[Asterisk-Dev] channel driver sample - Coding/Transcoding/Conferences
steveu at coppice.org
Sat Jul 3 10:42:28 MST 2004
Jeremy McNamara wrote:
> Miroslav Nachev wrote:
>> Dear Jeremy,
>> JM> Why? You are going to have two PCI bus transits adding totally
>> JM> unecessary latency.
>> Also the latency from Memory Switching combining with DSP coding
>> Speed is smaller than Host CPU Coding where you need of very power
>> Host CPU which is expensive variant.
> Say what?
> With todays CPU power there is absolutely no need for expensive DSPs.
> This is why Digium didn't design hardware with DSPs on board.
I'm all in favour of host DSP code, and put much of the DSP into *.
A high end DSP is *far* cheaper than a Pentium, and consumes a tiny
fraction of the power. Also, a Pentium doesn't really have the
processing grunt needed for serious DSP - say, several E1s worth of echo
cancellation + G.729 coding. You need clusters of DSP chips for that.
However, most people only use a few channels, or do lightweight
processing, and for them host CPU DSP is the effective choice.
The *appearance* of DSPs being expensive is an artifact of the way the
industry runs. DSP cards are priced at an extreme multiple of their
actual cost, leading to a vicious circle - DSP cards are expensive so
they have a small market. Why are they expensive? because they have a
small market. E1 cards were like that too, until recently. Apply the
Digium pricing strategy to a DSP card and it would not look too bad. Add
an H.100 port to Digium's E1/T1 cards and the DSP card and maybe you are
starting to build something nice. Sure, it starts to look a little like
a Dialogic card. That isn't all bad, though, if its a reasonably priced
open platform, instead of a Dialogic high priced straight-jacket.
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