NETWORKING CONCEPTS

Introduction 

The dynamic world today needs fast communication channels to move data
frequently from place to another, so, data transmission over distances has becomes essential esential. To move the data quickly from one place to another, the concept of
networking has been introduced. In networking the computers form different parts of the world are connected to each other to share data with each other.  

What is Network ? 

Network is an interconnected collection of autonomous Computers. Two Computers are said to be interconnected if they are capable of exchanging information. The term, Autonomous means, that the computers on network can start, stop, or control other. So a network allows the computer user to use computer equipment and programs, messages and the information available at one site. 

Need for Networking

Networking is necessary for the following reasons : 

                                                           

a) To share Computer files :

Networks provide a very effective method to share the files with the different users. For example, in an organization one file is to be shared by the different departments, we place this file on the network system. Now, all departments can use this file.   

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b) To share computer Peripheral :

Some computer devices are very expansive. For example laser printer and large hard disks are very costly. Network allows us share these costly devices.                                                             

c) To enable different computers to communicate with each other :     

Network allow different computer to communicate with each other. For example a computer with operating System Windows can communicate
with computer the operating system Linux.                                                                 

d)To improve communication speed and accuracy :

It is possible that the mail from one place to another could take several days. We can send the messages speedily through networking.                                                         

 e)To reduce cost of data transfer:

Computer is a cheaper way to transfer the data. So with the help of the computer, we can reduce the cost of data transfer.

Networking Terminology

Before going into details of networking let use look on some the basic terminology of network.                                                             

a) Nodes (Workstations):

The different terminals are attached to the network and share the resources of the network are called nodes. When we attach a computer to the network, it becomes the workstation of a network.

                                                                         b) Server :

We designate a particular node, which is at a well-known and a fixed address, to provide a service to the network as a whole. The node providing the service is called server.

c) Network Interface Unit : 

The interpreter, which helps in the
between the server and different nodes, is called network Interface Unit. The network interface unit is a device that is attached to server and all workstations to maintain the connection between them. Each network interface unit has a unique node address.

Types of Networking

A network can mean a small group of linked computers to a chain of a few hundred computers of different types (P.C., minis, mainframe etc.) spread around the world. Thus, network varies in size, complexity and geographical spread. Mostly, Computers are classified on the basis of geographical spread and on this basis; there can be three types of networks:

> Local Area Networks (LANs)

> Metropolitan Area Networks ( MANs)

> Wide Area Networks (WANs)                        

 1. Local area Networks (LANs):                    

LANs are privately owned networks within a single building / Campus of up to a few KM in Size. They used to connect PC’s and workstations in factories /offices to share resources (e.g. Printers) and exchange information.                                                          

2.Metropolitan Area Networks (MANs):       

MANs are the networks spread over the city.For example, Cable TV networks that are spread over a city. The purpose is also to share hardware & software resources among its users.     

                                         

3. Wide Area Networks (WANs):

The networks spread across Countries are known as WANs. It is a group of computers that are separated by large distances and tied together. It can even be a group of LANs 3. Wide Area Networks (WANs): that are spread across several locations and connected together to look like a big LAN. The WANs link computers are used to facilitate fast & efficient exchange of information at lesser costs & higher speeds.       

                                                                                                             

Network Topologies

What is a Topology ?

The physical topology of a network refers to the configuration of cables, computers, and other peripherals. Physical topology should not be confused with logical topology which is the method used to pass information between workstations.

Main Types of Physical Topologies

The following sections discuss the physical topologies used in networks and other related topics.  

Linear Bus Topology

Star Topology

Star Wired Ring Topology

Tree Topology 

Mesh Topology

Partial Mesh Topology

1.Linear bus

A linear bus topology consists of a main
run of cable with a terminator at each end. All nodes (file server, workstations, and peripherals) are connected to the linear cable. Ethernet and Local networks use a linear bus topology

Advantages of a Linear Bus Topology           

•Easy to connect a computer or peripheral to a linear bus.

•Requires less cable length than a star topology.                                                           

Disadvantages of a Linear Bus Topology     

•Entire network shuts down if there is a break in the main cable.

•Terminators are required at both ends of the backbone cable.

•Difficult to identify the problem if the entire network shuts down.

