[Asterisk-Users] Port density: DS3 cards?

[John Todd]

At 8:15 AM +0800 12/5/03, Steve Underwood wrote:
>
>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.
>>
>>[snip]
>
>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


The data-only cards for DS3 seem to be in the "reasonable" price 
range, though I have _no_ idea if they could be turned into 
TDM-capable cards.  Examples that were shown to me:

http://oem.imagestream.com/PCI_720.html
http://www.ace-electronics.com/Hardware/T1E1J1/wanPCI-1T3.html

A little more time with Google perhaps would discover other 
solutions.  These are, from what I gather, very inexpensive devices 
in the grand scheme of things, and I believe some already offer Linux 
drivers (though no mention of open source that I could find, I 
imagine that these companies will be all over opening up more markets 
for their cards.)

Of course, Digium could keep it's leadership and our (collective) 
money by starting to poke around at such a driver or card.  It's 
really a chicken-egg situation: nobody will want to muck with driver 
authorship or card production until there are buyers, and there won't 
be any buyers of such "experimental" technology unless it's cheap to 
experiment with, just like the T100P cards are.  Open source is still 
scary to bell-heads, and they will resist until they actually see 
(with their own eyes) a working system that replaces their $100k 
CisNorSiemAvaytelensaco boxes with a $7k PC/card combination.  Even 
then, it's still an uphill battle, but at least it's a battle, 
whereas right now it's a complete non-starter to open one's mouth 
about open source telephony gatewaying at truly large scale 
installations.  And, to be honest, the telco guys are correct at this 
moment.

JT