Abstract:
Voice packets transmitted by an originating wireless user for use in a half-duplex communication mode in a one to many communication session are monitored for an unexpected cessation. If an unexpected cessation of such voice packets is detected for a predetermined time period, the session server controlling the communications session is notified to release the supporting half-duplex communication paths associated with the originating user.

Description:
BACKGROUND 
   This invention generally relates to a wireless telecommunications system that provides a one-to-many voice conference mode, and more specifically relates to limiting the ability of a user in a packet system that loses communication with the system in the talk mode to disrupt communications. 
   One example of a wireless system providing a one-to-many transmission mode is a conventional police or fire radio system. In an analog system with a single base station, a first user captures the base station by an initial transmission activated by a push to talk button. The first user&#39;s voice transmission is received by the base station and retransmitted to the other users. The transmission by the first user ends by the first user releasing the push to talk button. This allows one of the other users to reply to the first user or initiate a new transmission by activating his radio with the push to talk button. In this system a radio frequency carrier is on during the entire voice transmission. Loss of the radio frequency carrier, whether caused by the user releasing the push to talk button or by the user leaving the area of coverage, causes the base station to release its retransmission and allows another user to be able to access the system. 
   A wireless network that carries speech as digitized samples in packets presents additional difficulties with regard to transmission control especially where the packets are transferred from the wireless portion of the network to a wired portion of the network. This is especially apparent where the system utilizes a half-duplex transmission mode in which only one user is permitted to transmit voice communications at a time. Unlike the above example of an analog wireless system in which a radio frequency carrier was always present during a speech transmission, the speech packets carried on the wired system are decoupled from the wireless portion of the system and hence information concerning the status of wireless communications link is normally not available at packet nodes in the wired system. A packet based system having both a wireless and wired portion typically relies upon an end of transmission signal transmitted from the active (talking) user at the end of voice transmission such as initiated by the release of a push to talk button. This signal is conveyed through the wireless and wired portions of the system informing all involved transmission nodes that the stream of packets carrying voice from the active user has ceased. Failure to receive the end of transmission signal at a node in the network may cause the node to take inappropriate actions or fail to take appropriate actions. Such a problem is especially acute where a node hinders further communications by other users due to the failure to receive an end of transmission signal. Thus, there exists the need for an improved method for minimizing problems associated with the lack of receipt of an end of transmission signal in a packet system. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to minimize problems associated with the lack of receipt of an end of transmission signal in a packet system. An object of the present invention includes, but is not limited to, minimizing such problems in packet system employing a half-duplex voice conference mode. 
   In accordance with an exemplary method of the present invention, a method is provided for releasing half-duplex communication paths in a telecommunications system where speech by an originating user is transmitted as packets and where an end of transmission signal for releasing the half-duplex communication paths is normally initiated by the originating user releasing a push to talk button. Half-duplex communication paths for speech from the originating user are established to a plurality of listing users by a session server. Packets of speech received from the originating user are replicated and transmitted to the plurality of listening users by a media resource function. The cessation of speech from the originating user for a predetermined time interval is monitored at the media resource function and a loss of speech signal is transmitted to the session server upon the cessation of speech for the predetermined time interval. The half-duplex communication paths are released by the session server upon receipt of the loss of speech signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a wireless communications system suited for practicing an embodiment of the present invention. 
       FIG. 2  is a diagram illustrating the transmission of signals in the system as shown in  FIG. 1  in which an end of transmission signal is received. 
       FIG. 3  is a diagram illustrating the transmission of signals in the system of  FIG. 1  in accordance with an embodiment of the present invention in which an end of transmission signal is not received from the originating user. 
       FIG. 4  is a block diagram of wireless communications system suited for practicing a further embodiment of the present invention. 
       FIG. 5  is a diagram illustrating the transmission of relevant signals in the system as shown in  FIG. 4  in which the location of users determines which users will receive half-duplex communications from the originating user. 
   

   The same reference numeral is used to identify like elements in different figures. 
