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

ES 2 264 156 T3

DESCRIPTION

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

Background of the invention

I. Field of the invention

The present invention relates generally to multiparty communication systems, and more particularly to a private point-to-multipoint communication network incorporated directly into a land line or mobile telephone system.

II. Description of Related Art

Mobile cellular telephone service has been in use for some time, and has traditionally been characterized by a central site transmitting with high power to a limited number of mobile or portable units over a large geographic area. In early mobile systems, only a limited number of radio channels were available, limiting the number of radiotelephone conversations within an entire metropolitan area to the number of channels available.

Mobile modem radiotelephone systems have a comparatively large number of radio channels, which can be effectively multiplied using identical channel frequencies within the different smaller coverage areas (ie, "cells") spanning a territory of service given. Each cell includes a cell-to-site transmitter, or base station, that transmits at a selected power level to ensure signal reception at the cell boundary without unduly interfering with the reception of adjacent cells. This allows channel frequencies used in one cell to be reused in another cell geographically separated from it according to a predetermined plan. Thus, a large number of channels can be made available in a metropolitan area and the service provided thereby can be identical to a standard wireline telephone.

There are numerous standards for the implementation of mobile phone communications. These standards include Advanced Mobile Phone System (AMPS), Global Mobile Communication System (GSM), and Code Division Multiple Access (CDMA). ). The CDMA spread spectrum modulation technique has significant advantages over other modulation techniques for multiple access communication systems. For example, the use of CDMA results in a much higher spectral efficiency than can be achieved using other multiple access schemes.

Although recent development efforts have enabled CDMA and other mobile systems to effectively provide “point-to-point” communication links between users, various public and private agencies have nonetheless continued to rely on land mobile radio communications networks (LMRs for its acronym in English) dedicated. This results from the inability of mobile systems to establish “point-to-multipoint” communication networks between a set of member users. For example, local law enforcement agencies use LMR networks in which a closed system of radio communication is established through relay stations. Such closed LMR networks are often characterized by a push-to-talk (PTT) operation, in which users press a talk button on the handset or the like when they wish to transmit voice information to other member users. However, the inability to provide relay stations across a large geographic area limits the degree to which the member user pool can be geographically dispersed.

Although both conventional land line and mobile telephone systems are capable of facilitating communication between distant users, “closed-type PTT” communication networks have not been incorporated up to now into either type of system. . This may be due in part to the absence of a convenient mechanism for automatically incorporating an identified set of users into such a closed network. On the other hand, even when such a mechanism is available, both types of systems are easily compromised by unauthorized third parties and are therefore not suitable for secure communication.

The conference calling capability provided by both land line and mobile line carriers is also an inappropriate substitute for a PTT-type communications network. In particular, the conference call between users within various mobile or land line systems requires a certain degree of prior coordination with the responsible service provider. Furthermore, in many conference call systems the conference call participant information signals are combined and the resulting composite signal is universally provided to each of those participants. This effectively makes it impossible to encode each information signal separately as a means of increasing communication security, since separately encoded information signals would generally not be recoverable from the composite signal.

EP-A-0 676 906 describes a voice and service signal transmission method. The digitized voice and service signals are each provided to a subscriber system via a B channel. The system uses a switching unit to forward the direct voice signals to a control module. Device

ES 2 264 156 T3 switching also transmits the service signals to the control module through a monitoring circuit. The control module is connected with a special terminal. The monitoring circuit converts the B-channel service signals to a respective D-channel and delivers them to the control module. The control module and the monitoring circuit are built as special peripheral modules in a commercially available subscriber system. Thus the data is transmitted according to a standard process.

US-A-5 119 375 describes a system and a method for the wireless transmission of information signals between a base station and a plurality of subscriber stations. A base station receives an information signal from the trunk lines to transmit it over an RF link to a predetermined receiver unit capable of receiving and processing the information signal. The information signal is assigned a route to process the information signal for transmission over the RF link. The information signal is sampled by default and processed according to the assigned path to produce representative signal samples of the information signal. The signal samples can be reconstructed in the predetermined receiving unit to provide substantially the same information as the information signal provided prior to being processed, with the compression step resulting in a selective removal of predetermined portions of the signal samples. the signal such that there will be samples of the reconstructed signal, substantially not degraded. Representative compressed signal samples of the information signal are placed at predetermined, discrete positions of repeater segments of a transmission signal channel, and transmitted over an RF link to the predetermined receiver unit.

