Method for changing between a packet-oriented PTT session and a circuit-oriented telephone connection between at least two radio communication appliances, associated radio communication appliance, network component and radio communication system

In order for, by way of example, two users in a radio communication system to be able to use their radio communication appliances to converse with one another or to interchange other user data, a “circuit-oriented”(“circuit switched”) telephone connection is usually set up between these two radio communication appliances using their air interfaces to the radio network. This circuit-oriented telephone connection allows the users of the two radio communication appliances to speak and to listen simultaneously (i.e., to communicate at the same time), using the “full duplex” method (i.e., in the forward and back transmission directions). In this case, the respective circuit-oriented telephone connection which has been set up between the radio communication appliances connected is maintained even if none of the users of the radio communication appliances connected is speaking or, considered in general terms, is transmitting user data. The telephone connection between the two radio communication appliances thus remains continually set up until one of the radio communication appliances actively initiates cleardown of the telephone connection.

By contrast, a “push-to-talk” (PTT) service is advantageous in practice for many communication situations. Such a PTT service involves a number of radio communication appliances, which means that they form a specific PTT group. In this context, only a respective one from a number of connected radio communication appliances simultaneously has an associated transmission authorization for transmitting or sending user data, particularly voice messages, to the remaining radio communication appliances connected to the PTT service. The user of a radio communication appliance is allocated the transmission authorization in this case, by way of example, by virtue of his/her actively requesting it from his/her appropriate network PTT server by pressing a special PTT key on his/her radio communication appliance. If this user presses the PTT key on his/her radio communication appliance first as compared with the other users connected to the PTT service, then he/she is granted the transmission or sending authorization to transmit a voice message or other user data to the other radio communication appliances connected by the PTT server as priority. While he/she keeps the PTT key pressed, only he/she has the transmission authorization allocated by the PTT server, while the ability to send is disabled for the users of the remaining radio communication appliances connected. In this case, the voice or user data are distributed in the radio network, while the sender is actually speaking, from the latter's radio communication appliance to the receiving radio communication appliances in the PTT group virtually in real time, particularly via the appropriate PTT server (streaming). In particular, the PTT server can, in this context, prescribe a maximum authorization period within which sending is possible only for the currently authorized sender. While voice or other user data are being sent by the respective radio communication appliance with authorization to transmit, the other connected radio communication appliances in the same PTT group can merely receive the voice or user messages sent by the radio communication appliance with authorization to transmit, and cannot themselves send or deliver their own voice messages using the PTT server. Only when the user with the current authorization to transmit lets go of or releases the PTT key on his radio communication appliance does he/she relinquish his/her exclusive authorization to transmit. The PTT server then preferably reallocates this authorization to that radio communication appliance whose user pressed the PTT key on his/her radio communication appliance next. In other words, when a voice message is sent by the respective radio communication appliance with authorization to transmit, the remaining radio communication appliances connected to the PTT service only listen to this voice message and cannot interrupt the user of this transmitting radio communication appliance.

In this way, the PTT service makes it possible for just a single radio communication appliance from the group of radio communication appliances connected to the respective PTT service to be able to dispatch or send a voice message or other user data to the radio communication appliances simultaneously using the “half duplex” method without being able to be interrupted by them in the process. Preferably, the respective user of a particular PTT service who has authorization to transmit is able to send one or more receiving radio communication appliances, as members of this PTT service, a voice or user message simultaneously and virtually in real time after he/she has pressed a special PTT key on his radio communication appliance. The users of the one or more receiving radio communication appliances connected to the PTT service are subsequently able to send a response in a corresponding manner when the PTT key has been let go on the radio communication appliance which currently has authorization to transmit. To this end, in turn, only a respective one of the radio communication appliances ready to respond is allocated authorization to transmit by the respective appropriate PTT server, while all the remaining connected radio communication appliances in the PTT group are merely able to receive this response message and are disabled for sending a response while it is being transmitted. Any radio communication appliance which belongs to the same PTT group and wishes to dispatch a voice message or user data is allocated authorization to transmit, on requesting it from the network's appropriate PTT server, in a corresponding manner by the latter, during which the remaining connected radio communication appliances in the PTT group are merely authorized to receive. It may be expedient, in particular, for the user of the respective, receiving radio communication appliance in the PTT group to be able to send voice messages or user data to the PTT server during the actual period of authorization of the respective radio communication appliance with authorization to transmit, or for the PTT server to continue to block forwarding of the voice messages or user data and to perform buffer-storage. Only when the transmission has ended or the maximum permitted authorization period for the current radio communication appliance with authorization to transmit has expired is the allocation of the transmission authorization by the appropriate PTT server controlled such that the latter forwards buffer-stored or current voice messages from that radio communication appliance whose user pressed the PTT key next before any of the other members of the PTT group. In this way, the PTT service is similar, from the user's point of view, to the known “walkie-talkie” service associated with conventional CB radio. Unlike the latter, however, the respective radio communication appliance with authorization to transmit can now also use the radio network in the respective radio communication system to address distant radio communication appliances which are registered with the same PTT service. In particular, the radio communication appliances logged onto the respective PTT service may be in different radio cells in a radio communication system.

Expediently, the maximum permissible authorization period for the transmission right can be set at an upper time limit by the PTT server. In that case, the user of the respective radio communication appliance with authorization to transmit is able to send voice or user messages to the remaining radio communication appliances connected only up to this maximum permissible upper time limit, even if he/she continues to keep his/her PTT key pressed. Furthermore, the respective radio communication appliance may be connected to a number of PTT services simultaneously.

For modem radio communication systems, it is desirable, in particular, to implement such a PTT service on a packet switched basis. In radio communication systems, this is preferably done using the IP multimedia subsystem (IMS) or a suitable system for implementing this. Appropriate activities in this regard are performed on international standardization committees, such as “Open Mobile Alliance (OMA)” and “3rd Generation Project Partnership (3GPP)”.

While the full duplex principle of the circuit-oriented telephone connection between two respective radio communication appliances promotes reciprocal, simultaneous interchange of voice messages and other user data in the forward and back directions, the half duplex method of a PTT service supports the sporadic dispatch of a voice message or of other user data by a single radio communication appliance in the PTT group of this PTT service simultaneously to all members of this PTT group in the forward direction only. If a member of the respective PTT group wishes to make a voice announcement to all other members of this PTT group, then he/she can do so spontaneously after operating a special PTT key, for example. As such, radio resources and radio network resources are used, with a corresponding resultant cost, only if a voice message is actually sent within the PTT group.

