Method and system for controlling a call handover between telecommunication networks

Abstract

A method for controlling a call handover between telecommunication networks includes determining whether a User Equipment (UE), in communication with a first network, is engaged in a call attempt when the UE is to be transferred from the first network to a second network, if the UE is engaged in a call attempt, maintaining the UE communicating with the first network, and if the UE is not engaged in a call attempt, initiating the handover from the first network to the second network.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an embodiment of a method for controlling handover performed by a network;

FIG. 2 shows an embodiment of a method for controlling handover performed by a UE;

FIG. 3 provides a message flow diagram for call establishment in GSM or UMTS in accordance with an embodiment of the present invention;

FIG. 4 provides a message flow diagram for call establishment in CDMA in accordance with an embodiment of the present invention; and

FIG. 5 provides a message flow diagram for sending an Answer message via an SMS message in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description of various embodiments of the present invention, reference is made to the accompanying drawings, which show, by way of illustration various embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural and functional modifications may be made without departing from the scope and spirit of the present invention.

FIG. 1 shows an embodiment of a method for controlling handover performed by a network when a UE is to be transferred from a first network to a second network. For example, the first network may be a CS domain, and the second network may be an IMS domain. In alternative, the first network may be an IMS domain, and the second network may be a CS domain.

In block 101, the UE detects a signal from the second network when the UE is to be transferred from the first network into an area which is covered by both the first network and the second network. The UE sends a handover request to the second network to initiate the handover from the first network to the second network. In an alternative embodiment, the UE sends the handover request voluntarily without detecting the changing of signals. The UE may be engaged in an on-going call, may be in a standby mode, or may be during a call attempt (a period of call negotiation, ringing, or ring-back tone), when the UE is to be transferred from the first network to the second network.

In block 102, the second network obtains the handover request from the UE and determines whether the UE is during a call attempt (a period of call negotiation, ringing, or ring-back tone).

In block 103, in response to determining that the UE is not during a call attempt, the second network initiates the handover from the first network to the second network. If the UE is not during a call attempt, the UE may be engaged in an on-going call. The on-going call may be handed over to the second network according to VCC. The UE continues the on-going call in the second network. If the UE is in the standby mode, the network hands over the UE connection from the first network to the second network. The UE can now accomplish communication in the second network.

In block 104, in response to determining that the UE is during a call attempt (a period of ringing or ring-back), the second network rejects the handover request. The UE maintains the connection with the first network. In an embodiment, after a connection between the UE and a calling terminal or a called terminal is established, the second network initiates the handover from the first network to the second network. The UE continues the call in the second network. In an alternative embodiment, in response to determining that the UE is during a call attempt (a period of call negotiation, ringing, or ring-back tone), the second network saves the handover request and returns a Pending message to the UE. A Pending message is used to communicate to the UE that the handover request is waiting to be processed or is being processed. The Pending message may be a SIP response message, such as “182 Queued” message, or “183 Session Progress” message. After determining that the UE is not during a call attempt, the second network performs the saved handover request and initiates the handover from the first network to the second network.

In one embodiment of the present invention, after obtaining a handover request from a UE, a second network determines whether the UE is involved in an on-going call. If a call is on-going, the second network hands over the call from the first network to the second network. The UE continues the call in the second network. If a call is not on-going (e.g., the UE is during a call attempt), the UE maintains the connection with the first network. After a connection between the UE and a calling terminal or a called terminal is established (i.e., the call is on-going), the second network hands over the call from the first network to the second network. The UE then continues the call in the second network.

FIG. 2 shows an embodiment of a method for controlling handover performed by the UE when the UE is to be transferred from the first network to the second network. For example, the first network may be a CS domain, and the second network may be an IMS domain. Also, the first network may be an IMS domain, and the second network may be a CS domain.

In block 201, the UE detects the state of a call for the UE when it is to be transferred from a first network to a second network.

In block 202, the UE determines whether a call is on-going.

In block 203, in response to determining that a call is on-going (i.e., the UE is not during a call attempt), the UE sends a call handover request to the second network.

In block 204, the second network obtains the call handover request and hands over the call from the first network to the second network. The UE continues the call in the second network. In this embodiment, the second network does not determine whether the call is on-going.

In block 205, in response to determining that the call is not on-going (i.e., the UE is during a call attempt), the UE maintains the communication with the first network. After the call is on-going (i.e., a connection between the UE and a calling terminal or a called terminal is established), the second network hands over the call from the first network to the second network. The UE then continues the call in the second network.

In an embodiment, the signaling traffic in an IMS domain uses SIP. Whenever the UE is calling or being called in an IMS domain, the state of the call (on-going, call attempt, or standby) can be obtained from the SIP signaling. If the call is on-going when the UE is to be transferred from the IMS domain to the CS domain, the call is handed over from the IMS domain to the CS domain according to VCC. If the UE is during a call attempt when the UE is to be transferred from the IMS domain to the CS domain, the UE maintains the connection with the IMS domain. When the call is on-going, the UE initiates the handover from the IMS domain to the CS domain. After the handover, the UE continues the call in the CS domain. The call is handed over smoothly from the IMS domain to the CS domain when the UE is to be transferred from the IMS domain to the CS domain, providing continuity of the voice call.