Correspondingly, it is an object of the present invention to incorporate a private communication network directly into a mobile telephone system and / or land line in such a way as to obviate the need for prior coordination with a telephone service provider.

It is another object of the invention that the private communication network emulates a LMR network characterized by the operation of PTT.

It is another object of the present invention that control of the private communication network is resident within a network call manager separately connected to an existing land line telephone system.

It is another object of the present invention that encryption techniques can be applied within the private communication network as means to increase the security of communication.

Summary of the invention

The present invention relates to a private communication network through which a plurality of member users communicate with the public switched telephone network (PSTN). Each member user uses a modified land line telephone, directly connected to the PSTN, or uses a modified mobile phone operatively coupled to the PSTN via a wireless communication system. The private communication network includes a network call manager having a telephone network interface for establishing a telephone connection with each of a plurality of telephone lines on the PSTN. Each of the plurality of telephone lines is associated with one of the plurality of member users.

The network call manager further includes a telephone line switching matrix, coupled to the telephone network interface, to provide an information signal received from an active member user through a selected telephone line to the remaining users. inactive members. A network administrator controller identifies the active member user based on the talk request signals, namely the push-to-talk (PTT) request signals, received from the member users' phones through the plurality of lines telephone. The active user may be identified as, for example, the member user from whom a PTT request signal is first received after the previously active member user has waived speaking privileges. Alternatively, the active member user can be chosen using predefined user priority criteria to evaluate all PTT request signals placed in the queue by the network call manager.

The telephone equipment of each member user will typically be capable of performing both standard telephone operation and PTT operation over the private communication network. When configured for PTT operation, each telephone system digitally receives and processes input data or voice information from a member user. The resulting vocoder data packets, as well as any PTT request signals initiated by the member user, will then be provided to a modem for reverse link transmission via the PSTN to the administrator's telephone network interface. network calls. The security of the private PTT network can be increased by configuring each telephone equipment for the encryption of all such reverse link transmissions, as well as for the corresponding decoding of the forward link information from the active member user.

Thus, according to a first aspect of the present invention, a network call manager is provided as set forth in claim 1.

According to a second aspect, a communication network is provided as set forth in claim 9.

ES 2 264 156 T3

According to a third aspect, a method is provided for establishing a private, multiparty telephone connection between a plurality of telephone equipment suitable for PTT request in a communication system as set forth in claim 21.

Brief description of the drawings

Other objects and additional features of the invention will be more readily apparent from the following detailed description and the appended claims viewed in conjunction with the drawings, where:

Figure 1 depicts by way of illustration the elements of an exemplary telephone system within which a private point-to-multipoint PTT communication network can be established;

Figure 2 is a block diagram of an exemplary network call manager of the private PTT network;

Figure 3A shows a block diagram of a dual mode PTT landline telephone line comprised of a transmitting section and a receiving section;

Figure 3B depicts the dual PTT land line of the mode of Figure 3A modified to facilitate encrypted communication within a private PTT network;

Figure 4 is a block diagram of an AMPS dual mode PTT telephone;

Figure 5 is a block diagram of a CDMA mobile phone configured for use within a private PTT network;

Figure 6 provides a functional block diagram of a network call manager designed for use within a private PTT network in which signaling is done using analog tones; Y

Figure 7 shows a landline phone configured to communicate with a network call manager using analog tones.

Detailed description of preferred representations

I. Structure of the private PTT network

Figure 1 depicts by way of illustration the elements of an exemplary telephone system within which a private PTT point-to-multipoint communication network ("private PTT network") can be established. Referring to Figure 1, the exemplary telephone system includes a public switched telephone network (PSTN) (10), a CDMA mobile communication system (14), and an analog mobile communication system (AMPS) (18). The CDMA system (14) provides service to CDMA compatible mobile radiotelephones (“CDMA mobiles”) (22) and (24), while the AMPS system (18) facilitates communication with the users of the mobile radiotelephones. compatible with AMPS (“AMPS mobiles”) (28) and (30). A network call manager (40), connected via a plurality of T1 channels (44) to the PSTN (10), functions as described below to create a private communication network between a corresponding plurality of member users. within the exemplary telephone system of Figure 1.

