IL115925A - Cellular telephone system - Google Patents

Description

mown wan )iflbu An improved cellular telephone system PELE-PHONE COMMUNICATION tt"i>ll nmVJpfl 1¼-N*a LTD.

C. 99495 FIELD OF THE INVENTION The present invention relates generally to the field of cellular telephones and more specifically concerns a cellular telephone system in which each subscriber possibly owns in addition to his/her normal subscriber telephone number, an extension number subordinated thereto.

BACKGROUND OF THE INVENTION The number of people using the cellular telephone networks is steadily increasing as more and more subscribe to service. Time which is seemingly lost, e.g. when traveling from one place to the other, or when caught in a traffic jam, is converted into effective working hours.

The ever decreasing cost of cellular telephones on the one hand, and of communication time at the other hand, encourage the average subscriber to have more than one cellular telephone at his/her disposal, e.g. one telephone mounted (possibly fixedly mounted) in his/her car, typically on, or nearby, the dashboard and being of relatively large size. Such a cellular telephone typically employs a clear and relatively large keypad as well as relatively high power display, thereby enabling the user to conveniently use the telephone whilst driving. Another cellular telephone, being preferably portable, light-weight and physically small can be conveniently conveyed in a conventional briefcase or pocket and can be readily used when the subscriber is not in his car and not in the vicinity of a telephone.

A natural solution for affording the use of two or more telephones by the same subscriber is to assign one or more extensions to the subscriber in addition to his normal telephone number.

Precision Systems Inc., purports to offer a solution for incorporating extensions. Thus, the subscriber is seemingly assigned with one unique telephone number serving for both the main telephone and the extensions. By "seemingly" it is meant that insofar as the "rest of the world" (i.e. anyone calling the subscriber) is concerned the subscriber is assigned with only one telephone number, but actually, a valid and different telephone number is internally assigned to each extension.

For a better understanding of the foregoing, consider for example, a given subscriber having a "main" cellular telephone (e.g. mounted in his/her car) and an "extension" cellular telephone (e.g. a portable hand-held cellular telephone). For internal use, the main telephone is assigned with e.g. the telephone number 333555, whereas the extension telephone is assigned with e.g. the telephone number 333666. Insofar as the rest of the world is concerned, this subscriber has only one telephone number, i.e. 333555 (e.g. in the telephone directory only the number 333555 appears).

Assume that a person makes a phone call from a conventional telephone network addressed to said given subscriber. To this end the person dials xxx-333555, where xxx stands for the area code of the cellular telephone network (e.g. in Israel, "050" stands for the area code of a first cellular system operator - 'Telephone", "052" which stands for the area code of a second cellular system operator - "Cellcom", etc.).

Having decoded xxx, the switching office of the conventional telephone network will relay a packet holding the telephone number of the addressed subscriber, i.e. 333555, to a selected switch of the cellular telephone network (having, of course, the area code xxx). Possibly, the packet holds additional data, e.g. the telephone number of the caller.

Having relayed the telephone number of the addressed subscriber to the switching office of the cellular telephone network, the latter, in addition to a series of operations that are normally performed when a telephone number is addressed thereto, checks against a pre-stored table to enquire whether the addressed subscriber has in addition to his/her normal number also one or more extensions. The network then operates in a known per se and pre-programmed manner to connect the caller to the called subscriber, i.e. routing the packet to the switching office which is assumed to be the nearest in location to the addressed subscriber and transmitting it therefrom.

Assuming that the network failed in establishing communication to the main telephone (e.g. the latter is switched off or simply does not reply), the network tries to communicate to the extension telephone, e.g. in the latter example, the system accesses a pre-stored table and retrieves therefrom the extension number 333666 that is related to the main subscriber number 333555. Following this, the extension number 333666 is transmitted from the switching office estimated to be physically nearest to the extension telephone. As is well known, cellular networks normally keeps track on the current location of its subscribed telephones.

If connection is established, the caller will conduct a telephone conversation with said subscriber (wherein the latter employs, of course, his portable telephone), without being aware that the actual telephone number of the addressed subscriber is 333666.

Whilst at a first glance, the fact that the called subscriber was contacted at 333666 instead of his "main" number 333555, seems to have no implications, a more thorough analysis reveals some significant drawbacks associated with this mode of operation.

