What Is a Switch?

What Is a Switch?

A switch is a device with one or more sets of electrical contacts that can be connected together or separated by the operation of a mechanism actuating them. Switches can be "on" or off". They may be a continuous switch (such as the switches on a doorbell or the caps lock key) or they may be momentary, such as a toggle switch that turns a keyboard to capital letters when it is pressed and back to lower-case letters when it is released.

A network switch is a network device that connects network devices like computers and VoIP phones to each other. Switches filter and forward data packets based on their destination address. A switch operates at the Data Link Layer of the OSI model and performs error checking before sending data to its intended devices. A switch supports unicast, multicast and broadcast communication.

Each network device has a unique identifier called a Media Access Control (MAC) address. The MAC address is used to identify the device and determine its location on the network. When a data frame arrives at a switch, it examines the MAC address in the frame header and then looks up its destination MAC address in a table. If the switch finds that the MAC address is in its table it sends the frame to that port. If the MAC address is not in the table, it forwards the frame to all ports except the port where the MAC address originated, and records the source MAC address in its table. Over time the switch will learn the MAC addresses of its connected devices and will be able to direct traffic to them without needing to look up their MAC addresses.

Another way a switch differs from a hub is that it can handle full-duplex traffic, where both sides of the communication are sent at the same time, instead of only half-duplex, which only transmits data in one direction at a time. The switch can also prioritize different types of packets, allowing for a greater speed and capacity for some packets over others.

In addition, a switch is designed to optimize its ports; they don't clog with transmissions continuously like hubs do, freeing them up for other transmissions. And they reduce the number of packets that get lost by limiting the amount of traffic that is sent to a single port, which increases efficiency and helps prevent bottlenecks.

Switches are available in a wide variety of configurations to meet the needs of the network. They can be small enough to fit on a desk or in a server rack, or they can be very large with many ports to support a large enterprise network. They are usually powered by either AC or DC voltage. They must be protected from surges and transients that can damage them or the wired connections to them. They must also be protected from power outages that can make them inoperable or cause data loss. Some switches can also be configured to provide Quality of Service (QoS) functions, which allow the network administrator to allocate bandwidth to different packets according to their importance, such as prioritizing voice packets over data packets.