In a typical communications network, also referred to as e.g. a wireless communications network, a wireless communications system, a communications network or a communications system, a device, communicates via a RAN to one or more CNs.
The RAN implements a radio access technology such as for example UTRAN, E-UTRAN, GERAN or any other Third Generation Partnership Project (3GPP) radio access technology. UTRAN is short for Universal Terrestrial Radio Access Network and comprises radio network nodes such as a Node B and Radio Network Controller (RNC). E-UTRAN is short for Evolved-UTRAN and is the air interface of Long Term Evolution (LTE). E-UTRAN comprises a radio network node referred to as an evolved NodeB (eNB) which performs tasks similar to those performed by the nodeB and RNC together in UTRAN. GERAN is short for GSM EDGE Radio Access Network, where GSM is an abbreviation for Global System for Mobile communications and EDGE is and abbreviation for Enhanced Data rates for Global Evolution. GERAN comprises the radio network nodes Base Transceiver Stations (BTS) and Base Station Controller (BSC). The radio access network node will be referred to as RAN node in some of the drawings.
The CN may be divided in circuit switched and packet switched domains. An example of a circuit switched CN node is Mobile services Switching Centre (MSC). An example of packet switched CN node is a Serving GPRS Support Node (SGSN). GPRS is short for General Packet Radio Service. The core network node will be referred to as CN node in some of the drawings.
The communications network is a geographical area which is divided into cell areas. The communication network may therefore also be referred to as a cellular network. Each cell area is served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. eNB, eNodeB, NodeB, B node, or BTS, depending on the technology and terminology used. The base stations communicate with the devices within range of the base stations.
The device may be a device by which a subscriber may access services offered by an operator's network and services outside operator's network to which the operators radio access network and core network provide access, e.g. access to the Internet. The device may be any device, mobile or stationary, enabled to communicate over a radio channel in the communications network, for instance but not limited to e.g. user equipment, mobile phone, smart phone, sensors, meters, vehicles, household appliances, medical appliances, media players, cameras, Machine to Machine (M2M) device or any type of consumer electronic, for instance but not limited to television, radio, lighting arrangements, tablet computer, laptop or Personal Computer (PC). The device may be portable, pocket storable, hand held, computer comprised, or vehicle mounted devices, enabled to communicate voice and/or data, via the radio access network, with another entity, such as another device or a server. The device is enabled to communicate wirelessly in the communications network. The communication may be performed e.g. between two devices, between a devices and a regular telephone and/or between the devices and a server via the radio access network and possibly one or more core networks and possibly the internet.
There are two operational modes of the device: idle mode and connected mode. In idle mode, after the device has been switched on, it selects a Public Land Mobile Network (PLMN) to connect to. The device searches for a cell of the selected PLMN that can provide available services and camps on the selected cell. In idle mode, the device is identified by parameters such as International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI) and Packet Temporary Mobile Subscriber Identity (P-TMSI). The RAN does not have any information about idle devices, i.e. information such as location, bearer information etc. The device stays in idle mode until it transmits a request to establish a radio connection. In connected mode, the device transmits and receives data. The device leaves the connected mode and returns to idle mode when the RRC connection is released or at RRC connection failure. In connected mode, the RAN has information about the connected devices, i.e. information such as location and bearer information etc.
PLMN, as mentioned above, is a network with the objective of providing wireless communication and of interlinking a wireless network with a fixed wired network. A PLMN is identified by a PLMN ID comprising a Mobile Country Code (MCC) and a Mobile Network Code (MNC). Each operator which provides mobile services may have its own PLMN. PLMNs interconnect with other PLMNs and Public Switched Telephone Networks (PSTNs) for telephone communications or with internet service providers for data and internet access of which links are defined as interconnect links between providers.
In 3GPP today, there are mobility situations when the device moves from a source side which may be UTRAN, E-UTRAN, GERAN or another radio access networks to a target GERAN shared network or a target UTRAN shared network. The source side may be either a shared network or a non-shared network. The mobility may be either connected mode mobility or idle mode mobility. Connected mode mobility refers to when a device in connected mode that moves from one place to another and idle mode mobility refers to when a device in idle mode moves from one place to another.
A 3GPP network may be organized using network sharing. A shared network allows different core network operators to connect to a shared RAN. The operators may share the radio network elements and/or radio resources and in addition the core network nodes. The target shared network is shared between core network operators. At network sharing, the 3GPP standard provides two reference architectures; GateWay Core Network (GWCN) and Multi-Operator Core Network (MOCN). In GWCN, core network nodes such as a Mobility Management Entity (MME) or a SGSN is shared between the CN operators in addition to the RAN. In MOCN, only the radio access network is shared between the core network operators.
