If you want to start dahdi service on system you should change /etc/asterisk/chan_dahdi.conf.
All setup for dahdi you can find on next link: chan_dahdi.conf Comments are with next color

Bellow are some examples for different countries. This is setup for Asterisk in Office1. In this example we have lines in channels 5,7,8,10,11. Group for communication is 2. This is content of /etc/asterisk/chan_dadhi.conf file

[trunkgroups]
[channels]
language=en
context=default where calls come (dial plan)
switchtype=euroisdn this is only used for PRI
signalling=pri_cp PRI signalling, CPE side, the best auto :)
usecallerid=yes
hidecalleridname=yes
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
canpark=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes
echotraining=yes
echotraining=800
rxgain=0
txgain=0
group = 1
callgroup = 1
pickupgroup = 1
group=2
context=default
signalling=bri_cpe_ptmp
for single ISDN card
channel => 5
channel => 7
channel => 8
channel => 10
channel => 11
callerid = asreceived

This is a setup for Asterisk in Office2. In this example we have lines in channels 6,7,8. Group for communication is number 2. This is content of /etc/asterisk/chan_dadhi.conf file

[channels]
context=default
switchtype=national
resetinterval = 25000
signalling=fxs_ks
rxwink=300
usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
canpark=yes
cancallforward=yes
callreturn=yes
echocancel=yes
echocancelwhenbridged=yes
rxgain=0.0
txgain=0.0
group=2
callgroup=2
pickupgroup=2
busydetect=yes
callprogress=no
context = default
signalling = fxs_ks
group = 2
channel => 6
channel => 7
channel => 8

After this you should start next command on both servers.

[root@asterisk1 ~]# dahdi_cfg

This will generate file /etc/asterisk/dahdi-channels.conf. It is not recommended to change this file. If you want to change config for dahdi you should change chan_dadhi.conf. It is recommended to call your number (card) when you compile drivers, because it is started on that way.