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In the IEEE 802 reference model of computer networking, the logical link control (LLC) data communication protocol layer is the upper sublayer of the data link layer (layer 2) of the seven-layer OSI model. The LLC sublayer acts as an interface between the medium access control (MAC) sublayer and the network layer.
The MAC sublayer and the logical link control (LLC) sublayer together make up the data link layer. The LLC provides flow control and multiplexing for the logical link (i.e. EtherType, 802.1Q VLAN tag etc), while the MAC provides flow control and multiplexing for the transmission medium. These two sublayers together correspond to layer 2 of the ...
The LLC header includes two eight-bit address fields, called service access points (SAPs) in OSI terminology; when both source and destination SAP are set to the value 0xAA, the LLC header is followed by a SNAP header. The SNAP header allows EtherType values to be used with all IEEE 802 protocols, as well as supporting private protocol ID spaces.
IEEE 802.2 is the original name of the ISO/IEC 8802-2 standard which defines logical link control (LLC) as the upper portion of the data link layer of the OSI Model. [1] The original standard developed by the Institute of Electrical and Electronics Engineers (IEEE) in collaboration with the American National Standards Institute (ANSI) was adopted by the International Organization for ...
The services and protocols specified in IEEE 802 map to the lower two layers (data link and physical) of the seven-layer Open Systems Interconnection (OSI) networking reference model. IEEE 802 divides the OSI data link layer into two sub-layers: logical link control (LLC) and medium access control (MAC), as follows: Data link layer. LLC sublayer
The OSI model uses a Service Access Point (SAP) to define the communication between layers (like Network, Transport, Session, and the other layers of the seven-layer model), that is to identify which protocol should process an incoming message. Within a given layer, programs can exchange data by a mutually agreed-upon protocol mechanism.
A simple example of how this works using metadata is transmitting the word "HELLO", by encoding each letter as its position in the alphabet. Thus, the letter A is coded as 1, B as 2, and so on as shown in the table on the right. Adding up the resulting numbers yields 8 + 5 + 12 + 12 + 15 = 52, and 5 + 2 = 7 calculates the metadata.
A historical example of this hybrid situation is the DECnet protocol, where the universal MAC address (with Digital Equipment Corporation's OUI AA-00-04) is administered locally. The DECnet software sets the last three bytes of the complete MAC address to 00-XX-YY (so that the full MAC address is AA-00-04-00-XX-YY ), where XX-YY reflects the ...