KR20050009115A - Method for Accounting Broadcast Service in a Mobile Communication System - Google Patents

Abstract

PURPOSE: A broadcast service accounting method in a mobile communication system is provided to use a short-term BAK(Broadcast Access Key) having a shorter life time than an existing encoding BAK, thereby effectively operating a time-based accounting function. CONSTITUTION: Traffic is set between an AT(Access Terminal)(16) and an AN(Access Network)/PCF(15)(501). The AT(16) sets a BAK request field of a periodically transmitted registration message as 10 or 11(502). The AN/PCF(15) receiving the BAK request message updates accounting information on the AT(16) through an AAA(10) to conduct a time-based accounting process, and generates a new BAK if information on a next encoding key is not received, then sends the new BAK to a broadcast server(12)(504). A BAK32 or a BAK is transmitted to the AT(16)(505). The AN/PCF(15) informs the AT(16) of a sequence number of an encoding key to be used for a BAK sequence number field(506). The AT(16) continuously receives a broadcast service(507).

Description

Method for Accounting Broadcast Service in a Mobile Communication System

The present invention relates to a broadcast service billing method in a mobile communication system, and more particularly, to a broadcast service billing method in a mobile communication system relating to billing of a broadcast service.

Today, due to the development of the telecommunications industry, the services provided by the code division multiple access (CDMA) mobile communication system are not only voice services but also large data such as packet data and circuit data. It is developing into multicasting multimedia communication. Accordingly, there is a broadcast service that provides a service from one data source to a plurality of user equipments in order to support the multicasting multimedia communication. The broadcast service may be classified into a cell broadcast service, a message-oriented service, and a multimedia broadcast / multicast service, which supports multimedia types such as real-time video, audio, still images, and text.

1 illustrates a structure of a system for a conventional broadcast service. Referring to FIG. 1, a broadcasting service server (CS) 12 compresses broadcast data including video and sound for a broadcast service. IP base station (BS) 15a, 15b, 15c through packet data service nodes (PDSNs) 14a, 14b through a packet communication network such as the Internet, generated in the form of a packet. , 15d). The base stations 15a, 15b, 15c, and 15d include a packet control function (PCF) added to a base transceiver station (BTS) and a base station controller (AN), which are well known in the mobile communication technology field. As indicated AN / PCF. In addition, the second broadcast service controller 11b connected to the first broadcast service controller 11a controls communication between the broadcast server 12 and the mobile terminal (Access Terminal (AT)) 16 and provides an air interface for broadcast service. It performs some functions of Air-Interface) and Radio Access Network (RAN). In this case, the broadcast server 12 is actually connected to a plurality of broadcast servers 12. Here, the first broadcast service controller 11a is connected not only to the second broadcast service controller 11b but also to other broadcast service controllers for each operator or region. Each broadcast service controller including the first broadcast service controller 11a constitutes the same network as the second broadcast service controller 11b.

In order to deliver the broadcast data generated by the broadcast server 12 to the packet data service nodes 14a and 14b, IP multicast or IP unicast is used, and packet data service nodes are used. CDMA2000 access network technology is used to deliver from base stations 14a, 14b to base stations 15a, 15b, 15c, 15d. When IP multicast is used, the packet data service nodes 14a and 14b form a multicast group that receives IP multicast data from the broadcast server 12. Membership information of the multicast group is maintained by a Multicast Router (MR) (not shown) connected to each of the packet data service nodes 14a and 14b. The packet data service nodes 14a and 14b are connected to a domain name system (DSN: DSN) for managing an IP address.

The IP data including the image and the sound generated by the broadcast server 12 may be broadcast to the plurality of data service nodes 14a and 14b forming the multicast group, or the respective data service nodes 14a and 14b. It is unicast to. Packet data service nodes 14a and 14b deliver IP data to the base stations 15a, 15b, 15c and 15d using CDMA2000 access network technology, and the base stations 15a, 15b, 15c and 15d. The IP data is converted into a form of a radio frequency (RF) signal and transmitted in a corresponding service area.

