Network and Management

There are two main LAN transmission or access methods for wire-based networks: Ethernet and token ring. They are defined by the IEEE through the 802 standards committee and Project 802. Ethernet is defined as a LAN standard in the IEEE 802.3 specifications, and token ring is defined through the IEEE 802.5 specifications. Ethernet is now installed in most places on LANs because it has the broadest options for expansion and high-speed networking. However, it is still valuable to understand token ring communications as an alternative to Ethernet and for token ring’s historical significance. A third LAN transmission method, Fiber Distributed Data Interface, is also introduced in this section as a high-speed variation of token ring.

Ethernet transport (the IEEE 802.3 specification) takes advantage of the bus and star topologies. At this writing, Ethernet transmission rates include 10 Mbps, 100 Mbps, 1 Gbps, 10 Gbps,40 Gbps, and 100 Gbps. Ethernet uses a control method known as Carrier Sense Multiple Access with Collision Detection (CSMA/CD). CSMA/CD is an algorithm (computer logic) that transmits and decodes formatted data frames. Using CSMA/CD, the Ethernet sending node encapsulates the frame to prepare it for transmission. All nodes that wish to transmit a frame on the cable are in contention with one another. No single node has priority over another node. The nodes listen for any packet traffic on the cable. If a packet is detected, the non-sending nodes go into “defer” mode.

The Ethernet protocol permits only one node to transmit at a time. Transmission is accomplished by sending a carrier signal. Carrier sense is the process of checking communication media for a specific voltage level indicating the presence of a data-carrying signal. When no signal traffic is detected on the communications medium for a given amount of time, any node is eligible to transmit.

Token Ring

The token ring (IEEE 802.5 specification) transmission method was developed by IBM in the 1970s but is no longer popular compared to Ethernet. Even though token ring is not used in modern LANs, it is still valuable to learn token ring basics to help in understanding the ring technologies used in WANs. Token ring works at the OSI Data Link layer (Layer 2). Data transmission in token ring networks is either 4 or 16 Mbps in older versions and 100 Mbps for fast token ring.

The token ring transport method uses a physical star topology along with the logic of a ring topology. Although each node is connected to a central hub, the packet travels from node to node as though there were no starting or ending point. Each node is joined by using a multi-station access unit (MAU). The MAU is a specialized hub that ensures the packet is transmitted around the ring of computers. Because the packets travel as though in a ring, there are no terminators at the workstations or in the MAU.