For one, the telephone number of the extension telephone (i.e. 333666), which is seemingly concealed, is in fact presented on the telephone unit's display by simply activating a pre-defined function, e.g. hitting the "recall" and "pause" keys on the device's keypad. Thus, once the extension number is known, it may be easily leaked to other persons, which may use a "short cut" and dial directly to the extension number (i.e. xxx-333666), when they assume that the addressed subscriber is in the vicinity of his/her portable device. This situation could possibly lead to undesired scenarios, wherein for example a subscriber calls from his main telephone set (so that the line 333555 becomes busy), whereas at the same time a person will be able to establish communication with the subscriber in his portable set by simply dialing xxx-333666, thereby effectively rendering the main cellular telephone and the extension cellular telephone into two independent telephones with two distinct numbers.

This approach is unacceptable since the underlying idea of extensions is aimed at providing the subscribers with an appealing service, for which they are charged less. As explained in the foregoing the solution offered by Precision Systems Inc. can easily be abused by subscribers allowing them to benefit from two distinct telephone numbers, whilst paying the cellular telephone company less than they should.

One could possibly cope with the drawbacks associated with the incorporation of extensions as offered by Precision systems Inc., by simply masking the option of directly calling to the telephone number of the extension, and/or prohibiting the situation wherein both the main and the extension telephones are simultaneously active. Unfortunately the latter improvement has an intrinsic shortcoming since it necessitates relatively large scale modifications in an already existing cellular telephone networks, which are not only cumbersome but also costly.

It is accordingly the object of the present invention to provide a novel method and system which provide extension service to subscribers of cellular telephone systems, whilst substantially reducing or eliminating the drawbacks of the hitherto known solutions.

SUMMARY OF THE INVENTION In the following description and the appended claims the term "calling subscriber" should be interpreted in a wide sense to include not only those paying a regular periodic fee for a telephone company but also to those paying only once in exchange for a one time service, e.g. a person calling from a public telephone.

In some of the conventional cellular telephone systems e.g. the known Narrow-Advanced-Mobile-Phone-Service (N-AMPS), Time-Division-Multiplexing- Access (TD MA), andCode-Division-Multiplexing-Access (CDMA) types, the telephone number (occasionally referred to as Mobile Identification Number (MIN)) that is transmitted when attempting to establish a telephone communication with a cellular telephone of a given subscriber has a larger number of digits than the cellular telephone number of said subscriber, ( the latter number refers to the cellular telephone number of the subscriber that appears in the telephone directory). This observation is exploited by the present invention for the provision of extension service. For a better understanding of the idea underlying the invention, consider, for example, the telephone cellular system in Israel, operated by 'Telephone", wherein 10 digits are a-priori allocated for storing each subscriber's telephone number, (i.e. a MIN of 10 digits) whereas only 6 of them, which stand for the subscriber's cellular telephone number, are actually significant. Thus, out of the 10 digits only the six trailing ones store the telephone number of the subscriber under consideration, and the leading four are redundant, i.e. consisting of the digits 9,7,2,x - wherein x stands for an arbitrary digit. Accordingly, whenever calling a subscriber of the cellular network of the kind specified, whilst only 6 digits, out of the 10, are of interest (i.e. the subscriber's telephone number), ajl 10 digits are transmitted.

Insofar as Israel and other countries having a similar system are concerned, the area code portion of the subscriber's cellular telephone number (e.g. 050 for the 'Telephone" cellular network), does not form part of the MIN, since the cellular network is classified as one area, having of course one area code. Normally, the area code (050) serves for routing telephone calls from different areas to the cellular network under consideration, e.g. 050 will be appended to the sought subscriber's telephone number by a subscriber who calls from the conventional wired network, or from the "Cellcom" cellular network, and will thereafter be stripped off, before transmitting the MIN number. Put differently, it is sufficient to check whether the area code is 050 in which case the phone call is relayed to the "Pelephone" network and therefore the need to append the area code to the MIN before transmitting it is obviated.

