Method for providing roaming services in which the home network uses S8HR model for out-bound roaming while the visited network uses LBO model for in-bound roaming
A roaming method that enables the home network (HPMN) to use S8 Home Routed (S8HR) model for out-bound roaming while the visited network (VPMN) uses Local Breakout (LBO) model for in-bound roaming. An IMS Roaming Gateway (IR-GW) establishes an IMS bearer between the IR-GW and the home network's Packet Data Network Gateway (P-GW). The IR-GW replaces the source IP address on the SIP-Register message with the client IP address assigned to the UE by the HPMN P-GW. Upon receiving a SIP-Response message responsive to successful authentication of the UE with the HPMN, the IR-GW inserts its own IP address into the SIP-Response message and forwards it to the UE. IR-GW performs network address translation (NAT) between the source IP assigned to the UE by the VPMN and the client IP assigned to the UE by the HPMN.
1. A method of providing roaming services to a user equipment (UE) in a scenario in which a Visited Public Mobile Network (VPMN) uses a local breakout (LBO) model for providing in-bound roaming services while a Home Public Mobile Network (HPMN) uses a home-based routing (S8HR) model for providing out-bound roaming services, the method comprising:
receiving a request from the UE to attach in the VPMN, wherein the UE is a subscriber of the HPMN;
establishing a data channel for Internet Protocol Multimedia Subsystem (IMS) traffic between a VPMN Serving Gateway (S-GW) and a VPMN Public Data Network Gateway (P-GW), wherein the VPMN P-GW assigns a source Internet Protocol address (IP address) to the UE, thereby enabling the VPMN to use the LBO model to provide in-bound roaming services to the UE;
providing an IMS Roaming Gateway (IR-GW), the IR-GW configured to replace the source IP address on a SIP-Register message with a client IP address assigned to the UE by the HPMN P-GW and performing network address translation (NAT) between the source IP assigned to the UE by the VPMN P-GW and the client IP assigned to the UE by the HPMN P-GW;
wherein data packets are transmitted to and from the UE via the HPMN, thereby enabling the HPMN to use the S8HR model to provide the out-bound roaming services to the UE.
2. The method of claim 1 , wherein the IR-GW identifies an IP address of the HPMN P-GW by performing the steps comprising:
identifying UE's IMSI within the IMS SIP Registration request message;
identifying MCC-MNC values within the UE's IMSI; and
performing an IMS access point name (APN) domain naming system (DNS) query using the MCC-MNC values;
receiving the HPMN P-GW's IP address in response to the APN DNS query.
3. The method of claim 1 , wherein establishing an IMS bearer between the IR-GW and the HPMN P-GW comprises the steps of:
the IR-GW sending a Create-Session-Request message to the HPMN P-GW;
the HPMN P-GW verifying with a Policy and Charging Rules Function (PCRF) of the HPMN that a policy corresponding to the UE permits establishing the IMS bearer; and
the HPMN P-GW sending to the IR-GW a Create-Session-Response message along with the client IP address assigned to the UE.
4. The method of claim 3 , wherein responsive to the Create-Session-Request message, the HPMN P-GW sends a HPMN Proxy-Call Session Control Function (P-CSCF) IP address to the IR-GW, and the IR-GW, after inserting the IR-GW IP address into the SIP-Register message, forwards the SIP-Register message to the HPMN P-CSCF IP address.
5. The method of claim 1 , wherein a Session Border Controller (SBC) inserts a SBC IP address into a PATH header of the SIP-Register message.
6. The method of claim 1 , wherein the IR-GW inserts the IR-GW IP address and a Session Border Controller (SBC) inserts a SBC IP address into a SERVICE-ROUTE header of the SIP-Response message.
7. The method of claim 1 , wherein an HPMN Serving-Call Session Control Function (S-CSCF) sends an authentication challenge to the UE, and the UE responds with a second SIP-Register message containing an authentication response.
8. The method of claim 1 , wherein establishing an originated call from the UE comprises the steps of:
the UE sending a SIP-Invite message in the VPMN, the SIP-Invite message having a plurality of ROUTE headers;
forwarding the SIP-Invite message to the IR-GW based on the IR-GW IP address in a first ROUTE header;
the IR-GW forwarding the SIP-Invite message to an IMS Core of the HPMN indicated in a second ROUTE header via the IMS bearer;
the IMS Core of the HPMN routing the SIP-Invite request to a called party; and
the IR-GW performing NAT for the signaling and data packets from a Session Border Controller (SBC) to the client IP address assigned to the UE by the HPMN P-GW.
