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1. (WO2001097483) DYNAMIC IP ADDRESS ALLOCATION SYSTEM AND METHOD
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WHAT IS CLAIMED IS:

1. A method of dynamically allocating an Internet Protocol (IP) address to a mobile terminal operating in a General Packet Radio Service (GPRS) network, said GPRS network having a Serving GPRS Service Node (SGSN) serving the mobile terminal and a Gateway GPRS Service Node (GGSN) connecting the GPRS network to a server that allocates IP addresses in an IP -based network, said method comprising the steps of:
setting on a counter in the GGSN, a maximum number (Ni) of requests for an IP address that are to be sent from the GGSN to the server;
setting on a timer in the GGSN, a maximum time period (Ti) that the GGSN will wait for a response from the server after each request for an IP address is sent; sending a sequence of requests for an IP address from the GGSN to the server, with each request being separated from the previous request by time period Ti, said sequence being halted if a response is received from the server within time period Ti after one of the requests is sent;
receiving in the GGSN, a response from the server that includes an IP address for the mobile terminal within time period Ti after one of the requests is sent; and sending the IP address from the GGSN to the mobile terminal.

2. The method of claim 1 wherein the step of sending a sequence of requests for an IP address from the GGSN to the server includes unicasting each of the requests in the sequence from the GGSN to a different server.

3. The method of claim 1 wherein the step of sending a sequence of requests for an IP address from the GGSN to the server includes sending a sequence of requests from the GGSN to a Radius server.

4. The method of claim 1 wherein the step of sending a sequence of requests for an IP address from the GGSN to the server includes sending a sequence of requests from the GGSN to a Dynamic Host Configuration Protocol (DHCP) server.

5. The method of claim 1 further comprising the steps of:
determining that the GGSN did not receive a response from the server within time period Ti after a last request was sent; and
allocating an IP address from an internal pool in the GGSN.

6. The method of claim 1 further comprising updating timers in the GPRS network to reflect actual response times experienced by the GGSN when requesting IP addresses from the server.

7. The method of claim 6 wherein the step of updating timers in the

GPRS network includes the steps of:
collecting statistics by the GGSN on the actual response time to receive responses from the server, how often time period Ti is exceeded, and how many requests are sent before a response is received;
determining by the GGSN an average number of requests (Nr) required to receive a response from the server, and an average time (Tr) to receive a response; calculating by the GGSN a new setting for a T3 timer in the SGSN; and sending the new setting for the T3 timer from the GGSN to the SGSN.

8. The method of claim 7 wherein the step of updating timers in the

GPRS network also includes sending by the GGSN the new setting for the T3 timer to any SGSN in the GPRS network from which an MT is attempting to obtain an IP address.

9. A method of dynamically allocating an Internet Protocol (IP) address to a mobile terminal operating in a General Packet Radio Service (GPRS) network, said GPRS network having a Serving GPRS Service Node (SGSN) serving the mobile terminal and a Gateway GPRS Service Node (GGSN) connecting the GPRS network to a server that allocates IP addresses in an IP-based network, said method comprising the steps of:
receiving in the GGSN, information regarding whether the mobile terminal is authorized to receive a backup IP address if an IP address cannot be obtained from the server, and whether the mobile terminal is a user of a real-time application;
setting on a timer in the GGSN, a maximum time period (Ti) that the GGSN will wait for a response from the server after a request for an IP address is sent from the GGSN to the server;
sending a request for an IP address from the GGSN to the server;
determining that time period Ti expired without receiving in the GGSN, a response from the server that includes an IP address for the mobile terminal;
determining from the information in the GGSN whether the mobile terminal is authorized to receive a backup IP address;
upon determining that the mobile terminal is authorized to receive a backup IP address, determining from the information in the GGSN whether the mobile terminal is a user of a real-time application;
sending a public JP address from the GGSN to the mobile terminal upon determining that the mobile terminal is a user of a real-time application; and
sending a private IP address from the GGSN to the mobile terminal upon determining that the mobile terminal is not a user of a real-time application.

10. A method of dynamically allocating an Internet Protocol (IP) address to a mobile terminal operating in a General Packet Radio Service (GPRS) network, said GPRS network having a Serving GPRS Service Node (SGSN) serving the mobile terminal and a Gateway GPRS Service Node (GGSN) connecting the GPRS network to a server that allocates IP addresses in an IP-based network, said method comprising the steps of:
setting on a counter in the GGSN, a maximum number (Ni) of requests for an

IP address that are to be sent from the GGSN to the server;
setting on a timer in the GGSN, a maximum time period (Ti) that the GGSN will wait for a response from the server after each request for an IP address is sent; sending a sequence of requests for an IP address from the GGSN to the server, with each request being separated from the previous request by time period Ti, said sequence being halted if a response is received from the server within time period Ti after one of the requests is sent;
determining that time period Ti expired following a last request in the sequence of Ni requests without receiving in the GGSN, a response from the server that includes an IP address for the mobile terminal;
determining from the information in the GGSN whether the mobile terminal is authorized to receive a backup IP address;
upon determining that the mobile terminal is authorized to receive a backup IP address, determining from the information in the GGSN whether the mobile terminal is a user of a real-time application;
sending a public IP address from the GGSN to the mobile terminal upon determining that the mobile terminal is a user of a real-time application; and
sending a private IP address from the GGSN to the mobile terminal upon determining that the mobile terminal is not a user of a real-time application.

