume corresponds to SNR margin in the Draytek) of 3.1 and Attenutation of 20, so that seems basically the same.
- From what I've read, I believe DLM happens continuously on VDSL, but on ADSL only in the days after the connection goes live. So perhaps requesting a reset would magically configure the line to be more friendly to the Draytek, though I can't say I understand how that works.

Any other suggestions for how I might tweak the Draytek? Or perhaps the best advice is just to lump it - 10% speed decrease is not too awful given that it plays nicely with the router.

[psychopomp1]

The difference is mostly likely down to the different chipset the modems use. The draytek 130 uses a Lantiq chipset and the Billion uses a Broadcom. Nothing to do with overheads ppoa >ppoe. For example on my talktalk adsl2+ line I used to get 18 meg sync with the Vigor 120 and 16 meg sync with the billion 7800n.

[ejs]

You could try enabling G.INP (ReTx) on the Draytek, it does exist for downstream only on ADSL2/2+, Sky LLU might use it.

[psychopomp1]

The draytek 130 has g.inp enabled as default (provided fw is recent) and from memory I don't think you can switch it off ( in gui anyway)

[Pockets]

I believe my firmware is up to date (it claims to be 3.7.9, although the latest on the website is called 3.7.4.BT which is a bit confusing).

It sounds like I should at least check the G.INP status, although I can't see any reference to G.INP or ReTx in the GUI.  Do you know what command can be used on telnet to verify whether G.INP is enabled? 

Also, I was under the impression that G.INP is only relevant for Fibre, not ADSL. Am I wrong about that?

[Weaver]

There's no such thing as a conversion loss. It's the other way round. The PPPoE is over an extremely fast LAN, and PPPoA, which is more efficient, not less, is in use over the ADSL link. So at identical sync speeds the Draytek will be faster than modems that speak PPPoEoA over DSL.

When I tested one, I just found that it wasn't that aggressive a modem. I agree with Psychopomp1. They're great but just not that fast.

[psychopomp1]

I believe my firmware is up to date (it claims to be 3.7.9, although the latest on the website is called 3.7.4.BT which is a bit confusing).

It sounds like I should at least check the G.INP status, although I can't see any reference to G.INP or ReTx in the GUI.  Do you know what command can be used on telnet to verify whether G.INP is enabled? 

Also, I was under the impression that G.INP is only relevant for Fibre, not ADSL. Am I wrong about that?

v3.7.9 is the latest international fw version for the 130, you need the latest UK fw which is 3.7.4BT which will be optimised for UK ISPs:
http://www.draytek.co.uk/support/downloads


You can see all your line stats via the Web Console incl G.INP status. Icon is top right of GUI.
Enter adsl status
and then on next line adsl status more

If there's no mention of ReTx then Sky don't support G.INP on your ADSL2+ line.

But like i said earlier, the different modem chipsets is the most likely reason for the sync rate difference.

Also on an ADSL2+ line with downstream attenuation of 20-22db you should be getting sync speed of ~20 meg @ 6db SNR, even higher with a 3db SNR. You need to get wiring checked out, check filters, connect router to test socket etc to see if sync rate can be improved upon.

http://www.kitz.co.uk/adsl/max_speed_calc.php

[Pockets]

Well this has taught me a lot.  First, updating the firmware to the UK-specific one looks seems to make for a very small improvement. (Not up to the Billion's speeds, but every little helps!)

Also, I can now see more information when I do the commans 'adsl status' and 'adsl status more'.
In particular, when I do 'adsl status more' I can now see amongst the various fields

ReTxEnable:
Near End 0
Far End 1
INP:
Near End 16
Far End 275

a couple of other fields which might be relevant
Trellis:
Near End 1
Far End 1
Bitswap:
Near End 0
Far End 1

Well, I'm not sure what these mean but it looks like ReTx isn't enabled.
Would the right command to enable it be 'adsl optn retx bi on'? And perhaps 'adsl optn bitswap bi 1'

[Weaver]

Bitswap is disabled on what appears to be the upstream direction? Madness. Makes it unreliable, or slow. I wonder how you can make persistent config changes.

