A network switch is a computer networking device that connects network segments or network devices. The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer (layer 2) of the OSI model. Switches that additionally process data at the network layer (layer 3) and above are often referred to as layer-3 switches or multilayer switches.

A switch is a telecommunication device which receives a message from any device connected to it and then transmits the message only to the device for which the message was meant. This makes the switch a more intelligent device than a hub (which receives a message and then transmits it to all the other devices on its network). The network switch plays an integral part in most modern Ethernet local area networks (LANs). Mid-to-large sized LANs contain a number of linked managed switches. Small office/home office (SOHO) applications typically use a single switch, or an all-purpose converged device such as a residential gateway to access small office/home broadband services such as DSL or cable Internet. In most of these cases, the end-user device contains a router and components that interface to the particular physical broadband technology. User devices may also include a telephone interface for VoIP.

An Ethernet switch operates at the data link layer of the OSI model to create a separate collision domain for each switch port. With 4 computers (e.g., A, B, C, and D) on 4 switch ports, any pair (e.g. A and B) can transfer data back and forth while the other pair (e.g. C and D) also do so simultaneously, and the two conversations will not interfere with one another. In full duplex mode, these pairs can also overlap (e.g. A transmits to B, simultaneously B to C, and so on). In the case of a repeater hub, they would all share the bandwidth and run in half duplex, resulting in collisions, which would then necessitate retransmissions.

Microsegmentation
Using a bridge or a switch (or a router) to split a larger collision domain into smaller ones in order to reduce collision probability and improve overall throughput is called segmentation. In the extreme of microsegmentation, each device is located on a dedicated switch port. In contrast to an Ethernet hub, there is a separate collision domain on each of the switch ports. This allows computers to have dedicated bandwidth on point-to-point connections to the network and also to run in full duplex without collisions. Full duplex mode has only one transmitter and one receiver per 'collision domain', making collisions impossible.


A network switch is a small hardware device that joins multiple computers together within one local area network (LAN). Technically, network switches operate at layer two (Data Link Layer) of the OSI model.

Network switches appear nearly identical to network hubs, but a switch generally contains more intelligence (and a slightly higher price tag) than a hub. Unlike hubs, network switches are capable of inspecting data packets as they are received, determining the source and destination device of each packet, and forwarding them appropriately. By delivering messages only to the connected device intended, a network switch conserves network bandwidth and offers generally better performance than a hub.

As with hubs, Ethernet implementations of network switches are the most common. Mainstream Ethernet network switches support either 10/100 Mbps Fast Ethernet or Gigabit Ethernet (10/100/1000) standards.

Different models of network switches support differing numbers of connected devices. Most consumer-grade network switches provide either four or eight connections for Ethernet devices. Switches can be connected to each other, a so-called daisy chaining method to add progressively larger number of devices to a LAN.
 

An image of switch -

Advantages of Switch

• Increased available network bandwidth.
• Reduced workload on individual computers.
• Increased network performance.
• Decreased packet collisions.

Switches have many features that make them different than hubs. The most compelling reason to choose a switch rather than a hub is bandwidth. When a 100Mbps hub has five workstations, each receives 20Mbps of bandwidth. When a 10/100Mbps switch is used, each workstation receives 100Mbps of bandwidth, dramatically increasing the speed of the connection. Switches also run in full duplex mode, which allows data to be sent and received across the network at the same time. Switches effectively double the speed of the network when compared to hubs, which only support half duplex mode.

A 10/100Mbps switch can also support hardware running at either 10Mbps or 100Mbps, allowing the continued use of older technology and delaying replacement.

Switches will increase the speed and efficiency of networks in any of the following situations:

• Any network that calls for a 10/100 hub will benefit from a 10/100Mbps switch. The switch will increase available bandwidth, drastically increasing the speed that the network is running at.
• Any network that requires enhanced performance for file servers, workstations, Web servers, etc. Any critical components should be connected directly to a 10/100Mbps switch.
• Any network that uses high-speed applications including multimedia and video. Any workstation or file server using the intensive applications should be connected directly to a 10/100Mbps switch.
• Any network that uses Fiber optic cabling should use a 10/100Mbps switch rather than a hub. A hub will not take full advantage of the speed possible with Fiber optic cabling.