RAD-Star User’s Guide
22
© 2015-2016 Intrepid Control Systems, Inc.
Version 1.2 - June 1, 2016
Wrapper Header and RAD-Star Header Formats
The formats of the wrapper header and RAD-Star header are illustrated in Figure 20.
6 bits
1 bit
1 bit
Wrapper
Destination Address
Wrapper
Source Address
Wrapper
Ethertype
6
6
2
Frame
Length
Serial Number
Timestamp
2
1
3
4
Split
Data
First
Flag
Last
Flag
Identifier
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.