The UE is made aware of its call state when being called in a CS domain. The called UE determines whether the call is on-going or whether the called UE is during the period of ringing, when the called UE is to be transferred from the CS domain to the IMS domain. If the call is on-going or the called UE is not during the period of ringing, the called UE initiates the VCC handover from the CS domain to the IMS domain. If the call is not on-going (the called UE is during the period of ringing), the called UE maintains the connection with the CS domain.

A calling UE is made aware of the call state by a CONNECT message in the CS domain of the GSM or UMTS. In GSM or UMTS, a Mobile Switching Center (MSC) communicating with the calling UE sends a CONNECT message to the calling UE after the called user picks up the phone to indicate that the call is received by the called user.

FIG. 3 provides a message flow diagram for call establishment in GSM or UMTS. The detailed flow is as follow:

301: The called UE sends an ALERTING message to the MSC communicating with it.

302: The MSC communicating with the called UE sends an Address Complete Message (ACM) to the MSC communicating with the calling UE to indicate that the called UE is ringing (i.e., the calling UE is during a call attempt).

303: The MSC communicating with the calling UE sends the ALERTING message to the calling UE to indicate that the called UE is ringing.

304: Once the call is received, the called UE sends a CONNECT message to the MSC communicating with it.

305: The MSC communicating with the called UE sends an ANSWER message to the MSC communicating with the calling UE to indicate that the call is on-going (i.e., the connection between the calling UE and the called UE is established).

306: The MSC communicating with the calling UE sends the CONNECT message to the calling UE to indicate that the call is on-going.

The calling UE determines whether to hand over when the calling UE is to be transferred from the CS domain of the GMS or UMTS to the IMS domain according to the messages as the indications of the call states described in above-mentioned flow.

The calling UE can not obtain the information of the call state in a Code Division Multiple Access (CDMA) network because the MSC communicating with the calling UE does not send the call state information to the calling UE. In one embodiment of the present invention, the calling UE can obtain the call state information by an expanded Flash with information (FWI) message.

FIG. 4 provides a message flow diagram for call establishment in CDMA. The detailed flow is as follow:

401: The called UE sends an Allocation Complete message to the MSC communicating with it.

402: The MSC in communication with the called UE sends an ACM to the MSC in communication with the calling UE to indicate that the called UE is ringing (i.e., the calling UE is during the period of ring-back tone).

403: Once the call has been received, the called UE sends a CONNECT message to the MSC communicating with it.

404: The MSC communicating with the called UE sends an ANSWER message to the MSC communicating with the calling UE to indicate that the call is on-going (i.e., the connection between the calling UE and the called UE has been established).

405: The MSC communicating with the calling UE sends the expanded FWI message with the information of the call state to the calling UE to indicate that the call is on-going (i.e., the call is answered).

The calling UE determines whether to hand over when the UE is to be transferred from the CS domain of the CDMA to the IMS domain according to the messages as the indications of the call states described in above-mentioned flow.

The VCC AS that serves as an anchor point for a voice call is aware of the call state. In one embodiment, a calling UE is to be transferred from a CS domain to an IMS domain. The VCC AS detects the call state after obtaining a handover request from the calling UE. If the call state is a call attempt, the VCC AS returns a reject message to the calling UE to reject the handover request, or it returns a Pending message to the calling UE to indicate that the handover request is waiting to be processed. In one embodiment, a Try-After header is inserted in the reject message to indicate that the calling UE can try again after a certain amount of time, such as 10 seconds. In alternative, the calling UE can try again after a certain amount of time voluntarily without the indication of a Try-After header.

In an alternative embodiment, the VCC AS sends the call state information to the calling UE. The VCC AS sends an Answer message to the calling UE to inform the calling UE that the call has entered a “call received” state (i.e., the call is now on-going) after informed by the called UE that the called UE has received the call. The calling UE may send a SUBSCRIBE message to the VCC AS to subscribe for the Answer message. The Answer information may be inserted in a message, which the VCC AS sends to the UE. The calling UE will not initiate the handover until receiving the Answer message from the VCC AS. The calling UE determines whether to hand over according to the information from the VCC AS. In this embodiment, the VCC AS will not determine whether the call is on-going after receiving the handover request from the calling UE. The Answer information may be sent via a Short Message Service (SMS).

FIG. 5 provides a message flow diagram for sending the Answer information via a SMS message. The detailed flow is as follow:

501: The VCC AS sends a Short Message service Delivery Point to Point (SMDPP) message to a Short Message Service Center (SMSC) to ask for a SMS message to the calling UE to indicate that the call has been received by the called UE.

502: The SMSC sends an SMS Request (SMSREQ) message to a Home Location Register (HLR) for obtaining the information of a MSC communicating with the UE.

503: The SMSC sends the SMDPP message with an original address to the MSC communicating with the calling UE to transmit the SMS message.

