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Introduction to Computer Networks
A network is a collection of computers connected to each other. The network allows
computers to communicate with each other and share resources and information. The
Advance Research Projects Agency (ARPA) designed "Advanced Research Projects
Agency Network" (ARPANET) for the United States Department of Defense. It was the
first computer network in the world in late 1960's and early 1970's.[citation needed
Network Classification
The following list presents categories used for classifying networks.
[edit] Scale
Based on their scale, networks can be classified as Local Area Network (LAN), Wide
Area Network (WAN), Metropolitan Area Network (MAN), Personal Area Network
(PAN),Virtual Private Network (VPN) etc.
[edit] Connection method
Computer networks can also be classified according to the hardware and software
technology that is used to interconnect the individual devices in the network, such as
Optical fiber, Ethernet, Wireless LAN, HomePNA, or Power line communication.
Ethernet uses physical wiring to connect devices. Frequently deployed devices include
hubs, switches, bridges and/or routers.
Wireless LAN technology is designed to connect devices without wiring. These devices
use radio waves or infrared signals as a transmission medium.
[edit] Functional relationship (Network Architectures)
Computer networks may be classified according to the functional relationships which
exist among the elements of the network, e.g., Active Networking, Client-server and
Peer-to-peer (workgroup) architecture.
[edit] Network topology
Computer networks may be classified according to the network topology upon which the
network is based, such as Bus network, Star network, Ring network, Mesh network, Starbus network, Tree or Hierarchical topology network,
Network Topology signifies the way in which devices in the network see their logical
relations to one another. The use of the term "logical" here is significant. That is, network
topology is independent of the "physical" layout of the network. Even if networked
computers are physically placed in a linear arrangement, if they are connected via a hub,
the network has a Star topology, rather than a Bus Topology. In this regard the visual and
operational characteristics of a network are distinct; the logical network topology is not
necessarily the same as the physical layout.
Types of networks
Below is a list of the most common types of computer networks in order of scale.
Personal Area Network (PAN)
A personal area network (PAN) is a computer network used for communication among
computer devices close to one person. Some examples of devices that are used in a PAN
are printers, fax machines, telephones, PDAs and scanners. The reach of a PAN is
typically about 20-30 feet (approximately 6-9 meters), but this is expected to increase
with technology improvements.
Personal area networks may be wired with computer buses such as USB[1] and FireWire.
A wireless personal area network (WPAN) can also be made possible with network
technologies such as IrDA and Bluetooth.
Local Area Network (LAN)
This is a network covering a small geographic area, like a home, office, or building.
Current LANs are most likely to be based on Ethernet technology. For example, a library
may have a wired or wireless LAN for users to interconnect local devices (e.g., printers
and servers) and to connect to the internet. On a wired LAN, PCs in the library are
typically connected by category 5 (Cat5) cable, running the IEEE 802.3 protocol through
a system of interconnected devices and eventually connect to the Internet. The cables to
the servers are typically on Cat 5e enhanced cable, which will support IEEE 802.3 at 1
Gbit/s. A wireless LAN may exist using a different IEEE protocol, 802.11b, 802.11g or
possibly 802.11n. The staff computers (bright green in the figure) can get to the color
printer, checkout records, and the academic network and the Internet. All user computers
can get to the Internet and the card catalog. Each workgroup can get to its local printer.
Note that the printers are not accessible from outside their workgroup.
Typical library network, in a branching tree topology and controlled access to resources
All interconnected devices must understand the network layer (layer 3), because they are
handling multiple subnets (the different colors). Those inside the library, which have only
10/100 Mbit/s Ethernet connections to the user device and a Gigabit Ethernet connection
to the central router, could be called "layer 3 switches" because they only have Ethernet
interfaces and must understand IP. It would be more correct to call them access routers,
where the router at the top is a distribution router that connects to the Internet and
academic networks' customer access routers.
The defining characteristics of LANs, in contrast to WANs (wide area networks), include
their higher data transfer rates, smaller geographic range, and lack of a need for leased
telecommunication lines. Current Ethernet or other IEEE 802.3 LAN technologies
operate at speeds up to 10 Gbit/s. This is the data transfer rate. IEEE has projects
investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s.
