Mobile radio communications systems have become increasingly common. Although they have been in use for many years, their application was often limited by power requirements for any useful range and the limited amount of radio spectrum that could be allocated for general use. More recently, modern radio communication networks allow a great number of communication sessions to take place simultaneously. Generally speaking, this is possible because users may communicate over an air interface with a relatively-local station, which in turn is connected to a larger network through which communications may be routed to practically any other area on earth. The number of users and the number of mobile applications available to those users have both increased dramatically. These applications involve not only mobile telephony, but data transmission to and from mobile units as well.
FIG. 1 is a simplified block diagram illustrating the relationship between selected components of a typical radio communication system 10. In this example, system 10 includes UE (user equipment) 12. UE 12 may be, for example, a mobile telephone, but my also be a laptop computer with wireless capability, a two-way pager, or even a dedicated gaming station. The term ‘UE’ is intended to broadly include all such devices. Typically, UE 12 is a mobile device, but of course could be any radio device whether it is operated as a fixed or mobile station.
In operation, UE 12 establishes a communication link with access point 14 via one or more radio channels 13. As used here, the access point 14 may include a single antenna coupled with a base station or controller, but may also represent an access network, that is, a collection of interconnected antennae and base stations, among other components. In any case, access point 14 is in communication with telecommunication system 15, which represents a typically large collection of interconnected switching nodes and other components that route communications to and from UE 12 (through access point 14) to and from their destination. This destination may, for example, be another UE communicating with telecommunications system 15. It may also be another entity accessible through another network, for example external packet data network (PDN) 17.
To access PDN 17, communications are routed through gateway 16. Even though only a single gateway depicted in FIG. 1, other gateways may exist for communication with other networks, or even for additional connections to the PDN 17. Switching nodes (not shown) within telecommunication system 15 determine when it is necessary to route communications with UE 12 through gateway 16, or some other gateway. In that event, a communication path such as a bearer channel is established to carry this traffic until it is no longer needed, for example when the communication session has been terminated.
The system 10 depicted in FIG. 1 is extremely simplified. In reality, systems involve a large number of interconnected components that interface with each other to not only carry voice and data traffic, but also signals forming messages that carry instructions from one component to one or more others. Because these systems can be very complex, and often must interface with very different types of networks, standard protocols have been developed to either standardize operations or provide a way for differently operated systems to interact with each other.
The 3GPP (3rd Generation Partnership Project) is a collaborative group for drafting and promulgating technical specifications for 3rd generation mobile telephony systems. Ideally, this will result in faster and more efficient service while ensuring smooth transitions so that discontinuity in existing services in minimized. For example, system architecture to accommodate roaming UE is defined in 3GPP technical specification TS 23.402.
FIG. 2 is a block diagram illustrating a roaming architecture for an SAE (System Architecture Evolution) system 50, as set forth in 3GPP TS 23.402 V.0.2.0. In FIG. 2, it may be seen that the system 50 may be generally organized into entities of the HPLMN (home public land mobile network) 30 and VPLMN (visiting public land mobile network) 40, with non-3GPP access networks 20 depicted in a third section. Note that some, but not all of the components in the 3GPP SAE roaming architecture will be referred to here as background for describing the present invention. The reference numbers in FIG. 2 have been added for convenience and are not part of the 3GPP technical specification.
The PDN 17 illustrated in FIG. 1 may, for example, be considered roughly analogous to the Operator IP (Internet protocol) Services Network 31 shown in FIG. 2. Examples of a PDN 31 are: an IP Multimedia Subsystem IMS, or a Packet-switched Streaming Service System PSS. An example of a node in PDN 31 is a Call Session Control Function CSCF. The remainder of the system 50, in general, communicates with node in 31 through a gateway (GW), specifically PDN SAE GW 33 over a defined interface that is referred to as SGi in the technical specification and FIG. 2. A PDN SAE GW 33 can be considered as an instantiation of a Mobile IP Home Agent (e.g. as defined by RFC 3775), which maintains a correlation between a device's Home Address (HoA, an IP address assigned by the user's home network e.g by the HA) and the Care-of-Address (CoA, an IP address used by the device on the foreign network so it is reachable while away from the home network). A UE (not shown in FIG. 2) communicates with the system 50 though a number of available access networks, some of which are defined in the 3GPP technical specifications and others (WLAN and WiMAX networks, for example) which are not. For this reason, as may be seen in FIG. 2, the SAE roaming architecture considers both 3GPP access networks and non-3GPP access networks. The communication path established for data communications will vary according to the type of access network to which a UE attaches.
