CORDLESS TELECOMMUNICATIONS SYSTEM AND IDENTIFICATION CODE MODIFICATION PROCESS

Abstract: The present invention relates to a telecommunications system comprising a base unit and a mobile unit intended for communicating with each other by radio link when their identification codes match. The invention proposes a modification process of modifying previously matched identification codes by radio link. Said process has verification steps so that the mobile unit need not be put back on the base station.

Description: CORDLESS TELECOMMUNICAΗONS SYSTEM AND IDENTiπCAπON CODE MODIFICAΗON PROCESS FIELD OF THE TNVENTION The present invention relates to a telecommunications system compπsing at least a first unit and a second unit having each: - an identification code, - matching means for matching said identification codes, - means for transmission by radio channel. The invention also relates to a modification process of modifying identification codes of a first unit and of a second unit of a telecommunications system, said units including means for transmission by radio channel. The invention also relates to a mobile unit intended to be used in a telecommunications system which includes a base unit with an identification code, said mobile unit having: - an identification code, - matching means for matching said identification code with that of the base unit, - means for transmission by radio channel. The invention finally relates to a base unit intended to be used in a telecommunications system which includes at least one mobile unit with an identification code, said base unit having: - an identification code, - matching means for matching said identification code with that of said mobile unit, - means for transmission by radio channel. The invention notably has highly significant applications in the field of cordless telecommunications where it permits of improving the communication security between base unit and mobile unit. BACKGROUND OF THE INVENTION French Patent Application No. 2559008 filed by Sony, 31 January 1985, describes a cordless telephone set comprising a base unit and a mobile unit having each an identification code: for a communication to be set up between the base unit and the mobile unit, their identification codes are to match. This Patent Application describes a mechanism for matching said identification codes by radio channel which requires that the mobile unit is put back on the base unit. Such a solution has various drawbacks. On the one hand, it necessitates the use of physical detection means for detecting that the mobile unit rests on the base unit, which considerably increases the cost price of the telephone. On the other hand, it does not permit of changing the identification code at an arbitrary instant: the only criterions applicable are of the type "change of identification codes every n time intervals in which the mobile unit rests on the base unit". Finally, this process does not provide total reliability for the user, notably in the case where the user lifts the mobile unit before the base unit has received a clearing from the mobile unit. SUMMARY OF THE INVENTION The present invention notably has for its object to propose a telecommunications system which remedies these drawbacks. Therefore, a telecommunications system according to the invention and as described in the opening paragraph is characterized in that: ■ said matching means comprise modification means for modifying previously matched codes, operating only by radio channel, for substituting codes called new identification codes for codes called old identification codes, ■ said modification means comprising verification means for ensuring that said units are correctly matched after such a modification before said old identification codes are deleted. Thus, according to the invention, the previously matching identification codes of a base unit and a mobile unit may be modified by radio channel at an arbitrary instant, without the necessity of putting the mobile unit back on the base unit. The verification means make it possible to protect the system against radio disturbance or interruptions of power supply, by avoiding that the identification code is modified in only either of the two units, which would result in that the system would be put out of operation. Moreover, as the identification codes of the mobile unit and base unit are to be matched beforehand, it is impossible to match a pirate mobile unit with the base unit by the mechanism of identification code modification according to the invention. In an advantageous embodiment, said modification means are utilized on the initiative of said first unit at a request transmitted to said second unit by radio channel. In another particularly advantageous embodiment, said verification means comprise: - means for transmitting a first clearing from said second unit to said first unit to permit said first unit to verify whether its new identification code has been correctly received by said second unit, - and means for transmitting a second clearing from said first unit to said second unit to permit said second unit to verify whether said first clearing has been correctly received by said first unit. In a preferred embodiment: ■ said units each have first and second storage means, ■ said transmitting means comprise: - for the first unit, transmitting frames which carry the identification code contained in its first storage means, - for the second unit, transmitting frames which carry the identification code contained in its second storage means, ■ and said verification means comprise: - for the first unit, writing its new identification code in its second storage means before transmitting said request, and in its first storage means upon reception of said first clearing, - for the second unit, writing its new identification code in its second storage means upon reception of said request, and in its first storage means upon reception of said second clearing. Finally, in another embodiment, said transmitting means comprise: - for the first unit, transmitting frames which carry the identification code contained in its first storage means, - and for the second unit, transmitting frames which carry the identification code contained in its second storage means. BRIEF DESCRIPTION OF THE DRAWINGS These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. In the drawings: - Fig. 1 represents an example of a telecommunications system according to the invention which comprises a mobile unit and a base unit, - Fig. 2 represents an example of an identification code modification process according to the invention, - Fig. 3 gives an example of a format of frames exchanged between the base unit and the mobile unit. DESCRIPTION OF PREFERRED EMBODIMENTS As shown in Fig. 1, a telecommunications system according to the invention comprises a base unit 1 and a mobile unit 2. The base unit 1 comprises an antenna and is connected to a telephone terminal by a cable 4. The mobile unit 2 also comprises an antenna 5. The mobile unit has a loudspeaker 