Next, FIG. 2 shows a broadcast service controller 11a, 11b for receiving a broadcast service by a mobile terminal in a CDMA system such as HRPD (High Rate Packet Data Service, also known as 1xEVDO), and is currently present from the broadcast service controller 11a, 11b. Receiving a broadcast access key (BAK), which is an encryption key necessary for receiving a selected service, and its life time from the broadcast service controllers 11a and 11b after receiving a list of possible broadcast services. The figure shows. The reference signs of the network connected to the broadcast service controllers 11a and 11b are the same as the generic names of the reference codes of the network connected to the second broadcast service controller of FIG. 1, but the broadcast service controller is the first broadcast of FIG. 1. It should be distinguished that it is a service controller.

First, in step 200, the mobile terminal 16 transmits a connection request message for data service with the base station 15. The mobile terminal 16 then establishes a traffic channel with the base station (AN / PCF) 15 and then a packet service node (PDSN) 14 and a protocol for broadcast service (hereinafter referred to as PPP). Connect Accordingly, a path for a broadcast service is established between the mobile terminal 16 and the packet data service node 14.

Then, in step 201, the mobile terminal 16 transmits a message including a broadcast service network ID (bcmcs network id) to the DNS 13 to request an IP address of the broadcast service controller 11. That is, the DNS server 13 requests information about the broadcast service controller 11 by using the DNS server 13 information obtained in the PPP connection process. Accordingly, in step 202, the DNS server 13 checks the IP address of the broadcast service controller 110 and transmits the IP address to the mobile terminal 16. Then, in step 203, the mobile terminal 16 transmits a content request message that is currently available from the broadcast service controller 11 to the DNS server 13 using a well-known protocol such as HTTP or WAP as the address of the broadcast service controller 11. If so, the DNS server 13 transmits a list of contents (eg, the name and description of the broadcast service) currently available to the broadcast service controller 11 in step 204. Then, in step 205, the mobile terminal 16 finds the broadcast service controller 11 corresponding to the received IP address and requests information on broadcast content desired by the user. Accordingly, in step 206, the broadcast service controller 11 provides broadcast service related information to the terminal after authentication processing for the corresponding user. In this case, the information includes BAK information capable of receiving broadcast content, corresponding broadcast service related information such as valid time of BAK information, multiple IP addresses and port information. After receiving the encryption information necessary to receive the broadcast service, the mobile terminal 16 receives the transmission period of the registration message or the actual transmission period of the broadcast service through the broadcast overhead message in step 207. In step 208, the registration message including the desired broadcast service ID is transmitted to the base station (AN / PCF) 15 to receive the broadcast service. When the mobile terminal 16 first receives the broadcast content and sends a registration message, the mobile terminal 16 sets up a bearer to establish a path with the packet data service node 14 in step 209. Perform the procedure. In operation 210, the mobile terminal 16 receives a broadcast service from the broadcast server 12 according to the command of the broadcast service controller 12. On the other hand, if a bearer for the broadcast service is already established, the broadcast service is directly provided without performing the bearer setup procedure.

The following relates to a method of generating broadcast security packet data using a link layer encryption proposed in the related art. The base station 15 generates a random seed after receiving the BAK from the broadcast controller (BCMCS Controller) 11 or the PDSN 14 or the like. This creates a short-term encryption key. In addition, a Crypto Sync is generated by using a timestamp value at the time of generating the broadcast security packet data, and is encrypted using an AES (Advanced Encryption Standard) algorithm together with the generated short period encryption key. Create an encryption mask. The broadcast security packet is generated by performing an XOR (Exclusive OR) with the broadcast frame packet.

