Network equipment is used to split, switch, boost, or direct packets of information along a network. Products include hubs, switches, routers, repeaters, bridges, gateways, multiplexers, transceivers, and firewalls. Hubs provide a central location for attaching wires to workstations. Passive hubs do not amplify signals. Active hubs serve to extend the cables that connect to workstations. Switches connect network devices to host computers and allow a large number of devices to share a limited number of ports. Routers are protocol-dependent network equipment that connects subnetworks. Repeaters are 802.3 network cable segments which use regeneration and retiming to ensure that a signal is transmitted clearly through all segments. Bridges interconnect local or remote networks and operate at the physical and link layers of the open systems interconnection (OSI) reference model. Gateways interface networks with incompatible communications protocols and operate through the session layer. Multiplexers are telecommunications devices that funnel multiple signals onto a single channel. Transceivers (transmitters-receivers) are devices that both transmit and receive analog or digital signals. Firewalls are a system or group of systems that, for purposes of security, enforce an access control policy between an organization's network and the Internet.