Introduction to computer network


computer network is a collection of computer and devices connected together via communication device and transmission media.



For example - It may connect computer to many other computer printer scanner.

The medium of connection of communication device is optical fiber, co-axial fiber, wireless (radio wave, microwave and satellite).

The computer network can be arranged by some topology like ring, star, bus, hybrid.




Advantage of computer network

  • Sharing of device such as printer and scanner.
  • Shading of program / software.
  • Sharing of data.
  • Sharing of information.
  • Sharing of single high speed internet connection.
  • Better communication using internet such as, email, mailing list and internet related chat.


Type of computer network



  • L A N (Local area network) 
  • M A N (Metropolitan area network) 
  • W A N (Wide area network)

L A N (Local area network)

  • A local area network is a network that connect computer and devices in a limited geographical area in the range of 500m to 1km.
  • It is a small computer network that cover building or a campus.
  •  High bandwidth.
  • They offer lower delay as they cover a smaller distance.
  • Very high security.
  • More than one LAN used in wide area network (W A N) to cover long distance.



M A N ( metropolitan area network )

  • A metropolitan area network connect computer and devices in metro city in the range of 100 kilometer.
  • A MAN typically include one or more LANs but it covered a small geographical area.



W A N ( Wide area network )

  • A wide area network is a network that cover large geographical area such as a country or the world.
  • WAN combines many type of media such as telephones line, cable and radio web.
  • A WAN can be one of the largest network.
  • WAN consist two or more LANs connect together.
  • The internet is the world largest WAN.
  • Low bandwidth.
  • They offer much greater delays as they cover far distance.
  • Security is high.



Example of computer networks :-

ARPANET

Full form of ARPANET is advanced research project as agency network. in earlier computer is used as a single machine and we cannot use internet. computer used to establish communication between different users.

ARPANET was design by advanced research agency (ARPA) for department of defence.

ARPANET was the first network in the world.

In 1969, the first ARPANET was established.

ARPANET was originally developed for long-distance (remote) computing. Remote computing was done by a utility program known as telnet. Which allow the user to connect one computer to another computer on a network.


Private network

Private network is a network that have specified network. Where many type of restrictions are established to create secure environment. In private network, the device outside the network does not connect. Only selected devices can access this type of network depending on setting of network return and access point.

Private network mostly used in business and private organization because they need high security for data / information.

Private network is complicated to setup. First we need to allow how many number of users or devices can be connect.

High security hardware and application like firewalls need to be install.


Internet

The internet or simply net is a worldwide network of computer network. It is a interconnection of large and small network around the world.

The internet is a public network which is accessed by anyone from any part of the world.


Working of internet

When we transfer any data through internet then it is broken into a lot of same size pieces called packet.

A header is added to each packets that explain where it come from and where it go.

Each packets is sent computer to computer until find its way to its destination. Each computer in the way decide where next to send the packet.

At the destination, the packets are examined, if there is any packet missing or damaged then a message sent to the sender for data to be resent.

Then the packets are reassembled into their original form.

Is computer connect to the internet has a software called TCP / IP (transmission control protocol or internet protocol). Which is responsible for sending comedy saving and checking packets. IP / TCP is the glue of internet.


Frequently used terms in internet :-

World Wide Web (www)

The world wide Web (www) is a source of information in which document and other web resources are identified by uniform resource locator (URLs) and it is accessed via the internet.


Web page

Web page is a document which is basically.

written in hypertext markup language (HTML). That can be accessed through internet using any web browser. A web page is page with in a website.


Website

It is a collection of many web pages. we can also said that webpage may content text, image, audio and video, pdf etc.


Hyper text

The text having link is called hypertext. It is also called linked text. You can click on a hypertext to go to another web page or website.


HTTP

Hypertext transfer protocol enable the internet user to access the webpage placed in the website.


Network topology

Network topology used to explain the manner in which network is physically connected.


Type of network topology :-

Bus Topology

  •  Multi point.
  •  Easy to install.
  • Use for small network.
  • Easy to expand.
  • Slow speed and only one system can transmit at a time.
  • Faulty cable bring down whole network.




Ring Topology

  • In this is computer connect to the next computer and the last computer connect to first computer.
  • Multiple data connection. 
  • Token passing is used.
  • Fault in any link disable entire network.
  • Difficult to troubleshoot the ring.


Star Topology

  • All the wire from the computer go to a control location device called a HUB.
  • All the communication goes through a HUB.
  •  If central HUB is failed then whole network fail. 
  • Cabling cost is more.



Tree Topology

  • It is similar as star topology. 
  • Nodes in a tree topology are linked to a central HUB. 
  • Cabling cost is most. 
  • If control HUB is failed then entire network is fail.



Hybrid Topology

  • Hybrid topology is a combination of two or more topologies (bus, comedy, star etc).
  • Very easy to detect the fail system.
  • Troubleshoot is easy.
  • It include both wired and wireless network.
  • Difficult to understand the network.
  • Cost is high because required lot of cable and cooling system.
  • M A U (multi station access unit) is required.





Complete Topology (mesh)

  • In complete topology all the system connected to each other.
  • High in cost because long wire required.
  • It is basically used in workstation.