Campus Area Network (CAN)
This is a network that connects two or more LANs but that is limited to a specific and
contiguous geographical area such as a college campus, industrial complex, office
building, or a military base. A CAN may be considered a type of MAN (metropolitan
area network), but is generally limited to a smaller area than a typical MAN. This term is
most often used to discuss the implementation of networks for a contiguous area. This
should not be confused with a Controller Area Network. A LAN connects network
devices over a relatively short distance. A networked office building, school, or home
usually contains a single LAN, though sometimes one building will contain a few small
LANs (perhaps one per room), and occasionally a LAN will span a group of nearby
buildings. In TCP/IP networking, a LAN is often but not always implemented as a single
IP subnet.
Metropolitan Area Network (MAN)
A Metropolitan Area Network is a network that connects two or more Local Area
Networks or Campus Area Networks together but does not extend beyond the boundaries
of the immediate town/city. Routers, switches and hubs are connected to create a
Metropolitan Area Network.
Wide Area Network (WAN)
A WAN is a data communications network that covers a relatively broad geographic area
(i.e. one city to another and one country to another country) and that often uses
transmission facilities provided by common carriers, such as telephone companies. WAN
technologies generally function at the lower three layers of the OSI reference model: the
physical layer, the data link layer, and the network layer.
Global Area Network (GAN)
Global Area networks (GAN) specifications are in development by several groups, and
there is no common definition. In general, however, a GAN is a model for supporting
mobile communications across an arbitrary number of wireless LANs, satellite coverage
areas, etc. The key challenge in mobile communications is "handing off" the user
communications from one local coverage area to the next. In IEEE Project 802, this
involves a succession of terrestrial Wireless local area networks (WLAN).[2]
Internetwork
Two or more networks or network segments connected using devices that operate at layer
3 (the 'network' layer) of the OSI Basic Reference Model, such as a router. Any
interconnection among or between public, private, commercial, industrial, or
governmental networks may also be defined as an internetwork.
In modern practice, the interconnected networks use the Internet Protocol. There are at
least three variants of internetwork, depending on who administers and who participates
in them:
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Intranet
Extranet
Internet
Intranets and extranets may or may not have connections to the Internet. If connected to
the Internet, the intranet or extranet is normally protected from being accessed from the
Internet without proper authorization. The Internet is not considered to be a part of the
intranet or extranet, although it may serve as a portal for access to portions of an extranet.
Intranet
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.
Extranet
An extranet is a network or internetwork that is limited in scope to a single organization
or entity but which also has limited connections to the networks of one or more other
usually, but not necessarily, trusted organizations or entities (e.g. a company's customers
may be given access to some part of its intranet creating in this way an extranet, 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, by definition, an extranet cannot consist of a single LAN; it must
have at least one connection with an external network.
Internet
The Internet is a specific internetwork. It consists of a worldwide interconnection of
governmental, academic, public, and private networks based upon the networking
technologies of the Internet Protocol Suite. It is the successor of the Advanced Research
Projects Agency Network (ARPANET) developed by DARPA of the U.S. Department of
Defense. The Internet is also the communications backbone underlying the World Wide
Web (WWW). The 'Internet' is most commonly spelled with a capital 'I' as a proper noun,
for historical reasons and to distinguish it from other generic internetworks.
Participants in the Internet use a diverse array of methods of several hundred
documented, and often standardized, protocols compatible with the Internet Protocol
Suite and an addressing system (IP Addresses) administered by the Internet Assigned
Numbers Authority and address registries. Service providers and large enterprises
exchange information about the reachability of their address spaces through the Border
Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.
Basic Hardware Components
All networks are made up of basic hardware building blocks to interconnect network
nodes, such as Network Interface Cards (NICs), Bridges, Hubs, Switches, and Routers. In
addition, some method of connecting these building blocks is required, usually in the
form of galvanic cable (most commonly Category 5 cable). Less common are microwave
links (as in IEEE 802.11) or optical cable ("optical fiber").
Network Interface Cards
A network card, network adapter or NIC (network interface card) is a piece of
computer hardware designed to allow computers to communicate over a computer
network. It provides physical access to a networking medium and often provides a lowlevel addressing system through the use of MAC addresses. It allows users to connect to
each other either by using cables or wirelessly.
Repeaters
A repeater is an electronic device that receives a signal and retransmits it at a higher
power level, or to the other side of an obstruction, so that the signal can cover longer
distances without degradation. In most twisted pair ethernet configurations, repeaters are
required for cable runs longer than 100 meters away from the computer.
