DSS1 LAYER2 - The LAPD frame structure
This frame is encapsulated into a HDLC frame.
HDLC
MSB | LSB Order of bit transmission:
bit: 8 7 6 5| 4 3 2 1 The bit 1 is the first bit to be transmitted.
+----------|-----------+
octet | Address |
2 |(high order octet) |
+----------------------+
octet | Address |
3 |(low order octet) |
+----------------------+
octet | Control Base frame formats:
4 | I-frame ,S-frame ,U-frame
+----------------------+
octet | Control |
5 | |
+- - - - - - - - - - - +
. | Information | max. 260 octet
. | |
+----------|-----------+
FCS
+----------------------+
octet | FCS (first octet) |
N-2| |
+----------------------+
octet | FCS (second octet)|
N-1| |
+----------------------+
octet | flag |
N |0 1 1 1 1 1 1 0|
+----------------------+