   DETAILED DESCRIPTION 
     FIG. 1  illustrates a wireless communications system that supports wireless user communication devices  102 ,  104  and  106  such as cellular telephones. A radio access network (RAN)  108  provides a wireless communication link between the system and the wireless user communication devices. This node may consist of a conventional wireless base station and a base station controller or a mobile switching center. The RAN  108  is representative of a plurality of radio access networks (not shown) disposed at different geographical locations to support wireless communications for the system. The RAN  108  is connected by a communication link  110  to a visiting location register (VLR)  112  that is connected by a signaling system  7  network  114  with a home location register (HLR)  116 . 
   The RAN node  108  is also connected by communication link  118  to a packet data serving node (PDSN)  120  that provides an interface that supports a data link layer protocol to the mobile station ( 102 ) and that directs packets to a particular over the air connection that the RAN ( 108 ) provides for the mobile station ( 102 ). The IP network  122  is connected to PDSN  120  and also connected to an authentication authorization and accounting (AAA) node  124 , session server  126 , media resource function  128 , home agent node  130 , and a communication link  132  illustrating that the IP node  122  is also connected to other networks and nodes. The session server  126  is also connected to the AAA node  124  and media resource function  128 . The AAA node  124  supports users of the system by providing authentication, authorization, and accounting functions. The session server  126  supports call control protocols and services such as one to many voice messaging. The media resource function  128  operates under the control of session server  126  and provides a packet duplication capability for supporting one to many voice messaging and a lost voice packet detector for detecting the loss of voice packets from an originating user prior to the receipt of an end of transmission signal. The home agent node  130  functions as an intermediate node for assigned wireless user communication devices by receiving packets from the assigned devices and transmitting packets from the network addressed to the assigned devices. The home agent node permits the user devices to roam over the entire coverage area of the wireless system by keeping track of which PDSN to use for communications with the user device. 
   The session server  126 , media resource function  128  and home agent node  130  may each be represented by the same architecture consisting of a microprocessor supported by read-only memory, random access memory, nonvolatile storage memory, and an input/output interface device for the transmission and reception of packets. The microprocessor operating instructions for each of these elements will be apparent to those skilled in the art based on the description of the functionality and signaling that follow. 
     FIG. 2  illustrates the signaling involved in establishing, conducting and terminating a one to many half-duplex voice messaging session in the telecommunications system shown in  FIG. 1 . The signaling diagram of  FIG. 2  assumes that the wireless users have been initially registered with the system and that the wireless devices are on and are recognized by the system. As part of the service configuration portion of registration, users are assigned an identity and security information for authentication. The users are also assigned one or more group identifications that can be used to select the audience of a one to many voice transmission. In addition to the normal registration associated with the AAA node  124 , the user also registers with the session server by providing the identity of the user&#39;s wireless device and the group identifications assigned to the user. Each user may belong to a plurality of groups that can be selected by an originating user for a one to many voice session. Following the completion of registration, the user&#39;s wireless device goes dormant so that air interface resources are not used when not needed. Handoffs are accommodated so that a user that moves outside the range of the RAN  108  but within the range of another RAN (not shown) of the system maintains communication with the system. 
     FIG. 2  illustrates a signaling diagram with lines  202 ,  204 ,  206  and  208  representing signals originating from or terminating to an originating station, session server, media resource node and other stations, respectively. In an illustrative example wireless device  102  corresponds to the originating station  202 , session server  126  corresponds to session server  204 , media resource node  128  corresponds to media resource node  206  and wireless devices  104  and  106  correspond to other stations  208 . In order to clarify the signals more relevant to the exemplary method of the present invention, the number of signals shown in  FIG. 2  has been limited. To assist in understanding, other signals may be described that are not depicted in  FIG. 2 . Reference should also be made to  FIG. 1  while considering the signaling discussed in  FIG. 2 . 