The private communications network may include member users receiving services from one or both CDMA and AMPS mobile systems (14) and (18), and / or may include one or more member users directly connected to the PSTN (10) to through modified land line telephones such as telephone (48). Although the mobile CDMA and AMPS systems are shown as being incorporated within the exemplary representation of Figure 1, it should be understood that the teachings of the present invention are also suitable for other mobile air interface standards for example for the Global System. for Mobile Communications (GSM) and Time Division Multiple Access (TDMA). A brief description of the constituent elements of the CDMA and AMPS mobile communication systems (14) and (18) shown in Figure 1 will be provided before discussing the operational principles of the embodiments of the present invention.

The CDMA mobile communication system (14) includes a plurality of cells, two of which are identified in Figure 1 as including cells at sites (ie, "base stations") (56) and (58). Each cell can be divided into a number of sectors, where communication with CDMA mobiles 22 and 24 within a given sector is handled by a cell-to-site transceiver that provides radio coverage over the sector. The base stations (56) and (58) function to receive and transmit the signals allowing a radio transceiver within each CDMA mobile to communicate with the PSTN (10). In the CDMA system 14, the data packets are used in the over-the-air exchange of information between the base stations (56) and (58) and the CDMA mobiles (22) and (24).

Telephone calls are routed by cell-to-site base stations (56) and (58) between mobiles (22) and (24) and a CDMA mobile switching center (MSC) (60), which will typically be located within a mobile phone switching office (not shown). The primary purpose of the MSC (60) is

ES 2 264 156 T3 providing voice path connections between the CDMA mobiles (22) and (24) and the PSTN (10). To this end, the MSC (60) performs functions such as data classification between the modems (62) of an MSC and the CDMA mobiles (22) and (24) through the CDMA base station (56) or ( 58) appropriate. The MSC (60) also performs other tasks, including searching for a CDMA mobile when a call is received from the PSTN (10) and switching calls to the available PSTN lines through a plurality of T1 channels ( 64). A set of MSC modems 62 serves to convert the digital information signals received from the CDMA mobiles 22 and 24 into analog signals suitable to be transmitted by the PSTN (10), and likewise converts the analog signals from the PSTN 10 into digital signals that are subsequently provided to the CDMA mobiles (22) and (24).

The AMPS mobile communication system (18) also includes a number of cells, two of which are identified in Figure 1 as including cell-to-site base stations (70) and (72). Each cell can be divided into a number of sectors, where communication with AMPS mobiles (28) and (30) within a given sector is managed by a cell-to-site transceiver that provides radio coverage over the sector. . Telephone calls are routed by cell-to-site base stations (70) and (72) between mobiles (28) and (30) and an AMPS mobile switching center (MSC) (76), which is linked to the PSTN (10) through a plurality of T1 channels (80).

II. Operation of the private PTT network

Turning to Figure 2, reference is made to a block diagram of an exemplary network call manager 40 to describe the operation of the private PTT network. The manner in which the land line or portable telephones associated with each member user are configured to cooperate with the network call manager 40 will be described below in relation to Figures 3 to 5. In what appears below, the communication links from the modified land line telephone (48), from the AMPS mobiles (28) and (30), and from the CDMA mobiles (22) and (24), to the network call manager (40) through the PSTN (10) are called "reverse links". The reverse link associated with the member user currently designated by the network call manager (40) as the active member user, is assumed to be the only reverse link carrier of valid voice or data information. The rest of the reverse links are available to be used to provide signaling to the network call manager (40). Each "direct link" through the PSTN (10) of the network call manager (40) with each member user carries the voice or data information provided by the active member user. As described in this document, the network call manager 40 is reconfigured on each new identification of an active member. This reconfiguration results in the reverse link data or voice information from the newly identified active member user being provided to the direct links associated with the rest of the member users, including the direct link from the previously active member user.