The present invention exploits the redundant digits of the MIN, for uniquely identifying the main and extension(s) cellular telephones of a subscriber. Thus, for example, if a subscriber having a cellular telephone number 333555 wishes to acquire an extension, one of said redundant leading digits, say said 'x', is rendered significant in the sense that e.g. '0' stands for the main telephone and T stands for the extension telephone. Thus, upon payment of a prescribed fee, for benefiting from the "extension" service, a table in the cellular system that holds the particulars of the subscriber under consideration is updated for reflecting the fact that this subscriber has 2 MINs, i.e. 9720333555 (main MIN) and 9721333555 (extension MIN). It should be appreciated that said subscriber has nevertheless only one valid cellular telephone number, i.e. 333555, and the decision whether to actually transmit 9720333555 or 9721333555 is decided upon locally according to predetermined criteria, preferably in a programmable manner, e.g. by first trying to contact the subscriber at his main telephone and in the absence of reply by trying the extension telephone. Obviously the main and extension cellular telephones of the subscriber store, respectively the numbers 9720333555 and 9721333555.

It is accordingly appreciated that the subscriber is unable to abuse the extension service for emulating two separate lines, e.g. for conducting simultaneous conversations from the main and the extension telephones.

The incorporation of extension services, according to the invention, does not impose undue constraints in terms of software/hardware modifications to the existing cellular system. In other words, only limited modifications are required in order to incorporate extension services into the cellular system.

It should be noted that the situation in Israel, as described in the foregoing, does not necessarily reflect the situation in other countries. Thus, for example, in the United States (US), the cellular network exploits all 10 digits of the MIN i.e. the trailing 7 digits for the local subscriber's number and the leading 3 digits for identifying the area code, and accordingly the solution offered by the present invention is not applicable in the U.S.

It should be further noted that, if desired, the solution according to the invention essentially retains the hitherto known billing system wherein all the debits on account of telephone conversations of a given subscriber are associated with the subscriber's telephone number. Thus, regardless of whether the telephone conversation is conducted through the main or one of the extension telephones, all the debits are associated with the telephone number of the subscriber (e.g. 333555 in the previous example).

There is thus provided in a accordance with the invention, a cellular telephone system of the kind transmitting a signal to one cellular telephone that is selected, in a preprogrammed manner, from among main and at least one extension cellular telephones of an addressed subscriber having associated therewith an n-digits subscriber's cellular telephone number in the cellular telephone system, in response to a request for establishing a telephone connection between a calling subscriber and said addressed subscriber ; each one of said main and at least one extension cellular telephones storing an m digit Mobile Identification Number (MIN) wherein said m digits consist of an n digit (n If desired only a portion of said m-n digits serves as said code for uniquely identifying said one cellular telephone with respect to the other.

According to one embodiment of the invention the cellular system of the invention, comprises, in combination: receiver means for receiving a signal indicative of a request for establishing telephone connection between a calling subscriber and said addressed subscriber; database querying means and associated transmitter means, responsive to said received signal for following a pre-planned procedure associated with said database, for transmitting a signal indicative of at least the MIN of said one selected cellular telephone of said addressed subscriber; and exceptional execution means responsive to failure of establishing communication with said addressed subscriber, for executing a "communication failure" procedure that is associated with said database.

There is further provided, for use in a cellular system of the kind specified, a cellular telephone storing therein a MIN having m digits consisting of an n digit (n By another aspect of the invention there is provided, in a cellular telephone system, of the kind comprising main and at least one extension cellular telephones of an addressed subscriber having associated therewith an n-digit subscriber's cellular telephone number in the cellular telephone system; each one of said main and at least one extension cellular telephones storing an m digit Mobile Identification Number (MIN) wherein said m digits consist of an n digit (n BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding, the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Fig. 1 is a simplified schematic illustration showing a cellular telephone network linked to a conventional wired telephone network; Fig. 2 is a simplified schematic illustration, partially in block diagram, of the main hardware components participating in the relaying of a telephone call from a conventional wired network to cellular network of the kind shown in Fig. 1; Fig. 3 is a block diagram illustrating a simplified sequence of operations that are executed in a cellular system, for relaying a received packet, in order to establish telephone connection between a calling and called subscribers.

Fig. 4 is a representation of a Mobile Identification Number according to one embodiment of the invention; Fig. 5 is a block diagram exemplifying the sequence of operations for establishing communication with an addressed subscriber, according to one embodiment of the invention.

