Method and apparatus for providing a private communication system in a public switched telephone network

(74) Agent

<td> (54)</td><td>Designation</td><td>Private communications network integrated into a public telecommunications network</td>

<td> (56)</td><td>cited publications</td><td>US 5054042, EP 0676906</td>

<td> (57)</td><td>Summary</td><td></td>

Private communication network in which a number of users can connect with each other, via a public switched telephone network (10. Each user uses either a modified landline telephone device (48) directly connected to the network (10) or a modified mobile phone (22) which is also operationally connected to the network, but via a wireless communication system (14). The private network comprises a network connection station ( 40) having a telephone network interface (92) for establishing a telephone connection with each of several telephone lines (44) for the network (10). Each of the telephone lines (44) is connected to one of several users. The network connection station (40) further comprises a switch matrix (110) connected to the interface and arranged to transmit an information signal received from an active user in the network, via a selected telephone line, to the other inactive users.

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This invention generally applies to multi-party connection systems, more specifically a private communications network extending from one point to several points and directly embedded in a cellular or landline based telephone system.

Telephone service in cellular networks for mobile devices, that is, mobile phones have already been in use for some time, and conventionally such services have been offered in a network with a central station which transmits with great transmitter power to a limited number of mobile / portable devices within a greater geographical area. In earlier cellular systems, there was only a limited number of available radio channels, so with the io mobile devices that were then largely radio telephones, there was limited opportunity for conversation within a larger urban area, precisely because of the limited number of channels.

However, modern radiotelephone systems with cellular networks as a base have a relatively large number of radio channels, and this number can be effectively multiplied by using identical channel frequencies within the various smaller coverage areas (ie, cells in the network), to obtain specific service territories. Each cell in such a network has a transmitter in a base station and which transmits at a power level selected sufficiently large to ensure good signal reception, even in the boundary regions without excessive interference with the reception in neighboring cells. This means that channel frequencies used in one cell can be reused, in another 20 cell geographically separated from the first, according to a given plan. Accordingly, a greater number of channels can be made available in an urban area, and the service provided through these channels may be the same as that obtained through a conventional telephone line transfer.

There are a number of standards for the handling of cell phone connections. These standards include the so-called advanced mobile phone system (AMPS), the global standard mobile phone system (GSM), and code-shared multiple access (CDMA). The spectral distribution of the latter technique has significant advantages over other modulation techniques for multi-access interconnection systems, and for example the use of CDMA leads to far better utilization of the frequency spectrum than can be achieved with other

3o multiple access systems.

Although recent developments have led to CDMA and other cellular connection systems being able to offer effective point communication between users, various public and private institutions have nonetheless continued to base communications on so-called dedicated land mobile radio (LMR) in the network. This is because cell systems have not been able to establish networks with type-to-multipoint connection for a set of users. In the US, for example, local authorities can use LMR networks where a closed radio connection system can be set up via relay stations (repeaters), and such closed LMR networks are often characterized by so-called PTT operation, with the abbreviation being pressurized. -talk. This means that the user presses a voice button or similar when it is desired to disseminate information to a particular user group. The problem that it is difficult to set up relay stations over larger geographical areas limits the extent such local radio networks can have.

Both cellular and conventional landline telephone systems are capable of handling connections between users who have a large geographical distance, but closed networks of type 5 PTT have so far not been of particular use within such system types. This may be partly due to the absence of an appropriate mechanism for automatically adding an identified set of users to such a closed network. Furthermore, both types of systems may easily be compromised by an unauthorized third party even if such a mechanism is available, and therefore the systems will be unsuitable for secure and eavesdropping communication. Io The conference connectivity offered by both cellular and landline-based information carriers or networks is also an inappropriate surrogate for a PTT network. In particular, conference setup between users within different cell-based or landline systems may require some degree of advance coordination, performed by the responsible service provider. Furthermore, the information signals in many such conference systems, ice cream from the participants will be combined and the result will form composite signals that are universally transmitted to each such participant. This will effectively exclude separate encryption of the information signals as a means of improving communication security, since such separately encrypted information signals will generally not be able to be extracted from a composite signal.

Accordingly, the object of the invention is to provide a private telephone network directly within a cellular and / or landline-based telephone system in such a way that there is no need for pre-coordination with a telephone service provider.

