computers

HTML TAG LIST

2011-11-23T03:34:00.000-08:00

HTML Tags Chart

To use any of the following HTML tags, simply select the HTML code you'd like and copy and paste it into your web page.

Tag

Name

Code Example

Browser View

Nothing will show (Tip)

<a - anchor <a href="http://www.domain.com/">
Visit Our Site</a> http://abhi-computers.blogspot.com/ (Tip)

<b> bold <b>Example</b> Example

<big> big (text) <big>Example</big> Example (Tip)

<body> body of HTML document <body>The content of your HTML page</body> Contents of your web page (Tip)

<br> line break The contents of your page<br>The contents of your page The contents of your web page
The contents of your web page

center

<center>This will center your contents</center>

This will center your contents

<dd>

definition description

<dl>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
</dl>

Definition Term: Definition of the term
Definition Term: Definition of the term

<dl>

definition list

<dl>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
</dl>

Definition Term: Definition of the term
Definition Term: Definition of the term

<dt>

definition term

<dl>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
<dt>Definition Term</dt>
<dd>Definition of the term</dd>
</dl>

Definition Term: Definition of the term
Definition Term: Definition of the term

<em> emphasis This is an <em>Example</em> of using the emphasis tag This is an Example of using the emphasis tag

<font> font <font face="Times New Roman">Example</font> Example (Tip)

<font> font <font face="Times New Roman" size="4">Example</font> Example (Tip)

<font> font <font face="Times New Roman" size="+3" color="#ff0000">Example</font> Example (Tip)

<form>

form

<form action="mailto:you@yourdomain.com">
Name: <input name="Name" value="" size="10"><br>
Email: <input name="Email" value="" size="10"><br>
<center><input type="submit"></center>
</form>

heading 1
heading 2
heading 3
heading 4
heading 5
heading 6

<h1>Heading 1 Example</h1>
<h2>Heading 2 Example</h2>
<h3>Heading 3 Example</h3>
<h4>Heading 4 Example</h4>
<h5>Heading 5 Example</h5>
<h6>Heading 6 Example</h6>

<head> heading of HTML document <head>Contains elements describing the document</head> Nothing will show

<hr>

horizontal rule

<hr />

Contents of your web page (Tip)

Contents of your web page

<hr>

horizontal rule

<hr width="50%" size="3" />

Contents of your web page

<hr>

horizontal rule

<hr width="50%" size="3" noshade />

Contents of your web page

<hr>
(Internet
Explorer)

horizontal rule

<hr width="75%" color="#ff0000" size="4" />

Contents of your web page

<hr>
(Internet
Explorer)

horizontal rule

<hr width="25%" color="#6699ff" size="6" />

Contents of your web page

<html> hypertext markup language <html><head>
<meta>
<title>Title of your web page</title>
</head>
<body>HTML web page contents
</body>
</html> Contents of your web page

<i> italic <i>Example</i> Example

<img> image <img src="Earth.gif" width="41" height="41" border="0" alt="text describing the image" /> (Tip)

<input>

input field

Example 1:

<form method=post action="/cgi-bin/example.cgi">
<input type="text" size="10" maxlength="30">
<input type="Submit" value="Submit">
</form>

<input>
(Internet Explorer)

input field

Example 2:

<form method=post action="/cgi-bin/example.cgi">
<input type="text" style="color: #ffffff; font-family: Verdana; font-weight: bold; font-size: 12px; background-color: #72a4d2;" size="10" maxlength="30">
<input type="Submit" value="Submit">
</form>

<input>

input field

Example 3:

<form method=post action="/cgi-bin/example.cgi">
<table border="0" cellspacing="0" cellpadding="2"><tr><td bgcolor="#8463ff"><input type="text" size="10" maxlength="30"></td><td bgcolor="#8463ff" valign="Middle"> <input type="image" name="submit" src="yourimage.gif"></td></tr> </table>
</form>

<input>

input field

Example 4:

<form method=post action="/cgi-bin/example.cgi">
Enter Your Comments:<br>
<textarea wrap="virtual" name="Comments" rows=3 cols=20 maxlength=100></textarea><br>
<input type="Submit" value="Submit">
<input type="Reset" value="Clear">
</form>

<input>

input field

Example 5:

<form method=post action="/cgi-bin/example.cgi">
<center>
Select an option:
<select>
<option >option 1</option>
<option selected>option 2</option>
<option>option 3</option>
<option>option 4</option>
<option>option 5</option>
<option>option 6</option>
</select><br>
<input type="Submit" value="Submit"></center>
</form>

<input>

input field

Example 6:

<form method=post action="/cgi-bin/example.cgi">
Select an option:<br>
<input type="radio" name="option"> Option 1
<input type="radio" name="option" checked> Option 2
<input type="radio" name="option"> Option 3
<br>
<br>
Select an option:<br>
<input type="checkbox" name="selection"> Selection 1
<input type="checkbox" name="selection" checked> Selection 2
<input type="checkbox" name="selection"> Selection 3
<input type="Submit" value="Submit">
</form>

<li>

list item

Example 1:

<menu>
<li type="disc">List item 1</li>
<li type="circle">List item 2</li>
<li type="square">List item 3</li>
</MENU>

Example 2:

<ol type="i">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Example 1: (Tip)

List item 1
List item 2
List item 3

Example 2:

List item 1
List item 2
List item 3
List item 4

<marquee>
(Internet
Explorer) scrolling text <marquee bgcolor="#cccccc" loop="-1" scrollamount="2" width="100%">Example Marquee</marquee> Example Marquee(Tip)

<menu>

menu

<menu>
<li type="disc">List item 1</li>
<li type="circle">List item 2</li>
<li type="square">List item 3</li>
</menu>

List item 1
List item 2
List item 3

<ol>

ordered list

Numbered

<ol>
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Numbered Special Start

<ol start="5">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Lowercase Letters<ol type="a">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Capital Letters
<ol type="A">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Capital Letters Special Start
<ol type="A" start="3">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Lowercase Roman Numerals
<ol type="i">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Capital Roman Numerals
<ol type="I">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Capital Roman Numerals Special Start
<ol type="I" start="7">
<li>List item 1</li>
<li>List item 2</li>
<li>List item 3</li>
<li>List item 4</li>
</ol>