Fig. 6 is a schematic illustration exemplifying the provision of an extension service, in a cellular telephone system, according to the prior art; and Fig. 7 is generalized block diagram illustrating the hardware infra-structure that is utilized for the realization of a system according to Fig. 6.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Attention is first directed to Fig. 1, showing a simplified schematic illustration of a cellular telephone network 1 linked to a conventional wired telephone network 2. As is well known, conventional telephone network 2 links, through known per se infra-structure 3, a plurality of telephone systems, of which there are shown in Fig. 1 only two telephone sets 4 and 5. Whilst, for sake of clarity, telephone network 2 communicates with cellular telephone network 1, via a single node (i.e. communication line 6), this does not reflect the situation in reality in which, as a rule, more than one node serves as a bridge between the conventional and cellular networks. Also shown in Fig. 1, are two, out of many, cellular telephones (7 and 8) which are inter-linked through a cellular infrastructure represented schematically as network 9.

Attention is also directed to Fig. 2, showing schematically and partially in block diagram, the main hardware components that participate in the relaying of a telephone call from a conventional wired network 2 to cellular network 1. A typical sequence of relaying a phone call from a calling subscriber, subscribed to a conventional network, to an addressed subscriber, subscribed to the cellular network will now be described. When a first subscriber, subscribed to the conventional network 2, wants to establish a telephone connection with a second subscriber, subscribed to the cellular network, he/she picks up the receiver of his telephone set 4 and dials the addressed subscriber's telephone number, say for example 050-333555, wherein the "050" stands for the area code of the "Pelephone" network and "333555" stands for the addressed subscriber's cellular telephone number. A packet 10, that is transmitted from the calling subscriber's telephone 4 and which holds the data that pertains, inter alia, to the telephone number of the calling and called subscriber, is relayed in a known per se manner to switch 12, being for example of the known Northern Telecom (NT) or Alcatel type. Packet 10 signifies that the calling subscriber (having a telephone number that is stored in field 1 of packet 10), wants to establish a telephone connection with an addressed subscriber, in the cellular system, having a cellular telephone number stored in field 11" of the packet 10. As is known per se, other data may also be stored in packet 10.

Having classified, in switch 12, the leading digits "050" as the area code of the cellular network, the packet is routed to the cellular switch 14 over communication line 16 (6 in Fig. 1), using a conventional 2Mbps (Mbps stands for Mega-byte-per-second) MFC-R2 communication protocol.

There follows a description of the sequence of operations, that are executed in the cellular system 1, for relaying the received packet in order to establish connection with the addressed subscriber, and to this end attention is also directed to the block diagram of Fig. 3. It should be noted that whilst in reality the block diagram illustrated in Fig. 3 is far more complex, the degenerated version thereof, shown in Fig. 3, is sufficient for explaining the principles of establishing a telephone connection with a called subscriber.

Thus, the entire dialed number (e.g. 050-333555, in the example above) portion of packet 10, is fed to a so called "PRETRE" receiver module 30 (standing for "Pre-translator"), for undergoing preliminary validation test in which the prefix digits are tested for validity against a pre-stored database. In the present example "050" is a valid prefix signifying that the addressed telephone number belongs to the cellular telephone system of area code 050. If, for example, the prefix were "052" (standing for the area code of the "Cellcom" cellular system) the latter test would fail.

Having met the preliminary validation stage, the particulars of the calling subscriber, being identifiable by the "calling subscriber telephone number" field (1Γ) of packet 10, are checked in module OCOS 32 (Standing for "Originate Class of Service"). Normally, in module OCOS, particulars, such as the credit/debit status of the calling subscriber are checked against pre-stored data pertaining to this particular subscriber, and control is transferred to "PREINX" module 34 (wherein PREINX stands for "Pre-index") in the case that the calling subscriber meets the criteria prescribed by the OCOS module 32, e.g. his/her debt did not exceed an authorized amount.

Obviously, the tests that are executed in module 32 necessitates holding data pertaining to the calling subscriber. These data is available, of course, only when the calling subscriber is subscribed to the cellular telephone system. Accordingly, in the example above, where the calling subscriber is a member of disjoint network (2), the tests of the OCOS module 32 are skipped.

Having approved the calling subscriber, control is transferred to PREINX module 34. The latter, produces a MIN number consisting of 10 digits (output RTE 1 in module 34), of which the trailing 6 digits are the addressed subscriber's cellular telephone number, taken from the packet 10 (e.g. 333555) and the leading 4 digits are "9720". The PREINX module, further determines the selected mode of operation with respect to the addressed subscriber. Thus, for example, if the addressed subscribed preprogrammed the "PREINX" module to a "follow me" mode in accordance with which he/she should be contacted at a pre-programmed desired destination, e.g. at 03-5664455, then the output of module 34 will be a so called world number 03-5664455 rather than said RTE 1 cellular telephone number 333555.