A typical instance of application for the PTT service arises, by way of example, when the organization control center in a logistics company wishes to make contact with one or more of its HGV drivers now and again in order to give new instructions. Conversely, it is desirable for the respective HGV driver to return a short voice message or response to the organization control center every now and then. To allow this sporadic sending of voice messages, a PTT session is continuously maintained between the organization control center and the respective HGV driver during work hours. If one of the HGV drivers connected or the organization control center wishes to make a voice announcement to the other connected members of this PTT group, such can be done spontaneously after respectively operating the PTT key on his/her/its radio communication appliance, for example. As such, radio resources and capacities in the radio network are engaged only if voice messages or user data are actually being sent by the respective radio communication appliance with authorization to transmit. In general terms, a PTT session is expedient when, from the point of view of time, voice messages or user data are being sent only now and then, and always in one particular direction of transmission. By contrast, it would be too complicated and too time-consuming in such cases to set up respective individual telephone connections between the respective radio communication appliance with authorization to send and all other receiving radio communication appliances in the respective PTT group involved. Such telephone connections set up on a continuous basis would be too expensive and would engage too much transmission capacity in the radio network and particularly on the air interface for the radio communication appliances connected.

If, by contrast, it is desirable not only to send a single voice message from the respective radio communication appliance to all other radio communication appliances in the respective PTT group in the forward direction, but rather to have a reciprocal discussion or conversation between at least two connected radio communication appliances simultaneously in the forward and back directions, then a PTT session's properties in connection with the half duplex transmission method are more of a drawback. This is because anyone wishing to use his/her radio communication appliance to dispatch a voice message to the other radio communication appliances in a PTT group disables dispatch of a voice message by the receiving radio communication appliances during the transmission period. The receiver thus cannot interrupt the sender or cannot cut him/her short if he/she is currently saying something. In addition, anyone wishing to dispatch a voice message is, in practice, given authorization to speak only if he/she has previously pressed a “PTT key” on his/her radio communication appliance. These are factors which are disadvantageous during a discussion or in the course of a conversation, wherein a telephone connection between the radio communication appliances connected would be more suitable.

The present invention is directed toward providing a way in which the user of a radio communication appliance can be provided flexibly and conveniently with a communication connection which is matched to the respective communication situation.

Accordingly, a method is provided for changing between a packet-oriented PTT session and a circuit-oriented telephone connection as selectable communication connections between at least one first connected radio communication appliance and at least one second connected radio communication appliance in a radio communication system, where a first of these two communication connections is selected and set up by at least one connected radio communication appliance and/or by at least one control unit in the radio network in the radio communication system, and where a change is made from this first communication connection, which has already been set up, to the second communication connection under the control of a radio communication appliance which is connected to the first communication connection and/or under the control of that control unit in the radio network in the radio communication system which is connected to the first communication connection by activating the second communication connection while the first communication connection still exists.

By activating the second communication connection while the first communication connection still exists, it is possible to change between the two communication connections largely fluently: depending on the communication situation involved, the user of the respective connected radio communication appliance can select and change to that of the two communication connection types whose situation is more favorable. The fact that activation of the second communication connection is actually initiated while the respective first communication connection still exists allows the user of the respective radio communication appliance to change from the first to the second communication connection largely seamlessly. Specifically, it is possible to change over from an already existing, packet-oriented PTT session between at least one first radio communication appliance and at least one second radio communication appliance to a circuit-oriented telephone connection between these connected radio communication appliances largely fluently while the PTT session or phase is ongoing. Conversely, it is possible to change over from an already existing circuit-oriented telephone connection which has been set up between at least one first and at least one second radio communication appliance to a packet-oriented PTT session largely fluently by activating the required PTT session while the existing, circuit-oriented telephone connection is still ongoing. This gives the respective user the flexible and convenient selection of that communication connection type which is more specifically suited to his/her respective communication situation currently involved; i.e., he/she is able to select that communication type which is better suited to a specific communication situation. This allows him/her to gear his/her respective communication connection to altered communication requirements on an individual basis.

It can be particularly advantageous if the first radio communication appliance uses the first communication connection, which has already been set up, to send the second radio communication appliance at least one control signal which is used to notify the second radio communication appliance of the request from the first radio communication appliance to change from the first communication connection, which has already been set up, to the second communication connection. Additionally or independently of this, it can be expedient for the first and/or the second radio communication appliance connected to the first communication connection, which has already been set up, to send that control unit which is responsible for the first communication connection, which has been set up, at least one control signal which is used to notify this control unit of the request from the first and/or the second radio communication appliance to change from the first communication connection to the second communication connection. Additionally or independently of this, it can be advantageous if the first and/or second radio communication appliance connected to the first communication connection, which has already been set up, sends that control unit which is responsible for the second communication connection, which needs to be set up, at least one control signal which is used to notify this control unit of the request from the first and/or the second radio communication appliance to change from the first communication connection to the second communication connection. It also may be expedient if the control unit connected to the first communication connection, which has already been set up, sends the control signal relating to the need to change from the first and/or the second radio communication appliance to that control unit which is responsible for activating and setting up the second communication connection.

Advantageously, such a control signal has inserted into it one or more address parameters for that radio communication appliance, connected to the first communication connection, to which the need to change is directed and/or for that radio communication appliance, connected to the first communication connection, from which the need to change issues, and/or at least one identification parameter for distinguishing the first communication connection, which has already been set up, for the second communication connection, which needs to be set up. The identification parameter in the control signal is used to associate the first communication connection, which has already been set up, with the second communication connection, which is yet to be set up, so that an explicit link is brought about between the first communication connection, which has already been set up, and the required, second communication connection.