6, a microphone 7 and a keypad 8. Moreover, either of these two units contains a microprocessor set (referenced 11 and 12 respectively, in the Figure) comprising a microprocessor proper (13 and 14), a random-access memory (15 and 16) and a backing store (17 and 18) of the EPROM type, for example. Identification codes permit the base unit 1 and the mobile unit 2 to identify themselves to each other and thus to avoid any pirate use of the line by another mobile unit. This code is transmitted in data frames exchanged between the base unit and the mobile unit. The frames received by a unit are accepted only if the identification code they contain matches that of the receiving unit. To improve the security of the communications, it is necessary to exchange the value of these identification codes regularly. This operation may be effected on the initiative of either unit by the transmission of a request which contains the new value of the identification code. In the following of the description, the unit that takes the initiative for the change is called the first unit and is denoted Ul, and the unit that receives the request for modification is called the second unit and is denoted U2. In Fig. 1, the base unit 1 is considered a first unit Ul and the mobile unit 2 is considered the second unit U2. But this example is not restrictive. In accordance with the invention, two locations 20 and 21, on the one hand, and 22 and 23, on the other hand, are reserved in the read-only memories of the first and second units Ul and U2 for storing the old and new values of the identification codes of either unit. The modification process of the identification codes will now be described with reference to Fig. 2. In Fig. 2 is shown in the form of Tables the development of the contents of the four memory locations 20, 21, 22 and 23. In this Table the old and new values of the identification codes are denoted XX and YY, respectively. In accordance with the invention, the frames transmitted by the first unit Ul contain the identification code which the memory location 20 contains, and the data frames transmitted by the second unit U2 contain the identification code which the memory location 23 contains. When the system is in normal operation, that is to say, outside the modification steps of the identification codes, the new and old values of the identification codes are the same: value XX is stored in the four locations 20 to 23. In step 100, the first unit Ul writes the new value YY of the identification code in the memory location 21, and, in step 101, it transmits a request for modification R containing this new value YY to the second unit U2. In step 110, the second unit U2 receives a request R coming from the first unit Ul. It writes the received code which is denoted Id R in Fig. 2 in its memory location 23. In step 120, the first unit receives a frame Dl coming from the second unit U2. The identification code Id D1 of this frame is equal to the identification code M 23 contained in the memory location 23. The first unit verifies whether the value of this code is equal to Id 2 ι (Id 2j being the value that is contained in the memory location 21). If it is, the frame Dl is accepted and processed. Since the request R has been correctly received by the second unit U2, the old value XX of the identification code is deleted in the first unit: therefore, the latter writes the new value YY of the identification code in its memory location 20. If, on the other hand, the value Id D1 contained in the data frame Dl is different from YY, this means that the new value of the identification code has not been correctly received, or has not been taken into account by the second unit U2 due to a radio disturbance or a problem of power supply of the batteries, for example. The first unit Ul examines whether the value of the identification code Id D1 is equal to that contained in the memory location 20. If it is, frame Dl is accepted and processed (which is symbolized by the words "Dl accepted" in Fig. 2), after which the process is resumed at step 101. If it is not, frame Dl is refused (which is symbolized by the words "Dl refused" in Fig. 2). In step 130, the second unit U2 receives a frame D2 coming from the first unit Ul. This frame D2 contains the value of the identification code Id 20 which is contained in the memory location 20. The second unit verifies whether the identification code Id D2 contained in this frame is equal to the code W 23 . This is the case when the value of Id 20 has been modified in step 120, that is, when the request for a modification of the identification code has been correctly taken into account by the second unit U2. The second unit U2 accepts and thus processes the received frame D2. And, in step 131, it writes the new value YY of the identification code in memory location 22. The four locations thus contain the new value YY. The modification process is terminated. On the other hand, if Id D2 is different from Id , the second unit verifies whether Id D2 is equal to Id 22 - If it is, the frame D2 is accepted and processed by the second unit. If it is not, the frame is refused because the identification code of the unit that has transmitted this frame does not correspond to the old identification code of the second unit. Thus, the transmission of a frame Dl by the second unit to the first unit forms a first clearing which permits the first unit to verify whether the second unit has correctly written the new value of the identification code. And the transmission of a frame D2 by the first unit to the second unit forms a second clearing which permits the second unit to verify whether the first unit has correctly received the first clearing. The old value of the identification code is not deleted in a unit until such a clearing has been received from the side of the other unit. In Fig. 3 is shown by way of example the format of the frames exchanged between the base unit and the mobile unit. Such a frame comprises: - a synchronization field Cl, - a field C2 indicating the length of the frame, - a field C3 indicating a frame number which permits of knowing whether or not it is a recurrent frame, - a field C4 which contains an identification code of the unit that transmits the frame, - a field C5 which contains the data. When such a frame transports a request R for modification of the identification code, the field C5 contains a code which permits of indicating the respective instmction (modification of the identification code in this case), followed by the new value of the identification code. Obviously, the invention is not restricted to the preferred embodiment which has just been described. In this example, there is notably considered that the identification codes of the mobile unit and of the base unit were the same. It is also possible that they are linked by a match relation that differs from the identity. Moreover, it has been considered that the request for modification was transmitted by the base unit. Such a request can be transmitted by either unit.