Another object of the invention is that the private communication network emulates an LMR network which is characterized by PTT operation. Another object of the invention is to make sure that the control and monitoring of the private communication network is in a network management center which is separately connected to an already existing landline telephone system, and a further object of the invention is that conventional encryption technology should be able to be curved within the private communication network, as a means of improving communication security.

On this basis, the invention proposes a private communication or communication network in a communication system where users communicate with each other via a switched telephone network, where the private communication network, to facilitate communication between multiple users, and this communication network is particular, such as according to claim 1, characterized by:

a network connection station which in turn comprises:

a telephone network interface for establishing a telephone connection with each of the users in the network, over several channels belonging to the telephone network, a switching matrix connected to the telephone network interface and arranged to provide an information signal received by the telephone network interface through one of the channels, to the other interfaces and via telephone , and control and monitoring circuits for configuring the switch matrix in response to voice request signals received via a selected by the channels, and several authorized telephone devices adapted for communication through the channels, each authorized telephone apparatus comprising circuits for generating one of the voice request signals.

Other features of the invention will be apparent from the other claims.

Thus, a number of users can connect with each other via the private network, using the available public digital telecommunications network (PSTN) for this. Each user has at his disposal either a modified landline telephone which is directly connected to the PST network or in a modified mobile phone which is operatively connected to this network via a wireless connection system. The private network comprises a network switching center with a telephone network interface (interface) for establishing a telephone connection with each of the telephone lines belonging to the PSTN. Each of these telephone lines is connected to one of the relevant users.

is The switchboard comprises a telephone line switching matrix connected to the interface to send an information signal received from an active user via a selected telephone line to the other non-active users based on a PTT request signal received from the users' phones via the telephone lines. For example, the active user may be identified as the user as a PTT request signal is received only after the previously active user has waived voice privileges. Alternatively, the active user may be selected using predetermined priority criteria for evaluating all PTT request signals queued by the network switchboard.

The telephone set of each user will typically be capable of both standard telephone use and PTT use via the private communication network. When the telephone is configured for 25 PTT use, each device receives incoming voice or other information in digital form from another user, and then processes the information digitally. The resulting vocode data packets as well as any PTT request signals sent from the user are then transmitted to a modem for return transmission over the network PSTN to the exchange's telephone network interface. The security of the PTT network can be improved by configuring each phone for encryption of all such return transfers as well as for decrypting pre-signals from the active user.

Further features of the invention will become apparent from the detailed description below, which relies on the drawings, in which:

Fig. 1 shows the individual elements of a typical telephone system within which one can set up a private PTT point / multipoint connection network, according to the invention; 2 is a block diagram of a typical network management center of the private PTT network according to the invention; FIG. Fig. 3A shows the block diagram of a landline telephone of the PTT / dual mode type with a transmitter and receiver part; 3B shows this telephone modified to facilitate encrypted connection within a private PTT network; FIG. 4 shows a block diagram of a dual-mode AMPS-PTT telephone; 5 is a block diagram of a CDMA cell phone configured for use within the invention's private PTT network; FIG. 6 shows a functional diagram for a network management center arranged for use with a private PTT network where the signaling is carried out with analog tones; and FIG. 7 shows a landline telephone set up for connection to a network switchboard via analog tones.

Fig. I illustrates how a private PTT network is constructed in typical form, for connection from one point to several points in the network. It contains a public digital telecommunications network PSTN 10, a CDMA cellular network system 14, and a corresponding AMPS cellular network system 18. CDMA system 14 provides services to CDMAio compatible mobile phones for radio communications (CDMA mobile phones) 22 and 24, while AMPS system 18 facilitates contact with users of AMPS compatible mobile radio telephones (AMPS mobile phones) 28 and 30. An internet management center 40 which is PSTN 10 works as will be described below to provide a private communication network between a number of users of the telephone system shown above in Fig. 1.

The private communications network may include users operated by one of the two systems 14 and 18 and / or may include one or more users directly connected to the public network 10 via modified landline telephones such as the telephone 48. Although the systems CDMA and AMPS is shown in the embodiment shown in FIG. 1 it is clear that the concept of the invention 20 may also apply to other cellular air interference standards as well as, for example, GSM and TDMA (time-division multiple access) of the individual elements of systems 14 and 18 of FIG. 1 and includes base stations 56 and 58, respectively. Each cell may be divided into several sectors where the connection to CDMA mobile phones 22 and 24 within a given sector is handled by a cell transmitter / receiver providing radio coverage over that sector. 25 The base stations 56 and 58 work to receive and transmit the signals that allow a transmitter within each CDMA mobile telephone to be connected to the public network 10.1 system 14, data packets are used for radio exchange of information between the base stations 56, 58 and

CDMA mobile phones 22 and 24.

