Method and system for handover of video calls from a packet switched network to a circuit switched network in a single radio environment

Description of equivalent WO 2011139083 A2

METHOD AND SYSTEM FOR HANDOVER OF VIDEO CALLS FROM A PACKET SWITCHED NETWORK TO A CIRCUIT SWITCHED NETWORK IN A SINGLE RADIO ENVIRONMENT

The present invention relates to the field of wireless communication systems, more particularly relates to handover of video call from a packet switched network to a circuit switched network in a single radio environment.

A SAE/LTE system is a packet switched (PS) system in which voice and video calls are "natively" established through a PS domain. Therefore as a "default option", voice calls uses the PS domain as packet video-calls and underlying call control protocol is SIP supported through an IP multimedia subsystem (IMS). Recently, there has been a slow migration of users from the SAE/LTE domain from the CS domain to the LTE packet switched domain. Hence, the LTE system may be deployed in "islands" overlaying parts of the CS domain. This means that if a user makes a video-call over the LTE, the video-call may not be just subject to an intra-domain handover (i.e., radio-level and intra-network-level handover) but is also likely to be subject to an inter-domain handover from the LTE packet domain to the CS domain due to mobility of the user during the video-call. This lead to the development of a functionality called Single Radio Voice Call Continuity (SRVCC) in the third generation partnership project (3GPP) technology. SRVCC is a functionality that allows a voice/video call in the LTE packet domain to be moved to the CS domain.

CS video-calls support a feature called "Service change for UDI/RDI fallback" (normally referred to as SCUDIF). This service is available to UDI/RDI multimedia calls and allows the users to achieve successful call establishment when end-to-end circuit-switched (CS) multimedia is not possible (fallback to speech) or when signalling of the feature is not possible in the CS network (fallback to preferred service or speech). Furthermore, it allows the users to swap between a multimedia service and basic speech during an established call.

Nevertheless, in the case that the call (either voice-call or video-call) has been established in the IMS, there is no negotiation that normally takes place between an user equipment (UE) and a mobile service centre (MSC) in order to mutually identify whether both the UE and MSC support the SCUDIF feature, hence it is not possible to use the SCUDIF feature when the UE moves to the CS domain from the PS domain. For example, if a voice/video call has been initiated with the PS network and later handed over to the CS network using an SRVCC, there is no communication that takes place between the UE and the MSC during the call setup time. As a consequence, the UE and the MSC are unaware of each other’s SCUDIF capabilities (user-initiated or network-initiated) when the voice/video call is transferred to the CS network.

Further, a delay may be introduced by H.324 when performing the following steps for call setup:

- H.223 Multiplexer level detection

- Terminal Capability Exchange

- Master Slave determination

- Open Logical Channels

- Multiplexer Table Entries Exchange

The procedure typically takes 5 ~ 8 seconds. If link quality deteriorates or media configurations between UEs are not well-matched, this delay may increase even further. The delay can be suppressed to as low as a few seconds in the limited cases when the acceleration techniques are supported by both UEs and little data is lost during the period. However, the call set up procedure of 3G-324M, outlined above, is likely to occur at cell edges under the SRVCC situations where radio link is unstable.

Given that the period of the current SRVCC handover with voice only is significantly smaller (e.g. in the area of 300-500ms) if simultaneous transfer of voice and video is performed when a handover from PS-to-CS network with vSRVCC (given that a 64kbps bearer is established on the UTRAN side and the increased call setup delay of 3G-324M from the negotiation between UEs using H.245 signaling procedures) interruption time might be significantly large, during which a message might be displayed to ask for patience from the user or recently-played video clips might be replayed until newly-decoded scenes become available.

<p num="13">The present invention provides a method and system for performing handover of a video call from a packet switched network to a circuit switched network in a single radio environment. </p>

<p num="14">According to an aspect of the present invention, there is provided a method for performing a handover of a video call from a packet switched network to a circuit switched network in a wireless network environment. The method includes detecting a need to perform a video single radio voice call continuity (vSRVCC) handover from a packet switched network to a circuit switched network during a video call session in the packet switched network by a network entity associated with the packet switched network, sending a vSRVCC handover request to a network entity associated with the circuit switched network for performing a vSRVCC handover of the video call session; wherein the handover request comprises vSRVCC capabilities of a user equipment (UE) associated with the video call session, and performing a vSRVCC handover procedure for handover of the video call session from the packet switched network to the circuit switched network based on the vSRVCC capabilities of the UE. </p><p num="15">According to another aspect of the present invention, there is provided a system comprising at least one user equipment, a packet switched network, and a circuit switched network, wherein the packet switched network comprises a first network entity for detecting a need to perform a video single radio voice call continuity (vSRVCC) handover from the packet switched network to the circuit switched network during a video call session in the packet switched network, and sending a vSRVCC handover request including vSRVCC capabilities of the at least one UE associated with the video call session to the circuit switched network for performing a vSRVCC handover of the video call session, and wherein the circuit switched network comprises a second network entity for performing a vSRVCC handover procedure for handover of the video call session from the packet switched network to the circuit switched network based on the vSRVCC capabilities of the at least one UE.</p>

Figure 1 is a block diagram of a wireless communication system for performing handover of video calls from a packet switched network to a circuit switched network, according to one embodiment.

