A method for transmitting downlink, DL, data in a wireless communication system, the method performed by a packet data network, PDN, gateway, P-GW, and comprising: receiving DL data in which an Internet protocol, IP, header including an IP address of a user equipment, UE, has been encapsulated from an application server; removing the IP header from the DL data; determining one of a plurality of groups to which the UE belongs based on the IP address; generating revised DL data by incorporating an identifier of the UE into the received DL data to identify the UE in the one of the plurality of groups; updating a group context for the UE when an evolved-NodeB, eNB, serving the UE changes; and transmitting the revised DL data to a serving gateway, S-GW, through a group bearer configured for the one of the plurality of groups in order to transmit the revised DL data to the UE, wherein the IP header is not incorporated into the revised DL data when the DL data is for a non-IP PDN connection, wherein the IP header is incorporated into the revised DL data when the DL data is for an IP PDN connection, wherein a different path is configured for each group bearer from the P-GW to the UE, wherein all UEs belonging to a same evolved-NodeB, eNB, are configured to a same group, wherein a tracking area update, TAU, procedure is performed when the eNB serving the UE changes, wherein a dedicated radio resource pool is configured for each of the plurality of groups, wherein a resource for transmitting uplink data is arbitrarily selected from the dedicated radio resource pool configured for a group to which the UE belongs, and wherein updating the group context comprises: receiving, from a serving gateway, a group context updating request including an in-group UE ID for identifying the UE in a group to which the UE belongs and a group ID for identifying a group bearer; checking whether the group context of the group to which the UE belongs has been generated; updating UE information in the group context; and transmitting a group context updating response message to the serving gateway. receiving DL data in which an Internet protocol, IP, header including an IP address of a user equipment, UE, has been encapsulated from an application server; removing the IP header from the DL data; determining one of a plurality of groups to which the UE belongs based on the IP address; generating revised DL data by incorporating an identifier of the UE into the received DL data to identify the UE in the one of the plurality of groups; updating a group context for the UE when an evolved-NodeB, eNB, serving the UE changes; and transmitting the revised DL data to a serving gateway, S-GW, through a group bearer configured for the one of the plurality of groups in order to transmit the revised DL data to the UE, wherein the IP header is not incorporated into the revised DL data when the DL data is for a non-IP PDN connection, wherein the IP header is incorporated into the revised DL data when the DL data is for an IP PDN connection, wherein a different path is configured for each group bearer from the P-GW to the UE, wherein all UEs belonging to a same evolved-NodeB, eNB, are configured to a same group, wherein a tracking area update, TAU, procedure is performed when the eNB serving the UE changes, wherein a dedicated radio resource pool is configured for each of the plurality of groups, wherein a resource for transmitting uplink data is arbitrarily selected from the dedicated radio resource pool configured for a group to which the UE belongs, and wherein updating the group context comprises: receiving, from a serving gateway, a group context updating request including an in-group UE ID for identifying the UE in a group to which the UE belongs and a group ID for identifying a group bearer; checking whether the group context of the group to which the UE belongs has been generated; updating UE information in the group context; and transmitting a group context updating response message to the serving gateway. receiving, from a serving gateway, a group context updating request including an in-group UE ID for identifying the UE in a group to which the UE belongs and a group ID for identifying a group bearer; checking whether the group context of the group to which the UE belongs has been generated; updating UE information in the group context; and transmitting a group context updating response message to the serving gateway.