A data transmission method, comprising: receiving, by a core network element, a first message sent by a first terminal device, wherein the first message is used to request to establish a first protocol data unit PDU session; determining, by the core network element based on group information corresponding to the first terminal device, that the first terminal device needs to perform local routing, wherein the group information comprises a group identifier ID and a group member list; obtaining, by the core network element, binding information, wherein the binding information comprises the group ID and session information of the first PDU session, and the session information comprises one or more of a session ID, a tunnel endpoint identifier TEID, and a flow identifier QFIs of the first PDU session; and sending, by the core network element, the binding information to a first access network node, characterized in that the first access node comprises integrated access and backhaul, IAB, donor node functionality; wherein the method further comprises: receiving, by the core network element, a group establishment request sent by an application function AF network element, wherein the group establishment request comprises the group ID; and storing, by the core network element, the group ID in the group information; wherein the group establishment request further comprises a local switching indication, and the method further comprises: sending, by the core network element, the local switching indication to the first access network node. receiving, by a core network element, a first message sent by a first terminal device, wherein the first message is used to request to establish a first protocol data unit PDU session; determining, by the core network element based on group information corresponding to the first terminal device, that the first terminal device needs to perform local routing, wherein the group information comprises a group identifier ID and a group member list; obtaining, by the core network element, binding information, wherein the binding information comprises the group ID and session information of the first PDU session, and the session information comprises one or more of a session ID, a tunnel endpoint identifier TEID, and a flow identifier QFIs of the first PDU session; and sending, by the core network element, the binding information to a first access network node, characterized in that the first access node comprises integrated access and backhaul, IAB, donor node functionality; wherein the method further comprises: receiving, by the core network element, a group establishment request sent by an application function AF network element, wherein the group establishment request comprises the group ID; and storing, by the core network element, the group ID in the group information; wherein the group establishment request further comprises a local switching indication, and the method further comprises: sending, by the core network element, the local switching indication to the first access network node. receiving, by the core network element, a group establishment request sent by an application function AF network element, wherein the group establishment request comprises the group ID; and storing, by the core network element, the group ID in the group information; wherein the group establishment request further comprises a local switching indication, and the method further comprises: sending, by the core network element, the local switching indication to the first access network node.