FIG. 1 illustrates an embodiment of a GWCN configuration for network sharing. FIG. 1 shows an example with three CN nodes operated by three different operators, operator A, B and C. The three CN nodes exemplified in FIG. 1 is: CN Node, operator A 101a, CN Node, operator B 101b and CN Node, operator C 101c. The three MSC/SGSN 103a, 103b, 103c are shared amongst the CN operators A, B and C, and is therefore referred to as a shared MSC/SGSN. The MSC is a network node responsible for coordinating communications channels and processes in the network. The MSC processes requests for service connections from the devices, and routes calls, SMS etc. between the base station and the PSTN. The SGSN performs the same functions as the MSC for voice traffic. Note that three CN operators are illustrated as an example, and that any suitable number of CN operators may be used, such as for example eight. The dotted lines illustrate the connection between the CN node operator A 101a and each of the respective shared MSC/SGSN 103a, 103b, 103c. The thin continuous lines illustrate the connection between the CN node operator B 101b and each of the respective shared MSC/SGSN 103a, 103b, 103c. The thick continuous lines illustrate the connection between the CN node operator C 101c and each of the respective shared MSC/SGSN 103a, 103b, 103c. The Iu interface 104 enables interconnection of the three RNCs, RNC 105a, RNC 105b and RNC 105c with the shared MSC/SGSN 103a, 103b, 103c. The Iu interface 104 is for CS data traffic between the RNCs 105a, 105b, 105c and the MSC and for PS data traffic between the RNCs 105a, 105b, 105c and the SGSN. The RNCs 105a, 105b, 105c are located in the RAN operated by operator X.
FIG. 2 illustrates a MOCN configuration for network sharing. FIG. 2 illustrates an example with three CN nodes operated by three operators A, B and C. The exemplified CN nodes are CN node, operator A 201a, CN node, operator B 201b and CN node, operator C 201c. The three CN nodes 201a, 201b, 201c share the same RNC 205. The Iu interface 204 enables interconnection between the RNC 305 and the three CN nodes 201a, 201b, 201c. The RNC 205 is located in the RAN and operated by operator X.
Note that FIGS. 1 and 2 illustrate example embodiments where the RAN node is an RNC, but the skilled person will understand that the RAN node may also be a BSC or an eNB.
Circuit switching is a methodology of implementing the communications network in which two network nodes establish a dedicated communications channel (circuit) through the communications network before the network nodes may communicate. The circuit functions as if the nodes were physically connected as with an electrical circuit. An example of a circuit switched network is the PSTN.
Circuit switching contrasts with packet switching which divides the data to be transmitted into small units, called packets, transmitted through the network independently. Packet switching shares available network bandwidth between multiple communication sessions. Packet switching features delivery of variable bit rate data streams (sequences of packets) over a shared network. When traversing network adapters, switches, routers and other network nodes, packets are buffered and queued, resulting in variable delay and throughput depending on the traffic load in the network.
When the device is camping in LTE there are two methods for providing voice service to the device: Circuit Switched FallBack (CSFB) from LTE to Second Generation/Third Generation (2G/3G) or VoLTE in combination with Single Radio Voice Call Continuity (SRVCC). CSFB defines a mechanism for using a CS network to provide voice services alongside of an LTE network, i.e. a PS network. A CS network may also be referred to as a CS domain and a PS network may also be referred to as a PS domain. Through the CSFB, the device is directed to Wideband Code Division Multiple Access (WCDMA)/GSM to initiate or take a voice call, and the call remains in the CS domain until it is completed, and returns to LTE when finished. Using the inter-technology mobility capabilities of LTE, CSFB allows devices to transition to a legacy CS network to receive voice services and then return to LTE when finished. The CSFB provides support for voice and Short Message Service (SMS). SRVCC is an LTE functionality that provides continuity between the Internet protocol Multimedia Subsystem (IMS) over PS access and CS access for calls that are anchored in IMS when the device is capable of transmitting/receiving on only one of those access networks at a given time.
In conventional networks, the same CN operator may always serve the device in CS and PS domains. In a shared network, supporting devices shall behave as devices in conventional networks with respect to registration with CS and PS domains. A conventional network is defined by the 3GPP as a PLMN consisting of a radio access network and a core network, by which only one serving operator provides services to its subscriber. Subscribers of other operators may receive services by national or international roaming.
CS/PS coordination may be described as a method for coordinating the registration of a device in CS and PS domains of a MOCN or GWCN. CS/PS coordination is achieved when the same operator is simultaneously serving the device in both the CS domain and the PS domain. In 3GPP today there are situations where CS/PS coordination is not achieved when the device is a GERAN or UTRAN network non-supporting device and/or the target shared network is broadcasting only a common PLMN. One problem is that the PS operator and the CS operator may be selected at different networks, one operator is selected at the source side while the other is selected at the target side and thus there is no common synchronization place. A non-supporting device is a device that does not support network sharing in the sense that it is not able to handle the additional broadcast system information that is specific for network sharing. A supporting device is a device that supports network sharing in the sense that it is able to select a CN operator as the serving operator within a shared network. The parameter common PLMN mentioned above is, according to the 3GPP, a PLMN ID indicated in the system broadcast information as defined for conventional networks, which non-supporting devices understand as the serving operator.
The CS/PS coordination problems may occur in idle mode mobility, in PS handover or CS handover, in non-Dual Transfer Mode (non-DTM) or DTM case, in MOCN or a GWCN network. DTM is a protocol that makes it possible for a wireless device to simultaneous transfer CS voice and PS data.
However, if the device changes access in a shared network in idle mode in both the CS domain and the PS domain, the problem does not arise.
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