Abstract:
A communication system ( 100 ) includes a first communication unit ( 101, 102, 103, 104 ) capable of communicating over a full-duplex persistent-connection link provided by a full-duplex network ( 105 ) and a second communication unit ( 151, 152 ) capable of communicating over a half-duplex dispatch link provided by a dispatch RF system ( 150 ). The system ( 100 ) also includes a dispatch gateway ( 120 ). The dispatch gateway ( 120 ) receives signals from a first communication unit ( 101, 102, 103, 104 ) over a full-duplex persistent link through a full-duplex network ( 105 ) and provides communication between the first communication unit and a single dispatch communication unit ( 151, 152 ) or a group of dispatch communication units ( 151, 152 ) over a half-duplex communication link through a dispatch RF system ( 150 ). The gateway operates in a manner so as to permit communication between full-duplex terminals ( 101, 102, 103, 104 ) and half-duplex terminals ( 151, 152 ).

Description:
TECHNICAL FIELD 
     The present application is directed to a communication system, and, in particular, to a system, a method and an apparatus for permitting communication between a radio network supporting half-duplex, push-to-talk communication and a network supporting full-duplex, persistent connections. 
     BACKGROUND 
     In two-way radio systems, push-to-talk represents a method of communication in which the talker is required to keep a switch activated while talking. In dispatch call processing, a mobile unit uses a half-duplex link to send voice packets to one or more mobile units. The half-duplex communication mode is referred to as push-to-talk because a button is pushed when transmitting talking and the same button is released when receiving listening. That is, after the user of the first mobile unit depresses the “talk” button, other mobile unit users are prevented from sending packets to other users in the group until the user of the first mobile unit releases the button. 
     A telephone network employs a full-duplex persistent connection, also known as a circuit, between terminals. In such a system, information is continuously transferred between all communicating terminals. Talk from a user of one terminal, however, does not prevent users at other terminals within a group of terminals from talking to other members of the group at any time during a group conversation or conference. All members of the group in the call are permitted equal access and share the voice channel simultaneously. 
     Telephone systems utilizing touch tone telephones employ DTMF Dual Tone Multi-Frequency, which assigns two specific frequencies, or tones, to each key so that it can easily be identified. With DTMF, each key pressed on a phone-terminal generates two tones of specific frequencies. These tones are generated when the user depresses a push button on the terminal. The tones are a form of in-band signaling that maybe interpreted for call-processing within a telephone system. 
     As the need for network interworking becomes more widespread, especially with the deployment of IP networks, there is an increasing need for service providers to interconnect with other networks that are using different signaling protocols. Network providers and operators of radio and telephony networks may employ intermediate systems proxies and call agents which may be used for inter-networking for call routing, call signaling, capabilities exchange, media control, and supplementary services. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of an embodiment of a communication system including an apparatus for communicating between a full-duplex telephony network and a half-duplex radio network. 
         FIG. 2  is an example of the call flow sequence between a full-duplex terminal a telephone network supporting DTMF tones, and a half-duplex radio network. 
         FIG. 3  is a state diagram of the states of an embodiment of the dispatch gateway shown in  FIG. 1  between a full-duplex telephony network and a half-duplex radio network. 
     
    
    
     DETAILED DESCRIPTION 
     This application describes a system, apparatus and method utilizing full-duplex terminals and signaling to establish a connection with a radio network utilizing and responding with push-to-talk. One example of full-duplex terminals is a standard telephone and an example of signaling in the full-duplex network is DTMF. 
     In the context of this application, a call lasts from the time a full-duplex terminal (e.g.,  101 ,  102 ,  103 ,  104  shown in  FIG. 1 ) user dials the telephone number of the dispatch gateway and the switch establishes a circuit connection until the full-duplex terminal user hangs up causing the telephony switch to release the circuit connection. During a call, several dispatch sessions may occur. A dispatch session lasts from the time push-to-talk is successfully initiated by a first user in a dispatch conversation until the time that all users remain idle for at least a preset time interval or until the dispatch system terminates or “drops” the dispatch conversation. Dispatch sessions may be initiated by the full-duplex terminal user or by dispatch RF system users. 
     With more particular reference to  FIG. 1 , a dispatch gateway  120  interacts with a full-duplex network  105 , a dispatch RF system  150  and any intermediary devices that may be used to proxy or redirect the call between these systems. The dispatch RF system  150  may be, for example, the iDEN system produced by Motorola, Inc. of Schaumburg, Ill. Other RF dispatch systems may be used. The full-duplex network  105  may be a telephone network such as the Public Switched Telephone Network PSTN and having Plain Old Telephone Service POTS full-duplex terminal  101 ,  102 ,  103 ,  104   s . While other full-duplex networks may be used, the PSTN example will be the one primarily used in this description for the sake of clarity. 
