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Question 1: Explain the major classification of Computer Networks.
A computer network is a group of interconnected computers. In the world of computers,
networking is the practice of linking two or more computing devices together for the purpose
of sharing data. Networks are built with a mix of computer hardware and computer software.
The network allows computers to communicate with each other and share resources and
Following can be the several factors for classifying different computer networks.
In networking, the communication language used by computer devices is called the protocol.
Yet another way to classify computer networks is by the set of protocols they support.
Networks often implement multiple protocols to support specific applications. Popular
protocols include TCP/IP, the most common protocol found on the Internet and in home
Wired Vs Wireless Networking:
Many of the same network protocols, like TCP/IP, work in both wired and wireless networks.
Networks with Ethernet cables predominated in businesses, schools, and homes for several
decades. Recently, however, wireless networking alternatives have emerged as the premier
technology for building new computer networks.
Computer networks also differ in their design. The two types of high-level network design are
called client-server and peer-to-peer. Client-server networks feature centralized server
computers that store email, Web pages, files and or applications. On a peer-to-peer network,
conversely, all computers tend to support the same functions. Client-server networks are
much more common in business and peer-to-peer networks much more common in homes.
Often, it is impractical for two devices to be directly, point-to-point connected. This is so for
one (or both) of the following contingencies:
The devices are very far apart. It would be inordinately expensive, for example, to
string a dedicated link between two devices thousands of miles apart.
There is a set of devices, each of which may require a link to many of the others at
various times. Examples are all of the telephones in the world and all of the terminals
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and computers owned by a single organization. Except for the case of a very few
devices, it is impractical to provide a dedicated wire between each pair of devices.
The solution to this problem is to attach each device to a communication network.
This is the most basic approach to classify networks. It defines the type of network according
to the geographic area it spans. Local area networks (LANs), for example, typically reach
across a single home, whereas wide area networks (WANs), reach across cities, states, or even
across the world. The Internet is the world's largest public WAN.
WAN spans a large geographic area, such as a state, province or country. WANs often connect
multiple smaller networks, such as local area networks (LANs) or metro area networks (MANs).
Typically, a WAN consists of a number of interconnected switching nodes. A transmission from
any one device is routed through these internal nodes to the specified destination device.
These nodes (including the boundary nodes) are not concerned with the content of the data;
rather, their purpose is to provide a switching facility that will move the data from node to
node until they reach their destination.
The world's most popular WAN is the Internet. Some segments of the Internet, like VPN-based
extranets, are also WANs in themselves. Finally, many WANs are corporate or research
networks that utilize leased lines.
WANs generally utilize different and much more expensive networking equipment than do
LANs. Key technologies often found in WANs include SONET, Frame Relay, and ATM.
In a circuit-switched network, a dedicated communications path is established between two
stations through the nodes of the network. That path is a connected sequence of physical links
between nodes. On each link, a logical channel is dedicated to the connection. Data
generated by the source station are transmitted along the dedicated path as rapidly as
possible. At each node, incoming data are routed or switched to the appropriate outgoing
channel without delay. The most common example of circuit switching is the telephone
A quite different approach is used in a packet-switched network. In this case, it is not
necessary to dedicate transmission capacity along a path through the network. Rather, data
are sent out in a sequence of small chunks, called packets. Each packet is passed through the
network from node to node along some path leading from source to destination. At each node,
Wide Area Network (WAN):
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the entire packet is received, stored briefly, and then transmitted to the next node. Packet-
switched networks are commonly used for terminal-to-computer and computer-to-computer
Packet switching was developed at a time when digital long-distance transmission facilities
exhibited a relatively high error rate compared to today's facilities. As a result, there is a
considerable amount of overhead built into packet-switched schemes to compensate for
errors. The overhead includes additional bits added to each packet to introduce redundancy
and additional processing at the end stations and the intermediate switching nodes to detect
and recover from errors.
With modern high-speed telecommunications systems, this overhead is unnecessary and
counterproductive. It is unnecessary because the rate of errors has been dramatically lowered
and any remaining errors can easily be caught in the end systems by logic that operates above
the level of the packet-switching logic; it is counterproductive because the overhead involved
soaks up a significant fraction of the high capacity provided by the network.
Frame relay was developed to take advantage of these high data rates and low error rates.
Whereas the original packet-switching networks were designed with a data rate to the end
user of about 64 kbps, frame relay networks are designed to operate efficiently at user data
rates of up to 2 Mbps. The key to achieving these high data rates is to strip out most of the
overhead involved with error control.
Asynchronous transfer mode (ATM), sometimes referred to as cell relay, is a culmination of all
of the developments in circuit switching and packet switching over the past 25 years.
ATM can be viewed as an evolution from frame relay. The most obvious difference between
frame relay and ATM is that frame relay uses variable-length packets, called frames, and ATM
uses fixed-length packets, called cells. As with frame relay, ATM provides little overhead for
error control, depending on the inherent reliability of the transmission system and on higher
layers of logic in the end systems to catch and correct errors. By using a fixed-packet length,
the processing overhead is reduced even further for ATM compared to frame relay. The result
is that ATM is designed to work in the range of 10s and 100s of Mbps, compared to the 2-Mbps
target of frame relay.
ATM can also be viewed as an evolution from circuit switching. With circuit switching, only
fixed-data-rate circuits are available to the end system. ATM allows the definition of multiple
virtual channels with data rates that are dynamically defined at the time the virtual channel is
created. By using full, fixed-size cells, ATM is so efficient that it can offer a constant-data-
rate channel even though it is using a packet-switching technique. Thus, ATM extends circuit
switching to allow multiple channels with the data rate on each channel dynamically set on
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A local area network (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.
Most local area networks are built with relatively inexpensive hardware such as Ethernet
cables, network adapters, and hubs. Wireless LAN and other more advanced LAN hardware
options also exist.
Traditionally, LANs make use of a broadcast network approach rather than a switching
approach. With a broadcast communication network, there are no intermediate switching
nodes. At each station, there is a transmitter and a receiver that communicates over a
medium shared by other stations. A transmission from any one station is broadcast to and
received by all other stations.
A simple example of this is a CB radio system, in which all users tuned to the same channel
may communicate. We will be concerned with networks used to link computers, workstations,
and other digital devices. In the latter case, data are usually transmitted in packets. Because
the medium is shared, i.e. only one station at a time can transmit a packet.
More recently, examples of switched LANs have appeared. The two most prominent examples
are ATM LANs, which simply use an ATM network in a local area, and Fibre Channel.
The most common type of local area network 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.
There are several key distinctions between LANs and WANs:
The scope of the LAN is small, typically a single building or a cluster of buildings. This
difference in geographic scope leads to different technical solutions.
It is usually the case that the LAN is owned by the same organization that owns the
attached devices. For WANs, this is less often the case, or at least a significant fraction
of the network assets are not owned. This has two implications. First, care must be
taken in the choice of LAN, as there may be a substantial capital investment (compared
Key Distinctions between LANs and WANs:
Local Area Network (LAN):