This is not meant to be used as a stand-alone solution in a large building

2.Star

A star topology is designed with each node (file server, workstations, & peripherals) connected directly to a central network hub or Concentrator. Data on a star network passes through the hub or concentrator before continuing to its destination.The hub or concentrator manages & controls all functions of the network. It also acts as a Repeater for the data flow. This configuration is common with twisted pair cable; however, it can also be used with Coaxial or fiber optic cable. It is more expensive than linear bus topologies because of the cost of the concentrators. The protocols used with  star configurations are usually Ethernet or Local Talk. Token Ring uses a similar topology, called the star-wired ring.

Advantages of a Star Topology                      

•Easy to install and wire.

•No disruptions to the network  connecting or removing devices.

•Easy to detect faults and to remove parts.

Disadvantages of a Star Topology

•Requires more cable length than a linear topology.

•If the hub or concentrator fails, nodes attached are disabled.                                      

3.Star-Wired Ring

A star-wired ring topology may appear (externally) to be the same as a star topology. Internally, the MAU (multistation access unit) of a star-wired ring contains wiring that allows information to pass from one device to another in a circle or ring The Token ring protocol uses a star-wired ring topology.      

4.Tree Topology                                                

A tree topology combines characteristics of linear bus and star topologies. It consists of groups of star-configured
workstations connected to a linear bus backbone cable Tree topologies allow for the expansion of an existing network, and enable schools to configure a network to meet their needs.                                                

Advantages of a Tree Topology                       
•Point-to-point wiring for individual segments.                                                        •Supported by several hardware and software vendors.                                            

Disadvantages of a Tree Topology   

•Overall length of each segment is limited by the type of cabling used.

•If the backbone line breaks, the entire segment goes down.

•More difficult to configure and wire than other topologies.

5.Mesh Topology

The topology of a network whose components are all connected directly to every other component. A mesh network is a local area network (LAN)) that employs one of two connection arrangements, full mesh topology or partial mesh topology.

In the full mesh topology, each node (workstation or other device) is connected directly to each of the others.

6.Partial Mesh Topology

In the partial mesh topology, some nodes are connected to all the others, but some of the nodes are connected only to those other nodes with which they exchange the most data. The illustration shows a full mesh network with five nodes. Each node is shown as a sphere, and connections are shown as straight lines. The connections can be wired or wireless.

A mesh network is reliable and offers redundancy. If one node can no longer operate, all the rest can still communicate with each other, directly or through one or more intermediate nodes. Mesh networks work well when the nodes are located at scattered points that do not lie near a common line. The main drawback of the mesh topology is expense, because of the large number of cables and connections required. In some scenarios, a ring network or star network may prove more cost effective than a mesh network. If all the nodes lie near a common line, the bus network topology is often the best alternative in terms of cost.

Protocols

A protocol can be one rule or a complete set of rules and standards that allow different devices to hold conversations. For example, Human communication would be impossible without language, grammar, and cultural rules. The following is an example of set rules and standards in which network service requestors and service providers can communicate :-          

•How the transmission media is physically setup ?
•How do network entities contact one another ?
•How do network entities know how much data can be transmitted ?
•How are network entities guaranteed that a message has been received correctly ?
•How is a message passed to the intended recipient(s) ?
•How are bits transmitted on the media ?
•How do network entities, with disparate languages, communicate?
•How do network entities know when to transmit data?

Uniform Resource Locator (URL)                    

A URL is the address of a resource accessible on the internet. The type of resources depends on the internet application Protocol.
Example of URL is http://www.wwe.org   

According to this URL, a web page needs to be accessed by using HTTP (a protocol) that is located on a computer named www.wwe.org

File Transfer Protocol & Hypertext Transfer Protocol These are described below :

File Transfer Protocol (FTP)

A standard Internet protocol is the simplest way to exchange files between computers on the Internet. FTP is an application protocol that uses the Internet’s TCP/up protocols. It’s also commonly used to download programs and other files to your computer from other servers. Basic FTP support is usually provided as part of a suite of programs that come with TCP/IP.

Hypertext Transfer Protocol (HTTP)               

This protocol is used by the WWW. The main task of HTTP is to deals the messages format and transmission and what actions Web servers and browsers should take in response to various commands. For Example When you enter a URL in Browser, this actually sends an HTTP Command to the Web server (a computer where web pages reside) directing it to fetch and transmit the Web works is HTML, Which deals with how Web Pages are formatted and displayed Each page on a web has a name/address. The address is preceded by http:// and most frequently http://www.cdac.org. This address/name is known as URL (Uniform Resource Locator. URL‘s have the following general format:

1. Type of the resource

(e.g. http:// or ftp ://)

2. Name of the server

(e.g. cdac.org )

3. Name of a specific file on the server

(e.g. /office03.html) this is optional.

