TRDP is used to exchange PD (process data) and MD (message data) on the ETB/ECN. TRDP is IP-based and operates above the TCP/UDP transport layer. The protocol stack is as follows:
TRDP uses UDP or TCP to transmit data:
• Process Data uses UDP
• Message Data can use either UDP or TCP, which is selected by the user. When the length of Message Data (Max: 64K bytes) exceeds the maximum MTU (approximately 1500 bytes), the message needs to be transmitted in segments, and TCP can be used
The port numbers used by TRDP
|
Protocol |
Destination Port |
|
Process Data |
20548 |
|
Message Data (UDP) |
20550 |
|
Message Data (TCP) |
20550 |
The ComId is carried in the PDU header, and the ComId is the unique identifier of the user data in the TRDP PDU.
The ComId + the source IP is the unique identifier of the TRDP message in the train.
The ComId is set to 0 in the following scenarios:
• PDUs with unspecified user data
• Acknowledgment messages for Message Data
• Error messages for Message Data
The ComId is of the UINT32 type, among which 1-999 are reserved for special purposes. When users define their own ComId, they should not use the reserved ComId.