Numbered

List item 1
List item 2
List item 3
List item 4

Numbered Special Start

List item 1
List item 2
List item 3
List item 4

Lowercase Letters

List item 1
List item 2
List item 3
List item 4

Capital Letters

List item 1
List item 2
List item 3
List item 4

Capital Letters Special Start

List item 1
List item 2
List item 3
List item 4

Lowercase Roman Numerals

List item 1
List item 2
List item 3
List item 4

Capital Roman Numerals

List item 1
List item 2
List item 3
List item 4

Capital Roman Numerals Special Start

List item 1
List item 2
List item 3
List item 4

listbox option

<form method=post action="/cgi-bin/example.cgi">
<center>
Select an option:
<select>
<option>option 1</option>
<option selected>option 2</option>
<option>option 3</option>
<option>option 4</option>
<option>option 5</option>
<option>option 6</option>
</select><br>
</center>
</form>

<p>

paragraph

This is an example displaying the use of the paragraph tag. <p> This will create a line break and a space between lines.

Attributes:

<p align="left">
Example 1:<br />
<br />
This is an example<br>
displaying the use<br>
of the paragraph tag.</p>
<p align="right">
Example 2:<br>
<br>
This is an example<br>
displaying the use<br>
of the paragraph tag.</p>
<p align="center">
Example 3:<br>
<br>
This is an example<br>
displaying the use<br>
of the paragraph tag.</p>

This is an example displaying the use of the paragraph tag.

This will create a line break and a space between lines.

Attributes:

Example 1:

This is an example
displaying the use
of the paragraph tag.

Example 2:

This is an example
displaying the use
of the paragraph tag.

Example 3:

This is an example
displaying the use
of the paragraph tag.

<small> small (text) <small>Example</small> Example (Tip)

<strike> deleted text <strike>Example</strike> ~~Example~~

<strong> strong emphasis <strong>Example</strong> Example

<table>

table

Example 1:

<table border="4" cellpadding="2" cellspacing="2" width="100%">
<tr>
<td>Column 1</td>
<td>Column 2</td>
</tr>
</table>

Example 2: (Internet Explorer)

<table border="2" bordercolor="#336699" cellpadding="2" cellspacing="2" width="100%">
<tr>
<td>Column 1</td>
<td>Column 2</td>
</tr>
</table>

Example 3:

<table cellpadding="2" cellspacing="2" width="100%">
<tr>
<td bgcolor="#cccccc">Column 1</td>
<td bgcolor="#cccccc">Column 2</td>
</tr>
<tr>
<td>Row 2</td>
<td>Row 2</td>
</tr>
</table>

Example 1: (Tip)

Column 1

Column 2

Example 2: (Tip)

Column 1

Column 2

Example 3: (Tip)

Column 1	Column 2
Row 2	Row 2

<td>

table data

<table border="2" cellpadding="2" cellspacing="2" width="100%">
<tr>
<td>Column 1</td>
<td>Column 2</td>
</tr>
</table>

Column 1

Column 2

<th>

table header

<div align="center">
<table>
<tr>
<th>Column 1</th>
<th>Column 2</th>
<th>Column 3</th>
</tr>
<tr>
<td>Row 2</td>
<td>Row 2</td>
<td>Row 2</td>
</tr>
<tr>
<td>Row 3</td>
<td>Row 3</td>
<td>Row 3</td>
</tr>
<tr>
<td>Row 4</td>
<td>Row 4</td>
<td>Row 4</td>
</tr>
</table>
</div>

Column 1	Column 2	Column 3
Row 2	Row 2	Row 2
Row 3	Row 3	Row 3
Row 4	Row 4	Row 4

<title> document title <title>Title of your HTML page</title> Title of your web page will be viewable in the title bar. (Tip)

<tr>

table row

<table border="2" cellpadding="2" cellspacing="2" width="100%">
<tr>
<td>Column 1</td>
<td>Column 2</td>
</tr>
</table>

Column 1

Column 2

<tt> teletype <tt>Example</tt> Example

<u> underline <u>Example</u> Example

<ul>

unordered list

Example 1:<br>
<br>
<ul>
<li>List item 1</li>
<li>List item 2</li>
</ul>
<br>
Example 2:<br>
<ul type="disc">
<li>List item 1</li>
<li>List item 2</li>
<ul type="circle">
<li>List item 3</li>
<li>List item 4</li>
</ul>
</ul>

Example 1:

List item 1
List item 2

Example 2:

List item 1
List item 2
- List item 3
- List item 4

SLIDING WINDOW PROTOCOL

2011-04-06T20:38:00.000-07:00

A sliding window protocol is a feature of packet-based data transmission protocols. Sliding window protocols are used where reliable in-order delivery of packets is required, such as in the Data Link Layer (OSI model) as well as in the Transmission Control Protocol (TCP).

Conceptually, each portion of the transmission (packets in most data link layers, but bytes in TCP) is assigned a unique consecutive sequence number, and the receiver uses the numbers to place received packets in the correct order, discarding duplicate packets and identifying missing ones. The problem with this is that there is no limit of the size of the sequence numbers that can be required.

By placing limits on the number of packets that can be transmitted or received at any given time, a sliding window protocol allows an unlimited number of packets to be communicated using fixed-size sequence numbers.

For the highest possible throughput, it is important that the transmitter is not forced to stop sending by the sliding window protocol earlier than one round-trip delay time (RTT). The limit on the amount of data that it can send before stopping to wait for an acknowledgment should be larger than the bandwidth-delay product of the communications link. If it is not, the protocol will limit the effective bandwidth of the link.

DOMAIN NAME SERVER OR SYSTEM (DNS)

2011-04-06T20:27:00.000-07:00

Short for Domain Name System (or Service or Server), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4.
The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.

Short for digital nervous system, a term coined by Bill Gates to describe a network of personal computers that make it easier to obtain and understand information.