Figure 2 is a process flowchart illustrating an exemplary method of performing handover video call sessions from the packet switched network to the circuit switched network, according to one embodiment.

Figure 3 is a process flowchart illustrating an exemplary method of performing the video single radio voice call continuity (vSRVCC) handover procedure based on the vSRVCC capabilities of a user equipment, according to one embodiment.

The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

In the following detailed description of the embodiments of the invention, reference is made to the accompanying drawings that form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that changes may be made without departing from the scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.

Figure 1 is a block diagram of a wireless communication system 100 for performing handover of video calls from a packet switched network to a circuit switched network, according to one embodiment. In Figure 1, the wireless communication system 100 includes a packet switched network 102 having a network entity 104 and a user equipment (UE) 106 communicatively connected to the network entity 104. The wireless communication system 100 also includes the circuit switched network 108 having a network entity 110 (e.g. Mobility Management Entity in LTE networks, serving GPRS service node in case of 3G plus network, etc.).

As can be seen, the packet switched network 102 is overlapping parts of the circuit switched network 108. Consider that, the UE 106 has a video call session through the network entity 104 of the packet switched network 102. In case, the UE 106 moves from the packet switched network 102 to the circuit switched network 108, a handover of the video call from the packet switched network 102 to the circuit switched network has to be performed. The below description is described with reference to Figures 1 and 2.

In an exemplary operation, an eNB 112 connected to the UE 106 detects a need to perform a video single radio voice call continuity (vSRVCC) handover from the packet switched network 102 to the circuit switched network 108 during the video call session (as in step 202 of Figure 2). The term 'video call session' refers to ongoing video call or a video call in alerting state. For example, the eNB 112 detects a need to perform a vSRVCC handover based on parameters in measurement reports received from the UE 106. The eNB 112 then communicates the need to perform the vSRVCC handover procedure to the network entity 104.

Accordingly, the network entity 104 sends a vSRVCC handover request to the network entity 110 for performing a vSRVCC handover of the video call session (as in step 204 of Figure 2). Exemplary vSRVCC handover request is given in 'Table 1'. In some embodiments, the network entity 104 communicates the vSRVCC capabilities of the UE 106 associated with the video call session to the network entity 104 in the vSRVCC handover request. The vSRVCC capabilities include a service change and unrestricted digital information fallback (SCUDIF) capabilities, a first set of bearer capabilities, a second set of bearer capabilities, and bearer capability elements associated with the UE 106. The SCUDIF capabilities indicate support for user initiated service change and fallback or network initiated in-call modification (ICM). Exemplary vSRVCC capabilities of the UE 106 are given in 'Table 2'. In these embodiments, the UE 102 shares the vSRVCC capabilities with the eNB 112 during an initial attach procedure with the network entity 104.

Table 1 <tables id="tabl01" num="1"><img file="WO2011139083A2_D0001.tif" /></tables>

Table 2 <tables id="tabl02" num="2"><img file="WO2011139083A2_D0002.tif" /></tables>

<img file="WO2011139083A2_D0003.tif" />

<img file="WO2011139083A2_D0004.tif" />

In one exemplary implementation, the eNB 112 shares the SCUDIF capabilities with the network entity 104 during the initial attach procedure itself. The network entity 104 then stores the SCUDIF capabilities in its memory. It can be noted that, the eNB 112 communicates the first and second sets of bearer capabilities and bearer capability elements to the network entity 104 while communicating a need for performing a vSRVCC handover procedure. Upon receiving the vSRVCC handover request, the network entity 110 performs a vSRVCC handover procedure to handover the video call session from the packet switched network 102 to the circuit switched network 108 based on the vSRVCC capabilities of the UE 106 (as in step 206 of Figure 2). The process of performing the vSRVCC handover procedure is explained in greater detail in description of Figure 3.

