CN1294785C - Switching method between systems - Google Patents

Abstract

The present invention discloses a switching method between systems for switching a mobile terminal from a WCDMA system to a GPRS system, which comprises the steps that the mobile terminal starts the update operation of a route area; in the process of encryption and negotiation, an SGSN can send an authentication and encryption message which comprises an encryption algorithm and an encryption key to the mobile terminal if a configuring GPRS system needs encrypting, while the SGSN can send an authentication and encryption message which comprises the information for forcing the mobile terminal to stop the encryption operation to the mobile terminal if the configuring GPRS system does not need encrypting; the mobile terminal returns an authentication and encryption response message to the SGSN after receiving the message; the SGSN executes the update of the route area. By using the method of the present invention, service interruption caused by the conflicts of encryption parameters between the SGSN of the GPRS system and the mobile terminal when the mobile terminal is switched from the WCDMA system to the GPRS system can be avoided, and the stability of the systems in switching can be enhanced.

Description

A method of switching between systems

technical field

The present invention relates to intersystem switching technology of wireless communication, in particular to an intersystem switching method for a mobile terminal from a Wideband Code Division Multiple Access (WCDMA) system to a General Packet Radio Service (GPRS) system.

Background technique

Due to the inherent characteristics of the mobile communication system, user data must be exposed to the air interface of the wireless access network during transmission. Therefore, the security of user data transmitted on the air interface is threatened to a certain extent. In order to ensure the security of information and protect the rights and interests of users and operators, the usual solution is to encrypt and transmit user data on the air interface of the wireless access network, so as to prevent user data from being monitored and cracked.

In the GPRS system, the encryption operation of user data and signaling is completed between the mobile terminal and the Serving GPRS Support Node (SGSN). Algorithm to ensure that the mobile terminal and the SGSN use the same encryption key and encryption algorithm. Among them, the protocol stipulates that the encryption algorithm that the GPRS system can use includes GPRS encryption algorithm (GEA, GPRS Encryption Algorithm) 1, GEA2, GEA3, GEA4, GEA5, GEA6, GEA7, GEA8, a total of 8 kinds.

Figure 1 shows the encryption negotiation process of the GPRS system. As shown in Figure 1, the encryption negotiation of GPRS system comprises the following steps:

Step 101: SGSN sends authentication and encryption request (Authentication and CipheringRequest) message to mobile terminal, initiates encryption negotiation process, and above-mentioned authentication and encryption request message carry authentication random parameter (RAND, Random Challenge) information element and encryption algorithm ( CipheringAlgorithm) cell;

Step 102: The mobile terminal calculates the authentication response parameter and the encryption key according to the received authentication random parameter RAND, and returns the calculated authentication response parameter to the SGSN through an authentication and encryption response message (Authentication and Ciphering Response), Complete the legality authentication of the mobile terminal.

In the above encryption negotiation process, the SGSN sends the encryption algorithm and encryption key to the mobile terminal, which can ensure that the encryption key and encryption algorithm used by the mobile terminal are consistent with those of the SGSN. After the above-mentioned encryption negotiation process, the SGSN and the mobile terminal can use the negotiated encryption key and encryption algorithm to encrypt user data and signaling, thereby ensuring safe transmission of user data on the air interface.

It should be noted that, in the encryption negotiation process of the above-mentioned GPRS system, only when the mobile terminal performs encryption for the first time or the key used by the mobile terminal is inconsistent with the SGSN, the authentication and encryption request message sent by the above-mentioned SGSN carries the authentication random key. parameter RAND, and in other cases, authentication and encryption request messages only carry encryption algorithm information.

In the WCDMA system, the encryption operation of user data and signaling is implemented between the mobile terminal and the radio network controller (RNC). When data encryption is started, an encryption negotiation between the RNC and the mobile terminal is required to determine the encryption key and encryption algorithm, so as to ensure that the mobile terminal and the RNC use the same encryption key and encryption algorithm. Among them, the encryption algorithm that can be used in the WCDMA system stipulated in the agreement is currently only one kind of UEA1. The encryption negotiation process of the WCDMA system is initiated by the SGSN.

