Patent Publication Number: US-11665641-B2

Title: Communications method and apparatus

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/729,690, filed on Dec. 30, 2019, which is a continuation of U.S. patent application Ser. No. 16/123,528, filed on Sep. 6, 2018, now U.S. Pat. No. 10,548,083, which is a continuation of U.S. patent application Ser. No. 15/401,805, filed on Jan. 9, 2017, now U.S. Pat. No. 10,085,212, which is a continuation of U.S. patent application Ser. No. 14/870,508, filed on Sep. 30, 2015, now U.S. Pat. No. 9,572,129, which is a continuation of International Patent Application No. PCT/CN2013/073814, filed on Apr. 7, 2013. All of the aforementioned patent applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to the field of communications, and in particular, to a communications method and apparatus. 
     BACKGROUND 
     Machine to machine (M2M) is widely applied in multiple fields, such as intelligent traffic, a building automation system, and a video surveillance system. An M2M device basically adopts a battery powered system, and one surveillance network has tens of thousands of M2M devices. Therefore, a work load of changing batteries for these M2M devices is quite heavy, such that people expect that an M2M device has low power consumption and long standby time, thereby reducing the number of times of battery change. 
     For a user equipment (UE) serving as an M2M device, power consumed in an idle state is far less than power consumed in a connected state, and most power consumption in the idle state originates from switching of the UE from the idle state to the connected state. 
     In other approaches, in order to reduce power consumption of a UE and increase standby time of the UE, a UE in an idle state usually receives a paging message from a network in a discontinuous reception (RDX) manner, in order to reduce the number of switches of the UE from the idle state to a connected state, thereby achieving an objective of saving power. Meanwhile, when a mobility management entity (MME) learns that a serving gateway (SGW) buffers downlink data that needs to be sent to the UE, the MME delays delivering the paging message to the UE or further increases a DRX period of the UE, in order to further reduce the number of switches of the UE from the idle state to the connected state, to enable the UE to remain in the idle state as far as possible, thereby further reducing power consumption of the UE and achieving an objective of saving power. 
     However, when the MME delays delivering the paging message or the UE uses a long DRX period, because the UE needs to wait for a long time each time before the UE receives the paging message from the MME, establishes a connection to the network according to the paging message, and receives corresponding downlink data, it is possible that an SGW/a packet data network (PDN) Gateway (PGW) cannot receive connection establishment information of the UE within a normal time interval, and cannot deliver downlink data of the UE to the UE, such that the SGW may mistakenly consider that an error or exception occurs in the network, and further discard the buffered downlink data of the UE. 
     SUMMARY 
     Embodiments of the present disclosure provide a communications method and apparatus, which can solve a problem in other approaches that, in order to save power, when an MME delays delivering a paging message or a UE uses a long DRX period, an exception may occur in an SGW. 
     In order to achieve the foregoing objective, the following technical solutions are used in the embodiments of the present disclosure. 
     According to a first aspect, an embodiment of the present disclosure provides a communications method, including: acquiring, by a mobility management entity (MME), information of a UE; determining, by the MME according to the information of the UE, whether the UE satisfies a first preset condition; if the UE satisfies the first preset condition, generating, by the MME, a first indication, where the first indication is used for instructing a serving gateway (SGW) to retain first data or discard the first data, and the first data is downlink data of the UE; and sending, by the MME, the first indication to the SGW, such that the SGW processes the first data according to the first indication. 
     According to a second aspect, an embodiment of the present disclosure further provides a communications method, including: receiving, by an SGW, a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and processing, by the SGW, the first data according to the first indication. 
     According to a third aspect, an embodiment of the present disclosure provides an MME, including: a first acquiring unit configured to acquire information of a UE; a first determining unit configured to determine, according to the information of the UE acquired by the first acquiring unit, whether the UE satisfies a first preset condition; a first generating unit configured to: if the first determining unit determines that the UE satisfies the first preset condition, generate a first indication, where the first indication is used for instructing an SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and a first sending unit configured to send the first indication generated by the first generating unit to the SGW, such that the SGW processes the first data according to the first indication. 
     According to a fourth aspect, an embodiment of the present disclosure provides an SGW, including: a second receiving unit configured to receive a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and a second processing unit configured to process the first data according to the first indication received by the second receiving unit. 
     According to a fifth aspect, an embodiment of the present disclosure further provides an MME, including a first processor configured to: acquire information of a UE; determine, according to the information of the UE, whether the UE satisfies a first preset condition; and if the UE satisfies the first preset condition, generate a first indication, where the first indication is used for instructing an SGW to retain first data or discard the first data, and the first data is downlink data of the UE. The MME further includes: a first memory configured to store the information of the UE acquired by the first processor and the first indication generated by the first processor; and a first transmitter configured to send the first indication stored in the first memory and generated by the first processor to the SGW, such that the SGW processes the first data according to the first indication. 
     According to a sixth aspect, an embodiment of the present disclosure further provides an SGW, including: a second receiver configured to receive a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard the first data, and the first data is downlink data of the UE; a second processor configured to store the first indication received by the second receiver into a second memory, and process the first data according to the first indication; and a second memory configured to store the first indication. 
     According to the communications method and apparatus provided in the embodiments of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     According to a seventh aspect, an embodiment of the present disclosure provides another communications method, including: acquiring, by an MME, information of a UE; determining, by the MME according to the information of the UE, whether the UE satisfies a first preset condition; if the UE satisfies the first preset condition, generating, by the MME, a third indication, where the third indication is used for instructing a packet data network gateway PGW to retain first data, and the first data is downlink data of the UE; and sending, by the MME, the third indication to an SGW, such that the SGW sends the third indication to the PGW, and further, the PGW processes the first data according to the third indication. 
     According to an eighth aspect, an embodiment of the present disclosure further provides another communications method, including: receiving, by an SGW, a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and sending, by the SGW, the third indication to the PGW, such that the PGW processes the first data according to the third indication. 
     According to a ninth aspect, an embodiment of the present disclosure further provides another communications method, including: receiving, by a PGW, a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE; and processing, by the PGW, the first data according to the third indication. 
     According to a tenth aspect, an embodiment of the present disclosure provides an MME, including: a first acquiring unit configured to acquire information of a UE; a first determining unit configured to determine, according to the information of the UE acquired by the first acquiring unit, whether the UE satisfies a first preset condition; a first generating unit configured such that if the first determining unit determines that the UE satisfies the first preset condition, the first generating unit generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and a first sending unit configured to send the third indication generated by the first generating unit to an SGW, such that the SGW sends the third indication to the PGW, and further, the PGW processes the first data according to the third indication. 
     According to an eleventh aspect, an embodiment of the present disclosure provides an SGW, including: a second receiving unit configured to receive a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and a second sending unit configured to send the third indication received by the second receiving unit to the PGW, such that the PGW processes the first data according to the third indication. 
     According to a twelfth aspect, an embodiment of the present disclosure provides a PGW, including: a third receiving unit configured to receive a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE; and a third processing unit configured to process the first data according to the third indication received by the third receiving unit. 
     According to a thirteenth aspect, an embodiment of the present disclosure further provides an MME, including a first processor configured to: acquire information of a UE; determine, according to the information of the UE, whether the UE satisfies a first preset condition; and if the UE satisfies the first preset condition, generate a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. The MME further includes: a first transmitter configured to send the third indication generated by the first processor to an SGW, such that the SGW sends the third indication to the PGW, and further, the PGW processes the first data according to the third indication; and a first memory configured to store the information of the UE acquired by the first processor and the third indication generated by the first processor. 
     According to a fourteenth aspect, an embodiment of the present disclosure further provides an SGW, including: a second receiver configured to receive a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; a second processor configured to store the third indication received by the second receiver into a second memory; the second memory configured to store the third indication; and a second transmitter configured to send the third indication stored in the second memory and generated by the second processor to the PGW, such that the PGW processes the first data according to the third indication. 
     According to a fifteenth aspect, an embodiment of the present disclosure further provides a PGW, including: a third receiver configured to receive a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE; a third processor configured to store the third indication received by the third receiver into a third memory, and process the first data according to the third indication; and a third memory configured to store the third indication. 
     According to the other communications method and apparatus provided in the embodiments of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the embodiments of the present disclosure more clearly, the following briefly introduces the accompanying drawings required for describing the embodiments. The accompanying drawings in the following description show merely some embodiments of the present disclosure, and a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without departing from the scope of the present disclosure. 
         FIG.  1    is a first flowchart of a communications method according to an embodiment of the present disclosure; 
         FIG.  2    is a second flowchart of a communications method according to an embodiment of the present disclosure; 
         FIG.  3    is a first flowchart of another communications method according to an embodiment of the present disclosure; 
         FIG.  4    is a second flowchart of another communications method according to an embodiment of the present disclosure; 
         FIG.  5    is a third flowchart of another communications method according to an embodiment of the present disclosure; 
         FIG.  6    is a third flowchart of a communications method according to an embodiment of the present disclosure; 
         FIG.  7    is a fourth flowchart of another communications method according to an embodiment of the present disclosure; 
         FIG.  8    is a first schematic structural diagram of an MME according to an embodiment of the present disclosure; 
         FIG.  9    is a second schematic structural diagram of an MME according to an embodiment of the present disclosure; 
         FIG.  10    is a first schematic structural diagram of an SGW according to an embodiment of the present disclosure; 
         FIG.  11    is a second schematic structural diagram of an SGW according to an embodiment of the present disclosure; 
         FIG.  12    is a first schematic structural diagram of a PGW according to an embodiment of the present disclosure; 
         FIG.  13    is a third schematic structural diagram of an MME according to an embodiment of the present disclosure; 
         FIG.  14    is a third schematic structural diagram of an SGW according to an embodiment of the present disclosure; 
         FIG.  15    is a second schematic structural diagram of a PGW according to an embodiment of the present disclosure; 
         FIG.  16    is a first structural block diagram of a communications system according to an embodiment of the present disclosure; and 
         FIG.  17    is a second structural block diagram of a communications system according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following clearly describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. The described embodiments are merely some but not all of the embodiments of the present disclosure. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure. 
