Distorted voice in an Asterisk conference?

Question

Asterisk

Good! We have virtual ubuntu 10.04 on XCP. On it, respectively, the assembly of Asterisk 1.8.20.1 + Web meemte. There was a problem with the voice in the conference, namely: when calling from phone to phone, the service does not suffer, excellent audibility, but when creating a conference, stuttering, sound loss, etc., etc. appear. ulaw codec. There is no high load on the percent. Installed Dahdi, Zaptel on this assembly of the asterisk is not possible to install. Where to look, what's the problem?

Answer 1

Bandwidth?

Answer 2

as expected, 100 Mbps, all within the local area

Answer 3

Faced the problem of running Asterisk in a virtual machine on VMWare ESXi, the same symptoms. Calls came to the call center and the sound was very slow and stuttered with simultaneous calls > 30. CPU load and memory consumption were within the acceptable range.
Then I found information that on virtual machines, due to competition for processor time, there may be delays > 5ms on the scheduler.
The problem was solved by transferring the server to a physical server without virtualization.
Hope the information helps.

Answer 4

Problem solved. For some reason, when installing dahdi from the sources, the dahdi_dummy module, which is responsible for timing, was not installed. Installing dahdi via apt-get solved the problem.
apt-get install dahdi-source
sudo m-a a-i dahdi
modprobe dahdi_dummy
Not kosher, but whatever.