Figure 2 shows the encryption negotiation process of the WCDMA system. As shown in Figure 2, the encryption negotiation process of the WCDMA system includes the following steps:

Step 201-Step 202: The SGSN sends an authentication and encryption request message to the mobile terminal, and initiates an encryption negotiation process. The above authentication and encryption request message carries the authentication random parameter RAND; after receiving the RAND, the mobile terminal calculates an authentication response parameter and encryption key, return the authentication response parameter to the SGSN through the authentication and encryption response message, and complete the legality authentication of the mobile terminal;

Step 203-Step 204: SGSN sends a security mode command (Security ModeCommand) message to RNC according to the system configuration, and commands RNC to initiate an encryption negotiation process to the mobile terminal. The encryption algorithm and encryption key allowed by the WCDMA system are carried in the above security mode command. key; RNC forwards the security mode command message to the mobile terminal, which carries the encryption algorithm allowed by the WCDMA system;

Step 205-Step 206: The mobile terminal receives the security mode command, and returns a security mode completion message to the RNC, confirming acceptance of the encryption algorithm specified by the RNC; after the RNC receives the confirmation message from the mobile terminal, it responds to the SGSN through the security mode completion message, and the above security The mode completion message carries the encryption algorithm successfully negotiated with the mobile terminal.

Through the above-mentioned encryption negotiation process, the SGSN first sends the encryption key directly to the mobile terminal, and then sends the encryption key and encryption algorithm to the RNC through the security mode command message. After receiving the encryption key and encryption algorithm configured by the SGSN, the RNC , sending the encryption algorithm to the mobile terminal through a security mode command message, so as to ensure that the encryption key and encryption algorithm used by the mobile terminal are consistent with the encryption key and encryption algorithm used by the RNC. After the above-mentioned encryption negotiation is performed, the RNC and the mobile terminal can use the negotiated encryption key and encryption algorithm to encrypt user data to ensure safe transmission of user data on the air interface.

It should be noted that, in the encryption negotiation process of the above-mentioned WCDMA system, only when the mobile terminal performs encryption for the first time or the key used by the mobile terminal is inconsistent with the SGSN, the authentication and encryption request message sent by the above-mentioned SGSN carries the authentication random key. parameter RAND, and in other cases, only the encryption algorithm negotiation process in steps 203 to 206 above is performed.

Since the encryption negotiation process of the above-mentioned GPRS system and WCDMA system is independent of each other, and the keys and encryption algorithms used in the user data encryption process of the GPRS system and the WCDMA system are different, therefore, if the mobile terminal can work in GPRS For a dual-mode terminal in the system that can work in the WCDMA system, in order to ensure that the service is not interrupted, when the mobile terminal is switched from the WCDMA system to the GSM system, the encryption negotiation process as shown in Figure 1 needs to be performed again; When the above-mentioned mobile terminal switches from the GPRS system to the WCDMA system, the encryption negotiation process shown in FIG. 2 needs to be performed again.

The following will describe in detail the inter-system handover process performed by the above-mentioned mobile terminal from the WCDMA system to the GPRS system. Since the SGSN equipment of the WCDMA system and the GPRS system can be co-located in the actual system, the above-mentioned inter-system handover process is divided into the inter-system handover process from the WCDMA system to the GPRS system within the same SGSN and the inter-SGSN WCDMA system to GPRS system. There are two cases of inter-system switching process of the system.

Figure 3 shows the inter-system handover process from the above-mentioned SGSN internal WCDMA system to the GPRS system. As shown in Figure 3, the switching includes the following steps:

Step 301: The mobile terminal and the wireless access network decide to execute the inter-system handover from the WCDMA system to the GPRS system after an inter-system handover decision.

In this step, the mobile terminal and the radio access network decide whether to perform inter-system handover through processes such as handover measurement and handover judgment.

Step 302: The mobile terminal sends a routing area update request message to notify the SGSN to initiate a routing area update operation. The above routing area update request message contains the last and current routing area information, temporary identity, and routing area update type of the mobile terminal and other parameters.

Step 303-step 304: if there is data transmission between the current serving RNC (SRNC) and the mobile terminal, then the SGSN sends an SRNC context request message to the SRNC earlier; after the SRNC receives the request message, it immediately stops sending downlink data to the mobile terminal, and Reply to the SGSN with a context response message, which includes the sequence numbers of the data packets currently cached by the SRNC and not yet successfully sent to the current mobile terminal; if there is no data transmission between the current SRNC and the mobile terminal, then directly execute step 305 .

Step 305: If the GPRS system requires encryption or authentication according to the operator's configuration, the SGSN starts the encryption negotiation process of the GPRS system; otherwise, does not start the encryption negotiation process of the GPRS system.

