A METHOD FOR STARTING A SHORT MESSAGE TRANSMISSION

Abstract: The invention relates to a method for starting a short message transmission in a cellular radio network, a corresponding cellular radio network, and a subscriber register for a cellular radio network, said subscriber register (10) comprising means (1) for sending a short message transmission start message to at least one short message service centre (SC1, SC2, SC3). For delaying start messages for short message transmission for a given subscriber, the subscriber register comprises a memory (8), control means (4), transmitter means (5, 6, 7) responsive to said control means (4) for sending start messages for short message transmission for a given subscriber to different short message service centres (SC1, SC2, SC3) after delays of variable duration, and a delaying means (9) responsive to the transmitter means (5, 6, 7), generating a variable delay for delaying sending of start messages for short message transmission for a given subscriber (MS) by the transmitter means (5, 6, 7) with a desired period of time.

Description: A method for starting a short message transmission The present invention relates to a method for starting a short message transmission in a cellular radio network, a corresponding cellular radio network and a subscriber register for a cellular radio net¬ work, in which method the subscriber register stores information on the fact that at least one short mess¬ age service centre holds short messages for transmis- sion to a subscriber that is not reachable, and when the subscriber requests process access to the cellular radio network or when the subscriber data of the sub¬ scriber are location updated, the subscriber register of the subscriber sends a short message transmission start message to said at least one short message ser¬ vice centre. In connection with cellular radio networks, it is known to send short messages through a short mess¬ age service centre (SC) separate from the cellular radio network. One specification for a system sending and relaying short messages is provided in the ETSI GSM system recommendation "GSM 03.40, February 1992, Technical Realisation of the Short Message Service Point-to-Point, ETSI/PT". This recommendation de- scribes the connection of a SC to a GSM Mobile Ser¬ vices Switching Centre and the operation of said SC in connection with sending and relaying short messages originating outside the cellular radio network and from a subscriber in the cellular radio network (A subscriber) to another subscriber in the network (B subscriber) or to an external data transmission means capable of receiving and/or sending short messages. When an SC attempts to send a short message to a B subscriber and the B subscriber cannot be reached, a list of waiting messages in accordance with the GSM recommendation 03.40 is set up in the home location register (H R), for B subscriber-specific storing of addresses of SCs holding short messages for delivery to the B subscriber. Thus, when the B subscriber accesses the network, that is, when a short message can be delivered to the mobile phone of the B sub¬ scriber, the visitor location register (VLR) in whose service area the B subscriber is registered sends information on the arrival of the B subscriber in the network to the HLR of the B subscriber. Thereupon the HLR, or subscriber register, of the B subscriber starts transmitting Alert messages to the SCs speci¬ fied in the Message Waiting Data List of the given subscriber; said Alert messages signal the SCs that the B subscriber has become active within the service area of the cellular radio network and that it is worth-while attempting to send a short message to the mobile phone of the B subscriber. This kind of situ¬ ation can arise for example when the subscriber has switched off his mobile phone for the night and switches it on in the morning, or respectively if the subscriber uses a mobile phone in work and switches his mobile phone on when his working hours begin. If a plurality of Alert messages arrive in a single SC, the SC may become overloaded and unable to deliver short messages to subscribers. If the SC is not overloaded, the Alert messages initiate short message transmission for the B subscriber from the SCs through the cellular radio system to the B subscriber. The short messages are stored in the SC according to the Mobile Station International PSTN/ISDN number (MSISDN) of the B sub¬ scriber; yet the SC does not recognize the different MSISDN numbers as belonging to the same subscriber, but can simultaneously initiate sending of several short messages to the same B subscriber. Likewise, if several SCs having access to the cellular radio net¬ work are attempting to send substantially simultane¬ ously short messages to the same B subscriber, the MSC with which the VLR is integrated cannot send the short messages that have arrived after the previous short message, but must send a negative acknowledgement to the SC. Thus collision of short messages in the MSC results in sending of negative signalling messages to the SC through the cellular radio network. In that situation, the SC will wait a predetermined period of time and retry sending the short message. A situation can now be contemplated where sending of several short messages to a given B subscriber has been attempted, but the B subscriber has had no access to the cellular radio network and the short messages addressed to the mobile phone of the B subscriber are stored in the memories of the different SCs for subsequent delivery to the B subscriber. When the B subscriber then becomes active within the area of the cellular radio network, the HLR of the B subscriber sends Alert mess¬ ages to all those SCs whose memories hold short mess¬ ages addressed to the B subscriber. Thereafter all the SCs attempt to deliver - nearly simultaneously - short messages to the B subscriber. A collision of short messages arises in the MSC of the location area of the B subscriber, since the MSC can only deliver one short message at a time. For example, if