The network call manager (40) includes a network controller (90), within which is stored at least a list of telephone numbers associated with member users of a first private PTT network. If access to the first private PTT network is desired, a calling member user dials an access number that identifies the first private PTT network. The network controller (90) can also store other lists of member users, each list is associated with a unique access number and defines another private PTT network.

The network call manager (40) is designed to appear to the PSTN (10) as a Private Telephone Switching system (PBX), and thus the call interposed by the calling member user can be received through any of the T1 channels (44). In this sense, a T1 interface of the telephone network (92) is provided to form a connection between the T1 channel (44) associated with the calling member user and one of a plurality of modems of the network administrator (98). As described in this document, the T1 interface (92) also serves to connect several of the other modems (98) to one of the T1 channels (44) associated with other member users.

If the CDMA mobile system (14) serves the calling member user, a telephone connection is established when the network call manager's modem (98 ') coupled to the T1 channel (44) that receives the incoming call is synchronized with one of the MSC modems (62) (Figure 1) assigned to the call. For a calling member user who has an AMPS landline or mobile phone, a similar phone connection is established once an internal modem synchronization (Figures 3A and 4) occurs within the member user's phone and the network administrator modem (98 ') member receiving the incoming call. In an exemplary embodiment, the modems of the network manager 98 comprise, for example, so-called "AMPS modems" which are particularly well suited for the transmission of information over the air.

When an incoming call to a private PTT network is received from a member user through one of the T1 channels (44), the T1 interface (92) uses standard techniques to determine the access number dialed during call imposition. . The dialed access number, which corresponds to a given private PTT network, is connected by the T1 interface (92) to the network controller (90). The T1 interface also connects the T1 channel (44) associated with the calling member user with an available network administrator's modem (eg, the network administrator's modem (98 ')). Once modem synchronization has been achieved, the network controller (90) may request the calling user to provide the authentication information used to verify that the calling user is a member of the private PTT network identified as that corresponds to the called access number. By confirming said membership, the network controller (90) can command the T1 interface (92) or a

ES 2 264 156 T3 network administrator modem (98) selected to initiate paging of the remaining member users of the identified private PTT network. It should be noted that in alternative representations the T1 interface (92) may comprise an E1 interface, or various other types of digital or "PBX-like" interfaces.

Once a first user of the other member users of the identified PTT private network responds to a web page (i.e. a phone call) issued by the calling network administrator's modems (98) over the interface T1 (92), a modem synchronization process similar to the type described above occurs again. In particular, if the calling member user is served by an AMPS or land line phone, the modem synchronization occurs between the internal modem to the called member user's phone (Figures 3A and 4) and one of the modems of the call manager. the network (98). If the CDMA mobile system 14 provides its service to the called member user, modem synchronization occurs between the network call manager's modem (98) and one of the MSC's modems (62) (Figure 1). It should be understood that the MSC (62) modems do not need to be physically close to the MSC (60), but may be located anywhere within the telephone system infrastructure.

When the calling network administrator's modem (98) achieves such synchronization, it produces a CONNECT signal that is detected by the network controller (90). The network controller (90) may then instruct the called network administrator's modem (98 ') to send a CONNECT signal to the member user who originally dials the access number of the identified private PTT network. The network controller may also periodically send each participating authenticated member user of the private PTT network a list, to be displayed on each authenticated user's phone, of the other currently participating member users.

A PTT controller 104 is provided to agree speech or data transmission privileges between two or more member users connected to the identified private PTT network. In particular, the PTT controller 104 responds to the PTT request signals ("PTT requests") generated by the landline or portable telephones associated with the member users of the identified private PTT network. Each PTT request is generated on a member user's phone in response to manual linking of a PTT switch, or in response to detected voice activity from the member user. A PTT request from a given member user is detected by the modem (98) assigned to it, which provides the PTT signal to the PTT controller (104).

In an exemplary embodiment the PTT controller 104 designates as the currently active member user, from which the first PTT request is received after a previously active member user relinquishes network talk privileges. The previously active member user relinquishes network talk privileges, in the case of manual PTT signaling, once the PTT switch link of the caller's phone is released. In the case of voice activated PTT signaling, network talk privileges are waived once a pause of predetermined duration occurs.

