Re: [asterisk-biz] ATA Bank for Asterisk, 400 phones

> I would like to add some information about the capacity of the USB 2.0
> connection. The USB 2.0 interface provides a theoretical speed of
> 480,000,000 bits per second. A typical uncompressed phone conversation
> uses about 64,000 bits per second per direction, plus some overhead; in
> total less than 200,000 bits per second per phone call is used. Thus, the
> theoretical concurrent number of conversations that the USB 2.0
> interface can handle is 480,000,000 divided by 200,000: roughly 2,400
calls for a
> single USB 2.0 port. For more info, see
> http://www.xorcom.com/astribank-technology/usb2-interface.html

Have you done this in production? Is there an actual case study and/or
company that is doing this with the hardware that I can speak with? I'd like
to see what performance is like with 256 active channels on a USB bus.

> Bottom line...the USB connection is not the bottleneck.

From a bandwidth perspective, yes.. but what about 8 devices interrupting on
the bus at the same time? What does that do to latency and jitter?

> Finding a PC with the required number of PCI slots would be a problem with
the suggested
> Sangoma solution.

How hard is it to find a piece of server hardware w/ two PCI-E slots? If you
are going to be running 200+ channels, you better be running a decent
enterprise piece of hardware...

> As for the channel banks, since the 1U Astribank supports 32 channels
> (as opposed to the typical 2U 24 channels supported by other types), the
> Astribank is obviously the better choice.

From a real-estate perspective, yes. It would be much better to have 8 1u
boxes connected to a pair of 2u servers. I agree it makes the wiring job a
lot less complicated. I've just never actually heard of anyone doing this in
production.

> For a point-by-point comparison, see
> http://www.xorcom.com/astribank-technology/astribank-vs-channel-banks.html

This discusses nothing about latency or jitter when using 8 devices on the
same USB bus. Other than that, it looks like a nice comparison, and there
are certainly some perceived advantages.

> I'd be happy to answer any other questions about this technology...

OK..

1. Do you have anyone in the field that I can talk to that is running 8
Astribank 32 port units on a single Asterisk server?

2. How do you deal with latency / jitter issues when you have 8 devices
interrupting on the USB bus?

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