Change directory to the buildsystem main dir sip_router/etc/buildsystem
Type ./configure
Answer the questions (or simply except the defaults by pressing ENTER)
Type: make (to create the default configuration file)
Type: make install (to install to the default config dir (/usr/local/etc/seri/), or copy the resulting ./ser_default.cfg to where SERi expects to find ser.cfg)
make install will copy ser_default.cfg to your config dir. Create a symbolic link to it for ser.cfg (ln -s ser_default.cfg ser.cfg). This way you can quickly change to a new config by creating a new symbolic link.
Start SER and congratulations you have a running SER installation!