In an alternative representation, PTT requests received before the currently active member user relinquishes network chat privileges are placed in a row. When the currently active member user subsequently relinquishes network chat privileges, queued PTT requests are evaluated against predefined criteria to determine the next currently active member user. Such predefined criteria could include, for example, the priority of the member user as well as the order of receipt of requests that are in line.

The network call manager 40 may employ still other techniques to select a new active member user based on received PTT requests. For example, each user who is a member of a given private PTT network can be assigned a relative level of priority within the network. In this case when a PTT request is received from a member user of a higher priority than the currently active member user, the network call manager (40) overrides the preferential right to the currently active member user and grants talk privileges from the network to the higher priority member user. It is also possible that each member user is allowed to alter his priority within prescribed limits known to the network call manager 40 as a way to obtain network talk privileges in urgent circumstances.

After the PTT controller (104) has identified a new active member user based on the received PTT requests, the PTT controller (104) configures a multicast switch (110) to accept the data or broadcast information. reverse link voice exclusively from the modem (98) associated with the currently active member user. That is, the backlink information from each of the other modems (98), each of which has been assigned to one of the remaining member users (that is, the non-active ones), is ignored by the switch. multicast (110). The PTT controller also configures the multicast switch (110) to provide the accepted backlink information of the newly identified active member user to the modems (98) associated with each inactive member user. Because PTT requests are transmitted only on the backlinks of the inactive member users, such PTT requests do not advantageously interfere with the receipt of the backlink information from the active member user.

Although the direct links of each private PTT network are nominally used to carry the data or voice information of the active member user to the rest of the member users, the network controller (90) also

ES 2 264 156 T3 can transmit the system status information through the direct links during pauses or intervals in the transmission of active member user information. In an exemplary representation this system status information includes the following:

(i) eligible member users (phone number, name, priority) of a given private PTT network, (ii) member users (phone number, name, priority) currently connected to the given private PTT network, (iii) the currently active member user (phone number, name, priority), and (iv) the row of member users (phone number, name, priority, request order) who have provided the PTT requests to the PTT controller 104.

This information on the state of the network is received and displayed by the phones associated with the member users. The following section provides a description of particular implementations of dual PTT mode phones suitable for use within a private PTT network.

III. Dual Mode PTT Landline and Mobile Phones

Referring now to Figure 3A, there is shown a block diagram of a dual mode PTT land telephone line comprising a transmitting section (140) and a receiving section (142). The transmit section (140) of the dual-mode telephone of Figure 3A is configured for standard telephone operation when the input switch (148) is toggled toward the pole (150), thereby engaging the input microphone (154). to the PSTN (10). The input switch (148) is toggled to the pole (158) when it is desired to configure the transmit section (140) for PTT operation within a private PTT network. Similarly, the receive section (142) is configured for standard telephone operation when the receive switch (162) is shifted to pole (168), and is configured for PTT operation when the receive switch (162 ) is shifted towards the pole (166).

During PTT operation, voice information from microphone 154 is coupled by switch 148 to an encoder 172. Encoder 172 is provided to transform this analog voice information, or data information from a peripheral device (not shown) coupled to switch 148, into a pulse code modulated (PCM) waveform provided at a speech coder (176). In an exemplary embodiment the speech scrambler 176 is implemented in accordance with the EIA / TIAIS-96A standard, and operates to convert the input PCM waveform into a sequence of data packets from the speech scrambler. These data packets from the vocoder are provided to a first input of a microprocessor (178), which also has a second input coupled to a processor (184) and to a PTT output coupled to a modem (180). When a PTT switch (188) is turned on by the associated member user, the PTT processor (184) provides the PTT data packets to the second input of the microprocessor (178). The microprocessor (178) then interleaves the PTT data packets with the voice coder data packets and provides the result to the modem (180), which is synchronized with one of the network administrator's modems (98) during operation. of PTT. Although the PTT processor (184) is represented as being functionally different from the microprocessor (178), both functional elements can be incorporated within a single microprocessor unit.