In order to encrypt the broadcast security packet generated as described above, the mobile terminal 16 may generate an encryption mask used by the base station 15 and perform an XOR with the received broadcast security packet. In order to generate an encryption mask in the mobile terminal 16, a broadcast access key, an arbitrary seed and a timestamp value used by the base station 15 are required. Here, since the timestamp value is transmitted at the time point at which the broadcast security packet is determined, the base station 15 and the mobile terminal 16 can know the same value. The broadcast access key BAK is included in a process in which a user accesses a BCMCS controller 11 to receive a broadcast service and receives broadcast session information of a desired broadcast. The random seed is included in a security parameter message in the middle of transmitting broadcast traffic and transmitted. The broadcast security packet is transmitted in order after configuring an error control block for applying R-S coding, and may transmit a security layer packet including the security parameter message at the beginning of the block.

When the mobile terminal 16 receives a random seed and a BAK, the encryption mask is generated in the same manner as the broadcast security packet generation method, and then decrypted from the broadcast security packet to broadcast frame packet. Get

3 is a scenario illustrating a signaling procedure for a broadcast service. In FIG. 3, when the user starts listening to the broadcast service, PPP is set in step 301. Since the process of setting up PPP has been described above, it will be omitted. In operation 302, the mobile terminal 16 transmits a broadcast request message (BCMCS Request) including a broadcast channel to be listened to by the user to the broadcast service controller 11. Prior to this process, channel information on a broadcast service provided by a mobile communication network may be received in advance. When the broadcast service controller 11 receives a broadcast service request from the user, in step 303, a security key necessary for receiving a broadcast together with related information about the broadcast channel, that is, a protocol stack, an IP address, a broadcast ID, and the like, is provided. Information, that is, a BAK (Broadcast Access Key) and the valid time of the BAK. In operation 304, the wireless channel may be terminated, and PPP connection may be terminated as necessary.

When the mobile station 16 obtains the relevant information of the broadcast channel desired by the user from the broadcast service controller 11, the mobile terminal 16 transmits a broadcast overhead message transmitted from the base station 15 to the control channel in step 305. Receive Overhead Message). In this case, the broadcast overhead message includes sector information and information on a physical cell for receiving a broadcast along with information on neighboring cells. In step 306, the mobile terminal 16 transmits a registration message (Registration) including the ID of the broadcast channel that the user wants to hear to the base station 15. Then, if the corresponding broadcast is already in progress, the base station 15 does not perform a separate procedure for delivering broadcast traffic. However, when not ready to deliver broadcast traffic, in step 307, a bearer pass connection to the packet data service node 14 is performed, and an IP connection procedure to the broadcast server 12 is performed. In operation 308, the broadcast server 12 transmits the broadcast traffic to the base station 15. Thereafter, the base station 15 proceeds to step 309-313 to start transmitting the broadcast packet data to the mobile terminal 16. At this time, an error control block is transmitted in sequence. In the first packet transmission of the error control block, a security layer packet including a security parameter message is transmitted first, and then If there is a broadcast security packet (Broadcast Security Packet) is transmitted together. Thereafter, the broadcast security packet is continuously transmitted. In addition, when a random seed is changed and needs to be notified to the mobile terminals 16, the process proceeds to step 312 and again transmits a security layer packet including a security parameter message, and transmits broadcast security packet data in step 313. do. As described above, the mobile terminal 16 receiving the broadcast type service establishes a dedicated channel and receives the BAK through the channel prior to the broadcast service. The mobile terminal 16 can quickly receive the broadcast service transmitted in an encrypted state by using the BAK, and the base station 15 could transfer the BAK only to an authorized user to account for each user. . However, a method of setting a dedicated channel for a mobile terminal 16 to receive a broadcast service and transferring an encryption key after a complicated authentication process, as in the prior art, generates a lot of network load, which makes it difficult to update frequent broadcast access keys. Key update of time intervals makes time charging difficult. That is, in the prior art, the billing was made on a weekly or monthly basis by a pay-as-you-go method. This pay-as-you-go method has a problem in that the user has to pay the semen even if never used.

Accordingly, an object of the present invention is to provide a realistic time-based charging method using a BAK having a shorter valid time than a conventional encryption key BAK.

