Re: USB ADSL Modems for Linux?

Jonathan Buzzard wrote:

I used to use a bewan PCI but while it was fine pre max it was quite unstable for max dsl - it won't do adsl2. I suppose it depends on your line as to how well various modems work, but I now use a TI AR7 based £20 solwise with www.routertech.org firmware and it's far better and adsl2 ready. More modern modems seem to be router on a chip devices so I don't think you will find usb/pci that can beat them. By which I mean the AFEs are much cleverer than the first generation modems which are >10 year old designs.


Really?

Yes really - well I did say on my line :-) I've still got it and have put it back on in the past just to see if it was the same.


jab@small:~$ sudo unicorn_status
Modem State : SHOWTIME_L0
Remote Report : Showtime
Last Failure :
Time Connected : 13:49:47
Modulation : ANSI
Rate Us/Ds (Kbps) : 448 7616
Cap. Occupation Us/Ds (%) : 56 94
Noise Margin Us/Ds (dB) : 26 8
Attenuation Us/Ds (dB) : 6 13
> Output Power Us/Ds (dBm) : 11 17

13 attenuation I can only dream of a line that short, I am sure my bewan would be stable on that. 8 margin seems a bit low.

Mine is 44 and margin 6-1 depending time of day.

FEC Errors Us/Ds : 21294 2
CRC Errors Us/Ds : 0 0
HEC Errors Us/Ds : 0 0

I've got a patch somewhere that fixes the reversed stats and one that polls at 1ms rather than 10. 20ms jitter on latency used to bug me, but it did affect the upstream rate a bit. It looked fixable - was just the wat their aal5/aal0 qos algorithm worked.

Driver Version : 0.9.3
Firmware Version : PCI-AML-1-0.4-0.1.0.10

I thought that you could only get >2Mbps if you where on a max product. It
has been generally stable for me. In the last 18 months I have lost
connectivity three times, though after the first monit restarted it
automatically :-)

Fair enough but on my line it would sync low 6xxx and be very unstable. I used to have to force it to sync low 5s or high 4's but it would still drop a few times in the evening. (ability to specify rate also required patching IIRC)

If by lost connectvity you mean dead ppp when it resynced then you can script around that. On 2meg/pipex I never had to - it just worked after a resync. On max/enta half the times a resync would also require a ppp drop after the line was back - routers seem to always do this anyway.

With a static IP I can now get away with a resync/manual ppp drop (eg. to change centrals with ukfsn/enta) without anyone noticing. Use SNAT rather than MASQUERADE so netfilter doesn't clear the conntrack state and block lan bound ICMP net unreachables from the router.


The limited connected time above is because I rebooted after an aptitude
upgrade earlier today.

My biggest grumble is the binary blob in the kernel module and getting it
working beyond 2.6.18 which appears to be rather hard. I can see me
installing CentOS 5 if Debian move away from a 2.6.18 kernel.

I used to like having PCIs apart from those reasons as well. I can't recall going higher that .18, though I think bewan did release a blob that was compiled with regparm which may help.

I have been up for 630 hours without resync so far (power cut). After years of being on fast path I now have 10ms interleaving. Apparently the underground cables between the green box and the houses are fucked and BT were messing around trying to sort next doors connection and I ended up with interleaving. He commented to her that I am the only person in the close that gets good sync. How much is luck in being closer to the box and how much is AR7 + decent filtered faceplate I don't know. He synced his kit on her line and said it should be good for 4meg.

Andy.

/var # cat /proc/avalanche/avsar_modem_stats

AR7 DSL Modem Statistics:
--------------------------------
[DSL Modem Stats]
US Connection Rate: 448 DS Connection Rate: 7136
DS Line Attenuation: 44 DS Margin: 5
US Line Attenuation: 29 US Margin: 24
US Payload : 2888639760 DS Payload: 63388080
US Superframe Cnt : 142303473 DS Superframe Cnt: 142303473
US Transmit Power : 11 DS Transmit Power: 19
LOS errors: 0 SEF errors: 0
Errored Seconds: 0 Severely Err Secs: 0
Frame mode: 3 Max Frame mode: 0
Trained Path: 1 US Peak Cell Rate: 1056
Trained Mode: 3 Selected Mode: 1
ATUC Vendor Code: 414C4342 ATUC Revision: 1
Hybrid Selected: 1 Trellis: 1
Showtime Count: 1 DS Max Attainable Bit Rate: 7136 kbps
BitSwap: 1 US Max Attainable Bit Rate: n/a
Annex: AnxA psd_mask_qualifier: 0x0000
ATUC ghsVid: 0f 00 41 4c 43 42 00 00
T1413Vid: 00 00 T1413Rev: 00 VendorRev: 00
ATUR ghsVid: b5 00 54 53 54 43 00 00
T1413Vid: 00 00 T1413Rev: 00 VendorRev: 00

[Upstream (TX) Interleave path]
CRC: 2829 FEC: 194548 NCD: 0
LCD: 0 HEC: 0

[Downstream (RX) Interleave path]
CRC: 60968 FEC: 15761390 NCD: 0
LCD: 0 HEC: 0





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