UE attaching to a non-3GPP network 21 or 22 communicate with the PDN SAE GW 33 with the aid of a 3GPP AAA (authentication, authorization, and accounting) server 32 (via, in system 50 of FIG. 2, an AAA proxy server 42). As another example, the LTE (Long Term Evolution) radio access network 41 communicates through serving SAE GW 43 with the aid of MME (mobility management entity) 44. AAA server 32 and MME 44 are sometimes referred to as control plane entities, and send messages for the control of communications for the various nodes they are associated with. Both communicate with HSS (home subscriber server) 35, which maintains information about, among other things, individual UEs and their whereabouts that is of use when they are roaming (visiting other networks outside of their home network). This information is sometimes referred to as soft state information and sometimes changes as the UEs travel from one area to another. In some cases, soft state information is also (or instead) maintained in the PCRF (policy and rules changing function) node 36.
The functions of each of these selected components is pointed out only generally because their operation is described in the 3GPP technical specifications TS 23.401 V.0.2.0. and TS 23.402 V.0.2.0., which are incorporated here by reference, but are also considered known in the art. Although these technical specifications are very detailed, some areas for development still exist where the existing standards allow for potential problems to arise. Two such issues will now be explained in more detail with reference to FIGS. 3a and 3b. FIGS. 3a and 3b are simplified block diagrams illustrating a potential disruption of service problem inherent in systems of the existing art, such as SAE systems operable according to current system specifications. The problems referred to here may occur when a UE that is attached to one access network moves, and becomes attached to another instead. The problems are especially likely when the switch is between 3GPP accesses and non-3GPP accesses. In FIGS. 3a and 3b, the access networks are referred to generally as 310 and include 3GPP access networks 315 and non-3GPP access networks 311. The 3GPP access networks 315 (including networks 316, 317, and 318) are in communication with serving SAE GW 345 and through it to GW pool 330. The 3GPP networks also communicate with control plane entity MME 344. The non-3GPP networks 311 (including networks 312 and 313) are in communication with GW pool 330 and AAA server 342. GW pool 330 includes PDN SAE GWs 331, 332, and 333.
In FIG. 3a, UE 320 is shown attached to LTE 318 and communicating with PDN SAE GW 332 via a communication path (in this example an SAE bearer) 325. PDN SAE 332 in turn communicates with an external PDN (not shown) via SGi interface 327. Note that PDN SAE GW 332 was assigned to this function when UE 320 attached to the LTE 320, and effectively terminated the bearer 325. UE 320 may change access networks, however, for example when roaming from one area to another; the UE 320 may wish to maintain the current services being used in the previous access without experiencing service disruption. In FIG. 3b, UE 320 has changed and attached to non-3GPP network 313. When this occurred, a new attach procedure was triggered, meaning that a new PDN SAE GW is going to be assigned. This new PDN SAE GW is not necessarily the same as the one previously handling communications between UE 320 and the external PDN. In FIG. 3b, for example, PDN SAE GW 331 has been assigned and is communicating with the external PDN via SGi interface 328. Unfortunately, data packets received in PDN SAE GW 332 (as it was previously assigned to the communication) can no longer be forwarded to UE 320 since bearer 325 has been replaced by bearer 326 terminating at PDN SAE GW 331. These packets may simply be discarded, perhaps resulting in a perceivable disruption in service. A similar problem may occur when UE 320 leaves a non-3GPP access network and attaches to a 3GPP access network.
In general, the current technical specifications do not provide adequately for situations where an access network change may trigger the assignment of a new PDN SAE GW from a GW pool and thus cause service disruption to the UE 320.