Step 306-Step 307: SGSN orders SRNC to forward the cached data to SGSN; SRNC forwards the cached data to SGSN after receiving the command message.

Step 308-Step 309: SGSN notifies SRNC to release the Iu connection between SRNC and core network (CN); SRNC releases Iu connection, and returns Iu release complete message to SGSN.

Step 310-Step 311: SGSN sends a routing area update acceptance message to the mobile terminal; informs the mobile terminal that the routing area update request has been accepted by the network; Temporary ID, the mobile terminal must respond to the routing area update completion message to the SGSN, indicating that it has received the routing area update acceptance message from the core network, and accepts the newly assigned temporary ID; otherwise, it does not need to respond to the above routing area update acceptance message .

Figure 4 shows the inter-system handover process from the WCDMA system to the GPRS system between the SGSNs mentioned above. As shown in Figure 4, the switching includes the following steps:

Step 401: The mobile terminal and the wireless access network determine to execute the inter-system handover from the WCDMA system to the GPRS system after an inter-system handover decision.

Step 402: The mobile terminal sends a routing area update request message to the new SGSN of the GPRS system, notifying the new SGSN to initiate a routing area update process.

The routing area update request message contains information elements such as last and current routing area information of the mobile terminal, temporary identity mark, routing area update type, and the like.

Step 403: The new SGSN sends an SGSN context request message to the original SGSN of the WCDMA system, requesting the original SGSN to forward to the new SGSN the data information that the SRNC will send to the mobile terminal.

Step 404-Step 406: After receiving the SGSN context request message, the original SGSN judges whether the current SRNC has data transmission to the mobile terminal. If there is data transmission, the original SGSN sends the SRNC context request message to the SRNC; the SRNC receives the request message After that, immediately stop sending downlink data to the mobile terminal, respond to the SRNC context response message to the original SGSN, and carry in the response message the serial number of the data packet that has not been sent to the mobile terminal and is buffered in the SRNC; the original SGSN The packet sequence numbers of the data packets buffered in the SRNC and not yet sent to the mobile terminal are passed to the new SGSN through the SGSN context response message.

If there is no data transmission between the SRNC and the mobile terminal, the original SGSN directly returns a response message to the new SGSN.

Step 407: If the GPRS system requires encryption or authentication according to the operator's configuration, the new SGSN starts the GPRS system encryption negotiation process; if the GPRS system does not need encryption or authentication, then does not start the GPRS system encryption negotiation process.

Step 408: The new SGSN sends an SGSN context confirmation message to the original SGSN, notifying the original SGSN to forward the data buffered by the SRNC to the new SGSN.

Step 409: After receiving the SGSN context confirmation message, the original SGSN instructs the SRNC to forward the buffered data to the original SGSN.

Step 410: After receiving the data forwarding command, the SRNC forwards the cached data to the original SGSN.

Step 411: The original SGSN continues to forward the received data to the new SGSN.

Step 412-step 413: the new SGSN of GPRS system sends update packet data protocol (PDP, Packet Data Protocol) context request message to GPRS Gateway Support Node (GGSN), informs GGSN that the current SGSN where the mobile terminal is located has changed; GGSN sends it The saved PDP context parameters related to the SGSN of the mobile terminal are updated from the original SGSN to the parameters of the new SGSN, for example: modify the saved PDP context parameters such as the IP address, port number and data transmission quality of the original SGSN of the WCDMA system to GPRS The IP address, port number and data transmission quality of the new SGSN of the system; and return the update PDP content response message to the new SGSN.

Step 414-step 421: the new SGSN initiates a location update process to the Home Location Register (HLR); HLR notifies the original SGSN to delete the user subscription data of the current mobile terminal; after the original SGSN deletes the user subscription data of the current mobile terminal, it instructs the SRNC to release the Iu connection ; Subsequently, the HLR inserts the subscription data of the mobile user into the new SGSN; after the above process is completed, the HLR notifies the new SGSN that the location update is successful.

Steps 422-423: The new SGSN sends a routing area update acceptance message to notify the mobile terminal that the routing area update request is accepted by the network; if the routing area update acceptance message contains the temporary identity redistributed by the core network for the mobile terminal, the mobile terminal It must respond to the routing area update completion message, indicating that it has received the routing area update acceptance message of the core network, and accepts the newly allocated temporary identity; otherwise, it does not need to respond to the routing area update acceptance message.

