|Router||a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. A data packet is typically forwarded from one router to another through the networks that constitute the internetwork until it reaches its destination node. It works on OSI layer 3.|
|Gateway||an interface providing a compatibility between networks by converting transmission speeds, protocols, codes, or security measures.|
|Switch||a device that connects devices together on a computer network, by using packet switching to receive, process and forward data to the destination device. Unlike less advanced network hubs, a network switch forwards data only to one or multiple devices that need to receive it, rather than broadcasting the same data out of each of its ports. It works on OSI layer 2.|
|Bridge||a device that connects multiple network segments. It works on OSI layers 1 and 2.|
|Repeater||an electronic device that receives a signal and retransmits it at a higher level or higher power, or onto the other side of an obstruction, so that the signal can cover longer distances.|
|Repeater hub||for connecting multiple Ethernet devices together and making them act as a single network segment. It has multiple input/output (I/O) ports, in which a signal introduced at the input of any port appears at the output of every port except the original incoming. A hub works at the physical layer (layer 1) of the OSI model. Repeater hubs also participate in collision detection, forwarding a jam signal to all ports if it detects a collision. Hubs are now largely obsolete, having been replaced by network switches except in very old installations or specialized applications.|
|Firewall||a piece of hardware or software put on the network to prevent some communications forbidden by the network policy. A firewall typically establishes a barrier between a trusted, secure internal network and another outside network, such as the Internet, that is assumed to not be secure or trusted.|
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