Technology Reference Guide

What is it?
A hub is a device used to concentrate and organize network wiring. There are two basic types of hubs, active and passive. A passive hub is simply a device that allows wiring connections in an orderly way. It requires no power, and does no processing or regeneration of the traffic coming through it. The IBM 8228 MAU (media access unit) is a common example of this type of hub. More common today are active hubs, which contain circuitry that can filter, amplify and control the traffic going through it. Hubs may also contain additional functionality, such as bridging, which separates the traffic local to the hub from the network backbone connecting other hubs and network devices. A hub may also be manageable, which means that it can be monitored and controlled remotely. Ports can be disabled, and traffic through the ports can be monitored.

What does it do?
Active hubs are based on an extension of the network repeater. A repeater is a device that can extend the allowable length of a network cabling system. It does this by accepting network traffic on its input side, and then amplifying the signal on its output. All traffic passes through the repeater, but it comes out as a stronger signal than it goes in, allowing it to travel farther. A hub is a multi-port repeater. Physically, it appears as a box with one input port, from the backbone, and a number of output ports that are typically wired to end-user workstation connections, although servers and other devices can be attached as well. Signals on any port are transmitted to all the other ports.

Although a basic hub provides a way to organize cableplant wiring, it does not segment or organize network traffic in any way. The addition of a bridge module on the input side of the hub can provide some segmentation, since it will only pass traffic that needs to leave the hub, or traffic that needs to get in.

A recent innovation is the concept of the switching hub. A switching hub basically extends the bridging concept above, by bridging the output as well as the input ports on the hub. With this arrangement, traffic from a port will not pass to the hub unless it needs to access a different port than it came in on. If it needs to traverse the hub to reach its destination, it only passes between the two ports it needs, and is isolated from the rest of the ports. This cuts down unnecessary traffic on all network segments attached to the hub, improving the capacity and speed of the network.

Be aware that this discussion covers the basic concept of the hub, and should not be construed as covering the range of configurations and options available on hub products.

How is it used?
Hubs are used in the design and implementation of a coherent and easily managed network cabling system. In a typical design, a company may run cabling from a wallplate in each users cubicle to a central wiring closet on each floor of the building. These cables, known as station drops are each connected to a port on the wiring hub. The hubs on each floor, are then connected to the network backbone, which runs from floor to floor in each wiring closet. This divides the network into logical and physical groupings that simplifies troubleshooting and network growth. Because of the signal boosting performed by the hub, it can also extend the physical scope of the network.

Where do I get more information?
Contact your local CBV Office.

	Technology Reference Guide 2. Hardware I. Hubs