11. In a General Packet Radio Service (GPRS) network, a Gateway GPRS

Service Node (GGSN) for dynamically allocating an Internet Protocol (B?) address to a mobile terminal operating in the GPRS network, said GPRS network including a Serving GPRS Service Node (SGSN) serving the mobile terminal, and said GGSN connecting the GPRS network to a server that allocates IP addresses in an IP-based network, said GGSN comprising:
a counter for setting a maximum number (Ni) of requests for an IP address that are to be sent from the GGSN to the server;
a timer for setting a maximum time period (Ti) that the GGSN will wait for a response from the server after each request for an IP address is sent;
a Network Access Server (NAS) that includes:
means for sending a sequence of requests for an IP address from the GGSN to the server, with each request being separated from the previous request by time period Ti, said sequence being halted if a response is received from the server within time period Ti after one of the requests is sent; and
means for receiving a response from the server that includes an IP address for the mobile terminal; and means for sending the IP address from the GGSN to the mobile terminal.

12. The GGSN of claim 11 wherein the means for sending a sequence of requests for an IP address from the GGSN to the server includes means for unicasting each of the requests in the sequence from the GGSN to a different server.

13. The GGSN of claim 11 wherein the means for sending a sequence of requests for an IP address from the GGSN to the server includes a Radius client for sending a sequence of requests from the GGSN to a Radius server.

14. The GGSN of claim 11 wherein the means for sending a sequence of requests for an IP address from the GGSN to the server includes a Dynamic Host Configuration Protocol (DHCP) client for sending a sequence of requests from the GGSN to a DHCP server.

15. In a General Packet Radio Service (GPRS) network having a Serving GPRS Service Node (SGSN) serving a mobile terminal operating in the GPRS network, and a Gateway GPRS Service Node (GGSN) connecting the GPRS network to a server that allocates IP addresses in an IP-based network, a system for dynamically allocating an Internet Protocol (IP) address to the mobile terminal, said system comprising:
a Home Location Register (HLR) that stores information regarding whether the mobile terminal is authorized to receive a backup IP address if an IP address cannot be obtained from the server, and whether the mobile terminal is a user of a real-time application;
means for sending the information to the GGSN,
a timer in the GGSN for setting a maximum time period (Ti) that the GGSN will wait for a response from the server after a request for an IP address is sent from the GGSN to the server;
a Network Access Server (NAS) in the GGSN that includes:
means for sending a request for an IP address from the GGSN to the server; and
means for determining that time period Ti expired without receiving a response from the server that includes an IP address for the mobile terminal;
means in the GGSN for determining from the information in the GGSN whether the mobile terminal is authorized to receive a backup IP address, and if so, determining from the information in the GGSN whether the mobile terminal is a user of a real-time application;
means for sending a public IP address from the GGSN to the mobile terminal upon determining that the mobile terminal is a user of a real-time application; and means for sending a private IP address from the GGSN to the mobile terminal upon determining that the mobile terminal is not a user of a real-time application.

16. A system for dynamically allocating an IP address to a mobile terminal operating in an access network, said system comprising:
a Network Access S erver (NAS) connecting the access network to a server that allocates IP addresses in an Internet Protocol (IP)-based network, said NAS including:
means for sending a request for an IP address to the server; and
means for receiving an IP address from the server; and
an Authorization, Authentication, and Accounting (AAA) server that stores information regarding whether the mobile terminal is authorized to receive a backup

IP address if an IP address cannot be obtained from the server, and whether the mobile terminal is a user of a real-time application;
means for sending a public IP address from the NAS to the mobile terminal upon determining that the mobile terminal is a user of a real-time application; and means for sending a private IP address from the NAS to the mobile terminal upon determining that the mobile terminal is not a user of a real-time application.

17. In a General Packet Radio Service (GPRS) network, a method in a Gateway GPRS Service Node (GGSN) for dynamically allocating Internet Protocol (IP) addresses to mobile terminals operating in the GPRS network, said GGSN connecting the GPRS network to a plurality of servers that allocate IP addresses in an IP-based network, said method comprising the steps of:
obtaining a first JP address for a first mobile terminal from a first server;
obtaining a second IP address for a second mobile terminal from a second server;
determining whether the first IP address and the second IP address are duplicate IP addresses;
releasing the second IP address upon determining that the first IP address and the second IP address are duplicate IP addresses; and
obtaining a third IP address for the second mobile terminal that is not the same as the first IP address.

18. In a General Packet Radio Service (GPRS) network, a method of dynamically setting up a Layer 2 Tunneling Protocol (L2TP) tunnel from a Gateway GPRS Service Node (GGSN) to a Virtual Private Network (VPN), said method comprising the steps of:
sending a predetermined number (Ni) of requests for an Internet Protocol (IP) address from the GGSN to a server, each of the requests being separated by time (Ti); determining that time period Ti expired following a last request in the sequence of Ni requests without receiving in the GGSN, a response from the server that includes an IP address for the mobile teπninal; and
examining by the GGSN, an Access Point Name (APN) to deduce tunnel endpoint parameters for setting up the L2TP tunnel.