A WTRU may initiate access for a PDU session over multiple access networks. The WTRU may register with two or more access networks. For example, the WTRU may register with a 3GPP access network (e.g., LTE Advanced) and a non-3GPP access network (e.g., Wi-Fi). The WTRU may determine to request a multi-access PDU session for a (e.g., at least one) PDU session. A multi-access PDU session may correspond to a PDU session where the WTRU communicates one or more PDUs associated with the PDU session over the 3GPP access network and one or more PDUs associated with the PDU session over the non-3GPP access network. The WTRU may receive a confirmation message indicating that a multi-access PDU session has been established. The WTRU may send uplink data over the 3GPP access network and the non-3GPP access network, e.g., in accordance with the established multi-access PDU session.