     The term “and/or” in this specification describes only an association relationship for describing associated objects and represents that three relationships may exist. For example, A and/or B may represent the following three cases: Only A exists, both A and B exist, and only B exists. In addition, the character “/” in this specification generally indicates an “or” relationship between the associated objects. 
     Various technologies described in this specification may be applied to various wireless communications systems, for example, current 2 nd  generation (2G) and 3 rd  generation (3G) communications systems and a next-generation communications system, a Global System for Mobile communications (GSM), a code-division multiple access (CDMA) system, a time-division multiple access (TDMA) system, a wideband CDMA (WCDMA) system, a frequency-division multiple access (FDMA) system, an orthogonal FDMA (OFDMA) system, a single-carrier FDMA (SC-FDMA) system, a General Packet Radio Service (GPRS) system, a Long-Term Evolution LTE system, and other communications systems. 
     A user equipment may be a wireless terminal or a wired terminal. The wireless terminal may refer to a device that provides a user with voice and/or data connectivity, a handheld device with a wireless connection function, or another processing device connected to a wireless modem. The wireless terminal may communicate with one or more core networks through a radio access network (RAN). The wireless terminal may be a mobile terminal, such as a mobile phone (also referred to as a “cellular” phone) or a computer with a mobile terminal, for example, may be a portable, pocket-sized, handheld, computer built-in, or in-vehicle mobile apparatus, which exchanges voice and/or data with the radio access network. For example, it may be a device such as a personal communication service (PCS) phone, a cordless telephone set, a Session Initiation Protocol (SIP) phone, a wireless local loop (WLL) station, or a personal digital assistant (PDA). The wireless terminal may also be called a system, a subscriber unit, a subscriber station, a mobile station, a mobile terminal (Mobile), a remote station, an access point (Access Point), a remote terminal (Remote Terminal), an access terminal, a user terminal, a user agent, or a user equipment. 
     Embodiment 1 
     This embodiment of the present disclosure provides a communications method, and relates to an MME side. As shown in  FIG.  1   , the method includes the following. 
     S 101 : An MME acquires information of a UE. 
     In the field of communications, an MME is a key control node of The 3rd Generation Partnership Project (3GPP) LTE access network, and is responsible for a process of positioning and paging a UE in an idle mode, and includes relay function. The MME involves a bearer activation/deactivation process, and when a UE is initialized and connected to a network, may select an SGW for the UE. The MME authenticates a user by interacting with a home subscriber server (HSS), and allocates a temporary ID (Identity, serial number) to the user. Meanwhile, the MME supports interception and listening of data when permitted by law. 
     The UE in this embodiment of the present disclosure may be a mobile phone, an intelligent terminal, a multimedia device, a streaming media device, or the like. 
     The SGW is responsible for routing and forwarding a user data packet, and is also responsible for user-plane data exchange when the UE moves between evolved base stations (e.g., eNodeBs) and between LTE and another 3GPP technology. For a UE in an idle state, the SGW is used as a node on a downlink data path, and when downlink data arrives, triggers paging of the UE. 
     The MME first needs to acquire the information of the UE, in order to perform corresponding determining on the UE according to the information, where the information of the UE may include a type of the UE or a DRX period of the UE. For information of the UE and the determining performed on the UE according to the information, reference may be made to a description in a subsequent embodiment. 
     S 102 : The MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. 
     After acquiring the information of the UE, the MME may determine, according to the information of the UE, whether the UE satisfies the first preset condition. 
     It should be noted that, the first preset condition is to be described in the subsequent embodiment. 
     S 103 : If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. 
     After the MME performs determining on the UE, if the UE satisfies the first present condition, the MME generates the corresponding first indication, where the first indication may be used for instructing the SGW to retain the first data or discard the first data, and the first data is the downlink data of the UE. The downlink data, which is provided in this embodiment of the present disclosure, of the UE may be data sent by another network device such as a gateway or a base station to the UE. On the contrary, uplink data of the UE is data sent by the UE to another network device such as a base station or a gateway. 
     Further, that the first indication is used for instructing the SGW to retain the first data or discard the first data may include that, the first indication is used for instructing the SGW to retain the first data, or the first indication is used for instructing the SGW to discard the first data. 
     After the MME performs determining on the UE, if the UE does not satisfy the first preset condition, the MME pages the UE and performs other operations according to other approaches. 
     S 104 : The MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. 
     The MME sends the generated first indication to the SGW, such that when receiving the first data, that is, the downlink data of the UE, the SGW may retain the first data for the UE or discard the first data according to the first indication. Therefore, for a case in which the SGW does not send the downlink data of the UE within a time for which the SGW retains the first data for the UE, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     This embodiment of the present disclosure further provides a communications method, and relates to an SGW side. As shown in  FIG.  2   , the method includes the following. 
     S 201 : An SGW receives first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard first data, and the first data is downlink data of the UE. 
     The SGW receives the first indication from the MME. After the MME acquires the information of the UE, the MME determines, according to the information of the UE, whether the UE satisfies the first preset condition, and the first indication is generated by the MME when the UE satisfies the first preset condition, the first indication is used for instructing the SGW to retain the first data for the UE or discard the first data, and the first data is the downlink data of the UE. 
     S 202 : The SGW processes the first data according to the first indication. 
     After receiving the first indication from the MME, the SGW retains the first data for the UE or discard the first data according to the first indication. 
     In this embodiment of the present disclosure, the SGW may learn, according to the first indication received from the MME, that the UE may need to wait for a period of time before establishing a signaling and data channel with a network, to implement transmission of the first data. Therefore, the SGW may buffer the first data, that is, the downlink data of the UE, for a period of time according to the first indication, and this way, for a case in which the SGW does not send the downlink data of the UE within a time for which the SGW retains the first data for the UE, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     According to the communications method provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     This embodiment of the present disclosure provides another communications method, and relates to an MME side. As shown in  FIG.  3   , the method includes the following. 
     S 301 : An MME acquires information of a UE. 
     The MME acquires the information of the UE, in order to perform corresponding determining on the UE according to the information of the UE. 
     S 302 : The MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. 
     After acquiring the information of the UE, the MME may determine, according to the information of the UE, whether the UE satisfies the first preset condition. 
     S 303 : If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. 
     The PGW provides interface transmission at a connection point between the UE and an external packet data network. One UE may access multiple packet data networks using multiple PGWs at the same time. The PGW implements an instruction to control data packet filtering, charging support, authorized interception, and data packet screening for each user. Another key function of the PGW is that the PGW is used as a core component of data exchange to bear data exchange between a 3GPP network and a non-3GPP network. 
     If the MME determines that the UE satisfies the first preset condition, the MME generates the third indication, where the third indication is used for instructing the PGW to retain the first data for the UE. 
     S 304 : The MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and further, the PGW processes the first data according to the third indication. 
     After generating the third indication, the MME sends the third indication to the SGW, such that the SGW further sends the third indication to the PGW, and the PGW can retain the first data for the UE according to the third indication; therefore, for a case in which the PGW does not send the downlink data of the UE to the SGW within a time for which the PGW retains the first data for the UE, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     This embodiment of the present disclosure further provides another communications method, and relates to an SGW side. As shown in  FIG.  4   , the method includes the following. 
     S 401 : An SGW receives a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. 
     The SGW receives the third indication from the MME. After acquiring the information of the UE, the MME determines, according to the information of the UE, whether the UE satisfies the first preset condition, and the third indication is generated by the MME when the UE satisfies the first preset condition, and the third indication is used for instructing the PGW to retain the first data for the UE. 
     S 402 : The SGW sends the third indication to the PGW, such that the PGW processes the first data according to the third indication. 
     After receiving the third indication from the MME, the SGW further forwards the third indication to the PGW, such that when receiving the first data, the PGW can retain the first data for the UE according to the third indication. Therefore, for the case in which the PGW does not send the downlink data of the UE to the SGW within a time for which the PGW retains the first data for the UE, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     This embodiment of the present disclosure further provides another communications method, and relates to a PGW side. As shown in  FIG.  5   , the method includes the following. 
     S 501 : A PGW receives a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE. 
     The PGW receives the third indication from the SGW. After acquiring the information of the UE, the MME determines, according to the information of the UE, whether the UE satisfies the first preset condition, and the third indication is generated by the MME when the UE satisfies the first preset condition, and the third indication is sent by the MME to the SGW, and the third indication may be used for instructing the PGW to retain the first data for the UE. This is a process of delivering the downlink data of the UE. 
     S 502 : The PGW processes the first data according to the third indication. 
     After receiving the third indication forwarded by the SGW, the PGW may retain the first data for the UE according to the third indication. 
     In this embodiment of the present disclosure, the PGW may learn, according to the third indication received from the SGW, that the UE may need to wait for a period of time before establishing a signaling and data channel to a network, to implement transmission of the first data. Therefore, the PGW may buffer the first data, that is, the downlink data of the UE, for a period of time according to the third indication, and in this way, for a case in which the PGW does not send the downlink data of the UE to the SGW within a time for which the PGW retains the first data for the UE, the SGW may not consider that the case is caused by the fact that an error or exception occurs. Alternatively, the PGW may refuse, according to the third indication, to receive the downlink data of the UE delivered by a network, and in this way, the PGW may not deliver too much downlink data of the UE to the SGW, in order to avoid that a buffer capacity of the SGW is exceeded because the SGW retains too much downlink data of the UE. 
