WO2012150212A1

WO2012150212A1 - Enhanced relocation in a communications network

Info

Publication number: WO2012150212A1
Application number: PCT/EP2012/057909
Authority: WO
Inventors: Dario Serafino Tonesi; Masatoshi Nakamata
Original assignee: Nokia Siemens Networks Oy
Priority date: 2011-05-02
Filing date: 2012-04-30
Publication date: 2012-11-08

Abstract

A method of enhanced relocation in a communications network is provided in which a first network node is connected to a second network node. It is attempted to establish a direct connection from the first network node to the core network, and a path is established from the first network node to the core network via the second network node if attempting to establish a direct connection from the first network node to the core network fails. In this way, a communication path between a mobile station and a core network via the first network node and the second network node is established.

Description

ENHANCED RELOCATION IN A COMMUNICATIONS NETWORK

FIELD OF THE INVENTION

The invention generally relates to enhanced relocation in a communications network, in particular to relocation during handover from one cell to another.

BACKGROUND OF THE INVENTION

Enhanced relocation is a protocol in 3GPP Release 8, which allows for the reduction of handover time, as well as the reduction of signalling load over the Iu interface .

Enhanced relocation starts to involve the core network in the relocation after handover to a new or target cell from an old or source cell has been completed in the radio access network.

However, a problem can occur if there is a failure during handover; for example a core network failure, when enhanced relocation is used. In this case it is not possible to keep an ongoing call alive and a call drop occurs .

SUMMARY OF THE INVENTION

Accordingly, embodiments of the invention provide a method of relocating a communication path between a mobile station and a core network. The method includes connecting a network node to another network node, attempting to establish a direct connection from the network node to the core network and establishing a path from the network node to the core network via the other network node if attempting to establish a direct connection from the network node to the core network fails. In this way, the communication path between the mobile station and a core network is via the first network node and the second network node.

Therefore, if establishment of the direct connection from the first network node to the core network fails, the communication path may instead be directed over the second network node.

Connecting the network node to the other network node may include anchoring the other network node to the communication path, or anchoring the communication path back to the other network node before the other network node is removed from the connection path.

Anchoring the first network node to the second communication path before it is removed from the second communication path provides the advantage that a call being made by the mobile station during handover will not be dropped.

Due to the first network node being anchored to the second communication path before it is removed from the second communication path, if the step of establishing fails, the second communication path may instead be relocated via the second cell, the second network node and the anchored first network node. In this way, a call may be directed from the mobile station over the second communication path via the first network node and will not be dropped should the establishment of a direct connection from the first network node to the core network fail.

Anchoring the other network node to the communication path may include instructing the other network node to save resources associated with the communication path .

In one embodiment, the core network is a circuit switched network.

In another embodiment, the core network is a packet switched network.

Alternatively, the core network may include a circuit switched network and a packet switched network. In this case, the communication path may be from the mobile station to both the circuit switched network and the packet switched network. Then the direct connection may be established between the network node and both the circuit switched network and the packet switched network.

Preferably, the network node is a control node, in which case the network node can be an RNC .

Embodiments of the invention further provide a communications network. The communications network includes a first network node related to a first cell and a second network node related to a second cell and coupled to the first network node. The first network node is configured to hand over a first communication path from a mobile station to a core network via the first cell and the first network node to a second communication path from the mobile station to the core network via the second cell, the second network node and the first network node. The second network node is configured to anchor the first network node to the second communication path, to remove the anchored first network node from the second communication path, and to establish a connection between the second network node and the core network after it has removed the anchored first network node from the second communication path.

In this way, the second communication path from the mobile station to the core network is relocated via the second cell and the second network node.

In an advantageous embodiment, the second network node is configured to direct the second communication path between the mobile station and the core network via the second cell, the second network node and the first network node if establishment of a connection between the second network node and the core network fails.

The core network can include a circuit switched network, a packet switched network or both a circuit switched network and a packet switched network.

In the case where the core network includes both a circuit switched network and a packet switched network, the first communication path and the second communication path can be from the mobile station to both the circuit switched network and the packet switched network. The second network node can then be configured to establish a connection with both the circuit switched network and the packet switched network . Preferably, the first and second network nodes are control nodes. In this case, the first network node may be a target RNC and the second network node may be a source RNC.