The receiving section (142) includes a modem demodulator (192), which is also synchronized with a companion network manager (98) modem within the network call manager (40) during PTT mode operation. The vocoder data packets generated by the second modem (192) in response to forward link information from its accompanying network manager (98) modem are provided to a vocoder (196) in the IS-96A reception, which alternatively produces a PCM signal from the data packets received from the vocoder for use by an encoder / decoder (200) of the reception section. The analog output from the encoder / decoder (200) is then applied to a conventional telephone handset (204). It should be noted that the functions performed by encoders / decoders 172 and 200 can be performed by a single device. Similarly, the encoding function of the speech scrambler (176) can be combined with the decoding function of the speech scrambler (196) in a single device.

As indicated in Figure 3A, certain information received from the network manager unit (40) by the receiving section (142) may be provided to the microprocessor (178) through the signal line (212). This information may include various network status data (eg, identities of other participating member users, currently active member user) that were provided by the microprocessor (178) to a conventional display (214) (eg, the display LCD).

Figure 3B depicts the dual mode PTT land line telephone of Figure 3A modified to facilitate encrypted communication within a private PTT network. Specifically, an alternate transmission section (140 ') for the Figure 3A telephone includes an encoding module (210) interposed between the IS-96A vocoder (176) and the microprocessor (178). In an exemplary embodiment the encoding module 210 functions to encode the speech encoder data packets in accordance with an industry standard algorithm such as the Data Encoding Standard (DES). Similarly, an alternative reception section (142 ') is seen to include a decoding module (214) to eliminate the

ES 2 264 156 T3 encoding of the voice coder data packets produced by the second modem (192). Once again we must point out that the functions performed by the encoders / decoders (172) and (200) can be performed by a single device. Similarly, the encoding function of the speech scrambler 176 can be combined with the decoding function of the speech scrambler 196 in a single device. Furthermore, the functions of the encoder module (210) and the decoding module (214) can also be combined in a single device. Landline and mobile phones associated with all member users of a given private PTT network capable of participating in encrypted communication will be configured with encryption and decryption modules of the same type.

When the land line telephone user of Figure 3B has been designated as a currently active member user, the microprocessor (178) will generate an encoding identification number (LD.) For transmission to the network call manager (40). . The LD encoding. it is associated with a particular "key" used in the decoding of the encoded information produced by the encoding module (210). The network call manager multicasts the LD encoding. for each of the phones associated with the remaining non-active (ie, non-speaking) member users, each of which includes a decoding module similar to the decoding module (214). Each decoding module will generally include a look-up table that identifies the encryption key associated with each LD encoding. In this way, each inactive member user can decode the encoded information of the currently active member user once it receives the LD encoding. provided by this.

Turning now to Figure 4, a block diagram is provided depicting an AMPS dual mode PTT telephone comprising a transmit section (240) and a receive section (242). The transmit section (240) of the AMPS dual-mode PTT telephone of Figure 4 is configured for standard telephone operation when the input switch (248) is switched to the (250) pole, thereby engaging the input microphone ( 254) to an AMPS transmitter (255). The input switch (248) toggles toward the pole (258) when it is desired to configure the transmit section (240) for PTT operation within a private PTT network. Similarly, the receive section (242) is configured for standard telephone operation when the receive switch (262) changes to pole (266), and is configured for PTT operation when the receive switch (262) shifts toward the pole (268).

During PTT operation, voice information from the microphone (254) is coupled by the switch (248) to an encoder / decoder (272). Encoder / decoder (272) is arranged to transform this analog speech information into a pulse code modulated (PCM) waveform provided to an IS-96A speech coder (276). Then, the data packets resulting from the speech scrambler can optionally be scrambled by a scrambler module (278). When encoding is not desired, the data packets from the vocoder are provided to a microprocessor (279) for interpolation with the PTT packets from a PTT processor (284). Once again, the PTT packets are generated by the PTT processor (284) in response to the link of the PTT switch (288). The vocoder data and the resulting interpolated PTT packets are processed by a transmission path modem (280) and provided to the AMPS transmitter (255) for transmission to the AMPS base station (70) or (72). . In an alternative representation, data information from a peripheral device (not shown) can be provided to the encoding module (278) or directly to the microprocessor (279).