   Users initiate half-duplex communications by pressing a push to talk button. In this example, a user of wireless device  102  first selects a set of users (other stations) by a group identification. Group identifications may be associated with buttons on device  102  or may consist of the entry of a numeric code by the user corresponding to the group, e.g. * 1 –* 9  representing 9 different groups. The user then presses the push to talk button causing a session server invite signal  210  to be transmitted from originating station  202  to the session server  204 . Signal  210  traverses RAN  108 , PDSN  120  and IP network  122  to reach session server  126 . The session server invite signal  210  includes, in addition to the identity of the originating wireless device, the group identification. The session server, after authenticating with AAA node  124  that the originating station is a valid registered user, determines the availability of members of the selected group by determining those members of the group that are currently registered with the session server. Based on the group identification selected by the originating station and the available members of the group, the session server selects a set of wireless devices to participate as audience members in a one to many conference. The session server  204  transmits a station invite  212  to the selected set of other stations. The session server may attempt to reach the selected members more than once. The session server transmits the station invite signal  212  by IP network  122  to home agent  130  that maintains an ongoing record of the PDSN associated with each registered user. The home agent  130  routes the station invite signal  212  by the IP network  122  to the corresponding PDSN  120  associated with each respective user to receive the station invite signal. Upon an other station  208  receiving the station invite signal  212 , the other station transmits an okay signal  214  to the session server  204 . Upon the session server receiving at least one okay signal  214 , the session server  204  generates a replicate signal  216  transmitted to media resource node  206 . The replicate signal identifies the originating station and the members selected by the session server to receive the one to many transmission from the originating station so that the media resource node  206  will be prepared to duplicate packets of voice received from the originating station. The session server also generates an activate voice signal  218  that is transmitted to the originating station. Upon receipt of the activate voice signal  218 , the originating station wireless device  102  preferably provides audible or visual indicia to the user indicating that voice communications can proceed. The user can then talk into the microphone of device  102  where the user&#39;s speech is transmitted as signal  220  arriving as digital information carried by IP packets at media resource node  206 . The media resource node duplicates the received voice packets from the originating station and addresses a corresponding packet to each member selected by the session server. These packets are transmitted as signal  222  to the selected members (other stations) by IP network  122  and home agent  130  which routes the received packets to the respective member by the corresponding PDSN  120 . Thus, each of the selected members receives the spoken message from the originating station user. Since this is a one to many half-duplex communication, the members receiving the spoken message from the originating station cannot provide an immediate spoken reply without first obtaining authorization from the session server. 
   When the user of the originating station has completed the verbal communication, the user releases the push to talk button of the originating station device  102  causing the device to transmit a bye signal  224  to the session server. The bye signal alerts the session server of the termination of the half-duplex voice communication by the originating station. This causes the session server  204  to tear down the supporting communication paths by transmitting a release signal  226  to the other stations (selected members receiving the transmission from the originating station) via IP network  122  and home agent  130  that routes the signal to the respective devices of the selected members by the corresponding PDSN  120 . The receipt of release signal  226  by the other stations preferably causes audible or visual indicia to be presented to the respective user as an indication that the transmission has been concluded. The session server also transmits a release signal  228  to the media resource node  206  indicating that resources associated with the duplication of packets transmitted from the originating station are released. This completes the half-duplex voice transmission by the originating station and releases the supporting telecommunication infrastructure that supported the transmission. 
     FIG. 3  illustrates signals in accordance with an illustrative embodiment of the present invention that avoids unduly tying up the telecommunication infrastructure of  FIG. 1  when communications are lost with the originating station during a half-duplex speech transmission. A common cause of such a loss of communication is the loss or significantly long disruption of the wireless signal between the user&#39;s wireless device  102  and any of the wireless base stations in the system.  FIG. 3  begins with half-duplex communications between the originating station  202  and the selected members of a designated group as illustrated by voice packet signals  220  being received by media resource node  206  from the originating station, and the media resource node in turn duplicating and transmitting packets to the selected members  208 . This condition will have been accomplished as explained above with regard to  FIG. 2 . 