Another object of the present invention is to provide a method capable of time-based charging at short intervals through a method of updating the encryption key more frequently.

In the mobile communication system according to an embodiment of the present invention, the broadcast service charging method includes a base station, a broadcast service controller, and a broadcast service server, and each broadcast service controller is connected to a plurality of base stations of the mobile communication system through a packet data service node. A method of charging a broadcast service in a mobile communication system providing a broadcast service, the method comprising: requesting, by the mobile terminal, a domain name system (DNS) that manages an IP address for a broadcast service controller address for receiving a broadcast service; When receiving a broadcast service controller address from the name system, requesting a broadcast service to a broadcast service controller corresponding to the received broadcast service controller address, and a broadcast access key (stBAK) for performing charging from the broadcast service controller in a short period. After receiving the information, broadcast service A it characterized in that it comprises the step of receiving.

1 is a structural diagram of a system for a conventional broadcast service;

2 is a scenario illustrating a conventional broadcast service setting procedure;

3 is a scenario illustrating a conventional broadcast signal procedure;

4 is a scenario showing an initial setting process of stBAK according to an embodiment of the present invention;

5 is a scenario illustrating a broadcast service using stBAK according to another embodiment of the present invention.

In the following description of the present invention, detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

In the mobile communication system according to the present invention, the system for explaining the broadcast content security method is the same as the system for the broadcast service of FIG. 1 and a description thereof will be omitted. In addition, the system for explaining the present invention will be described with reference to FIG.

4 shows an initial delivery process of a short term BAK (stBAK). The first stBAK is delivered in the setup phase of a broadcast service like the existing BAK.

First, in step 400, the mobile terminal 16 transmits a connection request message for data service with the base station 15. The mobile terminal 16 then establishes a traffic channel with the base station (AN / PCF) 15 and then a packet service node (PDSN) 14 and a protocol for broadcast service (hereinafter referred to as PPP). Connect Accordingly, a path for a broadcast service is established between the mobile terminal 16 and the packet data service node 14.

Then, in step 401, the mobile terminal 16 queries the broadcast service controller 11 by the broadcast service network ID. That is, the DNS server 13 requests information about the broadcast service controller 11 by using the DNS server 13 information obtained in the PPP connection process. Accordingly, in step 402, the DNS server 13 checks the IP address of the broadcast service controller 110 and transmits the IP address to the mobile terminal 16. Then, in step 403, the mobile terminal 16 can service the broadcast service controller 11 using a well-known protocol such as HTTP (Hypertext Transfer Protocol) or WAP (Wireless Application Protocol) as the address of the broadcast service controller 11. When the content request message is transmitted to the DNS server 13, the DNS server 13 transmits a list of contents (eg, the name and description of the broadcast service) currently available to the broadcast service controller 11 in step 404. . Then, in step 405, the mobile terminal 16 finds the broadcast service controller 11 corresponding to the received IP address and requests information on broadcast content desired by the user. Then, the broadcast service controller 11 transmits stBAK and stBAK life time (stBAK life time) having a short period of valid time instead of the existing BAK and BAK valid time indicating its expiration time, and in addition, higher security For this purpose, additional information such as a private key and a stBAK sequence number is passed. The stBAK may use 128 bits as used in the prior art to maintain higher compatibility with existing broadcast service schemes. The private key may have a length of 128 bits or more, which may be determined according to the level of security required by the operator. Therefore, the private key may be omitted as necessary. The stBAK delivered in this process should be set to have a shorter expiration time than the existing BAK (that is, stBAK valid time <BAK valid time). The broadcast service controller 11 sets the expiration time to the desired minimum charging time unit. Suitable.

