thanks for your reply
ADSL user can use NAT technology to share his line to others,
Now, I have heard a few method
1,check the MAC address in every IP pakage,if there are many diffrent MAC address,so he share his ineternet connection.
2, scan port 161 with snmp to check the LIB
3, check sessions
I only to get such a software with GPL
Help me and excue my poor english