Flow control method for short message service-busy subscriber

<u>BACKGROUND</u>

0001The present invention is directed to a global system for mobile communication (GSM) mobile telephone system which utilizes short message service (SMS) for sending short text messages to and from mobile stations. In particular, the present invention is directed to controlling the flow of short text messages to a mobile station after a busy condition is detected and several short message service centers for short messages attempt to send their messages to the same mobile station during the busy condition. Also, the present invention is directed to other standards such as personal communication system (PCS) 1900.

0002SMS for sending short text messages (hereinafter called SMs) to and from mobile stations (MSs) is presently used in GSM mobile telephone systems. To perform the SMS, at least a basic set of GSM public land mobile network (PLMN) entities or nodes must be used. The minimum set of entities includes a mobile services switching center (MSC), a visitor location register (VLR), a home location register (HLR), an SMS gateway MSC (SMS-GMSC) and an SMS interworking MSC (SMS-IWMSC). Another network entity that is not part of the GSM PLMN but is necessary for carrying out the SMS is a short message service center (hereinafter called SC).

0003Fig. 1 illustrates an example of conventionally used GSM PLMN entities. Fig. 1 includes an SC 10 for SMS connected to a GMSC/IWMSC 30 by a first interface 20, an HLR 50 connected to the GMSC/IWMSC 30 by an interface 40, an MSC/VLR 70 connected to the GMSC/IWMSC 30 by an interface 60 and an MS 90 connected to the MSC/VLR 70 by an interface 80. The SC 10 is a node which stores and forwards SMs over the interface 20, such as a known 03.47 protocol interface which is described in a GSM Technical Report, hereby incorporated by reference. The SC 10 communicates with the GMSC/IWMSC 30 which serve as the port into a PLMN and are, in most cases, the same node as illustrated in Fig. 1. The IWMSC portion of the GMSC/IWMSC 30 forwards SMs sent from MSs. The service for forwarding these SMs is called a mobile originated short message service (hereinafter called MO-SM). The GMSC portion of the GMSC/IWMSC 30 receives messages sent to MSs. The service for receiving these SMs is called a mobile terminated short message service (hereinafter called MT-SM). The HLR 50 stores subscriber data for subscribers having a subscription into a PLMN. The stored subscriber data may be location information, a directory number (MSISDN), radio numbering plan identification (IMSI), supplementary service profiles, teleservice profiles, etc.

0004The VLR portion of the MSC/VLR 70 controls service areas when an MS roams within or between PLMNs. In other words, at one specific time, the MS is roaming within one specific service area of the VLR. The VLR can best be described as a "copy" of the subscriber's HLR. For example, when registering the present location of an MS by sending a location update to the HLR, subscriber data stored in the HLR is transferred to the VLR. The VLR contains the data that is needed to establish calls and signal transactions towards a desired MS. The MSC portion of the MSC/VLR 70 performs call and transaction control by interworking with the VLR. The MSC is responsible for switching functions and controlling hardware when establishing a call or a signal connection. In particular, the MSC cooperates with a VLR where subscriber data for the call in question is stored. The MSC and VLR are illustrated as an integrated unit (node) for discussion purposes because the interface between the MSC and VLR is well known. The interfaces 40 and 60 between the GMSC/IWMSC 30, HLR 50 and MSC/VLR 70 are performed by a mobile application part (MAP) which is a signaling protocol used for roaming and handover signaling in GSM. The MSC also interfaces the radio network via a base station controller (BSC), not shown.

0005The flow of the SMs for MT-SM will be discussed with reference to Fig. 1. An MT-SM is sent over the interface 20 from the SC 10 to the GMSC/IWMSC 30. The MT-SM contains an SM which is to be delivered to the MS 90 and is identified by the MSISDN number contained in the MT-SM. The GMSC portion of the GMSC/IWMSC 30 interrogates the subscriber's HLR 50 for routing information before delivering the MT-SM to the MSC/VLR 70 where the MS 90 is roaming. The subscriber's MSISDN is used to find the HLR which is translated into a CCITT signaling system No. 7 address. This is a known MAP protocol used for this GSM cellular standard. The MAP message (operation) used to interrogate the HLR 50 is called "send routing information for SM." When the GMSC has received routing information, the MT-SM is forwarded to the MSC/VLR 70, which corresponds to where the MS 90 is roaming, in the "forward SM" MAP message (operation) over the interface 60. The MT-SM is delivered from the MSC/VLR 70 to the MS 90 over the interface 80 which is a known radio interface. This delivery is acknowledged back to the SC 10 mapped onto the "forward SM" MAP operation and onto the "03.47" protocol which interfaces the GMSC/IWMSC 30 with the SC 10.