Hubs
A hub contains multiple ports. When a packet arrives at one port, it is copied to all the
ports of the hub for transmission. When the packets are copied, the destination address in
the frame does not change to a broadcast address. It does this in a rudimentary way: It
simply copies the data to all of the Nodes connected to the hub.[3]
Bridges
A network bridge connects multiple network segments at the data link layer (layer 2) of
the OSI model. Bridges do not promiscuously copy traffic to all ports, as hubs do, but
learn which MAC addresses are reachable through specific ports. Once the bridge
associates a port and an address, it will send traffic for that address only to that port.
Bridges do send broadcasts to all ports except the one on which the broadcast was
received.
Bridges learn the association of ports and addresses by examining the source address of
frames that it sees on various ports. Once a frame arrives through a port, its source
address is stored and the bridge assumes that MAC address is associated with that port.
The first time that a previously unknown destination address is seen, the bridge will
forward the frame to all ports other than the one on which the frame arrived.
Bridges come in three basic types:
1. Local bridges: Directly connect local area networks (LANs)
2. Remote bridges: Can be used to create a wide area network (WAN) link between
LANs. Remote bridges, where the connecting link is slower than the end
networks, largely have been replaced by routers.
3. Wireless bridges: Can be used to join LANs or connect remote stations to LANs.
] Switches
A switch is a device that performs switching. Specifically, it forwards and filters OSI
layer 2 datagrams (chunk of data communication) between ports (connected cables)
based on the MAC addresses in the packets.[4] This is distinct from a hub in that it only
forwards the datagrams to the ports involved in the communications rather than all ports
connected. Strictly speaking, a switch is not capable of routing traffic based on IP address
(layer 3) which is necessary for communicating between network segments or within a
large or complex LAN. Some switches are capable of routing based on IP addresses but
are still called switches as a marketing term. A switch normally has numerous ports, with
the intention being that most or all of the network is connected directly to the switch, or
another switch that is in turn connected to a switch.[5]
Switch is a marketing term that encompasses routers and bridges, as well as devices that
may distribute traffic on load or by application content (e.g., a Web URL identifier).
Switches may operate at one or more OSI model layers, including physical, data link,
network, or transport (i.e., end-to-end). A device that operates simultaneously at more
than one of these layers is called a multilayer switch.
Overemphasizing the ill-defined term "switch" often leads to confusion when first trying
to understand networking. Many experienced network designers and operators
recommend starting with the logic of devices dealing with only one protocol level, not all
of which are covered by OSI. Multilayer device selection is an advanced topic that may
lead to selecting particular implementations, but multilayer switching is simply not a realworld design concept.
[
Routers
Router e: Routers are networking devices that forward data packets between networks
using headers and forwarding tables to determine the best path to forward the packets.
Routers work at the network layer of the TCP/IP model or layer 3 of the OSI model.
Routers also provide interconnectivity between like and unlike media (RFC 1812). This
is accomplished by examining the Header of a data packet, and making a decision on the
next hop to which it should be sent (RFC 1812) They use preconfigured static routes,
status of their hardware interfaces, and routing protocols to select the best route between
any two subnets. A router is connected to at least two networks, commonly two LANs or
WANs or a LAN and its ISP's network. Some DSL and cable modems, for home (and
even office) use, have been integrated with routers to allow multiple home/office
computers to access the Internet through the same connection. Many of these new devices
also consist of wireless access points (waps) or wireless routers to allow for IEEE
802.11g/b wireless enabled devices to connect to the network without the need for cabled
connections.
Client-server
The client-server software architecture model distinguishes client systems from server
systems, which communicate over a computer network. A client-server application is a
distributed system comprising both client and server software. A client software process
may initiate a communication session, while the server waits for requests from any client.
Client/server describes the relationship between two computer programs in which one
program, the client, makes a service request from another program, the server. Standard
networked functions such as email exchange, web access and database access, are based
on the client/server model. For example, a web browser is a client program at the user
computer that may access information at any web server in the world. To check your
bank account from your computer, a web browser client program in your computer
forwards your request to a web server program at the bank. That program may in turn
forward the request to its own database client program that sends a request to a database
server at another bank computer to retrieve your account balance. The balance is returned
to the bank database client, which in turn serves it back to the web browser client in your
personal computer, which displays the information for you.