504: The MSC sends an Application Data Delivery Service (ADDS) Deliver message to a Base Station Controller (BSC) communicating with the calling UE to transmit the SMS message.

505: The BSC sends the SMS message to the calling UE. The information of the call state is included in the SMS text.

506: The calling UE sends an Acknowledge (ACK) message to the BSC.

507: The BSC sends an ADDS Deliver ACK message to the MSC.

508: The MSC sends a SMDPPACK message to the SMSC.

509: The SMSC sends a SMDPP ACK message to the VCC AS to indicate that the SMS message has been sent to the calling UE.

In this embodiment, the calling UE obtains the call state via the SMS message, and determines whether to initiate the handover according to the SMS when the calling UE is to be transferred from the CS domain to the IMS domain. If the calling UE obtains the Answer information from the VCC AS, the calling UE will initiate the handover and send a handover request to the VCC AS. The VCC AS hands over the call from the CS domain to the IMS domain directly when receiving the handover request.

It should be emphasized that the above-described embodiments, particularly, any ‘preferred’ embodiments, are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described preferred embodiments without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the above-described preferred embodiments and protected by the following claims.

Claims

1. A method for controlling a call handover between telecommunication networks, comprising: determining whether a User Equipment (UE), in communication with a first network, is engaged in a call attempt when the UE is to be transferred from the first network to a second network;if the UE is engaged in a call attempt, maintaining the UE communicating with the first network; andif the UE is not engaged in a call attempt, initiating the handover from the first network to the second network.

2. The method of claim 1, wherein whether the UE is engaged in a call attempt is communicated via a Session Initiation Protocol (SIP) signaling.

3. The method of claim 1, wherein whether the UE is engaged in a call attempt is communicated via a message having call state information therein.

4. The method of claim 1, wherein the first network is a Circuit Switched (CS) domain, and the second network is an IP multimedia subsystem (IMS) domain.

5. The method of claim 1, wherein the first network is an IMS domain, and the second network is a CS domain.

6. The method of claim 1, wherein the determining whether the UE is engaged in a call attempt is performed by the UE.

7. The method of claim 1, wherein the determining whether the UE is engaged in a call attempt is performed by a VCC AS.

8. The method of claim 1, further comprising: obtaining a handover request by the second network;if the UE is engaged in a call attempt, rejecting the handover request.

9. The method of claim 1, further comprising: obtaining a handover request by the second network;if the UE is engaged in a call attempt, saving the handover request and returning a Pending message to the UE;processing the saved handover request and initiating the transfer from the first network to the second network when the UE is not engaged in a call attempt.

10. The method of claim 9, wherein the Pending message is used to indicate that the handover request is waiting to be processed.

11. The method of claim 1, wherein the call attempt is a period of call negotiation, ringing, or ring-back tone.

12. A method for controlling a call handover between telecommunication networks, comprising: determining whether a call is on-going when a UE, in communication with a first network, is to be transferred from the first network to a second network;if the call is not on-going, maintaining the UE communicating with the first network; andif the call is on-going, initiating the handover from the first network to the second network.

13. The method of claim 12, wherein whether the call is on-going is communicated via a SIP signaling.

14. The method of claim 12, wherein whether the call is on-going is communicated via a message having call state information therein.

15. The method of claim 12, wherein the first network is a CS domain, and the second network is an IMS domain.

16. The method of claim 12, wherein the first network is an IMS domain, and the second network is a CS domain.

17. The method of claim 12, wherein the determining whether the call is on-going is performed by the UE.

18. The method of claim 12, wherein the determining whether the call is on-going is performed by a VCC AS.

19. The method of claim 12, further comprising: obtaining a handover request by the second network;if the call is not on-going, rejecting the handover request.

20. The method of claim 12, further comprising: obtaining a handover request by the second network;if the call is not on-going, saving the handover request and returning a Pending message to the UE;processing the saved handover request and initiating the transfer from the first network to the second network when the call is on-going.

21. The method of claim 20, wherein the Pending message is used to indicate that the handover request is waiting to be processed.

22. A method for controlling a call handover between telecommunication networks, comprising: determining whether a call is on-going by a UE when the UE is to be transferred from a first network to a second network; andif the call is on-going, sending a call handover request to the second network;wherein the call is handed over from the first network to the second network in response to obtaining the handover request from the UE.

23. The method of claim 22, wherein whether the call is on-going is communicated via a message having call state information therein.

24. A system for controlling a call handover between telecommunication networks, comprising a User Equipment (UE), capable of determining whether a call is on-going when the UE is to be transferred from a first network to a second network;if the call is not on-going, maintaining the communication with the first network; andif the call is on-going, initiating the handover from the first network to the second network.

25. A system for controlling a call handover between telecommunication networks, comprising a voice call continuity application server (VCC AS), capable of determining whether a User Equipment (UE), in communication with a first network, is engaged in a call attempt when the UE is to be transferred from the first network to a second network;if the UE is engaged in a call attempt, maintaining the UE communicating with the first network; andif the UE is not engaged in a call attempt, initiating the handover from the first network to the second network.