INTERNET

2011-04-06T20:25:00.001-07:00

The Internet, sometimes called simply "the Net," is a worldwide system of computer networks - a network of networks in which users at any one computer can, if they have permission, get information from any other computer (and sometimes talk directly to users at other computers). It was conceived by the Advanced Research Projects Agency (ARPA) of the U.S. government in 1969 and was first known as the ARPANET. The original aim was to create a network that would allow users of a research computer at one university to be able to "talk to" research computers at other universities. A side benefit of ARPANet's design was that, because messages could be routed or rerouted in more than one direction, the network could continue to function even if parts of it were destroyed in the event of a military attack or other disaster.

INTRANET

2011-04-06T20:24:00.001-07:00

Intranet is the generic term for a
collection of private computer networks
within an organization. An intranet uses
network technologies as a tool to
facilitate communication between people
or workgroups to improve the data
sharing capability and overall knowledge
base of an organization's employees.

WWW

2011-04-06T20:23:00.001-07:00

A technical definition of the World Wide Web is: all the resources and users on the Internet that are using the Hypertext Transfer Protocol (HTTP).

A broader definition comes from the organization that Web inventor Tim Berners-Lee helped found, the World Wide Web Consortium (w3c):

"The World Wide Web is the universe of network-accessible information, an embodiment of human knowledge."

LEXICAL ANALYSER

2011-04-01T18:23:00.003-07:00

#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<stdlib.h>
main()
{
char buff[30],c,ch;
char key[5][10]={"int\0","char\0","float\0","main\0"};
FILE *fp;
int i,j,k,l,m;
clrscr();
fp=fopen("add.c","r");
while(1)
{
ch=fgetc(fp);
c=ch;
if(c==EOF)
break;
if(c=='+'||c=='-'||c=='*'||c=='/')
{
buff[0]=c;
c=fgetc(fp);
if(c=='+'||c=='-'||c=='=')
printf ("%c%c\t is operator\n",buff[0],c);
else
{
printf("%c is operator\n",buff[0]);
fseek(fp,0,-1);
}
}
else if(c=='=')
{
buff[0]=c;
c=fgetc(fp);
if(c=='=')
printf("%c%c\t is comparision\n",buff[0],c);
else
{
printf("%c is assignment\n",buff[0]);
fseek(fp,0,-1);
}
}
else if(isdigit(c))
{
i=0;
buff[i]=c;
c=fgetc(fp);
while (isdigit(c))
{
i++;
buff[i]=c;
c=fgetc(fp);
}
for(k=0;k<=i;k++)
{
printf("%c",buff[k]);
}
printf("\t is number\n");
fseek(fp,0,-1);
}
else if(isalnum(c))
{
m=0;
i=0;
do
{
buff[i]=c;
c=fgetc(fp);
i++;
}while(isalnum(c));
buff[i]='\0';
for(j=0;j<4;j++)
{
if(strcmp(buff,key[j])==0)
{
m=1;
printf(" %s is key word\n",buff);
break;
}
}
if(strcmp(buff,key[j])!=0)
{
printf(" %s is a identifier\n",buff);
}
fseek(fp,0,-1);
}
}
fclose(fp);
getch();
}

RECURSIVE PARSING

2011-04-01T18:23:00.001-07:00

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
char input[10];
int i=0;
void t();
void eprime();
void f();
void tprime();
void e()
{
if(input[i+1]=='+')
eprime();
else if(input[i+1]=='*')
{
t();
e();
}
else if(input[i]=='\0')
printf("string not accepted");

else
{
f();
e();
}
}
void t()
{
if(input[i+1]=='*')
tprime();
else if(input[i]=='\0')
printf("string not accepted");
else
f();
}
void f()
{
if(input[i]=='(')
{
i++;
e();
}
else if(input[i]==')' && input[i+1]=='\0')
printf("string is accepted");
else if(input[i]=='I')
{
i++;
if(input[i]=='\0'||input[i]==')')
{
printf("string is accepted");
exit(0);
}
}
}
void eprime()
{
f();
i++;
e();
}
void tprime()
{
f();
i++;
e();
}
main()
{
clrscr();
printf("enter the string replacing id with I\n");
scanf(" %s",input);
e();
getch();
}

3ADDRESS CODE

2011-04-01T18:22:00.001-07:00

#include<stdio.h>
#include<ctype.h>
main()
{
char expr[20],stack[20];
int i,top=0,k=0,num[20];
printf("enter the postfix expression\n");
scanf("%s",&expr);
for(i=0;expr[i]!='\0';i++)
if(isalnum(expr[i]))
stack[top++]=expr[i];
else
{
printf("T%d=",k);
if(stack[top-2]=='T')
printf("%c%d",stack[top-2],num[top-2]);
else
printf("%c",stack[top-2]);
printf("%c",expr[i]);
if(stack[top-1]=='T')
printf("%c%d",stack[top-1],num[top-1]);
else
printf("%c",stack[top-1]);
printf("\n");
top=top-2;
stack[top]='T';
num[top++]=k++;
}
}

