Networking Fundamentals

Computer Network: 

In information technology, a computer network, also called a data network, is a series of points, or nodes, interconnected by communication paths for the purpose of transmitting, receiving and exchanging data, voice and video traffic.
When you have two or more computers connected to each other, you have a network. The purpose of a network is to enable the sharing of files and information between multiple systems. The Internet could be described as a global network of networks. Computer networks can be connected through cables, such as Ethernet cables or phone lines, or wirelessly, using wireless networking cards that send and receive data through the air.

Global Network

Need of Networking:

• Shearing Expensive Resources like Laser printer
• Shearing Programs, files, Data etc..
• Reliability
• Financial Benefits
• Access to Remote Database
• Better communication medium

Networking Devices

Node:

Each and every device available on a network is called node. Every node on a network has a unique address called MAC address.

Node

Host:

All the computers available on the network called host. Hosts are also known as node.

Host

Workstation:

A workstation is a powerful PC used as a node on a network primarily uses to run application program. It has some responsibility on a network.

Workstation

Modems:

A modem (short form of modulator and demodulator) is a networking device that allows you to connect and communicate with other computers via telephone lines.

When digital signal are to be send over telephones lines, the digital signal must be converted to analog form. This process is called modulation. The reverse process, the conversion of analog signal to its digital form at the destination device is called demodulation.

The process of modulation and demodulation is carried out by a special device called modem.

Modem

Hub:

Simply hub is a networking  device for connecting multiple Computers (devices) together and making them act as a single network segment. Hub broadcast the signals to computers connected to it. A hub works at the physical layer (layer 1) of the OSI model. Most hubs are referred to as either active or passive.

Active hub: It regenerates a signal before forwarding it to all the ports on the device and requires a power supply.

Passive hub: It does not need power and they don’t regenerate the data signal.

* (A Multi station Access Unit (MAU) is a special type of hub used for token ring networks)

Hub

Switch:

A switch also connects computers or nodes to each other like hub but a network switch forwards data only to one or multiple devices that need to receive it, rather than broadcasting the same data out of each of its ports. Switch establishes a direct connection between originator and receivers. It works on Data link layer (layer 2) of OSI  Model.

 

Switch

(Switches are a special type of hub that offers an additional layer (Data link layer) of intelligence to basic, physical-layer repeater hubs. A switch must be able to read the MAC address of each frame it receives. This information allows switches to repeat incoming data frames only to the computer or computers to which a frame is addressed. By forwarding data only to the system to which the data is addressed, the switch decreases the amount of traffic on each network link dramatically.

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.

A MAC (Media Access control) addresses a unique number that is stamped into every NIC.)

Bridge:

Bridges are devices (Computers) that can transmit data between two LANs. Bridge divide a large network into smaller segments. They also filter data and keep the traffic separate for each segment. When packets enter a bridge, it reads the address contained in the frame and compares that address with a table. When the bridge finds a match, it sends the packet to destination segment.

Bridges operate at both the Physical Layer and the Data Link layer of OSI model.

• As a PHYSICAL layer, it regenerates the signal it receives.

• As a data link layer, the bridge can check the PHYSICAL/MAC addresses contained in the frame.

Bridge

* (A bridge is a networking device that is used for connecting two LANs and allows computers to access resources. They can also be used to divide large networks into smaller segments.

Function:

A bridge has a table used in filtering decisions. A bridge functions by blocking or forwarding data, based on the destination MAC address written into each frame of data. If the bridge believes the destination address is on a network other than that from which the data was received, it can forward the data to the other networks to which it is connected. If the address is not on the other side of the bridge, the data is blocked from passing.)

Gateways:

A gateway is a device used to connect dissimilar networks using different protocols. A gateway is necessary when there are different technologies implemented by the different network which are to be connected together. If data has to be sent from one place to another, we need to ensure that the network technologies that are being used by both the networks are the same. If not, we need to use a Gateway. (Networks in New York and a network in New Delhi that are differ from each other)

Gateway is also called protocols converter that converts data packets from one format to another. It works in the Transport layer and above, sometimes at the network layer of the OSI model.

