network devices

hub and switch

Both hubs and switches are used in Ethernet networks. Token Ring networks, which are few and far between, use special devices called multistation access units (MSAUs) to create the network.

The function of a hub is to take data from one of the connected devices and forward it to all the other ports on the hub.

Most hubs are considered active because they regenerate a signal before forwarding it to all the ports on the device. In order to do this, the hub needs a power supply.

Rather than forwarding data to all the connected ports, a switch forwards data only to the port on which the destination system is connected.

Switches make forwarding decisions based on the Media Access Control (MAC) addresses of the devices connected to them to determine the correct port.

In cut-through switching, the switch begins to forward the packet as soon as it is received.

In a store-and-forward configuration, the switch waits to receive the entire packet before beginning to forward it.

FragmentFree switching works by reading only the part of the packet that enables it to identify fragments of a transmission.

Hubs and switches have two types of ports: Medium Dependent Interface (MDI) and Medium Dependent Interface-Crossed (MDI-X).

A straight-through cable is used to connect systems to the switch or hub using the MDI-X ports.

In a crossover cable, wires 1 and 3 and wires 2 and 6 are crossed.

Both hubs and switches come in managed and unmanaged versions. A managed device has an interface through which it can be configured to perform certain special functions.

bridge and router

Bridges are used to divide up networks and thus reduce the amount of traffic on each network.

Unlike bridges and switches, which use the hardware-configured MAC address to determine the destination of the data, routers use the software-configured network address to make decisions.

Access Point

Wireless network devices gain access to the network via Wireless Access Points.

Wireless Access Points provide additional functionality such as DHCP, router, firewall, and hub/switch.

Gateway

A network gateway is an internetworking system, a system that joins two networks together. A network gateway can be implemented completely in software, completely in hardware, or as a combination of the two. Depending on their implementation, network gateways can operate at any level of the OSI model from application protocols to low-level signaling.

Because a network gateway by definition appears at the edge of a network, related functionality like firewalling tends to be installed on the network gateway.