Patent Application
20100172336
The invention relates to the handling of periodic location updates at a Mobile Switching Centre Server (MSC-S) in a Circuit Switched (CS) core network (CN) for a terminal attached to a Packet Switched (PS) cell of a radio access network and using the PS cell to access the CS services provided by the CS CN. In particular, though not exclusively, the invention relates to the provision of periodic location updates when the terminal is attached to an LTE radio access network.
Mobile Circuit Switched (CS) services based on Global System for Mobile Communications (GSM) and Wideband Code Division Multiple Access (WCDMA) radio access are used world-wide. They allow a user to obtain telecommunication services with a single user subscription in most countries of the world. The number of CS subscribers is growing rapidly, boosted by the roll-out of mobile CS services in countries with high populations such as India and China. One reason the number of subscribers is still growing rapidly is the evolution of the Mobile Services Switching Centre (MSC) architecture into a softswitch solution. In the softswitch solution case the traditional MSC/Visitor Location Register (VLR) is divided into a MSC server (MSC-S) and a Media Gateway (MGW). The present invention applies at least both to traditional MSC/VLR scenarios and to divided MSC-S and MGW scenarios.
A 3GPP work item, “Evolved UTRA and UTRAN”, defines a Long-Term Evolution (LTE), designed to improve efficiency, lower costs and improve services for 3GPP-based access technology. LTE will use Orthogonal Frequency-Division Multiplexing (OFDM) radio technology in the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink, allowing at least 100 Mbps peak data rate for downlink data rate and 50 Mbps for uplink data rate. LTE radio can operate in different frequency bands and is therefore very flexible for deployment in different regions of the world, where different frequency bands might be licensed.
In addition to the Radio Access Network (RAN) standardization, a 3GPP System Architecture Evolution (SAE) work item is being to develop an evolved core network for LTE radio access networks. This new core network is now also called Evolved Packet Core (EPC) as part of the SAE work. The nodes and interfaces of the SAE core network and LTE radio access network are illustrated schematically in
Common to both LTE and SAE is that only a Packet Switched (PS) domain will be specified, i.e. all services are to be supported via this domain. To date, LTE/SAE can be considered to be service “agnostic”. It does not care about the nature of the data. It has been assumed that services will be facilitated by a service layer network, and in particular by the IP Multimedia Subsystem (IMS). The service layer would be connected to the AGW within the SAE, via the standard Gi interface which is also called as a SGi interface in the SAE terminology and which is shown in
It appears however that the assumption referred to in the preceding paragraph is not necessarily valid, due to the fact that some LTE/SAE network operators may not wish to implement an IMS network at all or simultaneously with LTE/SAE deployment. In this case, it becomes imperative that the SAE is able to sustain or provide access to at least certain services in the CS services domain, normally available over GSM and WCDMA accesses, and in particular the traditional CS type services such as voice calls.
Solutions which allow access to the CS services domain over LTE/SAE are referred to as “CS over LTE/SAE”, or briefly just “CS over LTE” (CSoLTE) solutions. The basic architecture for these solutions is illustrated schematically in
The Packet MSC (PMSC) 4 may serve both traditional GSM/UMTS RANs 5 and the new CS over LTE based solutions 6. The PMSC 4 contains two logical functions referred to as a Packet CS Controller (PCSC) 7 and an Interworking Unit (IWU) 8. The communication between a terminal 9 and the PMSC 4 is conducted over the (S)Gi interface. This means that all direct communication between the terminal and the PCSC 7 and the IWU 8 in the PMSC 4 is based on IP (Internet Protocol) based protocols. The terminal is visible to the PMSC and reachable using an IP-address via an Access Gateway (AGW) 2. This communication is via two different interfaces, U8c for the control plane and U8u for the user plane. The U8c interface is between the terminal 9 and the PCSC 7 and the U8u interface is between the terminal 9 and the IWU 8. The PCSC 7 has also an Rx interface to the Policy Control and Charging Rules Function (PCRF) for allocation of LTE/SAE bearers for the CSoLTE services.
There are a number of possible alternatives for the actual provision of CS services using the PMSC. A first alternative is called “CS Fallback”. In CS Fallback, the terminal performs SAE Mobility Management (MM) procedures towards a SAE Mobility Management Entity (MME) 1 while using LTE access. The MME 1 registers the terminal in a MSC-S 12 for CS based services. When a mobile terminating call or other transaction request resulting in a page for CS services is received in the MSC-S 12 it is forwarded to the terminal via the MME 1, and the terminal performs fallback to a GSM/UMTS RAN 5 and responds to the CS Paging Request. This means that the terminal selects a cell in the GSM RAN (GERAN) or in the UMTS RAN (UTRAN) based on information received e.g. as part of the SAE MM procedures. A similar process is used for Mobile originated CS services, and when these are triggered and the terminal is using LTE access, it will fall back to a GSM or UMTS RAN and invoke the CS service there.
