Summary:ASTERISK-04284: Analog Modem transmission through Asterisk (fax included)
Reporter:Ramon Peek-Fares (ramonpeek)Labels:
Date Opened:2005-05-26 11:02:39Date Closed:2011-06-07 14:10:26
Versions:Frequency of
Environment:Attachments:( 0) Modemtraffic_test.xls
Description:I believe this is sounding familiar, although I cannot find any clear solution to this problem anywhere.

The problem is that I keep having troubles getting my analog modems connected to a TDM400P card to work. When I dialin, the connection is most oftenly 31.2kbps but often even lower. Compared to a dialin using our standard Siemens PBX this is crap!, we are used to having a steaday 33.6kbps or even 45kbps when using v90 56k6 modems.
I offcourse turned of echocanceling and expirimented with Rx & Tx volumes on the Zaptel card which did improve the connection (From 21.6kpbs to 31.2kpbs)

I at first layed down this problem at Beronet because I thought it was caused by the mISDN interface.
See:   http://www.beronet.com/bugs/bug_view_page.php?bug_id=0000072    for many specific details.

But the same problems occur when I use the Zaptel drivers from Junghanns.

(See attached modemtraffic.xls for test details)

Now I know that the problem is not in the ISDN-channel (ZAP or mISDN) but most likely Asterisk or the Kernel used.

I say this because a bridged call works fine:
Modem =>PSTN => BN8SO(HFC) => mISDN => BN8SO => PSTN => Modem

And a non-bridged call is very poor:
Modem =>PSTN => BN8SO(HFC) => mISDN => * => mISDN => BN8SO => PSTN => Modem

But also very poor is a call like:
Modem => TDM400P => Zaptel => * => Zaptel => TDM400P => Modem

Remarkable is what happens when installing kernel 2.6.9 !!
Now modem transmission are ONLY possible in bridged-mode, all others are very bad!

As you can see I've been quite busy with this.
And I must say: "I've learned alot!", but...
What is wrong, can anybody help ?

Thanks, Ramon


Using a DELL SC1420 Xeon 2.8Ghz, 256Mb RAM with;

- Fedora Core 2 2.6.5-1.358
- Zaptel 1.0.7 with TDM11B
- Chan_misdn-18_05_05.tgz with a Beronet BN8SO HFC-Card (8x BRI)
- mISDN-CVS-2005-05-08 by Jolly
- mISDNuser-CVS-2004-08-29 by Jolly
- Asterisk 1.0.7
Comments:By: Brian West (bkw918) 2005-05-26 13:03:37

This is by no means MAJOR.  It works just not as well as you like right?


By: twisted (twisted) 2005-05-26 15:03:31

Please test this using latest CVS head, and all stock interfaces, no patches.

By: Tilghman Lesher (tilghman) 2005-05-26 22:02:48

I can confirm the issue exists with CVS HEAD.  There are several people on the -dev list, including Rich Adamson, who are working on this issue.  The exact problem is that there are frame slips with the TDM400P.

By: Tilghman Lesher (tilghman) 2005-05-26 22:04:15

I might add that the official word from Digium tech support is that the TDM400P is not intended for use with analog modems or faxes.  Thus, Digium will not support use of modems or faxes on the TDM400P.

By: Ramon Peek-Fares (ramonpeek) 2005-05-27 02:00:39

OK, it's good to know that I'm not all alone in this :)
But what does Digium advise me to use for faxes and modems (channelbanks??)

P.S.: Is there a document explaining the different severity-levels?
To me this bug is "major", since it's withholding us from installing * at 8 other locations (a real showstopper!)
So without explanation the severity-level is open to the user interpretation.

By: Ramon Peek-Fares (ramonpeek) 2005-05-27 03:07:13

I must remark that even if there is a problem with frame slips on the TDM400P this should not be of any influence on the following situation:

A non-bridged call from PSTN to PSTN through asterisk:
Modem =>PSTN => BN8SO(HFC) => mISDN => * => mISDN => BN8SO => PSTN => Modem

But this connection is also very poor, and also very dependend on the Linux kernel used. (2.6.5 gives poor results, 2.6.9 give very bad results)

HOw can this be explained when frame slips on the TDM400P is the problem?

By: Brian West (bkw918) 2005-05-30 19:25:44

This is a chan_misdn issue please contact the author of that software.