     In one example scenario, described in  FIG. 2 , the user of a full-duplex terminal  101 ,  102  initiates the call  201  by going off hook and initiating a connection announcement  202  to the full-duplex network  105 . The full-duplex network  105  responds Ready to connect  203 , with, for example, a dial tone sent to the terminal. 
     A gateway request connect  204  is made by the user, for example by dialing a special telephone number using DTMF tones into the full-duplex network  105   205  such as 1-800-DISPATCH. The fall-duplex network  105  relays the connect request to the primary dispatch gateway  206 . The dispatch system responds to the request with an autoresponse message  207 . A connection is established  208  through the dispatch gateway  120  from the dispatch RF system  150  through the full-duplex network  105  to the full-duplex terminal  101 ,  102 ,  103 ,  104 . 
     The user enters a dispatch ID  210  using, for example, DTMF tones that is relayed through the full-duplex network  105  to the dispatch gateway  120 . The user could, for example, enter the dispatch identification number followed by a DTMF key such as “#”. The dispatch identification number may identify an individual or a group of users who have dispatch terminals  151 ,  152  connecting to the dispatch RF system  150  with whom the full-duplex network user wishes to communicate. The dispatch gateway  120  stores this dispatch ID in its memory  122  as the currently active dispatch ID and returns an audible dispatch acknowledgement signal through the switch to the full-duplex terminal  211 . 
     The user initiates a push-to-talk from the full-duplex terminal  101 ,  102 ,  103 ,  104  by, for example, depressing a DTMF key such as “*”, which is interpreted by the dispatch gateway  212 . The DTMF tone initiated in  212  is interpreted by the dispatch gateway as a push-to-talk request, and the dispatch gateway sends a dispatch session initiation request to the dispatch RF system  150 , and if the dispatch RF system  150  accepts the push-to-talk request, the dispatch gateway sends an audible acknowledgement through the switch to the full-duplex terminal  101 ,  102 ,  103 ,  104 . This acknowledgement informs the user that the request to talk has been accepted, that a dispatch session has started, and that the voice channel has been committed for communication  215 . Following this acknowledgement, the user on the full-duplex full-duplex terminal  101 ,  102 ,  103 ,  104  may begin sending voice communication to users of radios supported by the dispatch gateway. If the dispatch RF system  150  does not accept the push-to-talk request and does not initiate a dispatch session because, for example, the half-duplex users are unavailable, the dispatch gateway sends an audible error tone through the switch to the full-duplex terminal  101 ,  102 ,  103 ,  104  informing the user that the request failed. 
     The user of the full-duplex terminal  101 ,  102 ,  103 ,  104  may terminate and return control of the voice channel to the dispatch gateway by depressing a key on the full-duplex terminal  101 ,  102 ,  103 ,  104  keypad  217 . For example, a special key such as “*” will produce a DTMF tone that will be relayed through the full-duplex network  105  to the dispatch gateway and interpreted as a release and termination of push-to-talk. This action is analogous to releasing the push-to-talk button on a half-duplex voice terminal  151 ,  152 . An audible acknowledgement signal  220  will be sent from the dispatch gateway  120  to the full-duplex terminal  101 ,  102 ,  103 ,  104  indicating that push-to-talk has been released and the half-duplex users can reply. 
     A half-duplex radio terminal  151 ,  152  user may reply and initiate voice communication into a full-duplex full-duplex network  105  and supported terminals by depressing the push-to-talk mechanism a button on the radio. The dispatch RF system  150  signals the dispatch gateway that a target user has activated push-to-talk. The dispatch gateway generates a signal  221  that is relayed through the full-duplex network  105 , which in turn relays the signal to the full-duplex terminal  101 ,  102 ,  103 ,  104 . Voice communication initiated from the radio terminal  151 ,  152  to the full-duplex terminal  101 ,  102 ,  103 ,  104  may begin and continues until the half-duplex user releases push-to-talk. 
