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

id="REI-00001" date="20131105"

CROSS-REFERENCE TO RELATED APPLCATION

id="REI-00001"

This application is a reissue of application Ser. No. 08/595,566, filed Feb. 1, 1996, now Pat. No. 5,912,882.

BACKGROUND OF THE INVENTION

I. Field of the Invention

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

II. Description of the Related Art

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

Modern cellular radiotelephone systems have a comparatively large number of radio channels, which may be effectively multiplied by using identical channel frequencies within the differing smaller coverage areas (i.e., “cells”) comprising a given service territory. Each cell includes a cell-site transmitter, or base station, which broadcasts at a power level selected to ensure signal reception at the cell boundary without unduly interfering with reception in adjacent cells. This allows channel frequencies used in one cell to be reused in another cell geographically separated therefrom 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 wire line telephone.

Numerous standards exist for the implementation of cellular telephone communications. These standards include the advanced mobile phone system (AMPS), Global System for Mobile communicationCommunication (GSM), and Code Division Multiple Access (CDMA). The spread spectrum modulation technique of CDMA 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 cellular systems to effectively provide “point-to-point” communication links between users, various public and private agencies have nonetheless continued to rely upon dedicated land mobile radio (LMR) communication networks. This results from the incapability of cellular systems to establish “point-to-multipoint” communication networks among a set of member users. For example, local law-enforcement agencies utilize LMR networks in which a closed radio communication system is established through repeater stations. Such closed LMR networks are often characterized by push-to-talk (PTT) operation, in which users depress a handset talk button or the like when desiring to broadcast voice information to other member users. However, the infeasibility of providing repeater stations over a large geographic area limits the extent to which the set of member users may be geographically dispersed.

Although both cellular and conventional land line telephone systems are capable of facilitating communication between widely separated users, closed “PTT-type” communication networks have not hitherto been incorporated within either type of system. This may be due in part to the absence of a convenient mechanism for automatically joining an identified set of users into such a closed network. Moreover, even if such a mechanism were available, both types of systems are easily compromised by unauthorized third parties and are thus unsuitable for secure communication.

The conference calling capability provided by both cellular and land line carriers is also an unsuitable surrogate for a PTT-type communication network. In particular, conference calling between users within different cellular or land line systems requires some degree of prior coordination with the responsible service provider. Moreover, in many conference calling systems the information signals from the conference call participant are combined and the resultant composite signal universally provided to each such participant. This effectively precludes separately encrypting each such information signal as a means of increasing communication security, since the separately encrypted information signals would generally not be recoverable from the composite signal.

Accordingly, it is an object of the present invention to incorporate a private communication network directly within a cellular and/or land line telephone system 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 emulate an LMR network characterized by PTT operation.

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

It is a further object of the present invention that encryption techniques be capable of application within the private communication network as a means of enhancing communication security.

SUMMARY OF THE INVENTION

The present invention is directed to a private communication network through which a plurality of member users communicate using the public switched telephone network (PSTN). Each member user utilizes either a modified land line telephone directly connected to the PSTN, or uses a modified mobile telephone operatively coupled to the PSTN through 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 of 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 switch matrix, coupled to the telephone network interface, for providing an information signal received from an active member user over a selected telephone line to the remaining non-active member users. A network manager controller identifies the active member user on the basis of push-to-talk (PTT) request signals received from the member users' telephones over the plurality of telephone lines. The active member user may be identified as, for example, the member user from which a PTT request signal is first received after the previously active member user has relinquished speaking privileges. Alternately, the active member user may be chosen by using predefined user priority criteria to evaluate all PTT request signals queued by the network call manager.

The telephone set of each member user will typically be capable of both standard telephone operation, and of PTT operation over the private communication network. When configured for PTT operation, each telephone set receives and digitally processes input voice or data information from a member user. The resultant vocoder data packets, as well as any PTT request signals initiated by the member user, are then supplied to a modem for reverse link transmission via the PSTN to the telephone network interface of the network call manager. The security of the PTT private network may be enhanced by configuring each telephone set for encryption of all such reverse link transmissions, as well as for corresponding decryption of the forward link information from the active member user.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and features of the invention will be more readily apparent from the following detailed description and appended claims when taken in conjunction with the drawings, in which:

<figref idrefs="DRAWINGS">FIG. 1</figref> illustratively represents the elements of an exemplary telephone system within which may be established a PTT point-to-multipoint private communication network of the present invention;

<figref idrefs="DRAWINGS">FIG. 2</figref> is a block diagram of an exemplary network call manager of the PTT private network of the present invention;