This provides an association or link between the two communication connections which allows them to be explicitly associated with or related to one another. In this case, the identification parameter (as the link parameter or concatenation parameter) represents the first communication connection, which has already been set up and which is intended to be replaced by the new, second communication connection on the basis of the need for the user of one of the radio communication appliances connected to the first communication connection to change. This makes it possible to indicate, particularly to the respective radio communication appliance to which the need to change is directed, and/or to the control unit which is responsible for the new, second communication connection, that the first communication connection, which already exists, is associated with the second communication connection, to which the change is currently being made. This is advantageous, by way of example, when a change is made from the PTT service to the telephone connection between two connected radio communication appliances, and a telephone call is simultaneously arriving on one of the connected radio communication appliances from a third radio communication appliance, which is not connected to the PTT service. On the basis of the identification parameter, the radio communication appliance in question then receives an explicit indication of that telephone connection which is associated with the preceding PTT session. This implements a type of filter function which allows the respective radio communication appliance to find out or to distinguish which of the telephone calls arriving in parallel is actually associated with the previously existing PTT session. Similarly, the link or the relationship between a telephone connection which has already been set up between at least two radio communication appliances and a subsequent, specific PTT session is also communicated, with the involvement of the same radio communication appliances, when changing from the telephone connection to the PTT session by transferring an identification parameter for the telephone connection to the control unit which is responsible for the second communication connection and/or to that radio communication appliance connected to the first communication connection to which the need to change is directed and/or from which it is initiated. The respective identification parameter transferred, as a representative of the first communication connection, allows, in a particularly advantageous and convenient manner, an automatic change to the new required, second communication connection, without the user of the radio communication appliance to which the need to change is directed needing to intervene actively himself/herself.

Expediently, the identification parameter is sent to the radio communication appliance to which the need to change is directed by another radio communication appliance connected to the first communication connection. If the change is activated and controlled by a control unit in the radio network, then it is expedient for the identification parameters also to be sent to all the radio communication appliances which are connected to the first communication connection and are now affected by the change to the second communication connection.

The present invention also relates to a radio communication appliance having a control unit for performing the inventive method.

In addition, the present invention also relates to a network component having a control unit for performing the inventive method.

Furthermore, the present invention also relates to a radio communication system having a first group of network components for selecting and providing a packet-oriented PTT session and also having a second group of network components for selecting and providing a circuit-oriented telephone connection as selectable communication connections between at least one first connected radio communication appliance and at least one second connected radio communication appliance in a radio communication system, the two groups of network components each having control parts for carrying out the inventive method.

Additional features and advantages of the present invention are described in, and will be apparent from, the following Detailed Description of the Invention.

FIG. 1 shows a schematic illustration of the main components of the network architecture in a radio communication system for setting up a packet-oriented PTT session between at least two radio communication appliances, from which different variants of the inventive method are used to change to a circuit-oriented telephone connection between two connected radio communication appliances.

FIG. 2 shows a schematic illustration of additional network components in the network architecture shown in FIG. 1 , which can be used for simultaneously (i.e., in parallel with the packet-oriented communication connection which has already been set up between the two radio communication appliances), setting up a circuit-oriented communication connection using different variants of the inventive method.

FIG. 3 shows a schematic illustration of the required circuit-oriented telephone connection as a new, second communication connection between the two radio communication appliances shown in FIG. 2 after the PTT session has been cleared down or terminated.

FIGS. 4 and 5 each show a schematic illustration of the interchange of notification and control signals via the radio interfaces of the two radio communication appliances shown in FIG. 1 in order to initiate the latter's changing from the existing, packet-oriented PTT session to the circuit-oriented telephone connection.

FIG. 6 shows a schematic illustration of the signaling flow of information and control signals between components in the radio network shown in FIG. 1 and the radio communication appliance which has the need to change from the PTT session to the circuit-oriented telephone connection, in order to perform a further variant of the inventive method.

FIG. 7 shows a schematic illustration of components of the network architecture shown in FIG. 1 and FIG. 2 for changing from a packet-oriented PTT session to a circuit-oriented telephone connection between two connected radio communication appliances, where a further variant of the inventive method is used to control the changeover between these two communication connection types by a control unit for the PTT service.

FIG. 8 shows a schematic illustration of the signal flow between the network components in the radio network architecture shown in FIG. 1 and FIG. 2 and the first radio communication appliance shown in FIG. 1 , from which the need to change from the latter's previously circuit-oriented telephone connection to a packet-oriented PTT session using a further variant of the inventive method issues.

Elements having the same function and action are each provided with the same reference symbols in FIGS. 1 to 8 .

FIG. 1 schematically shows main components in a network architecture as part of a radio communication system FC which are used to provide two radio communication appliances UE 1 , UE 2 , for example, with a PTT service PC as a first communication connection type. In this case, the first radio communication appliance UE 1 and the second radio communication appliance UE 2 are connected to a common PTT server PTTS 1 , the first radio communication appliance UE 1 being connected via network components, such as PSNW 1 , IMS 1 , MSC 1 , belonging to a first network operator or network provider NWO 1 and the second radio communication appliance UE 2 being connected via network components PSNW 2 , IMS 2 , MSC 2 belonging to a second network operator NWO 2 . The PTT server controls the interchange of voice and/or other user messages between the two radio communication appliances UE 1 , UE 2 in line with the known “push-to-talk” principle. The association between the respective radio communication appliance UE 1 or UE 2 and between its network-allocated components and the respective network operator NWO 1 or NWO 2 is illustrated in FIG. 1 by a dotted dividing line TR. Signaling connections between the respective radio communication appliance and its network-allocated network components from the respective network operator are shown in dashes in FIG. 1 , while associated, separate data connections are shown via solid lines.

Specifically, the first radio communication appliance UE 1 has access to a network-allocated “packet switched network”, that is to say to a packet-oriented radio network PSNW 1 belonging to its provider NWO 1 , via a “radio access network”, which has been omitted in FIG. 1 in the present case for the sake of clarity of the drawing. Such a “packet switched network” can be formed by GPRS (General Packet Radio Service) network, for example. As primary components, it has an “SGSN” (Serving GPRS Support Node) element (i.e., for a GPRS network node SGNS 1 ), and also a “GGSN” (Gateway GPRS Support Node) element or gateway GGSN 1 . The first radio communication appliance UE 1 is connected to the SGSN element SGSN 1 in the “packet switched network” PSNW 1 via a communication connection SL 11 for the purpose of sending control or signaling signals and via a communication connection DL 11 for the purpose of sending user data. Control signals are interchanged between the SGSN element SGSN 1 to the GGSN element GGSN 1 via a signaling connection SL 12 , and data are interchanged via a data connection DL 12 . The GGSN element GGSN 1 provides a signaling connection SL 13 for the CSCF (“Call State Control Function”) element CSCF 1 in an “IP multimedia subsystem (IMS)” IMS 1 . This subsystem is a radio network part which uses the IP protocol to control the communication traffic between the radio communication appliance UE 1 and the PTT server PTTS 1 . The CSCF component CSCF 1 has, in turn, a signaling connection SL 15 for the PTT server PTTS 1 . In this way, the GGSN component GGSN 1 has a signaling connection indirectly via the CSCF component CSCF 1 for the PTT server PTTS 1 . In addition, it has a direct, separate data connection DL 13 for the PTT server PTTS 1 .