     According to the other communications method provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     Embodiment 2 
     This embodiment of the present disclosure provides a communications method. As shown in  FIG.  6   , the method includes the following. 
     S 601 : An MME acquires information of a UE. 
     In the field of communications, an MME is a key control node of a 3GPP protocol LTE access network, and is responsible for a process of positioning and paging a UE in an idle mode, and includes a relay. The MME involves a bearer activation/deactivation process, and when a UE is initialized and connected to a network, may select an SGW for the UE. The MME authenticates a user by interacting with an HSS, and allocates a temporary ID to the user. Meanwhile, the MME supports interception and listening of data when permitted by law. 
     The UE in this embodiment of the present disclosure may be a mobile phone, an intelligent terminal, a multimedia device, a streaming media device, or the like. 
     The SGW is responsible for routing and forwarding a user data packet, and is also responsible for user-plane data exchange when the UE moves between eNodeBs and between LTE and another 3GPP technology. For a UE in an idle state, the SGW is used as a node on a downlink data path, and when downlink data arrives, triggers paging of the UE. 
     The MME first needs to acquire the information of the UE, in order to perform corresponding determining on the UE according to the information of the UE. 
     Further, the information of the UE may include a type of the UE or a DRX period of the UE. 
     For example, a method, provided in this embodiment of the present disclosure, for acquiring, by the MME, the information of the UE, that is, the type of the UE or the DRX period of the UE, may be one of the following. 
     (1) The MME receives subscription data of the UE from an HSS, and acquires the type of the UE or the DRX period of the UE according to the subscription data of the UE. 
     (2) The MME receives a non-access stratum (NAS) message/an access stratum (AS) message from the UE, and acquires the type of the UE or the DRX period of the UE according to the NAS message/AS message of the UE. 
     (3) The MME acquires the type of the UE or the DRX period of the UE according to a preconfigured quality of service (QoS) of a bearer used by the UE. 
     S 602 : The MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. 
     After acquiring the information of the UE, the MME performs determining on the UE according to the information of the UE, in order to determine whether the UE satisfies the first preset condition, where the first preset condition may be that: the UE is a power-saving UE, or the DRX period of the UE is greater than a first preset threshold. 
     For example, the MME may determine, according to the type of the UE, whether the UE is a UE that needs to save power. Alternatively, the MME may determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold, in order to learn whether the UE is in a long DRX period. 
     A person of ordinary skill in the art may understand that, if the MME determines, according to the type of the UE, that the UE is the power-saving UE, the MME determines that the UE satisfies the first preset condition. Correspondingly, if the MME determines, according to the DRX period of the UE, that the DRX period of the UE is greater than the first preset threshold, the MME determines that the UE satisfies the first preset condition. 
     It should be noted that, as long as the UE satisfies either of the foregoing first preset conditions, the MME can determine that the UE is a UE satisfying the first preset condition, and then, the MME continues to perform the following steps according to the communications method provided in this embodiment of the present disclosure. 
     S 603 : If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. 
     After the MME performs determining on the UE, if the UE satisfies either of the foregoing first preset conditions, the MME may generate the first indication, where the first indication may be used for instructing the SGW to retain the first data for the UE or discard the first data, and the first data is the downlink data of the UE. 
     The first indication may include a first paging delaying instruction and/or a first suggested waiting time, or include a first paging delaying instruction and/or a first suggested waiting time, and an evolved packet system (EPS) bearer identifier. 
     It should be noted that, the first indication may include the first paging delaying instruction; the first suggested waiting time; the first paging delaying instruction and the first suggested waiting time; the first paging delaying instruction and the EPS bearer identifier; the first suggested waiting time and the EPS bearer identifier; or the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier. The first indication may be used for indicating that: when the MME determines that the UE is the power-saving UE, the MME needs to delay paging the UE; or when the MME determines that the DRX period of the UE is greater than the first preset threshold, that is, the UE is in a long DRX period, after the MME pages the UE, the UE needs to wait for a period of time before responding to the paging, and further the first indication is used for instructing the SGW to retain the first data for the UE within a period of time, or instructing the SGW to discard the first data. 
     For example, the first indication may include the first paging delaying instruction, and is used for instructing the SGW to determine a first time according to the first paging delaying instruction and retain the first data for the UE within the first time, or is used for instructing the SGW to discard the first data according to the first paging delaying instruction. 
     It should be noted that, when receiving the first paging delaying instruction, the SGW may determine, according to a time for which the MME delays paging the UE and which is indicated by the first paging delaying instruction, a first time for which the first data is retained for the UE, and retain the first data for the UE within the first time. Alternatively, when receiving the first paging delaying instruction, the SGW may learn, according to the first paging delaying instruction, that the MME needs to delay paging the UE, and therefore, the SGW may consider that the UE cannot receive the first data within a period of time, that is, the SGW chooses to directly discard the first data. 
     Alternatively, the first indication may include the first suggested waiting time, and is used for instructing the SGW to retain the first data for the UE within the first suggested waiting time. 
     Alternatively, the first indication may include the first paging delaying instruction and the first suggested waiting time, and is used for instructing the SGW to retain the first data for the UE within the first suggested waiting time after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     Alternatively, the first indication may include the first paging delaying instruction and the EPS bearer identifier, and is used for instructing the SGW to determine a first time according to the first paging delaying instruction and retain, for the UE within the first time, the first data corresponding to the EPS bearer identifier, or is used for instructing the SGW to discard, according to the first paging delaying instruction, the first data corresponding to the EPS bearer. 
     Alternatively, the first indication may include the first suggested waiting time and the EPS bearer identifier, and is used for instructing the SGW to retain, for the UE within the first suggested waiting time, the first data corresponding to the EPS bearer identifier. 
     Alternatively, the first indication may include the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, and is used for instructing the SGW to retain, for the UE within the first suggested waiting time, the first data corresponding to the EPS bearer identifier after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     It should be noted that, if the first indication includes the first paging delaying instruction, or the first paging delaying instruction and the EPS bearer identifier, the first time for which the SGW retains the first data is a time estimated by the SGW. Additionally, if the first indication includes the first suggested waiting time, or the first paging delaying instruction and the first suggested waiting time, or the first suggested waiting time and the EPS bearer identifier, or the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, the first suggested waiting time for which the SGW retains the first data is a suggested time provided by the MME. 
     It may be understood that, the EPS bearer identifier included in the first indication may be used to indicate a bearer, on which the first indication is based, of the UE. Certainly, if the first indication does not include the EPS bearer identifier, the first indication is based on the UE, that is, the first indication may be aimed at only downlink data on some bearers of the UE, or may be aimed at all downlink data of the UE, where the bearer, which is provided in this embodiment of the present disclosure, of the UE may be understood as a data channel for data transmission between the UE and a network. 
     S 604 : The MME sends the first indication to the SGW. 
     After generating the first indication, the MME adds the first indication into a message, and sends the message to the SGW, such that the SGW may retain the first data for the UE or discard the first data according to the first indication in the message. 
     It should be noted that the message may be an existing message, or may be a newly-defined message. For example, a method for sending, by the MME, the first indication to the SGW may be one of the following. 
     (1) After receiving a downlink data notification message from the SGW, the MME sends a downlink data notification acknowledgment message (that is, the message is an existing message) corresponding to the downlink data notification message to the SGW, where the downlink data notification acknowledgment message carries the first indication. 
     (2) The MME sends a path bearer releasing request message (that is, the message is an existing message) to the SGW, where the path bearer releasing request message carries the first indication. 
     (3) The MME sends a newly-defined message (that is, the message is a newly-defined message) to the SGW, where the newly-defined message carries the first indication. 
     In this embodiment of the present disclosure, the message may be a newly-defined message, and the newly-defined message carries the first indication; or the message may be an existing message, and the existing message carries the first indication. For example, the newly-defined message may be a message, which satisfies an instruction function of the first indication, in any format; and is not limited in the present disclosure. 
     That the existing message carries the first indication may be that a new cause value is added into the existing message, that is, “in order to save power, paging of the UE is delayed”, in order to indicate that because the MME delays paging the UE or the UE is in a long DRX period and needs to wait for a period of time before responding to the paging, the SGW may wait for a period of time before transmitting and receiving the downlink data of the UE (that is, the SGW needs to buffer the downlink data of the UE for a period of time); or may be that a new information element (IE) is added into the existing message, that is, “the first paging delaying instruction and/or the first suggested waiting time”, or “the first paging delaying instruction and/or the first suggested waiting time, and the EPS bearer identifier”; or may be that when a new cause value is added into the existing message, a new IE, that is, the first suggested waiting time, is also added. 
     A person of ordinary skill in the art may understand that, if the first indication is carried in the newly-defined message, the MME sends the first indication to the SGW by sending the newly-defined message. If the first indication is carried in the existing message, the MME may send the first indication to the SGW by sending the existing message. 
     If the first indication is carried in the newly-defined message, the MME may send, before receiving the downlink data notification message from the SGW or after receiving the downlink data notification message from the SGW, the first indication to the SGW by sending the newly-defined message. Correspondingly, the MME may send, before sending the path bearer releasing request message to the SGW or after sending the path bearer releasing request message to the SGW, the first indication to the SGW by sending the newly-defined message. 
     Further, the path bearer releasing request message in (2) is sent by the MME to the SGW when the UE is previously disconnected from the network. 
