Method for allowing and blocking a user PC which can use internet at the same time in a private network thereof a method for analyzing and detecting a judgement about whether NAT(network address translation) can be used or not using a traffic data, and the number of terminals sharing NAT

A method for allowing or blocking users' PCs selectively which can use the Internet at the same time by analyzing and detecting a judgement about whether NAT (Network Address Translation) can be used and a number of sharing terminals, the method comprising:

• monitoring data traffic of each of the sharing terminals that use the Internet;
• receiving a request by a target user corresponding to a target sharing terminal among the sharing terminals, to use the Internet;
• determining, after receiving the request by the target user, the times when the data traffic of each of the sharing terminals occurs;
• determining a user agent code corresponding to a user agent IP value in a packet, the user agent code representing the determined data traffic time of the target sharing terminal;
• storing the user agent IP value and the corresponding user agent code in a user agent pool (UA pool), wherein the UA pool is used to determine whether NAT use for the target user is allowed;
• receiving additional requests by additional users respectively corresponding to additional sharing terminals among the sharing terminals, to use the Internet;
• determining, after receiving the additional requests by the additional users, the times when the data traffic of each of the sharing terminals occur;
• determining additional user agent codes respectively corresponding to additional user agent IP values in corresponding packets, the additional user agent codes representing the determined data traffic times of the corresponding additional sharing terminals, respectively;
• storing all of the user agent codes in the UA pool in a real-time manner for the determined data traffic times of the corresponding sharing terminals, and maintaining real-time user code information in all of the user agent codes;
• storing, in a user agent collection table (UA collection table), user agent key values respectively including characters representing the day and hour of the determined times when the data traffic of the corresponding sharing terminals occur, and the corresponding user agent codes;
• identifying the length of time for each of the user agent codes stored in the UA collection table when there is the data traffic of the corresponding sharing terminal, grouping each of the user agent codes stored in the UA collection table into different ID values according to the corresponding identified length of time, and recording each of the grouped user agent codes with the corresponding ID value;
• determining which of the sharing terminals are allowed to use the Internet and managing the UA pool according to each of the grouped user agent codes recorded with the corresponding ID value by a comparison algorithm of a PMT (Policy Management Table) when sharing terminals using NAT connect to the Internet simultaneously;
• and
• allowing one of the sharing terminals which is subscribed by an ISP (Internet Service Provider) to use the Internet by transmitting a virtual packet according to a TCP hijacking manner when the number of the sharing terminals using NAT exceeds a predetermined policy number of allowed sharing terminals,
• wherein Internet use of the sharing terminals not allowed to use the Internet is blocked according to the predetermined policy number of allowed sharing terminals based on the PMT.