Embodiments of the invention also provide a first network node couplable to a core network and to mobile station such that a communication path can be established between the mobile station and the core network via the first network node, wherein the first network node is configured to connect to a second network node, to attempt to establish a direct connection to the core network, and to establish a path to the core network via the second network node if establishment of the direct connection to the core network fails .

Before attempting to establish a direct connection to the core network, the first network node can "anchor" the second network node to the communication path (or, rather, anchor back the communication path to the second network node before it is dropped from the communication path during handover) . This means that if establishment of a direct connection between the first network node and the core network fails, a communication path can still be established between a mobile station and the core network via the second network node. This provides the advantage that an ongoing call being made by the mobile station will not be dropped.

A switch may be provided, which is configured to switch the communication path from a first path from the mobile station to the first network node to the second network node to the core network to a second path from the mobile station to the first network node to the core network if establishment of a direct connection to the core network is successful.

The core network may be a circuit switched network or a packet switched network. Alternatively, the core network may include a circuit switched network and a packet switched network.

The first network node may be configured to establish the communication path from the mobile station to both the circuit switched network and the packet switched network .

Preferably, the first network node is a control node, for example an RNC .

The invention will now be described, by way of example only, with reference to specific embodiments, and to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a simplified schematic diagram of a communications network according to an embodiment of the invention;

Figure 2 is a flow diagram illustrating a method according to an embodiment of the invention; Figure 3 is a simplified schematic diagram illustrating communication paths in a communications network according to an embodiment of the invention;

Figure 4 is a message flow diagram illustrating message flow in a method according to an embodiment of the invention;

Figure 5 is a simplified schematic diagram of a communications network according to an embodiment of the invention;

Figure 6 is a flow diagram illustrating a method according to an embodiment of the invention;

Figure 7 is a message flow diagram illustrating message flow in a method according to an embodiment of the invention; and

Figure 8 is a message flow diagram illustrating message flow in a method according to an embodiment of the invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Figure 1 schematically shows a communications network. A mobile station or user equipment (UE) 1 can access the communications network via base stations or Node Bs NB1 and NB2 in cells CI and C2, respectively. The communications network has a radio access network (RAN) part 2, which includes the cells CI and C2 (and therefore the Node Bs NB1 and NB2) as well as radio network controllers (RNCs) Rl and R2 for controlling the cells CI and C2, respectively. Furthermore, the communications network includes a core network part CN. In this embodiment, the core network CN is a single core network; i.e., it may be a packet switched network or a circuit switched network but not both.

Each of the Node Bs NB1 and NB2 are connected to the respective RNCs Rl and R2 over an Iub interface. The Node B NB1 is connected to the RNC Rl and the Node B NB2 is connected to the RNC R2. The RNCs Rl and R2 are connected to each other over an Iur interface and both RNCs Rl and R2 are coupled to the core network part CN of the communications network over an IuC interface .

Figure 2 is a flow diagram illustrating enhanced relocation according to an embodiment of the invention. The UE 1 initially accesses the network via the cell CI and is handed over in step SI to the cell C2 so that the RNC Rl in this case is a serving RNC (S-RNC) and the RNC R2 is a target RNC (T-RNC) . As shown in Figure 3, illustrated by path PI, the communication path is initially from the UE 1 to the cell CI; from the cell CI (over the Iub interface) to the S-RNC Rl ; from the S-RNC Rl (over the IuC interface) to the core network CN (UE 1 - CI - Rl - CN) .