After receiving the encryption information required to receive the broadcast service, the mobile station 16 transmits the registration message or the actual transmission period of the broadcast service through a broadcast overhead message in step 407. In step 408, a registration message including the desired broadcast service ID is transmitted to the base station (AN / PCF) 15 to start receiving the broadcast service. When the mobile terminal 16 first receives the broadcast content and sends a registration message, in step 409, the mobile terminal 16 sets up a bearer to establish a path with the packet data service node 14. Perform the procedure. In step 410, the mobile terminal 16 receives a broadcast service from the broadcast server 12 according to the command of the broadcast service controller 12. On the other hand, if a bearer for the broadcast service is already established, the broadcast service is directly provided without performing the bearer setup procedure.

Meanwhile, the mobile terminal 16 receiving the stBAK and receiving the broadcast service receives the new key and updates the encryption key before the expiration of the stBAK, so that continuous broadcasting can be received. That is, the next stBAK must be delivered within the valid time of the minimum received stBAK. To this end, the present invention modifies a registration message periodically transmitted by the mobile terminal 16 in the conventional broadcast service so that a request for a new encryption key can be expressed. If there is no encryption key higher than the sequence number of the currently used stBAK, the mobile terminal 16 may periodically transmit a request for a new encryption key to the base station using the registration message. When the base station requests a key from the terminal, the base station updates the lower 32 bits of the currently used stBAK to generate stBAK 'to be used next. Then, the updated lower 32-bit information, stBAK32, is transmitted to the terminal to configure a new encryption key. As such, updating only the lower 32 bits is to reduce the amount of data transmission that is increased due to frequent key updates. The base station receiving the stBAK32 may generate a new stBAK by XORing the existing stBAK and the received stBAK32.

Table 1 below is a registration message structure proposed in the present invention. When the structure proposed in the present invention is adopted as a BAK used in a broadcast service, since the term 'short term' is no longer meaningful, the term 'short term' is not specified in the field names of the messages proposed below. . In other words, stBAK32 is expressed as BAK32 in the message.

In the present invention, the stBAKRequest field is added to the existing registration message. The BAKRequest field is a field having one or two bits. Its meaning is as follows. First, if the value of the BAKRequest field is 0, it means no request, and if it is 10, it indicates stBAK32, which means requesting the lower 32-bit information required for stBAK update, and 11 means full stBAK. This indicates that a 128-bit stBAK request is sent.

The base station 15 receiving the request of the mobile terminal 16 updates the stBAK to stBAK 'through the broadcast service controller 11 and transmits all of the updated lower 32 bits stBAK32 or stBAK' to the mobile terminal 16. To this end, the present invention proposes a BAK (Broadcast Access Key Message) message transmitted in a unicast manner through a forward control channel. Table 1 below shows the BAK message. The BAK message includes a message ID, a BAKSequenceNumber, a BAKLifeTime, a FullBAKIncl, a BAK, and a BAK32 field.

Among the fields of the BAK message, the message ID field has a value of a message identifier assigned to the BAK message. The BAKSequenceNumber field represents the sequence information of the encryption key carried by the BAK message. The BAKSequenceNumber field is defined as the same 4 bits for compatibility with the 4-bit sequence information of the encryption key used in the prior art. The BAKLifeTime represents a specific time unit. For example, it represents life information of an encryption key expressed in multiples of 30 seconds or 1 minute. The mobile terminal 16 must receive a new key to be used next to the current encryption key within the life of the encryption key from the first time that the encryption key is used in order to receive the continuous broadcast service. The lifetime information of the encryption key may be used as the maximum value of the spare time until the next encryption key is secured. The FullBAKIncl field is a field indicating whether stBAK included in the message is 128-bit information or lower 32-bit BAK32. The BAK and BAK32 fields transmit information of an encryption key corresponding to a BAK sequence number, and the mobile terminal 16 receiving the BAK stores the BAK and the sequence number information, and receives the BAK32. Combines the current BAK and BAK32 to create a new BAK 'and stores the BAK' and sequence number information. In order to provide higher security, the BAK and BAK32 fields may be encrypted using a private key corresponding to the mobile terminal 16. The additional encryption can prevent the encryption key being used or used in the broadcast service from being leaked when the control channel message is leaked.

