CN111818602B

CN111818602B - CSFB calling method, mobile management entity, service gateway and system

Info

Publication number: CN111818602B
Application number: CN202010668681.4A
Authority: CN
Inventors: 张余
Original assignee: China United Network Communications Group Co Ltd
Current assignee: China United Network Communications Group Co Ltd
Priority date: 2020-07-13
Filing date: 2020-07-13
Publication date: 2023-03-10
Anticipated expiration: 2040-07-13
Also published as: CN111818602A

Abstract

The invention provides a CSFB call method, a mobile management entity, a service gateway and a system, wherein the CSFB call method comprises the following steps: after the terminal in the 4G network performs fallback, judging whether a fallback cell of the terminal is a 2G/3G cell; if the fallback cell is a 2G/3G cell, sending a request for suspending a terminal bearing context to a Serving Gateway (SGW); and after the terminal returns to the 4G network, sending a request for recovering the bearer context of the terminal to the SGW. The CSFB call method, the mobile management entity, the service gateway and the system can reduce the consumption of time and resources, and solve the problem that the existing CSFB call method consumes time and resources because the bearing context needs to be reestablished when the terminal returns to the 4G network.

Description

CSFB (Circuit switched fallback) calling method, mobile management entity, service gateway and CSFB calling system

Technical Field

The present invention relates to the field of mobile communications technologies, and in particular, to a CSFB call method, a mobility management entity, a serving gateway, and a system.

Background

In a Long Term Evolution (LTE) network, when a terminal makes a voice call, it is usually implemented by a Circuit Switched Fallback (CSFB) Technology, that is, the terminal falls back from a fourth Generation Mobile Communication Technology (4G) network to a Second Generation Mobile Communication Technology (2G)/third Generation Mobile Communication Technology (3 rd Generation, 3G) network, and uses a 2G/3G network to implement a voice service.

During the research and practice of the prior art, the inventor finds that the prior art has the following problems:

when the 4G network falls back to the 2G/3G network, the bearer context of the terminal is deleted, so that when the terminal returns to the 4G network, the bearer context needs to be re-established, which consumes a certain amount of time and resources.

Disclosure of Invention

The technical problem to be solved by the present invention is to provide a CSFB call method, a mobility management entity, a serving gateway and a system for solving the above-mentioned deficiencies in the prior art, which can solve the problem of time and resource consumption caused by the need of re-establishing a bearer context when a terminal returns to a 4G network.

In a first aspect, an embodiment of the present invention provides a CSFB call method, which is applied to a mobility management entity MME, and the method includes:

after the terminal in the 4G network performs fallback, judging whether a fallback cell of the terminal is a 2G/3G cell;

if the fallback cell is a 2G/3G cell, sending a request for suspending a terminal bearing context to a Serving Gateway (SGW);

and after the terminal returns to the 4G network, sending a request for recovering the bearer context of the terminal to the SGW.

Preferably, after the terminal in the 4G network performs fallback and before determining whether the fallback cell of the terminal is a 2G/3G cell, the method further includes:

receiving terminal fall-back information sent by an evolved node B (eNB), wherein the terminal fall-back information comprises a fall-back cell of a terminal;

after the terminal returns to the 4G network, before sending a request for recovering the bearer context of the terminal to the SGW, the method further includes:

and receiving the information which is sent by the mobile switching center MSC and returned by the terminal to the 4G network.

In a second aspect, an embodiment of the present invention provides a CSFB call method, which is applied to a serving gateway SGW, and the method includes:

receiving a request for suspending a terminal bearing context sent by an MME, and suspending the terminal bearing context according to the request for suspending the terminal bearing context;

and receiving a request for recovering the terminal bearing context sent by the MME, and recovering the terminal bearing context according to the request for recovering the terminal bearing context.

Preferably, the method further comprises:

when detecting that a downlink data service arrives at a terminal and determining that the terminal activates an ISR, judging whether the terminal bearing context is in a suspended state;

and if the terminal is in the suspended state, sending a downlink data service paging request to a Serving GPRS Support Node (SGSN).