Assuming that the addressed subscriber is in the normal mode operation, i.e. requests for establishing communication are forwarded to his cellular telephone, the MIN number (said output RTE 1) is fed to "ROUTE TREE" module 36 which determines what switch should transmit the so determined MIN. In this connection, it should be noted that Fig. 3 describes a logical structure rather than a physical one, in the sense that the various modules of Fig. 3, may be physically located in different sites and components of the cellular system, all as is known per se. Thus, by way of non limiting example the testing sequence described in the foregoing is typically performed at a "main cellular switch" (referred to also as Home Location Register - HLR) e.g. cellular switch 14, that holds a database that is normally accessed, and queried during said testing sequence. The cellular switch which applies the testing sequence, is not necessarily the one, which will eventually transmit the MIN. Normally the latter is selected to be the one being geographically nearest to the telephone set of the addressed subscriber. Thus, for example, if cellular telephone 8 is to be accessed, the switching office that transmits the MIN is 18, whereas the HLR switch is 14.

Normally, switching offices (of which only three, 14; 18; and 20, are shown in Fig. 2), are capable of determining the position of the cellular telephones that are subscribed to the network (of which only telephone sets 7 and 8 are shown in Fig. 2) by analyzing a signal/noise value of a received "staying alive" signal that is repeatedly transmitted by the cellular telephone every predetermined time interval, in accordance with a known per se, so called "registration" algorithm . In the scenario described in Fig. 2, the signal/noise grading of the "staying alive" signal that is originated by cellular telephone 8 and received by switch 18 is the highest.

Reverting now to module 36 in Fig. 3, the latter (together with module "OUTTRE TABLE" 42, referred to later) is constantly updated by the respective switching offices as to their position with respect to the cellular telephones of the subscribers, and therefore module 36 (42) yields as an output a routing path which includes specification on the identity of the cellular switch that will eventually transmit the MIN of the addressed subscriber.

Having determined the identity of the transmitting switching office in module 36, control is transferred to module 38, ROUTE 2 TABLE, which includes a TCOS sub-module ( TCOS standing for "Target Class of Service"), which performs essentially the same function as the COCS module 32, however, not with respect to the calling subscriber but rather with respect to the addressed subscriber.

Having successfully passed the test of module 38, control is transferred to module 40, which specifies the tariff that is valid for the telephone conversation that is to be established. Thus, for example, some subscribers are charged according to reduced night tariff, which necessarily entails that any attempt to reach them by phone not during night hours, will be blocked by module 40.

As explained above, module 42, being responsive to module 40, determines, along with module 36, the routing path which prescribes the series of switches through which the MIN is relayed until it reaches a cellular switch from which it is transmitted.

Module 44 is the OUTPLS module (OUTPLS standing for "Out Pulse") in the transmitting switch, from which the MIN is transmitted, after having been routed through the path prescribed by module 42 in the main switch. Module 44 inherently employs a conversion table for obtaining valid numbers for transmittal. Thus, for example, if module 36 yields as output (not shown) a short code, say *66, which stands for dialing to predetermined destination, module 44 will convert *66 to a valid MIN number for transmittal, or world number, for transmitting to the wired network.

Reverting now to Fig. 2, since the switching office 18 is the nearest to the telephone set 8 of the sought subscriber, the former transmits all the 10 digits of the MIN that is pertinent to the sought subscriber i.e. "972x333555". The telephone 8 is the only one that replies to the transmitted message, since it is the only one that stores a matching number. Obviously, other cellular telephones nearby (not shown), albeit receiving the transmitted message, will disregard it, since they hold each a unique and different pre-stored subscriber number.

In the context of the specific example described in Fig. 3, with respect to the 'Telephone" cellular system, the MIN number is transmitted from switch 18 by utilizing a conventional N/AMPS air protocol.

The various modifications that are required in order to provide an extension service according to the invention will now be described with reference also to Figs. 4 and 5. Thus, suppose that telephone sets 7 and 8 signify, respectively, main and extension telephones of a given subscriber. The module "PREINX TABLE" 34 of Fig. 3 stores the relevant data with respect to said subscriber, e.g. a MIN 9720333555 for the main telephone and 9721333555 for the extension telephone. As shown, the two numbers are distinguished by the respective fourth insignificant leading digit, (highlighted for sake of clarity) i.e. '0' for the main telephone and for the extension telephone. Naturally, extension telephone set 7 stores the subscriber's extension number (9721333555) and main telephone set 8 correspondingly stores the subscriber's main number (9720333555). These numbers are store therein in the same manner that a cellular telephone number is normally assigned to a cellular telephone set by the cellular telephone company. As will be explained in greater detail below, table 34 determines as an output either the main MIN (9720333555) or the extension MIN (9721333555), depending upon the subscriber pre-programmed requirement.

