an attempt to define sensible categories for the major types
of network designs the networking industry has coined words
like “LAN” and “WAN”. Nearly every type of network is referred
to as an "area network." The most commonly-discussed
categories of computer networks include the following -
Area Network (LAN):
A LAN supplies networking capability to a group of computers
in close proximity to each other such as in an office building,
a school, or a home. A LAN is useful for sharing resources like
files, printers, games or other applications. A LAN in turn
often connects to other LANs, and to the Internet or other WAN.
LANs are built with relatively inexpensive hardware such as
Ethernet cables, network adapters, repeaters and switches. Wireless
LAN and other more advanced LAN hardware options also exist.
Most LANs connect workstations and personal computers. Each
node (individual computer) in a LAN has its own CPU with which
it executes programs, but it also is able to access data and
devices anywhere on the LAN. This means that many users can
share expensive devices, such as laser printers, as well as
data. Users can also use the LAN to communicate with each other,
by sending e-mail or engaging in chat sessions.
There are many different types of LANs – Ethernet, Token ring,
FDDI. The most common type of LAN is an Ethernet LAN. The smallest
home LAN can have exactly two computers; a large LAN can accommodate
many thousands of computers. Many LANs are divided into logical
groups called subnets. An Internet Protocol (IP) "Class
A" LAN can in theory accommodate more than 16 million devices
organized into subnets.
The following characteristics differentiate one LAN from another:
? topology : The geometric arrangement of devices on the network.
For example, devices can be arranged in a ring or in a straight
? protocols : The rules and encoding specifications for sending
data. The protocols also determine whether the network uses
a peer-to-peer or client/server architecture.
media : Devices can be connected by twisted-pair wire, coaxial
cables, or fiber optic cables. Some networks do without connecting
media altogether, communicating instead via radio waves.
LANs are capable of transmitting data at very fast rates, much
faster than data can be transmitted over a telephone line; but
the distances are limited, and there is also a limit on the
number of computers that can be attached to a single LAN.
Wide Area Network (WAN):
WAN interconnects LANs, which then provide access to computers
or file servers in other locations. A network device called
a router connects LANs to a WAN. In IP networking, the router
maintains both a LAN address and a WAN address.
A major factor impacting WAN design and performance is a requirement
that they lease communications circuits from telephone companies
or other communications carriers. Transmission rates are typically
2 Mbps, 34 Mbps, 45 Mbps, 155 Mbps, 625 Mbps (or sometimes considerably
Numerous WANs have been constructed, including public packet
networks, large corporate networks, military networks, banking
networks, stock brokerage networks, and airline reservation
networks. Some WANs are very extensive, spanning the globe,
but most do not provide true global coverage. Organisations
supporting WANs using the Internet Protocol are known as Network
Service Providers (NSPs). These form the core of the Internet.
The largest WAN in existence is the Internet.
· The basic WAN service which the public telecommunication companies
usually offer (for many years) is a Leased Line. A Leased Line
is a point-to-point connection between two places, implemented
by different transmission media (usually through public switched
telephone network Trunks), which creates one link between its
nodes. An organization whose networks are based on such lines
has to connect each office with one line, meaning that each
office is connected to as many lines as the number of offices
it is connected to.
The Packet Switched WAN defined the basis for all communication
networks today. The principle in Packet Switched Data Network
(PSDN) is that the data between the nodes is transferred in
small packets. This principle enables the PSDN to allow one
node to be connected to more than one other node through one
physical connection. That way, a fully connected network, between
several nodes, can be obtained by connecting each node to one
the design of WANs, transmission characteristics lay emphasis
on communication efficiency. Even today, new networks are being
designed for future demands. Those new networks are aimed to
work at enormous rates of Giga-bps, and are providing new challenges
for their designers.
Area Network (MAN):
MAN is a network that interconnects users with computer resources
in a geographic area or region larger than that covered by a
LAN but smaller than the area covered by a WAN. The term MAN
is applied to the interconnection of networks in a city into
a single larger network (which may then also offer efficient
connection to a wide area network). It is also used to mean
the interconnection of several local area networks by bridging
them with backbone lines. The latter usage is also sometimes
referred to as a campus network. It s usually in a ring configuration.
A new era of computer networking is emerging with new MAN technologies
that extend Ethernet LAN networks across the MAN via fiber-optic
links. Most important, these services are being offered by carriers
that compete with the incumbent phone companies, and they are
MAN can also be created using wireless bridge technology.
Area Networks (SAN):
A SAN is a dedicated, high-performance network used to move
data between servers and storage resources. In very basic terms,
a SAN can be anything from two servers on a network accessing
a central pool of storage devices to several thousand servers
accessing many millions of megabytes of storage. Conceptually,
a SAN can be thought of as a separate network of storage devices
physically removed from, but still connected to, the network.
SANs evolved from the concept of taking storage devices off
the LAN and creating a separate back-end network designed specifically
for storing data. Because it is a separate, dedicated network,
it avoids any storage traffic conflict between clients and servers.
SAN technology allows high-speed server-to-storage, storage-to-storage,
or server-to-server connectivity. This method uses a separate
network infrastructure that relieves any problems associated
with existing network connectivity. It connects servers to data
storage devices through a technology like Fibre Channel.
SANs offer the following features:
· Performance – SANs enable concurrent access of disk or tape
arrays by two or more servers at high speeds, providing enhanced
· Availability – SANs have disaster tolerance built in, because
data can be mirrored using a SAN up to 10 kilometers (km) or
6.2 miles away.
· Scalability – Like a LAN/WAN, it can use a variety of technologies.
This allows easy relocation of backup data, operations, file
migration, and data replication between systems.
But so far the technology is in its infancy as standards are
Private Network (VPN):
VPN is a private network that uses a public network (usually
the Internet) to connect remote sites or users together. Instead
of using a dedicated, real-world connection such as leased line,
a VPN uses "virtual" connections routed through the
Internet from the company’s private network to the remote site.
It enables one to send data between two computers across a shared
or public inter network in a manner that emulates the properties
of a point-to-point private link.
following are the three main types of VPNs:
· Remote-Access VPNs – Access VPNs provide remote access to
a mobile worker and small office/home office (SOHO) to the headquarters
of the Intranet or Extranet over a shared infrastructure. Access
VPNs use analog, dialup, ISDN, digital subscriber line (DSL),
mobile IP, and cable technologies to securely connect mobile
users and branch offices.
· Intranet-based - If a company has one or more remote locations
that they wish to join in a single private network, they can
create an intranet VPN to connect LAN to LAN. Intranet VPNs
differ from Extranet VPNs in that they allow access only to
the employees of the enterprise.
Extranet-based - When a company has a close relationship with
another company (for example, a partner, supplier or customer),
they can build an extranet VPN that connects LAN to LAN, and
that allows all of the various companies to work in a shared
environment. Extranet VPNs differ from Intranet VPNs in that
they allow access to users outside the enterprise.
follows a client and server approach. VPN clients authenticate
users, encrypt data, and otherwise manage sessions with VPN
servers utilizing a technique called tunneling.
A tunnel is a logical structure that encapsulates the frame
and data of one protocol inside the Data field of another protocol.
Thus, the encapsulated data frame may transit through networks
that it would otherwise not be capable of traversing.
Resources on the Internet :