Hamid-World

A Guide to Ethernet Components and Terminology

The power of an Ethernet LAN (Local Area Network) is tremendous when applied to a factory floor or other industrial application. However, to take full advantage of its features, it requires more than simple wire connections from one device to another. Following are descriptions and explanations of some of the infrastructure devices that can make your Ethernet LAN come alive.

Unmanaged Ethernet switches are a plug and play installation. Switches increase the number of nodes and the length of the LAN. They are designed to divide the network into separate collision domains. This reduces overall traffic on a LAN, improving communication speed and reducing errors.

Switches route communication to the desired end device instead of broadcasting the communication to everyone connected to the LAN. This is accomplished by the switch’s ability to set up a table of device addresses connected to each leg of the switch. With this information the switch knows where to send each Ethernet packet once it is received.

Managed Ethernet Switches allow advanced control of your LAN. They usually include software to configure your network and diagnostic ports to monitor LAN traffic. If communications fail, most managed switches will alert the manager via e-mail or by closing a relay to trigger an audible signal or flash a light. Another feature available on managed switches is QoS (Quality of Service) programming which prioritizes messages ensuring important data receives the highest priority on the LAN segment.

Ethernet Hubs are a simple way to increase the number of nodes, extend network distances while introducing the smallest amount of latency. Hubs don’t examine the Ethernet packets for destination information so they deliver
the packets even more quickly than a switch. All messages received by the hub are sent out on all legs to all the connected devices. Installation is a plug and play operation.

Media Converters change Ethernet twisted pair copper wires into fiber optic signals. Fiber optic is often preferable because it is impervious to interference that can disrupt the signals being carried by copper. Because fiber can extend the distance of a network up to 2 km in each segment, media converters can also increase the range of a network.

10BASE-T - 10 Mbps Ethernet communications over Category 3 or better cable.

100BASE-TX - 100 Mbps Fast Ethernet communications over Category 5 or better cable.

10BASE-FL - 10 Mbps Ethernet transmitted over fiber optic cable.

100BASE-FX - 100 Mbps Fast Ethernet transmitted over fiber optic cable.

Auto-negotiation - A protocol defined in the Ethernet standard that allows devices at either end of a link segment to advertise and negotiate modes of operation such as link speed (10 or 100 Mbps), half or full-duplex operation and full-duplex flow control.

MDI - Medium Dependent Interface. The name for the connector used to make a physical and electrical connection between a transceiver and a media segment. For example, the RJ45 style connector is the MDI for 10BASE-T and 100BASE-TX.

MDI-X - An MDI port on a hub or media converter with an internal crossover function. A “straight-through” cable can be used to connect a station to this port since the signal crossover is performed inside the port.

Quality of Service (QoS) - Some switches support QoS (per 802.1p and 802.1Q standards) wherein tagged messages can be assigned one of eight levels of priority. QoS can be important where time-critical applications can be affected by data delays.

VLAN - Virtual Local Area Network. A LAN that maps stations on a basis other than location — such as by department, user type or application. Managing traffic, workstations and bandwidth can be easier with a VLAN.
This improves network efficiency.

Structured Cabling — Nothing in Ethernet is left to chance. A set of cabling standards for design, installation, performance and testing provides a “structure” for Ethernet. (Refer to EIA/TIA 568 and ISO11801)