The client/server model has become one of the central ideas of network computing. Most
business applications being written today use the client/server model. So do the Internet's
main application protocols, such as HTTP, SMTP, Telnet, DNS, etc. In marketing, the
term has been used to distinguish distributed computing by smaller dispersed computers
from the "monolithic" centralized computing of mainframe computers. But this
distinction has largely disappeared as mainframes and their applications have also turned
to the client/server model and become part of network computing.
Each instance of the client software can send data requests to one or more connected
servers. In turn, the servers can accept these requests, process them, and return the
requested information to the client. Although this concept can be applied for a variety of
reasons to many different kinds of applications, the architecture remains fundamentally
the same.
The most basic type of client-server architecture employs only two types of hosts: clients
and servers. This type of architecture is sometimes referred to as two-tier. It allows
devices to share files and resources. The two tier architecture means that the client acts as
one tier and application in combination with server acts as another tier.
These days, clients are most often web browsers, although that has not always been the
case. Servers typically include web servers, database servers and mail servers. Online
gaming is usually client-server too. In the specific case of MMORPG, the servers are
typically operated by the company selling the game; for other games one of the players
will act as the host by setting his game in server mode.
The interaction between client and server is often described using sequence diagrams.
Sequence diagrams are standardized in the Unified Modeling Language.
When both the client- and server-software are running on the same computer, this is
called a single seat setup.
Characteristics of a client
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Initiates requests
Waits for replies
Receives replies
Usually connects to a small number of servers at one time
Typically interacts directly with end-users using a graphical user interface
Characteristics of a server
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Never initiates requests or activities
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Waits for and replies to requests from connected clients
A server can remotely install/uninstall applications and transfer data to the
intended clients
Comparison to Peer-to-Peer architecture
Another type of network architecture is known as peer-to-peer, because each host or
instance of the program can simultaneously act as both a client and a server, and because
each has equivalent responsibilities and status. Peer-to-peer architectures are often
abbreviated using the acronym P2P.
Both client-server and P2P architectures are in wide usage today.
[edit] Comparison to Client-Queue-Client architecture
While classic Client-Server architecture requires one of the communication endpoints to
act as a server, which is much harder to implement, Client-Queue-Client allows all
endpoints to be simple clients, while the server consists of some external software, which
also acts as passive queue (one software instance passes its query to another instance to
queue, e.g. database, and then this other instance pulls it from database, makes a
response, passes it to database etc.). This architecture allows greatly simplified software
implementation. Peer-to-Peer architecture was originally based on Client-Queue-Client
concept.
[edit] Advantages
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In most cases, a client-server architecture enables the roles and responsibilities of
a computing system to be distributed among several independent computers that
are known to each other only through a network. This creates an additional
advantage to this architecture: greater ease of maintenance. For example, it is
possible to replace, repair, upgrade, or even relocate a server while its clients
remain both unaware and unaffected by that change. This independence from
change is also referred to as encapsulation.
All the data is stored on the servers, which generally have far greater security
controls than most clients. Servers can better control access and resources, to
guarantee that only those clients with the appropriate permissions may access and
change data.
Since data storage is centralized, updates to that data are far easier to administer
than what would be possible under a P2P paradigm. Under a P2P architecture,
data updates may need to be distributed and applied to each "peer" in the network,
which is both time-consuming and error-prone, as there can be thousands or even
millions of peers.
Many mature client-server technologies are already available which were
designed to ensure security, 'friendliness' of the user interface, and ease of use.
It functions with multiple different clients of different capabilities.
[edit] Disadvantages
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Traffic congestion on the network has been an issue since the inception of the
client-server paradigm. As the number of simultaneous client requests to a given
server increases, the server can become severely overloaded. Contrast that to a
P2P network, where its bandwidth actually increases as more nodes are added,
since the P2P network's overall bandwidth can be roughly computed as the sum of
the bandwidths of every node in that network.
The client-server paradigm lacks the robustness of a good P2P network. Under
client-server, should a critical server fail, clients’ requests cannot be fulfilled. In
P2P networks, resources are usually distributed among many nodes. Even if one
or more nodes depart and abandon a downloading file, for example, the remaining
nodes should still have the data needed to complete the download.
Specific types of clients include web browsers, email clients, and online chat clients.
Specific types of servers include web servers, ftp servers, application servers, database
servers, mail servers, file servers, print servers, and terminal servers. Most web services
are also types of servers.
