8.3 The Data Link Layer
8.3.2 The 802 specifications

802.2 Logical Link Control (LLC)

802.2 is the IEEE standard, which defines the LAN-technology-independent Logical Link Control (LLC). LLC manages link control and provides Service Access Points (SAPs) - all in software. LLC adds headers to encapsulated upper layer data to identify which protocols a given frame will carry. It also provides communication between the hardware Media Access Control sublayer and the software implementations of Layer 3.

802.3 Ethernet

802.3 defines Ethernet based on a modification of the original Digital-Intel-Xerox (DIX) Ethernet standard. Specifically, this standard defines the frame format to be used by a variety of specific media and topological implementations of Ethernet. The 802.3 standard also defines the Carrier Sense Multiple Access with Collision Detection (CSMA/CD), which is an algorithm for dealing with a situation where two signals collide on a network. CSMA/CD sets the amount of time each device must wait to send a new frame.

802.5 Token Ring

802.5 defines the "passing" of the token around a network in order to allow each device to transmit data across physical star or logical ring networks. A token is created by the first node, then passed along the network until another device wants to transmit data and grabs the token. The data will flow along the network, past each node, until the destination node sees it and grabs the information. Once the data has been received, the destination device transmits a reply to the source device to indicate that the information was received.