Hi Aida,
Universal Datagram Protocol (UDP) is a packet-based protocol. You can construct a packet from Simulink data types such as double, int8, int32, uint8, or a combination of these data types. The Simulink Real-Time block library provides blocks for combining various signals into one packet (packing), and then transmitting it. It also provides blocks for splitting a packet (unpacking) into its component signals that can then be used in a Simulink model. That means that the receiving end must know the scructure of the transmitted packet in order to reconstruct the original signal from it correctly.
Best,
Dimitri