Telephone calls are routed via the base stations 56 and 58 between the mobile phones 22 and yes 24 and the central (MSC) 60 for the CDMA network, this exchange being typically located in a mobile telephone main station (not shown). The main purpose of the switchboard 60 is to provide voice connections between the mobile phones and the public network 10. Therefore, the switchboard 60 performs functions such as transmission of data between an MSC modem 62 and the mobile phones 22 and 24 via the correct CDMA base stations 56 or 58. The switchboard 60 also performs other tasks, including calling a mobile phone when a connection is desired to be set up and received as a call from the network 10, and connecting connections to available network lines through multiple T1 channels 64. A set of MSC modems 62 serve to convert the digital information signals received from the mobile phones 22 and 24 into analog signals suitable for transmission over the public network 10, as well as converting analog signals from this network to digital signals that are transmitted to mobile phones 22 and 24.

The AMPS cell connection system 18 also comprises several cells, two of which are shown in FIG. 1, including base stations 70 and 72. Each cell may be divided into several sectors where communication with mobile phones 28 and 30 in the network and within a given sector is handled by a transmitter / receiver located in the cell and provides coverage area over the sector. Telephone connections are routed by the base stations between the mobile phones in the AMPS network and a mobile telephone exchange (MSC) 76 in this network, this exchange being connected to the public network PSTN 10 via several TI channels 80.

Fig. 2 shows an example of the construction of the network connection station 40 included in the private PTT network according to the invention. The manner in which landline or cell phones connected to each user are configured to cooperate with station 40 will now be described, communication foil connections from modified landline telephone 40, from mobile phones 28 and 30 of the AMPS network and mobile phones 22 and 24 of the CDMA network are connected to the public i5 network PSTN 10 and the station 40 in what can be called reverse link. The return connection associated with the user currently specified by the network station 40 as the active user is believed to be the only return connection that carries valid voice and digital information. Other return connections will be available to provide signaling information to station 40. Each corresponding forward connection over the network 10 from station 40 and to each user carries the relevant speech or digital information from the active user. As described herein, station 40 is reconfigured with each new identification of an active user. The reconfiguration results in the return connection's speech or digital information, from the newly identified active user, to the forward connections associated with other users, including the connection of the previously active user.

The network connection station 40 comprises a network controller 90 where at least one list of telephone numbers associated with the users of a first private PTT network is stored. When you want to access this first private network, a user who wants a connection dials an access number that determines which network it is. The web controller 90 can also store other lists of users, and each list is assigned a unique access number and establishes a

3o separate PTT network.

The station 40 is designed to respond to the public network 10 as a private system branch corresponding to an exchanger (PBX), and the request for a connection entered by the user wishing that connection can be received through one of the T channels 44. In this regard, a telephone network interface 92 for TI connections is provided to establish a connection between the TI channel 44 assigned to the user and one of several network management modems 98. As described herein, interface 92 also serves to connect various other modems 98 to those belonging to the TI channel 44 assigned to other users.

If the user who wants the connection is served by the CDMA system 14, a telephone connection is established when the modem 98 'connected to the TI channel 44 receives the incoming call and is synchronized with one of the MSC modems 62 (Fig. 1) for the connection. For a user having a landline telephone or an AMPS cell phone, a corresponding telephone connection is established by synchronizing an internal modem (fig. 3A and 4) within the user's telephone, and the modem 98 'which receives the incoming request to establish a connection. For example, in a typical example, the network drive modems 98 comprise AMPS modems, particularly well suited for information transmission per. radio.