Claims: CLAIMS; 1. A telecommunications system comprising at least a first unit (1) and a second unit (2) having each: - an identification code (XX, YY), - matching means for matching said identification codes, - means for transmission by radio channel, characterized in that ■ said matching means comprise modification means for modifying previously matched codes, operating only by radio channel, for substituting codes called new identification codes (YY) for codes called old identification codes (XX), ■ said modification means comprising verification means for ensuring that said units (1, 2) are correctly matched after such a modification before said old identification codes (XX) are deleted. 2. A telecommunications system as claimed in Claim 1, characterized in that said modification means are utilized on the initiative of said first unit (Ul) upon request (R) transmitted by radio channel to said second unit (U2). 3. A telecommunications system as claimed in Claim 2, characterized in that said verification means comprise: - means for transmitting a first clearing (Dl) from said second unit (U2) to said first unit (Ul) to permit said first unit (Ul) to verify whether its new identification code (YY) has been correctly received by said second unit (U2), - and means for transmitting a second clearing (D2) from said first unit (Ul) to said second unit (U2) to permit said second unit (U2) to verify whether said first clearing (Dl) has been correctly received by said first unit (Ul). 4. A telecommunications system as claimed in Claim 3, characterized in that ■ said units each have first (20, 22) and second storage means (21, 23), ■ said verification means comprise: - for the first unit, writing its new identification code (YY) in its second storage means (21) before transmitting said request (R), and in its first storage means (20) upon reception of said first clearing (Dl), - for the second unit (U2), writing its new identification code in its second storage means (23) upon reception of said request (R), and in its first storage means (22) upon reception of said second clearing (D2). 5. A telecommunications system as claimed in Claim 4, characterized in that said transmission means comprise: - for the first unit (Ul), transmitting frames which transport the identification code contained in its first storage means (20), - and for the second unit (U2), transmitting frames which transport the identification code contained in its second storage means (23). 6. A process of modifying identification codes of a first unit (1) and of a second unit (2) of a telecommunications system, said units including radio transmission means, characterized in that it comprises ■ a substitution step, exclusively by radio channel, of codes called old identification codes (XX) beforehand matched by codes called new identification codes (YY), ■ a verification step for ensuring the correct match of said units (1, 2) after such a substitution before said old identification codes (XX) are deleted. 7. A modification process as claimed in Claim 6, characterized in that said substitution step is utilized on the initiative of said first unit (Ul), upon request transmitted by radio channel from this first unit to said second unit (U2). 8. A modification process as claimed in Claim 7, characterized in that said verification step comprises: - a transmission step for transmitting a first clearing (Dl) from said second unit to said first unit for permitting said first unit to verify whether its new identification code has been correctly received by said second unit, - and a transmission step for transmitting a second clearing (D2) from said first unit to said second unit, for permitting said second unit to verify whether said first clearing has been correctly received by said first unit. 9. A modification process of an identification code as claimed in Claim 8, characterized in that, while said units have each first and second storage means (20, 21, 22 and 23), said substitution step comprises: ■ for the first unit, writing its new identification code in its second storage means (21) before transmitting said request (R), and in its first storage means (20) upon reception of said first clearing (Dl), ■ for the second unit, writing its new identification code in its second storage means (23) upon reception of said request (R), and in said first storage means (22) upon reception of a frame which transports the new identification code of said first unit. 10. A modification process of an identification code as claimed in Claim 9, characterized in that said transmission means consist of: ■ for the first unit, transmitting frames which carry the identification code contained in its first storing means (20), ■ for the second unit, transmitting frames which carry the identification code contained in its second storing means (23). 11. A mobile unit intended to be used in a telecommunications system comprising a base unit with an identification code, said mobile unit having: - an identification code, - matching means for matching said identification code with that of said base unit, - radio transmission means, characterized in that ■ said matching means comprise modification means for modifying previously matched codes, operating only by radio channel, for substituting codes called new identification codes (YY) for codes called old identification codes (XX), ■ said modification means comprising verification means for ensuring that said units (1, 2) are correctly matched after such a modification before said old identification codes (XX) are deleted. 12. A base unit intended to be used in a telecommunications system comprising at least one mobile unit with an identification code, said base unit having: - an identification code, - matching means for matching said identification code with that of said mobile unit, - radio transmission means, characterized in that ■ said matching means comprise modification means for modifying previously matched codes, operating only by radio channel, for substituting codes called new identification codes (YY) for codes called old identification codes (XX), ■ said modification means comprising verification means for ensuring that said units (1, 2) are correctly matched after such a modification before said old identification codes (XX) are deleted.

Inventors: SANDRE BENOIT, SANDRE, BENOIT
Applicants: PHILIPS ELECTRONICS NV, SANDRE BENOIT, PHILIPS ELECTRONICS N.V., SANDRE, BENOIT
Application year: 1997
Main classification: H04M1
IPC codes: H04M1, H04Q7