Similarly, the second radio communication appliance UE 2 uses a signaling connection SL 21 and a data connection DL 21 to communicate with the SGSN component SGSN 2 in a “packet switched network”; i.e., a packet-switching network part PSNW 2 belonging to his provider NWO 2 . This SGSN component SGSN 2 interchanges control signals via a dedicated connection SL 22 and data signals via a dedicated data connection DL 22 with a GGSN component GGSN 2 which provides a gateway, that is to say an access to the “IP multimedia subsystem” IMS 2 . The GGSN component GGSN 2 provides a direct data connection DL 23 to the common PTT server PTTS 1 . Any signaling in the “IP multimedia system” IMS 2 is routed via a CSCF component CSCF 2 , which is a core element in the “IP multimedia subsystem” IMS 2 . For this purpose, the GGSN component GGSN 2 has a signaling connection SL 23 for the CSCF component CSCF 2 . The CSCF component CSCF 2 is also used to address the common PTT server PTTS 1 using a signaling connection SL 25 . The CSCF component CSCF 2 may also be used to control further application servers if appropriate.

Preferably, the “SIP” protocol (Session Initiation Protocol) is used for the signaling between the two radio communication appliances UE 1 , UE 2 and the common PTT server PTTS 1 and also the interposed network components SGSN 1 , GGSN 1 , CSCF 1 , CSCF 2 , GGSN 2 , SGSN 2 .

If, by way of example, the user of the first radio communication appliance triggered the PTT key on this appliance first, then the PTT server PTTS 1 allocates him/her an authorization to transmit for a maximum authorization period within which he is able to send the second radio communication appliance UE 2 a voice message or other user data under the mediation of the common PTT server PTTS 1 . While the right to send or transmit is being engaged by the first radio communication appliance UE 1 , the PTT server PTTS 1 removes the authorization to transmit from the second radio communication appliance UE 2 ; i.e., it can merely receive messages. Following termination of the sending of voice or user data by the first radio communication appliance UE 1 , which is brought about by letting go of the latter's PTT key, in particular, the PTT server PTTS 1 removes the authorization to transmit from the first radio communication appliance UE 1 . As such, although the first radio communication appliance UE 1 is still able to send voice messages or other user messages to the PTT server PTTS 1 in the form of packet data, the PTT server PTTS 1 disables forwarding thereof to the second radio communication appliance UE 2 and rejects these packet data. Alternatively, these packet data can be buffer-stored until the PTT server PTTS 1 reallocates the transmission authorization to the first radio communication appliance upon a fresh request from the latter's user. This presupposes that the user of the second radio communication appliance UE 2 has not already picked up authorization beforehand and is still speaking.

Considered on a general basis, the user of the respective radio communication appliance is able to press the PTT key on his/her radio communication appliance in order to request from the PTT server the sole authorization to transmit in order to send a message to other connected radio communication appliances occasionally. The PTT server then allocates this requesting radio communication appliance the sole authorization to transmit for a prescribable authorization period if another connected radio communication appliance does not have an earlier time ranking for its authorization request. As such, only one of the radio communication appliances connected to the PTT service is ever allocated the sole transmission right by the PTT server during the same time. In this case, the PTT server controls the forwarding of messages from the radio communication appliance with authorization to transmit. Hence, only the respective radio communication appliance with authorization to send is able to dispatch a message by switching through the common PTT server, while the one or more other radio communication appliances connected to the PTT service can merely receive this message and, for their part, are not simultaneously able to send voice messages to the connected radio communication appliances in the opposite direction. However, packet data transmission allows them to send messages to the common PTT server. There, any messages arriving from them are either rejected or buffer-stored until the radio communication appliance currently authorized to transmit has the authorization to transmit removed from it again by the PTT server. While the messages from the radio communication appliance currently authorized to transmit are being sent in the forward direction to the other connected radio communication appliances, the PTT server thus does not switch through messages from these other radio communication appliances in the opposite direction. While the user of the respective radio communication appliance with authorization to send is speaking, the users of the one or more other connected radio communication appliances can merely listen and cannot interrupt the speaking user of the radio communication appliance with authorization to send while his/her voice message is being dispatched.

Possibly, instead of the PTT server PTTS 1 jointly associated with the radio network parts belonging to the two providers NWO 1 , NWO 2 , a respective dedicated, separate PTT server may be provided for each radio network part belonging to the two providers NWO 1 , NWO 2 . Specifically, the “IP multimedia subsystem” IMS 1 and the “packet switched network” PSNW 1 belonging to the first provider NWO 1 then have just the PTT server PTTS 1 associated with them, while the “IP multimedia subsystem” IMS 2 and the “packet switched network” PSNW 2 belonging to the second provider NWO 2 have a dedicated PTT server PTTS 2 associated with them specifically. This dedicated PTT server is shown additionally by a dash-dot line in FIG. 1 . It has a signaling connection SL 25 * for the CSCF component CSCF 2 and a data connection DL 23 * for the GGSN 2 component GGSN 2 in a similar manner to the communication connection scheme for the PTT server PTTS 1 . The two PTT servers PTTS 1 , PTTS 2 , for their part, have a common communication connection KV 12 between them which can be used to transmit data and/or control signals. The connections DL 23 and SL 25 for the first PTT server PTTS 1 can then be expediently omitted. Preferably, that PTT server which is responsible for the radio communication appliance which initiated or started the PTT session has control over the PTT session. In this case, in the exemplary embodiment shown in FIG. 1 , the PTT session PC has been initiated by the radio communication appliance UE 1 , and therefore the PTT server PTTS 1 specifically allocated by its provider NWO 1 on the network is responsible for controlling the sequence of the PTT session PC. In this case, the second PTT server PTTS 2 forms a passive component and is used merely for simply forwarding the voice messages or user data sent by the first, controlling PTT server PTTS 1 to the second radio communication appliance UE 2 .