ten SCs have attempted to send a short message so that the trans¬ mission of the first, i.e. previous, of these messages has been in progress from the MSC of the location area to the B subscriber, the nine subsequent short mess¬ ages cannot be sent and the outcome is failed trans¬ mission; the SCs which have sent short messages re¬ ceive negative acknowledgements indicating that short message transmission from the MSC of the location area has failed. The nine SCs that failed in delivering a short message then resend the short messages to the MSC of the location area of the B subscriber for del¬ ivery to the B subscriber. In that situation, the first, i.e. previous, of these short messages reaches the B subscriber, but the eight subsequent, i.e. fol¬ lowing, short messages do not reach the B subscriber, and consequent on failed delivery, negative ack¬ nowledgements are sent to the pertinent SCs. The situ- ation is aggravated if several mobile phones or ter¬ minals to which attempts have been made to send short messages during their absence from the network subs¬ tantially simultaneously resume contact with the net¬ work. In such a situation, with mobile phones access- ing the cellular radio network, several SCs attempt to send short messages to the B subscriber, and only some of the transmissions are successful. Thus acknowledge¬ ments indicating failure of transmission and resending of short messages give rise to considerable signalling traffic in the cellular radio network, thus hindering the mobile telephony and jeopardizing the operation of the cellular radio network. It is an object of the present invention to eliminate the problems presented by substantially sim- ultaneous arrival in a MSC of short messages for a given subscriber, to speed up the successful relay of short messages, to diminish superfluous signalling and short message traffic in the cellular radio network, and to eliminate the risk of overloading the SC. This novel method for starting a short message transmission in a cellular radio network is character¬ ized in that the subscriber register sends the short message start messages for a given subscriber to dif¬ ferent SCs after delays of variable duration. The cellular radio system disclosed in the pres- ent application, comprising a mobile subscriber, at least one short message service centre for relaying short messages through a cellular radio network to the mobile subscriber, and a subscriber register of the subscriber for storing short messages when the mobile subscriber cannot be reached, said subscriber register storing information on the fact that said at least one short message service centre holds short messages for transmission to a subscriber that is not reachable and comprising means for sending a short message transmis¬ sion start message to said at least one short message service centre when the mobile subscriber can again be reached or when the subscriber data of the subscriber are location updated, is characterized in that the transmission means of the subscriber register comprise means for sending start messages for short message transmission for a given subscriber to different short message service centres after delays of variable dura¬ tion. The subscriber register for a cellular radio system disclosed in the present application, compris¬ ing means for sending a short message transmission start message to at least one short message service centre, is characterized in that the subscriber regis- ter comprises a memory for storing short message transmission start messages, control means for receiv¬ ing, storing in said memory, reading from said memory, and transmitting short message transmission start messages, transmitter means responsive to said control means for sending start messages for short message transmission for a given subscriber to different short message service centres after delays of variable dura¬ tion, and delaying means responsive to the transmitter means for generating a variable delay for delaying sending of short message transmission start messages for a desired period of time. The invention is based on the idea of delaying the sending of subscriber-specific start messages - i.e. Alert messages in the GSM system - for short message transmission that are sent by the subscriber register of the subscriber - in the GSM by the HLR - to the SCs. The advantage of this method for starting a short message transmission in a cellular radio system, cellular radio system and subscriber register for a cellular radio system resides in that the problems presented by substantially simultaneous arrival of short messages in a MSC are avoided. In other words, the collision of short messages in the MSC of the location area of the B subscriber and the resultant acknowledgements indicating failed transmission, and superfluous signalling and short message traffic are eliminated. Thus using the method and MSC according to the invention facilitates the successful relay of short messages and diminishes the risk of system fail¬ ure caused by overload on the cellular radio system and the SC. The invention will be more closely explained in the following, with reference to the accompanying drawings, in which Figure 1 illustrates schematically a cellular radio system in which the method and MSC of the inven¬ tion can be used, Figure 2 shows the subscriber data hierarchy in the subscriber's HLR, i.e. subscriber register, Figure 3 shows a block diagram of the cellular radio system of the invention and its subscriber register, Figure 4 shows a block diagram of a subscriber register, i.e. HLR, comprising means for sending short message transmission start messages. In the following, the method of the invention will be described in connection with the digital mobile telephone ^system GSM, which in fact is the primary application of the invention. The method of the invention can, however, also be applied in other similar mobile systems or modifications of the GSM. The basic configuration and basic facilities of the GSM mobile system are well-known to those skilled in