[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 11:36:47 PM:

> tmassey at obscorp.com wrote:
> 
> > 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!  :)
> 
> It only 'doubles the bandwidth required' when compared to a single-board 

> solution, which does not exist.

My statement was not meant as a criticism:  only a description as to the 
difference beween putting the coprocessor on the DS3 board versus putting 
it on the PCI bus.  As someone who has no need for a DS3 board, I am not 
familiar with whether there is a card that does everything on a single 
board.  I was just describing the difference in response to a question.

> When compared to doing the transcoding 
> and echo can in the host CPU, it would be a major win :-)

Ah, the magic of DSP's!  :)  There's no question that you would be 
challenged to do a DS3-worth of transcoding and echo cancelling with a 
general-purpose CPU (or even several).

> Also, keep in mind that a DS3 is _only_ 45 megabits per second. Any PCI 
> bus (even lowly 33MHz 32-bit PCI) can easily handle 90 megabits per 
> second of traffic. People looking a DS3 cards are also likely to deploy 
> them in servers with multiple independent PCI buses, which would then 
> allow for even more bandwidth.

There is no question about this.  Base PCI can handle a theoretical 
maximum of 132MB (That's *bytes*) per second.  A DS3 with separate 
co-processor board is a tiny part of that:  about equivilent to that of a 
100Mbit Ethernet controller.  Old hat.  The only issue is latency.  Either 
you transfer information in big chunks efficiently, or small pieces 
inefficiently.  Given that there will be at least three devices 
participating on the bus (the CPU, the DS3 card and that theoretical 
co-processor), that means bus contention.  If you're talking 33MHz 32-bit 
PCI (which, from the picture, seems to be what we're talking about here), 
you may run into problems when you add in the Ethernet controller, disk 
controller, etc.

Of course, high-end hardware makes this less of an issue:  if you can 
dedicate a PCI bus to the two cards, then go crazy!  And if you actually 
*need* to manage 672 channels, you can afford a decent server with dual 
PCI busses!  :) 

> The mind boggles at the possibilities!

My mind boggles at the need for a DS3 in the first place.  I thought I was 
pretty cool the day I got my first T1!  :)  Some of us have to slum it for 
a living...  :)

Tim Massey