Computer network diagram
A sample network diagram
A computer network diagram is a schematic depicting the nodes and connections
amongst nodes in a computer network or, more generally, any telecommunications
network.

Topology
The physical network topology can be directly represented in a network diagram, as it is
simply the physical graph (mathematics) represented by the diagrams, with network
nodes as vertices and connections as undirected or direct edges (depending on the type of
connection). The logical network topology can be inferred from the network diagram if
details of the network protocols in use are also given.
Network diagram
A network diagram is a general type of diagram, which represents some kind of
network. A network in general is an interconnected group or system, or a fabric or
structure of fibrous elements attached to each other at regular intervals, or formally: a
graph.
A network diagrams is a special kind of cluster diagram, which even more general
represents any cluster or small group or bunch of something, structured or not. Both the
flow diagram and the tree diagram can be seen as a specific type of network diagram
Network topologies
Diagram of different network topologies.
In computer science the elements of a network are arranged in certain basic shapes (see
figure):
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Ring: The ring network connects each node to exactly two other nodes, forming a
circular pathway for activity or signals - a ring. The interaction or data travels
from node to node, with each node handling every packet.
Mesh is a way to route data, voice and instructions between nodes. It allows for
continuous connections and reconfiguration around broken or blocked paths by
“hopping” from node to node until the destination is reached.
Star: The star network consists of one central element, switch, hub or computer,
which acts as a conduit to coordinate activity or transmit messages.
Fully connected: Self Explanatory
Line - Everything connected in a single line.
Tree: This consists of tree-configured nodes connected to switches/concentrators,
each connected to a linear bus backbone. Each hub rebroadcasts all transmissions
received from any peripheral node to all peripheral nodes on the network,
sometimes including the originating node. All peripheral nodes may thus
communicate with all others by transmitting to, and receiving from, the central
node only.

Bus: In this network architecture a set of clients are connected via a shared
communications line, called a bus.
Network model
Main article: Network model
The network model is a database model conceived as a flexible way of representing
objects and their relationships. Its original inventor was Charles Bachman, and it was
developed into a standard specification published in 1969 by the CODASYL Consortium.
Where the hierarchical model structures data as a tree of records, with each record having
one parent record and many children, the network model allows each record to have
multiple parent and child records, forming a lattice structure.
Network topology
Main article: Network topology
Network topology is the study of the arrangement or mapping of the elements (links,
nodes, etc.) of a network, especially the physical (real) and logical (virtual)
interconnections between nodes.[4]
Any particular network topology is determined only by the graphical mapping of the
configuration of physical and/or logical connections between nodes. LAN Network
Topology is, therefore, technically a part of graph theory. Distances between nodes,
physical interconnections, transmission rates, and/or signal types may differ in two
networks and yet their topologies may be identical
Definition: Ethernet is a physical and data link layer technology for local area networks
(LANs). Ethernet was invented by engineer Robert Metcalfe.
When first widely deployed in the 1980s, Ethernet supported a maximum theoretical data
rate of 10 megabits per second (Mbps). Later, Fast Ethernet standards increased this
maximum data rate to 100 Mbps. Today, Gigabit Ethernet technology further extends peak
performance up to 1000 Mbps.
Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission
medium. Data travels over Ethernet inside protocol units called frames.
The run length of individual Ethernet cables is limited to roughly 100 meters, but Ethernet
can be easily extended to link entire schools or office buildings using network bridge devices
Fast Ethernet
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<Full Glossary>
Definition: Fast Ethernet supports a maximum data rate of 100 Mbps. It is so
named because original Ethernet technology supported only 10 Mbps. Fast
Ethernet began to be widely deployed in the mid-1990s as the need for greater
LAN performance became critical to universities and businesses.
A key element of Fast Ethernet's success was its ability to coexist with existing
network installations. Today, many network adapters support both traditional and
Fast Ethernet. These so-called "10/100" adapters can usually sense the speed of
the line automatically and adjust accordingly. Just as Fast Ethernet improved on
traditional Ethernet, Gigabit Ethernet improves on Fast Ethernet, offering rates up
to 1000 Mbps instead of 100 Mbps.
Advantages and disadvantages of a bus network
[edit] Advantages
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Easy to implement and extend
Well suited for temporary or small networks not requiring high speeds (quick
setup)
Cheaper than other topologies.
