First download the Asterisk packages from here.

Once you have downloaded Asterisk packages, you need to follow this order to install those packages: zaptel, libpri, asterisk

-Installing zaptel
#cd /usr/src/asterisk/zaptel
#make clean
#make
Note: If you are using kernel 2.6 or later then enter the following command '#make linux26', instead of '#make'.
#make install

-Installing libpri
#cd /usr/src/asterisk/libpri
#make clean
#make
#make install

-Installing asterisk
#cd /usr/src/asterisk/asterisk
#make clean
Note: If you want to use a mp3 files for music-on-hold enter the following command '#make mpg123', before doing '#make install'.
#make install
#make samples

 If you encounter any critical problem during installation, click here to get support.