When a call enters a private PTT network from a user over one of the T channels 44, the T interface 92 uses standard technology to determine the access number dialed when establishing the connection. The dialed access number corresponding to a given private PTT network is handled by the T1 interface 92 and passed through the network controller 90. The interface also connects the T1 channel 44 assigned to the user with an available network management modem (i.e., the network management modem 98 '). Once modem synchronization is achieved, the network controller 90 may require that the user who has set up the connection provides authentication which is used to check if the user in question has membership in the private PTT network whose identification corresponds to the dialed access number. Upon confirmation of such membership, the controller 90 can either command the interface 92 or a selected network management modem 98 to activate the other users in the network. It should be noted that in alternative embodiments, the interface 92 comprising an EI interface or various other digital or PBX digital interfaces may be provided.

When a first of these other private network users answers a network request (for example, a telephone call) from one of modems 98 or via interface 92, a modem synchronization process corresponding to the type described above starts. If the dialed user is specifically operated by an AMPS or landline telephone, synchronization will occur between the internal modem and the user's telephone (Figures 3A and 4) and one of the network management modems 98. Instead, if the user is operated by CDMA system 14, modem synchronization occurs between modem 98 and one of MSC modems 62 (Fig. 1). It is obvious that the MSC modems 62 need not be physically close to the central MSC 60, but may be located elsewhere within the telephone system infrastructure.

When modem 98 achieves such synchronization, a connection signal called CONNECT is generated and this signal is recorded by the network controller 90 which can then instruct the network management modem 98 'to send this signal to the user who originally set up the connection by dialing the access number of the determined and identified private PTT. networks the. The network controller can also periodically send each authenticated user in the private PTT network a list that can be displayed in each telephone device, over the other relevant users on the network.

A PTT controller 104 is further arranged for corresponding transmission of voice or digital information in the form of privileged transmission, between the two or other users who

Ί is connected to the private PTT network, in addition to the first user. In particular, the controller 104 may be responsive to PTT request signals (PTT requests) generated by landline or cell phones assigned to users in the private PTT network. Each PTT request is made in a user's phone, either in response to manual operation of a PTT switch or in response to recorded speech activity on the user's part. A PTT request from a particular user will be registered by the modem 98 assigned to him, and from there the PTT signal is provided to the controller 104.

In a typical example of such a controller 104, it specifies the active user from the users sending PTT requests, namely the first of these users, the request following the voice privileges released by a previously active user. Speech privileges are handled by the previously active user in case of manual PTT signaling by releasing the PTT switch in the phone. In the case of voice-activated PTT signaling, voice privileges are created in the presence of a pause of a given duration.

In an alternative embodiment, PTT requests received prior to handling the voice privileges of the currently active user are added to a queue. When the user then handles the privileges, the queued requests are evaluated according to given criteria to determine who the next active user is. For example, such predetermined criteria may include user priorities as well as the order of the incoming requests.

The network drive 40 may also use other techniques to select a new active user based on the received PTT requests. For example, each user in a given private PTT network can be assigned a relative level of priority within the network. In the event that a PTT request is received from a higher priority user, the currently active user may be taken to the page by being handled by the station 40, so that the voice privileges are given to the user with the highest priority, but it is also possible enabling each user to change priority within given boundaries registered with the station 40, as a means of obtaining voice privileges under compelling circumstances or the like.

After a new active user is identified by the PTT network controller 104, on the basis of the received PTT requests, the device can configure a multipath switch 110 to accept return information in the form of analog voice or digital format, exclusive of the modem 98 which is assigned to the currently active user, and this means that the return information from each of the other modems 98 is assigned to its respective other (that is, inactive) user in the network, is ignored by switch 110. PTT controller 104 also configures switch 110 to transmit the return information accepted from the newly identified active user to the modems 98 which are connected to each of the other inactive users, and the PTT requests page is only transmitted in the return direction for the non-active users, as such PTT requests will preferably not interfere with the reception of information in the return direction from the active user.

Although the forward signals in each private PTT network are nominally used to transmit analog speech or digital information (data) from the active user and to all other users within the group, the PTT controller 104 may also transmit system state information via the forward channels during breaks or stays in the information transmission from the active user. In a typical example, this state information will include the following:^- (i) a given private PTT network's potential current users (their telephone number, name, priority), (ii) users (with the same data information) belonging to the group in the given PTT network, (iii) the current active user (same data), and (iv) the queue of the users (same data) who sent PTT requests to the network controller 90.

This information is received and displayed in the telephone sets that are intended for users. The following sections describe a particular embodiment of PTT dual mode telephones suitable for use within the invention's private PTT networks.