CYCLIC REDUNDANCY CHECK PROGRAM

2011-03-04T21:35:00.000-08:00

#include<iostream.h>
#include<conio.h>
#include<stdio.h>
int main() //int avgc,char *avgv[];
{
int val1[20],val2[20],val3[20],val4[20];
int x,i,j,n,m,a,s;
clrscr();
cout<<"enter no .of generating fu.bits";
cin>>n;
cout<<"\n";
cout<<" enter gen.fu";
cout<<"\n ";
for (i=0;i<n;i++)
{
cin>>val1[i];
}
cout<<"gen.fu";
cout<<"\n";
for(i=0;i<n;i++)
{
cout<<val1[i];
}
cout<<"\n";
cout<<" enter no .of bits of polynomial";
cout<<"\n";
cin>>n;
cout<<"enter polynomial ";
cout<<"\n";
for(i=0;i<m;i++)
{
cin>>val2[i];
val4[i]=val2[i];
}
cout<<"\n";
cout<<" polynomial";
cout<<"n";
for(i=0;i<m;i++)
{
cout<<val2[i];
}
cout<<"\n";
cout<<"\n";
for(i=m;i<m+n-1;i++)
{
val2[i]=0;
}
cout<<"\n";
cout<<"appened polynomial i";
for(i=0;i<m+n-1;i++)
{
cout<<val2[i];
}
a=m+(n-1);
for(i=0;i<m;i++)
{
if(val2[i]==0)
{
for(i=1;j<n+i;++j)
val2[j]=val2[j]^0;
}
else
{
val2[i]=val2[i]^val2[0];
val2[i+1]=val2[i+1]^val1[1];
val2[i+2]=val2[i+2]^val1[2];
val2[i+3]=val2[i+3] ^val1[3];
}
}
cout<<"\n \t the crc is !";
for(i=m;i<a;++i)
cout<<val2[i];
for(i=m,j=m;j<a,i<m+n-1;j++,i++)
{
val4[i]=val2[j];
}
cout<<"crc matrix is :";
cout<<"\n";
for(i=0;i<m;i++)
{
if(val4[i]==0)
{
for(j=i;j<n+i;++j)
val4[j]=val4[i]^val1[0];
val4[i+1]=val4[i+1]^val1[1];
val4[i+2]=val4[i+2]^val1[2];
val4[i+3]=val4[i+3]^ val1[3];
}
}
cout<<"\n\t after error check is :";
for(i=m;i<a;i++)
{
cout<< val4[i];
}
cin>>x;
return 0;
}

CHARACTER STUFFING PROGRAM

2011-03-04T21:33:00.001-08:00

#include<stdio.h>
#include<conio.h>
#include<string.h>
void start();
void end(char);
FILE *of;
FILE *cf;
int b,i=0;
char c,a='@',z='$',d[25];
void main()
{
clrscr();
cf=fopen("andy.txt","r");
of=fopen("ani.txt","w");
do
{
c=getc(cf);
d[i++]=c;
}while(c!=EOF);
fprintf(of,"%c",a);
for(i=0;i<strlen(d);i++)
{
if(d[i]==' '||d[i]=='\t')
{
end(d[i]);
}
else if(d[i]=='\n')
{
start();
}
else if(d[i]==EOF)
{
fprintf(of,"%c",z);
}
else
{
fprintf(of,"%c",d[i]);
}
}
printf("file sucessfully stuffed");
fclose(cf);
fclose(of);
getch();
}
void start()
{
fprintf(of,"%c\n",z);
fprintf(of,"%c",a);
}
void end(char k)
{
fprintf(of,"%c",z);
fprintf(of,"%c",a);
fprintf(of,"%c",k);
fprintf(of,"%c",z);
fprintf(of,"%c",a);
}

ROUND ROBIN

2011-03-04T19:10:00.001-08:00

#include<stdio.h>
#include<conio.h>
void main()
{
int n,i,t=0,s=1;
int a,q,x,*b;
clrscr();
printf("enter number of processes");
scanf("%d",&n);
for(i=1;i<=n;i++)
{
printf("process %d",i);
scanf("%d",&b[i]);
}
printf("enter time quantum");
scanf("%d",&q);
x=0;
for(i=1;i<=n;i++)
  t=t+b[i];
printf("total time is = %d\n",t);
for(i=0;i<=n;i++)
{
for(a=1;a<=n;a++)
{
if(b[a]>0)
{
if(b[a]<q && b[a]>0)
   x=x+b[a];
else
   x=x+q;
printf("current program is p %d...%d \n",a,x);
b[a]=b[a]-q;
s++;
}
}
}
getch();
}

PRIORITY SCHEDULING PROGRAM

2011-03-04T18:48:00.000-08:00

#include<stdio.h>
#include<conio.h>
void main()
{
int i,j,n,r,s,t,x,d=0,p[20],b[20],pr[20];
clrscr();
printf("enter the no. of process");
scanf("%d",&n);
for(i=1;i<=n;i++)
{
printf("enter burst time %d:",i);
scanf("%d",b[i]);
}
for(i=1;i<=n;i++)
{
printf("priority %d",i);
scanf("%d",pr[i]);
}
for(i=1;i<=n;i++)
{
for(j=i+1;j<=n;j++)
{
if(pr[i]>pr[j])
{
r=p[j];
s=b[j];
t=pr[j];
p[j]=p[i];
b[j]=b[i];
pr[j]=pr[i];
p[i]=r;
b[i]=s;
pr[i]=t;
}
}
}
for(i=1;i<=n;i++)
{
x=x+b[i];
printf("process %d interval is from %d to %d",p[i],d,x);
d=x;
}
getch();
}

NETWORK CLASSIFICATION

2011-02-19T10:47:00.000-08:00

The following list presents categories used for classifying networks.

Connection method

Computer networks can be classified according to the hardware and software technology that is used to interconnect the individual devices in the network, such as optical fiber, Ethernet,wireless LAN, HomePNA, power line communication or G.hn.

Ethernet as it is defined by IEEE 802 utilizes various standards and mediums that enable communication between devices. Frequently deployed devices include hubs, switches, bridges, or routers. Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium. ITU-T G.hn technology uses existing home wiring (coaxial cable, phone lines and power lines) to create a high-speed (up to 1 Gigabit/s) local area network.

Wired technologies

Twisted pair wire is the most widely used medium for telecommunication. Twisted-pair cabling consist of copper wires that are twisted into pairs. Ordinary telephone wires consist of two insulated copper wires twisted into pairs. Computer networking cabling consist of 4 pairs of copper cabling that can be utilized for both voice and data transmission. The use of two wires twisted together helps to reduce crosstalk and electromagnetic induction. The transmission speed ranges from 2 million bits per second to 100 million bits per second. Twisted pair cabling comes in two forms which are Unshielded Twisted Pair (UTP) and Shielded twisted-pair (STP) which are rated in categories which are manufactured in different increments for various scenarios.

Coaxial cable is widely used for cable television systems, office buildings, and other work-sites for local area networks. The cables consist of copper or aluminum wire wrapped with insulating layer typically of a flexible material with a high dielectric constant, all of which are surrounded by a conductive layer. The layers of insulation help minimize interference and distortion. Transmission speed range from 200 million to more than 500 million bits per second.

