Plural packet data units are encapsulated into a datagram of a user datagram protocol. Each of the plural packet data units includes a respective header of a tunneling protocol and a respective user data packet. Each of the headers indicates a length of the respective packet data unit. The plural packet data units include a first packet data unit and are arranged in the datagram in an order starting with the first packet data unit. It is informed, by at least the header of the first packet data, that the encapsulating encapsulates the plural packet data units into the datagram.