HDLC become derive an extensive Layer-2 protocol from him/it sub variations like LAPB or LAPD. LAPB is included the Layer 2 from the CCITT recommendation to X25.
The here presented data (representing Modulo-8) only serve as short overview over the types of LAPB-pakets. For detailierte information, the ISO 7776 only is responsible.

broadly:

    7Eh                                                                                           7Eh

Types:

This overview treats exclusively the most frequently use variant in Germany at the representing modulo-8.

" set asyncronous balanced mode "

" disconnected mode "

" unnumbered acknowledgment "

" disconnect "

" frame reject "

" reject "

" receive not ready "

" receive ready "

" data-frame "

In the standard to LAPB, costly State-diagrams are represented to the respective transitions and mistake treatments. Getting a variation about a space-saving and simultaneously good to in the habit of state/change-mechanism is the implementation by means of a State-Table. The current status is used as line and the received Paket-Typ on that occasion as columns. The there deposited byte returns the necessary reaction and the low Nibble the new State in the upper Nibble. There sufficiently exceptions exists, however even further evaluations are around necessary about such a table, sees ISO 7776.