It is naturally also possible for the second PTT server PTTS 2 allocated at the reception end to control or coordinate the sending of messages to the second radio communication appliance UE 2 instead of the first, transmission end PTT server PTTS 1 . To this end, the first PTT server PTTS 1 uses the communication connection KV 12 for the purpose of directly routing the voice messages dispatched by the first radio communication appliance UE 1 to the second PTT server PTTS 2 , which then actively regulates or controls delivery thereof.

It may now arise that the users of the two radio communication appliances UE 1 , UE 2 do not wish to send each other just occasional voice messages now and then, but rather wish to hold a reciprocal, continuous conversation or discussion with one another. Since a normal telephone connection is better suited to this altered communication requirement, the activation of a circuit-oriented telephone connection between the radio communication appliances UE 1 , UE 2 connected to the PTT service PC is initiated while the PTT session PC still exists. Considered in general terms, an ongoing PTT session between two or more connected radio communication appliances thus encounters a change to a normal telephone connection between these connected radio communication appliances. In this case, the PTT session is preferably implemented in the “packet switched domain” (i.e., in the packet-oriented network part), using the “IP multimedia subsystem”, while the normal telephone connection is implemented in the “public switched telephone network domain (circuit switched)” (i.e., in a circuit-oriented network part).

In the present exemplary embodiment shown in FIG. 1 with the common PTT server PTTS 1 , the first radio communication appliance UE 1 , for example, initiates the change from the PTT session PC, which has already been set up, that is to say already exists, to a line-oriented telephone connection TC for the second radio communication appliance UE 2 by virtue of its communicating its need to change to the second radio communication appliance UE 2 connected to the PTT session using a control or notification signal IS 1 . In this control signal IS 1 , the first radio communication appliance UE 1 preferably also transmits its own telephone number PN 1 and, in particular, the telephone number PN 2 of the second radio communication appliance UE 2 , which is to be called, to a switching unit MSC 1 , which is responsible for the provider NWO 1 on the network, in the circuit-oriented network part. The switching unit MSC 1 then sends a corresponding control signal IS 1 * with the telephone numbers PN 1 , PN 2 to a switching unit MSC 2 , which is responsible at the reception end, in the circuit-oriented network part belonging to the second provider NWO 2 , with which the second radio communication appliance UE 2 is associated. The switching unit MSC 2 uses a request signal IS 1 ** to ask the user of the second radio communication appliance UE 2 whether the latter accepts the need to change from the first radio communication appliance. The user of the second radio communication appliance acknowledges this using a response signal RIS 1 , which is returned from the switching units MSC 1 , MSC 2 to the requesting radio communication appliance UE 1 . Only in the event of positive acknowledgement of the need to change by the second radio communication appliance UE 2 is a circuit-oriented telephone connection in the forward and back directions made available between the two radio communication appliances by the switching units MSC 1 , MSC 2 . The first radio communication appliance UE 1 can thus use the network components which are responsible for a circuit-oriented telephone connection to initiate setup of a normal telephone connection to the second radio communication appliance UE 2 . In FIG. 1 , for the sake of clarity of the drawing, only the switching units, particularly the “mobile switching centers” MSC 1 , MSC 2 as main components, are shown to represent the components of the circuit-oriented part of the radio network. In this case, the switching unit MSC 1 is associated with the first radio communication appliance, while the second switching unit MSC 2 serves the second radio communication appliance UE 2 .

Possibly, the switching unit MSC 1 , MSC 2 allocated at the transmission end and/or at the reception end may also automatically set up a circuit-oriented telephone connection in the forward and back directions immediately without consulting the user of the second radio communication appliance UE 2 , to which the need to change from the first radio communication appliance UE 1 is directed. In other words, the radio communication appliance with the need to change to the circuit-oriented telephone connection can set up this telephone connection to the second radio communication appliance UE 2 directly, using the switching units MSC 1 , MSC 2 , without the need for it to send the request signal IS 1 ** to the second radio communication appliance UE 2 . For the purpose of activation, it suffices for the first radio communication appliance UE 1 merely to transmit the control signal IS 1 to its responsible switching unit MSC 1 , which then performs all further steps to set up the circuit-oriented telephone connection. This is possible because the switching unit MSC 1 is also sent the telephone number PN 2 of the second radio communication appliance UE 2 in the control signal IS 1 .

If an “SIP” (Session Initiation Protocol) session already exists between the two radio communication appliances UE 1 , UE 2 via the “IP multimedia subsystems” IMS 1 , IMS 2 responsible on the network, the first radio communication appliance UE 1 already knows the SIP address of the second radio communication appliance UE 2 and can therefore send the control or notification signal IS 2 to the second radio communication appliance UE 2 via the components CSCF 1 , CSCF 2 on a direct transmission path, without the interposition of the PTT server PTTS 1 , using the SIP protocol. If appropriate, the radio communication appliance UE 1 wishing to change may also form a “TelURI” as an SIP address from the telephone number (which is known) of the second radio communication appliance UE 2 , if the TelURI is stored on the network. This SIP address formation for the second user may be performed, particularly using the known telephone number of the second radio communication appliance, by a network component, such as the common PTT server PTTS 1 . Preferably, the control signal with the need to change from the user of the first radio communication appliance UE 1 is also routed via the PTT server PTTS 1 to the second radio communication appliance UE 2 , so that it is known to the latter. This notification signal is shown additionally by a dash-dot line in FIG. 1 and is provided with the reference symbol IS 2 *. If the user of the second radio communication appliance UE 2 now accepts the need to change from the user of the first radio communication appliance UE 1 , he/she returns an acknowledgement signal RIS 1 to the latter. In this case, the acknowledgement signal RIS 2 can be actively generated by the user of the second radio communication appliance. In the same way, it may be expedient for the second radio communication appliance UE 2 to generate the acknowledgement signal RIS 2 independently (without consulting its user) and to return it to the requesting, first radio communication appliance UE 1 .