Meanwhile, the broadcast service controller 11 receiving the request of the mobile terminal 16 for the new key may generate a new BAK 'by updating the lower 32 bits of the currently used BAK. The broadcast controller generating BAK 'takes an XOR of the lower 32 bits of the BAK' and the lower 32 bits of the BAK to generate a BAK32 and transmits the BAK32 to the mobile station 16 through the base station 15.

The mobile station 16 receiving the BAK32 transmitted by the base station 15 takes XOR with the lower 32 bits of the BAK currently being used by the BAK32 received from the base station 15, and returns this value to the BAK order information. It can be used as a corresponding new BAK '.

On the other hand, in the broadcast type service, since the receiving mobile terminals 16 do not need to continuously maintain a dedicated channel, it is possible that a large number of users exist in one sector unlike the conventional data service. In order to continuously receive the broadcast service, these mobile terminals 16 must continuously update stBAK. When a large number of users simultaneously request the update of stBAK, congestion of the control channel may occur if the base station 15 attempts to deliver a new stBAK for all mobile terminals 16. Therefore, the present invention intends to propose a more efficient method for transmitting stBAK.

If the mobile terminal 16 does not have an encryption key that is later than the sequence number of the encryption key used to receive the current broadcast service, the mobile terminal 16 periodically receives a new encryption key whose sequence number is larger than the current key. Set BAKRequest to 10 or 11 in the registration message to be sent. The base station 15 can know the actual lifetime of the current encryption key and the number of mobile terminals 16 receiving the broadcast service, and the mobile terminals 16 that have not received the new encryption key continue to send BAKRequests within that lifetime. Therefore, by dividing the remaining life of the current encryption key by the number of terminals can be distributed evenly over the remaining time. For example, when there are 50 mobile terminals 16 that are receiving broadcasts and the remaining lifespan of the current encryption key is 10 minutes, the base station 15 may transmit the encryption keys to avoid congestion for 5 units per minute. .

Meanwhile, a method of generating a security layer packet through link layer encryption by applying stBAK proposed in the present invention is shown in the scenario of FIG. 5. When the life of the current BAK expires, the base station XORs the BAK32 received from the broadcast controller and transmitted to the terminals and the current BAK to generate a new BAK and use it to perform link layer encryption. . Link layer encryption at the point where the BAK update is not necessary can maintain the high compatibility since the method proposed in the prior art can be used as it is.

The base station 15 attaches a security parameter message (SPM) indicating an encryption information used for encryption of the current broadcast service to a broadcast security packet generated in the above process, and thereby an error control block. block). The conventional SPM (Security Parameter Message) includes a BAK sequence number (BAKSequenceNumber) and arbitrary seed (RandomSeed) information, as shown in Table 3. The stBAK proposed by the present invention is a method for replacing the conventional BAK. The SPM may be used as it is to transmit encrypted information. That is, the sequence number of stBAK can be assigned to BAKSequenceNumber and transmitted, and a method of improving security by using a random seed proposed in the prior art can also be applied. As described above, the stBAK proposed in the present invention has the advantage of enabling time-based charging by introducing a fast encryption key update technique while maintaining maximum compatibility with an existing system.

5 shows a process of performing a broadcast service using stBAK. In step 501, the traffic between the mobile terminal 16 and the base station 15 is established. Then, the mobile terminal 16 receiving the stBAK should receive the new encryption key within the valid time of the encryption key. To this end, the mobile terminal 16 transmits the BAKRequest field of the registration message periodically transmitted in step 502 to 10 or 11. Upon receipt of the BAKRequest, the base station 15 updates the charging information of the mobile terminal 16 through AAA (Authentication Authorization Accounting) 10 in step 503 to perform the timed charging, and then, from the broadcast service controller 11 If the information on the encryption key is not received, a new BAK to be transmitted to the mobile terminal 16 is generated in step 504 and the BAK32 is transmitted to the broadcast server 12. Thereafter, in step 505, the BAK32 or the BAK is delivered to the mobile terminal 16 through the BAK message. Thereafter, in step 506, when the encryption key of the broadcast service is changed, the base station 15 informs the mobile stations 16 of the sequence number of the encryption key to be used through the BAKSequenceNumber field of the SPM and informs the new BAK corresponding to the number already. The received mobile terminal 16 may continuously receive a broadcast service in step 507.

