[Asterisk-Users] Port density: DS3 cards?

[Nicolas Bougues]

On Thu, Dec 04, 2003 at 02:53:43PM -0600, Steven Critchfield wrote:
> On Thu, 2003-12-04 at 14:06, John Todd wrote:
> > Obviously, there are no DS3 TDM cards that are currently compatible 
> > with Zap channels.  (or are there?)
> > 
> > Does anyone know of an inexpensive DS3 card that could perhaps be 
> > used with Asterisk if one were to try to port the Zap drivers to such 
> > a card?  PCI, of course, would be the bus of choice.
> 
> Your first problem will be bus speeds. A single DS3 is 44.736Mbps. each
> way. So if you double this and get the 89.472Mbps, you are going to be
> coming close to the real limits of the 32/33mhz PCI bus without having
> done any work on the data you are shuffling. So while it could be done
> here, I'd start worrying about stability. Sure you could switch up to
> faster PCI buses like the 64/66mhz bus, but then you will start limiting
> what systems you can use. Then again, if you are putting that many
> channels through a single machine, there wasn't many choices for the
> hardware to begin with.
> 

Don't get confused by Megabits and megabytes. A 32/33 PCI bus has a
max (theoritical) bandwidth of 133 Megabytes per second. That's about
1 Gigabit.

So as long as you don't do much other things on the bus (for latency
concerns), 89 Mbps is ok on standard PCI.

Channelized DS3 boards do exist, and writing a zaptel driver for it
should not be too hard. What I'm not sure, though, is whether
telcos provide it to end users for voice services. At least here in
Europe, the telco would rather run the DS3 to your building, then
split it up in a bunch of E1 on their own CPE.

-- 
Nicolas Bougues
Axialys Interactive