|  | 3.1 | Basic LAN Devices
| 3.1.6 | Hubs
The purpose of a hub is to regenerate and retime network signals. This is done at the bit level to a large number of hosts (e.g. 4, 8, or even 24) using a process known as concentration. You will notice that this definition is very similar to the repeater's, that is why a hub is also known as a multi-port repeater. The difference is the number of cables that connect to the device. The reasons for using hubs is to create a central connection point for the wiring media, and an increase in the reliability of the network. The reliability of the network is increased by allowing any single cable to fail without disrupting the entire network. This differs from the bus topology where having one cable fail will disrupt the entire network. Hubs are considered Layer 1 devices because they only regenerate the signal and broadcast it out all of their ports (network connections). There are different classifications of hubs in networking. The first classification is active or passive hubs. Most modern hubs are active; they take energy from a power supply to regenerate network signals. Some hubs are called passive devices because they merely split the signal to multiple users, like using a "Y" cord on a CD player to use more than one set of headphones. Passive hubs do not regenerate bits, so they do not extend a cables length, they only allow two or more hosts to connect to the same cable segment. Another classification of hubs is intelligent and dumb. Intelligent hubs have console ports, which means they can be programmed to manage network traffic. Dumb hubs simply take an incoming networking signal and repeat it to every port without the ability to do any management. The hub's role in a token-ring network is played by a Media Access Unit (MAU). Physically it resembles a hub, but token-ring technology is very different, as you will learn later. In FDDIs, the MAU is called a concentrator. MAUs are also Layer 1 devices. The symbol for a hub is not standardized. You will use the symbol shown, here, throughout this curriculum. For more information about commercially available repeaters, visit:
| Web Links
| Blackbox Network Services
| Micro Warehouse
| Hubs