Logical Link Control

Logical Link Control (LLC ) is the name for a network protocol of telecommunications which has been standardized by the Institute of Electrical and Electronics Engineers as IEEE 802.2. Objective of the Protocol is the transparency of different inserted at the MAC level practices on media allocation. It offers an unacknowledged, connectionless service (LLC 1), a connection-oriented service (LLC 2), as well as a confirmed connectionless service (LLC 3). LLC is assigned to layer 2 of the OSI model. Also as the LLC sublayer is referred to, on which the protocol operates. Therefore LLC is sometimes also called layer 2b and thus, together with the MAC layer (2a ), the data link layer (2). It distributes incoming data, by forwarding them to the appropriate instance protocols of OSI layer 3. Data 3 sends the OSI layer for transmission be disclosed by LLC to the MAC layer.

LLC structure

The Protocol LLC adds a given data packet from a parent layer ( usually the OSI layer 3 " network layer " ) two each 8 bits wide flag called DSAP ( Destination Service Access Point: entry address of the recipient ) and SSAP ( Source Service Access Point: entry point of the sender ) added. In addition, an 8 or 16 bit large field ( Control) exists with control information for auxiliary functions such as data flow control.

The LLC protocol is modeled on the bit-oriented HDLC protocol. However LLC only uses the Asynchronous Balanced Mode (ABM ), so each station can be primary station.

LLC frame types

LLC - classes

Individual stations can offer more than one type of service. Classes of service are combinations of available types of services.

• Network protocol (data link layer )