A second alternative is referred to as “CS over LTE Integrated” (CSoLTE-I). In this solution the same SAE MM procedures as for “CS Fallback” are used, but instead of performing fallback to a 2G or 3G RAN, the terminal invokes all the CS services over the LTE radio access network. CS services (also called Connection Management, CM, procedures) are transported over IP-based protocols between a PMSC 4 and the terminal 9 using the LTE radio access network and SAE CN nodes such as the AGW 2.
A third solution is referred to as “CS over LTE Decoupled” (CSoLTE-D). In this solution both MM and CM procedures are transported using IP-based protocols directly between the PMSC 4 and the terminal using the LTE radio access network and SAE CN user plane nodes such as the AGW 2. The terminal needs to initially perform a specific registration or attachment procedure to the PMSC 4 (or more precisely to the PCSC 7) using the U8c interface signalling. This is needed mainly to inform the network that the terminal is connected to the PCSC, and is then also needed for handling of terminating calls and other transactions. As part of the initial registration between the terminal and the PCSC, there is also a need to perform an initial Location Area Update (LAU) procedure towards the MSC-S.
The initial LAU procedure could be performed in the same way as in GSM/WCDMA networks (i.e. from the terminal) or could be triggered from the PCSC 7 when the terminal performs the initial registration/attachment to the PCSC. All CS paging procedures are triggered from the MSC-S 12 to the PCSC 7 and then further to the terminal 9. This means that the PCSC 7 needs to have a way to communicate with the terminal to forward the CS paging indications to the terminal, and the initial registration is used to fulfil this purpose. The terminal 9 informs the PCSC 7 about its IP-address (in the AGW) and provides necessary additional addressing information (e.g. UDP or TCP port).
In addition, some form of “keep alive” or “heartbeat” mechanism is needed between the terminal and the PCSC, to let the PCSC know that the terminal is still attached to the PCSC. Once the keep alive or heartbeat signalling is not received in the PCSC, the PCSC can remove all information about the terminal.
In GSM/WCDMA networks, each terminal is required to provide periodic LAUs to indicate to the CS domain part of the core network that the terminal is still reachable. In this case the periodicity of these periodic LAUs, i.e. the relevant timer value, is indicated to the terminal as part of the system information broadcast in each cell. If periodic LAUs are not received at the MSC/VLR, then the VLR may decide to detach the terminal from the network. When this happens, the terminal becomes unreachable for terminating transactions. Furthermore, it cannot perform originating transactions until it is again attached to the MSC/VLR. Similar procedures apply also towards the PS domain part of the GSM/WCDMA core networks. In this case the procedure is called Routing Area Update (RAU) and the CN node is called Serving GPRS Support Node (SGSN). The minor difference is that the timer indicating the periodicity of RAUs is communicated from the SGSN to the terminal using normal unicast signalling (i.e. this timer is not part of the broadcast system information).
As previously discussed, it is possible to provide CS services from a Mobile Switching Centre Server (MSC-S) in a Circuit Switched (CS) core network (CN) for a terminal attached to a Packet Switched (PS) cell of a radio access network and using the PS cell to access the CS services provided by the CS CN. Different MM procedures, e.g. LAUs or TAUs, are triggered based on the terminal moving in the radio access network. The most obvious procedures that apply for the CSoLTE-D solution are the TAU procedures performed between the terminal and the MME 1, the registration and “heartbeat/keep alive” procedures between the terminal and the PCSC 7 and the LAU procedures towards the MSC-C 12 part of the PMSC 4.
One simple solution would be to perform all the different MM procedures independently of each other and without any coordination or optimization. In this case, there would be a large amount of different MM related signalling between the terminal and the different parts of the network. This would mean that the battery lifetime of the terminal would decrease. It would also mean that the network would be loaded with a large amount of signalling, thus possibly decreasing the capacity of the network to handle other transactions such as normal calls or PS sessions.
It is therefore an object of the present invention to provide an improved way of handling procedures for keeping the LAU-procedure related information in the MSC-S 12 updated in an optimal way. It is a further object to provide a system in which the MSC-S 12 part does not need to be modified, and existing MSC-S 12 functionality can be reused.
