[Asterisk-Users] Port density: DS3 cards?

John Todd jtodd at loligo.com
Thu Dec 4 16:05:57 MST 2003

I am uncertain of PCI bus speed limits - too many conflicting reports 
are wedged into my head.

However, the intent here is to dump calls out via VoIP and not simply 
switch between channels elsewhere on the DS3, so overcoming that 
limitation needs to be addressed (if it exists at all, as a follow-up 
post has countered) or some other non-PCI solution created.  Ideally, 
I'd like to see TDM on DS3 in, IAX2 on ethernet out after some 
minimal call control through a context.

To Steven's comments: Yes, I have considered multiple Asterisk 
devices and I am very aware of de-muxing DS3's into individual T1's 
or PRI's (which bring it's own set of problems, since there is no 
multi-PRI D-channel support in * at the moment) but the primary 
concern is that space, power, and heat are at a premium in the 
circumstances under which I am speculating.  10u is much more than 2u.

I'll note that expensive solutions at this density already exist from 
several vendors, and are better than Asterisk right now at handling 
these types of call volumes and media translations.  However, I pose 
the question to the list to note that there _is_ an interest at these 
sizes, and that for Asterisk to step to the next level (no longer 
just a PBX) that type of support is desired.  One step at a time.... 


>I don't want to criticize your idea, but you do have to consider certain
>points. Starting from (as has already been mentioned) the bandwidth of DS3
>is far too much to reasonably shove down the PCI bus without data loss /
>excessive overheads. Thus a sensible approach would be one where the card
>performs the switching, (H100/H110 or otherwise), leaving the Asterisk unit
>to maybe handle signalling and call control only. You could go one further,
>and if you require 'voice' resource, to switch that onto the PCI bus as well
>for processing.
>The way I see this, the best implementation plan would actually be to take a
>standard DS3 card with a H110/H100 bus, and then look for a third party card
>which could switch timeslots on the H110/H100 bus to the PCI bus. This
>composite approach would allow a zero latency switching path, but still
>include the flexibility of Asterisk.
>However, considering the traffic volumes that you are talking about, is it
>really true to say that the traditional telco cards are astronomically
>priced, given the amount of revenue that can be generated per month on a
>----- Original Message -----
>From: "John Todd" <jtodd at loligo.com>
>To: <asterisk-users at lists.digium.com>
>Sent: Thursday, December 04, 2003 8:06 PM
>Subject: [Asterisk-Users] Port density: DS3 cards?
>>  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.
>>  JT
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