Figure 3 is a process flowchart 300 illustrating an exemplary method of performing the vSRVCC handover procedure based on the vSRVCC capabilities of the UE 106, according to one embodiment. When the vSRVCC handover request is received from the network entity 104, it is determined whether the UE 106 supports a network initiated in-call modification and services corresponding to the first set of bearer capabilities and the second set of bearer capabilities based on the vSRVCC capabilities in the vSRVCC handover request, at step 302.

If the UE 106 supports the network initiated in-call modification procedure, then at step 304, the network initiated in-call modification procedure for handover of the video call session from the packet switched network to the circuit switched network is performed. In one embodiment, a SRVCC handover procedure for establishing a voice call session associated with the video call session is performed. Then, a video component is added to the established voice call session by performing the network initiated in-call modification procedure to complete the voice and video SRVCC handover.

If the UE 106 does not support the network initiated in-call modification procedure, then it is determined whether the UE 106 supports an user-initiated service change and fallback and services corresponding to the first set of bearer capabilities and the second set of bearer capabilities based on the vSRVCC capabilities in the vSRVCC handover request, at step 306. If the UE 106 supports user-initiated service change and fallback, then at step 308, a request to perform the user-initiated service change and fallback procedure is received from the UE 106.

At step 310, the user initiated service change and fallback procedure is performed based on the received request. In one embodiment, a SRVCC handover procedure for establishing a voice call session associated with the video call session is performed based on the received request. Then, a video component is added to the already established voice call session by performing the user-initiated service change and fallback procedure. If the UE 106 does not support user-initiated service change and fallback, then at step 312, the ongoing voice call associated with the UE 106 is continued based on the vSRVCC capabilities without adding video media component to the ongoing voice call.

In accordance with the one or more embodiments described above, the present invention proposes to include IEs that indicate to MME/SGSN 104, capability of the UE 106 with respect to supporting user-initiated and/or network-initiated SCUDIF.

The MME/SGSN 104 can then later (at the time of the SRVCC handover) pass the relevant information related to the SRVCC for video capability with respect to vSRVCC capabilities through an Sv interface to the MSC 110 in order to determine the right course of action for the handling of the handed over session.

In order for the MSC 110 to execute SCUDIF based network initiated in call modification procedure, it needs to know the bearer capabilities BC1 and BC2 which are provided by the UE 106 in SETUP message during the call establishment procedure. BC1 defines the first preferred service and BC2 defines the less preferred service. At call setup the required call type, 3G-324M, is indicated by the originating UE in the SETUP message with the bearer capability IE parameter with other Rate Adaptation set to "H.223 and H.245". The MSC 110 converts the elements into the basic services subscribed by the UE 106 and checks these values against the UE's 106 subscription. Based on the response from the HSS, the MSC 110 may either proceed with the call or drop it. For the SRVCC handover procedure, since the UE doesn't send the SETUP message towards the MSC 110, the MSC 110 is unaware of BC1 and BC2.

The following methods can be used for resolving this issue:

1. Statically configuring the elements BC1 and BC2 at the MSC 110 for vSRVCC capable UEs.

a. The elements BC1 and BC2 will be statically configured at the MSC and the MSC uses these statically configured values during the vSRVCC handover procedures.

2. To be transferred during video SRVCC handover via the MME 104

a. The eNodeB provides the capability elements BC1 and BC2 to the MME 106 in the handover request. The MME 104 then provides these to the MSC 110 in the vSRVCC handover request over Sv interface during the SRVCC handover procedure.

3. Using SIP procedures

The UE provides BC1 and BC2 to the SCC AS as SDP extensions in the SIP INVITE during the session establishment procedures. The SCC AS provides the BC1 and BC2 information to the MSC 110 as a part of the session transfer procedure using the provisional responses or subscription to the dialog event package.

When the MSC 110 receives the Sv request from the MME/SGSN 104 and the value of the IE is other than 00 (i.e. Video SRVCC is supported) contains the RAB, alternative RAB parameters IE in the RANAP Relocation Request message indicating the RAB configuration for multimedia in addition to the RAB configuration for speech. It then decides based on the logic indicated in whether to initiate enhanced network initiated ICM procedures, wait for user-initiated service change and fallback or follow up with "existing" SRVCC procedures.

The present embodiments have been described with reference to specific example embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the various embodiments. Furthermore, the various devices, modules, selectors, estimators, and the like described herein may be enabled and operated using hardware circuitry, for example, complementary metal oxide semiconductor based logic circuitry, firmware, software and/or any combination of hardware, firmware, and/or software embodied in a machine readable medium. For example, the various electrical structure and methods may be embodied using transistors, logic gates, and electrical circuits, such as application specific integrated circuit.