[Asterisk-Users] Dialogic supported well?

Steve Underwood steveu at coppice.org
Fri Mar 5 21:18:59 MST 2004

Scott Stingel wrote:

>If you'll be running commercial apps, I would recommend that you do a lot of
>testing, especially load testing, with the types of applications you'll be
>running.  Dialogic boards, although incredibly expensive, do have lots of
>horsepower built in for the purposes of encoding and decoding the voice
>streams, decoding single and DTMF codes, voice energy and cadence detection,
>etc.  Digium boards rely 100% on the processor that they run in to perform
>these functions.  I was a little disappointed to find that I can (so far)
>reliably only handle 4 E1's in a (very) high-volume IVR app.  In the past
>I've run Dialogic-based systems which handled much more load (but also which
>cost 4 times as much in hardware!)  Although Digium's newer TE410P board is
>capable of bus mastering, I found that it made little difference in the
>number of channels I could run.
Actually, there isn't that much processing power on the Dialogic boards. 
They have rather limited DSP and MCU resources. That is why they only 
handle codecs of trivial complexity. The reason they get better high 
load results for IVRs is they have huge latency, which helps enormously 
with the response times the applications level code needs to achieve. 
Such high latency kills phone calls, but nobody notices for IVR use. 
Most Dialogic cards are incapable of doing anything other than IVR or 
call switching through their mezzanine buses, as they are not full 
duplex. Even so, the throughput you can achieve in pure IVR applications 
is not that great. When you hear of people with a large bunch of T1s or 
E1s into a Dialogic box, it is normally some limited IVR work plus a lot 
of call switching. That call switched data passes across the mezzanine 
bus, and has no impact on the main processor.

Some of the JCT cards from Dialogic can be set to a lower latency, and 
are full duplex. This is aimed at TTS + ASR use, rather than VoIP calls. 
The lowest latency is still much higher than the Digium cards, but even 
with this the number of channels you can handle reliably is a lot lower 
than when you use the traditional high latency Dialogic modes.

Dialogic support was great 10 years ago, but is now almost non-existant. 
Their drivers are buggy, and not keeping up with the times. Their 
previously active forums seem to be in serious decline. Most of their 
long term customers find it hard to say nice things about them. They are 
expensive. On the other hand, they do have broad approvals across the 
globe. I think that is their biggest asset.


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