[Asterisk-Users] DS3000P - 20 E1 capacity on single card

[tmassey at obscorp.com]

asterisk-users-bounces at lists.digium.com wrote on 04/12/2005 10:51:49 AM:

> Andrew Kohlsmith wrote:
> 
> > secondary card for DSP functions is very inefficient of the PCI 
> bus.  I'd be 
> > curious to know if the Digium cards can even do PCI-PCI DMA.
> 
> The Digium TDM cards can DMA into any RAM accessible over the PCI bus, 
> regardless of whether it is located on the motherboard or on a PCI card.

That's not the point.  The point is that you have to transfer voice data 
twice:  once from the DS3 card to the co-processor, and once from there to 
the eventual destination (probably system RAM).  If the co-processor is 
integrated into the DS3 card that first transfer is handled and 
echo-cancelling is performed *before* the data hits the PCI bus.

In other words, a PCI-based co-processor would double the PCI bus 
bandwidth necessary.  And with a latency-sensitive product like voice, bus 
contention is not something you want to add to!  :)

Tim Massey