Optical fiber cable consists of one or more filaments of glass fiber wrapped in protective layers. It transmits light which can travel over extended distances. Fiber-optic cables are not affected by electromagnetic radiation. Transmission speed may reach trillions of bits per second. The transmission speed of fiber optics is hundreds of times faster than for coaxial cables and thousands of times faster than a twisted-pair wire.

Wireless technologies

Terrestrial microwave – Terrestrial microwaves use Earth-based transmitter and receiver. The equipment look similar to satellite dishes. Terrestrial microwaves use low-gigahertz range, which limits all communications to line-of-sight. Path between relay stations spaced approx, 30 miles apart. Microwave antennas are usually placed on top of buildings, towers, hills, and mountain peaks.

Communications satellites – The satellites use microwave radio as their telecommunications medium which are not deflected by the Earth's atmosphere. The satellites are stationed in space, typically 22,000 miles (for geosynchronous satellites) above the equator. These Earth-orbiting systems are capable of receiving and relaying voice, data, and TV signals.

Cellular and PCS systems – Use several radio communications technologies. The systems are divided to different geographic areas. Each area has a low-power transmitter or radio relay antenna device to relay calls from one area to the next area.

Wireless LANs – Wireless local area network use a high-frequency radio technology similar to digital cellular and a low-frequency radio technology. Wireless LANs use spread spectrum technology to enable communication between multiple devices in a limited area. An example of open-standards wireless radio-wave technology is IEEE.

Infrared communication , which can transmit signals between devices within small distances not more than 10 meters peer to peer or ( face to face ) without any body in the line of transmitting.

Scale

Networks are often classified as local area network (LAN), wide area network (WAN), metropolitan area network (MAN), personal area network (PAN), virtual private network (VPN),campus area network (CAN), storage area network (SAN), and others, depending on their scale, scope and purpose, e.g., controller area network (CAN) usage, trust level, and access right often differ between these types of networks. LANs tend to be designed for internal use by an organization's internal systems and employees in individual physical locations, such as a building, while WANs may connect physically separate parts of an organization and may include connections to third parties.

Functional relationship (network architecture)

Computer networks may be classified according to the functional relationships which exist among the elements of the network, e.g., active networking, client–server and peer-to-peer(workgroup) architecture.

Network topology

Computer networks may be classified according to the network topology upon which the network is based, such as bus network, star network, ring network, mesh network. Network topology is the coordination by which devices in the network are arranged in their logical relations to one another, independent of physical arrangement. Even if networked computers are physically placed in a linear arrangement and are connected to a hub, the network has a star topology, rather than a bus topology. In this regard the visual and operational characteristics of a network are distinct. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

SCHEDULER

2011-02-07T07:17:00.000-08:00

Types of operating system schedulers

Operating systems may feature up to 3 distinct types of a long-term scheduler (also known as an admission scheduler or high-level scheduler), amid-term or medium-term scheduler and a short-term scheduler . The names suggest the relative frequency with which these functions are performed.

Long-term scheduler

The long-term, or admission, scheduler decides which jobs or processes are to be admitted to the ready queue; that is, when an attempt is made to execute a program, its admission to the set of currently executing processes is either authorized or delayed by the long-term scheduler. Thus, this scheduler dictates what processes are to run on a system, and the degree of concurrency to be supported at any one time - ie: whether a high or low amount of processes are to be executed concurrently, and how the split between IO intensive and CPU intensive processes is to be handled. In modern OS's, this is used to make sure that real time processes get enough CPU time to finish their tasks. Without proper real time scheduling, modern GUI interfaces would seem sluggish. [Stallings, 399].

Long-term scheduling is also important in large-scale systems such as batch processing systems, computer cluster, supercomputers and render farms. In these cases, special purpose job scheduler software is typically used to assist these functions, in addition to any underlying admission scheduling support in the operating system.

Mid-term scheduler

The mid-term scheduler temporarily removes processes from main memory and places them on secondary memory (such as a disk drive) or vice versa. This is commonly referred to as "swapping out" or "swapping in" (also incorrectly as "paging out" or "paging in"). The mid-term scheduler may decide to swap out a process which has not been active for some time, or a process which has a low priority, or a process which is page faulting frequently, or a process which is taking up a large amount of memory in order to free up main memory for other processes, swapping the process back in later when more memory is available, or when the process has been unblocked and is no longer waiting for a resource. [Stallings, 396] [Stallings, 370]

In many systems today (those that support mapping virtual address space to secondary storage other than the swap file), the mid-term scheduler may actually perform the role of the long-term scheduler, by treating binaries as "swapped out processes" upon their execution. In this way, when a segment of the binary is required it can be swapped in on demand, or "lazy loaded". [stallings, 394]

Short-term scheduler

The short-term scheduler (also known as the CPU scheduler) decides which of the ready, in-memory processes are to be executed (allocated a CPU) next following a clock interrupt, an IO interrupt, an operating system call or another form of signal. Thus the short-term scheduler makes scheduling decisions much more frequently than the long-term or mid-term schedulers - a scheduling decision will at a minimum have to be made after every time slice, and these are very short. This scheduler can be preemptive, implying that it is capable of forcibly removing processes from a CPU when it decides to allocate that CPU to another process, or non-preemptive (also known as "voluntary" or "co-operative"), in which case the scheduler is unable to "force" processes off the CPU. [Stallings, 396]. In most cases short-term scheduler is written in assembler because it is critical part of operating system.

Dispatcher

Another component involved in the CPU-scheduling function is the dispatcher. The dispatcher is the module that gives control of the CPU to the process selected by the short-term scheduler. This function involves the following:

Switching context
Switching to user mode
Jumping to the proper location in the user program to restart that program

The dispatcher should be as fast as possible, since it is invoked during every process switch. The time it takes for the dispatcher to stop one process and start another running is known as the dispatch latency.

