A computer network is an interconnection of various computer systems located at different places. In computer network two or more computers are linked together with a medium and data communication devices for the purpose of communicating data and sharing resources. The computer that provides resources to other computers on a network is known as server. In the network the individual computers, which access shared network resources, are known as workstations or nodes.
Type
of Network:
Type of Network
according to geographical area
Local
area network (LAN)
Networks used to
interconnect computers in a single room, rooms within a building or buildings
on one site are called Local Area Network (LAN). LAN transmits data with a
speed of several megabits per second (106 bits per second). The transmission
medium is normally coaxial cables.
LAN links computers,
i.e., software and hardware, in the same area for the purpose of sharing
information. Usually LAN links computers within a limited geographical area
because they must be connected by a cable, which is quite expensive. People
working in LAN get more capabilities in data processing, work processing and
other information exchange compared to stand-alone computers. Because of this
information exchange most of the business and government organizations are
using LAN. ARCNET, Token Ring and other technology standards have been used in
the past, but Ethernet over twisted pair cabling, and Wi-Fi are the two most
common technologies currently used to build LANs. LANs can be connected to Wide
area network by using routers.
Major Characteristics of LAN
Fig: LAN
• Every computer has the potential to
communicate with any other computers of the network
• High degree of interconnection between
computers
• Easy physical connection of computers
in a network
• Inexpensive medium of data
transmission
• High data transmission rate
Advantages
• The reliability of network is high
because the failure of one computer in the network does not affect the
functioning for other computers.
• Addition of new computer to network is easy.
• High rate of data transmission is
possible.
• Peripheral devices like magnetic disk
and printer can be shared by other computers.
If the communication line fails, the entire network system breaks down.
Use
of LAN
Followings are the
major areas where LAN is normally used
• File transfers and Access
• Word and text processing
• Electronic message handling
• Remote database access
• Personal computing
• Digital voice transmission and storage
MAN:
MAN is short for Metropolitan Area Network and refers to low-speed networks
that cover a large distance, for example a network that spans several cities.
MAN is a collection of some LAN network.
Fig: MAN
·
Bigger version of a LAN and might be
either private or public.
·
It might covers a group of nearby
corporate offices or a city (50 kms).
·
Developed in 1980s.
·
Medium : Usually connected with optical
fiber cables.
Wide area network
A wide area network
(WAN) is a computer network that covers a large geographic area such as a city,
country, or spans even intercontinental distances, using a communications
channel that combines many types of media such as telephone lines, cables, and
air waves. For example, for a large company the headquarters might be at Delhi
and regional branches at Bombay, Madras, Bangalore and Calcutta. Here regional
centers are connected to headquarters through WAN. The distance between computers
connected to WAN is larger. Therefore the
transmission medium used are normally telephone lines, microwaves and satellite
links.
Characteristics
of WAN
Followings are the
major characteristics of WAN.
1) Communication Facility: For a big company
spanning over different parts of the country the employees can save long
distance phone calls and it overcomes the time lag in overseas communications.
Computer conferencing is another use of WAN where users communicate with each
other through their computer system.
2) Remote Data Entry: Remote data entry is
possible in WAN. It means sitting at any location you can enter data, update
data and query other information of any computer attached to the WAN but
located in other cities. For example, suppose you are sitting at Madras and
want to see some data of a computer located at Delhi, you can do it through
WAN.
3) Centralized Information: In modern
computerized environment you will find that big organizations go for
centralized data storage. This means if the organization is spread over many
cities, they keep their important business data in a single place. As the data
are generated at different sites, WAN permits collection of this data from
different sites and save at a single site.
Examples
of WAN
1. Ethernet: Ethernet
developed by Xerox Corporation is a famous example of WAN. This network uses
coaxial cables for data transmission. Special integrated circuit chips called
controllers are used to connect equipment to the cable.
2. Arpanet:
The Arpanet is another example of WAN. It was developed at Advanced Research
Projects Agency of U.
S. Department. This
Network connects more than 40 universities and institutions throughout USA and
Europe.
Virtual
private network
A virtual private
network (VPN) is a computer network in which some of the links between nodes
are carried by open connections or virtual circuits in some larger network
(e.g., the Internet) instead of by physical wires. The data link layer
protocols of the virtual network are said to be tunneled through the larger
network when this is the case. One common application is secure communications
through the public Internet, but a VPN need not have explicit security
features, such as authentication or content encryption. VPNs, for example, can
be used to separate the traffic of different user communities over an
underlying network with strong security features.
VPN may have
best-effort performance, or may have a defined service level agreement (SLA)
between the VPN customer and the VPN service provider. Generally, a VPN has a
topology more complex than point-to-point.
Intranets
and extranets
Intranets and extranets
are parts or extensions of a computer network, usually a LAN.
An intranet is a set of
networks, using the Internet Protocol and IP-based tools such as web browsers
and file transfer applications, that is under the control of a single
administrative entity. That administrative entity closes the intranet to all
but specific, authorized users. Most commonly, an intranet is the internal
network of an organization. A large intranet will typically have at least one
web server to provide users with organizational information.
An extranet is a
network that is limited in scope to a single organization or entity and also
has limited connections to the
networks of one or more
other usually, but not necessarily, trusted organizations or entities—a
company's customers may be given access to some part of its intranet—while at
the same time the customers may not be considered trusted from a security
standpoint. Technically, an extranet may also be categorized as a CAN, MAN,
WAN, or other type of network, although an extranet cannot consist of a single
LAN; it must have at least one connection with an external network.
Internet
The Internet is a
network of networks. Millions of computers all over the world are connected
through the Internet. Computer users on the Internet can contact one another
anywhere in the world. If your computer is connected to the Internet, you can
connect to millions of computers. You can gather information and distribute
your data. It is very much similar to the telephone connection where you can
talk with any person anywhere in the world.
In Internet a huge
resource of information is accessible to people across the world. Information
in every field starting from education, science, health, medicine, history, and
geography to business, news, etc. can be retrieved through Internet. You can
also download programs and software packages from anywhere in the world. Due to
the tremendous information resources the Internet can provide, it is now
indispensable to every organization.
Intranets and extranets
Figure 3.4 The relationship between intranets, extranets
and the Internet
© Marketing Insights Limited
2004
Private
and Public Networks
Two other terms used to
categorize networks are private networks and public networks.
A private network is
typically within the premises of a corporation and can be accessed only by
users working for, or related to, that corporation. Example: Network of Brac
Bank Limited.
A public network
Internet can be accessed by multiple individuals and/or corporations, the best
example of a public network is, the Internet.