[Asterisk-Users] Ordering digital trunks?

[Steven Critchfield]

On Sun, 2003-07-27 at 13:29, John Laur wrote:
> OK, this is probably a dumb question for a lot of you, but I have no
> experience with digital lines outside of a tiny bit of ISDN, so I'll
> just bite the bullet and ask some newbie questions. I am attempting to
> plan an asterisk installation with about 20 SIP phones and the
> following incoming lines:
> 
> 1) At least 6 (as many as 10) lines for voice to the SIP phones
> 2) 2 incoming/outgoing fax
> 3) 4-10 lines for an IVR application
> 
> I feel like a T1 with 24 channels should suffice, but what exactly do
> I order and what to I have to have in my asterisk unit to interface?
> Does the line they terminate just plug into a T100P or do I need some
> extra hardware? What services do I need to be sure I order on the T1?
> Is there a way using the T100P to dynamically allocate unused voice
> channels for data?

There is config options for this, but you will want to have a PRI to do
this. A PRI only gives you 23 channels to work with. This will also help
make sure your FAX lines are clean as can be. You will want at least a
block of DID numbers. 

With your question about dynamic allocation of empty channels for data,
you would have to find someone who will let you dial in and bond up
channels. Then you need to calculate the estimated number of lines used
a any time, add in a bit for the idle lines so new calls come in, and
your left with the number of possible 64k channels for data. To take
your low estimates, 6+4+1 = 11 + 3 for spares and you have 14. 23-14 =
9*64kbit. So your low usage, high speed bandwidth is ~576kbit. If you
don't like this speed, you really need to think about maybe a DSL line
to augment or be your bandwidth.

> Finally, how do I get the best fax performance for two analog fax
> machines out of this setup? Will an ATA-186 serve, or will I get much
> better performance using a TDM400P with zaptel bridging?

The TDM400P would be a good choice, and price isn't too much different.
Not to mention that it will help making sure your T1 is up as it is
easier to configure.

-- 
Steven Critchfield <critch at basesys.com>