Categories of Networks

There are three primary types of networks including local area networks, metropolitan area networks and wide area networks. Here we differentiate them by their size, ownership, distance and structure.

Local Area Network (LAN) :
A local area network is a private network having links of devices within a campus,building or office. A LAN can have two or more systems connected or devices i.e printers in a office. It also depend on the technology used in the networking.
In LAN we basically share data or sometimes  hardware. The restrictions can be used on some particular software or hardware for the usage, by the number of  users. It also depends which topology and transmission medium is used.
LANs have data rate from 4 to 6 Mbps range. Now a days its increasing and may be 100 Mbps depending on the speed of systems.

Metropolitan Area Network (MAN) :
A metropolitan area network is more widely can be used. It can be used in a entire city. It may be a single network or it can be combination of some LANs. A MAN can be used for a company having many offices in a city.
A MAN is owned by a company. Some service provider can also provide the MAN to a company by switched  multi megabit data services (SMDS).

Wide Area Network (WAN) :
A wide area network provides a long distance transmission of data. It may be overr large geographical areas thay may be acountry, a continent or whole world.
A WAN can use public or private communication devices or usually in combination. It can be on unlimited number of miles.

Internetworks:
When two or more networks are connected, they become an internetwork or internet. The networks are connected by internetworking devices i.e routers,gateways.
The term internet is a generic term used to mean an interconnection of networks.
The Internet is the name of a specific worldwide network.

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Transmission Mode

The direction of a signal between two devices is defined by a transmission mode.
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The transmission mode defines the direction of a signal between two devices.There are three types of transmission mode given as below;

Simplex Mode:
In the simplex mode the communication is unidirectional. Only one can send data and other can receive. No any other possibility is available. A remote is an example of simplex mode.

Half Duplex Mode:
In half duplex  mode both devices can send and receive data, but not at the same time. At a time one device send data and other receives. Walkie talkie is an example of half duplex mode.

Full Duplex Mode:
In full duplex mode both devices can send and receive data at the same time. It has two way traffic at the same time. The telephone network is an example of full duplex mode.

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Network Criteria

For an effecient and effective networking the following criteria is most important.

Performance:
The performance depends on many factor some are discussed below:

Number of  Users:
A large number of users on a network can slow its reponse time if it is designed for heavy traffic loads. In peak times on a certain network can slow its performance.

Transmission Medium:
The transmission medium used for the network also a main factor for its performance. As data has to travel on it. It can be fibre optics for a faster transfer of data.

Hardware:
The hardware used in networking affect the speed and capacity of transmission. A high computer with big storage will perform better.

Software:
The software used for running applications and data processig at sender reciever end and intermediary nodes also effects the performance of the network.

Reliability:


Rliability of a network on the followings;

Frequency of Failure:
All networks fail occasionally. But a network that fails often have little value to a user.

Recovery Time:
The time taken to restore itself after the failure is recovery time. The network quickly restores is more useful than the other takes much time.

Catastrophe:
The network must be protected by fire,earthquake or theft. There may be a system for back up of network software.

Security:
Network security isues include unauthrized access and viruses.

Unauthorized Access:
On a network there may be sensitive data, therfore it must be protected by an unauthorized access. It may be user identification and password or at higher level it can be encryption techniques.

Viruses:
As network can be accessed at many points, it may have computer virus. A virus is a code that damages the system. A good network must have the virus protection by hardware or software based.

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Distributed Processing

In a network a task is divided into multiple computers using multiple processing. Instead of a single large machine for different processes, many computers are used and following advantages can be gained by using distributed processsing.

Security/Encapsulation:
A system designer can limit the interaction of a user to an interface. for example in banks, the particular use only can see his own account not the whole bank data or accounts.

Distributed Databases:
A single system can not store the data of whole network. Therefore world wide web provide the access to information stored or available on the Internet.

Faster Problem Solving:
Different computers working on a problem can solve it earlier than a single computer solving it.

Security through Redundancy:
Multiple computers running the same program at the same time can provide security through redundancy. In space three computers runs the same application at a time so if one fails then other can override it.

Collaborative Processing:
Multiple computers and users can interact on a task. In network games each player see the action and effect of all others on the application running.

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