0006For MT-SM, only one MT-SM dialog for each MS may be established according to GSM specifications over which several SMs may be sent. In contrast, one of several SMs may be delivered on the same dialog with the MS for MT-SM. Thereby, one MT-SM dialog can be used to send many SMs to the same MS and no fixed time for a MT-SM dialog can be set or estimated.

0007However, when using the SMS in known GSM mobile telephone systems, a problem occurs if several SCs send MT-SMs to the same MS subscriber at the same time. In this case, the SC originating the MT-SM which arrives first to the MSC/VLR where the subscriber is roaming will have an established SM-dialog with the MS. As a result, MT-SMs originated from other SCs cannot be delivered to the MS due to a "busy" condition in known systems (compare with a busy condition for a telephone call).

0008Fig. 2 illustrates the general structure for a plurality of SCs which may attempt to establish an MT-SM dialog with an MS 90. Fig. 2 illustrates a plurality of SCs for SMS 10₁, 10₂, ... 10_n, which are respectively connected to a plurality of GMSC/IWMSCs 30₁, 30₂, ... 30_n by interfaces 20₁, 20₂, ... 20_n. The plurality of GMSC/IWMSCs 30₁, 30₂, ... 30_n are connected to the MSC/VLR 70 by a plurality of interfaces 60₁, 60₂, ... 60_n, respectively. To illustrate the problem when more than one SC tries to send an SM to the same MS 90, it is assumed that SC1 10₁ and the MS 90 have established an MT-SM dialog. Subsequently, if SC2 10₂ tries to establish an MT-SM dialog with the MS 90, a signal illustrating that the MS subscriber is busy is reported back to SC2 10₂ as either "a system failure" or "a SMS-busy." In GSM Phase 1, "a system failure" is reported back to SC2 10₂ which is a somewhat inappropriate report of the MS 90 status, but is nevertheless used. In the GSM Phase 2 Enhancement, the specification for this condition is reported back to the SC2 10₂ as "SMS-busy." When the MS 90 is determined to be in the busy condition, SMs from SC2 10₂ through SCn 10_n cannot establish an MT-SM dialog with MS 90. As a result, a congestion situation occurs for each of the SCs which have attempted to send an SM. When the MT-SM dialog between SC1 10₁ and MS 90 has been completed, the radio connection is released and each of the SCs having attempted to send SMs must re-establish a MT-SM dialog and a radio connection. Releasing the radio connection is not an efficient way to deliver the additional SMs to the MS 90.

0009ETSI technical specification GSM 03.40, Version 4.8.1 and patent application WO-A-94 07338 already describe such mobile telephone systems with a plurality of service centers and an MSC/VLR for connection to the subscriber. To allow a resending when a short message could not be delivered to a subscriber due to a temporary absence of the mobile station or an exceeded memory capacity of the mobile station, both documents propose to maintain a list of service centers in the HLR, in which those service centers are stored which made an unsuccessful delivery attempt. For this purpose, alert messages are sent by the HLR to the respective service centers when the mobile station is available again. In addition, patent application WO-A-9407338 proposes to send the alert messages with individual delays to avoid collisions of the resent short messages. However, an efficient use of radio resources cannot be achieved in this way.

0010As a starting point of a solution for this congestion situation, buffering the messages that arrive during the time when the MS 90 has already established an MT-SM dialog was considered by the present applicant. The implementation of such a buffering feature is fairly complicated because both the number of messages to buffer and the length of time must be handled. Also, it would be necessary to have a timer running in the SC that originates the SM and upon expiration, the sending of the MT-SM would be aborted by this SC. This timer would have to be coordinated with the time for buffering in the MSC/VLR. Another complication is that the timers would be specified as value ranges in the specifications, and thereby chosen and set differently by each operator. As a result of these problems, the present applicant determined that this buffering solution would not efficiently resolve the above-described congestion situation.