Cost effective as only a single cable is use
Cable faults are easily identified
[edit] Disadvantages
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Limited cable length and number of stations.
If there is a problem with the cable, the entire network goes down.
Maintenance costs may be higher in the long run.
Performance degrades as additional computers are added or on heavy traffic.
Proper termination is required (loop must be in closed path).
Significant Capacitive Load (each bus transaction must be able to stretch to most
distant link).
It works best with limited number of nodes.
It is slower than the other topologies
Definition: A network adapter interfaces a computer to a network. The term "adapter"
was popularized originally by Ethernet add-in cards for PCs.
Modern network adapter hardware exists in several forms. Besides traditional PCI Ethernet
cards, some network adapters are PCMCIA devices (also know as "credit card" or "PC Card"
adapters) or USB devices. Some wireless network adapter gear for laptop computers are
integrated circuit chips pre-installed inside the computer.
Windows and other operating systems support both wired and wireless network adapters
through a piece of software called a "device driver." Network drivers allow application
software to communicate with the adapter hardware. Network device drivers are often
installed automatically when adapter hardware is first powered on
A network adapter allows a computing device to interface with a local network. Adapters are
a required component to include when building a network.
Types of Network Adapters
A network adapter is typically a small unit of hardware. Several types of hardware adapters
exist:

Traditional PCI adapters fit inside a desktop personal computer (often called a NIC).

A newer type of PCI adapter, "PC Card" adapters (sometimes called PCMCIA cards)
insert into the side of a notebook computer.
A USB adapter plus into a standard USB port of any computer
A media adapter connects to the Ethernet port of an Xbox or Playstation game
console or other home entertainment product, providing a bridge to Wi-Fi wireless
capability.
Newer notebook computers contain integrated wireless adapter chips
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Every common adapter supports either Wi-Fi (wireless) or Ethernet (wired) standards.
Special-purpose adapters that support very specialized network protocols also exist, but
these are not found in homes or most business networks.
Determine Whether a Network Adapter Is Present
Newer computers often include a network adapter when sold. Determine whether a
computer already possesses a network adapter as follows:
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In desktop computers. look for an RJ-45 jack on the back of the computer. The RJ45 jack appears similar to a phone line jack but is slightly larger.
In notebook computers, look for a thin, removable metal device roughly the size of
credit card, but thicker.
For notebook computers running Windows that may contain integrated adapter
chips, open the Windows Device Manager. Device Manager can be accessed from
the Hardware tab of the System Properties section of Windows Control Panel
In any type of computing device, look for a small external device with LED lights
connected to a USB port
Purchasing a Network Adapter
A network adapter can be purchased separately from most manufacturers that supply
routers and other forms of networking equipment. When purchasing a network adapter,
some prefer to choose the brand of adapter that matches their router. To accommodate
this, manufacturers sometimes sell one or two network adapters together with a router in a
bundle called a home network kit. Technically, however, network adapters all offer very
similar functionality according to the Ethernet or Wi-Fi standard they support.
Installing a Network Adapter
Installing any network adapter hardware involves two steps:
1. Connecting the adapter hardware to the computer
2. Installing any required software associated with the adapter
For PCI adapters, first power down the computer and unplug its power cord before
proceeding with installation. A PCI adapter is a card that fits into a long, narrow slot inside
the computer. The computer's case must be opened and the card firmly inserted into this
slot.
Other types of network adapter devices can be attached while a computer is running
normally. Modern computer operating systems automatically detect newly connected
hardware and complete the basic software installation required.
Some network adapters, however, additionally require custom software installation.
Such an adapter will often be accompanied by a CD-ROM containing the installation media.
Alternatively, the necessary software can be downloaded for free from the manufacturer's
Web site.
Software installed with a network adapter includes a device driver that allows the
operating system to communicate with the hardware. In addition, a software management
utility may also be supplied that provides a user interface for advanced configuration and
troubleshooting of the hardware. These utilities are most commonly associated with Wi-Fi
wireless network adapters.
Network adapters can normally be disabled through their software. Disabling an adapter
provides a convenient alternative to installing and uninstalling it. Wireless network adapters
are best disabled when not in use, for security
Network model
The network model is a database model conceived as a flexible way of representing
objects and their relationships. The network model original inventor was Charles
Bachman, and it was developed into a standard specification published in 1969 by the
CODASYL Consortium