Additionally or independently of this, it also may be expedient for the first radio communication appliance UE 1 to send the PTT server PTTS 1 a control or notification signal relating to its need to change, and for the latter then to forward a notification signal, with mediation by the CSCF component CSCF 1 of the “IP multimedia subsystem” IMS 1 , to the switching unit MSC 1 , which belongs to the circuit-oriented network part of the radio communication system. In FIG. 1 , this notification signal transmitted from the PTT server PTTS 1 to the switching unit MSC 1 via a signaling connection LSM 11 is indicated by a dash-dot arrow denoted by SM 1 . The signaling connection LSM 11 is likewise shown by a dash-dot line there. In general terms, a control unit which is responsible for the PTT session PC which has been set up thus sends a notification signal about the first radio communication appliance's need to change to that network-end control unit which is responsible for activating and setting up the circuit-oriented telephone connection TC. In particular, the control unit for the PTT session is formed by a PTT server in this case. The control unit used for the circuit-oriented telephone connection is an MSC switching unit, in particular.

The control or notification signals IS 1 , IS 2 , IS 2 *, SM 1 additionally can be used to deliver, besides the telephone numbers PN 1 , PN 2 , an identification parameter P 1 , which explicitly identifies the active PTT session, so that the circuit-oriented telephone connection TC which has been freshly set up can be explicitly associated with the existing PTT session PC. The transfer parameters PN 1 , PN 2 , P 1 each appear in brackets after the control signals IS 1 , IS 2 , IS 2 *, SM 1 in FIG. 1 . Only the added identification parameter P 1 is able to bring about an explicit link, coupling or relationship between the already existing, specific PTT session PC and the required telephone connection TC (and vice versa), which makes it possible to distinguish this pair of communication connections PC, TC from other incoming calls and/or other PTT sessions. In particular, this formed pair including associated PTT session and telephone connection can be extracted, or identified, from other, normal telephone calls and/or PTT sessions.

FIG. 2 shows the circuit-oriented telephone connection TC which additionally has been set up between the two radio communication appliances UE 1 , UE 2 . This circuit-oriented telecommunication connection TC now exists in parallel, that is to say simultaneously, with the PTT session PC which has already been set up or exists beforehand and from which the change to the normal telephone connection TC was initiated. In this case, the group of network components for selecting and providing the packet-oriented PTT session PC is denoted by G 1 in FIG. 2 , and the group of network components for selecting and providing the circuit-oriented telephone connection TC is denoted by G 2 . The telephone connection TC which has been set up includes a signaling connection SI 1 and a data connection D 1 to the switching unit MSC 1 allocated on the network from the first radio communication appliance UE 1 . This switching unit is representative of the other components of the circuit-oriented part CSNW 1 of the radio network. The switching unit MSC 1 is linked to the switching unit MSC 2 via a signaling connection SI 12 and a data connection D 12 . The switching unit MSC 2 also represents the other components of the radio network's circuit-oriented part CSNW 2 , which is associated with the second radio communication appliance UE 2 . The second switching unit MSC 2 is likewise connected to the second radio communication appliance UE 2 via a corresponding signaling connection SI 2 and a data connection D 2 .

In the next step, the PTT session PC is cleared down immediately after activation or possibly not until after setup of the circuit-oriented telephone connection TC. This state is shown in FIG. 3 . There, the two radio communication appliances UE 1 , UE 2 no longer have communication connections to the components of the packet-oriented network part or to the PTT server PTTS 1 .

It goes without saying that the change from the packet-oriented PTT session PC to the circuit-oriented telephone connection TC can also be initiated and made by the second radio communication appliance UE 2 in a corresponding manner.

To be able to generate a respective control or notification signal for the change from the communication connection type PTT service to the circuit-oriented telephone connection (and vice versa), the respective radio communication appliance UE 1 or UE 2 has a control unit ST 1 or ST 2 . Preferably, the user of the respective radio communication appliance is provided with an associated selection procedure in the latter's control menu in order to be able to address the control unit in his/her radio communication appliance.

As a generalization, changing from the packet-oriented PTT session PC to the circuit-oriented telephone connection TC involves one or more address parameters for at least one radio communication appliance connected to the PTT session and/or at least one PTT session identification parameter being sent to the control unit which is responsible for the circuit-oriented telephone connection using at least one control signal. Such address parameters are formed, in particular, by the telephone numbers PN 1 , PN 2 of the respective connected radio communication appliance. In the exemplary embodiment shown in FIG. 1 , the PTT server PTTS 1 , as control unit for the PTT session PC, in this case uses the signaling connection LSM 11 to transmit, by way of example, the telephone numbers PN 1 , PN 2 of the two radio communication appliances UE 1 , UE 2 and also the identification parameter P 1 to the control unit MSC 1 in the control signal SM 1 .

If, conversely, a circuit-oriented telephone connection TC has already been set up between the two radio communication appliances UE 1 , UE 2 , and if one of these radio communication appliances UE 1 , UE 2 now wishes to change to a PTT session PC, then one or more address parameters for at least one radio communication appliance UE 1 , UE 2 connected to the circuit-oriented telephone connection TC and also an identification parameter T 1 as an explicit identifier for the circuit-oriented telephone connection are likewise sent, using at least one control signal, to the PTT server PTTS 1 as control unit which is responsible for the packet-oriented PTT session PC. Such a control signal can be generated, in particular, by that control unit which is responsible for the circuit-oriented telephone connection TC, and can be transmitted directly to the control unit which is responsible for the packet-oriented PTT session PC. FIG. 3 additionally shows in a dash-dot line that, by way of example, the switching unit MSC 1 , which is associated with the first radio communication appliance UE 1 , uses a signaling connection LMS 1 to send a control signal MS 1 (IP 1 , IP 2 , T 1 ) via the CSCF component CSCF 1 in the “IP multimedia subsystem” IMS 1 directly to the PTT server PTTS 1 . This control signal MS 1 contains, in particular, the IP or SIP addresses IP 1 , IP 2 of the radio communication appliances UE 1 , UE 2 connected to the circuit-oriented telephone connection TC and also the identification parameter T 1 for the already existing telephone connection TC. The addresses IP 1 , IP 2 of the two radio communication appliances UE 1 , UE 2 for the required, packet-oriented PTT service connection setup are either already known to the switching unit MSC 1 from a previous PTT session, or the switching unit MSC 1 has previously polled the two radio communication appliances UE 1 , UE 2 for these addresses. If appropriate, the respective radio communication appliance wishing to change to the PTT session automatically sends its own packet-oriented address (for the PTT session) and that of the requested interlocutor, or forms these from the telephone numbers which are known to it, particularly in the form of URI (uniform resource identifier) addresses. In this case, the packet-oriented address of the interlocutor may also be polled using a request signal from that radio communication appliance which is activating the change from the circuit-oriented telecommunication connection to the packet-oriented PTT session. This check may be performed, if appropriate, by the network-allocated switching or control unit which is associated with that radio communication appliance which wishes to change from the telephone connection to the PTT session.