<u>SUMMARY</u>

0011An object of the present invention is to efficiently utilize the radio resources when delivering messages received from other service centers while a short message dialog is established between one service center and the mobile station by maintaining the same radio connection.

0012Another object of the present invention is to provide message control after a busy condition is detected between one service center and a desired mobile station as other messages are attempted to be sent by other service centers to the same mobile station by using the same radio connection for the other messages and allowing the other messages to be sent in the order that they have attempted to be sent.

0013A still further object of the present invention is to provide flow control for messages during busy conditions for a short message service which better utilizes the radio network, the switching center and the location register resources.

0014The objects of the present invention are fulfilled by providing a mobile telephone system for sending messages to and from mobile stations comprising a plurality of service centers for sending and receiving messages to and from the mobile stations and a switching center for detecting a message being sent to one of the mobile stations by one of the plurality of service centers while a message is attempted to be sent to the one mobile station by another one of the service centers and sequentially developing a list of each of the service centers attempting to send messages to the one mobile station.

0015The objects of the present invention are also fulfilled by providing a mobile telephone system for sending messages to and from mobile stations comprising a plurality of service centers for sending and receiving messages to and from the mobile stations, and a switching center for controlling messages during busy conditions for each of the service centers attempting to send messages while a message is being sent by one of the service centers.

0016The system, network and method according to the embodiments of the present invention provide control of the messages attempting to be sent after a message dialog is established between one service center and a desired mobile station. This flow control efficiently utilizes the radio resources by maintaining the same radio connection for sending the messages attempting to be sent by the other service centers while the message dialog is established between the one service center and the mobile station.

0017Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

0018The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, wherein: <ul id="ul0001" list-style="none" compact="compact"><li>Fig. 1 illustrates the network entities necessary for performing short message services;</li><li>Fig. 2 illustrates a system where a plurality of service centers for short message services are interfaced with a mobile station;</li><li>Fig. 3 illustrates a flow diagram for controlling mobile terminated short messages to a desired mobile station in an embodiment of the present invention;</li><li>Fig. 4 illustrates the MSC/VLR unit in an embodiment of the present invention; and</li><li>Fig. 5 illustrates the SC unit in an embodiment of the present invention.</li></ul>

<u>DETAILED DESCRIPTION</u>

0019The embodiments of the present invention will be described with respect to Figs. 3-5 and in combination with Fig. 2. As described above in the conventional system, Fig. 2 illustrates, a system where a plurality of service centers SC1 through SCn attempt to send short text messages to one desired mobile station. Even though the same Fig. is used to discuss the present embodiment, the operation of this system, and in particular, the operation of the MSC/VLR 70, differs in the present embodiment from the known system. The operation of this system will be further described in the control operation illustrated in Fig. 3. Fig. 4 illustrates the structure of the MSC/VLR 70 used in an embodiment of the present invention. The MSC/VLR 70 includes an SMS-Busy detector 72, a wait list storage 74 and an SC-alert processor 76. The SMS-Busy detector 72 detects when an SM-dialog has been established between an SC and MS. The wait list storage 74 registers the addresses of SCs attempting to send SMs while an SM-dialog (an SMS-Busy condition) has been established. The SC-Alert processor 76 determines when the SM-dialog has been completed for the SC and MS which have established the SM-dialog and develops an SC-Alert signal to alert the next SC in the wait list. Fig. 5 illustrates an SC used in an embodiment of the present invention where an SC-Alert processor 12n is included in the SC_n 10_n. The SC-Alert processor 12_n interpretes the SC-Alert signal sent from the MSC/VLR 70 and initiates sending of the SMs thereafter.

0020In Fig. 3, an SM is attempted to be sent from one of the SCs to a desired MS at step S10. For illustrative purposes, it will be assumed that the initial SM is sent from SC1 10₁ to MS 90. Because this is an MT-SM, the SM proceeds over the interface 20₁, corresponding to the known "03.47" protocol interface to the GMSC portion of the GMSC/IWMSC1 30₁.