<figref idrefs="DRAWINGS">FIG. 3A</figref> shows a block diagram of a land line PTT dual-mode telephone comprised of a transmit section and a receive section;

<figref idrefs="DRAWINGS">FIG. 3B</figref> depicts the land line dual mode PTT telephone of <figref idrefs="DRAWINGS">FIG. 3A</figref> as modified to facilitate encrypted communication within a PTT private network;

<figref idrefs="DRAWINGS">FIG. 4</figref> is a block diagram of an AMPS dual-mode PTT telephone;

<figref idrefs="DRAWINGS">FIG. 5</figref> is a block diagram of an CDMA cellular telephone configured for use within a PTT private network of the present invention;

<figref idrefs="DRAWINGS">FIG. 6</figref> provides a functional block diagram of a network call manager designed for employment within a PTT private network in which signaling is effected using analog tones; and

<figref idrefs="DRAWINGS">FIG. 7</figref> shows a land line telephone configured for communication with a network call manager using analog tones.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

I. Structure of PTT Private Network

<figref idrefs="DRAWINGS">FIG. 1</figref> illustratively represents the elements of an exemplary telephone system within which may be established a PTT point-to-multipoint private communication network (“PTT private network”) of the present invention. Referring to <figref idrefs="DRAWINGS">FIG. 1</figref>, the exemplary telephone system includes a public switched telephone network (PSTN) <b>10</b>, a CDMA cellular communication system <b>14</b> and an analog (AMPS) cellular communication system <b>18</b>. The CDMA system <b>14</b> provides service to CDMA-compatible mobile radiotelephones (“CDMA mobiles”) <b>22</b> and <b>24</b>, while the AMPS system <b>18</b> facilitates communication with users of AMPS-compatible mobile radiotelephones (“AMPS mobiles”) <b>28</b> and <b>30</b>. A network call manager <b>40</b>, connected through a plurality of T<b>1</b> channels <b>44</b> to the PSTN <b>10</b>, operates as described hereinafter to create a private communication network among a corresponding plurality of member users within the exemplary telephone system of <figref idrefs="DRAWINGS">FIG. 1</figref>.

The private communication network may include member users serviced by one or both of the CDMA and AMPS cellular systems <b>14</b> and <b>18</b>, and/or may include one or more member users directly connected to the PSTN <b>10</b> through modified land line telephones such as the telephone <b>48</b>. Although CDMA and AMPS cellular systems are shown as being incorporated within the exemplary embodiment of <figref idrefs="DRAWINGS">FIG. 1</figref>, it is to be understood that the teachings of the present invention are pertinent to other cellular air interface standards as well for example Global System for Mobile Communications (GSM) and Time Division Multiple Access (TDMA). A brief description of the constituent elements of the CDMA and AMPS cellular communication systems <b>14</b> and <b>18</b> shown in <figref idrefs="DRAWINGS">FIG. 1</figref> will be provided prior to discussion of the operative principles of the present invention.

The CDMA cellular communication system <b>14</b> includes a plurality of cells, two of which are identified in <figref idrefs="DRAWINGS">FIG. 1</figref> as including cell-sites (i.e., “base stations”) <b>56</b> and <b>58</b>. Each cell may be partitioned into a number of sectors, where communication with CDMA mobiles <b>22</b> and <b>24</b> within a given sector is handled by a cell-site transceiver providing radio coverage over the sector. The base stations <b>56</b> and <b>58</b> operate to receive and transmit the signals enabling a radio transceiver within each CDMA mobile to communicate with the PSTN <b>10</b>. In the CDMA system <b>14</b>, data packets are used in the over-the-air exchange of information between the base stations <b>56</b> and <b>58</b> and the CDMA mobiles <b>22</b> and <b>24</b>.

Telephone calls are routed by the cell-site base stations <b>56</b> and <b>58</b> between the CDMA mobiles <b>22</b> and <b>24</b> and a CDMA mobile switching center (MSC) <b>60</b>, which will typically be located within a mobile telephone switching office (not shown). The primary purpose of the MSC <b>60</b> is to provide voice path connections between the CDMA mobiles <b>22</b> and <b>24</b> and the PSTN <b>10</b>. To this end the MSC <b>60</b> performs functions such as, ratingrouting data between a MSC modems <b>62</b> and CDMA mobiles <b>22</b> and <b>24</b> by way of the appropriate CDMA base station <b>56</b> or <b>58</b>. The MSC <b>60</b> also performs other tasks, including paging of a CDMA mobile when a call is received from the PSTN <b>10</b> and switching calls to available PSTN lines via a plurality of T<b>1</b> channels <b>64</b>. A set of MSC modems <b>62</b> serves to convert the digital information signals received from the CDMA mobiles <b>22</b> and <b>24</b> to analog signals suitable for transmission over the PSTN <b>10</b>, and likewise converts analog signals from the PSTN <b>10</b> to digital signals subsequently provided to the CDMA mobiles <b>22</b> and <b>24</b>.

