有許多公司生產用於 Asterisk 的 PSTN 板卡。這些板卡需要安裝驅動程序，這樣 Linux纔可以識別
它們 （DAHDI 包含了 Digium 的板卡驅動） 。 從這一點看， 配置是被 Asterisk module chan_dahdi 處理的。
當安裝電話板卡硬件時，請確保升級了 /etc/dahdi/modules 文件以使能與你的硬件適應的 modules，
然後通過初始化腳本（/etc/init.d/dahdi）重載DAHDI，你也可以使用 dahdi_genconf modules 命令生成 modules 文件
要配置一張FXO板卡能夠在Asterisk系統上工作，需要修改以下的兩個文件：
/etc/dahdi/system.conf //這個是DAHDI的配置文件，主要用來指定系統中可用的Channels
/etc/asterisk/chan_dahdi.conf //這個主要是告訴Asterisk系統中有效的Channels以及它們各自使用的信令。
下面假設我這裏有一張DAHDI的板卡，上面有4個FXO端口，/etc/dahdi/system.conf的內容如下：
# Echo Cancellers
迴音抵消器
# ^^^^^^^^^^^^^^^
# DAHDI uses modular echo cancellers that are configured per channel. The echo
DAHDI在每個通道上的迴音抵消器是模塊化的。
# cancellers are compiled and installed as part of the dahdi-linux package.
迴音抵消器作爲dahdi-Linux包的一部分被編譯和安裝
# You can specify in this file the echo canceller to be used for each
你可以在本文件中爲每個通道指定其使用的迴音抵消器
# channel. The default behavior is for there to be NO echo canceller on any
默認每個通道上是沒有任何迴音抵消器的
# channel, so it is very important that you specify one here.
所以你在這裏設置迴音抵消器是非常重要的。
# Valid echo cancellers are: hwec, mg2, kb1, sec2, and sec.
可用的迴音抵消器有：hwec mg2 kb1 sec2 sec
# 'hwec' is a special echo canceller that should be used if hardware echo
hwec是一個特別的迴音抵消器，如果硬件迴音抵消器想在指定的通道上可用
# cancellation is desired on and available on the specified channels.
# If compiled, 'hpec' is also a valid echo canceller.
hpec也是一個可用的迴音抵消器，如果編譯了的話。
# To configure the default echo cancellers, use the format:
配置默認的迴音抵消器，用法如下：
# echocanceller=<echocanceller name>,<channel(s)>
#
# Example:例如：
# Configure channels 1 through 8 to use the mg2 echo canceller
配置通道1到通道8使用mg2迴音抵消器，如下：
#echocanceller=mg2,1-8
#
# And change channel 2 to use the kb1 echo canceller.
通道2使用kb1迴音抵消器，如下：
#echocanceller=kb1,2
loadzone = us //我的理解是區域(國家的代碼，兩個字母如：中國=cn)的選擇，然後板卡會根據你的區域來播放匹配的音樂如：撥號音、忙音等
defaultzone = us //設置默認的區域
fxsks = 1-4 //指定板卡上使用FXS信令的通道，也就是FXO端口有哪些。
echocanceller=oslec,1-4 //指定通道1-4所使用的 迴音抵消器
一旦你的板卡上的channels被操作系統所識別，那麼你就必須在/etc/asterisk/chan_dahdi.conf文件中來配置，以讓asterisk來知道有哪些channels
在板卡上是可以使用的。/etc/asterisk/chan_dahdi.conf的內容如下：
/etc/asterisk/chan_dahdi.conf
[channels]
signalling = fxs_ks //指定Channels所使用的信令爲FXS_KS
channel => 1-4 //定義可以使用的Channels爲1、2、3、4
context = fxo-incoming //定義呼叫開始的context
在這個例子中，我們告訴 Asterisk，系統中的頭 4 個 DAHDI channels 是 FXO 端口
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在這個配置文件中還可以配置一個通道組group，然後把這些通道都加入到相應的組中。
Channels and Groups
There are three different kind of groups in Asterisk:
在Asterisk中有三種不同的Group
(1) group=blah
— This is used to bundle (typically trunk) interfaces together so that you can use something like Dial,Zap/g2/.... to use any of the channels in group 2.
這種是用在中繼線路中的，你可以用“Dial,Zap/g2/” 來使用group 2中的任何一個線路
(2) callgroup=blah
— This is a list of group memberships that you belong to for call pickup purposes
(3) pickupgroup=blah
— This is a list of groups that you are permitted to pickup in.
For #2 and #3, basically, you just dial *8# and you can pickup a ringing phone if you have a group in your pickupgroup that is in their callgroup.
hint: pickupgroup is for FXS interfaces while callgroup is for FXO interfaces.
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group = 1
channel => 1-4
group = 1,2
channel => 5-6
group = 2,3
channel => 7-8
group = 4
channel => 9-12
group =
channel => 13-16
Channnels 1-4 are in just group 1.
Channels 5 and 6 are in groups 1 and 2.
Channels 7 and 8 are in groups 2 and 3.
Channels 9-12 are in group 4, and
Channels 13-16 are in no groups... so...
1,1,Dial,Zap/g1...would give you the first channel in the range 1-6 that was available.
將會把group 1中可用的，第一個通道給你使用。
1,1,Dial,Zap/G1...would give you the largest channel in the range 1-6 that was available see http://www.voip-info.org/wiki/view/Asterisk+ZAP+channels.
將會把group 1中可用的，最大的那個通道給你用。
1,1,Dial,Zap/g2...would give you the first channel in the range 5-8 that was available.
1,1,Dial,Zap/g3...would give you the first channel in the range 7-8 that was available
1,1,Dial,Zap/g4...would give you the first channel in the range 9-12 that was available.