Using the LLC Service Access Points, the LLC provides different services to the users. Generally specified in terms of service primitives, the uppermost layer of the services is the Logical Link Control (LLC) which addresses and controls the data links. It is the main layer of the IEEE 802 Protocol Reference Model providing the flow control, acknowledgement and error recovery.
Logical Link Control forms an essential part of 802.2 specifications that is placed in the Data Link Layer among the MAC layer and the layer 3 protocols. The computer and other devices on the network transmit data using the LLC. There are 3 specific forms of service provided to the LLC User- the Unacknowledged Connectionless Service, the Connection-Oriented Service and the rarely used Acknowledged Connectionless Service.
When the data frames are transmitted from one source to the other without any acknowledgement or connection established between the source and destination the one is said to be using the Unacknowledged Connectionless Service. Error control and Flow control across the interface among the next higher layer and LLC are the functions of this service.
With the Connection-Oriented Service that only supports individual addressing, the data frames are transmitted with established acknowledgment and connection among source and destination machines. Without supporting any multicast or broadcast addressing the services provides a point-to-point link connection among LSAP (Link Service Access Points).
The rarely used Acknowledged Connectionless Service is used to transmit the data frames with acknowledgement but without any connection established between the source and destination machine. It too does not support any multicast or broadcast addressing.
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