Repeater – A repeater amplifies the input signal to an appropriate level and works at the physical level of the OSI model. Sometimes the signal on the Internet becomes weak before reaching the destination node. Thus, repeater is used to regenerate the incoming packet and amplify it and then transmit it to another segment of the network.
Router – A router is a device or, in some cases, software in a computer which is connected to at least two networks and decides which way to send each information packet based on its current understanding of the state of the networks it is connected to.
Bridge – A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN by dividing it into two segments. Bridges inspect incoming traffic and decide whether to forward or discard it. An Ethernet bridge, for example, inspects each incoming Ethernet frame - including the source and destination MAC addresses, and sometimes the frame size - in making individual forwarding decisions.
Gateway – A network gateway is an internetworking system capable of joining together two networks that use different base protocols. A network gateway can be implemented completely in software, completely in hardware, or as a combination of both. Depending on the types of protocols they support.