   Media resource node  206  (element  128  in  FIG. 1 ) includes a time monitoring function that constantly measures the time interval since the last voice packet was received from the originating station. If this time interval exceeds a predetermined amount of time, indicated by bracket  230  in  FIG. 3 , then the media resource node  206  transmits a signal  232  to session server  204  representing an alert that communications with the originating station  200  into may have been lost. The predetermined amount of time is preferably set by the system administrator of the telecommunications system based on statistical data concerning the normal maximum length of times between received voice packets so that the alert signal  232  is not unnecessarily generated. In general, a few seconds, e.g. 2–5 seconds, may represent an appropriate predetermined time. 
   The session server  204  generates release signals  226  and  228  as explained above with regard to  FIG. 2 . This releases the system infrastructure resources associated with supporting the half-duplex transmission initiated by the originating station  202 . This prevents infrastructure resources and members receiving the voice transmission from the originating station from being unnecessarily occupied. 
   Generally such push to talk half-duplex communications systems are not utilized in a manner where a user captures a communication path and does not transmit voice information for significant periods of time. After requesting a voice path, an originating user will typically initiate voice communications quickly after receiving the path and does not typically employ long pauses of no speech activity while retaining the original path. 
     FIG. 4  is a block diagram of a further embodiment of the present invention in which the current location of users is at least part of the decision of which members of a group selected by an originating user will receive the one to many communication. Since this embodiment is substantially similar to the embodiment described in  FIG. 1 , an explanation of the common elements and operation of these elements will not be repeated. 
   A session server  302  contains all of the functionality of session server  126  and contains additional functionality as will be described. The session server  302  is connected by a communication channel to location server  304  that is in turn connected to a location source  306  that is coupled to the IP network  122 . The session server  302 , location server  304  and location source  306  may each have an architecture as described for session server  126 . The purpose of location source  306  is to monitor the geographic location of each of the registered, that is active, wireless devices in the telecommunication system. 
   Location source  306  may utilize any of a number of known techniques to monitor the geographic location of the wireless telephones with various degrees of granularity. For example, global positioning satellite systems can determine location within a few meters, known triangulation systems targeting on the transmitter of the wireless telephone can provide reasonable accuracy of its location, and monitoring the base station with which a wireless telephone is currently registered can determine location within the area of coverage of the base station. The location server  304  collects and maintains the location information from the location source  306 , and stores the location for each active wireless telephone. The location information stored in location server  304  can be arranged for access on a per wireless device basis and/or all active wireless devices within a defined geographic region can be grouped together. 
   Dashed lines  310  and  312  indicate boundaries between different geographic regions. These regions may utilize different base stations to serve wireless devices in the respective regions, or may represent regions that are within a predetermined distance of a landmark, e.g. within 1 kilometer of a major roadway or within three kilometers of an airport or major building. The users of wireless devices  104  and  106  are in region  1 , user of wireless device  102  is in region  2  and the user of wireless device  308  is in region  3 . 
   Session server  302  is provided access to the geographic location information stored and maintained by location server  304 . When a request for a one to many communication session is received from an originating user, the session server  302  can, depending on the nature of the requested communication session, select members of the group designated by the originating user based on the geographic location of all registered members of the group. For example, assume one group of subscribers is taxicab drivers and a taxicab driver needs to communicate with other taxicab drivers in the vicinity of a particular airport. The wireless device used by each taxi cab driver includes a plurality of buttons associated with major locations of activity for taxicabs, including the particular airport. The originating taxicab driver will push the button associated with the particular airport. This will cause a group identification associated with the particular airport to be transmitted as part of a path request upon pressing the push to talk button. The session server  302  upon receiving the request for a one to many session will access the location server  304  and identify active cab drivers that are near the airport. The session server  302  uses this location information in order to limit the selected members of the requested group to only those members that are in the requested geographic area. This eliminates establishing one to many communication paths with cab drivers that are not in a position to satisfy the request. This is advantageous from a telecommunications infrastructure perspective in that it limits the amount of bandwidth required to satisfy a one to many communication session since only those users at the required geographic location are provided with communication paths. It is also advantageous to subscribers because registered users within the group or fleet that are not in the desired audience group due to geographic location will not be bothered with listening to communications that are not relevant to them. 