HDLC

2011-02-07T07:09:00.001-08:00

HDLC: High Level Data Link Control
The High Level Data Link Control (HDLC) protocol, an ISO data link layer protocol based on the IBM SDLC, is to ensure that data passed up to the next layer has been received exactly as transmitted (i.e error free, without loss and in the correct order). Another important function of HDLC is flow control, which ensures that data is transmitted only as fast as the receiver can receive it. There are two distinct HDLC implementations: HDLC NRM (also known as SDLC) and HDLC Link Access Procedure Balanced (LAPB), the later is a more popular implementation. HDLC is usually used by X.25.
LAPB is a bit-oriented synchronous protocol that provides complete data transparency in a full-duplex point-to-point operation. It supports a peer-to-peer link in that neither end of the link plays the role of the permanent master station. HDLC NRM, on the other hand, has a permanent primary station with one or more secondary stations.
HDLC LAPB is a very efficient protocol, which requires a minimum of overhead to ensure flow control, error detection and recovery. If data is flowing in both directions (full duplex), the data frames themselves carry all the information required to ensure data integrity.
The concept of a frame window is used to send multiple frames before receiving confirmation that the first frame has been correctly been received. This means that data can continue to flow in situations where there may be long "turn-around" time lags without stopping to wait for an acknowledgement. This kind of situation occurs, for instance in satellite communication.
There are three categories of frames:

Information framestransport data across the link and may encapsulate the higher layers of the OSI architecture.
Supervisory framesperform the flow control and error recovery functions.
Unnumbered framesprovide the link initialization and termination.

SDLC

2011-02-07T07:00:00.000-08:00

The System Development Life Cycle framework provides system designers and developers to follow a sequence of activities. It consists of a set of steps or phases in which each phase of the SDLC uses the results of the previous one.

A Systems Development Life Cycle (SDLC) adheres to important phases that are essential for developers, such as planning, analysis, design, and implementation, and are explained in the section below. A number of system development life cycle (SDLC) models have been created: waterfall, fountain, spiral, build and fix, rapid prototyping, incremental, and synchronize and stabilize. The oldest of these, and the best known, is the waterfall model: a sequence of stages in which the output of each stage becomes the input for the next. These stages can be characterized and divided up in different ways, including the following:

Project planning, feasibility study: Establishes a high-level view of the intended project and determines its goals.

Systems analysis, requirements definition: Refines project goals into defined functions and operation of the intended application. Analyzes end-user information needs.

Systems design: Describes desired features and operations in detail, including screen layouts, business rules, process diagrams, pseudocode and other documentation.

Implementation: The real code is written here.

Integration and testing: Brings all the pieces together into a special testing environment, then checks for errors, bugs and interoperability.

Acceptance, installation, deployment: The final stage of initial development, where the software is put into production and runs actual business.

Maintenance: What happens during the rest of the software's life: changes, correction, additions, moves to a different computing platform and more. This, the least glamorous and perhaps most important step of all, goes on seemingly forever.

In the following example (see picture) these stage of the Systems Development Life Cycle are divided in ten steps from definition to creation and modification of IT work products:

fragmentation

2011-02-05T21:21:00.000-08:00

In computer storage, fragmentation is a phenomenon in which storage space is used inefficiently, reducing storage capacity and in most cases performance. The term is also used to denote the wasted space itself.

Two kinds of fragmentations are present. they are:-

   a) INTERNAL FRAGMENTATION

   b) EXTERNAL FRAGMENTATION

Internal fragmentation occurs when storage is allocated without intention to use it. This space is wasted. While this seems foolish, it is often accepted in return for increased efficiency or simplicity. The term "internal" refers to the fact that the unusable storage is inside the allocated region but is not being used.

External fragmentation is the phenomenon in which free storage becomes divided into many small pieces over time. It is a weakness of certain storage allocation algorithms, occurring when an application allocates and deallocates ("frees") regions of storage of varying sizes, and the allocation algorithm responds by leaving the allocated and deallocated regions interspersed. The result is that although free storage is available, it is effectively unusable because it is divided into pieces that are too small to satisfy the demands of the application. The term "external" refers to the fact that the unusable storage is outside the allocated regions.

OSI REFERENCE MODEL

2011-01-24T07:37:00.000-08:00

The OSI, or Open System Interconnection, model defines a networking framework for implementing protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.

Application (Layer 7)

This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Presentation (Layer 6)

This layer provides independence from differences in data representation (e.g.,encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Session (Layer 5)

This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Transport (Layer 4)

This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Network (Layer 3)

This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, inter networking, error handling, congestion control and packet sequencing.

Data Link (Layer 2)

At this layer, data packets are encoded and decoded into bits. It furnishestransmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.

Physical (Layer 1)

This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

NETWORK TOPOLOGIES

2011-01-24T07:30:00.000-08:00

Physical Topology means the physical design of a network including the devices, location and cable installation.
Logical Topology refers to the fact that how data actually transfers in a network as opposed to its design.
Topology can be considered as a virtual shape or structure of a network. This shape actually does not correspond to the actual physical design of the devices on the computer network. The computers on the home network can be arranged in a circle shape but it does not necessarily mean that it presents a ring topology.

Computer network topologies can be categorized in the following categories.
• bus
• star
• ring
• mesh
• Tree.
Hybrid networks are the complex networks, which can be built of two or more above mentioned topologies.

Bus Topology
Bus topology uses a common backbone to connect all the network devices in a network in a linear shape. A single cable functions as the shared communication medium for all the devices attached with this cable with an interface connector. The device, which wants to communicate send the broadcast message to all the devices attached with the shared cable but only the intended recipient actually accepts and process that message.

Ring Topology
In ring Network, every computer or devices has two adjacent neighbors for communication. In a ring network, all the communication messages travel in the same directory whether clockwise or anti clockwise. Any damage of the cable of any cable or device can result in the breakdown of the whole network. Ring topology now has become almost obsolete.
FDDI, SONET or Token Ring Technology can be used to implement Ring Technology. Ring topologies can be found in office, school or small buildings.