the art and are relatively precisely defined in the GSM system specifications, particularly in "GSM Recom¬ mendations 01.02; 11.30; 11.31; 11.32; 03.40." The GSM network, illustrated in Figure 1, gener¬ ally comprises one home location register HLR, which is a database in which mobile phone data, such as location data, are stored permanently. The HLR per¬ forms substantially the same functions as the sub¬ scriber register of the invention. The system further comprises several visitor location registers VLR, one or several of such being provided for one MSC service area. The VLR is a database in which mobile phone data are stored while the mobile phone visits the area of the VLR, i.e., the location area of the mobile phone. The VLR has information on the location of the mobile phone MS with an accuracy of one location area. The HLR in turn has information on the VLR that the mobile phone MS visits, and provides routing information to the telephone network for calls terminating in the mobile phone MS, that is, provides the VLR address of the location register of the B subscriber. The HLR in turn receives the required routing information from the VLR. The HLR and VLR have solely a signalling con¬ nection with the other components of the mobile net¬ work. In the system of Figure 1, each MSC service area has its own visitor location register VLR integrated with the mobile or radio switching centre MSC of that particular service area. The arrangement shown in the figure illustrates two service areas, one with a mobile services switching centre MSCl and a visitor location register VLR1 and the other with a mobile services switching centre MSC2 and a visitor location register VLR2. There are one or more location areas under each of the two service areas, and within each location area a Base Station Controller (BSC) control- ling several fixed radio stations or Base Transceiver Stations (BTS) is provided for traffic control. Each radio cell referred to above comprises one base trans¬ ceiver station BTS, and one base station controller BSC provides services to several cells. The mobile phone MS located in the cell establishes a duplex radio connection with the base transceiver station BTS of the cell. A signalling connection and voice chan¬ nels are provided between the base station controller BSC and the mobile services switching centre MSC. Cor- respondingly, within the second service area the MSC2 has control over a location area comprising a base station controller BSC2 and base transceiver stations BTS3 and BTS4. The GSM network usually communicates with other networks, such as the public switched telephone net¬ work PSTN, another mobile network PLMN, a packet switched data network PSPDN, an ISDN network or a short message service centre SC, through a specific mobile services switching centre called a gateway MSC (GMSC). One or several (all) of the MSCs of the net¬ work may serve as a gateway MSC. It is possible to establish a voice channel connection from the GMSC to any other MSC of the network. The GMSC further has a signalling connection with the HLR. The HLR in turn has a signalling connection with the VLR. Altern- atively, the switching centre of another data trans¬ mission system, such as an ISDN centre, may serve as the gateway MSC. Figure 1 further shows several short message service centres SC sending a short message through the cellular radio network to the mobile phone MS of the B subscriber, and storing, while the sub¬ scriber is not reachable, short messages to be later delivered to the subscriber. Figure 2 shows the subscriber data hierarchy in the subscriber's HLR, i.e. subscriber register. The subscriber data are stored according to the Inter¬ national Mobile Subscriber Number IMSI of the sub¬ scriber in the HLR of the subscriber as subscriber- specific data files, in which the supplementary ser- vices to which the subscriber is entitled are stored in addition to the subscriber basic service. The sub¬ scriber basic service includes normal telephony ser¬ vice, transmission and reception services for short messages, and various data transmission services. The supplementary subscriber services include call trans¬ fer and call barring services and call waiting ser¬ vice, for instance. One subscriber MSISDN number can correspond to a given subscriber basic service, i.e. to the "telephone directory number" of a specific telecommunications service for a given subscriber. The GSM system affords the possibility of sending short messages to a given subscriber according to any tele¬ phone directory number of the subscriber, that is, on the basis of the subscriber's corresponding basic ser- vice, i.e. the MSISDN number. Each subscriber MSISDN number and each corresponding basic service has a Message Waiting Data (MWD) list of its own, storing the addresses Scl, Sc2 of the short message service centres from which attempts have been made to transmit short messages to the subscriber basic service iden- tified with said MSISDN (telephone directory number) but which have failed in transmission for some reason, for example because the subscriber has been out of reach while his terminal has been located outside the coverage area of the base transceiver station of the radio network, i.e. in a shadow region, or because the subscriber terminal has been switched off. Figure 3 shows a subscriber MS having connection with the cellular radio system through a base trans- ceiver station BTS1, BTS2 and through a base station controller BSC and the mobile services switching centre VMSC/VLR of the location area of the sub¬ scriber. Short messages are in store in one or several short message service centres SC for delivery to the subscriber MS. The short message service centres access the cellular radio network through a gateway MSC (GMSC/IWMSC). The visitor location register VLR of the location area of the subscriber has information (Message Waiting Flag) on the fact that short messages are stored in the short message service centre SC for delivery to the subscriber. The subscriber register 10, the GSM