Receiving a connection establishment request message sent by a user equipment; establishing a signaling connection with the user equipment according to the connection establishment request message; and transmitting a user plane IP data packet through the signaling connection. After a signaling connection is established between a UE in an idle state and a mobility management device, an uplink user plane IP data packet or a downlink user plane IP data packet, is directly transmitted between the UE and the network side through the signaling connection, with no need to specifically establish (recover) an RAB between the UE and an S-GW, which can save the signaling overhead, thus reducing the network load and lowering the operating cost of an operator.