The reception section (242) includes an AMPS receiver (291) to receive the forward link information provided by the network call manager (40). The analog output of the AMPS receiver (291) is coupled to a receive path modem (292), which is synchronized with a network manager modem (98) during PTT mode operation. Speech scrambler data packets generated by the receive path modem (292) are provided to a decoding module 294 during periods of private encrypted PTT communication. When encoding is not performed, the data packets from the speech coder are processed by a speech coder (296) of the reception section to produce a PCM signal that will be used by an encoder / decoder (300) of the section of reception. Then, the analog output from the encoder / decoder (300) is applied to a conventional telephone handset (304). When encoding is performed, the status information of the private network and the like received from the network manager unit (40) is decoded and provided to the microprocessor (178) via the signal line (212 ').

As discussed with respect to Figures 3A and 3B, it should be noted once again that the functions performed by encoders / decoders 272 and 300 can be performed by a single device. Similarly, the encoding function of the speech scrambler (276) can be combined with the decoding function of the speech scrambler (296) in a single device. Furthermore, the functions of the encoding module (278) and the decoding module (294) can also be combined in a single device.

Figure 5 shows a block diagram of a CDMA mobile phone configured for use within a private PTT network. The CDMA mobile phone of Figure 5 comprises a CDMA transmission section (340) and a CDMA transmission section (342). During PTT operation, voice information from microphone 354 is provided to an encoder / decoder 372 arranged to produce a pulse code modulated (PCM) waveform. The PCM waveform is provided to a speech scrambler (376), which in turn generates speech scrambler data packets for optional encoding within an encoding module (378). When encryption is not desired, the data packets from the vocoder are provided.

ES 2 264 156 T3 are attached to a microprocessor (379) to be interpolated with the PTT packets from a PTT processor (384). Once again the PTT packets are generated by the PTT processor (384) in response to the link of the PTT switch (388). The vocoder data and the resulting interpolated PTT packets are then provided by the microprocessor (379) to the CDMA transmitter (355).

The CDMA receiving section (342) includes a CDMA receiver, which generates data packets from the vocoder in response to the forward link information from the network call manager (40). The data packets from the vocoder are provided to a module (394) during periods of private coded PTT communication. When encoding is not performed, the speech coder data packets are processed by a CDMA receiving section speech coder (396) that operates to produce a PCM signal that will be used by an encoder / decoder (400). from the CDMA reception section. The analog output from the encoder / decoder (400) of the CDMA receiving section is then applied to a conventional telephone handset (404). The functions of the encoders / decoders 372 and 400 can be performed within a single device, in the same way that the functions of the speech coders 376 and 396 can also be performed within a single device. Furthermore, the functions of the encoding module (378) and the decoding module (394) can also be combined in a single device.

III. Analog PTT Private Network

Figure 6 shows a functional block diagram of a network call manager (40) designed to be used within a private PTT network in which signaling is done using analog tones. The network call manager (40) includes a network controller (490), within which one or more lists of the telephone numbers associated with the member users of the corresponding private PTT networks are stored. If it is desired to have access to a given private PTT network, a calling member user dials an access number that identifies the given private PTT network.

The network call manager (40) is designed to appear to the PSTN (10) as if it were a private telephone switching system (PBX), and therefore the call placed by the calling member user can be received by the channel T1 (44) associated with a plurality of network administrator tone detectors (498). The tone detector (498 ') that receives the incoming call prints a detection signal on its output line (500'), which is detected by the network controller (490). The network controller 490 then begins to scan the sequence of the tone detected by the called network manager 498 'tone detector to authenticate the calling PTT user. Once the dialed access number has been recognized by the network controller (490) and the member users of the associated private PTT network have been identified, the network controller (490) starts paging the member users of the network. the private PTT network identified through the remaining T1 channels (44) using standard telephone network procedures. Upon detecting that a first user of the other member users of the identified private PTT network answers a call from the network, the network controller (490) sends a CONNECT signal in the form of tones to the member user who originally dials the number identified private PTT network access point - thus indicating to the calling member user that at least one other member user has joined the identified private PTT network.