Star Topology
In the computer networking world the most commonly used topology in LAN is the star topology. Star topologies can be implemented in home, offices or even in a building. All the computers in the star topologies are connected to central devices like hub, switch or router. The functionality of all these devices is different. I have covered the detail of each networking devices in the separate portion of my website. Computers in a network are usually connected with the hub, switch or router with the Unshielded Twisted Pair (UTP) or Shielded Twisted Pair Cables.
As compared to the bus topology, a star network requires more devices & cables to complete anetwork. The failure of each node or cable in a star network, won’t take down the entire network
as compared to the Bus topology.
However if the central connecting devices such as hub, switch or router fails due to any reason,then ultimately all the network can come down or collapse.

Tree Topology
Tree topologies are comprised of the multiple star topologies on a bus. Tree topologies integrate multiple star topologies together onto a bus. Only the hub devices can connect directly with the tree bus and each Hub functions as a root of a tree of the network devices. This bus/star/hybrid combination supports future expandability of the computer networks, much better than a bus or star.

Mesh Topology
Mesh topology work on the concept of routes. In Mesh topology, message sent to the destination can take any possible shortest, easiest route to reach its destination. In the previous topologies star and bus, messages are usually broadcasted to every computer, especially in bus topology. Similarly in the Ring topology message can travel in only one direction i.e clockwise or anticlockwise. Internet employs the Mesh topology and the message finds its route for its destination. Router works in find the routes for the messages and in reaching them to their destinations.The topology in which every devices connects to every other device is called a full Mesh topology unlike in the partial mesh in which every device is indirectly connected to the other devices.

ROUTERS AND FIREWALLS

2011-01-24T07:27:00.001-08:00

Routers

A router is an internetworking device that forwards packets between networks by processing information found in the datagram or packet (Internet protocol information from Layer 3 of the OSI Model). In many situations, this information is processed in conjunction with the routing table (also known as forwarding table). Routers use routing tables to determine what interface to forward packets (this can include the "null" also known as the "black hole" interface because data can go into it, however, no further processing is done for said data).

Firewalls

Firewalls are the most important aspect of a network with respect to security. A firewalled system does not need every interaction or data transfer monitored by a human, as automated processes can be set up to assist in rejecting access requests from unsafe sources, and allowing actions from recognized ones. The vital role firewalls play in network security grows in parallel with the constant increase in 'cyber' attacks for the purpose of stealing/corrupting data, planting viruses, etc.

WAN

2011-01-24T06:58:00.001-08:00

WANs are used to connect the computers in the one part of the world with the other part of the world. So the users and computers from the different parts of the world can communicate with each other. Many WANs are generally built for one organization. Other types of WAN networking are the Internet service providers that connect the LANS or individual computers to the Internet. WAN networks are built using the leased lines and a router is connected to the one end of the WAN and a hub is connected to the other end.

There are three basic types of computer networking LAN (local area network), MAN (metropolitan area network) and WAN (Wide area network). A wide area network is a geographically dispersed large network. A wide area network can be privately owned or rented. A WAN covers a large geographical area such as a city, province or a country.

A widea area network may consist of a multiple LANs or MANs. The world’s most popular wide arae network in the world is is the internet. WANs are the corporate network that utilizes leased lines.
Wide area networks generally utilize much expensive equipment. The main communication technologies that are included in the WAN are SONET, Frame Relay and ATM. The computers that are connected to the WANs are generally connected through the public networks and they can also be connected through the satellites.

With this hub a number of computers and other hubs and switches are connected. Among the other methods of building the WANs are the circuit switching or packet switching methods. The general protocols and the communication technologies that are involved in the overall wide area networking/communication are TCP/IP, SONET, MPLS, ATM and X.25, which closely works with frame relay. Typical a WAN consists of a number of interconnected switching nodes.
Networking Methods
Networking is a complex part of the computing and it covers the broader range of the IT industry. All the communication in the world including satellite communication, mobile communication, internet, telephones and WANs is due to the networking. There are two main types of the networking.
Local Area Network (LAN)
A local area network is relatively covers small space and provides services to a small amount of people. A local area can be divided into two major types, peer to peer and the client server. Depending on the number of the users a network is configured. Among the few examples of the peer to peer networks are small office network and home networks. On the other hand, in the client/server networking model all the client computers depends on the server for resources like (modem, printer, scanner, cd-rom) and they are connected with the server. The servers in the client/server networking model works in different capacities like single service server and multiple service servers.
Wide Area Network (WAN)
A wide area network is a network where are large number of the resources are deployed in a very wide geographically area. The best example of the WAN is the internet itself which is a largest network in the world.
In order for communication to take place between the computers the mediums must be used. These mediums can be cables, Routers, Repeaters, Ethernet, Protocols and switches etc. These different mediums make the data communication possible in different scenarios.
Types of WANs
There are two basic types of Widea Area Networking.
A computer network is set of computers and devices that are connected with each other. Examples of the networks are the Internet, local area network, Wide area network and satellite networks.
Centralized WANS:
A WAN that consists of a server or a group of servers in a central location to which client computers connect, the server provides the most of the functionalities of a network. Many banks, large stores, large schools and universities use centralized WAN. A centralized wide area network may have a number of the servers in the centralized location.
Distributed WAN:
A widea area network that consists of the client and server computers that are distributed throughout the WAN, the functionalities of the network are distributed throughout the WAN. The internet is an example of the wide area network.
The impact of Wide Area Networking on business
In this age of information, data communication (sending and receiving data) over a long distance is a necessity. There have been number of technologies developed that enable networks and their users to communicate with each other, and exchange data easily even if they are at the different end of the world. Geographical area is no more a matter in today’s communication age. Because of this the communication through WAN has been become vital. Wide area networks make it feasible for the companies to have a single network, which will connect their several offices and departments. Companies, banks, large organizations often have their offices spread over a large distance. Without wide area networking the people of a multinational organization can face difficulties to communicate with each. WANs are important in connecting institutes they are very far from each other.

WIRELESS COMMUNICATION

2011-01-24T06:50:00.000-08:00

Wireless networking is very useful in the public places, libraries, hotels, schools, airports, railway stations where one might find wireless access to the internet. A drawback in the wireless internet is that quality of service (QOS) is not guaranteed if there is any interference then the connection may be dropped.