Private Networks

Some networks are specifically designed for organizations and used completely by
individual. These are called private networks. The Communication Equipment that forms the network is purchase/lease in the name of the organization. The first wan to be designed and developed was the private network, ARPANET , a United States network. The objective was to make the interesting and unique computer facilities available in some computer centers accessible to large community of users.

Concept of Channel

What is Communication Channel ?

When we send the message/data from one PC to another, we first convert the data into electrical/electromagnetic energy using some conversion mechanism. This is then passed through a communication channel. This channel may be in the form of electric wires or in the form of high-energy electromagnetic beam. This channel conveys the electromagnetic energy to the receiver end, which is again converted to give the message.                                                          

Characteristics of an ideal  Communication Channel                                                             

a) It should be able to deliver maximum amount of electromagnetic energy from the transmitter to the receiver with the minimum amount of cost.

b) It should not add much noise on the way so that the receiver is able to
understand the message correctly.

c) There should not be any restriction on the distance between the transmitter where sender is located and the receiver where the signal received.                                                                                                        

 Digital Channel Capacity                                       

It is the number of digits values the channel conveys in one second. The
measurement is in bits per second (bps), also called as bit rate of a channel. The bit rate for networking ranges from kilobits per second or Kbps to million of bits per Seconds (megabits per Second or Mbps)

The duration of the bit rate determines the bit rate. The shorter the duration of a bit signal, the greater the bps rating of the signal.                                                       

Baud

Baud is a unit of measuring data transmission speed. It is used to describe the capacity of a carrier. In general usage, Baud is identical to bits per Second.

Bandwidth

Bandwidth In electronic communication, bandwidth is the width of the range of frequencies that an electronic signal uses on a given transmission medium. In this usage, bandwidth is expressed in terms of the difference between the highest frequency signal component and the lowest-frequency signal component. Since the frequency of a signal is measured in hertz (the number of cycles of change per second), a given bandwidth is the difference in hertz between the highest frequency the signal uses and the lowest frequency it uses. A typical voice signal has a bandwidth of
approximately three kilohertz (3 KHz) an analog television (TV) broadcast video
signal has a bandwidth of six megahertz (6 MHz) — some 2,000 times as wide as the voice signal.

The wider the bandwidth of a communication system, the more it can transmit in a given period of time. It is expressed in Kilobits per Second. Hence determines rate at which information can be sent through a communication channel.

Bandwidth domain

In a LAN, it is the set of devices that shares and compete for bandwidth.

Data Transfer Rate

In computer networks, bandwidth is often used as a synonym for Data Transfer Rate.
The amount of data that can be carried from one point to another in a given time
period (usually a second). This kind of bandwidth is usually expressed in bits (of data) per second (bps). Occasionally, it’s expressed as bytes per second (Bps). A Modem that works at 57,600 bps has twice the bandwidth of a modem that works at 28,800 bps. In general, a link with a high bandwidth is one that may be able to carry enough information to sustain the succession of images in a video presentation. Data transfer speed on the other hand is expressed in bits.In bit rates the abbreviations are as follows:

•1 kbps = 1,000 bits per second

•1 Mbps = 1,000,000 bits per second

•1 Gbps = 1,000,000,000 bits per second   
Kbps (kilobits/sec) means thousands of bits per second                                             
 Mbps (megabits/sec) means millions of bits per second                             

Gbps (gigabits/sec) means billions of bits per second  (where “billion”= 1,000,000,000.00")                           

Tbps (terabits/sec) means trillions of bits per second (as in “terabit router” or “terabit speeds”)                             

Pbps  (peta bits/sec) means quadrillions of bits per second

Alternate forms

bbps = billion bits per second (where b = 1 000 000 000)

mbps = million bits per second (where m = 1 000 000)

 kbps = thousand bits per second (where k = 1 000)

tbps = trillion bits per second (where t = 1 000 000 000 000) [theoretical]                       

Bits and Bytes

1 Byte = 8 bits; kbps* 0.1220703125 =KB/s                                                               
Because there are 8 bits in a Byte, to get a bit-rate (speed) from values given in
Bytes, you must multiply the total no. of Bytes by 8. Conversely, to get KB/s values from bit rates, you must divide the total no. of bits by 8, then divide by 1,024.
For converting KB/s to kbps (bit rate from Byte values), the equation is as follows :

<K> Kilobytes * 1,024 = <t> total Bytes

<t> total Bytes * 8 = <b> bits

<b> bits / 1,000 = <k> kilobits