     S 605 : The SGW processes the first data according to the first indication. 
     After receiving the first indication from the MME, the SGW may retain the first data for the UE within a period of time or directly discard the first data according to the first indication. This way, for a case in which the SGW does not send the first data, that is, the downlink data of the UE, within a period of time, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     S 606 : If subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, the MME generates a second indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, where the second indication is used for instructing the SGW to normally transmit and receive the first data. 
     If the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE changes, that is, if the subscription data of the UE and the QoS parameter of the bearer used by the UE is modified, or the UE has actively initiated a connection to the network and establishes a data channel within the foregoing period of time, the MME may generate the second indication according to the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE that is obtained after the change, where the second indication may be used for instructing the SGW to normally transmit and receive the first data. 
     It should be noted that, related information of the UE includes, but is not limited to the two pieces of information of the UE, which are the subscription data of the UE and the QoS parameter of the bearer used by the UE, that is, if other related information of the UE changes, the MME may also generate the second indication according to related information of the UE that is obtained after the change. 
     S 607 : The MME sends the second indication to the SGW. 
     After generating the second indication, the MME sends the second indication to the SGW, in order to instruct the SGW to normally transmit and receive the first data. 
     S 608 : The SGW processes the first data according to the second indication. 
     After receiving the second indication from the MME, the SGW may normally transmit and receive the first data according to the second indication, that is, the SGW may continue to transmit and receive the first data that needs to be sent to the UE. 
     It should be noted that, the second indication sent by the MME to the SGW may be carried in a newly-defined message, that is, the newly-defined message carries an indication for instructing the SGW to stop buffering the first data; or may be carried in the newly-defined message that is provided in this embodiment of the present disclosure and carries the first indication, and the first suggested waiting time in the first indication in the newly-defined message carrying the first indication needs to be set to 0 or another similar value representing the meaning, which is not limited in the present disclosure. 
     In this embodiment of the present disclosure, the SGW may learn, according to the first indication received from the MME, that the UE may need to wait for a period of time before establishing a signaling and data channel with a network, to implement transmission of the first data. Therefore, the SGW may buffer the first data, that is, the downlink data of the UE, for a period of time according to the first indication. This way, for a case in which the SGW does not send the downlink data of the UE within a period of time, the SGW may not consider that the case is caused by the fact that an error or exception occurs. After the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE changes, the MME may generate the second indication according to the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE that is obtained after the change, and sends the second indication to the SGW, in order to instruct the SGW to continue to transmit and receive the first data that needs to be sent to the UE, such that the SGW can process the first data more flexibly. 
     According to the communications method provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     This embodiment of the present disclosure provides another communications method. As shown in  FIG.  7   , the method includes the following. 
     S 701 : An MME acquires information of a UE. 
     The MME first needs to acquire the information of the UE, in order to perform corresponding determining on the UE according to the information of the UE. 
     Further, the information of the UE may include a type of the UE or a DRX period of the UE. 
     For example, a method, provided in this embodiment of the present disclosure, for acquiring, by the MME, the information of the UE, that is, the type of the UE or the DRX period of the UE, may be one of the following. 
     (1) The MME receives subscription data of the UE from an HSS, and acquires the type of the UE or the DRX period of the UE according to the subscription data of the UE. 
     (2) The MME receives an NAS message/an AS message from the UE, and acquires the type of the UE or the DRX period of the UE according to the NAS message/AS message of the UE. 
     (3) The MME acquires the type of the UE or the DRX period of the UE according to a preconfigured QoS of a bearer used by the UE. 
     S 702 : The MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. 
     After acquiring the information of the UE, the MME performs determining on the UE according to the information of the UE, in order to determine whether the UE satisfies the first preset condition, where the first preset condition may be that: the UE is a power-saving UE, or the DRX period of the UE is greater than a first preset threshold. 
     For example, the MME may determine, according to the type of the UE, whether the UE is a UE that needs to save power. Alternatively, the MME may determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold, in order to learn whether the UE is in a long DRX period. 
     A person of ordinary skill in the art may understand that, if the MME determines, according to the type of the UE, that the UE is the power-saving UE, the MME determines that the UE satisfies the first preset condition. Correspondingly, if the MME determines, according to the DRX period of the UE, that the DRX period of the UE is greater than the first preset threshold, the MME determines that the UE satisfies the first preset condition. 
     It should be noted that, as long as the UE satisfies either of the foregoing first preset conditions, the MME can determine that the UE is a UE satisfying the first preset condition, and then, the MME continues to perform the following steps according to the communications method provided in this embodiment of the present disclosure. 
     S 703 : If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. 
     After the MME performs determining on the UE, if the UE satisfies either of the foregoing first preset conditions, the MME may generate the third indication, where the third indication may be used for instructing the PGW to retain the first data for the UE, and the first data is the downlink data of the UE. 
     The third indication may include a third paging delaying instruction and/or a third suggested waiting time, or include a third paging delaying instruction and/or a third suggested waiting time, and an EPS bearer identifier. 
     It should be noted that, the third indication may include the third paging delaying instruction; the third suggested waiting time; the third paging delaying instruction and the third suggested waiting time; the third paging delaying instruction and the EPS bearer identifier; the third suggested waiting time and the EPS bearer identifier; or the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier. The third indication may be used for indicating that: when the MME determines that the UE is the power-saving UE, the MME needs to delay paging the UE; or when the MME determines that the DRX period of the UE is greater than the first preset threshold, that is, the UE is in a long DRX period, after the MME pages the UE, the UE needs to wait for a period of time before responding to the paging, and further the third indication is used for instructing the PGW to retain the first data for the UE within a period of time. 
     For example, the third indication may include the third paging delaying instruction, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain the first data for the UE within the first time, and send the first data to an SGW after the first time. 
     It should be noted that, when receiving the third paging delaying instruction, the PGW may: determine, according to a time for which the MME delays paging the UE and which is indicated by the third paging delaying instruction, a first time for which the first data is retained for the UE; retain the first data for the UE within the first time; and send the first data to the SGW after the first time. 
     Alternatively, the third indication may include the third suggested waiting time, and is used for instructing the PGW to retain the first data for the UE within the third suggested waiting time, and send the first data to the SGW after the third suggested waiting time. 
     Alternatively, the third indication may include the third paging delaying instruction and the third suggested waiting time, and is used for instructing the PGW to retain the first data for the UE within the third suggested waiting time after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data to the SGW after the third suggested waiting time. 
     Alternatively, the third indication may include the third paging delaying instruction and the EPS bearer identifier, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain, for the UE within the first time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the first time. 
     Alternatively, the third indication may include the third suggested waiting time and the EPS bearer identifier, and is used for instructing the PGW to retain, for the UE within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Alternatively, the third indication may include the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the PGW to: retain, for the UE within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE; and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     It should be noted that, if the third indication includes the third paging delaying instruction, or the third paging delaying instruction and the EPS bearer identifier, the first time for which the PGW retains the first data is a time estimated by the PGW. If the third indication includes the third suggested waiting time, or the third paging delaying instruction and the third suggested waiting time, or the third suggested waiting time and the EPS bearer identifier, or the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, the third suggested waiting time for which the PGW retains the first data is a suggested time provided by the MME. 
     It may be understood that, the EPS bearer identifier included in the third indication may be used to indicate a bearer, on which the third indication is based, of the UE. Certainly, if the third indication does not include the EPS bearer identifier, the third indication is based on the UE, that is, the third indication may be aimed at only downlink data on some bearers of the UE, or may be aimed at all downlink data of the UE, where the bearer, which is provided in this embodiment of the present disclosure, of the UE may be understood as a data channel for data transmission between the UE and a network. 
     S 704 : The MME sends the third indication to the SGW. 
     After generating the third indication, the MME adds the third indication into a message, and sends the message to the SGW, such that the SGW may further send the message to the PGW. 
     The PGW provides interface transmission at a connection point between the UE and an external packet data network. One UE may access multiple packet data networks using multiple PGWs at the same time. The PGW implements an instruction to control data packet filtering, charging support, authorized interception, and data packet screening for each user. Another key function of the PGW is that the PGW is used as a core component of data exchange to bear data exchange between a 3GPP network and a non-3GPP network. 
     It should be noted that the message may be an existing message, or may be a newly-defined message. For example, a method for sending, by the MME, the third indication to the SGW may be one of the following. 
     (1) After receiving a downlink data notification message from the SGW, the MME sends a downlink data notification acknowledgment message (that is, the message is an existing message) corresponding to the downlink data notification message to the SGW, where the downlink data notification acknowledgment message carries the third indication. 
     (2) The MME sends a path bearer releasing request message (that is, the message is an existing message) to the SGW, where the path bearer releasing request message carries the third indication. 
     (3) The MME sends a newly-defined message (that is, the message is a newly-defined message) to the SGW, where the newly-defined message carries the third indication. 
     In this embodiment of the present disclosure, the message may be a newly-defined message, and the newly-defined message carries the third indication; or the message may be an existing message, and the existing message carries the third indication. For example, the newly-defined message may be a message, which satisfies an instruction function of the third indication, in any format; and is not limited in the present disclosure. 
     That the existing message carries the third indication may be that a new cause value is added into the existing message, that is, “in order to save power, paging of the UE is delayed”, in order to indicate that because the MME delays paging the UE or the UE is in a long DRX period and needs to wait for a period of time before responding to the paging, the PGW may wait for a period of time before transmitting and receiving the downlink data of the UE (that is, the PGW needs to buffer the downlink data of the UE for a period of time); or may be that a new IE is added into the existing message, that is, “the third paging delaying instruction and/or the third suggested waiting time”, or “the third paging delaying instruction and/or the third suggested waiting time, and the EPS bearer identifier”; or may be that when a new cause value is added into the existing message, a new IE, that is, the third suggested waiting time, is also added. 