Through the above-mentioned inter-system handover process within the SGSN and between SGSNs, the dual-mode mobile terminal can be switched from the WCDMA system to the GPRS system, and through the encryption negotiation process of step 305 and step 407, when the GPRS system needs to be encrypted Next, the SGSN initiates the encryption negotiation process with the mobile terminal, and the mobile terminal will use the new encryption algorithm and encryption key set by the SGSN according to the new encryption negotiation result to implement the encryption operation of the user data, ensuring that the user data is Secure transmission over the air.

At present, in practical applications, most GPRS system operators do not require user data to be encrypted. In this way, according to the above-mentioned inter-system handover process, when users switch to the GPRS system, SGSN will not actively initiate encryption negotiation process, that is, the encryption negotiation process is not performed in step 305 or step 407. In this way, the mobile terminal should directly transmit user data and signaling without encrypting data and signaling without the SGSN actively initiating the encryption negotiation process.

However, in practical applications, due to the immature understanding of the protocol by many mobile terminal design manufacturers, after switching between systems, the mobile terminals designed by these manufacturers will use the encryption algorithm and encryption key used by the system before the switching. In this way, when the mobile terminal is switched to the same system as the system before the switch, and no new encryption negotiation is performed, the encryption algorithm and encryption key saved will be automatically restored, and user data and signaling to encrypt. For example, if the GPRS system where the mobile terminal currently resides needs to be encrypted, after the mobile terminal switches from the GPRS system to the WCDMA system, it will save the encryption algorithm and encryption key used in the GPRS system, so that the mobile terminal can use it again When switching to the GPRS system, and the GPRS system does not perform new encryption negotiation, the saved encryption algorithm and encryption key are automatically restored, and user data and signaling are encrypted.

In this way, if the above-mentioned mobile terminal is switched to a GPRS system that does not need to encrypt user data and signaling again, it will cause the GPRS system to fail to recognize the encrypted user data and signaling sent by the mobile terminal, that is, because the GPRS system The SGSN of the mobile terminal does not know what encryption algorithm and encryption key the mobile terminal uses, and the encryption key and encryption algorithm used by the mobile terminal and the SGSN of the GPRS system conflict. The above switching process is completely interrupted.

Since there are many operators currently operating the GPRS system and the WCDMA system, and the configuration of each operator is different, the above situation is very likely to happen.

Contents of the invention

In order to solve the above technical problems, the present invention provides a method for switching a mobile terminal from a WCDMA system to a GPRS system, which can ensure that the encryption key used by the mobile terminal and the SGSN of the GPRS system will not appear after the mobile terminal switches to the GPRS system And the conflict of encryption algorithm, so as to ensure that the business will not be interrupted.

The method of the present invention comprises the following steps:

a. The mobile terminal requests the GPRS service support node to start the routing area update operation from the WCDMA system to the GPRS system;

B, if configuration GPRS system does not encrypt, then GPRS service support node sends authentication and encryption request message to mobile terminal, and this authentication and encryption request message include the information of forcing mobile terminal to terminate encryption operation;

After receiving the authentication and encryption request message, the mobile terminal returns the authentication and encryption response message to the GPRS service support node;

c. The GPRS service support node executes the routing area update operation from the WCDMA system to the GPRS system.

The authentication and encryption request message in the method is: an authentication and encryption request message with an algorithm cell value of 0.

In the method, the authentication and encryption request message does not contain the authentication random parameter information element;

The authentication and encryption request response message does not include an authentication response parameter information element.

The step b of the method further includes: if the GPRS system is configured for encryption, the GPRS service support node sends an authentication and encryption request message including an encryption algorithm and an encryption key to the mobile terminal.

The GPRS service support node described in the method is a GPRS service support node jointly established by the GPRS system and the WCDMA system.

The GPRS service support node of the method GPRS system is separated from the GPRS service support node of the WCDMA system;

The GPRS service support node described in steps a to c is a GPRS service support node of the GPRS system.