In accordance with a first aspect of the present invention there is provided a method for periodically indicating to a Mobile Service Switching Centre Server (MSC-S) (or to a traditional MSC/VLR) in a CS core network that a terminal attached to a PS cell of a radio access network is still also attached to CS services in the CS core network. The method comprises sending periodic Location Area Updates (LAUs) from a PCSC in the CS core network to the MSC-S (or MSC/VLR) for as long as the terminal is attached to or registered with the Packet Circuit Switched Controller (PCSC).
The PCSC may know that access to the terminal is available because the terminal is registered with the PCSC and performs the needed keep alive/heartbeat procedures, in which case the PCSC sends periodic LAUs to the MSC-S for as long as the terminal is registered with the PCSC.
The terminal may be configured to send periodic Tracking Area Updates (TAUs) to a Mobility Management Entity (MME), in which case a LAU is preferably sent from the terminal to the PCSC every time a Tracking Area Update is sent to the MME. The main benefit with this coordination is that the terminal needs to enter active state only as decided by the interval of the TAU procedure, and so the battery lifetime of the terminal can be increased. The PCSC will then know that access to the terminal is available for as long as it is receiving LAUs from the terminal. It does not need to send a LAU to the MCS-S every time it receives a LAU from the terminal: it may run its own clock/timer and perform the LAUs on behalf of the terminal, although in one embodiment it may react to the LAU from the terminal by sending a LAU to the MSC-S.
In one embodiment a Mobility Management (MM) Procedure requiring involvement by the terminal may be initiated by the MSC-S or MSC/VLR. If this is the case a message relating to the MM procedure may be sent from the PCSC to the terminal. A response from the terminal may then be forwarded from the PCSC back to the MSC-S. When the MM procedure is first initiated the PCSC may instruct the terminal to send an immediate LAU, All the procedures related to the LAU between the terminal and the MSC-S may then be relayed by the PCSC.
In an alternative embodiment, when the MM procedure is initiated by the MSC-S or MSC/VLR, the signalling connection between the PCSC and the MSC-S pr MSC/VLR may be disconnected. The PCSC may then ensure that any subsequent LAUs sent by the terminal are forwarded to the MSC-S or MSC/VLR.
The terminal may be configured to send Location Area Updates (LAUs) in addition to TAUs, although these may be transmitted with different periodicities. If this is the case, both the LAUs and the TAUs are preferably sent from the terminal to the PSCS (and to the MME) with whichever time interval is shorter out of the LAU time interval and TAU time interval.
The terminal may be also configured to send a heartbeat message in addition to both LAUs and TAUs, and all these three procedures may be transmitted with different periodicities. If this is the case, then all these procedures are preferably performed together by the terminal with whichever time interval is shorter out of the three different time intervals
The radio access network is preferably a LTE radio access network, which may be associated with a SAE core network. The CS core network providing CS services for terminals camped on LTE cells may be a GSM CS core network or UMTS CS core network including the additions related to CSoLTE solutions as described in this application, for example.
In accordance with another aspect of the present invention there is provided a PCSC for use in a GSM or UMTS CS network, comprising:
The first two alternatives described above for providing CS services using the P-MSC (“CS Fallback” and “CSoLTE-I”) are based on the use of the Gs+ interface between the MME and the MSC-S for Mobility Management procedures. This means that location updates to the MSC-S are based on user mobility in the LTE/SAE, for which 3GPP currently provides no solution. However, it is clear that LTE/SAE mobility will be based on a geographical structure called a tracking area (TA). Two possible concept have been raised in 3GPP: one is that these TAs may overlap; the other is that the terminal may be present in several TAs.
As previously discussed, in GSM/UMTS, each terminal is required to provide periodic location updates to indicate to the network that the terminal is still reachable. If periodic location updates are not received at the MSC/VLR, then the VLR may decide to detach the terminal from the network. When this happens, the terminal becomes unreachable for terminating transactions. Furthermore, it cannot perform originating transactions until it is again attached to the MSC/VLR.
When connected to an LTE radio access network, the terminal may initiate a periodic Tracking Area Update (TAU) when the related timer has expired. Whether the periodic TAUs will be supported in LTE is not yet settled in 3GPP.
Regardless of which concept is finally chosen, when roaming within the LTE radio access area, the terminal 9 will report its mobility to the MME 1 as shown in
If periodic TAU is not supported in the LTE 6, the MME 1 runs a timer which periodically initiates a LAU to the PMSC 4 over the Gs+ interface. For as long as contact is maintained between the terminal 9 and MME 1, the MME will continue to send LAUs to the MSC-S. When the PMSC subscribes to mobility events in the MME, the PMSC also indicates whether periodic mobility information is required.
