High error rate on UMTS modem

I have the same problem with my UMTS pcmcia modem : Novatel Wireless Merlin U530

I can connect, but the data transfer rate is very very low and I have a lot of errors : here is an example for a 30 seconds connection (sorry it's in french):

ppp0 Lien encap:Protocole Point-à-Point
          inet adr:10.15.150.149 P-t-P:212.234.96.27 Masque:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1500 Metric:1
          Packets reçus:21 erreurs:2 :0 overruns:0 frame:0
          TX packets:25 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 lg file transmission:3
          Octets reçus:2107 (2.0 KiB) Octets transmis:3239 (3.1 KiB)

I HAD NOT these problems with breezy, it happens only since I upgraded do Dapper...

Forgot to tell, no changes (still not working properly) after getting kernel 2.6.15-25 :-(

Could anyone give me some advices/hints to try to track this bug, I'd like to help !

Maybe this can help, here is my dmesg when I insert the card :

[17261823.772000] pccard: PCMCIA card inserted into slot 0
[17261823.772000] pcmcia: registering new device pcmcia0.0
[17261823.772000] pcmcia: registering new device pcmcia0.1
[17261823.908000] 0.0: ttyS0 at I/O 0x3f8 (irq = 3) is a 16550A

Is it normal that I got 2 devices registred ??

> Is it normal that I got 2 devices registred ??
Windows XP also registers two devices, so this is normal - I think.

My error rates were even more dramatical, "solved" the problem by downgrading to Debian Sarge on the machine providing UMTS access. Not optimal, but better than no internet access at all.

Ok, so this "two device registered is not an issue"... :-(

I would'nt like to revert to Breezy just for my UMTS access...

Which tools could I use to track this bug and find where does it comes from ?

I was tracking the bug by playing with the MTU for the point-to-point link (smaller packets -> higher probability for the packet to pass the lossy link), by watching the output of ifconfig and by switching kernels. Guess you have to put you hands on the source code for finding the bug (trying kernel.org version of 2.6.15+, 2.6.8; compare them); reported the bug here 'cause it is some kind of Ubuntu issue, but also because I do not care enough for fixing it/reporting it upstream to the right kernel hacker.

From the MAINTAINERS file:

8250/16?50 (AND CLONE UARTS) SERIAL DRIVER
P: Russell King
M: <email address hidden>
L: <email address hidden>
W: http://serial.sourceforge.net
S: Maintained

Maybe i've found something here :

http://www.timberwolf.ukfsn.org/debian-orange-3g.html

"I also have problems with lots of ppp0 rx errors when I use the 3G card and I think this may be due or contributed to by the ACPI code. My workaround, to reduce the rx errors, is to disable the ACPI with the kernel parameter acpi=off. I have two menu items in my grub's menu.lst file to either boot kernel 2.6.13-ck1 with or without ACPI."

I'll try this (I still don't know how to disable ACPI), and keep you advised.

I tried... but with no luck :-(

Maybe the 2.6.17 kernel will help on this one ?

No improvement with kernel 2.6.15-2-6... :-(

As specified in bug #42578, this is a kernel bug.

It seems that kernel from 2.6.13 up ti 2.6.15 have a broken pp support.

I have compiled a custom 2.6.17 kernel, and my UMTS modem is working again.

I think now all we have to do is wait for ubuntu to have a 2.6.16+ kernel. I suppose it will be ok with edgy (2.6.17 kernel)

What are the chances of getting the fix linked from bug #42578 backported, given that a full backport of a new kernel has been ruled out?

I tried doing it myself but there were too many conflicts for a C n00b like myself to be able to deal with.

Beginning with the Hardy Heron 8.04 development cycle, all open Ubuntu kernel bugs need to be reported against the "linux" kernel package. We are automatically migrating this linux-source-2.6.15 kernel bug to the new "linux" package. We appreciate your patience and understanding as we make this transition. Also, if you would be interested in testing the upcoming Intrepid Ibex 8.10 release, it is available at http://www.ubuntu.com/testing . Please let us know your results. Thanks!

The Ubuntu Kernel Team is planning to move to the 2.6.27 kernel for the upcoming Intrepid Ibex 8.10 release. As a result, the kernel team would appreciate it if you could please test this newer 2.6.27 Ubuntu kernel. There are one of two ways you should be able to test:

1) If you are comfortable installing packages on your own, the linux-image-2.6.27-* package is currently available for you to install and test.

--or--

2) The upcoming Alpha5 for Intrepid Ibex 8.10 will contain this newer 2.6.27 Ubuntu kernel. Alpha5 is set to be released Thursday Sept 4. Please watch http://www.ubuntu.com/testing for Alpha5 to be announced. You should then be able to test via a LiveCD.

Please let us know immediately if this newer 2.6.27 kernel resolves the bug reported here or if the issue remains. More importantly, please open a new bug report for each new bug/regression introduced by the 2.6.27 kernel and tag the bug report with 'linux-2.6.27'. Also, please specifically note if the issue does or does not appear in the 2.6.26 kernel. Thanks again, we really appreicate your help and feedback.

This was a bug in the Dapper kernels. Last time I checked it was still a problem with the Dapper kernels. If a fix isn't going to be backported to Dapper, then I think it should be closed as "WONTFIX" with a note saying that a fix won't be backported to Dapper but it works in later versions.

Dave summed this up nicely with his previous comment:

https://bugs.edge.launchpad.net/ubuntu/+source/linux-source-2.6.15/+bug/45928/comments/14

This bug does not qualify for a Stable Release Update for Dapper, but should be resolved in subsequent releases. Marking this "Won't Fix" against 2.6.15. Thanks.