equivalent of which is the home location register HLR, comprises a HLR functions block 3. When the subscriber has become accessible in the cellular radio network, the subscriber register 10 receives information on this from the visitor location register VLR, since the visitor location register stores in¬ formation, i.e. holds a Message Waiting Flag, as an indication of the fact that the short message service centre SC stores short messages in wait to be sent to the subscriber MS. In that situation, the HLR func¬ tions block 3 of the subscriber register HLR requests the means 1 for sending short message transmission start messages, i.e. the start message transmission functions included in the subscriber register 10, to send start messages for the short messages, i.e. Alert messages in the GSM system, for a given subscriber to the short message service centres SC holding short messages for delivery to the subscriber MS. The start message transmission means 1 sends the start messages for short messages in such a manner that one short message transmission start message is sent to the first short message service centre SCI in succession on the HLR Message Waiting Data List of the subscriber register 10, corresponding to the subscriber's IMSI- related telephone directory number, i.e. MSISDN num¬ ber, whereafter the start message transmission means 1 wait a predetermined period of time prior to sending the second start message for short messages in succes- sion to the next short message service centre SC2. For example in the GSM system, the sending of Alert mess¬ ages is performed in such a way that the start message transmission means 1 requests the communications protocol of the Mobile Applications Part MAP 2 to send a short message transmission Alert message to the short message service centre SC, whereupon the MAP attends to sending the Alert message. Figure 4 shows a block diagram of a subscriber register, i.e. home location register HLR, 10. When the HLR functions block 3 of the subscriber register 10 receives information via the Mobile Applications Part MAP 2 from the visitor location register VMSC/VLR on the fact that the subscriber MS has become acces¬ sible, the HLR functions block 3 sends the IMSI-rel- ated MSISDN numbers of the telecommunications services of a given subscriber MS, obtained from the Message Waiting List of the subscriber database 11 of the sub¬ scriber register 10, and the telephone numbers of the short message service centres SCI, SC2, SC3 pertaining to said MSISDN numbers to the control means 4 forming part of the start message transmission means 1. The control means 4 is integrated with one or more trans¬ mitter means 5, 6, 7 and a memory 8 storing start messages. The control means 4 checks whether one of the transmitter means 5, 6, 7 is unoccupied, and if an unoccupied transmitter means is found, the control means 4 transfer the corresponding data files compris¬ ing the IMSI-related MSISDN numbers of a given sub¬ scriber and the telephone numbers of the short message service centres SC to the transmitter means 5, 6, 7. If, on the other hand, the control means 4 do not find an unoccupied transmitter means 5, 6, 7, the control means 4 stores said information in the start message memory 8. When one of the transmitter means subse- quently becomes available, the control means 4 sends the above information to said available transmitter means 5, 6, 7. The transmitter means 5, 6, 7 then sends a start message for transmission of short mess¬ ages for a given subscriber to the address SCI (i.e. telephone number) of the first short message service centre stored in connection with the IMSI-related MSISDN number of the subscriber. If the transmitter means 5, 6, 7 still holds addresses of short message service centres SC2, SC3 to which a short message transmission start message should be sent, the trans¬ mitter means 5, 6, 7 requests the delaying means 9 for permission to send start messages, by sending an in¬ quiry to the delaying means 9. Thereafter the delaying means 9 will wait a predetermined period of time, defined in advance for instance by means of a software parameter, and thereafter sends a positive acknow¬ ledgement to the transmitter means 5, 6, 7. his ack¬ nowledgement message, the delaying means 9 gives the transmitter means 5, 6, 7 permission to send a short message transmission start message to the pertinent short message service center SC2, SC3. The transmitter means 5, 6, 7 then sends the information required for sending the start message to the Mobile Applications Part MAP 2 of the HLR, which attends to the actual sending of the short message transmission start mess¬ age by sending a corresponding message to the desired short message service centre SCI, SC2, SC3. The trans¬ mitter means 5, 6, 7 sends start messages to the MAP as long as it holds undelivered start messages under one transmission request received from the control means 4, i.e. messages for one given subscriber MS. Thereafter the transmitter means 5, 6, 7 informs the control means 4 of its unoccupied status, and the con¬ trol means 4 possibly assigns the transmitter means 5, 6, 7 a new task. When the short message service centre SCI, SC2, SC3 receives a start message, it sends the message addressed to said subscriber MS through the GMSC to the cellular radio network, for delivery to the desired subscriber MS. It is to be noted in the realization of the apparatus according to the inven¬ tion that said start message transmission means 1 is intended to be substantially realized in software. The drawings and the description pertaining thereto are only intended to illustrate the idea of the invention. The method for starting a short message transmission in a cellular radio network, the cellular radio network and the subscriber register for a cel¬ lular radio network according to the invention may vary in their details within the scope of the claims. Even though the invention has been explained in the foregoing mainly in connection with the GSM system, it can also be used in another kind of radio system.

