Newbie Question


While I understand the Asterisk software, I am unclear about how it works with the equipment and phone lines. Here is our situation:

We are a small company with about a dozen people working in their home offices all across the country. Presently, our customers and vendors must direct dial all of these folks. What we’d like is to establish a main number to which all calls are made. The caller then selects an extension and the call is routed to the appropriate person and/or thrown into voicemail. Staff would continue to use their own phone service to make outbound calls. basically provides this service but is expensive and doesn’t allow room for growth and customization.

Here’s the part about which I am unclear: What do I need to connect to Asterisk to allow these transfers to take place? How many phone lines will I need to handle both the incoming and outgoing calls? Or can this be done entirely using VoIP and, if so, does Asterisk act as a gateway to the PTSN? Or do we need to contract with a provider for that service?

I guess what I need is an Asterisk 101 primer.


Your questions are more “telecom” than Asterisk specifically.

To size the system, you need to figure out what kind of concurrent calling you would like to support.

If you want to be able to reach 20 people with 1 phone call each, you would need 20 incoming lines, plus 20 routes to their phones. It doesn’t matter what the outgoing routes are;VOIP, TDM, or some combination of both. Could be anything.

Asterisk connects to the telephone network using any method you like. T1, ISDN-PRI, ISDN-BRI, Analog line, anything. You should use the most economical method (per line basis) that you need. If you’re going to only support 4 or 5 connections, you might choose analog lines. If you’re planning to support 40 or 50, you might choose T1’s.

The Asterisk server can easily catch calls, and re-direct them to specific individuals and even take messages for them if not answered. It’s a very simple application.

As far as sizing goes, you should seek help from your local telecom provider. A good sales rep can help you properly size your calling capacity and reccomend the right connectivity type. Be prepared to supply information about the calling habits of your employees. (Minutes of usage and frequency of call.) That will be the key information. You don’t want to undersize your system (and return busy signals) and you don’t want to oversize your system (and waste money).