Switch

NETWORK SWITCH

Definition: A network switch is a computer networking device that links network segments or network devices together in a 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.

Switches aren’t used to create internetworks (they do not break up broadcast domains by default); they’re employed to add functionality to a network LAN. The main purpose of a switch is to make a LAN work better – to optimize its performance – providing more bandwidth for the LAN’s users. And switches don’t forward packets to other networks as routers do. Instead, they only “switch” frames from one port to another within the switched network.

    By default, switches break up collision domains. This is an Ethernet term used to describe a network scenario wherein one particular device sends a packet on a network segment, forcing every other device on that same segment to pay attention to it. At the same time, a different device tries to transmit, leading to a collision, after which both devices must retransmit, one at a time. Not very efficient! This situation is typically found in a hub environment where each host segment connects to a hub that represents only one collision domain and only one broadcast domain. By contrast, each and every port on a switch represents its own collision domain.

Advantages of a Switched Network

Switched networks have virtually replaced hub-based networks due to their ability to provide all of the bandwidth available on the wire by eliminating collisions. This advantage of switched networks played a large role in the battle between Ethernet and Token Ring technologies in the last decade of the twentieth century.



LAN switches significantly reduce, or even eliminate, the number of collisions on a LAN. Unlike hubs, switches do not create a single shared bus. Instead, switches do the following:

• Switches interpret the bits in the received frame so that they can typically send the frame out to the one required port, rather than all other ports.
• If a switch needs to forward multiple frames out the same port, the switch buffers the frames in memory, sending one at a time, thereby avoiding collisions

·         Devices connected to one switch port do not share their bandwidth with devices connected to another switch port. Each has its own separate bandwidth, meaning that a switch with 100 Mbps ports has 100 Mbps of bandwidth per port.

·         MAC filtering and other types of "port security" features which prevent MAC flooding. MAC Filtering refers to a security access control method whereby the 48-bit address assigned to each network card is used to determine access to the network. MAC addresses are uniquely assigned to each card, so using MAC filtering on a network permits and denies network access to specific devices through the use of blacklists and whitelists.

·         Switch increases the available network bandwidth.

·         It reduces workload on individual computers.

·         Increased network performance.