Both hubs and switches are important exchange points at the logical centre of an Ethernet network. Each computer or other network node connects to a hub or switch through a cable plugged into a port. In a small network, a hub or switch is almost always a tabletop box with indicator lights on the front and Ethernet ports on the back. In a larger network, the hub or switch might be a panel that mounts in an equipment rack.
The maximum data transfer speed of a network is the data-handling speed of the hub or switch. Today, the most common hubs and switches are designed for both 10Mbps and 100 Mbps operation. The latest generation of switches and hubs supports even faster Gigabit Ethernet (1000 Mbps) switches but only at slightly higher prices than those of older 100 Mbps versions.
Hub
A hub is a broadcast domain and when a data packet enters a hub, the hub relays that packet to all of the hub’s ports. Each node compares the address on the packet with its own address and either accepts it if the address is the same or ignores it if the packet is addressed to some other node. Because the hub sends each packet to every port, only one packet can travel through the network at a time. If two or more computers try to send packets at exactly the same time, Ethernet’s collision detection feature forces them to stop, wait, and try again a fraction of a second later. Also the hub adopts the shared bandwidth working mode.
In order to prevent collisions, each node must examine the network to be certain that no other node is already using the hub before it transmits a packet. Therefore, a network with a 10/100 hub is no faster than the slowest node. If all the computers in your network use 100 Mbps network adapters but the printer connects through a 10 Mbps port, the whole network will run at only 10 Mbps or less.
As more nodes try to use a hub at the same time, the data transfer speed through the entire network drops. This could have a significant effect on a busy network that uses a hub: The actual data transfer could be only a fraction of the nominal 10 Mbps or 100 Mbps. In general, hubs are slow, simple, and cheap.
Switch
The switch is a device of data link layer, forwards and floods data frames based on the MAC address. It connects the nodes of a network to one another but rather than sending every packet to every port, a switch reads the MAC address of each incoming packet and sets up a direct connection from the source of each packet to its destination. In the meantime, if some other node tries to send a data packet to another unused port, the switch can set up the link without breaking the other connection.
A switch can handle more than one connection at the same time. Because a network node connected to a switch doesn't have to monitor the entire network for possible collisions, it can send and receive data at the same time.
Networks in larger business offices usually run cables from each computer back to a central space where all the switching equipment is mounted on a wall plate or an equipment rack. This is often the same room where in-house telephone equipment connects to the telephone company’s outside lines. This space is often called a wiring closet.
Switches increases the number of collisions domains in the network. Switches that are configured with VLANs will reduce the size of the collision domains by increasing the number of collision domains in a network, but making them smaller than that of one big, flat network.
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