The AMPS cellular communication system <b>18</b> also includes a number of cells, two of which are identified in <figref idrefs="DRAWINGS">FIG. 1</figref> as including cell-site base stations <b>70</b> and <b>72</b>. Each cell may be partitioned into a number of sectors, where communication with AMPS mobiles <b>28</b> and <b>30</b> within a given sector is handled by a cell-site transceiver providing radio coverage over the sector. Telephone calls are routed by the cell-site base stations <b>70</b> and <b>72</b> between the AMPS mobiles <b>28</b> and <b>30</b> and an AMPS mobile switching center (MSC) <b>76</b>, which is coupled to the PSTN <b>10</b> via a plurality of T<b>1</b> channels <b>80</b>.

II. Operation of PTT Private Network

Turning now to <figref idrefs="DRAWINGS">FIG. 2</figref>, reference will be made to a block diagram of an exemplary network call manager <b>40</b> in describing operation of the PTT private network of the present invention. The manner in which the land line or cellular telephones associated with each member user are configured for cooperation with the network call manager <b>40</b> will be described below with reference to <figref idrefs="DRAWINGS">FIGS. 3-5</figref>. In what follows, communication links from the modified land line telephone <b>48</b>, from the AMPS mobiles <b>28</b> and <b>30</b>, and from the CDMA mobiles <b>22</b> and <b>24</b>, to the network call manager <b>40</b> via the PSTN <b>10</b> are termed “reverse links”. The reverse link associated with the member user currently designated by the network call manager <b>40</b> as the active member user is assumed to be the only one of the reverse links carrying valid voice or data information. All other reverse links are available for use in providing signaling information to the network call manager <b>40</b>. Each “forward link” through the PSTN <b>10</b> from the network call manager <b>40</b> to each member user carries the voice or data information provided by the active member user. As is described herein, the network call manager <b>40</b> is reconfigured upon each new identification of an active member. This reconfiguration results in the reverse link voice or data information from the newly identified active member user being provided to the forward links associated with all other member users, including the forward link of the previously active member user.

The network call manager <b>40</b> includes a network controller <b>90</b>, within which is stored at least one list of the telephone numbers associated with the member users of a first PTT private network. When desiring to access the first PTT private network, a calling member user dials an access number identifying the first PTT private network. The network controller <b>90</b> may also store other lists of member users, each list being associated with a unique access number and defining a separate PTT private networks.

The network call manager <b>40</b> is designed to appear to the PSTN <b>10</b> as would a private branch exchange (PBX) system, and thus the call placed by the calling member user may be received over any one of the T<b>1</b> channels <b>44</b>. In this regard a telephone network (T<b>1</b>) interface <b>92</b> is provided for forming a connection between the T<b>1</b> channel <b>44</b> associated with the calling member user and one of a plurality of network manager modems <b>98</b>. As is described herein, the T<b>1</b> interface <b>92</b> also serves to connect various other ones of the network manager modems <b>98</b> to ones of the T<b>1</b> channels <b>44</b> associated with other member users.

If the calling member user is serviced by the CDMA cellular system <b>14</b>, a telephone connection is established when the network call manager modem <b>98</b>′ coupled to the T<b>1</b> channel <b>44</b> receiving the incoming call becomes synchronized with the one of the MSC modems <b>62</b> (<figref idrefs="DRAWINGS">FIG. 1</figref>) assigned to the call. For a calling member user having a land line telephone or AMPS cellular telephone, a similar telephone connection is established upon synchronization of an internal modem (<figref idrefs="DRAWINGS">FIGS. 3A and 4</figref>) within the member user's telephone and the network manager modem <b>98</b>′ receiving the incoming call. In an exemplary embodiment the network manager modems <b>98</b> comprise, for example, so-called “AMPS modems” especially well-suited for over-the-air information transfer.