     A person of ordinary skill in the art may understand that, if the third indication is carried in the newly-defined message, the MME sends the third indication to the SGW by sending the newly-defined message. If the third indication is carried in the existing message, the MME may send the third indication to the SGW by sending the existing message. 
     If the third indication is carried in the newly-defined message, the MME may send, before receiving the downlink data notification message from the SGW or after receiving the downlink data notification message from the SGW, the third indication to the SGW by sending the newly-defined message. Correspondingly, the MME may send, before sending the path bearer releasing request message to the SGW or after sending the path bearer releasing request message to the SGW, the third indication to the SGW by sending the newly-defined message. 
     Further, the path bearer releasing request message in (2) is sent by the MME to the SGW when the UE is previously disconnected from the network. 
     S 705 : The SGW sends the third indication to the PGW. 
     After receiving the third indication from the MME, the SGW may further send the third indication to the PGW, such that the PGW may retain the first data for the UE within a period of time according to the third indication and send the first data to the SGW after the period of time. 
     It should be noted that the third indication may be carried in another message, where the other message may be an existing message, or may be a newly-defined message. If the third indication is carried in a newly-defined message, after receiving the message from the MME, the SGW may send the third indication to the PGW by sending the other message. If the third indication is carried in an existing message, the SGW may send the third indication to the PGW by sending the existing message. For example, a method for sending, by the SGW, the third indication to the PGW may be one of the following. 
     (1) The SGW sends a default bearer establishment request message (that is, the other message is an existing message) to the PGW, where the default bearer establishment request message carries the third indication. 
     (2) The SGW sends a newly-defined message (that is, the other message is a newly-defined message) to the PGW, where the newly-defined message carries the third indication. 
     The newly-defined message in (2) may be the newly-defined message sent by the MME to the SGW, that is, after receiving the newly-defined message, the SGW sends the newly-defined message to the PGW; or may be another newly-defined message sent by the SGW to the PGW, that is, the message and the other message both are newly-defined messages, and the message and the other message may be the same message, or may be different messages. 
     S 706 : The PGW processes the first data according to the third indication. 
     After receiving the third indication from the SGW, the PGW may retain the first data for the UE within a period of time according to the third indication, and send the first data to the SGW after the period of time, such that the SGW further sends the first data to the UE, to complete a process of delivering the first data. This way, for a case in which the PGW does not send the first data, that is, the downlink data of the UE, to the SGW within a period of time, the SGW may not consider that the case is caused by the fact that an error or exception occurs. 
     Further, the PGW may also refuse, according to the third indication, to receive the downlink data of the UE delivered by the network. This way, the PGW may not deliver too much downlink data of the UE to the SGW, in order to avoid that a buffer capacity of the SGW is exceeded because the SGW retains too much downlink data of the UE. 
     S 707 : If subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, the MME generates a fourth indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, where the fourth indication is used for instructing the PGW to normally transmit and receive the first data. 
     If the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE changes, that is, if the subscription data of the UE and the QoS parameter of the bearer used by the UE is modified, or the UE has actively initiated a connection to the network and establishes a data channel within the foregoing period of time, the MME may generate the fourth indication according to the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE that is obtained after the change, where the fourth indication may be used for instructing the PGW to normally transmit and receive the first data. 
     It should be noted that, related information of the UE includes, but is not limited to the two pieces of information of the UE, which are the subscription data of the UE and the QoS parameter of the bearer used by the UE, that is, if other related information of the UE changes, the MME may also generate the fourth indication according to related information of the UE that is obtained after the change. 
     S 708 : The MME sends the fourth indication to the SGW. 
     After generating the fourth indication, the MME sends the fourth indication to the SGW, such that the SGW sends the fourth indication to the PGW. 
     S 709 : The SGW sends the fourth indication to the PGW. 
     After receiving the fourth indication from the MME, the SGW may further send the fourth indication to the PGW, such that the PGW normally transmits and receives the first data according to the fourth indication. 
     S 710 : The PGW processes the first data according to the fourth indication. 
     After receiving the fourth indication from the SGW, the PGW may normally transmit and receive the first data according to the fourth indication, that is, the PGW may continue to transmit and receive the first data that needs to be sent to the UE. 
     It should be noted that, the fourth indication sent by the MME to the SGW and then sent by the SGW to the PGW may be carried in a newly-defined message, that is, the newly-defined message carries an indication for instructing the PGW to stop buffering the first data; or may be carried in the newly-defined message or the other message provided in this embodiment of the present disclosure, and the third suggested waiting time in the third indication in the newly-defined message or the other message needs to be set to 0 or another similar value representing the meaning, which is not limited in the present disclosure. 
     In this embodiment of the present disclosure, the PGW may learn, according to the third indication received from the SGW, that the UE may need to wait for a period of time before establishing a signaling and data channel to a network, to implement transmission of the first data. Therefore, the PGW may buffer the first data, that is, the downlink data of the UE, for a period of time according to the third indication, and in this way, for a case in which the PGW does not send the downlink data of the UE within a period of time, the SGW may not consider that the case is caused by the fact that an error or exception occurs. Alternatively, the PGW may refuse, according to the third indication, to receive the downlink data of the UE delivered by a network, and in this way, the PGW may not deliver too much downlink data of the UE to the SGW, in order to avoid that a buffer capacity of the SGW is exceeded because the SGW retains too much downlink data of the UE. After the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE changes, the MME may generate the fourth indication according to the subscription data of the UE, the QoS parameter of the bearer used by the UE, or the state of the UE that is obtained after the change, and sends the fourth indication to the SGW, such that the SGW sends the fourth indication to the PGW, in order to instruct the PGW to continue to transmit and receive the first data that needs to be sent to the UE, such that the PGW can process the first data more flexibly. 
     According to the other communications method provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     Embodiment 3 
     As shown in  FIG.  8   , this embodiment of the present disclosure provides an MME  1 , corresponding to the communications method on the MME side provided in the embodiment of the present disclosure. The MME  1  includes: a first acquiring unit  10  configured to acquire information of a UE; a first determining unit  11  configured to determine, according to the information of the UE acquired by the first acquiring unit  10 , whether the UE satisfies a first preset condition; a first generating unit  12  configured such that if the first determining unit  11  determines that the UE satisfies the first preset condition, the first generating unit  12  generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and a first sending unit  13  configured to send the first indication generated by the first generating unit  12  to the SGW, such that the SGW processes the first data according to the first indication. 
     Further the information of the UE acquired by the first acquiring unit  10  may include a type of the UE. Additionally, the first preset condition is that the UE is a power-saving UE, and the first determining unit  11  is configured to determine, according to the type of the UE, whether the UE is the power-saving UE. 
     Further, the information of the UE acquired by the first acquiring unit  10  may include a DRX period of the UE. Additionally, the first preset condition is that the DRX period of the UE is greater than a first preset threshold, and the first determining unit  11  is configured to determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold. 
     Further, the first indication generated by the first generating unit  12  includes a first paging delaying instruction, and is used for instructing the SGW to determine a first time according to the first paging delaying instruction and retain the first data within the first time, or is used for instructing the SGW to discard the first data according to the first paging delaying instruction. Alternatively, the first indication generated by the first generating unit  12  includes a first suggested waiting time, and is used for instructing the SGW to retain the first data within the first suggested waiting time. Alternatively, the first indication generated by the first generating unit  12  includes the first paging delaying instruction and the first suggested waiting time, and is used for instructing the SGW to retain the first data within the first suggested waiting time after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. Alternatively, the first indication generated by the first generating unit  12  includes the first paging delaying instruction and an EPS bearer identifier, and is used for instructing the SGW to determine the first time according to the first paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, or is used for instructing the SGW to discard, according to the first paging delaying instruction, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication generated by the first generating unit  12  includes the first suggested waiting time and the EPS bearer identifier, and is used for instructing the SGW to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication generated by the first generating unit  12  includes the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, and is used for instructing the SGW to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     Further, as shown in  FIG.  9   , the MME  1  further includes: a first receiving unit  14  configured to receive subscription data of the UE from an HSS, where the first acquiring unit  10  is configured to acquire the information of the UE according to the subscription data of the UE received by the first receiving unit  14 . Alternatively, the first receiving unit  14  is configured to receive a NAS message/an AS message from the UE, and the first acquiring unit  10  is configured to acquire the information of the UE according to the NAS message/AS message of the UE received by the first receiving unit  14 . Alternatively, the first acquiring unit  10  is configured to acquire the information of the UE according to a pre-configured QoS parameter of a bearer used by the UE. 
     Further, the first generating unit  12  is further configured to: if the subscription data of the UE, the QoS parameter of the bearer used by the UE, or a state of the UE changes, generate a second indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, where the second indication is used for instructing the SGW to normally transmit and receive the first data. Additionally, the first sending unit  13  is further configured to send the second indication generated by the first generating unit  12  to the SGW, such that the SGW processes the first data according to the second indication. 
     According to the MME provided in this embodiment of the present disclosure, the MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  10   , this embodiment of the present disclosure provides an SGW  2 , corresponding to the communications method on the SGW side provided in the embodiment of the present disclosure. The SGW  2  includes: a second receiving unit  20  configured to receive a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and a second processing unit  21  configured to process the first data according to the first indication received by the second receiving unit  20 . 