As an alternative to control of the change from the circuit-oriented telephone connection TC to the packet-oriented PTT session PC by that control unit which is responsible for the circuit-oriented telephone connection TC, one preferred variant allows that radio communication appliance which is requesting this change to transmit a corresponding control signal to the PTT server directly as well. In FIG. 3 , the first radio communication appliance UE 1 transmits such a direct control signal MS 1 *, which contains the address parameters IP 1 , IP 2 and also the identification parameter T 1 , to the PTT server PTTS 1 via the components SGSN 1 , GGSN 1 , CSCF 1 . In this case, the control signal MS 1 * with the address parameters IP 1 , IP 2 and also with the identification parameter T 1 is generated by the control unit ST 1 in the radio communication appliance UE 1 , that is to say that the radio communication appliance UE 1 fully controls the change from the circuit-oriented telephone connection TC, which has already been set up, to the packet-oriented PTT session PC. If appropriate, the control unit ST 1 can also check the second radio communication appliance UE 2 or the latter's responsible switching unit MSC 2 for the address parameter IP 2 using the already existing telephone connection TC, or can generate the address parameter from the telephone number PN 2 known or sent to it.

Alternatively, on the basis of the control signal MS 1 *, the PTT server instead of the radio communication appliance UE 1 can preferably fully control the change from the circuit-oriented telephone connection TC, which has already been set up, to the packet-oriented PTT session PC. For this purpose, it has a control unit SVS (see FIG. 1 ). The first radio communication appliance UE 1 thus uses the control signal MS 1 * directly to signal to the PTT server PTTS 1 its need to change to a specific PTT service. The PTT server PTTS 1 then takes over control of the further steps for changing.

In summary, a change is made from a first communication connection, which has been set up, to a second communication connection under the control of at least one radio communication appliance connected to the first communication connection and/or at least one control unit (connected to the radio network in the radio communication system) connected to the first communication connection by activating the second communication connection while the first communication connection still exists.

This allows a largely seamless changeover:

1. from a PTT session to a telephone connection, and/or

2. from a telephone connection to a PTT session for the user of the respective connected radio communication appliance. In principle, two solution variants are distinguished in this context:

A—a user-equipment controlled solution, and

B—a network controlled solution.

1. Changeover from a PTT Session to a Telephone Connection:

In a first initial situation, a PTT session has already been set up between two radio communication appliances, such as UE 1 , UE 2 shown in FIG. 1 , that is to say that there is both signaling processing and useful data processing on an IP basis between these two radio communication appliances. The users of the two radio communication appliances now wish to change as seamlessly as possible from the PTT session to a normal telephone connection in the PSTN-CS (Public Switched Telephone Network-Circuit Switched) domain, that is to say in the circuit-oriented part of the radio network.

1.A User-Equipment Controlled Solution:

“User-equipment (UE) controlled solution” refers to that radio communication appliance initiating the change also having and maintaining control over the change. In the exemplary embodiments below, this is always the first radio communication appliance UE 1 (see FIG. 1 ). Starting from the basic principle, this first radio communication appliance UE 1 now sets up a telephone connection via the PSTN-CS (Public Switched Telephone Network-Circuit Switched) network, that is to say via the circuit-oriented part of the radio network, to the second radio communication appliance UE 2 independently of the PTT session. The second radio communication appliance can either take this call automatically or can notify its user of this call in a manner which can be chosen by the user. By way of example, the need for the user of the first radio communication appliance to change can be indicated to the user of the second radio communication appliance visually or audibly. In particular, the identification parameter P 1 which is sent indicates to the user of the second radio communication appliance that the call is part of the PTT session PC already in progress and is not a further call with no relation to the PTT session PC. When the telephone connection has been set up, all the voice data are now routed via the PSTN-CS_based telephone connection instead of via the IP_based PTT session. The PTT session can then be automatically terminated immediately, for example by the first radio communication appliance UE 1 , or only after a certain period of time, such as after 5 minutes. Alternatively, however, it may also continue to be maintained in parallel until the communication between the first and second radio communication appliances UE 1 , UE 2 is terminated finally. Holding the PTT session and simultaneously the telephone connection between the two radio communication appliances UE 1 , UE 2 in parallel makes it possible to change quickly again from the telephone connection to the PTT session at any time, i.e. it is possible to switch flexibly forward and back without the need for completely setting up the respective requested communication connection again.

1.B Network Controlled Solution:

“Network controlled solution” refers to the PTT server, such as PTTS 1 in FIG. 1 , which is used to run the PTT session having control over the change instead of a participating radio communication appliance, as in the variant embodiment 1.A. For this network controlled solution, that radio communication appliance, such as UE 1 , which wishes to change from the PTT session to the telephone connection signals this need to change, using a notification signal, such as IS 2 (see FIG. 1 ) and IS 2 *, to the PTT server, such as PTTS 1 in FIG. 1 . The PTT server then uses a control signal, such as SM 1 , to signal to the switching unit MSC 1 which is responsible for the first radio communication appliance UE 1 in the PSTN-CS domain that a telephone connection needs to be set up between the first and second radio communication appliances UE 1 , UE 2 . The switching unit MSC 1 then starts appropriate activities for setting up the telephone connection. In this case, the radio communication appliances UE 1 , UE 2 can take their respective incoming call, in particular automatically. Alternatively, the respective call may also not be taken until after active acknowledgement by the user of the respective radio communication appliance. As soon as the telephone connection has been made, all voice data are now routed via the PSTN-CS_based telephone connection instead of via the IP_based PTT session. If appropriate, the switching unit which is responsible for the telephone connection, such as MSC 1 in this case, signals to the PTT server that the telephone connection has been successfully set up. As in example 1.A, the PTT session may then be terminated immediately by the PTT server PTTS 1 if appropriate.