The S-RNC Rl is "anchored" to the communication path (step S2) by instructing the T-RNC R2 to save resources on the Iur interface before the S-RNC Rl is removed from the communication path (step S3) . A direct connection is then established from the T-RNC R2 to the core network CN (step S4) . However, if the direct connection established between the T-RNC R2 and the core network CN fails, the communication path may still be directed to the core network CN via the S-RNC Rl due to the S-RNC Rl being anchored to the communication path so that it is between the UE1 and the core network CN via the cell C2 ; from the cell C2 (over the Iub interface) to the T-RNC R2 ; from the T- RNC R2 (over the IuC interface) to the S-RNC Rl (over the Iur interface) ; from the S-RNC Rl (over the IuC interface) to the core network CN illustrated by path P2 in Figure 3. If on the other hand the direct connection between the T-RNC R2 and the core network CN is successfully established, enhanced relocation of the communication path between the UE 1 and the core network CN may take place directly via the cell C2 and the T-RNC R2, illustrated by path P3 shown in Figure 3.

The message flow which takes place during enhanced relocation when there is a single core network and establishment of the direct connection between the T- RNC and the core network CN is illustrated in Figure 4 and described below.

The S-RNC Rl informs T-RNC to keep the Iur resource even after the RNSAP: Enhanced Relocation procedure is completed in RNSAP: Enhanced Relocation Request message. A new information element IE_A is introduced into the message for this indication.

If the T-RNC R2 supports keeping the Iur resource, the T-RNC R2 informs the S-RNC Rl that the T-RNC R2 will keep the Iur resource in the RNSAP Enhanced Relocation Response message, thereby anchoring the S-RNC Rl to the communication path. A new information element IE_B is introduced into the message for this indication. After the completion of the Enhanced Relocation at the RAN side of the network, the T-RNC R2 informs the core network CN that Iur anchoring of the S-RNC Rl is possible in case of failure in the RANAP Enhanced Relocation Complete Request message. A new information element IE_C is introduced into the message for this indication .

After reception of a RANAP: Enhanced Relocation Complete Failure message, the T-RNC R2 informs the S- RNC Rl that the S-RNC Rl should execute the anchoring back, i.e. restart to use the Iur resource in RNSAP: Enhanced Relocation Release. A new information element IE_D is introduced into the message for this indication. Alternatively, a new RNSAP: Enhanced Relocation Failure message may be introduced for the T-RNC R2 to signal to the S-RNC Rl that it should again start to use the Iur resource.

After the reception of the indication (the new information element IE_D or the new RNSAP Message) for instructing it to use the anchoring back, the S-RNC Rl starts to use the Iur interface resource again and informs the UE 1 that S-RNC Rl is changed by using an RRC message.

In case that there are multiple core networks, the invention can be implemented as described in the following example in a similar manner to a single core network implementation.

Figure 5 schematically shows a communications network similar to that shown in Figure 1, except that there are multiple core networks. In other words, the core network CN includes at least a packet switched network PS and a circuit switched network CS . A mobile station or user equipment (UE) 10 can access the communications network via base stations or Node Bs NBlo and NB20 in cells CIO and C20, respectively. The communications network has a radio access network (RAN) part 20, which includes the cells CIO and C20 (and therefore the Node Bs NB10 and NB20) as well as radio network controllers (RNCs) RIO and R20 for controlling the cells CIO and C20, respectively.

In this embodiment, the core network CN includes both a circuit switched network CS and a packet switched network PS .

Each of the Node Bs NB10 and NB20 are connected to the respective RNCs RIO and R20 over an Iub interface. The Node B NB10 is connected to the RNC RIO and the Node B NB20 is connected to the RNC R20. The RNCs RIO and R20 are connected to each other over an Iur interface and both RNCs RIO and R20 are coupled to both the circuit switched network CS and the packet switched network PS of the communications network over an IuCS and an IuPS interface, respectively.

The UE 10 initially accesses the network via the cell CIO and is handed over to the cell C20 so that the RNC R10 in this case is a serving RNC (S-RNC) and the RNC R20 is a target RNC (T-RNC) (although both S-RNC R10 and the T-RNC R20 may be structurally and functionally exactly the same as each other) .

In an embodiment according to the invention illustrated in the flow chart shown in Figure 6, a communication path between the UE 10 and the core network (the circuit switched network CS and the packet switched network) is relocated during handover of the UE 10 from the cell CIO to the cell C20. The T-RNC R20 is connected to the S-RNC RIO over the Iur interface in step S10 and the S-RNC RIO instructs the T-RNC R20 to save Iur resources so that the S-RNC RIO is anchored to the communication path.

