Network Interface Cards:

The network interface card (NIC) provides the physical connection between the network and the computer workstation. Network interface cards are a major factor in determining the speed and performance of a network. The most common network interface connections are Ethernet cards.

1. Switches:

A switch is a hardware device that provides a central connection point for cables from workstations, servers, and peripherals, switch forwards data only to the port on which the destination system is connected.

Most switches are active, that is they electrically amplify the signal as it moves from one device to another. Switches manage the data flow on the connection, it can send and receive data on the connection at the same time. Switches use three methods to deal with data as it arrives. They are Cut-through, Store-and-forward, and Fragment-free.

2. Repeaters:
Since a signal loses strength as it passes along a cable, it is often necessary to boost the signal with a device called a repeater. The repeater electrically amplifies the signal it receives and rebroadcasts it.

3. Bridges:
Bridges are networking devices that connect networks. Sometimes it is necessary to divide networks into subnets to reduce the amount of traffic on each larger subnet or for security reasons. Once divided, the bridge connects the two subnets and manages the traffic flow between them.

Three types of bridges are used in networks are Transparent bridge, Translational bridge, Source-route bridge.

Most bridges can “listen” to the network and automatically figure out the address of each computer on both sides of the bridge. The bridge can inspect each message and, if necessary, broadcast it on the other side of the network. The bridge manages the traffic to maintain optimum performance on both sides of the network.

a. Routers:
Routers are network devices that route data around the network. By examining data as it arrives, the router can determine the destination address for the data; then, by using tables of defined routes, the router decides the best way for the data to reach a destination. The router can direct traffic to prevent a crash.

b. Hubs:
A network hub contains multiple ports. When a packet arrives at one port, it is copied to all ports of the hub for transmission.
The two types of hubs are active or passive hubs. Active hubs regenerate signal before forwarding it to all the ports and require a power supply. Passive hubs, do not need power and they don’t regenerate the data signal.

c. Gateways:
It is a device that connects dissimilar networks. The term gateway is applied to any device, system, or software application that can perform the function of translating data from one format to another. The key feature of a gateway is that it converts the format of the data, not the data itself. The conversion from one data format to another takes time, and so the flow of data through a gateway is always slower than the flow of data without one.

d. Modems:

The modem is a short form of the terms modulator and demodulator. Modems translate digital signals from a computer into analog signals that can travel across phone lines. The modem modulates the signal at the sending end and demodulates at the receiving end.

Modems provide a relatively slow method of communication. Modems are available as internal devices that plug into expansion slots in a system; external devices that plug into serial or USB ports;