     Further, the first indication received by the second receiving unit  20  includes a first paging delaying instruction, and is used for instructing the second processing unit  21  to determine a first time according to the first paging delaying instruction and retain the first data within the first time, or is used for instructing the second processing unit  21  to discard the first data according to the first paging delaying instruction. Alternatively, the first indication received by the second receiving unit  20  includes a first suggested waiting time, and is used for instructing the second processing unit  21  to retain the first data within the first suggested waiting time. Alternatively, the first indication received by the second receiving unit  20  includes the first paging delaying instruction and the first suggested waiting time, and is used for instructing the second processing unit  21  to retain the first data within the first suggested waiting time after the second processing unit  21  determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. Alternatively, the first indication received by the second receiving unit  20  includes the first paging delaying instruction and an EPS bearer identifier, and is used for instructing the second processing unit  21  to determine the first time according to the first paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, or is used for instructing the second processing unit  21  to discard, according to the first paging delaying instruction, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication received by the second receiving unit  20  includes the first suggested waiting time and the EPS bearer identifier, and is used for instructing the second processing unit  21  to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication received by the second receiving unit  20  includes the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, and is used for instructing the second processing unit  21  to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier after the second processing unit  21  determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     Further, the second receiving unit  20  is further configured to receive a second indication from the MME, where the second indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the second indication is used for instructing the SGW to normally transmit and receive the first data. Additionally, the second processing unit  21  is further configured to process the first data according to the second indication received by the second receiving unit  20 . 
     According to the SGW provided in this embodiment of the present disclosure, the SGW receives a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  8   , this embodiment of the present disclosure provides an MME  1 , corresponding to the other communications method on the MME side provided in the embodiment of the present disclosure. The MME  1  includes: a first acquiring unit  10  configured to acquire information of a UE; a first determining unit  11  configured to determine, according to the information of the UE acquired by the first acquiring unit  10 , whether the UE satisfies a first preset condition; a first generating unit  12  configured such that if the first determining unit  11  determines that the UE satisfies the first preset condition, the first generation unit  12  generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and a first sending unit  13  configured to send the third indication generated by the first generating unit  12  to an SGW, such that the SGW sends the third indication to the PGW, and further, the PGW processes the first data according to the third indication. 
     Further, the information of the UE acquired by the first acquiring unit  10  may include a type of the UE. Additionally, the first preset condition is that the UE is a power-saving UE, and the first determining unit  11  is configured to determine, according to the type of the UE, whether the UE is the power-saving UE. 
     Further, the information of the UE acquired by the first acquiring unit  10  may include a DRX period of the UE. Additionally, the first preset condition is that the DRX period of the UE is greater than a first preset threshold, and the first determining unit  11  is configured to determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold. 
     Further, the third indication generated by the first generating unit  12  includes a third paging delaying instruction, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain the first data within the first time, and send the first data to the SGW after the first time. Alternatively, the third indication generated by the first generating unit  12  includes a third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first generating unit  12  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first generating unit  12  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the PGW to determine the first time according to the third paging delaying instruction, retain, within the first time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication generated by the first generating unit  12  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first generating unit  12  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, as shown in  FIG.  9   , the MME  1  further includes: a first receiving unit  14  configured to receive subscription data of the UE from an HSS, where the first acquiring unit  10  is configured to acquire the information of the UE according to the subscription data of the UE received by the first receiving unit  14 . Alternatively, the first receiving unit  14  is configured to receive an NAS message/an AS message from the UE, and the first acquiring unit  10  is configured to acquire the information of the UE according to the NAS message/AS message received by the first receiving unit  14 . Alternatively, the first acquiring unit  10  is configured to acquire the information of the UE according to a pre-configured QoS parameter of a bearer used by the UE. 
     Further, the first generating unit  12  is further configured to: if the subscription data of the UE, the QoS parameter of the bearer used by the UE, or a state of the UE changes, generate a fourth indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, where the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the first sending unit  13  is further configured to send the fourth indication generated by the first generating unit  12  to the SGW, such that the SGW sends the fourth indication to the PGW, and further, the PGW processes the first data according to the fourth indication. 
     According to the MME provided in this embodiment of the present disclosure, the MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  11   , this embodiment of the present disclosure provides an SGW  2 , corresponding to the other communications method on the SGW side provided in the embodiment of the present disclosure. The SGW  2  includes: a second receiving unit  20  configured to receive a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and a second sending unit  22  configured to send the third indication received by the second receiving unit  20  to the PGW, such that the PGW processes the first data according to the third indication. 
     Further, the third indication received by the second receiving unit  20  includes a third paging delaying instruction, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain the first data within the first time, and send the first data to the SGW after the first time. Alternatively, the third indication received by the second receiving unit  20  includes a third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiving unit  20  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiving unit  20  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the PGW to determine the first time according to the third paging delaying instruction, retain, within the first time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication received by the second receiving unit  20  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiving unit  20  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, the second receiving unit  20  is further configured to receive a fourth indication from the MME, where the fourth indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the second sending unit  22  is further configured to send the fourth indication received by the second receiving unit  20  to the PGW, such that the PGW processes the first data according to the fourth indication. 
     According to the SGW provided in this embodiment of the present disclosure, the SGW receives a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, the first data is downlink data of the UE. Additionally, the SGW sends the third indication to the PGW, such that the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW, and further, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  12   , this embodiment of the present disclosure provides a PGW  3 , corresponding to the other communications method on the PGW side provided in the embodiment of the present disclosure. The PGW  3  includes: a third receiving unit  30  configured to receive a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE; and a third processing unit  31  configured to process the first data according to the third indication received by the third receiving unit  30 . 
     Further, the third indication received by the third receiving unit  30  includes a third paging delaying instruction, and is used for instructing the third processing unit  31  to determine a first time according to the third paging delaying instruction and retain the first data within the first time, and is used for instructing a third sending unit  32  to send the first data to the SGW after the first time. Alternatively, the third indication received by the third receiving unit  30  includes a third suggested waiting time, and is used for instructing the third processing unit  31  to retain the first data within the third suggested waiting time, and is used for instructing the third sending unit  32  to send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiving unit  30  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the third processing unit  31  to retain the first data within the third suggested waiting time after the third processing unit  31  determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and is used for instructing the third sending unit  32  to send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiving unit  30  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the third processing unit  31  to determine the first time according to the third paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, and is used for instructing the third sending unit  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication received by the third receiving unit  30  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the third processing unit  31  to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and is used for instructing the third sending unit  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiving unit  30  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the third processing unit  31  to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the third processing unit  31  determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and is used for instructing the third sending unit  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, the third receiving unit  30  is further configured to receive a fourth indication from the SGW, where the fourth indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the fourth indication is sent by the MME to the SGW, and the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the third processing unit  31  is further configured to process the first data according to the fourth indication received by the third receiving unit  30 . 
     According to the PGW provided in this embodiment of the present disclosure, the PGW receives a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, the first data is downlink data of the UE. Additionally, the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW, and further, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     Embodiment 4 
     As shown in  FIG.  13   , this embodiment of the present disclosure provides an MME  1 , corresponding to the communications method on the MME side provided in the embodiment of the present disclosure. The MME  1  includes a first transmitter  15 , a first receiver  16 , a first processor  17 , and a first memory  18 . 
     The first transmitter  15  may be configured to send an uplink signal to a network device such as a gateway. When the MME  1  receives a downlink data notification message from the gateway, the first transmitter  15  may send a downlink data notification acknowledgment message of the downlink data notification message to the gateway. 
     The first receiver  16  may be configured to receive a downlink signal from the network device such as the gateway. When the gateway delivers the downlink data notification message to the MME  1 , the receiver  16  may receive the downlink data notification message from the gateway. 
     The first processor  17  is a control and processing center of the MME  1 , runs a software program stored in the first memory  18 , and invokes and processes data stored in the first memory  18 , to control the MME  1  to transmit and receive a signal, and to implement another function of the MME  1 . 
     The first memory  18  may be configured to store a software program and data, such that the first processor  17  may run the software program stored in the first memory  18 , in order to implement a signal transmitting and receiving function of the MME  1  and another function of the MME  1 . 
     For example, the first processor  17  is configured to: acquire information of a UE, and stores the information of the UE into the first memory  18 ; determine, according to the information of the UE, whether the UE satisfies a first preset condition; if the UE satisfies the first preset condition, generate a first indication; store the first indication into the first memory  18 , where the first indication is used for instructing an SGW to retain first data or discard the first data, and the first data is downlink data of the UE; and instruct the first transmitter  15  to send the first indication to the SGW, such that the SGW processes the first data according to the first indication. 
     Further, the information of the UE acquired by the first processor  17  may include a type of the UE. Additionally, the first preset condition is that the UE is a power-saving UE, and the first processor  17  is configured to determine, according to the type of the UE, whether the UE is the power-saving UE. 
     Further, the information of the UE acquired by the first processor  17  may include a DRX period of the UE. Additionally, the first preset condition is that the DRX period of the UE is greater than a first preset threshold, and the first processor  17  is configured to determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold. 