Upon an incoming call to a PTT private network being received from a member user over one of the T<b>1</b> channels <b>44</b>, the T<b>1</b> interface <b>92</b> uses standard techniques to determine the access number dialed during placement of the call. The dialed access number, which corresponds to a given PTT private network, is communicated by the T<b>1</b> interface <b>92</b> to the network controller <b>90</b>. The T<b>1</b> interface also connects the T<b>1</b> channel <b>44</b> associated with the calling member user to an available network manager modem (e.g., network manager modem <b>98</b>′). Once modem synchronization has been achieved, the network controller <b>90</b> may require the calling user to furnish authentication information used for verification of the calling user's membership in the PTT private network identified as corresponding to the called access number. Upon confirmation of such membership, the network controller <b>90</b> may command either the T<b>1</b> interface <b>92</b> or a selected network manager modem <b>98</b> to initiate paging of the remaining member users of the identified PTT private network. It is noted that in alternate embodiments the T<b>1</b> interface <b>92</b> may comprise an E<b>1</b> interface, or various other digital or “PBX-type” interfaces.

Upon a first of the other member users of the identified PTT private network answering a network page (i.e., a telephone call) issued by the calling network manager modems <b>98</b>, or by the T<b>1</b> interface <b>92</b>, a modem synchronization process similar of the type described above again occurs. In particular, if the called member user is serviced by an AMPS or land line telephone, modem synchronization occurs between the modem internal to the called member user's telephone (<figref idrefs="DRAWINGS">FIGS. 3A and 4</figref>) and one of the network manager modems <b>98</b>. If the called member user is serviced by the CDMA cellular system <b>14</b>, modem synchronization occurs between the calling network manager modem <b>98</b> and one of the MSC modems <b>62</b> (<figref idrefs="DRAWINGS">FIG. 1</figref>). It is to be understood that the MSC modems <b>62</b> need not be physically proximate the MSC <b>60</b>, but may be located elsewhere within the telephone system infrastructure.

When the calling network manager modem <b>98</b> achieves such synchronization, it produces a CONNECT signal which is detected by the network controller <b>90</b>. The network controller <b>90</b> may then instruct the called network manager modem <b>98</b>′ to send a CONNECT signal to the member user originally dialing the access number of the identified PTT private network. The network controller may also periodically send each authenticated participating member user of the PTT private network a list, to be displayed at each authenticated user's phone, of the other current participating member users.

A PTT controller <b>104</b> is provided for according speaking or data transmission privileges among the two or more member users joined to the identified PTT private network. In particular, the PTT controller <b>104</b> is responsive to PTT request signals (“PTT requests”) generated by the land line or cellular telephones associated with the member users of the identified PTT private network. Each PTT request is generated at a member user's telephone either in response to manual engagement of a PTT switch, or in response to detected voice activity of the member user. A PTT request from a given member user is detected by the modem <b>98</b> assigned thereto, which provides the PTT signal to the PTT controller <b>104</b>.

In an exemplary embodiment the PTT controller <b>104</b> designates as the currently active member user the one from which the first PTT request is received subsequent to network speaking privileges being released by a previously active member user. Network speaking privileges are relinquished by the previously active member user, in the case of manual PTT signaling, upon releasing engagement of the PTT switch of the speaker's telephone. In the case of voice-activated PTT signaling, network speaking privileges are relinquished upon the occurrence of a pause of predetermined duration.

In an alternate embodiment, PTT requests received prior to relinquishment of network speaking privileges by the currently active member user are queued. When the currently active member user subsequently relinquishes network speaking privileges, the queued PTT requests are evaluated in accordance with predefined criteria to determine the next currently active member user. Such predefined criteria could include, for example, member user priority as well as order of receipt of the queued requests.

The network call manager <b>40</b> may employ yet other techniques for selecting a new active member user on the basis of the received PTT requests. For example, each member user of a given PTT private network may be assigned a relative level of priority within the network. In this case when a PTT request is received from a member user of higher priority than the currently active member user, the network call manager <b>40</b> preempts the currently active member user and grants network speaking privileges to the higher priority member user. It is also possible that each member user would be allowed to alter its priority within prescribed limits known to the network call manager <b>40</b> as a means of obtaining network speaking privileges under urgent circumstances.

