An apparatus (135, 500) comprising: a first interface that is configured to communicate with control-plane functions in a mobile core network; a second interface that is configured to communicate with a remote unit over a non-3GPP, third Generation Partnership, access network; and a processor that is configured to: receive a request via the first interface to establish access resources for enabling data communication between the remote unit and the mobile core network via a data connection, wherein the data connection supports a plurality of quality of service, QoS, flows, and the request includes a first indicator that requests round trip time, RTT, measurements using a first QoS flow; transmit a first message to the remote unit via the second interface and using the first QoS flow of the data connection, wherein the first message includes a first encapsulation header comprising an echo request indication; receive a second message via the second interface, wherein the second message includes a second encapsulation header comprising an echo response indication; and measure the RTT for the first QoS flow of the data connection using the echo response indication, wherein the processor is further configured to: receive a third message from the remote unit via the second interface by using the first QoS flow of the data connection, wherein the third message includes the first encapsulation header comprising a second echo request indication; and transmit a fourth message via the second interface, wherein the fourth message includes the second encapsulation header comprising a second echo response indication, wherein the second echo response indication is for use by the remote unit to measure the RTT for the first QoS flow of the data connection. a first interface that is configured to communicate with control-plane functions in a mobile core network; a second interface that is configured to communicate with a remote unit over a non-3GPP, third Generation Partnership, access network; and a processor that is configured to: receive a request via the first interface to establish access resources for enabling data communication between the remote unit and the mobile core network via a data connection, wherein the data connection supports a plurality of quality of service, QoS, flows, and the request includes a first indicator that requests round trip time, RTT, measurements using a first QoS flow; transmit a first message to the remote unit via the second interface and using the first QoS flow of the data connection, wherein the first message includes a first encapsulation header comprising an echo request indication; receive a second message via the second interface, wherein the second message includes a second encapsulation header comprising an echo response indication; and measure the RTT for the first QoS flow of the data connection using the echo response indication, wherein the processor is further configured to: receive a third message from the remote unit via the second interface by using the first QoS flow of the data connection, wherein the third message includes the first encapsulation header comprising a second echo request indication; and transmit a fourth message via the second interface, wherein the fourth message includes the second encapsulation header comprising a second echo response indication, wherein the second echo response indication is for use by the remote unit to measure the RTT for the first QoS flow of the data connection. receive a request via the first interface to establish access resources for enabling data communication between the remote unit and the mobile core network via a data connection, wherein the data connection supports a plurality of quality of service, QoS, flows, and the request includes a first indicator that requests round trip time, RTT, measurements using a first QoS flow; transmit a first message to the remote unit via the second interface and using the first QoS flow of the data connection, wherein the first message includes a first encapsulation header comprising an echo request indication; receive a second message via the second interface, wherein the second message includes a second encapsulation header comprising an echo response indication; and measure the RTT for the first QoS flow of the data connection using the echo response indication, wherein the processor is further configured to: receive a third message from the remote unit via the second interface by using the first QoS flow of the data connection, wherein the third message includes the first encapsulation header comprising a second echo request indication; and transmit a fourth message via the second interface, wherein the fourth message includes the second encapsulation header comprising a second echo response indication, wherein the second echo response indication is for use by the remote unit to measure the RTT for the first QoS flow of the data connection. receive a third message from the remote unit via the second interface by using the first QoS flow of the data connection, wherein the third message includes the first encapsulation header comprising a second echo request indication; and transmit a fourth message via the second interface, wherein the fourth message includes the second encapsulation header comprising a second echo response indication, wherein the second echo response indication is for use by the remote unit to measure the RTT for the first QoS flow of the data connection.