As can be seen from this, the intersystem handover method of applying the WCDMA system of the present invention to the GPRS system can obtain the following beneficial effects:

1. Apply the inter-system switching method of the present invention. During the encryption negotiation process, if the GPRS system needs to be encrypted or authenticated according to the configuration of the operator, then the SGSN starts a normal encryption negotiation process, and configures the mobile terminal correspondingly during the negotiation process. encryption algorithm and encryption key; if the GPRS system does not require encryption or authentication according to the configuration of the operator, the SGSN will also start the normal encryption negotiation process, forcing the mobile terminal not to encrypt user data and signaling, thereby avoiding the After the switchover, the terminal automatically restores the last used encryption algorithm and the service interruption caused by the encryption key to ensure the reliability of data transmission during the switchover process between systems;

2. Applying the inter-system handover method described in the present invention solves the above-mentioned problems and at the same time does not greatly modify the current protocol flow. Therefore, the above-mentioned inter-system method is simple to implement.

Description of drawings

Fig. 1 is the encryption negotiation flowchart of GPRS system;

Fig. 2 is the encryption negotiation flowchart of WCDMA system;

Fig. 3 is the intersystem handover process diagram of SGSN internal WCDMA system to GPRS system in the prior art;

Fig. 4 is a handover process diagram between WCDMA systems to GPRS systems between SGSNs in the prior art;

Fig. 5 is the method flowchart of the intersystem handover from WCDMA system to GPRS system in SGSN internal WCDMA system described in the present invention;

FIG. 6 is a flow chart of the method for inter-system handover from a WCDMA system to a GPRS system between SGSNs according to the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

According to the method for the mobile terminal of the present invention to switch from the WCDMA system to the GPRS system, when the GPRS system needs to be encrypted, the SGSN normally starts the encryption negotiation process, and completes the negotiation of the key and the encryption algorithm; and does not need to be encrypted in the GPRS system. In the case of GPRS, the SGSN also starts the normal encryption negotiation process, forcing the mobile terminal not to encrypt in the GPRS system, so as to ensure the synchronization of encryption keys and encryption algorithms between the mobile terminal and the SGSN of the GPRS system.

The following is also divided into two cases of intra-SGSN handover and inter-SGSN handover, and specifically describes the method for handover from the WCDMA system to the GPRS system in the present invention.

FIG. 5 shows the flow of the method for inter-system handover from the WCDMA system to the GPRS system within the SGSN according to the present invention. As shown in Figure 5, the method of the present invention specifically includes the following steps:

Step 501: After the mobile terminal and the wireless access network decide to initiate an inter-system handover from the WCDMA system to the GPRS system through an inter-system handover decision, they send a routing area update message to the SGSN to start the routing area update operation.

The routing area update process message above contains parameters such as the last and current routing area information of the mobile terminal, the temporary identity mark, and the type of routing area update.

In addition, in this step, the mobile terminal and the radio access network judge whether to perform inter-system handover through processes such as handover measurement and handover judgment, wherein the handover measurement and handover judgment can use the method specified in the protocol, and the present invention addresses this The method used for the steps is not intended to be limiting.

Step 502-Step 503: If there is data transmission between the current SRNC and the mobile terminal, the SGSN notifies the SRNC to stop sending downlink data to the mobile terminal, and reports the sequence number of the buffered data packet; if there is no data between the current SRNC and the mobile terminal transmission, go to step 504 directly.

So far, the mobile terminal completes the request for starting the routing area update.

Step 504-Step 505: The SGSN starts the encryption negotiation process of the GPRS system.

In this step, if the GPRS system needs to be encrypted according to the configuration of the operator, the SGSN starts the normal encryption negotiation process, and configures the corresponding encryption algorithm and encryption key of the mobile terminal during the negotiation process. For the encryption negotiation process above, refer to the encryption negotiation process shown in FIG. 1 .

If the GPRS system does not need encryption according to the operator's configuration, the SGSN will also start the normal encryption negotiation process and force the mobile terminal to not encrypt user data and signaling. For the encryption negotiation process, refer to the encryption negotiation process shown in FIG. 1 . According to the protocol, the authentication and encryption request message shown in step 101 needs to carry a Ciphering Algorithm cell, and the mobile terminal selects a different encryption algorithm to encrypt user data and signaling according to the value of the Ciphering Algorithm cell . The protocol stipulates that when the value of the above-mentioned encryption algorithm information element is 0, the mobile terminal will not encrypt user data. Therefore, when the operator configures the GPRS system without encryption, the encryption algorithm information element carried in the authentication and encryption request message If the value of is set to 0, the mobile terminal can be forced not to encrypt user data, so as to prevent the mobile terminal from automatically restoring the previously used encryption algorithm and encryption key after switching, thereby causing service interruption.

