An apparatus (105, 500) comprising: a transceiver configured to communicate with a mobile communication network (140, 210) via a first access network (120, 220) and a second access network (130, 230); and a processor that is configured to: establish a multi-access data connection with the mobile communication network (140, 210) capable of communicating Protocol Data Units, "PDUs", over the first access network (120, 220) and the second access network (130, 230); establish a measurement session via the multi-access data connection; send uplink PDUs over the multi-access data connection; store a first set of parameters for each PDU sent over the multi-access data connection, the first set of parameters comprising a PDU identity "PDU ID", an access type, and a transmit time for each PDU sent on the multi-access data connection; receive a first message via the measurement session, the first message including the PDU identity of a PDU sent over the multi-access data connection; calculate a Round Trip Time, "RTT", value based on the first message and the first set of parameters; and determine to which of the first (120, 220) and second (130, 230) access networks subsequent PDUs of the multi-access data connection are to be sent, said determination being based on the calculated RTT value and a set of provisioned traffic steering rules; wherein the PDU ID is a unique identifier that distinguishes the PDU over all other PDUs transmitted by the apparatus (105, 500) within a certain time window and is derived from header information or from one of: hashing at least a portion of data in the PDU; and generating a checksum value from at least a portion of the data. a transceiver configured to communicate with a mobile communication network (140, 210) via a first access network (120, 220) and a second access network (130, 230); and a processor that is configured to: establish a multi-access data connection with the mobile communication network (140, 210) capable of communicating Protocol Data Units, "PDUs", over the first access network (120, 220) and the second access network (130, 230); establish a measurement session via the multi-access data connection; send uplink PDUs over the multi-access data connection; store a first set of parameters for each PDU sent over the multi-access data connection, the first set of parameters comprising a PDU identity "PDU ID", an access type, and a transmit time for each PDU sent on the multi-access data connection; receive a first message via the measurement session, the first message including the PDU identity of a PDU sent over the multi-access data connection; calculate a Round Trip Time, "RTT", value based on the first message and the first set of parameters; and determine to which of the first (120, 220) and second (130, 230) access networks subsequent PDUs of the multi-access data connection are to be sent, said determination being based on the calculated RTT value and a set of provisioned traffic steering rules; wherein the PDU ID is a unique identifier that distinguishes the PDU over all other PDUs transmitted by the apparatus (105, 500) within a certain time window and is derived from header information or from one of: hashing at least a portion of data in the PDU; and generating a checksum value from at least a portion of the data. establish a multi-access data connection with the mobile communication network (140, 210) capable of communicating Protocol Data Units, "PDUs", over the first access network (120, 220) and the second access network (130, 230); establish a measurement session via the multi-access data connection; send uplink PDUs over the multi-access data connection; store a first set of parameters for each PDU sent over the multi-access data connection, the first set of parameters comprising a PDU identity "PDU ID", an access type, and a transmit time for each PDU sent on the multi-access data connection; receive a first message via the measurement session, the first message including the PDU identity of a PDU sent over the multi-access data connection; calculate a Round Trip Time, "RTT", value based on the first message and the first set of parameters; and determine to which of the first (120, 220) and second (130, 230) access networks subsequent PDUs of the multi-access data connection are to be sent, said determination being based on the calculated RTT value and a set of provisioned traffic steering rules; wherein the PDU ID is a unique identifier that distinguishes the PDU over all other PDUs transmitted by the apparatus (105, 500) within a certain time window and is derived from header information or from one of: hashing at least a portion of data in the PDU; and generating a checksum value from at least a portion of the data.