A device that establishes, maintains, and changes logical connections over physical circuits. Switches flexibly connect transmitters and receivers across networks of interconnected links, thereby allowing network resources to be shared by large numbers of end users. Without switches, each transmitter/receiver pair would require a dedicated circuit in order to transfer data. There are a number of types of switches. In terms of switching technology, there are circuit switches and packet switches. a.
Circuit switches establish connections between circuits, on demand and as available. Those connections are temporary, continuous, and exclusive in nature. Circuit switches were developed for voice communications, but will support any type of information transfer. Common examples of circuit switches include private branch exchanges (PBXs) and central office exchanges (COs or COEs). b.
Packet switches switch data organized into packets, discrete sets of data that may take the specific form of packets, frames, or cells depending on the network technology specifics. For example, packet switches switch packets in networks based on the Internet Protocol (IP), frames in networks based on the frame relay or Ethernet protocols, and cells in those based on the asynchronous transfer mode (ATM) protocol. Packet switches were initially developed for data networking, but can support other forms of data, as well, although with varying degrees of success. With respect to physical placement, there are edge switches and core switches. c.
Edge switches are positioned at the physical edge of a public network.The user organization gains access to an edge switch via an access link, or local loop. A central office (CO) is an example of an edge switch in the context of the circuit-switched public switched telephone network (PSTN). In a Local Area Network (LAN), a workgroup switch is the equivalent of an edge switch in a public network. d.
Core switches, also known as tandem switches
and backbone switches
, are high-capacity switches positioned in the physical core, or backbone, of a network and serving to interconnect edge switches. Although switches can be very intelligent in many respects, they operate only at the Layer 2, the Data Link Layer of the OSI Reference Model.That is to say that they operate link-by-link, or hop-by-hop, generally under the control of a centralized set of logic that can coordinate their activities in order to establish end-to-end connectivity across a multi-link circuit.A switch has no concept of the network as a whole, from end-to-end. See also ATM
, backbone switch
, core switch
, Data Link Layer
, edge switch
, frame relay
, LAN switch
, OSI Reference Model
, and tandem switch