Referring first to FIG. 3A which provides an overview of a dual-mode telephone apparatus for landline PTT use and with a transmitter portion 140 and a receiver portion 142, The transmitter portion is set up for normal telephone operation when the indicated input turns 148 are added to the bypass position 150 where microphone 150 shown therein is diverted to the public network. 10. The switch 148 is instead added to the process position 158 when it is desired to use the telephone for PTT operation in the transmitter part 140. Similarly, the receiver part 142 is added to bypass in position 168 or PTT operation in the process position 166.

During PTT operation, analog speech is switched from microphone 154 via the input switch 148 to the process position 158 and then to an encoder / decoder 172 (codec). In order to transmit the incoming information which may thus be analog speech or possibly digital information (data) from a peripheral device (not shown), but also connected to the switch 148, to a pulse code modulated (PCM) waveform for transmission to the displayed voice code circuit (vocals) 176. In a typical embodiment, this vocoder is executed according to the EIA / TLA standard IS-96A and works to convert the incoming PCM waveform into a sequence of voice code processed data packets. These sequences of data are passed to a first input on a subsequent microprocessor 178 which also has a second input, and this is connected to a PTT processor 184. The output of the microprocessor goes to a modem 180. When the displayed PTT switch 188 is activated by the current user, a subsequent PTT processor 184 transmits PTT data packets to the second input of the microprocessor 178 which then merges these packets with the vocoder data packets and presents the result to the modem 180, which is synchronized with one of the the network management modems 98 (Fig. 2) during PTT operation. Although the PTT processor 184 is designed to be functionally different from the microprocessor 178, both of these processors may be part of a common processor unit.

The receiver portion 142, as shown, comprises a modem modulator 192 which is also synchronized with an associated network management modem 98 within a network connection station 40 during PTT mode operation. The data packets produced by the modem modulator 192 in response to forward information of the associated modem 98 go to an IS-96A vocoder 196 which in turn generates a PCM signal from the received vocoder data packets for use of a receiver encoder / decoder (codec) 200. The analog output of this unit 200 is then routed to a conventional telephone speaker (the telephone portion of a telephone handset). It should be noted that the functions performed by the units 172 and 200 may also be incorporated into a common circuit. Similarly, the code function of the vocoder 176 can be combined with the decode function of the vocoder 196 of a common unit.

As illustrated in FIG. 3A, a portion of the information received from the network connection station 40 via the receiver portion 142 is transmitted to the microprocessor 178 via a signal line 212. This information may include various network state data (e.g., the identity of other participating users, the currently active user) for transmission from the microprocessor. 178 to a conventional display 214 (for example, a liquid crystal display or window).

FIG. 3B shows the same telephone apparatus as that shown in FIG. 3A, but now modified to handle encrypted connection with a private PTT network. An alternate transmitter portion 140 'indicates that an encryption module 210 is inserted between the vocoder 176 and the microprocessor 178. In a typical example, this module 210 performs encryption of the vocoder data packets according to an industry standard algorithm such as, for example, the DES (data encryption standard). Similarly, in an alternate receiver portion 142 ', a decryption module 214 is inserted to remove the encryption from the data packets produced by the modem modulator 192' shown at the bottom right of the drawing. It should again be noted that the functions performed by the elements 172 and 200 can be performed by a combined circuit, and correspondingly the function of the vocoder 176 can be combined with the function of the vocoder 196 in one and the same unit. Finally, the function of modules 210 and 214 can also be combined. The landline and cell phones belonging to or associated with the use of individual users within a given private PTT network capable of handling encrypted interactions will be similarly configured with encryption and decryption modules of similar type.

When the landline telephone user shown in FIG. 3B is designated as the currently active user, microprocessor 178 generates an encryption identification number (ID) for transmission to the network connection station 40. The number ID is associated with a particular key used in the decryption of the encrypted information provided by module 210. The station 40 sends the encryption number ID to all telephones connected to the remaining inactive (non-speaking) users in the network, each of which has at its disposal a decryption module corresponding to the decryption module 214 'shown in FIG. 3B. Each such decryption module typically includes a lookup table that defines the decryption key assigned to each encryption ID. Thus, each passive user is able to decrypt the encrypted information from the active user upon receipt of the encryption number (ID).

