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| +----------------------+