In a third aspect, an embodiment of the present invention provides a mobility management entity, including:

the first judgment module is used for judging whether a fallback cell of a terminal is a 2G/3G cell after the terminal in the 4G network performs fallback;

the first sending module is connected with the first judging module and used for sending a request for hanging a terminal bearing context to a Serving Gateway (SGW) when receiving a judgment result of the first judging module that the fallback cell is a 2G/3G cell;

and a second sending module, configured to send, to the SGW, a request to restore the bearer context of the terminal after the terminal returns to the 4G network.

Preferably, the method further comprises the following steps: a first receiving module, connected to the first determining module, configured to receive terminal fallback information sent by an evolved node b (eNB), and send the terminal fallback information to the first determining module, where the terminal fallback information includes a fallback cell of a terminal;

and the second receiving module is connected with the second sending module and used for receiving the information of the terminal returned to the 4G network sent by the Mobile Switching Center (MSC) and sending the information of the terminal returned to the 4G network to the second sending module.

In a fourth aspect, an embodiment of the present invention provides a serving gateway, including:

a suspension module, configured to receive a request for suspending a terminal bearer context sent by an MME, and suspend the terminal bearer context according to the request for suspending the terminal bearer context;

and the restoring module is connected with the suspending module and used for receiving a request for restoring the terminal bearing context sent by the MME and restoring the terminal bearing context according to the request for restoring the terminal bearing context.

Preferably, the method further comprises the following steps:

the second judging module is connected with the suspension module and used for judging whether the terminal bearing context is in a suspension state or not when the terminal is detected to have downlink data service arrival and the terminal is determined to activate ISR;

and a third sending module, connected to the second determining module, for sending a downlink data service paging request to a serving GPRS support node SGSN when the terminal bearer context is in a suspended state.

In a fifth aspect, an embodiment of the present invention provides a CSFB call system, including: eNB, SGSN, MSC, MME and SGW;

the MSC is used for sending a paging request to the MME when a call comes from the terminal, wherein the ISR function of the terminal is activated;

the MME is used for forwarding the paging request to the terminal and receiving an extended service request sent by the terminal;

the MME is also used for sending an indication of a terminal fallback cell to the eNB after receiving the extended service request;

the eNB is used for sending the frequency point information of the fallback cell to the terminal according to the indication of the terminal fallback cell, receiving the measurement result of the fallback cell reported after the terminal performs measurement, and indicating the terminal to fallback to a proper cell according to the measurement result of the fallback cell;

the MME is also used for receiving terminal fallback information sent by the eNB after the terminal is fallback, wherein the terminal fallback information comprises a fallback cell of the terminal, and sending a request for hanging a terminal bearing context to an SGW when the fallback cell is a 2G/3G cell;

the SGW is used for suspending the bearing context of the terminal according to the request for suspending the bearing context of the terminal;

the MSC is also used for sending information of a 4G network returned by the terminal to the MME when the terminal conversation is judged to be finished;

the MME is also used for sending a request for recovering the bearing context to the SGW after receiving the information of the 4G network returned by the terminal;

the SGW is further configured to recover the bearer context of the terminal according to the request for recovering the bearer context.

Preferably, the SGW is further configured to, when it is detected that a downlink data service arrives at the terminal and it is determined that the terminal activates the ISR function, determine whether a bearer context of the terminal is in a suspended state, and send a downlink data service paging request to the SGSN if the determination result is yes;

the SGSN is used for sending the downlink data service paging request to the terminal.

According to the CSFB call method, the mobile management entity, the service gateway and the system provided by the embodiment of the invention, when the terminal falls back to the 2G/3G network from the 4G network, the bearing context of the terminal is suspended, and when the terminal returns to the 4G network after the conversation is finished, the bearing context of the terminal is recovered, so that the consumption of time and resources can be reduced, and the problem that the time and resources are consumed due to the fact that the bearing context needs to be reestablished when the terminal returns to the 4G network in the existing CSFB call method is solved.

Drawings

FIG. 1: is a flow chart of a CSFB calling method of embodiment 1 of the present invention;

FIG. 2: a flow chart of a CSFB call method according to embodiment 2 of the present invention;

FIG. 3: a structure diagram of a mobility management entity in embodiment 3 of the present invention;

FIG. 4: is a structure diagram of a service gateway in embodiment 4 of the present invention;

FIG. 5 is a schematic view of: an interaction diagram of a CSFB call system in embodiment 5 of the present invention is shown.

Detailed Description

In order to make those skilled in the art better understand the technical solutions of the present invention, the following detailed description will be made with reference to the accompanying drawings.