Fig. 4 is a block diagram of a dual mode PTT telephone for AMPS, that is, for an advanced mobile telephone system, and this telephone comprises a transmitter part 240 and a receiver part 242 as before. The transmitter portion 240 is set up for standard telephone operation when the input switch 248 is added to the position 250 for connecting the microphone 254 to the displayed AMPS transmitter 255.1, the second position 258 of the switch, the transmitter portion 240 is added to PTT operation within a private PTT network. Similarly, receiver portion 242 is set up for standard telephone operation when receiver receiver 262 is added to its position 266, and to PTT operation when the switch is added to position 268.

During PTT operation, voice information is transmitted from microphone 254 via input transceiver 248 to an encoder / decoder 272 which converts the analog speech into pulse coded modulated waveforms to an IS-96A vocoder 276. The resulting vocode data packets may then optionally be encrypted in an encryption module 278. If desired, the packets go to a microprocessor 279 for merging with PTT packets from a PTT processor 284. This processor produces such PTT packets in response to the operation of the PTT switch 288 shown in the diagram. The resulting braided vocode data and PTT packets are then processed in a transmitter channel modem 280 and sent to transmitter 255 to be sent to the former AMPS base stations 70, 72.1, an alternative embodiment digital information from an external circuit (not shown) to the encryption module 278 or directly to the microprocessor 279.

Receiver portion 242 comprises an AMPS receiver 291 for receiving forward information from the network connection station 40. The analog output of the receiver 291 is coupled to a receiver channel modem 292, and this modem is synchronized with a network management modem 98 during PTT mode operation. The vocoder data packets generated by modem 292 go to a decryption module 294 during encrypted private PTT connection periods. When encryption is not performed, the vocoder data packets are processed by a receiver vocoder 296 arranged to generate a PCM signal for use of an encoder / decoder 300 in the receiver portion. The analog output of this unit goes to a conventional telephone receiver 304. When encryption is in progress, state information for the private network and the like, received from station 40, is decrypted to microprocessor 178 via the signal line 212 '.

As reviewed in connection with FIG. 3A and 3B should again be noted that the functions performed by the units 272 and 300 can be performed by a single unit, and correspondingly the code functions of the vocoder 276 can be combined with the decode functions of the vocoder 296, in a single unit. Finally, the functions of the encryption module 278 and the functions of the decryption module 294 can also be combined into a single component.

Fig. 5 shows a block diagram of a CDMA cell phone configured for use within a private PTT network. The telephone of FIG. 5 consists of a CDMA transmitter portion and a CDMA receiver portion 342. During PTT operation, analog speech goes from microphone 354 to encoder / decoder 372 which is arranged to produce a pulse code modulated (PCM) waveform. The waveform proceeds to a voice code circuit (vocoder) 376, which in turn generates vocode data packets for possible encryption in an encryption module 378. When encryption is not desired, the vocoder data packets go to a microprocessor 379 for merging with ΡΤΊ packets from a PTT processor 384. As before, the PTT packets of the PTT processor 384 generate in response to operation of the PTT switch 388. The resulting merged vocoder data and The PTT packets then go from microprocessor 379 to CDMA transmitter 355.

CDMA receiver portion 342 comprises a CDMA receiver 392 which generates vocoder data packets in response to transmitted information from station 40. These packets extend to a decryption module 394 during periods of encrypted private PTT connection. When the encryption is not in use, the packets go to processing a vocoder 396 which produces PCM signals for use of an encoder / decoder 400 in the receiver portion. The analog output of this element is then fed to a conventional loudspeaker 404. The functions of the units 372 and 400 can be combined in a single assembly, and the same applies to the vocoder functions in the ice vocals 376 and 396. Finally, the modules 378 and 394 can be connected to a single unit.

Fig. 6 shows a schematic diagram of a network connection station 450 for use in a private PTT network where signaling is performed with analog ΐοηετ. The station 450 comprises a network controller 490 which in turn has stored one or more lists of the telephone numbers that apply to 20 the users of the corresponding private PTT networks. When it is desired to access a given such network, a user enters an access number that determines which network it is.

