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As 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 -
Local 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 line.
? 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):
A 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
more).
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 physical connection.
In 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.
Metropolitan Area Network (MAN):
A 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
cheap.
A MAN can also be created using wireless bridge
technology.
Storage 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. |
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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 system performance.
· 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 still evolving.
Virtual Private Network (VPN):
A 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. |
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The 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.
VPN 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. |
