Intrepid Control Systems RAD-Star User Manual page 25

Wrapper Header and RAD-Star Header Formats
The formats of the wrapper header and RAD-Star header are illustrated in Figure 20.
6
Wrapper
Destination Address
Figure 20: Wrapper Header / RAD-Star Header Format.
The wrapper header has the standard three header fields found in all Ethernet frames, which
are assigned the following values:
• Wrapper Destination Address (6 Bytes): Always set to the Ethernet broadcast MAC
address, FF:FF:FF:FF:FF:FF.
• Wrapper Source Address (6 Bytes): Set to the Source Address of the original frame.
• Wrapper Ethertype (2 Bytes): Set to 0xBEEF, a special value that indicates to
software such as Vehicle Spy that the message is a wrapped frame.
Here are the fields in the RAD-Star header and how their values are used:
• Frame Length (2 Bytes): Carries the length of the original frame.
• Split Data (1 Byte): Special information used to control splitting and reassembling large
frames, when necessary, as described above. This field has three subfields:
• First Flag: Set to 1 for the first (or only) part of a complete message; 0 otherwise.
• Last Flag: Set to 1 for the last (or only) part of a complete message; 0 otherwise.
• Identifier: A number generated by the RAD-Star and placed in both pieces of a split
frame to aid in reassembly by the receiving device.
• Serial Number: Carries the serial number of the RAD-Star that generated the frame.
• Timestamp: The hardware timestamp generated by the RAD-Star when the original
frame was received.
Version 1.2 - June 1, 2016
RAD-Star User's Guide
6
Wrapper Wrapper
Source Address Ethertype
First
Flag
1 bit
22
2 2 1
Frame
Split
Serial Number
Length
Data
Last
Identifier
Flag
1 bit 6 bits
© 2015-2016 Intrepid Control Systems, Inc.
3 4
Timestamp