The T-RNC R20 then attempts to establish a direct connection to both the circuit switched network CS and the packet switched network PS in step Sll. If the attempt to establish a direct connection from the T- RNC R20 to both the circuit switched network CS and the packet switched network PS fails (step S12), a path is established from the T-RNC R20 to the circuit and packet switched networks CS and PS via the S-RNC RIO over the Iur interface (step S13) . This means that the communication path between the UE 10 and the circuit and packet switched networks is via both the S-RNC RIO and the T-RNC R20, even though the UE 10 is accessing the network via the cell C2 controlled by the T-RNC R20. In this way, any calls or data transfer to and from the UE 10 are not dropped in the event that the T-RNC R20 fails to establish a connection directly with the circuit and packet switched networks CS and PS. On the other hand, if establishment of a direct connection from the T-RNC R20 to both the circuit and packet switched networks CS and PS is successful, the communication path between the UE 10 and the circuit and packet switched networks CS and PS is only via the T-RNC R20 after handover (step S14) .

The message flow between the S-RNC R10 and the T-RNC R20 in the event of failure to establish a connection between the T-RNC R20 and multiple core networks is illustrated in the message flow diagram in Figure 7 and described below.

The S-RNC RIO informs the T-RNC R20 to keep the Iur resource even after the RNSAP: Enhanced Relocation procedure is completed in the RNSAP: Enhanced Relocation Request message. A new information element IE_A is introduced into the message for this indication .

If the T-RNC R20 supports keeping of the Iur resource after completion of the RNSAP: Enhanced Relocation procedure, the T-RNC R20 informs the S-RNC RIO that the T-RNC R20 will keep the Iur resource in the RNSAP Enhanced Relocation Response message. A new information element IE_B is introduced into the message for this indication.

In addition, the following steps are performed.

After the completion of the enhanced relocation in the RAN side of the network, the T-RNC R20 informs the core network CN (including at least the circuit switched and the packet switched networks CS and PS) that (1) Iur anchoring is possible in case of failure of connection between the T-RNC R20 and the core network CN (using a new information element IE_C) and (2) the core network CN shall not release the old Iu resource until it does not receive a RANAP Enhanced Relocation Complete Confirm message (a new information element IE_E is introduced into the message for this indication) in the RANAP Enhanced Relocation Complete Request message. In case of failure in at least one of the packet switched network PS and/or the circuit switched network CS, after the reception of RANAP : Enhanced Relocation Complete Failure message, the T-RNC R20 sends a newly defined RANAP: Enhanced Relocation Cancel message to any core network nodes that have successfully executed Enhanced Relocation, in order to inform them to switch back to the previous Iu resource .

After having received the RANAP: Enhanced Relocation Cancel message, the CN nodes that have successfully executed Enhanced Relocation send a newly defined RANAP: Enhanced Relocation Cancel Confirm to the T-RNC R20 in order to confirm the Enhanced Relocation procedure has been cancelled. In an alternative embodiment, the CN nodes not sending this message to the T-RNC R20 indicates that the Enhanced Relocation procedure has been cancelled.

After the reception of the RANAP: Enhanced Relocation Cancel Confirm message, the T-RNC R20 informs the S- RNC RIO to execute anchoring back; i.e. to restart to use the Iur resource in RNSAP: Enhanced Relocation Release. A new information element IE_D is introduced into the message for this indication. Alternatively, a newly defined RNSAP: Enhanced Relocation Failure message may be sent from the T-RNC R20 to the S-RNC RIO to inform it to start using the Iur resource again in the RNSAP: Enhanced Relocation Release. In case this alternative solution is employed, the T-RNC R20 sends the RNSAP: Enhanced Relocation Failure message after having sent the RANAP: Enhanced Relocation Cancel message to all the CN nodes that have successfully executed Enhanced Relocation. After the reception of the indication for the anchoring back, the S-RNC RIO starts using the Iur resource again and informs the UE 10 that SRNC is changed by RRC message.

The message flow between the S-RNC RIO and the T-RNC R20 in the event of successful relocation and establishment of a direct connection between the T-RNC R20 and multiple core networks is illustrated in the message flow diagram in Figure 8 and described below.