Claims: Claims : 1. A method for starting a short message trans¬ mission in a cellular radio network, in which method - a subscriber register (10) stores information on the fact that at least one short message service centre (SC) holds short messages for transmission to a subscriber (MS) that is not reachable, and when the subscriber (MS) requests process access to the cellular radio network or when the sub¬ scriber data of the subscriber (MS) are location up¬ dated, the subscriber register (10) of the subscriber (MS) sends a short message transmission start message to said at least one short message service centre (SC), c h a r a c t e r i z e d in that - the subscriber register (10) sends the short message start messages for a given subscriber (MS) to different SCs (SCI, SC2, SC3) after delays of variable duration. 2. A cellular radio system, comprising - a mobile subscriber (MS), - at least one short message service centre (SC) for relaying short messages through a cellular radio network to the mobile subscriber (MS) and for storing short messages when the mobile subscriber (MS) cannot be reached, - a subscriber register (10) of the subscriber, storing information on the fact that said at least one short message service centre (SC) holds short messages for transmission to a subscriber (MS) that is not reachable, and said subscriber register (10) compris¬ ing means (1) for sending a short message transmission start message to said at least one short message ser- vice centre (SC) when the mobile subscriber (MS) can again be reached or when the subscriber data of the subscriber (MS) are location updated, c h a r a c t e r i z e d in that the transmission means (1) of the subscriber register (10) comprise means for sending start messages for short message transmission for a given subscriber to different short message service centres (SCI, SC2, SC3) after delays of variable duration. 3. A cellular radio system as claimed in claim 2, c h a r a c t e r i z e d in that said means (1) for sending start messages for short message transmission for a given subscriber (MS) comprise - a memory (8) for storing short message trans¬ mission start messages, - control means (4) for receiving, storing in said memory (8), reading from said memory (8), and transmitting short message transmission start mess¬ ages, - transmitter means (5, 6, 7) responsive to said control means (4) for sending start messages for short message transmission for a given subscriber (MS) to different short message service centres (SCI, SC2, SC3) after delays of variable duration, and - a delaying means (9) generating a variable delay and responsive to the transmitter means (5, 6, 7) for delaying sending of start messages for short message transmission for a given subscriber (MS) by said transmitter means (5, 6, 7) for a desired period of time. 4. A subscriber register (10) for a cellular radio system, comprising - means (1) for sending a short message trans¬ mission start message to at least one short message service centre (SCI, SC2, SC3), c h a r a c t e r i z e d in that it comprises - a memory (8) for storing short message trans¬ mission start messages, - control means (4) for receiving, storing in said memory (8), reading from said memory (8), and transmitting short message transmission start mess¬ ages, - transmitter means (5, 6, 7) responsive to said control means (4) for sending start messages for short message transmission for a given subscriber to differ- ent short message service centres (SCI, SC2, SC3) after delays of variable duration, and - a delaying means (9) responsive to the trans¬ mitter means (5, 6, 7), generating a variable delay for delaying sending of start messages for short mess- age transmission for a given subscriber (MS) by the transmitter means (5, 6, 7) with a desired period of time. 5. A subscriber register (10) as claimed in claim 4, c h a r a c t e r i z e d in that it is a home location register (HLR) in a GSM system.

Inventors: SALIN HANNU-PEKKA, SALIN, HANNU-PEKKA
Applicants: NOKIA TELECOMMUNICATIONS OY, SALIN HANNU PEKKA
Application year: 1993
Main classification: H04Q7
IPC codes: H04M3, H04W4