Page 106 - Asterisk™: The Future of Telephony

; default
usecallerid=yes
hidecallerid=no
callwaiting=no
threewaycalling=yes
transfer=yes
echocancel=yes
echotraining=yes

; define channels
context=incoming ; Incoming calls go to [incoming] in extensions.conf
signaling=fxs_ks ; Use FXS signaling for an FXO channel
channel => 2 ; PSTN attached to port 2
The [trunkgroups] section is used for connections where multiple physical lines are
used as a single logical connection to the telephone network, and won’t be discussed
further in this book. If you require this type of functionality, see the
zapata.conf.sample file and your favorite search engine for more information.
The [channels] section determines the signaling method for hardware channels and
their options. Once an option is defined, it is inherited down through the rest of the
file. A channel is defined using channel =>, and each channel definition inherits all of
the options defined above that line. If you wish to configure different options for dif-
ferent channels, remember that the options should be configured before the channel
=> definition.
We’ve enabled Caller ID with usecallerid=yes and specified that it will not be hidden
for outgoing calls with hidecallerid=no. Call waiting is deactivated on an FXO line
with callwaiting=no. Enabling three-way calling with threewaycalling=yes allows an
active call to be placed on hold with a hook switch flash (discussed in Chapter 7) to
suspend the current call. You may then dial a third party and join them to the conver-
sation with another hook switch. The default is to not enable three-way calling.

Allowing call transfer with a hook switch is accomplished by configuring trans
fer=yes; it requires that three-way calling be enabled. The Asterisk echo canceller is
used to remove the echo that can be created on analog lines. You can enable the echo
canceller with echocancel=yes. The echo canceller in Asterisk requires some time to
learn the echo, but you can speed this up by enabling echo training (echotrain
ing=yes). This tells Asterisk to send a tone down the line at the start of a call to measure
the echo, and therefore learn it more quickly.
When a call comes in on an FXO interface, you will want to perform some action. The
action to be performed is configured inside a block of instructions called a context.
Incoming calls on the FXO interface are directed to the incoming context with con
text=incoming. The instructions to perform inside the context are defined within
extensions.conf.
Finally, since an FXO channel uses FXS signaling, we define it as such with signal
ing=fxs_ks.

78 | Chapter 4: Initial Configuration of Asterisk