After having routed the MIN, as specified in the foregoing, the latter is transmitted (see also block 50 in Fig. 5). As shown in Fig. 4, the transmitted signal consists of the trailing portion representing the subscriber's cellular telephone and a leading digit serving as identification code for either the main or extension cellular telephone set.

Normally, module 34 is programmed such that, in the first stage, the main telephone number is transmitted, i.e. 9720333555. All telephone sets that are capable of receiving the transmitted signal (i.e. being in the operational range of transmitting switch 18) compare the received number with their self stored number, and respond only in the case of a match. Accordingly, telephone set 8 responds and communication is established. If, on the other hand, telephone set 8 is unavailable, communication is not established (following the "Yes" arrow from block 51) and switch 18 proceeds according to a pre-stored plan as prescribed by PREINX table 34, which necessitates of course transfer of control back to the main switch 14.

Assuming that upon failing to establish communication with the main cellular telephone, communication should be established with the extension telephone, (following the "Yes" arrow from block 52) the cellular system reverts to search mode, in the manner specified, for detecting the cellular switch having the shortest range to the extension telephone. More specifically, module 34 yields as an output 9721333555 and modules 36 and 42 determine the routing path that the MIN 9721333555 should be relayed until it is transmitted from the appropriate switching office, which is, of course, not necessarily the same switching office that transmitted the main MIN (see also block 54 in Fig. 5).

Having determined the switch of the cellular system that is responsible for establishing communication with the extension telephone, the MIN 9721333555 is transmitted. Obviously, only the extension telephone, from among the cellular telephones that receive the transmitted signal, will reply to the transmitted signal due to the matching 9721333555 number stored therein. In Fig. 5, blocks 54 and 55 illustrate a procedure of attempting to establish communication with successive extension telephones, until either communication is established with one of them (block 56), or the attempts fail, in which case a known per se procedure is activated (not shown in Fig. 5), e.g. invoke a voice mail service for leaving a message for the addressed subscriber.

Preferably, but not necessarily, the subscriber, can optionally program the cellular system for either activating or disabling the extension support. For example, dialing *38, from either the main or extension telephone, activates a follow-me extension service as described above and shown in the "Yes" arrow of block 52, whereas *380 reverts to normal mode of operation wherein the extension service is not provided (following the "No" arrow of block 52 and the following block 53 in Fig. 5). In other words when "*38" or equivalent symbol is stored in module 34 with respect to a given subscriber, the system is programmed to follow the aforementioned procedure of attempting to establish communication with the main cellular telephone, and upon failing to do so, an attempt is made to establish communication with the extension cellular telephone of the subscriber. If, on the other hand, "*380" or equivalent symbol is stored in module 34 with respect to said subscriber, the system is programmed to establish communication with the main cellular telephone, and upon failing to do so, no attempt is made to establish communication with the extension cellular telephone of the subscriber.

If desired, module 34 can be programmed for temporarily substituting the extension service for the conventional voice mail, i.e. when the main cellular telephone is not available the extension telephone is accessed rather than providing a voice mail service for recording a message from the calling subscriber. As is no doubt clear to those versed in the art, these are, only some of many possible variants for providing an extension service or modified version thereof to subscribers. Preferably, but not necessarily, the various modes of operations of the cellular system, as described in the foregoing, can be remotely programmed from either the main or extension cellular telephones of the subscriber.

It should be noted that despite the provision of an extension service, the subscriber is still associated with only one cellular telephone number, i.e. in the latter example 333555, simply since the appending of the leading 9720 or 9721 digits that serve for identifying the main or extension cellular telephones is done internally in the system, and cannot be executed by the calling subscriber. Put differently, the calling subscriber cannot dial the 9720 or 9721 prefixes in order to accomplish communication directly to the respective main or extension cellular telephone of the called subscriber.