It is to be understood that the specific embodiments and figures described herein are merely illustrative of the invention and are not limiting of the invention.

It is to be understood that the various embodiments and features of the embodiments may be combined with each other without conflict.

It is to be understood that, for the convenience of description, only parts related to the present invention are shown in the drawings of the present invention, and parts not related to the present invention are not shown in the drawings.

It should be understood that each unit and module related in the embodiments of the present invention may correspond to only one physical structure, and may also be composed of multiple physical structures, or multiple units and modules may also be integrated into one physical structure.

It will be understood that, without conflict, the functions, steps, etc. noted in the flowchart and block diagrams of the present invention may occur in an order different from that noted in the figures.

It is to be understood that the flowchart and block diagrams of the present invention illustrate the architecture, functionality, and operation of possible implementations of systems, apparatus, devices and methods according to various embodiments of the present invention. Each block in the flowchart or block diagrams may represent a unit, module, segment, code, or portion thereof, which comprises executable instructions for implementing the specified function(s). Furthermore, each block or combination of blocks in the block diagrams and flowchart illustrations can be implemented by a hardware-based system that performs the specified functions or by a combination of hardware and computer instructions.

It should be understood that the units and modules referred to in the embodiments of the present invention may be implemented by software, or may be implemented by hardware, for example, the units and modules may be located in a processor.

Example 1:

the present embodiment provides a CSFB call method, which is applied to a Mobility Management Entity MME (Mobility Management Entity), and as shown in fig. 1, the method includes:

step S102: after the terminal in the 4G network performs fallback, judging whether a fallback cell of the terminal is a 2G/3G cell;

step S104: if the fallback cell is a 2G/3G cell, sending a request for suspending a terminal bearing context to a Serving Gateway (SGW);

step S106: and after the terminal returns to the 4G network, sending a request for recovering the bearer context of the terminal to the SGW.

In this embodiment, the terminal is a 4G multi-mode card, and the 4G multi-mode card selects a CSFB technique to implement a voice call, and the terminal has an ISR (Idle mode Signaling Reduction ) function, and after the terminal is powered on, the terminal is in a coverage Area of a 2/3G network, attaches to the 2/3G network, releases a connection after the attachment is completed, starts an RAU (Route Area Update) timer, does not activate the ISR at this time, and when the terminal moves to a coverage Area of the 4G network, the terminal resides in the 4G network, and the terminal performs a joint location Update. The specific process of the joint location update comprises the following steps: the MME sends context request information to SGSN (Serving GPRS Support Node) after receiving the joint location update request, and after receiving the context response information of the SGSN, the MME sends a request for modifying the bearing relationship to SGW (Serving GW, serving gateway), the request for modifying the bearing relationship comprises an ISR activation instruction, the SGW modifies the bearing relationship and stores the ISR activation instruction, the MME sends a location update request to MSC (Mobile Switching Center), the MSC sends location update completion response information to the MME after completing the location update, the MME sends joint location update acceptance information to the terminal, the ISR activation instruction is included, and the terminal activates ISR.

It should be noted that the CSFB call method provided in this embodiment is applicable to a calling (MO) CSFB procedure and a called (MT) CSFB procedure, where the terminal may be a calling terminal or a called terminal, and when the terminal falls back from the 4G network to the 2G/3G network, the SGW suspends the bearer context of the terminal according to a request for suspending the bearer context of the terminal, and resumes the bearer context of the terminal after the call is ended. Taking a called party (MT) CSFB procedure as an example to illustrate the CSFB call method provided in this embodiment, if the terminal has an incoming call, the MME receives a paging request and sends an indication that the terminal falls back to the eNB (evolved Node B). If the terminal falls back to the 2G/3G cell, the MME sends a request for suspending the bearing context of the terminal to the SGW, so that the SGW suspends the bearing context of the terminal, and the SGW recovers the bearing context of the terminal after the terminal conversation is finished, thereby avoiding the problem of time and resource waste caused by the fact that the bearing context of the terminal needs to be reestablished after the terminal returns to the 4G network because the falling back 2G/3G cell deletes the bearing context of the terminal. The bearer context may include IMSI, ME ID, terminal security context, terminal network capability, AMBR, selected CN operator ID, APN restriction, S-GW address and TEID of control signaling, EPS bearer context, and the like. The EPS bearer context may include the PDN GW address and TEID (GTP-based S5/S8) for uplink traffic or GRE keys (PMIP-based S5/S8) within the P-GW, APN, S-GW address and TEID for uplink traffic, and TI, among others.