0021At step S20, the MSC/VLR 70 determines whether the MS 90 has already established an SM dialog with another of the SCs (whether an SMS-Busy condition exists). When the MS is determined to have established an SM dialog (an SMS-Busy condition exists) at step S20, an SMS-Busy message is sent to the SC attempting to establish an SM-dialog during the already established SM-dialog at step S30. Step S40 checks to determine if the address of the SC attempting to send the SM is already stored in a waiting list. If the SC address is determined as failing to be in the wait list at step S40, the SC address is registered in the wait list at step S50 before proceeding back to step S20. The waiting list compiled in the MSC/VLR 70 follows the principle where the SC address registered becomes the first SC address in the waiting list, the second SC address registered is the second SC address in the waiting list, etc. If the SC is determined to have been already registered in the waiting list at step S40, the flow proceeds back to step S20 without registering the SC-address again in the waiting list.

0022Whenever another SM-dialog is desired to be established, the flow begins again at step S20 for the next SM. As long as another SM is not attempted to be sent, the flow proceeds to step S20 where it is again determined whether the desired MS is still SMS-Busy. When no additional SMs are attempted to be sent while the desired MS is in a SMS-Busy condition, a waiting loop of steps S20, S30, and S40 is cycled through until the SM-dialog has been completed. In effect, the system is waiting for the established SM-dialog to be completed and registers a waiting list of the SC address attempting to send SMs to the desired MS while this SM-dialog is established.

0023After establishing the radio connection and delivering the SM to the desired SM, the flow proceeds to step S100 where it is determined whether any SC addresses are in the waiting list. If there are no SC addresses in the waiting list, the control operation ends. However, if at least one other SC address is in the waiting list, the flow proceeds to step S110. At step S110 the data for the first SC in the waiting list is obtained. Then, an SC-Alert signal is sent to the first SC address in the waiting list at step S120. When it is determined at step S20 that the desired MS is not SMS-Busy, the flow proceeds to step S60.

0024A determination is made at step S70 on whether a radio condition exists with the desired MS. If it is determined that a radio connection does not exist, a radio connection is established at step S80 before proceeding to step S90 where the SM is delivered to the desired MS over the newly established radio connection. If the radio connection is determined to be existing at step S70, the radio connection which has been established for the previous SM-dialog is not released and the SM is delivered to the desired MS over the same radio connection. By alerting the first SC address in the waiting list, the SMs corresponding to this SC now attempts to establish an SM-dialog for sending the SM to the desired MS. Alerting is performed by using a GSM MAP (09.02) operation in a new context. The known operation performed by the GSM MAP (09.02) is SC-Alert which is herein incorporated by reference. The SC-Alert operation is normally used by an HLR to alert SCs when a subscriber becomes available after having not been reachable such as in power-off conditions, no radio coverage, etc. However, the SC-Alert operation is sent by the MSC/VLR instead of the HLR in the present embodiment. This action performed by the MSC/VLR is not specified by GSM but does not meet any compatibility problems within a PLMN. The SC-Alert operation is simply forwarded to the SC indicated by the SC-address via the IWMSC portion of the GMSC/IWMSC corresponding to the SC. The SC-Alert signal received by the SC is used as a trigger to resend the SMs which have failed to be delivered due to the "SMS-busy" or "system failure."

0025Next, the waiting list is updated at step S130 by deleting the SC address that has just been obtained at step S110 from the waiting list so that the second entry in the waiting list, if any entry exists, now becomes the first entry in the waiting list. Then, the flow control proceeds to step S20 where the control determines whether the SMS-Busy condition exists. When the SMS-Busy condition fails to exist and the control proceeds from step S20 to step S60, the SMs are sent from the SC receiving the SC-Alert signal.

0026This system and flow control method essentially controls messages sent to a desired MS during a SMS-Busy condition for enabling a better utilization of the radio network and MSC/VLR resources since the same radio connection is used for a plurality of MT-SMs received from other SCs. As a result, paging, authentication, and ciphering can be avoided for subsequent MT-SM transfers. The embodiments described are also applicable to other standards such as PCS 1900.

0027The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included with the scope of the following claims.