The S-RNC RIO informs T-RNC R20 to keep the Iur resource even after the RNSAP: Enhanced Relocation procedure is completed in RNSAP: Enhanced Relocation Request message. A new information element IE_A is introduced into the message for this indication.

If the T-RNC R20 supports keeping the Iur resource, the T-RNC R20 informs the S-RNC RIO that it will keep the Iur resource in the RNSAP Enhanced Relocation Response message. A new information element IE_B is introduced into the message for this indication.

After completion of the Enhanced Relocation in the RAN side of the network, the T-RNC R20 informs the core network CN (including at least the circuit and packet switched networks CS and PS) that (1) Iur anchoring is possible in case of failure (using a new information element IE_C provided in the signalling between the T- RNC R20 and the S-RNC RIO) and (2) the core network CN shall not release the old Iu resource until it does not receive a RANAP Enhanced Relocation Confirm message (a new information element IE_E is introduced into the message for this indication) in the RANAP Enhanced Relocation Complete Request message.

In case of successful relocation, after the reception of all RANAP: Enhanced Relocation Complete Response messages from all CN nodes (including at least the circuit switched network CS and the packet switched network PS), the T-RNC R20 sends RANAP: Enhanced Relocation Complete Confirm messages to all the CN nodes involved to inform them the Enhanced Relocation procedure has completed.

After the Enhanced Relocation procedure has completed, all CN nodes send a RANAP: Iu Release Command to the S-RNC RIO in order to release the lur resource. The S- RNC replies with RANAP: lur Release Complete.

For the purpose of the present invention as described herein above, it should be noted that

- method steps likely to be implemented as software code portions and being run using a processor at a network control element or terminal (as examples of devices, apparatuses and/or modules thereof, or as examples of entities including apparatuses and/or modules therefore) , are software code independent and can be specified using any known or future developed programming language as long as the functionality defined by the method steps is preserved;

generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the embodiments and its modification in terms of the functionality implemented;

- method steps and/or devices, units or means likely to be implemented as hardware components at the above- defined apparatuses, or any module (s) thereof, (e.g., devices carrying out the functions of the apparatuses according to the embodiments as described above) are hardware independent and can be implemented using any known or future developed hardware technology or any hybrids of these, such as MOS (Metal Oxide Semiconductor), CMOS (Complementary MOS), BiMOS

(Bipolar MOS), BiCMOS (Bipolar CMOS), ECL (Emitter Coupled Logic) , TTL (Transistor-Transistor Logic) , etc., using for example ASIC (Application Specific IC

(Integrated Circuit)) components, FPGA (Field- programmable Gate Arrays) components, CPLD (Complex Programmable Logic Device) components or DSP (Digital Signal Processor) components;

devices, units or means (e.g. the above-defined apparatuses and network devices, or any one of their respective units/means) can be implemented as individual devices, units or means, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device, unit or means is preserved;

- an apparatus may be represented by a semiconductor chip, a chipset, or a (hardware) module comprising such chip or chipset; this, however, does not exclude the possibility that a functionality of an apparatus or module, instead of being hardware implemented, be implemented as software in a (software) module such as a computer program or a computer program product comprising executable software code portions for execution/being run on a processor;

- a device may be regarded as an apparatus or as an assembly of more than one apparatus, whether functionally in cooperation with each other or functionally independently of each other but in a same device housing, for example. In general, it is to be noted that respective functional blocks or elements according to above- described aspects can be implemented by any known means, either in hardware and/or software, respectively, if it is only adapted to perform the described functions of the respective parts. The mentioned method steps can be realized in individual functional blocks or by individual devices, or one or more of the method steps can be realized in a single functional block or by a single device.

Generally, any method step is suitable to be implemented as software or by hardware without changing the idea of the present invention. Devices and means can be implemented as individual devices, but this does not exclude that they are implemented in a distributed fashion throughout the system, as long as the functionality of the device is preserved. Such and similar principles are to be considered as known to a skilled person.