     Further, the first indication generated by the first processor  17  includes a first paging delaying instruction, and is used for instructing the SGW to determine a first time according to the first paging delaying instruction and retain the first data within the first time, or is used for instructing the SGW to discard the first data according to the first paging delaying instruction. Alternatively, the first indication generated by the first processor  17  includes a first suggested waiting time, and is used for instructing the SGW to retain the first data within the first suggested waiting time. Alternatively, the first indication generated by the first processor  17  includes the first paging delaying instruction and the first suggested waiting time, and is used for instructing the SGW to retain the first data within the first suggested waiting time after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. Alternatively, the first indication generated by the first processor  17  includes the first paging delaying instruction and an EPS bearer identifier, and is used for instructing the SGW to determine the first time according to the first paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, or is used for instructing the SGW to discard, according to the first paging delaying instruction, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication generated by the first processor  17  includes the first suggested waiting time and the EPS bearer identifier, and is used for instructing the SGW to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication generated by the first processor  17  includes the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, and is used for instructing the SGW to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier after the SGW determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     Further, the first receiver  16  is configured to receive subscription data of the UE from an HSS, and the first processor  17  is configured to acquire the information of the UE according to the subscription data of the UE. Alternatively, the first receiver  16  is configured to receive an NAS message/an AS message from the UE, and the first processor  17  is configured to acquire the information of the UE according to the NAS message/AS message of the UE. Alternatively, the first processor  17  is configured to acquire the information of the UE according to a pre-configured QoS parameter of a bearer used by the UE. 
     Further, the first processor  17  is further configured to: if the subscription data of the UE, the QoS parameter of the bearer used by the UE, or a state of the UE changes, generate a second indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change; and store the second indication into the first memory  18 , where the second indication is used for instructing the SGW to normally transmit and receive the first data. Additionally, the first transmitter  15  is further configured to send the second indication stored by the first processor  17  into the first memory  18  to the SGW, such that the SGW processes the first data according to the second indication. 
     According to the MME provided in this embodiment of the present disclosure, the MME acquires information of a UE and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  14   , this embodiment of the present disclosure provides an SGW  2 , corresponding to the communications method on the SGW side provided in the embodiment of the present disclosure. The SGW  2  includes a second transmitter  23 , a second receiver  24 , a second processor  25 , and a second memory  26 . 
     The second transmitter  23  may be configured to send a downlink signal to a network device such as an MME. When the SGW  2  needs to send a downlink data notification message to the MME, the second transmitter  23  may send the downlink data notification message to the MME. 
     The second receiver  24  may be configured to receive an uplink signal from the network device such as the MME. If the SGW  2  delivers the downlink data notification message to the MME, the second receiver  24  may receive a downlink data notification acknowledgment message from the MME, where the downlink data notification acknowledgment message corresponds to the downlink data notification message. 
     The second processor  25  is a control and processing center of the SGW  2 , runs a software program stored in the second memory  26 , and invokes and processes data stored in the second memory  26 , to control the SGW  2  to transmit and receive a signal, and to implement another function of the SGW  2 . 
     The second memory  26  may be configured to store a software program and data, such that the second processor  25  may run the software program stored in the second memory  26 , in order to implement a signal transmitting and receiving function of the SGW  2  and another function of the SGW  2 . 
     For example, the second processor  25  instructs the second receiver  24  to receive a first indication from the MME, and store the first indication into the second memory  26 , where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW  2  to retain first data or discard the first data, and the first data is downlink data of the UE. Additionally, the second processor  25  processes the first data according to the first indication. 
     Further, the first indication received by the second receiver  24  includes a first paging delaying instruction, and is used for instructing the second processor  25  to determine a first time according to the first paging delaying instruction and retain the first data within the first time, or is used for instructing the second processor to discard the first data according to the first paging delaying instruction. Alternatively, the first indication received by the second receiver  24  includes a first suggested waiting time, and is used for instructing the second processor  25  to retain the first data within the first suggested waiting time. Alternatively, the first indication received by the second receiver  24  includes the first paging delaying instruction and the first suggested waiting time, and is used for instructing the second processor  25  to retain the first data within the first suggested waiting time after the second processor  25  determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. Alternatively, the first indication received by the second receiver  24  includes the first paging delaying instruction and an EPS bearer identifier, and is used for instructing the second processor  25  to determine the first time according to the first paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, or is used for instructing the second processor  25  to discard, according to the first paging delaying instruction, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication received by the second receiver  24  includes the first suggested waiting time and the EPS bearer identifier, and is used for instructing the second processor  25  to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier. Alternatively, the first indication received by the second receiver  24  includes the first paging delaying instruction, the first suggested waiting time, and the EPS bearer identifier, and is used for instructing the second processor  25  to retain, within the first suggested waiting time, the first data corresponding to the EPS bearer identifier after the second processor  25  determines, according to the first paging delaying instruction, that the MME needs to delay paging the UE. 
     Further, the second receiver  24  is further configured to receive a second indication from the MME, and the second processor  25  stores the second indication into the second memory  26 , where the second indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the second indication is used for instructing the SGW to normally transmit and receive the first data. Additionally, the second processor  25  is further configured to process the first data according to the second indication, that is, instruct the second receiver  24  and the second transmitter  23  to normally transmit and receive the first data. 
     According to the SGW provided in this embodiment of the present disclosure, the SGW receives a first indication from an MME, where the first indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the first indication is used for instructing the SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  13   , this embodiment of the present disclosure provides an MME  1 , corresponding to the communications method on the MME side provided in the embodiment of the present disclosure. The MME  1  includes a first transmitter  15 , a first receiver  16 , a first processor  17 , and a first memory  18 . 
     The first transmitter  15  may be configured to send an uplink signal to a network device such as a gateway. When the MME  1  receives a downlink data notification message from the gateway, the first transmitter  15  may send a downlink data notification acknowledgment message of the downlink data notification message to the gateway. 
     The first receiver  16  may be configured to receive a downlink signal from the network device such as the gateway. When the gateway delivers the downlink data notification message to the MME  1 , the receiver  16  may receive the downlink data notification message from the gateway. 
     The first processor  17  is a control and processing center of the MME  1 , runs a software program stored in the first memory  18 , and invokes and processes data stored in the first memory  18 , to control the MME  1  to transmit and receive a signal, and to implement another function of the MME  1 . 
     The first memory  18  may be configured to store a software program and data, such that the first processor  17  may run the software program stored in the first memory  18 , in order to implement a signal transmitting and receiving function of the MME  1  and another function of the MME  1 . 
     For example, the first processor  17  acquires information of a UE, and stores the information of the UE into the first memory  18 . Additionally, the first processor  17  is configured to: determine, according to the information of the UE, whether the UE satisfies a first preset condition; if the UE satisfies the first preset condition, generate a third indication; store the third indication into the first memory  18 , where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE; and instruct the first transmitter  15  to send the third indication to the SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. 
     Further, the information of the UE acquired by the first processor  17  may include a type of the UE. Additionally, the first preset condition is that the UE is a power-saving UE, and the first processor  17  is configured to determine, according to the type of the UE, whether the UE is the power-saving UE. 
     Further, the information of the UE acquired by the first processor  17  may include a DRX period of the UE. Additionally, the first preset condition is that the DRX period of the UE is greater than a first preset threshold, and the first processor  17  is configured to determine, according to the DRX period of the UE, whether the DRX period of the UE is greater than the first preset threshold. 
     Further, the third indication generated by the first processor  17  includes a third paging delaying instruction, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain the first data within the first time, and send the first data to the SGW after the first time. Alternatively, the third indication generated by the first processor  17  includes a third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first processor  17  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first processor  17  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the PGW to determine the first time according to the third paging delaying instruction, retain, within the first time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication generated by the first processor  17  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication generated by the first processor  17  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, the first receiver  16  is configured to receive subscription data of the UE from an HSS, and the first processor  17  is configured to acquire the information of the UE according to the subscription data of the UE. Alternatively, the first receiver  16  is configured to receive a NAS message/an AS message from the UE, and the first processor  17  is configured to acquire the information of the UE according to the NAS message/AS message of the UE. Alternatively, the first processor  17  is configured to acquire the information of the UE according to a pre-configured QoS parameter of a bearer used by the UE. 
     Further, the first processor  17  is further configured to: if the subscription data of the UE, the QoS parameter of the bearer used by the UE, or a state of the UE changes, generate a fourth indication according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change; and store the fourth indication into the first memory  18 , where the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the first transmitter  15  is further configured to send the fourth indication to the SGW, such that the SGW sends the fourth indication to the PGW, and the PGW processes the first data according to the fourth indication. 
     According to the MME provided in this embodiment of the present disclosure, the MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  14   , this embodiment of the present disclosure provides an SGW  2 , corresponding to the communications method on the SGW side provided in the embodiment of the present disclosure. The SGW  2  includes a second transmitter  23 , a second receiver  24 , a second processor  25 , and a second memory  26 . 
     The second transmitter  23  may be configured to send a downlink signal to a network device such as an MME, and send an uplink signal to a network device such as a PGW. When the SGW  2  needs to send a downlink data notification message to the MME, the second transmitter  23  may send the downlink data notification message to the MME. 
     The second receiver  24  may be configured to receive an uplink signal from the network device such as the MME, and receive a downlink signal from the network device such as the PGW. If the SGW  2  delivers the downlink data notification message to the MME, the second receiver  24  may receive a downlink data notification acknowledgment message from the MME, where the downlink data notification acknowledgment message corresponds to the downlink data notification message. 
     The second processor  25  is a control and processing center of the SGW  2 , runs a software program stored in the second memory  26 , and invokes and processes data stored in the second memory  26 , to control the SGW  2  to transmit and receive a signal, and to implement another function of the SGW  2 . 
     The second memory  26  may be configured to store a software program and data, such that the second processor  25  may run the software program stored in the second memory  26 , in order to implement a signal transmitting and receiving function of the SGW  2  and another function of the SGW  2 . 
     For example, the second processor  25  instructs the second receiver  24  to receive a third indication from the MME, and store the third indication into the second memory  26 , where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE. Additionally, the second processor  25  instructs the second transmitter  23  to send the third indication to the PGW, such that the PGW processes the first data according to the third indication. 