2. Changeover from a Telephone Connection to a PTT Session:

In a second initial situation, a normal telephone connection in the PSTN-CS domain has now been set up between the two radio communication appliances UE 1 , UE 2 . The two users of the radio communication appliances UE 1 , UE 2 wish to change from this telephone connection to an IP_based PTT session as seamlessly as possible.

2.A User-Equipment Controlled Solution:

In this context, one of the radio communication appliances connected to the telephone connection again has control over the change. In the present exemplary embodiment, this is the first radio communication appliance UE 1 . In parallel with the existing telephone connection TC, this radio communication appliance UE 1 initiating the change sets up a PTT session PC. As soon as the PTT session is active, all voice data are sent via the PTT session instead of via the telephone connection. The telephone connection is then terminated by the first radio communication appliance UE 1 or is maintained in parallel therewith for a required period of time.

2.B Network Controlled Solution:

In this context, that control unit in the radio network which is responsible for the telephone connection has control over the change to the PTT session. This network-end control unit is preferably formed by that switching unit, such as MSC 1 (see FIG. 1 ), which is associated with the radio communication appliance, such as UE 1 , which has the need to change. The radio communication appliance UE 1 uses a notification signal IS 5 , which is shown additionally by a dash-dot line in FIG. 3 , to signal to its network-allocated switching unit MSC 1 that a change to the PTT session PC is wanted. The switching unit MSC 1 then uses the control signal MS 1 , for example, to signal to the appropriate PTT server that it needs to set up a PTT session between the two radio communication appliances UE 1 , UE 2 . The PTT server PTTS 1 then starts appropriate activities. In particular, it transmits to the two radio communication appliances UE 1 , UE 2 corresponding request signals, for which the radio communication appliances UE 1 , UE 2 can take the PTT session, in particular automatically. These request signals from the PTT server have been omitted in FIG. 3 for the sake of clarity of the drawing. In particular, the user of the respective receiving radio communication appliance can also actively acknowledge the respective incoming request signal for setting up a PTT session by returning a corresponding response signal to the PTT server. As soon as the PTT session is running, all voice data are now routed via the PTT session instead of via the telephone connection. Preferably, the PTT server signals to the switching unit MSC 1 that the PTT session has been successfully set up. The telephone connection may then be terminated immediately by the switching unit MSC 1 if appropriate, or may be maintained in parallel if a later, fast return to the telephone connection by the user is not yet ultimately out of the question.

The network-end control unit which has control over the change to the PTT session is alternatively formed by the PTT server PTTS 1 associated with the radio communication appliance UE 1 . The radio communication appliance UE 1 uses the control or notification signal MS 1 * (which is shown additionally in the form of a dash-dot line in FIG. 3 ) to signal to its network-allocated PTT server PTTS 1 that a change is required from the existing circuit-oriented telephone connection TC to the PTT session PC. The PTT server PTTS 1 then starts appropriate activities, whose further progression has already been explained previously, particularly in the previous paragraph.

The fact that a second communication connection is activated while a first communication connection which has already been set up between at least two connected radio communication appliances still exists allows the users of the services “PTT” and “telephony” to change between these two services in each case without any great complexity and also without interrupting the communication between them. Thus, depending on the current need for communication and the present communication situation, it is possible to use that service which is currently considered to be more agreeable or more advantageous by the users. A particular advantage of the user-equipment controlled solution is that no complex or additional functionalities are required in the radio network for the purpose of implementation. A particular advantage of the network-controlled implementation is that the network elements which have a service's logic and also control the resource and cost outlay, that is to say in this case the switching units MSC 1 , MSC 2 and also the PTT server PTTS 1 , for example, also have technical control over a service change. In the case of this variant, it is then even possible for a service change to be initiated by the network. In that case, it is not necessary for the radio communication appliances connected to be additionally provided with complex control parts. Instead, it is possible to use already existing radio communication appliances.

So that it is possible to change from the first communication connection type to the second communication connection type satisfactorily, that is to say largely without interruption, the user equipment controlled solution preferably involves the user identity in a respective connected radio communication appliance, such as telephone number and/or SIP address, being transferred from one application, such as PTT to the respective other, such as telephony. It is also expedient to extend the signaling about communication of the need to change when additionally setting up the telephone connection or the PTT session such that the respective radio communication appliance at the other end automatically needs to accept the call or the PTT session. In that case, the additional communication connection is implemented in parallel with the existing communication connection without any additional intervention by the user at the other end. In order to be able to produce the association with the first communication connection type when setting up the second communication connection type, and for this association to be explicit, the signaling operations advantageously involve, in addition, an identification parameter, such as T1, which clearly identifies the already existing first communication connection, being concomitantly delivered in the control signal in the respective radio communication appliance with the need to change or in the control signal in the control unit which is responsible for the already existing communication connection on the network.

In the case of the network controlled solution, the radio communication appliance initiating the change, such as UE 1 , transmits a corresponding notification signal to the switching unit which is responsible for it on the network, such as MSC 1 , when a change is required from the PTT session to the telephone connection, and also to the PTT server, such as PTTS 1 , when a change is required from the telephone connection to the PTT session. In response to such a request signal, the appropriate switching unit, such as MSC 1 , sends a control signal, such as MS 1 , to that control unit, such as the PTT server PTTS 1 in this case, which is responsible for the circuit-oriented telephone connection in the event of the need to change from the packet-oriented PTT session to the circuit-oriented telephone connection. Changing from the packet-oriented PTT session to the circuit-oriented telephone connection involves the PTT server, such as PTTS 1 , sending at least one control signal, such as SM 1 , to that control unit in the radio network which is responsible for the circuit-oriented telephone connection. In this context, this control unit is formed, in particular, by that switching unit, such as MSC 1 , which is responsible for that radio communication appliance which initiates the change from the packet-oriented PTT session to the circuit-oriented telephone connection. To acknowledge that a call or a PTT session has been set up successfully, it may be expedient to acknowledge the respectively sent notification signal or control signal in the opposite direction using a response signal.

In practice, the following variant embodiments can be implemented, in particular: