1. KINDS OF NETWORKS
Peer-to-Peer Networks
In a peer-to-peer network, there are no dedicated servers, and there is
no hierarchy among the computers. All the computers are equal and
therefore are known as peers. Each computer functions as both a client
and a server.
And there is no administrator responsible for the entire network. The user
at each computer determines what data on that computer is shared on
the network. Below figure shows a peer-to-peer network in which each
computer functions as both a client and a server.
Computers in a peer-to-peer network are called peers. In a peer-to-peer
network, all computers are considered equal; they all have the same
abilities to use the resources available on the network. Each computer can
function both as a client and a server. Computers are not dedicated to
function as servers. They use the network to share resources among the
independent peers. The computer whose applications are required by the
other networked computers functions as a server. The other computers
function as clients. Therefore, a dedicated administrator is not assigned
for network management.
A peer-to-peer network is a small group of people using a network. Peer-
to-peer networks members usually perform similar tasks, which
necessitates the sharing of resources. The peer-to-peer networks support
10 computers. The users in a peer-to-peer network are located in the
same geographical area. Operating systems, such as Microsoft Windows
98 or Microsoft Windows XP, can be used to set up a peer-to-peer

2. network. Additional software is not required because peer-to-peer
networking is built into the systems.
Another important point of peer-to-peer networks is that the users of
each computer plan and control the security of their resources. The users
determine the resources on their computers, which can be shared on the
network. The shared network resources, such as disk space, printers or
faxes, can be used by anyone who has access to the network. This is
possible only if the shared network resources are not password protected.
Peer-to-peer networks have weak and intrusive security because a central
server is not used to administer and secure the network. In addition,
some users may not implement security.
A peer-to-peer network does not support a central login process. This
implies that a user who logs on to one peer can access any shared
network resource, which is not controlled by a specific password. Peer-to-
peer networks are relatively simple. Because each computer functions as
a client and a server, there is no need for a powerful central server or for
the other components required for a high-capacity network. Peer-to-peer
networks can be less expensive than server-based networks.
Peer-to-peer networks are simple and inexpensive to install and maintain.
The cost of implementing peer-to-peer networks is low because a central
server is not used to administer the network. In addition, the components
for a high-capacity network are not required in a peer-to-peer network.
In a peer-to-peer network, the users handle administration. This means
that all the users need to be trained in how to share files, folders, and
printers. In a peer-to-peer network, suddenly shutting down your
computer can cause one of your colleagues to be unable to print.
Peer-to-peer networks are appropriate for environments where all the
users are located in the same geographical area and the network security
is not an important factor. In addition, these networks are useful when
the network expansion is limited.
Advantages of a peer-to-peer network:
Less initial expense - No need for a dedicated server.
Setup - An operating system (such as Windows XP) already in place
may only need to be reconfigured for peer-to-peer operations.
Disadvantages of a peer-to-peer network:
Decentralized - No Centralized server.
Security - Does not provide the security available on a peer-to-peer
network.

3. Server Based Networks
A dedicated server is one that functions only as a server and is not used
as a client or workstation. Server based networks (see below Figure) have
become the standard models for networking.
In a server-based network, clients rely on the services that the server
provides, such as file storing and printing. Client computers are generally
less powerful than server computers.
A server-based network using network operating system is that the
networks are organized into domains. A domain is a collection of networks
and clients that share security information. Domain security and logon
permissions are controlled by special servers called domain controllers.
Users cannot access the resources of servers in a domain until a domain
controller has authenticated them.
In server-based networks, a network administrator centrally manages the
resource security. The administrator defines and manages user access to
network resources.
Another beneficial of server-based networks is central file storage.
Server-based networks provide easy backup of critical data. Data backup
is another useful characteristic of server based networks.
Server based networks can support a larger number of users than peer-
to-peer networks. To support a large number of users, server-based
networks use monitoring and network management tools. Servers must
perform varied and complex tasks. (See below figure)

4. Security is often the primary reason for choosing a server-based approach
to networking. In a server-based environment, one administrator who
sets the policy and applies it to every user on the network can manage
security. (see below figure)
Advantages of a client/server network
Centralized - Resources and data security are controlled through the
server.
Security - More security then Peer-to-peer network.
Flexibility - New technology can be easily integrated into system.
Interoperability - All components (client /server) work together.
Accessibility - Server can be accessed remotely and across multiple
platforms.

5. Disadvantages of a client/server network
Expense - Requires initial investment in dedicated server.
Maintenance - Large networks will require a staff to ensure efficient
operation.
Dependence - When server goes down, operations will cease across
the network.
A LAN is a network with two or more computers connected to each other in a single location
Wired Local Area Network (LAN)
It is the simplest type of network in which computers are connected to
each other by cables.
Each of the computers on the LAN is also called a node .
A LAN is characterized by three primary attributes:
Topology
The topology is the pattern used to connect the computers together. With
a bus topology, a network cable connects each computer to the next one,
forming a chain. With a star topology, each of the computers is connected
to a central nexus called a hub/Switch. A ring topology is essentially a bus
network with the two ends joined together. (You will see more about
network topologies in Chapter 6)
Medium

6. Four basic types of media are used in local-area networks; coaxial cable,
twisted-pair wires, fiber-optic cable, And wireless.
Each medium has its advantages and disadvantages relative to cost,
speed, and expandability. Coaxial cables provide high speed and low error
rates. Twisted-pair wires are cheaper than coaxial cables, can sustain the
speeds common to most personal computers, and are easy to install.
Fiber-optic cable is the medium of choice for high-speed local-area
networks. Wireless local-area networks have the advantage of
expandability. (You will see more about network medium in Chapter 5.2)
Protocols
The topology and the medium used on a particular network are specified
by the protocol. (You will see more about protocol in Chapter 8).
LAN computer networks that usually cover a limited range, say, within the
boundary of a building. A LAN computer network is two or more
computers that communicate with each other through some medium.
The primary usage of local-area networks (LANs) is the sharing of
hardware, software, or information, such as data files, multimedia files, or
electronic mail. Resource sharing provided by local-area networks
improves efficiency and reduces overhead.
There are a number of ways in which nodes can communicate over a
network. The simplest is to establish a dedicated link between the
transmitting and receiving stations. This technique is known as circuit
switching. A better way of communicating is to use a technique known as
packet switching, in which a dedicated path is not reserved between the
source and the destination. Data are wrapped up in a packet and
launched into the network. In this way, a node only has exclusive access
to the medium while it is sending a packet. During its inactive period,
other nodes can transmit. A typical packet is divided into preamble,
address, control, data, and error-check fields.
The computers in a LAN are connected by using cables. This method
cannot be used to connect computers that are in different locations, for
example, in buildings across a town or city. Therefore, a LAN is not
suitable for large businesses with offices in several locations.
Wireless Local Area Network
The term wireless networking refers to technology that enables two or
more computers to communicate using standard network protocols, but
without network cabling.

7. Peer-to-peer wireless network consists of a number of computers each
equipped with a wireless networking interface card. Each computer can
communicate directly with all of the other wireless enabled computers.
They can share files and printers this way, but may not be able to access
wired LAN resources, unless one of the computers acts as a bridge to the
wired LAN using special software.
A wireless network can also use an access point, or base station. In this
type of network the access point acts like a hub, providing connectivity for
the wireless computers. It can connect the wireless LAN to a wired LAN,
allowing wireless computer access to LAN resources, such as file servers
or existing Internet Connectivity.
There are two types of access points:
Hardware access points (HAP)
Hardware access points offer complete support of most wireless features,
but check your requirements carefully.
Software Access Points

8. Software Access Points which run on a computer equipped with a wireless
network interface card as used in peer-to-peer wireless network. The
software routers that can be used as a basic Software Access Point, and
include features not commonly found in hardware solutions.
Connected wireless LAN to wired LAN
To do this you will need some sort of bridge between the wireless and
wired network. This can be accomplished either with a hardware access
point or a software access point.
Hardware access points are available with various types of network
interfaces, such as Ethernet or Token Ring, but typically require extra
hardware to be purchased if you're networking requirements change. If
networking requirements go beyond just interconnecting a wired network
to a small wireless network, a software access point may be the best
solution.
A software access point does not limit the type or number of network
interfaces you use. It may also allow considerable flexibility in providing
access to different network types, such as different types of Ethernet,
Wireless and Token Ring networks. Such connections are only limited by
the number of slots or interfaces in the computer used for this task.
Further to this the software access point may include significant additional
features such as shared Internet access, web caching or content filtering,
providing significant benefits to users and administrators.
Wireless networking offers a cost-effective solution to users with difficult
physical installations such as campuses, hospitals or businesses with
more than one location in immediate proximity but separated by public
thoroughfare.
This type of installation requires two access points. Each access point acts
as a bridge or router connecting its own LAN to the wireless connection.

9. The wireless connection allows the two access points to communicate with
each other, and therefore interconnect the two LAN's.
Wireless network range
Each access point has a finite range within which a wireless connection
can be maintained between the client computer and the access point. The
actual distance varies depending upon the environment; manufacturers
typically state both indoor and outdoor ranges to give a reasonable
indication of reliable performance. Also it should be noted that when
operating at the limits of range the performance may drop, as the quality
of connection deteriorates and the system compensates.
Typical indoor ranges are 150-300 feet, but can be shorter if the building
construction interferes with radio transmissions. Longer ranges are
possible, but performance will degrade with distance. Outdoor ranges are
quoted up to 1000 feet, but again this depends upon the environment.
There are ways to extend the basic operating range of Wireless
communications, by using more than a single access point or using a
wireless relay /extension point. Multiple access points can be connected to
a wired LAN, or sometimes even to a second wireless LAN if the access
point supports this.
In most cases, separate access points are interconnected via a wired LAN,
providing wireless connectivity in specific areas such as offices or rooms,
but connected to a main wired LAN for access to network resources, such
as file servers.

10. If a single area is too large to be covered by a single access point, then
multiple access points or extension points can be used. Note that an
"extension point" is not defined in the wireless standard, but have been
developed by some manufacturers.
When using multiple access points, each access point wireless area should
overlap its neighbors. This provides a seamless area for users to move
around in using a feature called "roaming.” See Roaming for further
information.
Some manufacturers produce extension points, which act as wireless
relays, extending the range of a single access point. Multiple extension
points can be strung together to provide wireless access to far away
locations from the central access point.

11. Roaming
A wireless computer can "roam" from one access point to another, with
the software and hardware maintaining a steady network connection by
monitoring the signal strength from in-range access points and locking on
to the one with the best quality.
Usually this is completely transparent to the user; they are not aware that
a different access point is being used from area to area. Some access
point configurations require security authentication when swapping access
points, usually in the form of a password dialog box.
Access points are required to have overlapping wireless areas to achieve
this as can be seen in the following diagram.

12. A user can move from Area 1 to Area 2 transparently. The Wireless
networking hardware automatically swaps to the Access Point with the
best signal.
Sharing an internet connection in wireless network
To share an Internet connection across a LAN you need two things:
an Internet sharing hardware device or software program
a LAN
If your LAN is wireless. You need hardware or software access point and a
wireless LAN. Any computer equipped with a wireless network card
running suitable Internet sharing software can be used as a software
access point. A number of vendors offer hardware access points.
A hardware access point may provide Internet Sharing capabilities to
Wired LAN computers, but does not usually provide much flexibility
beyond very simple configurations.
If an existing wired LAN already has an Internet connection, then the
hardware access points simply connect to LAN and allow wireless
computers to access the existing Internet connection in the same way as
wired LAN computers.

13. Wireless Network security
Wireless communications obviously provide potential security issues, as
an intruder does not need physical access to the traditional wired network
in order to gain access to data communications. However, 802.11 wireless
communications cannot be received much less decoded by simple
scanners, short wave receivers etc. This has led to the common
misconception that wireless communications cannot be eavesdropped at
all. However, eavesdropping is possible using specialist equipment.
To protect against any potential security issues, 802.11 wireless
communications have a function called WEP (Wired Equivalent Privacy), a
form of encryption which provides privacy comparable to that of a
traditional wired network. If the wireless network has information that
should be secure then WEP should be used, ensuring the data is protected
at traditional wired network levels.
IEEE 802.11
Wireless networking hardware requires the use of underlying technology
that deals with radio frequencies as well as data transmission. The most
widely used standard is 802.11 produced by the Institute of Electrical and
Electronic Engineers (IEEE). This is a standard defining all aspects of
Radio Frequency Wireless networking.
Also it should be noted that traditional Virtual Private Networking (VPN)
techniques will work over wireless networks in the same way as
traditional wired networks.

14. Wide Area Network (WAN)
A wide area network (WAN) is a telecommunications network, usually
used for connecting computers, that spans a wide geographical area.
WANs can by used to connect cities, states, or even countries.
An example of a WAN connection would be a company with two offices in
distant cities, each with its own LAN and connected by a leased telephone
line. This type of WAN is illustrated in below figure. Each end of the
leased line is connected to a router and the routers are connected to
individual LANs. Any computer on either of the LANs can communicate
with any one of the other computers at the other end of the WAN link or
with a computer on its own LAN.
WANs are often used by larger corporations or organizations to facilitate
the exchange of data and in a wide variety of industries, corporations with
facilities at multiple locations have embraced WANs. Increasingly,
however, even small businesses are utilizing WANs as a way of increasing
their communications capabilities.
Although WANs serve a purpose similar to that of local area networks
(LANs), WANs are structured and operated quite differently. The user of a
WAN usually does not own the communications lines that connect the
remote computer systems; instead, the user subscribes to a service
through a telecommunications provider. Unlike LANs, WANs typically do
not link individual computers, but rather are used to link LANs. WANs also
transmit data at slower speeds than LANs.
WANs have existed for decades, but new technologies, services, and
applications have developed over the years to dramatically increase their
efficacy for business. WANs were originally developed for digital leased-
line services carrying only voice, rather than data. As such, they

15. connected the private branch exchanges (PBXs) of remote offices of the
same company. WANs are still used for voice services, but today they are
used more frequently for data and image transmission (such as video
conferencing). These added applications have spurred significant growth
in WAN usage, primarily because of the surge in LAN connections to the
wider networks.
WANs are either point-to-point, involving a direct connection between two
sites, or operate across packet-switched networks, in which data is
transmitted in packets over shared circuits. Point-to-point WAN service
may involve either analog dial-up lines, in which a modem is used to
connect the computer to the telephone line, or dedicated leased digital
telephone lines, also known as "private lines." Analog lines, which may be
either part of a public-switched telephone network or leased lines, are
suitable for batch data transmissions, such as congruent order entry and
point-of-sale transactions. Dedicated digital phone lines permit
uninterrupted, secure data transmission at fixed costs.
Point-to-point WAN service providers include both local telephone
companies and long distance carriers. Packet-switched network services
are typically chosen by organizations which have low volumes of data or
numerous sites, for which multiple dedicated lines would be too
expensive.
Depending on the service, WANs can be used for almost any data sharing
purpose for which LANs can be used. Slower transmission speeds,
however, may make some applications less practical for WANs. The most
basic uses of WANs are for electronic mail and file transfer, but WANs can
also permit users at remote sites to access and enter data on a central
site's database, such as instantaneously updating accounting records.
New types of network-based software that facilitate productivity and
production tracking, such as groupware and work-flow automation
software, can also be used over WANs. Using groupware, workers at
dispersed locations can more easily collaborate on projects. WANs also
give remote offices access to a central office's other data communications
services, including the Internet.
Wireless Fidelity Wi-Fi

16. A typical Wi-Fi setup contains one or more Access Points (APs) and one or
more clients. An AP broadcasts its SSID (Service Set Identifier, "Network
name") via packets that are called beacons, which are usually broadcast
every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of
relatively short duration and therefore do not have a significant effect on
performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the
client who receives the beacon can communicate at least 1 Mbit/s. Based
on the settings (e.g. the SSID), the client may decide whether to connect
to an AP. If two APs of the same SSID are in range of the client, the client
firmware might use signal strength to decide which of the two APs to
make a connection to.
The Wi-Fi standard leaves connection criteria and roaming totally open to
the client. This is a strength of Wi-Fi, but also means that one wireless
adapter may perform substantially better than the other. Since Wi-Fi
transmits in the air, it has the same properties as a non-switched
ethernet network.
Wi-Fi Devices
Wireless Access Point (WAP)
A wireless access point (AP) connects a group of wireless stations to an
adjacent wired local area network (LAN). An access point is similar to an
ethernet hub or switch, but instead of relaying LAN data only to other LAN
stations, an access point can relay wireless data to all other compatible
wireless devices as well as to a single (usually) connected LAN device, in
most cases an ethernet hub or switch, allowing wireless devices to
communicate with any other device on the LAN.
Wireless Routers
A wireless router integrates a wireless access point with an IP router and
an ethernetswitch . The integrated switch connects the integrated access
point and the integrated ethernet router internally, and allows for external
wired ethernet LAN devices to be connected as well as a (usually) single
WAN device such as cable modem or DSL modem . A wireless router
advantageously allows all three devices (mainly the access point and
router) to be configured through one central configuration utility, usually
through an integrated web server .
Wireless Ethernet Bridge
A wireless Ethernet bridge connects a wired network to a wireless
network. This is different from an access point in the sense that an access
point connects wireless devices to a wired network at the data-link layer .
Two wireless bridges may be used to connect two wired networks over a

17. wireless link, useful in situations where a wired connection may be
unavailable, such as between two separate homes.
Advantages of Wi-Fi
Allows LANs to be deployed without cabling, typically reducing the costs of
network deployment and expansion. Spaces where cables cannot be run,
such as outdoor areas and historical buildings, can host wireless LANs.
Wi-Fi silicon pricing continues to come down, making Wi-Fi a very
economical networking option and driving inclusion of Wi-Fi in an ever-
widening array of devices.
Wi-Fi products are widely available in the market. Different brands of
access points and client network interfaces are interoperable at a basic
level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi
Alliance are interoperable and include WPA2 security.
Wi-Fi networks support roaming, in which a mobile client station such as a
laptop computer can move from one access point to another as the user
moves around a building or area.
Wi-Fi networks support roaming, in which a mobile client station such as a
laptop computer can move from one access point to another as the user
moves around a building or area.
Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi
client works in different countries around the world.
Disadvantages of Wi-Fi
Wi-Fi can be interrupted by other devices, notably 2.4 GHz cordless
phones and microwave ovens.
Power consumption is fairly high compared to some other standards,
making battery life and heat a concern.
The most common wireless encryption standard, Wired Equivalent Privacy
or WEP, has been shown to be breakable even when correctly configured.
Wi-Fi Access Points typically default to an open ( encryption -free) mode.
Novice users benefit from a zero configuration device that works out of
the box but might not intend to provide open wireless access to their LAN.
Wi-Fi networks have limited range. A typical Wi-Fi home router using
802.11b or 802.11g with a stock antenna might have a range of 45 m
(150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with
frequency band, as Wi-Fi is no exception to the physics of radio wave
propagation. Wi-Fi in the 2.4 GHz frequency block has better range than
Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi

18. (and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennas
can be several kilometres or more with line-of-sight.
Wi-Fi networks can be monitored and used to read and copy data
(including personal information) transmitted over the network when no
encryption such as VPN is used.