Example: A common example, we use a telephone network and internet networks, which works on different technologies. The telephone network follows the ISDN, and the Internet follows the IP.

Gateway

* (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. Gateway is a viable tool to translate the data format, although the data itself remains unchanged.

Gateway: an interface providing a compatibility between networks by converting transmission speeds, protocols, codes, or security measures

Examples.

• In the more common example, we use a telephone network and internet networks, which works on different technologies. The telephone network follows the ISDN, and the Internet follows the IP. Here, 2 different technologies are being used. In this case, the router fails to work, since the router cannot understand the functionalities of both the networks. Hence, we require a Gateway, which acts as a translator in communicating between the 2 networks.
• Gateways between a Systems Network Architecture (SNA) host and computers on a TCP/IP network, such as the one provided by Microsoft SNA Server)

Router:

Routers are devices (computers) containing software that helps in determining the best path out of available paths for a particular transmission. The two main pieces of software in a router are the operating system and the routing protocols. Routers perform the "traffic directing" functions on the Internet. It works on Network layer of OSI model.

 Routing tables: Routing tables are the means by which a router selects the fastest or nearest path to the next "hop" on the way to a data packets final destination.

Router

* (Routers are network devices that literally 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 determines the best way for the data to continue its journey. Any computer can be connected to the internet via MODEM, which performs the Modulation and the Demodulation operations. But, when there are more than one computer at home or in an organization, and you have a single internet connection, you need a Router. Router is a device which is used when multiple devices need to connect to the Internet using the same IP.

Routing tables

Routers contain internal tables of information called routing tables that keep track of all known network addresses and possible paths throughout the internetwork, along with cost of reaching each network. Because routers use destination network addresses of packets, they work only if the configured network protocol is a routable protocol such as TCP/IP or IPX/SPX. The routing tables are the heart of a router; without them, there's no way for the router to know where to send the packets it receives.

Routable Protocols

Transmission Control Protocol/Internet Protocol (TCP/IP)

Internetwork Packet Exchange/Sequenced Packet Exchange (IPX/SPX)

AppleTalk)

Brouters: 

Bridging Routers, Combine features of bridges and routers. Capable of establishing a bridge between two networks as well as routing some messages from the bridge networks to other networks, Are sometimes called (Layer 2/3) switches and are a combination of bridge/router hardware and software

Brouter (Bridging Router) is a device which has two functions. Brouter acts as a router for known protocols (known by the router and those on the network) and hence works in the network layer. For data packets with unknown protocols, it acts as a bridge by connecting two different networks which is the function of a bridge - and this works in the data-link layer.

Brouters

NICs (Network Interface Card)

NICs—sometimes called network cards—are the mechanisms by which computers connect to a network. Network Interface Card, or NIC is a hardware card installed in a computer so it can communicate on a network. The network adapter provides one or more ports for the network cable to connect to, and it transmits and receives data onto the network cable.

NIC

Repeater:

A repeater is a device that operates only at the PHYSICAL layer. The repeaters are necessary since, during the transmission of the signals over long distances, the signal has attenuation, delay distortions and noise, which lead in loss of data. Hence, in order to prevent this, the regenerative repeaters are used. Hence, the repeater regenerates the faded signal.

A repeater can be used to increase the length of the network by eliminating the effect of attenuation on the signal

Repeater

It connects two segments of the same network, overcoming the distance limitations of the transmission media

A repeater forwards every frame; it has no filtering capability.

A repeater is a regenerator, not an amplifier

If the input signal has noise induced into it, both the desired signal and noise signal are together amplified. But, in the case of a repeater, it regenerates the input signal, and amplifies only the desirable signal. Hence, the noise component of the signal is eliminated.