Optionally, after the terminal in the 4G network performs fallback and before determining whether the fallback cell of the terminal is the 2G/3G cell, the method may further include:

optionally, after the terminal returns to the 4G network, before sending, to the SGW, a request for recovering the bearer context of the terminal, the method may further include:

It should be noted that, in the existing CSFB call method, when an ISR is introduced and the ISR is activated, when a terminal has an incoming call and a downlink data service is available at this time, an SGW determines that the ISR is in an activated state, and simultaneously sends a data service paging request to an MME and an SGSN, which respectively page within a TAI list (Tracking Area Identity list) and a RAI (Routing Area) range. During the research and practice of the prior art, the inventor finds that: if the terminal is located in a 2G or 3G cell, after receiving the paging request of the SGSN, the terminal is connected to the SGSN to receive downlink data services, but the paging request of the MME is invalid paging, and air interface resources are wasted.

In this embodiment, to avoid invalid paging, air interface resources are saved, when there is an incoming call and there is a downlink data service at this time, the SGW determines whether the bearer context of the terminal is in a suspended state, and if the bearer context is in the suspended state, only sends a downlink data service paging request to the serving GPRS support node SGSN. If the bearer context is not in the suspended state, the bearer context data packet is discarded, and a downlink data service paging request is not sent to the serving GPRS support node SGSN, where the downlink data service refers to other services that need to be processed in a 2G or 3G network, such as a pushed information service, except for a voice call.

The CSFB call method provided by the embodiment of the invention can reduce the consumption of time and resources by suspending the bearing context of the terminal when the terminal falls back to the 2G/3G network from the 4G network and restoring the bearing context of the terminal when the terminal returns to the 4G network after the call is finished, thereby solving the problem that the time and resources are consumed because the bearing context needs to be reestablished when the terminal returns to the 4G network in the existing CSFB call method.

Example 2:

as shown in fig. 2, this embodiment provides a CSFB paging method, which is applied to a serving gateway, and the method includes:

step S202: receiving a request for suspending a terminal bearing context sent by an MME, and suspending the terminal bearing context according to the request for suspending the terminal bearing context;

step S204: and receiving a request for recovering the terminal bearing context sent by the MME, and recovering the terminal bearing context according to the request for recovering the terminal bearing context.

Optionally, the method further comprises:

when detecting that a downlink data service arrives at the terminal and determining that the terminal activates ISR, judging whether the terminal bearing context is in a suspended state;

and if the mobile terminal is in the suspended state, sending a downlink data service paging request to a Serving GPRS Support Node (SGSN).

Example 3:

as shown in fig. 3, the embodiment provides a mobility management entity, including:

a first determining module 302, configured to determine whether a fallback cell of a terminal is a 2G/3G cell after the terminal in the 4G network performs fallback;

a first sending module 304, connected to the first determining module 302, configured to send a request for suspending a terminal bearer context to a serving gateway SGW when receiving that the determination result of the first determining module 302 is that the fallback cell is a 2G/3G cell;

a second sending module 306, configured to send, to the SGW, a request to restore the bearer context of the terminal after the terminal returns to the 4G network.

Optionally, the method may further include:

a first receiving module, connected to the first determining module 302, configured to receive terminal fallback information sent by an evolved node b (eNB), and send the terminal fallback information to the first determining module 302, where the terminal fallback information includes a fallback cell of a terminal;

a second receiving module, connected to the second sending module 306, configured to receive information, sent by the mobile switching center MSC, of the terminal returning to the 4G network, and send the information, sent by the terminal returning to the 4G network, to the second sending module 306.

Example 4:

as shown in fig. 4, the present embodiment provides a service gateway, including:

a suspending module 402, configured to receive a request for suspending a terminal bearer context sent by an MME, and suspend the terminal bearer context according to the request for suspending the terminal bearer context;

a restoring module 404, connected to the suspending module 402, configured to receive a request for restoring the bearer context of the terminal sent by the MME, and restore the bearer context of the terminal according to the request for restoring the bearer context of the terminal.