Irregular Network Topology

  • An irregular network topology is similar to complete topology but in this topology not need to connect each computer to all the computer.
  • The effect of failure depend on exact network topology.


OSI model (open system interconnection model)

OSI stand for open system interconnection. It has developed by ISO (international organization of standardization) in the year 1947.

It has seven layer architecture with each layer having their own function to perform. All these seven layer used to transmit data from one person to another across the world.








Physical Layer ( layer 1)

The lowest layer of OSI model is physical layer. It is responsible for actual physical connection between the devices. The physical layer contain information in the form of bits. when receiving data, this layer get the signal received and convert into 0 and 1 and sent to the data link layer.

Device used :- cable, HUB, repeater, fiber etc.

Protocol :- IEEE 802-11


Data Link Layer ( layer 2 )

The data link layer is responsible for delivery of the message, nodes to nodes. The packet received from network layer is further divided into frames.

Device use :- bridge, NIC (network interference card), 2 layer switch.

Protocol :- IEEE 802.3, HDLC, IEEE 802.5 .


Network Layer ( layer 3 )

Network layer work for transmission of data from one host/user to other user located in different network. Here data in packet form and network layer select shortest path to transmit the packet.

Device use :- router, B router, 3 layer switch.

Protocol :- IP, ipv4, IPv6, ICMP, IGMP.


Transport Layer ( layer 4 )

Transport layer provide service to application layer and take service from the network layer. It responsible for end to end delivery of complete message. The data in the transport layer is refer to as segment.

Device use :- Gateway, Firewalls .

Protocol :- TCP, UDP, SCTP.


Session Layer ( layer 5 )

This layer is responsible for establishment of connection, maintenance of session, authentication and also ensure its security.

Device use :- firewall

Protocol :- PAP, RPC


Presentation Layer ( layer 6 )

This layer deal with Syntax and semantics of the info exchange between two system.

Device use :- firewall

Protocol :- MIME, SSL


Application Layer ( layer 7 )

It enables the user to access the network.

Device use :- firewalls, gateway, PC, phones

Protocol :- DNS, HTTP, FTP, telnet, SMTP, POP


TCP / IP

TCP stands for transmission control protocol. It is a set of networking protocol that allow two or more computer to communicate using internet. It is developed before OSI model.

It contain 4 layer but now it contain 5 layer.


Layer of TCP / IP model :-




Physical Layer (layer 1)

  • It responsible for actual physical connection between the device.
  • The physical layer contain information in the form of beats.
  • No specific protocol.


Data Link Layer (layer 2)

No specific protocol.

The data link layer is responsible for delivery of the message from nodes to nodes.

The packet received from network further divided into frames.


Network Layer (layer 3)

Network layer work for transmission of data from one host / user to other user located in different network.

Here data in packet form and network layer select shortest path to transmit the packet.


Transport Layer (layer 4)

It is possible for end to end delivery of complete message. The data in the transport layer is referred to as segment.


Application Layer (layer 5)

It enables the user to access the network. Device used PC, mobile etc. and protocols are HTTP, FTP, telnet, POP, SMTP etc.


Protocol

Protocol is a set of rules used in communication or ensure systematic and safe transfer of data over network. Everything we send or receive through the internet work according to protocols and all this protocols exist in seven layer of OSI model.


Type of protocol :-

Internet protocol (IP)

It is working with TCP. When we send data over internet is broken into many pieces called packet and these packets are reassembled by IP and convert into original form and send to destination address.


Transmission control protocol (TCP)

Transmission control protocol is used for communication over the network. In TCP data is broken into small packet and sent to the destination.



User datagram protocol (UDP)

It is same as TCP but it used for transfer small size data packet and these data packet are called datagram. It is also work with Internet protocol (IP). If any packet are missing then it does not send a message to sender for resent data and it continuously working with missing data packet.

In this UDP head and UDP data is 8 bytes each.


IP addressing

It identify a network on internet. Using this we can find range of address in a network and total possible number of hosts / user on network. IP addresses is most important for communicate between two or more computer / device because IP address find the actual computer to communicate.


Subnet addressing

Subnet address in use to share same internet address to multiple network on autonomous system. The sub network capability of TCP / IP also make it possible to divide a sub network into multiple logical network.

For example - An organization can have a single internet network address that is known to user outside the organization, yet it can configure its network internally into departmental subnet.


Network Address ( 8 bits ) Local Host Address ( 24 bit )
   Network Address
Subnet Address
Host Address
 01111101     00001101         0100     1001             000011


IP address classes

  • IP address has five classes.
  • A B C D E are the classes of IP address.
  • IP address from first to three classes (A B & C) can use for host / user address. 
  • Class D use for multicast.
  • class used for experimental purpose.

Class of IP address are :-

Class
First Octet Value
Subnet Mask
A
0 - 127
8
B
128 - 191
16
C
192 - 223
24
D
224 -  239
-
E
240 - 255
-

For IP address from class A, the first 8 bit (the first decimal number) represent the network part and remaining part be host / user part.

For example - 10.50.120.7 Here, the first number (10) represent network part and remaining 50.120.7 represent host part.


