IEEE LAN STANDARD

IEEE LAN Standards

Institute of Electrical and Electronic Engineers (IEEE) has published a set of standards for LANs. The standards are collectively known as the IEEE 802.x standards. These standards have gained industry acceptance in the development and implementation of LANs.

The commonly used IEEE 802.x standards for LANs are:

1. IEEE 802.1
2. IEEE 802.2
3. IEEE 802.3
4. IEEE 802.4
5. IEEE 802.5

IEEE 802.1

The IEEE 802.1 LAN standard provides information about the prerequisites for the interface of LAN standards. This standard is also known as the Higher Layer Interface (HILI).
An interface is a set of services that a layer offers to the layer above it in the protocol suite.

IEEE 802.2

The IEEE 802.2 LAN standard is a part of the Logical Link Control (LLC) sublayer of the Data Link layer. LLC compensates for the difference between the various 802 networks by providing a single format and interface to the Network layer.

IEEE 802.3

The IEEE 802.3 LAN standard is used for 1-persistent Carrier Sense Multiple Access/ Collision Detection (CSMA/CD) LAN, which is commonly known as Ethernet. Using the CSMA protocol, a node transmits data packets when it finds the channel or the transmission media idle. Due to this, it is known as 1-persistent CSMA.

If the channel is free, the node transmits data; otherwise, the node waits for it to become idle. If there is a collision in the channel, all nodes terminate their transmission, wait for a random time, and retransmit the data.
The IEEE 802.3 LAN standard falls under the MAC sublayer of the Data Link layer and the OSI Physical layer.

IEEE 802.4

The IEEE 802.4 LAN standard, which is also known as the token bus, was developed to avoid collisions on a network.

The token bus comprises of nodes, which are physically arranged linearly but logically organized to form a ring. Each node on the ring knows the addresses of the nodes to its immediate left and right. The following figure shows a token bus.

Token Bus

The token bus is based on a principle of a calculated wait period for each node in the ring. If the token bus takes time t for each node to transmit a frame and there are y nodes in the ring, the wait period for each node would be at most t*y. Each node in the ring holds the token for an equal time, transmits its frames within that period, and then passes the token to its neighbor.

NB: A token is a special control frame required by a node to send the frames on the logical ring. A control frame carries the administrative information responsible for maintaining the ring or delivering data from the source to the destination.

IEEE 802.5

The IEEE 802.5 LAN standard is also known as the Token Ring. The standard defines the specification for ring networks.
When the ring is initially set up, all the nodes are idle and the token circulates in the ring. When a node needs to transmit data frames to the ring, it would need to acquire the token and remove it from the ring. There is only one token traversing the ring and only the token holder can transmit its frames to the ring.