Optionally, the method may further include:

a second determining module, connected to the suspending module 402, configured to determine whether the bearer context of the terminal is in a suspended state when it is detected that a downlink data service arrives at the terminal and it is determined that the terminal activates ISR;

and the third sending module is connected with the second judging module and is used for sending a downlink data service paging request to the serving GPRS support node SGSN when the bearing context of the terminal is in a suspended state.

Example 5:

the present embodiment provides a CSFB paging system, including: eNB, SGSN, MSC, MME and SGW;

the MSC is used for sending a paging request to the MME when the terminal has an incoming call, wherein the ISR function of the terminal is activated;

the MME is also used for sending an indication of the terminal falling back to the cell to the eNB after receiving the service expansion request;

the MME is also used for receiving terminal fallback information sent by the eNB after the terminal fallback, wherein the terminal fallback information comprises a fallback cell of the terminal, and sending a request for hanging a terminal bearing context to the SGW when the fallback cell is a 2G/3G cell;

the SGW is further configured to restore the bearer context of the terminal according to the request for restoring the bearer context.

Optionally, the SGW is further configured to, when it is detected that a downlink data service arrives at the terminal and it is determined that the terminal activates the ISR function, determine whether a bearer context of the terminal is in a suspended state, and send a downlink data service paging request to the SGSN if the determination result is yes;

the SGSN is used for sending a downlink data service paging request to the terminal.

Fig. 5 shows an interaction diagram of a CSFB call system according to an embodiment of the present invention. The terminal is a 4G multimode card, the 4G multimode card selects a CSFB technology to realize voice communication, and the CSFB calling method specifically comprises the following procedures:

s01: the terminal sends a joint location update request to the MME;

specifically, after the terminal is started, an attachment flow is started within a 2/3G network range, when the terminal moves to a 4G network coverage area, the terminal resides in the 4G network, the terminal performs joint position updating, and a joint position updating request is sent to the MME;

s02: the MME sends context request information to the SGSN after receiving the joint location updating request;

s03: SGSN sends context response information to MME;

s04: the MME sends a request containing an ISR activation indication for modifying the bearing relation to the SGW;

s05: SGW modifies the bearing relationship and saves ISR activation indication;

s06: MME sends a position updating request to MSC;

s07: MSC completes the position update;

s08: MSC sends the position updating completion response information to MME;

s09: MME sends joint location update acceptance information containing ISR activation indication to the terminal;

s10: the terminal activates ISR;

s11: when the terminal has an incoming call, the MSC sends a paging request to the MME;

s12: MME sends a paging request to the terminal;

s13: the terminal sends an extended service request to the MME after receiving the paging request;

s14: the MME sends an indication that the terminal falls back to the cell to the eNB;

s15: the eNB sends the frequency point information of the fallback cell to the terminal;

s16: after the terminal performs measurement, reporting a measurement result of the fallback cell to an eNB;

s17: the eNB indicates the terminal to fall back to a proper cell according to the measurement result;

s18: if the fallback cell is the 2G/3G cell, the eNB sends the information that the terminal falls back to the 2G/3G cell to the MME;

s19: after receiving the information that the terminal falls back to the 2G/3G cell, the MME sends a request for suspending the terminal bearing context to the SGW;

s20: the SGW suspends the terminal bearing context;

s21: when the downlink data service of the terminal arrives at the moment, the SGW judges that the bearing context of the terminal is in a suspended state and sends a downlink data service paging request to the SGSN;

s22: SGSN sends a downlink data service paging request to the terminal;

s23: the terminal is located in a 2G or 3G cell, and the terminal is connected to the SGSN to receive downlink data services after receiving the paging request of the SGSN;

s24: after the terminal call is finished and returns to the 4G network, the MSC judges that the terminal call is finished and sends information of the terminal return network to the MME;

s25: after receiving the information returned by the terminal to the network, the MME sends a request for recovering the bearing context to the SGW;

s26: and after receiving the request for restoring the bearing context, the SGW restores the bearing context of the terminal.