     The voice initiated by the half-duplex user may be terminated by the release of the push-to-talk mechanism button on the radio terminal  151 ,  152 . The dispatch RF system  150  signals the dispatch gateway that push-to-talk has been released. The dispatch gateway generates an audible signal to indicate release of push-to-talk which is relayed through the full-duplex network  105  to the full-duplex terminal  101 ,  102 ,  103 ,  104 . The full-duplex terminal  101 ,  102 ,  103 ,  104  user may then initiate another push-to-talk with the special DTMF key to continue the conversation. The full-duplex terminal  101 ,  102 ,  103 ,  104  user may also allow the dispatch session to time out after a pre-set time. After the dispatch session times out, the full-duplex terminal  101 ,  102 ,  103 ,  104  user may select another dispatch ID for further communication with another user or group of users. The full-duplex terminal  101 ,  102 ,  103 ,  104  user may also initiate another dispatch session to the same group of users. The full-duplex terminal  101 ,  102 ,  103 ,  104  user may also hang up at any time. The telephone user&#39;s act of hanging up terminates any active dispatch sessions and disconnects the call. Disconnection of the call 226-228 between the radio terminal  151 ,  152  and the full-duplex terminal  101 ,  102 ,  103 ,  104  is completed. All dispatch system and full-duplex network resources are returned. 
       FIG. 2  illustrates communication initiated by the full-duplex network user. In this embodiment, the dispatch user may also initiate communication provided that the full-duplex user is in a call as previously defined herein and provided that the full-duplex user is not in a dispatch session as previously defined herein. The state diagram of  FIG. 3  illustrates this case as well, and is described more fully below. 
     The system illustrated in  FIG. 1  may include a traditional telephone system also known as a Public Switched Telephone Network or PSTN providing plain old telephone service or POTS as part of the full-duplex network  105 . Those skilled in the art will readily recognize that this invention is applicable to other full-duplex networks. For example, the full-duplex terminal could be an Integrated Services Digital Network or ISDN terminal attached to the PSTN. The full-duplex terminal  101 ,  102 ,  103 ,  104  could also be an H.323 or SIP terminal which could, for example, be implemented in software on a personal computer. In H.323-based, SIP-based, and other alternative embodiments, the signaling from the full-duplex terminal may be out-of-band signals rather than DTMF in-band signaling. However, as described herein, an interface between the full-duplex and half-duplex RF systems remains. 
     Referring now to  FIG. 3 , a state diagram of a dispatch gateway is shown. The dispatch gateway  120  may concurrently run many of these state machines to simultaneously support many dispatch conversations. The dispatch gateway state machines start in a Standby state  301  waiting for a call. Once a call is received through the full duplex network  105 , the gateway answers the call and enters the In Call state  302 . Many state transitions are possible from this point. State transitions are represented on the diagram by directional arrows. Text on or near the directional arrow indicates what inputs and outputs are associated with the state transition. The “T:” portion of this text indicates action and/or input from the full-duplex terminal  101 ,  102 ,  103 ,  104  received by the gateway from the full-duplex network  105 . The “G:” portion of this text indicates action by the gateway  120 . The “D:” portion of this text indicates the input from the dispatch RF system  150  preceding the arrow and/or action to be taken by the dispatch RF system  150  following the arrow. The notation “n/a” in any of the three portions of the state transition label text indicates that no input or action is associated with that part of the system full duplex terminal “T:”, dispatch gateway “G:”, or dispatch system “D:”. The state diagram of  FIG. 3  shows the state transitions for both dispatch-initiated and full-duplex initiated sessions. In the In Call state  302  the dispatch gateway waits for the full-duplex terminal user to enter a dispatch ID that the gateway will store as the currently active dispatch ID until the full-duplex user changes it or until a dispatch user or group initiates a dispatch session in which case the dispatch ID of that user or group becomes the current dispatch ID stored in the gateway. In the Dispatch Ready state  303  the full-duplex terminal user is ready to participate in dispatch sessions initiated by the full-duplex terminal user or by the dispatch system&#39;s users. In the Dispatch Session state  304 , the Dispatch Outbound state  305 , and the Dispatch Inbound state  306  the full-duplex terminal user is actively engaged in a dispatch session with a dispatch user or a dispatch group. In the Dispatch Outbound state  305 , the dispatch user or group transmits voice through the dispatch gateway and the full-duplex system to the full-duplex terminal user. In the Dispatch Inbound state  306 , the full-duplex terminal user transmits voice through the full-duplex system to the dispatch gateway and through the dispatch system to the dispatch user or dispatch group. Transitions between the Dispatch Session  304 , Dispatch Outbound  305 , and Dispatch Inbound  306  states can be caused by PTT requests from the dispatch and full-duplex users, by inactivity timeouts, and by dispatch system drops.