I'm not sure if this answer is technical or low level enough, but the need for a timing device would primarily stem from the fact that traditional digital voice is a synchronous data stream, and thus requires a reference clock to ensure it is delivered at a consistent rate. If a T1 is connected to the system, the system can obtain a clock signal from the network. If an analogue card is in the system, it obviously has a very basic clock built in which is sufficient to generate a signal. If you've ever taken piano lessons you've probably used a metronome. In telecom, a reference clock serves the exact same function - it provides the pacing that the system needs to coordinate the various audio streams passing through the system. That doesn't answer your technical questions, but hopefully sheds some light on what the clock is needed for. Jim.
-- Jim Van Meggelen [EMAIL PROTECTED] HYPERLINK "http://www.oreillynet.com/pub/au/2177"http://www.oreillynet.com/pub/au/2177 "A child is the ultimate startup, and I have three. This makes me rich." Guy Kawasaki -- _____ From: Reza - Asterisk Enthusiast [mailto:[EMAIL PROTECTED] Sent: March 23, 2006 2:29 AM To: TAUG Subject: [on-asterisk] Timing Device Hardware (zaptel interfaces) and Software (ztdummy) 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 " HYPERLINK "http://www.voip-info.org/wiki/view/Asterisk+timer"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! -- No virus found in this incoming message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.3.0/290 - Release Date: 23/03/2006 -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.385 / Virus Database: 268.3.0/290 - Release Date: 23/03/2006
