[Asterisk-Users] Digium should develop and sell just Dummy card. For timing...

[Steven Critchfield]

On Wed, 2003-10-15 at 13:57, Chris Albertson wrote:
> Lets see if I understand this logic.  I'll restate it:
> 
> 1) Asterisk's MOH is only broken if you attempt to build a
>    VOIP-only system

Supposedly this was fixed recently. As I don't use MOH, nor am I ever in
a VoIP only system I can't validate that. The message was in the archive
fairly recently.

> 2) Asterisk is not intended for such use. It is a PSTN
>    oriented PBX that just happens to handle VOIP.
> 3) Therefore Asterisk is not broken
> 
> OK. If you believe #2 you are right.
> 
> My comment was outside of the above argument.  Let me restate
> my argument that is intended to counter those thinking timing
> hardware should be required
> 
> 1) There is no requirement that outbound VOIP media packets be
>    precisly timmed
> 2) Therefore there is no reson to use a hardware timmer card.
> 3) Software that depends on a hardware timmer card
>    for timming outbound VOIP media is doing so needlessly.
> 
> To support the above argument you can look at the RFCs to support
> #1 and you can look at other VOIP software to support #3

While #1 is true for VoIP, it isn't true for PSTN. So when you merge
these two sets of statements, you have a system that was designed around
precise timing so that PSTN could be achieved. When ztdummy and ztrtc
where developed they took #1 into account for those systems. This is why
the RTC driver generates 1024hz interupts. It isn't a precise 1000hz,
but it is close enough for the need.

Now, while taking into account #3 of your second set of statements, if
you make a software timer like what is used in other VoIP software, you
loose your PSTN functionality. 

So this appears to be designing to the higher needs. The higher needs
are the precise timing of PSTN. When you don't have this need, you use
the less precise drivers.

> The bottom line is that it would be silly for anyone to offer a
> timming-only PCI card

This is fully agreed upon as there is hardware already in the systems
that can be used. Maybe the drivers need by updated a bit more, but none
the less they are there.

> --- Steven Critchfield <critch at basesys.com> wrote:
> > On Wed, 2003-10-15 at 12:50, Chris Albertson wrote:
> > > 
> > > Steven,
> > > 
> > > Good comments but remember good enginerring starts with reading
> > > the requirements and desiging to those requirements.
> > > in the case of SIP at least these is an RFC.  What is the
> > > timming requirement on media packets?  How is the stream
> > > synchronized?  I'll read it in the next few days but I'd
> > > bet a beer there is no requirement for precise timming.
> > > 
> > > Any discusion about PCI cards, RTC timmers and the like is in
> > > a complete vacuum unless you know what exactly it is that the
> > > software is required to do.
> > 
> > And this means what to a system designed around a PSTN board? How
> > many
> > of us use this system for PSTN and IAX with no SIP or h323 in sight? 
> > 
> > So far these timing problems arise from people doing VoIP only
> > systems
> > on a system that was started as a PSTN platform and is able to handle
> > VoIP.
> > 
> > So while reading the RFC is a good idea, and maybe it will be good in
> > determining a new timing source for SIP only systems, it shouldn't
> > take
> > over asterisk.
> > -- 
> > Steven Critchfield  <critch at basesys.com>
> > 
> > _______________________________________________
> > Asterisk-Users mailing list
> > Asterisk-Users at lists.digium.com
> > http://lists.digium.com/mailman/listinfo/asterisk-users
> 
> 
> =====
> Chris Albertson
>   Home:   310-376-1029  chrisalbertson90278 at yahoo.com
>   Cell:   310-990-7550
>   Office: 310-336-5189  Christopher.J.Albertson at aero.org
>   KG6OMK
> 
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-- 
Steven Critchfield  <critch at basesys.com>