Auto-sensing

- Autosensing is a feature of so-called "10/100" Ethernet hubs, switches, and NICs.
- Compatible Ethernet speeds can be selected using low-level signaling techniques probing the capability of the network.
- Autosensing was developed to make the migration from traditional Ethernet to Fast Ethernet products easier.

When first connected, 10/100 devices automatically exchange information with each other to agree on a common speed setting. The devices run at 100 Mbps if the network supports it, otherwise they drop down to 10 Mbps to ensure a "lowest common denominator" of performance. Many hubs and switches are capable of autosensing on a port-by-port basis; in this case, some computers on the network may be communicating at 10 Mbps and others at 100 Mbps. 10/100 products often incorporate two LEDs of different colors to indicate the speed setting that is currently active.

Auto-sensing is an active method of determining link mode. Each interface is expected to transmit specific information in a specific format. If an interface that is expecting to use auto-sensing does not receive this information from the other side, it assumes the other side cannot detect or change its mode.

Ethernet Hubs

A hub connects multiple devices together. Ethernet hubs, and are most commonly used in computers for networking purposes. Ethernet hubs are available in different types, depending on the speed of the network connection or broadband speed. The number of ports an Ethernet hub supports also varies. Older Ethernet hubs were relatively large in size and sometimes noisy as they contained built in fans for cooling the unit. Newer devices are much smaller, designed for mobility, and noiseless.

Working of an Ethernet Hub

The main purpose of the Ethernet hub is to transmit the large pockets or cluster of data it receives from one computer onto another through all the ports connected to it. Ethernet uses a protocol called CSMA/CD, which stands for Carrier Sense, Multiple Access with Collision Detection.

- Carrier Sense - When a device connected to an Ethernet network wants to send data it first checks to make sure it has a carrier on which to send its data.
- Multiple Access - This means that all machines on the network are free to use the network whenever they like so long as no one else is transmitting.
- Collision Detection - A means of ensuring that when two machines start to transmit data simultaneously, that the resultant corrupted data is discarded, and re-transmissions are generated at differing time intervals.

Hubs and their types

Hubs have become an integral part of various network and business systems. Hub, sometimes referred to as a concentrator or repeater Hub, refers to a networking component which acts as a convergence point of a Network, allowing the transfer of data packets.

Characteristics of Hubs :
- Hub is a small plastic box which takes its power from an ordinary wall outlet.
- Multiple computers are joined through a hub.
- On this network segment, all computers can communicate directly with each other.
- A hub includes a series of ports that each accept a network cable.
- Hubs are the layer 1 devices while switches and routers are layer 2 and layer 3 devices respectively.
- Hubs do not read any of the data passing through them and are not aware of their source or destination. Essentially, a hub simply receives incoming packets, possibly amplifies the electrical signal, and broadcasts these packets out to all devices on the network - including the one that originally sent the packet.

Types of Hubs :
- Passive Hubs : They do not amplify the electrical signal of incoming packets before broadcasting them out to the network. Their contribution in enhancing the performance is very less. It does not help in any way in the troubleshooting operations. Most of the passive hubs are easily obtainable at a lesser cost.
- Active Hubs : They amplify the incoming signals. An active hub is sometimes referred to as multiport repeater. An active hub takes a larger role in Ethernet communications with the help of technology called store & forward. If the data received being weak but readable, the active hub restores the signal before rebroadcasting the same. An active hub provides information n devices on the network which are not yet fully functional.
- Intelligent Hubs : This hub typically behaves like a stack. It is built in such a way that multiple units can be placed one on top of the other to conserve space. It has the ability to manage the network from one central location. With the help of an intelligent hub, one can easily identify, diagnose problems and even come up with remedial solutions.