Moreover, if the operator configures the GPRS system to disable the authentication function at the same time, the authentication random number parameter RAND information element is not included in the authentication and encryption request message sent by the SGSN to the user terminal.

Step 506-Step 511: SRNC performs routing area update operation, that is, SRNC first forwards its cached data to SGSN; then releases the Iu connection with CN.

It should be noted that, except for the above-mentioned steps 504-505, the signaling flow used in steps 501-511 is the same as the signaling flow used in the corresponding steps of step 301-step 311 shown in FIG. 3 in the prior art.

Fig. 6 shows the flow of the method for inter-system handover from the WCDMA system to the GPRS system between SGSNs according to the present invention. As shown in Figure 6, the method specifically includes the following steps:

Step 601: After the mobile terminal and the wireless access network decide to initiate an intersystem handover from the WCDMA system to the GPRS system through an intersystem handover decision, they send a routing area update message to the SGSN of the new GPRS system to start the routing area update operation.

The routing area update process message above contains parameters such as the last and current routing area information of the mobile terminal, the temporary identity mark, and the type of routing area update.

In this step, the mobile terminal and the radio access network judge whether to perform inter-system handover through processes such as handover measurement and handover judgment;

Step 602-step 605: If there is data transmission between the current SRNC and the mobile terminal, then stop sending downlink data to the mobile terminal, and report the buffered data packet sequence number to the new SGSN of the GPRS system; If there is no data transmission, step 603 is directly executed.

So far, the mobile terminal completes the request for starting the routing area update.

Step 606-Step 607: The GPRS system SGSN starts the encryption negotiation process of the GPRS system.

It should be noted that the operation performed in this step is the same as the operation performed in step 503 above, so no detailed description is given here.

Step 608-Step 623: SGSN performs the routing area update operation, that is, the SRNC forwards the buffered data to the new SGSN through the original SGSN of the WCDMA system; then, the GGSN updates the SGSN identification of the mobile user; Iu connects; Finally, HLR deletes the user's subscription information stored in the original SGSN, and inserts the user's subscription information into the GPRS system SGSN.

It should be noted that, except for the above-mentioned steps 606-607, the signaling flow used in steps 601-622 is the same as the signaling flow used in the corresponding steps of step 401-step 423 shown in FIG. 4 in the prior art.

In the inter-system handover process in the above two cases, through the encryption negotiation process between the SGSN and the mobile terminal, when the GPRS system does not require encryption, the mobile terminal is forced not to perform encryption negotiation, thereby preventing the mobile terminal from switching Business interruption caused by automatically enabling the encryption function.

The preferred embodiments above are cited to further describe the purpose, technical solutions and advantages of the present invention in detail. It should be understood that the above descriptions are only preferred embodiments of the present invention, and are not intended to show the present invention. Within the spirit and principles of the present invention, any modifications, equivalent replacements, improvements, etc., shall be included in the protection scope of the present invention.

Claims (6)

1, a kind of intersystem handover method that mobile terminal is handed over to GPRS system from WCDMA system, it is characterized in that, described method comprises the following steps: a. The mobile terminal requests the GPRS service support node to start the routing area update operation from the WCDMA system to the GPRS system; B, if configuration GPRS system does not encrypt, then GPRS service support node sends authentication and encryption request message to mobile terminal, and this authentication and encryption request message include the information that forces mobile terminal to terminate encryption operation; Mobile terminal receives described After authentication and encryption request message, return authentication and encryption response message to GPRS service support node; c. The GPRS service support node executes the routing area update operation from the WCDMA system to the GPRS system. 2. The method according to claim 1, wherein the authentication and encryption request message is: an authentication and encryption request message with an algorithm cell value of 0. 3. The method according to claim 2, wherein the authentication and encryption request message does not contain authentication random parameter information elements; The authentication and encryption request response message does not include an authentication response parameter information element. 4. The method according to claim 1, wherein said step b further comprises: if the GPRS system is configured for encryption, the GPRS service support node sends an authentication and encryption request message comprising an encryption algorithm and an encryption key to mobile terminal. 5. The method according to claim 1, wherein the GPRS service support node is a GPRS service support node co-established by the GPRS system and the WCDMA system. 6. The method according to claim 1, wherein the GPRS service support node of the GPRS system is separated from the GPRS service support node of the WCDMA system; The GPRS service support node described in steps a to c is a GPRS service support node of the GPRS system.

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