Part II : THEORY GUIDE Network

NETWORK DEVICES

The basic Network devices are: Individual Networks, Server, Hub, Switch, Bridges, Routers, Modems, Printers, DSL Modems & Routers, Gateways, Network Interface Cards, Cabling & Wireless Access Point. 

1. NIC (Network Interface Card): Network Interface Cards are attached with the Computer or other Network devices and are used to provide the connectivity between the two Networks. Each Network card is specifically designed for the different types of the Network like Ethernet, FDDI (Fibre Distributed Data Interface), Token Ring and Wireless Networks. NIC basically defines the physical connection methods and the control signals that provide the timings of the data transfer over the Network. 

2. Modems: Modems are the devices, which are used to translate the analog format into the digital data and vice versa. It performs the two main functions, Modulation and Demodulation. A modulated data can travel across the conventional telephone lines. The Modem modulates the signals at the sending end and demodulates at the receiving end. Modems are required for different types of the access methods such ISDN (Integrated Services Digital Network), DSL (Digital Subscriber Line) and 56K data modem. Modems can be the internal devices that plug into the Expansion Slots in a System or can be external devices that plug into the serial or USB ports. In Laptops, PCMCIA (Personal Network Memory Card International Association) cards are used for this purpose. In ISPs where the large scaled Modems are required, rack-mounted modems are used.

3. Hub: Hubs are used in Networks that use twisted-pair cabling to connect devices. Hubs can also be joined together to create larger Networks. Hubs are simple devices that direct data Packets to all devices connected to the Hub. 

Hubs come in a variety of shapes and sizes. Small Hubs with five or eight connection ports are commonly referred to as workgroup Hubs. Others can contain larger numbers of devices (Normally up to 32-64 connection port). These are referred to as high-density devices. Ports on a Hub are jacks (i.e., female connectors). In the case of a Hub for twisted pair cable, they are standard RJ-45 jacks. 

4. Switch: Switch is similar to Hubs. Like Hubs, Switches are the connectivity points of an Ethernet Network. Devices connect to Switches through twisted-pair cabling, one cable for each device. The difference between Hubs and Switches is in how the devices deal with the data that they receive. Whereas a Hub forwards the data it receives to all of the ports on the device, a Switch forwards it only to the port that connects to the destination device. It does this by learning the MAC (Media Access Control) address of the devices attached to it, and then by matching the destination MAC addresses in the data it receives. 

5. Router: Routers are used to create larger Networks by joining two Network segments. A Router can be a dedicated hardware device or a Network System with more than one Network interface and the appropriate routing Software. All modern Network Operating Systems include the functionality to act as a Router. 

Routers can route data it receives from one Network onto another. When a Router receives a packet of data, it reads the header of the packet to determine the destination address. Once it has determined the address, it looks in its routing table to determine whether it knows how to reach the destination and, if it does, it forwards the packet to the next destination, or it might be another Router.

6. Bridge: A Bridge is a device that connects and controls the flow of data between two LANs (Local Area Network)s or two segments of the same LAN. A device that connects two LAN segments together, which may be similar or dissimilar, such as Ethernet and Token Ring. 

A bridge is inserted in the Network to keep traffic contained within the segments to improve performance. By monitoring which station acknowledged (recognized) receipt of the address, bridges learn which nodes belong to the segment and maintain their own address tables. Multi-port bridges have more than two ports and perform a switching function just like a LAN switch.

7. Repeater: A Repeater is a Network device that is used to regenerate or replicate signals that are weakened or distorted by transmission over long distances and through areas with high levels of EMI (Electromagnetic Interference). 

Repeater is a hardware device that moves all Packets from one LAN segment to another. Repeaters boost (increase) a signals ability to travel farther on the Network. For example, 10Base2 coaxial has a maximum length of 185 meters, and 10/10BaseT twisted pair has a maximum length of 100 meters. Somewhere before the 185 and 100 meters are finished, it needs to provide a Repeater to extend the signal.

8. Gateway: A Gateway is also called an IP Router. A Gateway can be a Device, System or Software. A device connected to multiple physical TCP/IP Networks capable of routing or delivering IP packets between them. A Gateway performs the function of translating the data from one format to another format without changing the data itself. A Network with two NIC cards can function as a Gateway. Router acts as a Gateway, e.g a router that routes the data from an IPX (Internet Packet eXchange) Network to an IP (Internet Protocol) Network is technically a Gateway. The same can be said of translational switch converts from an Ethernet Network to a Token Ring Network.