In wireless communications, bit errors are very common. However, Ethernet frames lacking an EtherType have no LLC identifier in the Ethernet header, and, instead, use an IEEE 802.2 LLC header after the Ethernet header to provide the protocol multiplexing function. Instead, retransmissions rely on higher layer protocols.Īs the EtherType in an Ethernet frame using Ethernet II framing is used to multiplex different protocols on top of the Ethernet MAC header it can be seen as an LLC identifier. Since bit errors are very rare in wired networks, Ethernet does not provide flow control or automatic repeat request (ARQ), meaning that incorrect packets are detected but only cancelled, not retransmitted (except in case of collisions detected by the CSMA/CD MAC layer protocol).
IEEE 802.2 is also used in some non-IEEE 802 networks such as FDDI. The IEEE 802.2 standard specifies the LLC sublayer for all IEEE 802 local area networks, such as IEEE 802.3/ Ethernet (when Ethernet II frame format is not used), IEEE 802.5, and IEEE 802.11. This extensive handshaking between the nodes made the networks slow.
For these protocol stacks only the multiplexing capabilities of the LLC sublayer are used.Īpplication examples X.25 and LAPB Īn LLC sublayer was a key component in early packet switching networks such as X.25 networks with the LAPB data link layer protocol, where flow control and error management were carried out in a node-to-node fashion, meaning that if an error was detected in a frame, the frame was retransmitted from one switch to next instead. re-transmission is done from the original source to the final destination, rather than on individual physical segments. These higher layer protocols work in an end-to-end fashion, i.e. In these cases flow control and error management are taken care of by a transport layer protocol such as TCP or by some application layer protocol. However, most protocol stacks running atop 802.2 do not use LLC sublayer flow control and error management. The flow control and error management capabilities of the LLC sublayer are used by protocols such as the NetBIOS Frames protocol.
It can also provide node-to-node flow control and error management. The LLC sublayer is primarily concerned with multiplexing protocols transmitted over the MAC layer (when transmitting) and demultiplexing them (when receiving).
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