If periodic TAU is supported in LTE, this is mapped to periodic LAU in the MME. It will be appreciated that there is a possibility that the time interval for periodic TAU (in the LTE 6) and LAU (in the MME 1) is not the same. The mapping ensures that the MME 1 can implement both timer and TAU based periodic LAUs. One way of implementing this is to ensure that the timer in the MME 1 for periodic LAUs is kept active for as long as the periodic (or other) TAUs are received by the MME.
The third alternative described above (“CSoLTE-D”) is not based on the usage of the Gs+ interface for CS mobility management. Instead, CS mobility management relies on the terminal 9 performing separate Location Area Update (LAU) signalling towards the PMSC 4 using the (S)Gi-based U8c-interface, as shown in
A suitable mobility management (MM) protocol architecture between the terminal 9 and the PMSC 4 for the CSoLTE-D solution is shown in
If periodic TAU is not supported in LTE, the PCSC 7 makes use of the fact that the terminal 9 is registered with it and is performing the keep alive/heartbeat signalling related to the registration to the PCSC 7. As shown in
If periodic TAU is supported in LTE, then in one embodiment it is defined that the terminal 9 must send periodic LAUs to the PCSC 7 each time periodic TAUs are sent to the MME 1. The PCSC 7 then sends periodic LAUs to the MSC-S 12. The PCSC 7 may also run its own timer for periodic LAUs, and it may be that the time intervals for periodic TAU (by the terminal 9) and LAUs (by the PCSC) are not the same. In this case, the timer at the PCSC 7 for periodic LAUs to the MSC-S 12 should be kept active for as long as periodic LAUs or registration heartbeat/keep alive messages are being received from the terminal 9. In other words, whenever the timer expires in the PCSC 7, then (as long as LAUs are still being received from the terminal 9) it initiates a periodic LAU towards the MSC-S 12.
In another embodiment—applicable if periodic TAU (or similar) is performed in LTE/SAE—the terminal 9 runs its own LAU timer, separated from the TAU periodic timer. If the TAU and LAU timers are different, the terminal 9 will use the shorter time period of the two, and carry out TAU and LAU at the same instance in time. This reduces the overall time for which that the terminal needs to enter an active state, thus increasing the battery lifetime of the terminal.
In further embodiment the terminal 9 runs its own LAU, TAU and registration keep alive/heartbeat timers. If these timer values are different, the terminal 9 will use the shortest time period of the three timers, and carry out registration keep alive/heartbeat, TAU and LAU at the same instance in time (i.e. once the used timer is triggered).
An initial or periodic LAU (or really any type of LAU) may trigger the MSC-S to initiate some MM procedures that require involvement with the terminal. These procedures are defined in the 3GPP TS 24.008 (e.g. v6.15.0) and may, for example, contain Authentication, Identification or TMSI reallocation procedures. In a similar way, the terminal needs to be informed if the MSC-S rejects a LAU. This means that special handling is needed for the cases when the PCSC is sending, for example, periodic LAUs on behalf of the terminal and the MSC-S triggers any of the MM procedures that need involvement from the terminal.
Two examples of such special handling are as follows:
In one example, the PCSC should indicate (with new signalling specific for this purpose) to the terminal that it needs to perform a LAU right now (i.e. when the MSC-S triggers the authentication procedure). Once the PCSC receives the first message related to LAU from the terminal, it will not forward it to the MSC-S and instead it will forward the messages sent from the MSC-S needing involvement from the terminal to the terminal. This means that the PCSC ensures that the terminal and the MSC-S become synchronized as part of the LAU initially triggered from the PCSC. Once the terminal replies, the PCSC may forward the needed responses towards the MSC-S. Alternatively, the PCSC disconnects the signalling connection towards the MSC-S and makes sure that the terminal performs a LAU, either by explicitly ordering it to do so via a new procedure or by waiting for it to perform a periodic LAU. This procedure needs to be performed all the way to the MSC-S.
Referring to
Thus the invention has the advantage that the existing mechanisms for terminal detachment can be kept in the MSC-S (and/or in a traditional MSC/VLR). Since LAUs are received from the PCSC there is no requirement to change any mechanisms in the MSC-S. The installed MSS infrastructure can thus be reused. There is also no need to co-ordinate periodic timers in MSC and LTE.
It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiments without departing from the scope of the present invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/56273 | 6/22/2007 | WO | 00 | 12/22/2009 |