Whilst in the specific example described above, only one extension is provided and the digit that serves for identifying the main or extension telephone is the fourth from among said leading digits, in alternative embodiments, more than one extension may be utilized and the leading places in the MIN number may be exploited in any desired manner for rendering them identifying code as shown in Fig. 4 On the basis of the foregoing, those versed in the art will readily appreciate that the incorporation of an extension service to a conventional cellular system, according to the invention, necessitates only limited modification in the system's hardware/software, resulting in essentially no degradation in the system's performance, insofar as providing normal services is concerned. More specifically, in the simplified example of Fig. 3, module 34 has been modified, and the modules 30, 32, 36, 40 and 42 should be slightly modified in order to classify a MIN number of an extension telephone as a valid number in the system (for either a calling or addressed subscriber), and having done so, they can treat a MIN indicative of an extension essentially as if they treat any normal MIN number in the system.

Conversely, and as is clearly evident from Figs. 6 and 7, the hitherto known solution offered by Precision systems, not only necessitates the utilization of a valid cellular telephone number per extension (i.e., in Fig. 6, 632-5086 and 632-7380, being the extensions of 632-5000), but also require an expensive hardware and software add-on, i.e, in Fig. 7, Switching fabric 60, Voice Response Unit - VRU (61) and Unix server 62, all interlinked by Ethernet Local Area Network 63.

The present invention fulfills, thus, a long felt want.

Claims (14)

CLAIMS:

1. A cellular telephone system of the kind transmitting a signal to one cellular telephone that is selected, in a preprogrammed manner, from among main and at least one extension cellular telephones of an addressed subscriber having associated therewith an n-digit subscriber's cellular telephone number in the cellular telephone system, in response to a request for establishing a telephone connection between calling subscriber and said addressed subscriber ; each one of said main and at least one extension cellular telephones storing an m digit Mobile Identification Number (MIN) wherein said m digits consisting of an n digits (n

2. The cellular system according to Claim 1, wherein said m has the value of 10 and n has the value of 6.

3. The cellular system according to Claims 1 or 2, wherein only a portion of said m-n digits serves as said code for uniquely identifying said one cellular telephone with respect to the other.

4. The cellular system according to Claim 3, wherein said m-n digits are the leading digits and the n digits are the trailing digits of the m digits of said MIN.

5. The cellular system according to Claim 4, wherein said subscriber having a main and one extension cellular telephone; said m has the value of 10 and n has the value of 6 and the fourth digit of the m-n digits of the MIN stored in said main and extension telephones, are have the values 0 and 1, respectively.

6. A cellular system according to any one of the preceding claims, comprising, in combination: receiver means for receiving a signal indicative of a request for establishing telephone connection between a calling subscriber and said addressed subscriber; database querying means and associated transmitter means, responsive to said received signal for following a pre-planned procedure associated with said database, for transmitting a signal indicative of at least the MIN of said one selected cellular telephone of said addressed subscriber; and exceptional execution means responsive to failure of establishing communication with said addressed subscriber, for executing a "communication failure" procedure that is associated with said database.

7. The system according to Claim 6, wherein said pre-planned procedure necessitates the transmittal, in a first stage, of a signal indicative of at least the MIN of said main cellular telephone.

8. The system according to Claims 6 or 7, wherein said "communication failed" procedure necessitates successively transmitting signals indicative of said Mins stored in the at least one extension telephones, until communication is established.

9. A system according to any one of Claims 1 to 8, wherein anyone of said selected subscribers is capable of programming said cellular system from anyone of said main and at least one extension cellular telephones, for enabling or disabling the possibility of establishing communication with said at least one extension telephone.

10. A cellular telephone system according to anyone of the preceding Claims, being of the Narrow- Advanced-Mobile-Phone-Service (N-AMPS) type.

11. A cellular telephone system according to anyone of the Claims 1 to 9, being of the Time-Division-Multiplexing-Access (TDMA) type.

12. A cellular telephone system according to anyone of the Claims 1 to 9, being of the Code-Division-Multiplexing-Access (CDMA) type.

13. For use in a cellular system according to any one of the preceding Claims, a cellular telephone storing therein a MIN having m digits consisting of an n digit (n

14. In a cellular telephone system, of the kind comprising main and at least one extension cellular telephones of an addressed subscriber having associated therewith an n-digit subscriber's cellular telephone number in the cellular telephone system; each one of said main and at least one extension cellular telephones storing an m digit Mobile Identification Number (MIN) wherein said m digits consists of an n digit (n