[asterisk-dev] ztscan checks __ZT_SIG_DACS for a digital span

[Tzafrir Cohen]

On Tue, Mar 04, 2008 at 10:20:42AM -0600, Kevin P. Fleming wrote:
> Tzafrir Cohen wrote:
> 
> > BRI devices can only use the third channel as a D channel - it is
> > defined to be a different channel. So AFAIK there is no equivalent of
> > DAKS for BRI and hence BRI is digital but incapable of DAKS .
> 
> I have no idea what you are talking about; DACS has nothing to do with D
> channels at all. DACS is 'Digital Access Cross Connect', and it is a
> method of directly connecting digital channels together to reduce
> latency and provide transparent connectivity.
> 
> This means connecting two B channels together at the closest possible
> point to where they entered the system that is handling them. In the
> case of a BRI card, I'd expect the BRI interface chip to be able to DACS
> the two B channels on a single BRI, and if the chip supports more than
> one BRI it should be able to DACS B channels between any of the BRIs it
> is connected to.

To conclude this: it seems that there are a number of drivers that don't
claim to support DACS (e.g: tor2 and torisa) besides the Astribank ones.

  http://svn.digium.com/view/zaptel?view=rev&revision=3996

It seems that the CAS capability bit is also a good indication of a
digital span. I ended up simply checking for either of them. From what I
could see all the in-tree digital span drivers provide CAS and most
provide DACS. I did find some external drivers that provide DACS but not
CAS (the Junghanns qozap and cwain drivers. The zaphfc driver prvides 
CAS and not DACS).

("provide" in the above means: claim to support it in their capability
bits).

-- 
               Tzafrir Cohen
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