A session management function (SMF) sends, to an access and mobility management function (AMF), a first message for user plane activation of a wireless device. The first message comprises an identifier of a packet data unit session of the wireless device. A second message is received from the AMF and in response to the wireless device being unreachable. The second message is used to determine an extended buffering time. A third message is sent to a user plane function (UPF). The third message comprises the extended buffering time and indicates buffer downlink data of the wireless device.