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

Although the forward links of each PTT private network are nominally used to carry voice or data information from the active member user to all other member users, the network controller <b>104</b> may also transmit system status information over the forward links during pauses or gaps in information transmission by the active member user. In an exemplary embodiment this system status information includes the following: <ul><li id="ul0001-0001" num="0000"><ul><li id="ul0002-0001" num="0045">(i) eligible member users (phone number, name, priority) of a given PTT private network,</li><li id="ul0002-0002" num="0046">(ii) member users (phone number, name, priority) currently joined to the given PTT private network,</li><li id="ul0002-0003" num="0047">(iii) the currently active member user (phone number, name, priority), and</li><li id="ul0002-0004" num="0048">(iv) the queue of member users (phone number, name, priority, order of request) who have provided PTT requests to the PTT controller <b>90</b>.</li></ul></li></ul>

This network status information is received and displayed by the telephones associated with the member users. The following section provides a description of particular implementation of PTT dual-mode telephones suitable for use within a PTT private network of the invention.

III. Land Line and Cellular PTT Dual-Mode Telephones

Referring now to <figref idrefs="DRAWINGS">FIG. 3A</figref>, a block diagram is shown of a land line PTT dual-mode telephone comprised of a transmit section <b>140</b> and a receive section <b>142</b>. The transmit section <b>140</b> of dual-mode telephone of <figref idrefs="DRAWINGS">FIG. 3A</figref> is configured for standard telephone operation when input switch <b>148</b> is thrown to pole <b>150</b>, thereby coupling input microphone <b>154</b> to the PSTN <b>10</b>. The input switch <b>148</b> is thrown to pole <b>158</b> when it is desired to configure the transmit section <b>140</b> for PTT operation within a PTT private network. Similarly, the receive section <b>142</b> is set for standard telephone operation when receive switch <b>162</b> is thrown to pole <b>168</b>, and is set for PTT operation when receive switch <b>162</b> is thrown to pole <b>166</b>.

During PTT operation, voice information from microphone <b>154</b> is coupled by switch <b>148</b> to a codec <b>172</b>. The codec <b>172</b> is disposed to transform this analog voice information, or data information from a peripheral device (not shown) coupled to switch <b>148</b>, into a pulse code modulated (PCM) waveform provided to a vocoder <b>176</b>. In an exemplary embodiment the vocoder <b>176</b> is realized in conformance with EIA/TIA standard IS-96A, and operates to convert the input PCM waveform into a sequence of vocoder data packets. These vocoder data packets are supplied to a first input of a microprocessor <b>178</b>, which also has a second input coupled to a PTT processor <b>184</b> and an output coupled to a modem <b>180</b>. When a PTT switch <b>188</b> is engaged by the associated member user, the PTT processor <b>184</b> provides PTT data packets to the second input of the microprocessor <b>178</b>. The microprocessor <b>178</b> then interleaves the PTT data packets with the vocoder data packets and provides the result to modem <b>180</b>, which becomes synchronized with one of the network manager modems <b>98</b> during PTT operation. Although the PTT processor <b>184</b> is depicted as being functionally distinct from the microprocessor <b>178</b>, both of these functional elements may be incorporated within a single microprocessor unit.

The receive section <b>142</b> includes a modem demodulator <b>192</b>, which also becomes synchronized with a companion network manager modem <b>98</b> within the network call manager <b>40</b> during PTT mode operation. The vocoder data packets generated by the second modem <b>192</b> in response to forward link information from its companion network manager modem <b>98</b> are provided to a receive section IS-96A vocoder <b>196</b>, which in turn produces a PCM signal from the received vocoder data packets for use by a receive section codec <b>200</b>. The analog output from the codec <b>200</b> is then applied to a conventional telephone speaker <b>204</b>. It should be noted that the functions performed by codecs <b>172</b> and <b>200</b> may be performed by a single device. Similarly the encoding function of vocoder <b>176</b> may be combined with the decoding function of vocoder <b>196</b> in a single device.

As is indicated by <figref idrefs="DRAWINGS">FIG. 3A</figref>, certain information received from the network manager unit <b>40</b> by the receive section <b>142</b> may be provided to microprocessor <b>178</b> via signal line <b>212</b>. This information may include various network status data (e.g., identities of other participating member users, currently active member user) to be provided by the microprocessor <b>178</b> to a conventional display <b>214</b> (e.g., LCD screen).