     The third indication received by the second receiver  24  includes a third paging delaying instruction, and is used for instructing the PGW to determine a first time according to the third paging delaying instruction, retain the first data within the first time, and send the first data to the SGW after the first time. Alternatively, the third indication received by the second receiver  24  includes a third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiver  24  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the PGW to retain the first data within the third suggested waiting time after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiver  24  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the PGW to determine the first time according to the third paging delaying instruction, retain, within the first time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication received by the second receiver  24  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication received by the second receiver  24  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the PGW to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the PGW determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, the second receiver  24  is further configured to receive a fourth indication from the MME, and the second processor  25  stores the fourth indication into the second memory  26 , where the fourth indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the second transmitter  23  is further configured to send the fourth indication to the PGW, such that the PGW processes the first data according to the fourth indication. 
     According to the SGW provided in this embodiment of the present disclosure, the SGW receives a third indication from an MME, where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, the third indication is used for instructing a PGW to retain first data, the first data is downlink data of the UE. Additionally, the SGW sends the third indication to the PGW, such that the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and the PGW does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  15   , this embodiment of the present disclosure provides a PGW  3 , corresponding to the communications method on the PGW side provided in the embodiment of the present disclosure. The PGW  3  includes a third transmitter  32 , a third receiver  33 , a third processor  34 , and a third memory  35 . 
     The third transmitter  32  may be configured to send a downlink signal to a network device such as an SGW. When the PGW  3  needs to send data to the SGW, the third transmitter  32  may send the data to the SGW. 
     The third receiver  33  may be configured to receive an uplink signal from the network device such as the SGW. When the PGW  3  delivers data to the SGW, the third receiver  33  may receive an acknowledgment message from the SGW, where the acknowledgment message corresponds to the data. 
     The third processor  34  is a control and processing center of the PGW  3 , runs a software program stored in the third memory  35 , and invokes and processes data stored in the third memory  35 , to control the PGW  3  to transmit and receive a signal, and to implement another function of the PGW  3 . 
     The third memory  35  may be configured to store a software program and data, such that the third processor  34  may run the software program stored in the third memory  35 , in order to implement a signal transmitting and receiving function of the PGW  3  and another function of the PGW  3 . 
     For example, the third processor  34  instructs the third receiver  33  to receive a third indication from the SGW, and store the third indication into the third memory  35 , where the third indication is generated by the MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, and the first data is downlink data of the UE. Additionally, the third processor  34  processes the first data according to the third indication. 
     Further, the third indication received by the third receiver  33  includes a third paging delaying instruction, and is used for instructing the third processor  34  to determine a first time according to the third paging delaying instruction and retain the first data within the first time, and is used for instructing the third transmitter  32  to send the first data to the SGW after the first time. Alternatively, the third indication received by the third receiver  33  includes a third suggested waiting time, and is used for instructing the third processor  34  to retain the first data within the third suggested waiting time, and is used for instructing the third transmitter  32  to send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiver  33  includes the third paging delaying instruction and the third suggested waiting time, and is used for instructing the third processor  34  to retain the first data within the third suggested waiting time after the third processor  34  determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and is used for instructing the third transmitter  32  to send the first data to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiver  33  includes the third paging delaying instruction and an EPS bearer identifier, and is used for instructing the third processor  34  to determine the first time according to the third paging delaying instruction and retain, within the first time, the first data corresponding to the EPS bearer identifier, and is used for instructing the third transmitter  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the first time. Alternatively, the third indication received by the third receiver  33  includes the third suggested waiting time and the EPS bearer identifier, and is used for instructing the third processor  34  to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier, and is used for instructing the third transmitter  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. Alternatively, the third indication received by the third receiver  33  includes the third paging delaying instruction, the third suggested waiting time, and the EPS bearer identifier, and is used for instructing the third processor  34  to retain, within the third suggested waiting time, the first data corresponding to the EPS bearer identifier after the third processor  34  determines, according to the third paging delaying instruction, that the MME needs to delay paging the UE, and is used for instructing the third transmitter  32  to send the first data corresponding to the EPS bearer identifier to the SGW after the third suggested waiting time. 
     Further, the third receiver  33  is further configured to receive a fourth indication from the SGW, and the third processor  34  stores the fourth indication into the third memory  35 , where the fourth indication is generated, if subscription data of the UE, a QoS parameter of a bearer used by the UE, or a state of the UE changes, by the MME according to subscription data of the UE, a QoS parameter of the bearer used by the UE, or a state of the UE that is obtained after the change, and the fourth indication is sent by the MME to the SGW, and the fourth indication is used for instructing the PGW to normally transmit and receive the first data. Additionally, the third processor  34  is further configured to process the first data according to the fourth indication, that is, instruct the third receiver  33  and the third transmitter  32  to normally transmit and receive the first data. 
     According to the PGW provided in this embodiment of the present disclosure, the PGW receives a third indication from an SGW, where the third indication is generated by an MME when the MME acquires information of a UE and determines, according to the information of the UE, that the UE satisfies a first preset condition, and the third indication is sent by the MME to the SGW, the third indication is used for instructing the PGW to retain first data, the first data is downlink data of the UE. Additionally, the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     Embodiment 5 
     As shown in  FIG.  16   , this embodiment of the present disclosure provides a communications system  4 , corresponding to the communications method provided in the embodiment of the present disclosure. The communications system  4  includes the MME  1  and the SGW  2  provided in the foregoing embodiments. Structures of the MME  1  and the SGW  2  and methods corresponding to the structures have been described in the foregoing embodiments, which are not described herein again. 
     According to the communications system provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a first indication, where the first indication is used for instructing an SGW to retain first data or discard first data, and the first data is downlink data of the UE. Additionally, the MME sends the first indication to the SGW, such that the SGW processes the first data according to the first indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding first indication to the SGW, such that when receiving the downlink data of the UE from a network, the SGW can buffer the downlink data of the UE for a long time according to the first indication. In this way, the SGW may not consider that buffering the downlink data of the UE for a long time is caused by the fact that an error or exception occurs, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     As shown in  FIG.  17   , this embodiment of the present disclosure provides a communications system  4 , corresponding to the other communications method provided in the embodiment of the present disclosure. The communications system  4  includes the MME  1 , the SGW  2 , and the PGW  3  provided in the foregoing embodiments. Structures of the MME  1 , the SGW  2 , and the PGW  3  and methods corresponding to the structures have been described in the foregoing embodiments, which are not described herein again. 
     According to the communications system provided in this embodiment of the present disclosure, an MME acquires information of a UE, and the MME determines, according to the information of the UE, whether the UE satisfies a first preset condition. If the UE satisfies the first preset condition, the MME generates a third indication, where the third indication is used for instructing a PGW to retain first data, and the first data is downlink data of the UE. Additionally, the MME sends the third indication to an SGW, such that the SGW sends the third indication to the PGW, and the PGW processes the first data according to the third indication. Using this solution, if the UE satisfies the first preset condition, the MME sends a corresponding third indication to the SGW, such that the SGW further sends the third indication to the PGW. Thus, when receiving the downlink data of the UE from a network, the PGW can buffer the downlink data of the UE for a long time according to the third indication, and does not send the downlink data to the SGW immediately. In this way, an error or exception may not be caused by the fact that the SGW needs to buffer the downlink data of the UE for a long time, thereby solving the problem in other approaches that, in order to save power, when the MME delays delivering a paging message or the UE uses a long DRX period, an exception may occur in the SGW. 
     It may be understood by a person skilled in the art that, for the purpose of convenient and brief description, division of the foregoing functional modules is used as an example for illustration. In an actual application, the foregoing functions may be allocated to different functional modules and implemented according to a requirement, that is, an inner structure of an apparatus is divided into different functional modules to implement all or some of the functions described above. For a detailed working process of the foregoing system, apparatus, and unit, reference may be made to a corresponding process in the foregoing method embodiments, and details are not described herein again. 
     In the several embodiments provided in the present application, it should be understood that the disclosed system, apparatus, and method may be implemented in other manners. For example, the described apparatus embodiment is merely exemplary. For example, the module or unit division is merely logical function division and may be other division in actual implementation. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not performed. In addition, the displayed or discussed mutual couplings or direct couplings or communication connections may be implemented through some interfaces. The indirect couplings or communication connections between the apparatuses or units may be implemented in electronic, mechanical, or other forms. 
     The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one position, or may be distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the objectives of the solutions of the embodiments. 
     In addition, functional units in the embodiments of the present disclosure may be integrated into one processing unit, or each of the units may exist alone physically, or two or more units are integrated into one unit. The integrated unit may be implemented in a form of hardware, or may be implemented in a form of a software functional unit. 
     When the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, the integrated unit may be stored in a computer-readable storage medium. Based on such an understanding, the technical solutions of the present disclosure essentially, or the part contributing to other approaches, or all or some of the technical solutions may be implemented in a form of a software product. The computer software product is stored in a storage medium and includes several instructions for instructing a computer device (which may be a personal computer, a server, or a network device) or a processor to perform all or some of the steps of the methods described in the embodiments of the present disclosure. The foregoing storage medium includes: any medium that can store program code, such as a Universal Serial Bus (USB) flash drive, a removable hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disc. 
     The foregoing descriptions are merely example implementation manners of the present disclosure, but are not intended to limit the protection scope of the present disclosure. Any variation or replacement readily figured out by a person skilled in the art within the technical scope disclosed in the present disclosure shall fall within the protection scope of the present disclosure. Therefore, the protection scope of the present disclosure shall be subject to the protection scope of the claims.