A PTT controller (504) is provided to agree talk privileges between two or more member users connected to the identified private PTT network. In particular, the PTT controller (504) responds to the PTT request signals, in the form of a combination of analog tones ("PTT tone request"), generated by the telephones associated with the member users of the identified private PTT network. Each request for the PTT tone is generated on the telephone of a member user in response to manual linking of a PTT switch, or in response to detected voice activity from the member user. A request for the PTT tone of a given member user is detected by the tone detector (498) assigned to it, which then provides a PTT request signal to the PTT controller (504) through one of the output lines (500 ). In an exemplary embodiment the PTT controller (504) functions to assign conversation privileges among requesting member users in the manner previously described with respect to the PTT controller (104) (Figure 2).

After a new active member user has been identified based on the received PTT tone requests, the PTT controller (504) configures a multicast switch (510) to accept the reverse link data or voice information exclusively. from the T1 channel (44) associated with the currently active member user. That is, the backlink information from each of the other T1 channels, each of which has been assigned to one of the remaining member (ie, non-active) users, is not multicast by the multicast switch (510). The PTT controller (504) also configures the multicast switch (510) to provide the accepted backlink information from the newly identified active member user through the T1 channels associated with each of the inactive member users. Because requests for the PTT tone are transmitted only on the reverse links of the inactive member users, such requests for the PTT tone do not advantageously interfere with the reception of the reverse link information from the active member user.

Although the direct links of each private PTT network are nominally used to carry the voice or data information of the active member user to the rest of the member users, the network controller (490) can also transmit the status information of the system through direct links during pauses or spaces in the transmission of information of the active member user. In an exemplary representation this system status information includes the following:

ES 2 264 156 T3 (i) eligible member users (phone number, name, priority) of a given private PTT network, (ii) member users (phone number, name, priority) currently connected to the given private PTT network , (iii) the currently active member user (phone number, name, priority), and (iv) the row of member users (phone number, name, priority, request order) who have made the tone requests PTT to PTT Controller 504.

Such information could be transmitted using sequences of tones or combinations of tones that can be detected within the telephone of each member user. The different information of the private PTT network (i.e. lists, priorities of the member users) could be stored in the telephone of each member user, and specific entries could be retrieved to be displayed once the tone or combination is received. associated tones of the network call manager (40). In this sense, a land telephone line configured to be used within a private PTT network organized by the network call manager (40) is described immediately below in relation to Figure 7.

Referring to Figure 7, a block diagram of a PTT land line is shown having transmit and receive sections 540 and 542 designed for communication using analog tones. During PTT operation, an input switch (548) is nominally switched to pole (550) by the PTT processor (552) to couple voice information from an input microphone (554) to the PSTN. However, when the PTT switch (560) is linked by the associated member user, the processor (552) changes the switch (548) to pole (562) and enables a tone generator (566). This allows the requests for the PTT tone generated by the generator (566) to be transmitted through the PSTN to the network call manager (40).

The receiving section (542) includes a loudspeaker (568), and an internal tone detector (570) for detecting analog tones or combinations of tones transmitted by the network call manager (40) during the PTT mode of operation. These tones or tone combinations can be used to convey a variety of status and control information to the PTT telephone of Figure 7. In an exemplary representation this information may include:

(i) identification of the currently active member user (name, priority), (ii) an indication that it has been agreed to grant conversation privilege to the member user associated with the PTT phone.

(iii) notification that the conversation privileges of the member user associated with the PTT telephone have been revoked in favor of a member user of highest priority, and (iv) identification of the member users currently connected to the private PTT network.

Each tone or tone combination will have associated a character string or other message stored within a display processor (574). In response to each detected tone or tone combination, the display processor (574) provides the associated message to an alphanumeric display (578). The aforementioned status and control information is intended to be used merely as an example, and in alternative representations the network administrator may provide other types of information to the PTT telephone.

The preceding description of the preferred representations is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these representations are readily apparent to those skilled in the art, and the generic principles defined herein can be applied to other representations without the use of innovative faculty. Accordingly, the present invention was not made with the intention of being limited to the representations shown in this document, but to correspond with the broader scope defined by the claims.