Definition of Switch in Network Encyclopedia.
What is a Switch?
Switch is any device that can control the flow of electrical signals. A number of special-purpose switches are used in networking.
For example, the following types of switches are used to control access to computers by printers, keyboards, and monitors:
- Matrix switches: Have a keypad for mapping input ports to output ports and are typically used to connect several printers to several workstations
- Code-operated switches: Use a data string sent by the PC to select the printer port to be used
- Port-contention or scanning switches: Use several input ports but only one output port and monitor the input ports continually for data to route to the output port
- KVM switches: Allow one keyboard/video-monitor/mouse to be used for several servers
Switch in data flow control
In the context of controlling data flow within a network, the term “switch” is also used to describe a data-link layer device that routes frames between connected networks.
Data flow switches include
- Local area network (LAN) switches: Used to route Ethernet frames over a TCP/IP internetwork; also called Ethernet switches
- Asynchronous Transfer Mode (ATM) switches: Used to switch ATM cells at high speeds over an ATM network
In the context of high-speed Ethernet networks, the term “switch” usually refers to an Ethernet switch. Thus, the phrase “routers and switches” is understood to mean “routers and Ethernet switches.”
The term “switch” can also refer to a device used at a telco central office (CO) for establishing connections in circuit-switched services or for forwarding packets in packet-switched services.
Layer 1 Switch
Layer 1 Switch is a Layer 1 network device that transfers data but does not manage any of the traffic coming through it. An example is an Ethernet hub. Any packet entering a port is repeated to the output of every other port except for the port of entry. Specifically, each bit or symbol is repeated as it flows in. A repeater hub can therefore only receive and forward at a single speed. Since every packet is repeated on every other port, packet collisions affect the entire network, limiting its overall capacity.
Layer 2 Switch
A switch operating as a network bridge may interconnect devices in a home or office. The bridge learns the MAC address of each connected device. Bridges also buffer an incoming packet and adapt the transmission speed to that of the outgoing port. While there are specialized applications, such as storage area networks, where the input and output interfaces are the same bandwidth, this is not always the case in general LAN applications. In LANs, a switch used for end user access typically concentrates lower bandwidth and uplinks into a higher bandwidth.
Layer 3 Switch
A layer-3 switch can perform some or all of the functions normally performed by a router. Most network switches, however, are limited to supporting a single type of physical network, typically Ethernet, whereas a router may support different kinds of physical networks on different ports.
A common layer-3 capability is awareness of IP multicast through IGMP snooping. With this awareness, a layer-3 switch can increase efficiency by delivering the traffic of a multicast group only to ports where the attached device has signaled that it wants to listen to that group.
Layer-3 switches typically support IP routing between VLANs configured on the switch. Some layer-3 switches support the routing protocols that routers use to exchange information about routes between networks.
Layer 4 Switch
While the exact meaning of the term layer-4 switch is vendor-dependent, it almost always starts with a capability for network address translation and may add some type of load distribution based on TCP sessions or advanced QoS capabilities.