Eu suspeito de um erro de roteamento. Execute um wireshark para garantir que o pacote UDP seja recebido. Como eu vi que está em uma WAN, o roteador geralmente não permite os pacotes.
1.5 Prerequisites/Preconditions
The protocol endpoints require UDP connectivity to be established. The network path between the endpoints should allow the transfer of UDP datagrams in both directions.
The prerequisites for this protocol are identical to those for the UDP protocol.
1.3.2.1
UDP Connection Initialization In this phase, both endpoints are initialized with mutually agreeable parameters for the connection. The terminal client initiates the connection by sending a SYN datagram. The terminal client also determines the mode of operation, RDP-UDP-R or RDP-UDP-L, as described in section 1.3.1. The terminal server responds with a datagram with the SYN flag set, along with an ACK flag, to acknowledge the receipt of the SYN datagram. The terminal client acknowledges the SYN datagram by sending an ACK. The terminal client can append the Coded Packets along with the ACK datagram. This datagram indicates that a connection has been set up and data can be exchanged. All datagrams in this phase – the SYN, SYN+ACK, and ACK – are delivered reliably by using persistent retransmits, irrespective of the mode that the transport is operating in.