Internet control protocols

Internet control protocols are rule for transmission of the data over the internet.


Internet control protocols are :-

ARP

Address resolution protocol used when we want to communicate between one device to another device then, there should be each device has IP address (system address) but this IP address is not sufficient for communications so, the address resolution protocol request the Mac address of the other device then we communicate with each other.


RARP

Reverse address resolution protocol used when we want to communicate between one device to another device then, the system know the Mac address of other system but do not know the IP address of another device so there RARP request IP address of the other device to communicate between them.

ICMP

Internet control message protocol is network diagnostic and error reporting protocol. ICMP belongs to IP protocol and it use IP as carrier protocol. If some error in network occur then it send message to origin host. ICMP contain dozens of diagnostic and error reporting message. It resolve the problem occur in Internet protocol like no error reporting.


Error reporting of ICMP are :-

  • Destination 
  • unreachable time exceed
  • Source quench
  • Redirection 
  • Parameter problem


Email

Message distributed by electronic means from one computer to one or more computer by the help of or via a network.


Email protocols

Email protocols are set of rules that help the client to properly transmit the information to or from the mail server.


We will discuss various protocols :-

 SMTP

SMPT stand for simple mail transfer protocol. It is used for send mail. It is working under port 25.


SMTP commands :-

  • Hello - This command initiates the SMTP conversation.
  • Mail from - This indicate the sender address.
  • RCPT to - This indicate the receiver address on multiple receiver address.
  • SIZE - Size of attached message in bytes. 
  • QUIT - The command is used to terminate the SMTP connection.


IMAP

IMAP stand for internet message access protocol. It is used to store mail in mail server (when we open mail like Gmail Yahoo, we can access all mail because this mail are store in mail server).

All the user request mail server to show their messages and then mail server ask to login with their own ID and password to access mail.


IMAP commands :-

  • IMAP login - This command open the connection. 
  • SELECT - This command helps to select a mailbox to access the message.
  • CREATE - It is used to create mailbox with specific name.
  • DELETE - It is used to permanently delete mailbox.
  • RENAME - It is used to change the name of a mailbox.
  • LOGOUT - it is used to come out from the server and mailbox.


POP

It stand for post office protocol. It is used to receive mail from mail server using TCP / IP.


Currently used pop is POP3 fridge has version 3. POP support offline access to the message or required less internet.


POP commands :-

  • LOGIN - this command open the connection.
  • STAT - This used to display number of message currently in the mailbox.
  • RETR - This command help to select a mailbox to access the message.
  • DELE - It is used to delete a message. 
  • QUIT - It is used to log off the session.
  • RSET - It is used to reset the session to initial stage.


IEEE 802 standards

IEEE standard for institute of electrical and electronics engineering.

IEEE dealing with LAN and MAN.

The service and protocol specified in IEEE is lower two level of OSI model (data link layer and physical layer).

IEEE 802 splits the data link layer into sub layer.

  1. Logical link control (LLC) 
  2. Media access control (MAC)

The most widely used standard is Ethernet, token ring, wireless LAN.


IEEE standard for LANs :-


Working group :-

  • IEEE 802.1 - Standard for network management.
  • IEEE 802.2 - Standard for logical link control sublayer of data link layer.
  • IEEE 802.3 - Standard for Ethernet (MAC) media access control.
  • IEEE 802.4 -Token bus network. 
  • IEEE 802.5 - Token ring network (MAC).
  • IEEE 802.7 - Broadband LAN using coaxial cable.
  • IEEE 802.8 - Fiber optic.
  • IEEE 802.9 - Integrated service LAN ( ISLAN or ISO Ethernet). 
  • IEEE 802.11 - Wireless LAN (WLAN). 
  • IEEE 802.15 - Bluetooth.


Channel access methods

When many user try to access a channel then we apply some method called channel access method.


Channel access methods are :-

Aloha

Aloha are also called aloha method. It is simple communication scheme in which each source (transmitter) in a network send data where ever in a frame. If the frame successful is send then next frame is Sent. If frame fail to send then it need to resend.


There are two type of aloha :-

Pure aloha

Pure aloha in networking allowed the station to transmit the data at anytime and continuously.

In pure aloha station has sent continuously. There should be possibilities of collision due to continuous send data from station.

Pure aloha is also called continuous time system.


Continuous time system flow chart -


Working :-

Start and set back of time initially as 0 then send frame and acknowledgment from station. If an acknowledgment received than success. If acknowledgment not received then increment the back of time then check the limit reached or not, If yes then abort. If limit not reached then wait for a particular time and recent the frame again.


Slotted aloha

In slotted aloha user wait till the next station being to transmit the data.

It is discrete time system.

Efficiency :-

Efficiency of slotted aloha (x) = G * e-G

Where G = Number of station willing to transmit data at the beginning of the same time slot.

Maximum efficiency :-

Maximum efficiency of slotted aloha (x) = 36.8 % .


CSMA

CSMA stand for carrier sensing multiple access.

CSMA is a network access method used on shared network topology.

There are three categories for CSMA :-

Non-persistence CSMA