[Asterisk-Users] Port density: DS3 cards?

[Steve Underwood]

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.
>
> I think there are quite a few discouraging comments to be made on that 
> question.  Firstly, most companies that produce telecom hardware have 
> silly overhead, and thus the price of their cards is astronomical.  
> Secondly, most companies that produce telecom hardware are of the 
> opinion that transcoding (compression) should be done via DSP's, which 
> inflates the cost of the card significantly.  Thirdly, most telecom 
> hardware vendors would not consider allowing their drivers into the 
> public domain if such development were to happen. I've talked to some 
> parties (you know who you are) who have expressed some interest in 
> building this type of interface, but a situation where I can actually 
> put my hands on equipment is far better than speculative interest by 
> those who have not even decided to go forward with design, no matter 
> how interesting the end product sounds on the whiteboard.
>
> However, regardless of all these negatives, I'm interested in any 
> vendors anyone can offer as a starting point.
>
> Please, don't pester me with comments like "Why do you need 28 PRI's?" 
> or "You'll never use that much capacity."  Assume that I actually DO 
> have that volume of traffic, and assume there are several dozen other 
> people on this list (lurkers and active people) who have the same 
> requirements, and assume there are hundreds more people out there who 
> have the requirement but haven't considered Asterisk because DS3 isn't 
> an option.

I think this is a worthwhile thing to investigate. Does anyone here have 
experience with higher order cards under Linux? Which ones work well, 
and have solid drivers? Although the driver would (probably) need to be 
heavily modified if it is currently a data, rather than telephony, 
oriented driver, a good existing driver should save a lot of work. A DS3 
is well within a PCI channel's capacity (the sum of the two directions 
is less than a 100mb Ethernet, although the DS3 is continuous), but it 
is quite a lot of data. A suitable card would need an efficient 
interface if this is to work. For the Zaptel environment that would mean 
that it can burst data in 1ms (8 sample chunks), and would need to bus 
master the data into memory in a form that doesn't require masses of 
manipulation by software - e.g. reshuffling out of sequence data. Doing 
that for so many channels might create interesting latency challenges 
:-) Still, if you don't try, you can't start to address these issues, 
and work out a solution. It shouldn't be impractical to make a DS3 to 
TDMoE solution, provided the DS3 hardware is right, and the PC  has no 
quirky throughput issues.

This subject often comes up on the IRC channel. There seem to be a 
number of people interested in higher order links, but it really needs 
some positive action somewhere to kick off a real project.

Regards,
Steve