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The Network

The Network

A computer network is a group of interconnected computers. Networks may be classified according to a wide variety of characteristics. This article provides a general overview of some types and categories and also presents the basic components of a network.

Introduction

A network is a collection of computers and devices connected to each other. The network allows computers to communicate with each other and share resources and information. The Advance Research Projects Agency (ARPA) designed "Advanced Research Projects Agency Network" (ARPANET) for the United States Department of Defense. It was the first computer network in the world in late 1960's and early 1970's.

Network classification

The following list presents categories used for classifying networks.

Connection method

Computer networks can also 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, or Power line communication.

Ethernet uses physical wiring to connect devices. Frequently deployed devices include hubs, switches, bridges and/or routers.

Wireless LAN technology is designed to connect devices without wiring. These devices use radio waves or infrared signals as a transmission medium.

Scale

Based on their scale, networks can be 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), etc.

 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, star-bus network, tree or hierarchical topology network. Network topology signifies the way in which devices in the network see their logical relations to one another. The use of the term "logical" here is significant. That is, network topology is independent of the "physical" layout of the network. Even if networked computers are physically placed in a linear arrangement, if they are connected via a hub, the network has a Star topology, rather than a bus topology. In this regard the visual and operational characteristics of a networkare distinct; the logical network topology is not necessarily the same as the physical layout. Networks may be classified based on the method of data used to convey the data, these include digital and analog networks.

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IP Addressing

IP Addressing

 

An IP address is a unique logical identifier for a node or host connection on an IP network. An IP address is a 32 bit binary number, and represented as 4 decimal values of 8 bits each. The decimal values range from 0 to 255. This is known as "dotted decimal" notation.

Example: 192.189.210.078

It is sometimes useful to view the values in their binary form.

192     .189     .210     .078
11000000.10111101.11010010.1001110

 

Every IP address consists of network identifier and node identifier. The IP network is divided based on Class of network. The class of network is determined by the leading bits of the IP address as shown below. 

Address Classes

There are 5 different address classes. You can determine which class any IP
address is in by examining the first 4 bits of the IP address.
  • Class A addresses begin with 0xxx, or 1 to 126 decimal.
  • Class B addresses begin with 10xx, or 128 to 191 decimal.
  • Class C addresses begin with 110x, or 192 to 223 decimal.
  • Class D addresses begin with 1110, or 224 to 239 decimal.
  • Class E addresses begin with 1111, or 240 to 254 decimal.

Addresses beginning with 01111111, or 127 decimal, are reserved for loopback and for internal testing on a local machine. Class D addresses are reserved for multicasting. Class E addresses are reserved for future use. They should not be used for host addresses.

Now we can see how the Class determines, by default, which part of the IP address belongs to the network (N) and which part belongs to the Host/node (H).

  • Class A: NNNNNNNN.HHHHHHHH.HHHHHHHH.HHHHHHHH
  • Class B: NNNNNNNN.NNNNNNNN.HHHHHHHH.HHHHHHHH
  • Class C: NNNNNNNN.NNNNNNNN.NNNNNNNN.HHHHHHHH

In the example, 192.189.210.078 is a Class C address so by default the Network part of the address (also known as the Network Address) is defined by the first three octets (192.189.210.XXX) and the node part is defined by the last one octets (XXX.XXX.XXX.078).

In order to specify the network address for a given IP address, the node section is set to all "0"s. In our example, 192.189.210.0 specifies the network address for 192.189.210.078. When the node section is set to all "1"s, it specifies a broadcast that is sent to all hosts on the network. 192.189.210.255 specifies the broadcast address.

Private Subnets

There are three IP network addresses reserved for private networks. The addresses are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. They can be used by anyone setting up internal IP networks, such as an intranet. Internet routers never forward the private addresses over the public Internet.

source: simulationexams.com

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