The terms "user equipment (UE) " and "mobile station" described herein may refer to any mobile or stationary device including a mobile telephone, a portable computer, a mobile broadband adapter, a USB stick for enabling a device to access to a mobile network, etc.

Although the invention has been described hereinabove with reference to specific embodiments, it is not limited to these embodiments and no doubt further alternatives will occur to the skilled person that lie within the scope of the invention as claimed.

Claims

1. A method of relocating a communication path between a mobile station and a core network, the method comprising:

connecting a first network node to a second network node;

attempting to establish a direct connection from the first network node to the core network; and establishing a path from the first network node to the core network via the second network node if attempting to establish a direct connection from the first network node to the core network fails such that a communication path between the mobile station and a core network via the first network node and the second network node is established.

2. The method according to claim 1, wherein the step of connecting comprises anchoring the communication path to the second network node.

3. The method according to claim 2, wherein the step of anchoring comprises instructing the second network node to save resources associated with the communication path.

4. The method according to claim 2 or claim 3, wherein the core network is a circuit switched network

5. The method according to claim 2 or claim 3, wherein the core network is a packet switched network.

6. The method according to claim 4 or claim 5, wherein the core network includes a circuit switched network and a packet switched network.

7. The method according to claim 6, wherein the communication path is from the mobile station to both the circuit switched network and the packet switched network .

8. The method according to claim 7, comprising attempting to establish a direct connection between the first network node and both the circuit switched network and the packet switched network.

9. The method according to any of claims 1 to 8, wherein the first network node and the second network node are control nodes.

10. The method according to claim 9, wherein the first network node is a target RNC and the second network node is a source RNC.

11. A communications network, comprising:

a first network node related to a first cell; and

a second network node related to a second cell and coupled to the first network node, wherein

the first network node is configured to hand over a first communication path from a mobile station to a core network via the first cell and the first network node to a second communication path from the mobile station to the core network via the second cell, the second network node and the first network node, and

the second network node is configured to anchor the first network node to the second communication path, to remove the anchored first network node from the second communication path, and to establish a connection between the second network node and the core network after it has removed the anchored first network node from the second communication path such that the second communication path from the mobile station to the core network is relocated via the second cell and the second network node.

12. The communications network according to claim 11, wherein the second network node is configured to direct the second communication path between the mobile station and the core network via the second cell, the second network node and the first network node if establishment of a connection between the second network node and the core network fails.

13. The communications network according to claim 11 or claim 12, wherein the core network is a circuit switched network.

14. The communications network according to claim 11 or claim 12, wherein the core network is a packet switched network.

15. The communications network according to claim 11 or claim 12, wherein the core network includes a circuit switched network and a packet switched network.

16. The communications network according to claim 15, wherein the first communication path and the second communication path are from the mobile station to both the circuit switched network and the packet switched network .

17. The communications network according to claim 16, wherein the second network node is configured to establish a connection with both the circuit switched network and the packet switched network.

18. The communications network according to any of claims 11 to 17, wherein the first and second network nodes are control nodes.

19. The communications network according to claim 18, wherein the first network node is a target RNC and the second network node is a source RNC.

20. A first network node couplable to a core network and to a mobile station such that a communication path can be established between the mobile station and the core network via the first network node, wherein the first network node is configured to connect to a second network node, to attempt to establish a direct connection to the core network, and to establish a path to the core network node via the second network node if establishment of the direct connection to the core network fails.

21. The first network node according to claim 20, further comprising a switch configured to switch the communication path from a first path from the mobile station to the first network node to the second network node to the core network to a second path from the mobile station to the first network node to the core network if establishment of a direct connection to the core network is successful.

22. The first network node according to claim 20 or claim 21, wherein the core network is a circuit switched network.

23. The first network node according to claim 20 or claim 21, wherein the core network is a packet switched network.

24. The first network node according to claim 20 or claim 21, wherein the core network includes a circuit switched network and a packet switched network.

25. The first network node according to claim 24, further configured to establish the communication path from the mobile station to both the circuit switched network and the packet switched network.

26. The first network node according to any of claims 20 to 25, wherein the first network node is a control node.

27. The first network node according to claim 26, wherein the first network node is a target RNC .