Network Devices - Ethernet hub

A LAN (Local Area Network) comprises of different communication devices such as

• Hubs
• Bridges
• Switches
• Routers

Ethernet Hubs:
Ethernet Hubs are centralized device in a star topology. A hub takes incoming signal and repeats it out to all ports on a network. A Multi-port twisted pair hub allows several point-to-point segments to be joined in to one network. One end point of the point-to-point link is attached to the hub and other is attached to the computer.

An Ethernet hub (or) active hub (or) network hub (or) repeater hub or hub is a device for connecting multiple twisted pair or fiber optic Ethernet devices together and making them act as a single network segment. Hubs work at the layer 1 ( physical layer ) of the OSI model. The device is a form of multi-port repeater. The Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision.

Hubs also often come with a BNC and/or Attachment Unit Interface (AUI) connector to allow connection to legacy 10BASE2 or 10BASE5 network segments. The availability of low-priced network switches has largely rendered hubs obsolete but they are still seen in older installations and more specialized applications.

Hubs don't manage any of the traffic that comes through them, and any packet entering any port is regenerated and broadcast out on all other ports. Since every packet is being sent out through all other ports, packet collisions result — which greatly impedes the smooth flow of traffic.

For 10 Mbit/s networks built using repeater hubs, the 5-4-3 rule must be followed: up to 5 segments (4 hubs) are allowed between any two end stations. For 100 Mbit/s networks, the limit is reduced to 3 segments (2 hubs) between any two end stations, and even that is only allowed if the hubs are of the a delay variety

Hubs are classified as ( Layer 1) physical layer devices in the OSI model. At the physical layer, hubs support little in the way of sophisticated networking. Hubs don't read any of the data passing through them and are not aware of their source or destination. A hub, simply receives incoming Ethernet frames, regenerates the electrical signal, and broadcasts these packets out to all other devices on the network.

Types of Hubs :
There are many types of hubs with different features / specification, which provide the type of functionality required to build a network. There are three main types of hubs : Active Hub, Passive Hub and Intelligent Hub.

• Active Hubs : It can regenerate and retransmit the signal the same way as repeater does. In fact, active hubs usually have twelve ports for network computers to connect; they are sometime called as multi-port hubs. Active hubs require electrical power to run. Usually active hubs are more expensive than passive hubs as they provide additional feature.
• Passive Hubs : It acts as a connection point and do not amplify or regenerate the signal; the signal passes through the hub. a Passive hub simply receives on the input port and broadcasts its on the output port without even repairing it. Passive hubs do not require electrical power to run.
• Intelligent Hubs : An intelligent hub has all features of a passive and active hub, also help to improving the performance of network. As active hub helps in finding out where the problem exits., an intelligent hub diagnoses it and tries to correct it without affecting the performance of the network. Intelligent hubs provide features which helps to determine the exact cause and location of the problem and helps in identifying the solution for the problem. An intelligent hub helps in controlling and minimizing data traffic in the network, which results in improved performance of the network.