9. The method of claim 1 , wherein establishing a terminating call to the UE comprises the steps of:
receiving, by an IMS Core of the HPMN, a SIP-Invite message from a calling party;
the IMS Core adding ROUTE headers to the SIP-Invite message;
routing the SIP-Invite message from the IR-GW to a Session Border Controller (SBC) based on a PATH header in SIP-Register message;
routing the SIP-Invite message to a VPMN P-CSCF;
routing the SIP-Invite message to the UE; and
routing a successful response message to the calling party.
10. The method of claim 1 , wherein the IR-GW is hosted by an Internet Packet Exchange framework (IPX), the VPMN, or the HPMN.
11. A communication system configured to provide roaming services to a User Equipment (UE), the communication system having an Internet Protocol Multimedia Subsystem Roaming Gateway (IR-GW) configured to perform the steps comprising:
detecting an IMS SIP-Register message originating from the UE, the UE requesting to register in a Visited Public Mobile Network (VPMN), the UE being a subscriber of a Home Public Mobile Network (HPMN), wherein the SIP-Register message carries a source IP address assigned to the UE by the VPMN, thereby enabling the VPMN to use a Local Breakout (LBO) model to provide in-bound roaming services to the UE;
establishing an IMS bearer between the IR-GW and a HPMN Packet Data Network Gateway (P-GW), whereby the HPMN P-GW assigns a client IP address to the UE;
replacing the source IP address on the SIP-Register message with the client IP address assigned to the UE by the HPMN P-GW; and
performing network address translation (NAT) between the source IP assigned to the UE by the VPMN P-GW and the client IP assigned to the UE by the HPMN P-GW;
wherein data packets are transmitted to and from the UE via the HPMN, thereby enabling the HPMN to use an S8HR model to provide the out-bound roaming services to the UE.
12. The communication system of claim 11 , wherein the IR-GW identifies an IP address of the HPMN P-GW by performing the steps comprising:
identifying UE's IMSI within the IMS SIP Registration request message;
identifying MCC-MNC values within the UE's IMSI; and
performing an IMS access point name (APN) domain naming system (DNS) query using the MCC-MNC values;
receiving the HPMN P-GW's IP address in response to the APN DNS query.
13. The communication system of claim 11 , wherein establishing an IMS bearer between the IR-GW and the HPMN P-GW comprises the steps of:
the IR-GW sending a Create-Session-Request message to the HPMN P-GW;
the HPMN P-GW verifying with a Policy and Charging Rules Function (PCRF) of the HPMN that a policy corresponding to the UE permits establishing the IMS bearer; and
the HPMN P-GW sending to the IR-GW a Create-Session-Response message along with the client IP address assigned to the UE.
14. The communication system of claim 13 , wherein responsive to the Create-Session-Request message, the HPMN P-GW sends a HPMN Proxy-Call Session Control Function (P-CSCF) IP address to the IR-GW, and the IR-GW, after inserting the IR-GW IP address into the SIP-Register message, forwards the SIP-Register message to the HPMN P-CSCF IP address.
15. The communication system of claim 11 , wherein a Session Border Controller (SBC) inserts a SBC IP address into a PATH header of the SIP-Register message.
16. The communication system of claim 11 , wherein the IR-GW inserts the IR-GW IP address and a Session Border Controller (SBC) inserts a SBC IP address into a SERVICE-ROUTE header of the SIP-Response message.
17. The communication system of claim 11 , wherein establishing an originated call from the UE comprises the steps of:
the UE sending a SIP-Invite message in the VPMN, the SIP-Invite message having a plurality of ROUTE headers;
forwarding the SIP-Invite message to a Session Border Controller (SBC) based on a SBC IP address in a ROUTE header;
forwarding the SIP-Invite message to the IR-GW based on the IR-GW IP address in a first ROUTE header;
the IR-GW forwarding the SIP-Invite message to an IMS Core of the HPMN indicated in a second ROUTE header via the IMS bearer;
the IMS Core of the HPMN routing the SIP-Invite request to a called party; and
the IR-GW performing NAT for the signaling and data packets from a Session Border Controller (SBC) to the client IP address assigned to the UE by the HPMN P-GW.
18. The communication system of claim 11 , wherein establishing a terminating call to the UE comprises the steps of:
receiving, by an IMS Core of the HPMN, a SIP-Invite message from a calling party;
the IMS Core adding ROUTE headers to the SIP-Invite message;
routing the SIP-Invite message to the IR-GW according to the ROUTE headers;
routing the SIP-Invite message to a VPMN P-CSCF;
routing the SIP-Invite message to the UE; and
routing a successful response message to the calling party.
19. The communication system of claim 11 , wherein the IR-GW is hosted by an Internet Packet Exchange framework (IPX), the VPMN, or the HPMN.