[App_rpt-users] AllStar nodes in the Cloud

[David McGough]

Hi Everyone,

I've got some thoughts to consider about VPS based AllStar installations.

AllStar uses the Asterisk dahdi drivers for critical timing and the
conference/bridging capability we all depend on.

Most VPS installations will have very poor dahdi timer quality, due to
the inherent "jitter" the VPS instances incur from sharing CPU time slices
with many other guests. This jitter has minimal impact on most
applications you might host on a VPS---like a web server, file server,
etc.  However, the jitter can have serious side effects for VoIP
applications, like AllStar.

The way you test the dahdi timing performance is with the dahdi_test
program. On older ACID installations, this program was called zttest.

As dahdi_test numbers fall below about 99.97%, poor timing quality has
more and more of an impact. There are several symptoms of this problem to
watch out for. Whether or not ANY of these symptoms will impact a given
VPS user depends on how you use your AllStar installation.

AllStar timing-related problems fall into two basic categories:

1) Call quality issues--pops, clicks and stuttering audio. Most frequently 
this is heard when using Asterisk to transcode between multiple audio 
CODECs or when playing audio files (like the localplay of playback 
commands). Recording/archiving audio from the node could be impacted, too.

2) General timing woes. For example: a timeout timer is slower or faster
than the speed you've set. Or, the node is configured to ID every 10
minutes. In reality, it IDs every 9 or 10.5 minutes. This list of
potential problems includes all the various timer settings found in the
rpt.conf file, etc. Fortunately, a lot of these timing concerns aren't
typically applicable to VPS-based pseudo nodes---for example: of what use 
is a CW ID on a pseudo node anyway?

For more info about dahdi timing concerns, just google search phrases 
like: "dahdi_test results"  or "bad dahdi_test".

Anyhow, with all the interest in VPS based installs of AllStar, it's worth
remembering about timer quality concerns---strange audio quality problems
are likely not AllStar's fault!


73, David KB4FXC