<figref idrefs="DRAWINGS">FIG. 3B</figref> depicts the land line dual mode PTT telephone of <figref idrefs="DRAWINGS">FIG. 3A</figref> as modified to facilitate encrypted communication within a PTT private network. Specifically, an alternate transmit section <b>140</b>′ for the telephone of <figref idrefs="DRAWINGS">FIG. 3A</figref> includes an encryption module <b>210</b> interposed between the IS-96A vocoder <b>176</b> and the microprocessor <b>178</b>. In an exemplary embodiment the encryption module <b>210</b> operates to encrypt the vocoder data packets in accordance with an industry standard algorithm such as, for example, the Data Encryption Standard (DES). Similarly, an alternate receive section <b>142</b>′ is seen to include a decryption module <b>214</b> for removing encryption from the vocoder data packets produced by the second modem <b>192</b>. It should again be noted that the functions performed by codecs <b>172</b> and <b>200</b> may be performed by a single device. Similarly the encoding function of vocoder <b>176</b> may be combined with the decoding function of vocoder <b>196</b> in a single device. Furthermore the functions of encryption module <b>210</b> and decryption module <b>214</b> may also be combined into a single device. The land line and cellular telephones associated with all of the member users of a given PTT private network capable of participating in encrypted communication will be similarly configured with encryption and decryption modules of like type.

When the user of the land line telephone of <figref idrefs="DRAWINGS">FIG. 3B</figref> has been designated as the currently active member user, the microprocessor <b>178</b> will generate an encryption identification number (I.D.) for transmission to the network call manager <b>40</b>. The encryption I.D. is associated with a particular “key” used in decryption of the encrypted information produced by the encryption module <b>210</b>. The network call manager <b>40</b> multicasts the encryption I.D. to each of the telephones associated with the remaining non-active (i.e., non-speaking) member users, each of which includes a decryption module similar to the decryption module <b>214</b>. Each decryption module will typically include a look-up table identifying the decryption key associated with each encryption I.D. Each non-active member user is thus able to decrypt the encrypted information from the currently active member user upon receipt of the encryption I.D. provided thereby.

Turning now to <figref idrefs="DRAWINGS">FIG. 4</figref>, a block diagram is provided depicting an AMPS dual-mode PTT telephone comprised of a transmit section <b>240</b> and a receive section <b>242</b>. The transmit section <b>240</b> of the AMPS dual-mode PTT telephone of <figref idrefs="DRAWINGS">FIG. 4</figref> is configured for standard telephone operation when input switch <b>248</b> is thrown to pole <b>250</b>, thereby coupling input microphone <b>254</b> to the an AMPS transmitter <b>255</b>. The input switch <b>248</b> is thrown to pole <b>258</b> when it is desired to configure the transmit section <b>240</b> for PTT operation within a PTT private network. Similarly, the receive section <b>242</b> is set for standard telephone operation when receive switch <b>262</b> is thrown to pole <b>266</b>, and is set for PTT operation when receive switch <b>262</b> is thrown to pole <b>268</b>.

During PTT operation, voice information from microphone <b>254</b> is coupled by switch <b>248</b> to a codec <b>272</b>. The codec <b>272</b> is disposed to transform this analog voice information into a pulse code modulated (PCM) waveform provided to an IS-96A vocoder <b>276</b>. The resultant vocoder data packets may then optionally be encrypted by an encryption module <b>278</b>. When encryption is not desired, the vocoder data packets are supplied to a microprocessor <b>279</b> for interleaving with PTT packets from a PTT processor <b>284</b>. Again, PTT packets are generated by PTT processor <b>284</b> in response to engagement of the PTT switch <b>288</b>. The resulting interleaved vocoder data and PTT packets are then processed by a transmit path modem <b>280</b> and provided to the AMPS transmitter <b>255</b> for transmission to the AMPS base station <b>70</b> or <b>72</b>. In an alternate embodiment, data information from a peripheral device (not shown) may be supplied to the encryption module <b>278</b> or directly to the microprocessor <b>279</b>.

The receive section <b>242</b> includes an AMPS receiver <b>291</b> for receiving forward link information provided by the network call manager <b>40</b>. The analog output from the AMPS receiver <b>291</b> is coupled to a receive path modem <b>292</b>, which becomes synchronized with a network manager modem <b>98</b> during PTT mode operation. The vocoder data packets generated by the receive path modem <b>292</b> are provided to a decryption module <b>294</b> during periods of encrypted PTT private communication. When encryption is not being effected, the vocoder data packets are processed by a receive section vocoder <b>296</b> operative to produce a PCM signal for use by a receive section codec <b>300</b>. The analog output from the codec <b>300</b> is then applied to a conventional telephone speaker <b>304</b>. When encryption is in effect, private network status information and the like received from the network manager unit <b>40</b> is decrypted and provided to microprocessor <b>178</b> via signal line <b>212</b>′.