The station 450 is designed to act on the public network 10 as a private exchange branch (PBX), and the number dialed by the user can therefore be received via a TI channel 44 connected to one of several web management tone detectors 498. The tone detector 498 'w receiving the incoming call (the in incoming call) prints a detection signal on the corresponding output line 500', and this line is scanned by the network controller 490 which, upon detecting a signal, starts analyzing this signal or the transmitted tone sequence, for to authenticate the calling PTT user. When the dialed access number is recognized by the device 490 and the user is thereby also identified, the device 490 30 calls the users in the PTT network via the other TI channels 44 by means of standard telephone network procedures. Upon detecting that a first of the other users of the identified private PTT network answers a call, the device 490 sends a connection signal (CONNECT) in the form of tones to the user who initially dialed the access number thereby indicating to the calling user that at least one other user has connected to the identified private PTT network.

A PTT controller 504 is provided for managing voice privileges among the two or more users who have entered the private PTT network. In particular, this controller 504 is responsible for the PTT request signals in the form of an analog tone or a combination of multiple tones (PTT tone requests) and generated by the telephone sets of the users of the identified private PTT network. Each tone request is made in such a telephone apparatus by a user, either in response to manual operation of a PTT switch or in response to recorded speech activity of the user. A PTT tone request from a given user is recorded by the assigned tone detector 498 which transmits a request signal to the controller 504 via one of the T1 channels 500 (the lines). In a typical embodiment, the controller 504 is adapted to confer voice privileges among the users in the manner described above in connection with the review of the corresponding controller 104 (FIG. 2).

After a new active user is identified by the controller 504 on the basis of the received PTT tone requests, the device performs a multicast switch 510 io (multicast switch) configuration to accept the return voice transmission or digital information on the return channel, assigned exclusively from the T-channel 44 the active current user. This means that the information on other return channels assigned to one of the other (i.e., inactive) users is not transmitted over multiple channels via switch 110. PTT controller 504 also configures switch 510 to produce return information which is accepted by the newly identified active user, to the T channels assigned to each of the inactive users. Since the tone requests are transmitted only through the return channels of the inactive users, they will preferably not interfere with the reception of returned information from the active user.

Although the forwarding of. information in each private PTT network is nominally used 20 to transmit analogue voice or digital information (data) from the active user and to the other users, the PTT controller 504 may also transmit system state information over the forward channels during breaks or stays in the information transmission from the active user. . In one example, this information may include:

(i) a given private PTT network's potential current users (their telephone number, name, priority 25), (ii) users (with the same data information) belonging to the group in the given PTT network, (iii) the current active user ( same data), and (iv) the queue of the users (same data) who sent PTT requests to the web controller 490.

Such information could be transmitted using tone sequences or combinations suitable for detection in each user's own telephone. Various network information in the private PTT network (for example, user lists, priorities) could also be stored in each user's telephone, and particular inputs desired to be retrieved for display upon receipt of the corresponding tone or tone combination from the grid connection station 450 recliners may be applicable. In this regard, a landline telephone configured for use in a private PTT network orchestrated by the network connection station 450 will be described, referring to FIG.

7.

The figure shows a block diagram of such a landline PTT telephone with a transmitter part 540 and a receiver part 542 and arranged for communication by analog tones. In PTT operation, an input switch 548 is nominally set to its position 550 by the displayed PTT processor 552 to connect the voice information from an input microphone 554 to the public telecommunications network (PSTN). When the switch 560 on the output is operated by the current user, the processor 552 switches the input switch to the second position, position 562 and engages a tone generator 566 and so that the PTT tone requests can be transmitted over the telephone network to the network connection station 450, the tone requests being generated by the tone generator 56.

Receiver portion 542 includes a speaker 568 and an internal tone detector 570 for detecting analog tones or combinations thereof transmitted by the network connection station 450 during PTT mode operation. These tones or tone combinations can be used to convey a variety of state and control information groups to the PTT telephone shown in FIG. 7.1 A typical embodiment may include this information:

(i) identification of the currently active user (name, priority), is (ii) an indication that the user assigned to the relevant PTT phone has been granted voice privileges, (iii) a note that the user's voice privileges are waived in favor of a and (iv) identification of the user who was thereby included in the private PTT network.

Each tone or tone combination will have a character string or other message stored in a display processor 574, and in response to each recorded tone or tone combination, this processor generates the assigned message for transfer to an alphanumeric display 578 (generally a display unit). The control and state information set forth above is intended to be taken as a pure example, and in alternative embodiments, another type of information may be provided by the PTT telephone by means of the network command center or connection station.