I could be wrong but the analog cards require a clock reference to use TDM
(Time Division Multiplexing) to switch, conference, or provide MOH.
The clock has to be very stable as it is "slicing and dicing" audio sources
and then reconstructing them into what appears to be a continuos audio stream.
The actual clock frequency is not that important as long as it has enough
divisions to be none-blocking. ie. must be able to connect all extensions and
lines
to each other at the same time.
Henry
Reza - Asterisk Enthusiast wrote:
Ok...
I've asked this question to at least a dozen so called Asterisk Gurus,
who are doing quite well down south in the US of A with their *
enterprises. Unfortunately NONE of them could give me a good answer
and hoping that fellow Torontonians can provide me with the answer that
I am seeking!
My question is quite simple: What is the real purpose of a "timing
device" for Asterisk, and in this * case, what really is a "timer". Is
it just a traditional "timing" device keeping track of time etc... or
something more?
We all take it for granted that it provides some sort of timing
feature/mechanism that is needed for Asterisk to function properly, if
we wish to have the MeetMe function or the Music On Hold function... to
supposedly improve the sound quality of the music when MoH is activated.
The exact same answers I have continued to receive is, "You need the
timing device for the MoH & MeetMe function... if you want * to work
well... you need it... you have no choice... ztdummy isn't good
enough so it's best that you have a zaptel hardware to provide accurate
timing capability". -- and of course my question comes back to "what
is this timing capability" and then there is no answer.
The response to my question is analogous to blind faith, and doing
something simply because one is told to... not understanding really,
what is involved under the hood. The answer I am seeking is more with
regards to understanding the theoretical aspect (for personal
satisfaction), that makes all this magic possible!
So... here are my questions again in brief:
1. What really is a Timing Device in Asterisk?
2. Why do we need this for the MoH & MeetMe function?
3. Is ztdummy good enough in a 100% VOIP setting (100% of traffic is
through your NIC)?
4. Does ztdummy have any limitations when compared to timing devices
in ZAPTEL interfaces?
5. Does ztdummy utilize a lot of CPU process?
6. Technically the ztdummy under Linux 2.4 utilizes the UHCI-USB
which is the hardware minus the FXO/FXS - so why would ztdummy not
be good enough?
7. In Linux 2.6, according to
" http://www.voip-info.org/wiki/view/Asterisk+timer ", ztdummy
uses high resolution kernel timer. Is this "high res. kernel
timer", 100% software driven, or takes advantage of the internal
hardware clock on the motherboard or takes advantage of the
UHCI/OHCI USB controller?
I guess people who work with or write device drivers will truly
appreciate my questions. Would love to hear thoughts & inputs on these
theoritical questions, my soul is seeking for, up until it finds other
things to ponder about :)
Cheers!