As was discussed with reference to <figref idrefs="DRAWINGS">FIGS. 3A and 3B</figref>, it should again be noted that the functions performed by codecs <b>272</b> and <b>300</b> may be performed by a single device. Similarly the encoding function of vocoder <b>276</b> may be combined with the decoding function of vocoder <b>296</b> in a single device. Furthermore the functions of encryption module <b>278</b> and decryption module <b>294</b> may also be combined into a single device.

<figref idrefs="DRAWINGS">FIG. 5</figref> provides a block diagram of a CDMA cellular telephone configured for use within a PTT private network. The CDMA cellular telephone of <figref idrefs="DRAWINGS">FIG. 5</figref> is comprised of a CDMA transmit section <b>340</b> and a CDMA receive section <b>342</b>. During PTT operation, voice information from microphone <b>354</b> is provided to a codec <b>372</b> disposed to produce a pulse code modulated (PCM) waveform. The PCM waveform is provided to a vocoder <b>376</b>, which in turn generates vocoder data packets for optional encryption within an encryption module <b>378</b>. When encryption is not desired, the vocoder data packets are supplied to a microprocessor <b>379</b> for interleaving with PTT packets from a PTT processor <b>384</b>. Again, PTT packets are generated by PTT processor <b>384</b> in response to engagement of the PTT switch <b>388</b>. The resulting interleaved vocoder data and PTT packets are then provided by the microprocessor <b>379</b> to the CDMA transmitter <b>355</b>.

The CDMA receive section <b>342</b> includes a CDMA receiver <b>392</b>, which generates vocoder data packets in response to forward link information from the network call manager <b>40</b>. The vocoder data packets are provided to a decryption module <b>394</b> during periods of encrypted PTT private communication. When encryption is not in effect, the vocoder data packets are processed by a CDMA receive section vocoder <b>396</b> operative to produce a PCM signal for use by a CDMA receive section codec <b>400</b>. The analog output from the CDMA receive section codec <b>400</b> is then applied to a conventional telephone speaker <b>404</b>. The functions of codecs <b>372</b> and <b>400</b> may be performed within a single device, as may the functions of vocoders <b>376</b> and <b>396</b> may also be performed within a single device. Furthermore the functions of encryption module <b>378</b> and decryption module <b>394</b> may also be combined into a single device.

III. Analog PTT Private NetworkIV. Analog PTT Private Network

<figref idrefs="DRAWINGS">FIG. 6</figref> provides a functional block diagram of a network call manager <b>450</b> designed for employment within a PTT private network in which signaling is effected using analog tones. The network call manager <b>450</b> includes a network controller <b>490</b>, within which is stored one or more lists of the telephone numbers associated with the member users of corresponding PTT private networks. When desiring to access a given PTT private network, a calling member user dials an access number identifying the given PTT private network.

The network call manager <b>450</b> is designed to appear to the PSTN <b>10</b> as would a private branch exchange (PBX) system, and thus the call placed by the calling member user may be received by the T<b>1</b> channel <b>44</b> associated with any one of a plurality of network manager tone detectors <b>498</b>. The tone detector <b>498</b>′ receiving the incoming call impresses a detection signal upon its output line <b>500</b>′, which is sensed by the network controller <b>490</b>. The network controller <b>490</b> then begins to scrutinize the tone sequence detected by the called network manager tone detector <b>498</b>′ in order to authenticate the calling PTT user. Once the dialed access number has been recognized by the network controller <b>490</b> and the member users of the associated PTT private network identified, the network controller <b>490</b> initiates paging of the member users of the identified PTT private network over the remaining T<b>1</b> channels <b>44</b> using standard telephone network procedures. Upon sensing that a first of the other member users of the identified PTT private network answers a network call, the network controller <b>490</b> sends a CONNECT signal in the forms of tones to the member user originally dialing the access number of the identified PTT private network —thereby indicating to the calling member user that at least one other member user has joined the identified PTT private network.

A PTT controller <b>504</b> is provided for according speaking privileges among the two or more member users joined to the identified PTT private network. In particular, the PTT controller <b>504</b> is responsive to PTT request signals, in the form of one or a combination of analog tones (“PTT tone requests”), generated by the telephones associated with the member users of the identified PTT private network. Each PTT tone request is generated at a member user's telephone either in response to manual engagement of a PTT switch, or in response to detected voice activity of the member user. A PTT tone request from a given member user is detected by the tone detector <b>498</b> assigned thereto, which then provides a PTT request signal to the PTT controller <b>504</b> over one of the output lines <b>500</b>. In an exemplary embodiment the PTT controller <b>504</b> is operative to assign speaking privileges among requesting member users in the manner described above with reference to the PTT controller <b>104</b> (<figref idrefs="DRAWINGS">FIG. 2</figref>).

