killppp purpose is to kill ppp pid after n time of no traffic.
Depending on how your linux is configured you may need to be root to have the right to kill a ppp process and it may have to be the ppp daemon (pppd).
To find the pid of your ppp process type: ps aux | grep ppp
How this script works? Once activated, killppp checks every minute for network traffic on the ppp0 device. As long as data is passing through, killppp does nothing. Upon no traffic killppp starts counting time until it reaches the specified time and kills the ppp process.
killppp [-hl] < pid > < n >s|m|h|d
< pid >, process ID
< n >s|m|h|d, n seconds|minutes|hours|days of no traffic
-h, usage and options (this help)
-l, see this script"