Wireless Network Types

Wireless Local Area Networks (WLANS)

WLANS allow users in local area, such as in a university or a library to form a network and gain wireless access to the internet. A temporary network can be formed by a small number of users without the need of access point; given that they do not need to access the resources.

Wireless Personal Area Networks (WPANS)

There are two current technologies for wireless personal network Bluetooth and Infra Red. These technologies will allow the connectivity of personal devices within an area of 30 feet. Infra Red requires a direct line and the range is less as compared to Bluetooth technology.

Wireless Metropolitan Area Networks (WMANS)

WMANS allow the connectivity of multiple networks in a metropolitan area such as building in a city. The network connectivity is the alternative of copper or fiber cabling.

Wireless Wide Area Networks (WWANS)

WWANS or Wireless Area Networks can be maintained over large areas such as in different cities or between different countries, via multiple satellite systems or antenna sites. The types of system are called 2G systems.
The following table shows the range those different types of wireless network covers.
Network Meter
Personal Area Network 0-10
Local Area Network 0-100
Wide Are Network 0-10000
Security in Wireless Networking
The following different types of security methods are available in the wireless networking.

Wired Equivalent Privacy (WEP)

Wired Equivalent Privacy is intended to stop the interference of radio frequency that is signaled by unauthorized users and this security measure is most suitable for the small networks. There is not key management protocol and each key is entered manually into the clients that’s why this is very time consuming administrative task. The WEP security method is based on the RC4 encryption algorithm. In the WEP all the client computers and Access points are configured with the same encryption and decryption keys.

Service Set Identifier (SSID)

Service Set Identifier (SSID) acts a simple password by allowing WLAN network to be split up into different networks and each having a unique identifier. These identifiers are configured in the multiple access points. To access any of any networks, a computer is configured in such a way that each is having a corresponding SSID identifier for that network. If the SSID match between the two computers or networks then access is granted to each other.

Media Access Control filtering (MAC Access Control)

A list of the MAC addresses of the client computers can be inputted into an Access point and only those computers are granted to give the access to the network. When a computer makes a request, its MAC address is compared to the list of the MAC addresses to the Access point and based on this access permission granted to deny.
This is a good security method but it is mainly involved in the small wireless networks because there is more manual work is involved of entering the MAC address into the Access point.

Bluetooth

Bluetooth is a simple type of the wireless networking that operates in the digital devices, like mobiles phones, personal computers, PDA, Laptops, digital camera, MP3 players and other Bluetooth enabled devices to form a small network. In the Bluetooth technology eight devices can be connected to each other at the same time. Bluetooth can also be found in the headsets, hands-free kits, wireless keyboards and mouse. Bluetooth technology was invented by Ericsson in 1994 and after four years in 1998 some major mobile phone companies such as Nokia, Ericsson, Intel and Toshiba formed a group to promote this technology.

Bluetooth technology falls in the category of personal area networking because it operates in the range of 30 to 300 feet. Bluetooth uses the radio waves technology, which is not very expensive and has low power consumption. Many different companies are intended to add the Bluetooth chip in their digital devices. Bluetooth technology is getting very popularity because of its low cost and portability.

The Future of Wireless Networking

WLANS wireless networking type is very popular in home networking and more than 20 percent homes with broadband internet are using WLANS and this number is increasing. In a general estimate worldwide hotspots have now reached more than 30,000 and will grow about 210,000 in the next few years. Most large hotels already offer Wi-Fi and the business travelers are willing to pay wireless access. 802.11 is the next Wi-Fi speed standard is set to offer bandwidth around 108Mbps and is still under development. With the speed of 70 Mbps and a range up to 30 miles, the 80216 standard, known as WiMAX is sure to get boost.

Some Tips & Tricks

• When purchasing a wireless NIC card try to get one that is having external antenna. When you are out and using Wi-Fi enabled laptop, disable Microsoft file and sharing, which enables other computers in a network to access data and resources on your computer. In this way, your computer or laptop will be saved from hackers.
• If you are concerned about the interference from the other wireless access point set the AP and wireless computers to use a non-overlapping channel.
• Change the configuration interface password of the access point before you enable it.
• Only buy an access point that is having upgradeable capabilities. By this way you can take the advantage of security enhancements.
• Keep the access point up to date.

TCP IP

2011-01-24T06:42:00.003-08:00

A common communication language is used by the computers and the communication devices is known as protocols. The most commonly used and popular protocol on the internet and in the home and other networks is called TCP/IP. TCP/IP is not a single protocol but it is a suite of several protocols.A computer network can be a wired or wireless and TCP/IP protocol can work both in types of a network.Data flow or communication can be divided into seven logical layers called OSI layers model that was developed by Intel and Xerox Corporation and was standardized by ISO.

1. Application layer
2. Presentation layer
3. Session layer
4. Transport layer
5. Network layer
6. Data Link layer
a. Media access control sub-layer
b. Logical link control sub-layer
7. Physical layer
A network can be divided into different scales and ranges and it depends on the requirement of the organization and the geographical location. Computer Network can be divided into Local Area Network, Personal Area Network, Campus Area Network, Wireless Local Area Network, Metropolitan Area Network and Wide Area Network.

COMPUTER NETWORKS

2011-01-24T06:38:00.000-08:00

A computer network can be divided into a small segments called Local Area Network (LAN), networking between computers in a building of a office, medium sized networks (MAN), communication between two offices in a city and wide area networks (WAN) networking between the computers, one is locally placed and the other can be thousands of miles away in another city or another country in the world.

WAN connectivity is achieved by a device known as “Router”. The internet is the world’s largest WAN, where millions of computers from all over the globe and connected with each other.

Networking is the practice of linking two or more computers or devices with each other. The connectivity can be wired or wireless. A computer network can be categorized in different ways, depends on the geographical area as mentioned above.

A network topology defines the structure, design or layout of a network. There are different topologies like bus, ring, star, mesh, hybrid etc. The star topology is most commonly used topology. In the star topology, all the computers in the network are connected with a centralized device such as hub or switch. Thus forms a star like structure. If the hubs/switch fails to work for any reason then all the connectivity and communication between the computers will be halted.