After a new active member user has been identified by the PTT controller <b>504</b> on the basis of the received PTT tone requests, the PTT controller <b>504</b> configures a multicast switch <b>510</b> to accept the reverse link voice or data information exclusively from the T<b>1</b> channel <b>44</b> associated with the currently active member user. That is, the reverse link information from each of the other T<b>1</b> channels, each of which has been assigned to one of the remaining (i.e., non-active) member users, is not multicast by the multicast switch <b>110</b>510. The PTT controller <b>504</b> also configures the multicast switch <b>504</b>510 to provide the reverse link information accepted from the newly identified active member user to the T<b>1</b> channels associated with each non-active member user. Because PTT tone requests are transmitted only on the reverse links of non-active member users, such PTT tone requests advantageously do not interfere with the receipt of reverse link information from the active member user.

Although the forward links of each PTT private network are nominally used to carry voice or data information from the active member user to all other member users, the network controller <b>504</b> may also transmit system status information over the forward links during pauses or gaps in information transmission by the active member user. In an exemplary embodiment this system status information includes the following: <ul><li id="ul0003-0001" num="0000"><ul><li id="ul0004-0001" num="0067">(i) eligible member users (phone number, name, priority) of a given PTT private network,</li><li id="ul0004-0002" num="0068">(ii) member users (phone number, name, priority) currently joined to the given PTT private network,</li><li id="ul0004-0003" num="0069">(iii) the currently active member user (phone number, name, priority), and</li><li id="ul0004-0004" num="0070">(iv) the queue of member users (phone number, name, priority, order of request) who have provided PTT tone requests to the PTT controller <b>490</b>.</li></ul></li></ul>

Such information could be transmitted using sequences of tones or tone combinations capable of being detected within the telephone of each member user. Various PTT private network information (i.e., member user lists, priorities) could be stored within the telephone of each member user, and specific entries retrieved for display upon receipt of the associated tone or tone combination from the network call manager <b>450</b>. In this regard a land line telephone configured for use within a PTT private network orchestrated by the network call manager <b>450</b> is described immediately below with reference to <figref idrefs="DRAWINGS">FIG. 7</figref>.

Referring to <figref idrefs="DRAWINGS">FIG. 7</figref>, a block diagram is shown of a land line PTT telephone having transmit and receive sections <b>540</b> and <b>542</b> designed for communication using analog tones. During PTT operation, an input switch <b>548</b> is nominally set to pole <b>550</b> by PTT processor <b>552</b> so as to couple voice information from an input microphone <b>554</b> to the PSTN. However, when PTT switch <b>560</b> is engaged by the associated member user, the PTT processor <b>552</b> sets switch <b>548</b> to pole <b>562</b> and enables a tone generator <b>566</b>. TheThis allows the PTT tone requests generated by the tone generator <b>566</b> to be transmitted via the PSTN to the network call manager <b>450</b>.

The receive section <b>542</b> includes a speaker <b>568</b>, and an internal tone detector <b>570</b> for detecting analog tones or combinations thereof transmitted by the network call manager <b>450</b> during PTT mode operation. These tone or tone combinations may be used to convey a variety of status and control information to the PTT telephone of <figref idrefs="DRAWINGS">FIG. 7</figref>. In an exemplary embodiment this information may include: <ul><li id="ul0005-0001" num="0000"><ul><li id="ul0006-0001" num="0074">(i) identification of the currently active member user (name, priority),</li><li id="ul0006-0002" num="0075">(ii) an indication that the member user associated with the PTT telephone has been accorded speaking privileges,</li><li id="ul0006-0003" num="0076">(iii) notice that the speaking privileges of the member user associated with the PTT telephone are being revoked in favor of a member user of higher priority, and</li><li id="ul0006-0004" num="0077">(iv) identification of the member users currently joined to the PTT private network.</li></ul></li></ul>

Each tone or tone combination will have associated therewith a character string or other message stored within a display processor <b>574</b>. In response to each detected tone or tone combination, the display processor <b>574</b> provides the associated message to an alphanumeric display <b>578</b>. The control and status information enumerated above is intended to be merely exemplary, and in alternate embodiments other types of information may be provided to the PTT telephone by the network manager.

The previous description of the preferred embodiments is provided to enable any person skilled in the art to make or use the present invention. The various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without the use of the inventive faculty. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.