Categories of Networks


A Network is a set of devices or nodes connected by media links.A node can be a  computer, printer,scanner,VoIP phone etc.Computer network means an interconnected collection of autonomous computers.Computer networks are generally organized as a series of layers or levels.

Factors like Performance,Reliability,Security etc are highly significant in network communication.
Categories of Networks
  • Local Area Network
  • Metropolitan Area Network
  • Wide Area Network
  • Internet-work (internet)
  • Internet 
  • Intranet
Local Area Network are privately owned networks with in a single building or a campus.Metropolitan Area Network is basically a bigger version of a LAN that is it covers various offices of a company in a city. Wide Area Network covers a large geographical area , a country or a continent.
Internet-work(internet) is the connection of two or more networks. The internet is an example for Internet-work.
The most prominent internet is the Internet(Uppercase letter I) is a collection of more than hundreds of thousands  inter connected networks.
Intranet is a private network that is contained with in an enterprise.Intranet may consist of many interlinked Local Area Networks.

Wave Division Multiplexing (WDM)

Wave Division Multiplexing (WDM)

Wave Division Multiplexing (WDM) is an analog multiplexing technique to combine optical signals. Wave Division Multiplexing (WDM) is conceptually the same as Frequency Division Multiplexing (FDM),except that the multiplexing and demultiplexing involve optical signals transmitted through fiber-optic channels.The idea is the same:We are combining different signals of different frequencies.However,the difference is that the frequencies are very high.


Application of WDM

 SONET network : Multiple optical fiber lines are multiplexed and demultiplexed


Frequency Division Multiplexing or FDM

Frequency Division Multiplexing ( FDM )    


FDM is an analog technique,where each communication channel is assigned a carrier frequency.To ensure the channels do not interfere a guard band is used in between them.

Multiplexing in FDM

Each sending device generate a signal of similar frequency range. Inside the multiplexer these similar signals are modulated on to different carrier frequencies. The resulting modulated signals are then combined into a single composite signal and is sent over a shared media link that has enough bandwidth.

Demultiplexing in FDM

The demultiplexer uses a series of filters to decompose the multiplexed signal into its constituent component signals.The individual signals are then passed to a demodulator that separate them from their carriers,and passes them to the waiting receivers.

 Applications of FDM

       1. AM and FM radio broadcasting : The signals which goes to the air is a combination of all signals.A receiver receives all these signals,but filters(by tuning)only the one which is desired.

       2. Television broadcasting

       3. First generation of cellular telephones uses FDM.



Routing Algorithms in Computer Networks

Routing Algorithms: 


Routing algorithms is using for  preparing the routing information table.
  • Non-Adaptive Routing Algorithm
  • Adaptive Routing Algorithm
Non-Adaptive Routing Algorithm
Non-adaptive routing algorithm is based on initial permanent information.The information in the routing information table (RIT) cannot accommodate changes in the network.
Example: Static Algorithm
Adaptive Routing Algorithm: 
This accommodates changes in the network that is the information in the routing information table (RIT) can be updated dynamically.
  • Centralized Routing Algorithm
  • Isolated Routing Algorithms
  • Distributed Routing Algorithm 


Centralized Routing Algorithm:

Here the routing information table (RIT) is prepared by the Routing Control Center (RCC).The routing information table (RIT) is prepared based on global knowledge.

Disadvantages of Centralized Routing Algorithm :
  • Heavy traffic near Routing Control Center (RCC)

  • Inconsistency in Routing information Table (RIT)

  • If RCC fails, updates in RIT is not possible

Status information from all routers coming continuously to RCC and updates in RIT is sending to all routers from RCC, thus there is heavy traffic near RCC. The Updates from RCC reaches soon to routers near to RCC and later to others.,hence there is inconsistency in RIT.

Isolated Routing Algorithms

In Isolated Routing Algorithms each router prepares it’s Routing Information table (RIT)  based on local knowledge.The following are isolated routing algorithms.

  • Hot Potato

  • Backward Learning

  • Flooding

  • In Hot Potato the router forward the incoming packet to the less traffic route.

  • In Backward Learning the router makes entries in RIT based on the information from the incoming packets.

  • In Flooding the router forwards the incoming packet to all other route except the incoming route.

Disadvantages of Flooding : Vast number of duplicate packets.


Distributed Routing Algorithm

Each router based on the local and global knowledge prepares RIT.
  • Link state routing Algorithm




IPv4 Address Classes

IP Version 4 Address Classes

IP version 4  is a 32 bit addressing system. The 32 bits are divided as 4 octets of 8 bits each.In IPv4 the ip address is categorized as Class  A, Class B, Class C, Class D,Class E.


IP version 4  is a 32 bit addressing system. The 32 bits are divided as 4 octets of 8 bits each.In IPv4 the ip address is categorized as Class  A, Class B, Class C, Class D,Class E.

 Class Leftmost Bit
              IP Address Range
 A  0       to
 B  10      to
 C  110      to
 D  1110      to
 E  1111      to

Class A, Class B, and Class C addresses are used on IP networks as host IP address. Class D, Class E addresses are not be used as host IP address on the network. Class D is used for multicasting where as class E is used for limited broadcasting.

  • Class A,Class B,Class C for host IP address
  • Class D for Multicast
  • Class E 

IP Address Class D for Multicast

Multicast addressing is  a technique which define a group of nodes and sending IP message to that group alone.It uses the link only once for message delivery.It use the class D addressing system.The 32 bit indicate a group name. It uses IGMP (Internet Group Management Protocol).
IP Address Class E 
In the IPv4  standard Class E addresses as reserved, that is they are not  used as host ip address on IP networks.The IP addresses  range from through  are reserved and is  not  considered for the normal Class E range. The  IP broadcast to deliver IP message to all node on the local network(LAN), that is this broadcast is limited with in the local network as the packet does not reach all node on the Internet.