Step 4: Configure Connections

Now that Asterisk is installed and running you need to edit the system configuration files to implement connections to VoIP and PSTN services. Since this step is common to all applications (Asterisk doesn't do much good if it is not connected to anything) it contains information on creating both service connections (connections to VoIP or PSTN services) and endpoint connections (connections to phones or terminal adapters). Some applications require both service and endpoint connections (PBX, ACD) while others may require only service connections.

DAHDi Connections

DAHDi is the "Digium Asterisk Hardware Device Interface" project and is the standard means for connecting Asterisk with PSTN interface cards. If your application doesn't require PSTN connections (i.e. your solution is VoIP-only) you can skip to the VoIP Connections section.
To configure your DAHDi interfaces, be sure that your cards are installed and properly connected to the computer. If you are using analog cards with FXS (station) ports, remember to connect one of the power connectors from the PC's power supply with the molex coupler on the edge of the card. FXS draws more power than the PCI and PCI Express buses can provide, so the connection is mandatory. Analog with FXO (line) interfaces only don't need the power connection.
To configure the cards you need to edit two files. This can be done using any standard text editor (emacs, vi, vim, gedit, kedit, etc.). Note that you will need to be logged in as the root user to edit these files (or use the sudo command if your Linux distribution uses sudo instead of direct root access). The first file is the /etc/dahdi/system.conf file. This file configures the parameters for the low-level card drivers. There are only a few options that need to be set in this file. Below are configurations for both a system with one digital card (in T1 mode):

# Autogenerated by /usr/sbin/dahdi_genconf on Wed Sep 23 08:25:39 2009
# If you edit this file and execute /usr/sbin/dahdi_genconf again,
# your manual changes will be LOST.
# Dahdi Configuration File
#
# This file is parsed by the Dahdi Configurator, dahdi_cfg
#
# Span 1: TE2/0/1 "T2XXP (PCI) Card 0 Span 1" (MASTER) 
span=1,1,0,esf,b8zs
# termtype: te
bchan=1-23
dchan=24
echocanceller=mg2,1-23

# Span 2: TE2/0/2 "T2XXP (PCI) Card 0 Span 2" 
span=2,2,0,esf,b8zs
# termtype: te
bchan=25-47
dchan=48
echocanceller=mg2,25-47

# Global data

loadzone        = us
defaultzone     = us