The present invention efficiently utilizes a short term BAK (stBAK) with a shorter valid time than the existing proposed encryption key BAK instead of using a new encryption key other than BAK as a method for timed charging. The billing can be operated. That is, the base station transmits the stBAK and the valid time for the broadcast service to the mobile terminal during the initial setup process, and then updates the lower 32 bits of the stBAK whenever the mobile terminal requests a new stBAK for the expiration of the valid time. Pass stBAK32 to the terminal. The mobile terminal can generate a new encryption key from its own stBAK using the stBAK32. In this encryption key generation and update method, encryption keys can be updated at shorter intervals than in the prior art. Instead of updating the entire encryption key, only a part of the encryption key can be updated to prevent the load on frequent key updates. It becomes possible. In addition, if the partial update is continued for a long time, the security of the encryption key may be lowered, so that the base station may update the full stBAK by sending a full stBAK every long time interval.

Claims (8)

In the broadcast service charging method comprising a base station, a broadcast service controller and a broadcast service server, each broadcast service controller is connected to a plurality of base stations of the mobile communication system through a packet data service node to provide a broadcast service, Requesting, by the mobile terminal, a domain name system (DNS) that manages an IP address for a broadcast service controller address for receiving a broadcast service; Receiving a broadcast service controller address from the domain name system, requesting a broadcast service from a broadcast service controller corresponding to the received broadcast service controller address; And receiving the broadcast access key (stBAK) information for performing the charging in a short period from the broadcast service controller, and then receiving the broadcast service. The method of claim 1, The broadcast access key (stBAK) information includes a short period broadcast access key life time (Private key) and a private service (Private key). The method of claim 1, Transmitting, by the mobile terminal receiving the broadcast access key information (stBAK), a registration message to the base station to receive a new encryption key before the expiration time of the broadcast access key for charging in a short period; And receiving the updated encryption key from the base station. The method of claim 3, wherein The registration message includes a message ID, a channel count, a channel ID, a broadcast access key request (stBAKRequest), and reservation information (Reserved). Service billing method. And a broadcast service controller and a broadcast service server, each broadcast service controller being connected to a plurality of base stations of a mobile communication system through a packet data service node to provide a broadcast service to a mobile terminal. To Receiving a new broadcast access key request from the mobile terminal; Generating a new broadcast access key (stBAK) by updating a lower bit of the currently used broadcast access key; And transmitting the generated broadcast access key (stBAK) to the mobile terminal through a broadcast access key message. The method of claim 5, wherein The broadcast access key message includes a message ID, a BAK sequence number, a BAK validity time, and BAK information. And a base station, a broadcast service controller, and a broadcast service server, each broadcast service controller being connected to a plurality of base stations of a mobile communication system through a packet data service node to provide a broadcast service to a mobile terminal. In the method for generating a security packet, When the life of the broadcast access key (stBAK) currently in use has expired, a new broadcast access key (XOR) is obtained by XORing a predetermined bit of the broadcast access key (stBAK) received from the broadcast service controller and the current broadcast access key (stBAK) bit. stBAK), Generating a broadcast security packet by performing link layer encryption using the new broadcast access key (stBAK); And transmitting a security parameter message in the broadcast security packet to a mobile terminal. The method of claim 7, wherein The security parameter message includes a message ID, a broadcast access key (stBAK) sequence number indicating a sequence number of a broadcast encryption key, random seed count information indicating the number of terminals to transmit a broadcast access key (stBAK), and encrypted broadcast. Broadcast service security method in a mobile communication system comprising a random seed (Random Seed) information for transmitting the access key (stBAK).