1 Network Inter-Connecting Devices

Network Interface Card (NIC)

Any computer that is to be connected to a network needs to have a network interface card (NIC). NIC card stands for Network Interface Card, When the end-user devices does no provides suitable port or network interface board, printed circuit broads called NIC cards are used. These cards include the circuitry and mechanical connections to convert the computer's electric signal to be electric or electromagnet signals used on medium. A card usually includes a signal transceiver but may provide one or more connector type.
Most modern computers have these devices built into the motherboard, but in some computers you have to add an extra expansion card (small circuit board)
A Network Interface Card, or NIC, is a circuit board inserted into each network station (PC/workstation or server) to allow communication with other stations. Depending on the stations, the bus of a NIC could be ISA, PCI, EISA, MCA, S-bus…and so on.

HUB

A hub is a center of activities. In network terminology, it is a device where all connecting mediums come together. It is a medium used to collect signals from the input line(s) and redistribute them in various available wirings around a topology (topologies such as: Arcnet, 10base-T, 10base-F etc). It basically acts as signal splitter, it accepts signal through its input port and passes it to the output ports. Some hubs help in regenerating the weak signals prior to sending them to the intended output lines, whereas some help in synchronizing the data communication (in simple words, the hub not only provides the means of interface within the network, it also provides some additional and useful features). Sometimes, multiple hubs are interconnected in the network. Generally they are used more commonly where star topology is used.

The Need of a Hub

Generally when we build a network using two or more computers, we need a hub. However, it is possible to connect two computers to each other directly without the need of a hub but when we add a third computer in the network, we need a hub to allow proper data communication within the network.

Types of Hubs

There are many types of hubs with various features/specifications, which provide the type of functionality you need in building a network. There are three main types of hubs: Passive, Active and Intelligent hub.

Passive Hubs

As the name suggests, passive hubs are the ones, which do not provide any additional feature except for working just as an interface between the topology. These types do not help in rectifying/enhancing the signals they pass on in the network, in other terms, they do not help in enhancing the performance of the network/LAN. It is very hard to get any help from the passive hubs while troubleshooting in case there is any fault in the hardware or the network. It simply receives signal(s) on input port(s) and broadcasts it (them) on the output port(s) without even rectifying it (them).



Active Hubs

As you must have guessed from the name, active hub takes active participation in data communication within the network/LAN. They come with various features, such as receiving the signal (data) from the input port and storing it for some time before forwarding it, this feature allows the hub to monitor the data it is forwarding, some hubs come with a feature that helps in transmitting data that has high priority before the data that has lower priority (this feature is very important for some applications and some types of network), some hubs help in synchronizing data communication (by retransmitting the packets, which are not properly received at the receiving computer or by adjusting re-transmission of the data packets to compensate timing), and some active hubs come with a feature that rectifies the data/signal before forwarding it in the network/LAN.

Active hubs also help in troubleshooting at a certain level. If there is a bottleneck within the network/LAN, they can be used to find out the problem to a certain extent. They have some benefits over the use of passive hubs; however, they are more expensive than passive hubs as they provide additional features.

Switch

A switch, like a hub, is a device that connects a number of computers together to make a LAN.
Switch offer a direct network connection between source and destination computers when a switch receives a data packet, it creates a separate internal connection or segment, between any two of its ports and forward the data packet to the appropriate port of destination computers only.
Unlike a hub, switches are comparable to a telephone system with private lines, in such a system, if one calls someone, if one calls someone, the operator or telephone switch connects then one dedicated line.

The typical use of a switch is at the center of a star network (or as part of a hybrid network) - the switch has cables plugged into it from each computer.

A switch is a more ‘intelligent’ device than a hub: if it receives a message, it checks who it is addressed to, and only sends it to that specific computer. Because of this, networks that use switches are more secure than those that use hubs, but also a little more expensive.
A switch is an intelligent device that works in the data link layer. The term intelligent refers to the decision making capacity of the Switch. Since it works in the Data link layer, it has knowledge of the MAC addresses of the ports in the network.
Hence, in the Fig, if data has to be sent from Computer A to Computer B, then, the data is transferred to the Computer B only, and not to any other computers connected on the network. Hence, it establishes a link between the sender and the receiver based on the MAC addresses. This also means that when data is being sent from A to B, Computer C can establish a link with Computer D and communication can take place between them. So, simultaneous data transfer is possible in a switch. Also, Hub divides bandwidth, but a Switch does not.
It is also to be noted that a switch is a secure device, because it sends information only to the desired destinations, and also certain security features such as firewalls can be implemented in the Switches.