[Asterisk-Users] Strange Quality problems with Asterisk, Gentoo, Redhat and Kernels - /dev/dsp

[Deon Rodden]

I've compiled Asterisk on Redhat 9 and Fedora Core 1 in the past, 
generally without any problems. Especially w/ the stock kernel, which I 
generally loathe. When I tried to upgrade my Redhat 9 Server to the 
2.4.27 kernel, doing a manual/clean compile, I had massive quality 
issues. I was forced to go back down to a stock 2.4.24 kernel. Never 
figured out why.

Now, I've installed Gentoo and am using the 2.4.26 kernel, and things 
initially appeared ok. I emerge'd Asterisk, the dependencies were 
downloaded compiled, Asterisk 0.9.0 was compiled, I then used cvs to 
update to the latest libpri/zaptel/asterisk. Everything seemed fine. 
However, I'm noticing the occasional quality issue. First I just thought 
the music on hold was a little choppy, but that always seems normal, I 
blamed the zaprtc/rtcsetup thing I'm using to get zaptel timing.

But then we noticed problems with Grandstream phones. The grandstream 
would connect to the Gentoo Asterisk Server via SIP, then go out via IAX 
across a T1 to the main asterisk server (Redhat 9), which then pushes 
the call via SIP to a Cisco Router that's connected to several PRI's. My 
last clue therem ay be a problem with Gentoo is the T1 card we put in 
another server. We put a T100P in another Gentoo server, therefore 
didn't need zaprtc/rtcsetup, and it uses pri-net to simulate a Voice T1 
PRI for a PBX system. Calls will come in via IAX2, from my main asterisk 
server, and it will then (using Zap) go out the T100P into the PBX. 
There's an intermittant quality issue there as well.

The only clues in the log files was something about /dev/dsp missing. 
This didn't seem a big deal, music on hold worked, etc. but I noticed 
that /dev/dsp existed on my redhat machines, even though they're the 
same servers, no sound cards or anything. The kernel on the Redhat 
machines was compiled with several sound card modules, but nothing 
integrated. An 'lsmod' reveals a module called soundcore loaded, but I 
can't find soundcore on my Gentoo machines.

Is there anything mandator in the compilation of the kernel that will 
affect Asterisk's quality? The CPU load on the systems is nothing. 
Everything "appears" normal. The only common factor is custom compiled 
kernel. A custom compiled 2.4.27 on Redhat had problems, and a Custom 
Compiled 2.4.26-gentoo on Gentoo has not-so-apparent problems too.  I've 
always been on top of the latest CVS updates on Zaptel/Asterisk/libPRI