Wherein, the step S01: -S10: and carrying out a combined position updating process after carrying out combined attachment for terminal startup. Step S11: -S26: when there is an incoming call for the terminal, the interaction flow between network elements of the CSFB call system provided in this embodiment is that, after receiving the information that the terminal falls back to the 2G/3G cell, the MME sends a request for suspending the bearer context of the terminal to the SGW, the SGW suspends the bearer context of the terminal according to the request for suspending the bearer context, and after the call of the terminal is completed, the SGW restores the bearer context of the terminal, thereby avoiding the problem of time and resource waste caused by the need to reestablish the bearer context after returning to the 4G network because the fall-back 2G/3G cell deletes the bearer context of the terminal.

Embodiments 2 to 5 provide a CSFB call method, a mobility management entity, a serving gateway, and a system, which are capable of reducing time and resource consumption and solving a problem that an existing CSFB call method consumes time and resources due to the need to reestablish a bearer context when a terminal returns to a 4G network, by suspending the bearer context of the terminal when the terminal falls back to a 2G/3G network from the 4G network and restoring the bearer context of the terminal when the terminal returns to the 4G network after a call is completed.

It will be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present invention, and the present invention is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and scope of the invention, and such modifications and improvements are also considered to be within the scope of the invention.

Claims

1. A CSFB call method applied to a Mobility Management Entity (MME), the method comprising:

receiving a paging request sent by an MSC when a terminal has an incoming call, wherein the ISR function is activated by the terminal;

forwarding the paging request to a terminal, and receiving an extended service request sent by the terminal;

sending an indication of a terminal fallback cell to an evolved node B (eNB), so that the eNB sends fallback cell frequency point information to the terminal according to the indication of the terminal fallback cell, receives a fallback cell measurement result reported after the terminal performs measurement, and indicates the terminal to fall back to a proper cell according to the fallback cell measurement result;

and after the terminal returns to the 4G network, sending a request for recovering the terminal bearing context to the SGW.

2. The CSFB call method of claim 1, wherein:

and receiving the information of the 4G network returned by the terminal sent by the mobile switching center MSC.

3. A CSFB call method, applied to a serving gateway SGW, comprising:

receiving a request for suspension of a terminal bearer context sent by the MME of any of claims 1-2, and suspending the terminal bearer context according to the request for suspension of the terminal bearer context;

receiving a request for recovering the terminal bearing context sent by the MME, and recovering the terminal bearing context according to the request for recovering the terminal bearing context;

before receiving a request sent by an MME for suspending a terminal bearing context, the SGW judges whether a fallback cell of a terminal is a 2G/3G cell after the MME performs fallback on the terminal in a 4G network, and sends the request for suspending the terminal bearing context to a serving gateway SGW if the fallback cell is the 2G/3G cell; and after the terminal returns to the 4G network, sending a request for recovering the terminal bearing context to the SGW.

4. The CSFB call method of claim 3, wherein the method further comprises:

5. A mobility management entity configured to:

the mobility management entity further comprises:

the first receiving module is connected with the first judging module and used for receiving terminal fallback information sent by an evolved node B (eNB) and sending the terminal fallback information to the first judging module, wherein the terminal fallback information comprises a fallback cell of a terminal;

and the second sending module is used for sending a request for recovering the bearing context of the terminal to the SGW after the terminal returns to the 4G network.

6. The mobility management entity according to claim 5, wherein: further comprising:

7. A service gateway, comprising:

a suspension module, configured to receive a request for suspension of a terminal bearer context sent by the MME according to any one of claims 5-6, and suspend the terminal bearer context according to the request for suspension of the terminal bearer context;

a restoring module, connected to the suspending module, configured to receive a request for restoring a terminal bearer context sent by the MME, and restore the terminal bearer context according to the request for restoring the terminal bearer context;

8. The serving gateway of claim 7, further comprising:

the second judging module is connected with the suspension module and is used for judging whether the terminal bearing context is in a suspension state or not when the arrival of downlink data service of the terminal is detected and the terminal is determined to activate the ISR;

9. A CSFB call system, comprising: eNB, SGSN, MSC, MME and SGW;

the MSC is used for sending a paging request to the MME when a terminal has an incoming call, wherein the ISR function of the terminal is activated;

10. The CSFB call system of claim 9, wherein:

the SGW is also used for judging whether the bearing context of the terminal is in a suspended state or not when detecting that the downlink data service arrives at the terminal and determining that the terminal activates the ISR function, and sending a downlink data service paging request to the SGSN under the condition that the judgment result is yes;