I would  like to use one of these devices if the speed were any good.

Since you are on ADSL2 or ADSL2+, iirc, it might be worth taking a look at the DLink DSL-320B-Z1 modem. This is what I use. It's essential that if you get one of those you configure it safely as the default config is as a disastrous router not a straight modem. In that state it’s insecure and buggy, and the default config is also wrong as bitswap needs to be enabled. SRA and INP should be enabled too, in case you ISP supports it. Getting it configured correctly is very quick and easy. See earlier threads about this device as a lot of testing has been done by other kitizens.

[psychopomp1]

OP, I would be more concerned about why your 20db attenuation line isn't syncing closer to 20 meg. For the time being forget about G.INP, concentrate on getting any line issues resolved, first thing to do would be to connect your router directly to the test socket to rule out wiring issues. Also try the Sky supplied router and the D Link modem which weaver has suggested.

[Weaver]

Definitely do the test socket thing, as psychopomp1 said.

[Pockets]

OP, I would be more concerned about why your 20db attenuation line isn't syncing closer to 20 meg.

The top ends of the speeds I'm seeing (15-16 MBps) tally with what the BT broadband checker promises https://www.btwholesale.com/includes/adsl/adsl.htm, so I'd be very surprised if I could get much more. 

I ought to look into the test-socket question.  But the fact remains that the Bilion syncs a bit faster than the Draytek on my line, with the same wiring. I can't see the Sky router's sync speed directly, but its speedtest scores are about on par with the billion. (Unfortunately it has other failings...)

Maybe as you say, it's simply down to the Lantiq vs Broadcom chipset.

[Weaver]

It was a disappointment to me on my ultra-long G.992.1 line compared to the aggressive DLink, otherwise it would be my first choice for ADSL because of its use of PPPoA which is slightly more efficient (the odd percentage point on long packets, much more on short packets). The DLink uses a different chipset - an old MediaTek / Trendchip device. The DLink doesn't support VDSL2 if memory serves and is much much cheaper, so much so that I've got three of them, one per line, plus three spares ready for the next lightning strike.

Speculation: Speed isn't (quite) everything. Having said that the Draytek synced slower, it might be that it would have been more reliable for me at the lower sync rate, so now I'm on ADSL2 and can adjust the target SNRM a little, although I don't have fine-grained control, I might be able to offset the less aggressive nature of the device by running at a lower target SNRM, but I very much doubt it.

[psychopomp1]

The top ends of the speeds I'm seeing (15-16 MBps) tally with what the BT broadband checker promises https://www.btwholesale.com/includes/adsl/adsl.htm, so I'd be very surprised if I could get much more. 

Data from BT speedchecker site should be taken with a pinch of salt, your speed can be better or worse, depending on your actual line length. As you have a downstream attenuation of 20-22db (you can't argue with physics!) you should be syncing around ~20 mbps and that's at 6db SNR, not 3db as your current stats show. Enter your attenuation here and be surprised:
http://www.kitz.co.uk/adsl/max_speed_calc.php

Of course you're currently on a reasonably fast speed for an ADSL2+ connection (16 mbps) but you should be able to squeeze another 4-6 meg out of this line. So getting your router stats from the test socket would be a good start

[ejs]

ReTxEnable:
Near End 0
Far End 1
INP:
Near End 16
Far End 275

Well, I'm not sure what these mean but it looks like ReTx isn't enabled.

Actually, I think it looks like ReTx is not only enabled, but is actually in use. Because G.INP is only specified for the downstream with ADSL2+, "Far End" here must indicate the downstream. The INP value probably represents 27.5, and such a high value is impossible to obtain using FEC+interleaving.

Since you are on ADSL2 or ADSL2+, iirc, it might be worth taking a look at the DLink DSL-320B-Z1 modem. ... SRA and INP should be enabled too

I think this would be a poor choice because I don't think the DSL-320B-Z1 will support retransmission (G.INP). INP and G.INP are not the same thing. INP is just a measure of how much impulse noise protection is provided, from the interleaving+FEC or retransmission. G.INP uses retransmission to provide higher levels of INP than what interleaving+FEC can achieve.