   An on-going exchange will consist of as series of push to talk events by different users participating in the conversation. If rapid motion of the mobile station ( 102 ) takes place during the exchange, the group membership might change such that recently communicating users are no longer able to speak to each other. To prevent this situation, the session controller ( 302 ) maintains a recent activity timer such that it accepts push to talk INVITE from the mobile station with a changed location and will send an INVITE to a recently communicating mobile station even if it is outside a location boundary. Stored or cached information about the previous (recent) communications paths serving wireless users can be employed to maintain a communication path even if the wireless user moves outside a geographic region designated for audience members. Such cached information can be stored at any convenient node, e.g. session server or media resource node. 
     FIG. 5  illustrates a signal flow diagram illustrating selected signals in accordance with the embodiment as shown in  FIG. 4 . Signals are shown among the originating station  350 , session server  352 , location server  354 , media resource node  356  and other stations  358 . In accordance with an illustrative example, originating station  350  corresponds to wireless device  102 , session server  352  corresponds with session server  302 , location server  354  corresponds with location server  304 , media resource node  356  corresponds with media resource node  128  and other paths  358  correspond with wireless device  308 . 
   In an example, wireless devices  102 ,  104 ,  106  and  308  are all used by employees of the same construction company. A project manager of the construction company uses wireless device  102  at the home office in region  2 . A site manager and construction foreman of the construction company use wireless devices  104  and  106 , respectively, at a first construction site in region  1 . A civil engineer of the construction company uses wireless device  308  at a second construction site in region  3 . The project manager needs to communicate with all employees at the first construction site (region  1 ) concerning an issue that only relates to the first construction site. 
   The project manager pushes a button on wireless device  102  corresponding to the first construction site. Alternatively, the project manager could have entered a predetermined code, e.g. * 01 , corresponding to the first construction site. The project manager then presses the push to talk button of wireless device  102 . In this example, wireless device  102  is the originating station  350  of  FIG. 5  and pressing its push to talk button causes a session server invite signal  360  to be generated and transmitted to the session server. The session server invite signal  360  will include information identifying the originating wireless device  102  and the group information entered by the user. On receiving signal  360 , session server  352  generates a member query signal  362  including the group information entered by the user and transmits it to the location server  354 . In response to receiving signal  362 , location server  354  uses the group information to identify active members of the group that are in the specified location. In this example location server  354  determines that wireless devices  104  and  106  (the site manager and construction foreman) are the only two members of group located in region  1 . The civil engineer of the construction company although active using wireless device  308  is determined to be in region  3  and hence is not selected as a member by location server  354 . A member location reply signal  364  is transmitted by the location server  354  to session server  352  and contains the identities of wireless units  104  and  106  as members of the audience to receive the one to many communication session requested by wireless device  102 . The session server  352  generates a station invite signal  366  that is transmitted to the other stations  358  which in this example consist of wireless devices  104  and  106 . As previously explained with regard to  FIG. 1 , the station invite signal  366  will be transmitted by session server  302  via IP network  122  to home agent  130  that determines the PDSN through which the devices  104  and  106  are connected and routes appropriately addressed IP packets to the selected wireless devices. The remaining signaling associated with setting up the one to many communication session and tearing it down will proceed as previously explained with regard to  FIGS. 2 and 3 . 
   The embodiments of the present invention have been described above with regard to a one to many communication session. However, it will be apparent to those skilled in the art that some of the aspects of the embodiments could be advantageously employed when the telecommunications system is utilized for a private call to a single wireless device. Monitoring for the possible loss of communication with the originating user during a voice transmission is also applicable to a private call. Also, aspects of the embodiments of the present invention could be advantageously applied when a small group of users is permitted to speak (transmit) simultaneously to an audience of other users such that packets from the small group of speakers are all delivered in a mixed audio output to the audience. Various modifications can be made to the illustrative embodiments without departing from the scope of the present invention.