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IMDAD HUSSAIN

Subject:

COMUNICATION NETWORK

NETWORK TOPOLOGY

NETWORK CABLES

NETWORK DEVICES

SOFTWARE ENGINEER

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Networking and communications is one of the most important aspects in nowadays life. Every

person can reach any other person in any part of the world with seconds. With networking and

communications, life became much easier and progress is much faster. There are many different

ways to reach any thing or persons, but the two main and common things are by internet and

phones. With telephones and mobile phones, you can reach each person individually. But with

internet, you can communicate with any person individually or in a group. But nowadays, it is

possible to communicate with a group of people in a group by mobile phones.

Networking is a set of computers or devices that are connected to each others with that

can exchange data. Internet, intranet, and extranet are three types of networking. Examples of

different networks are Local area network (LAN), Wide area network (WAN), and Wireless

LANs and WANs (WLAN & WWAN).

Local area network is the smallest rang between the other 2, it is a small network given to

a small geographic area. Wide area network covers a large geographic area, and it is a large

network. Wireless LANs and WANs is a wireless that covers both LANs and WANs.

The possible medias that network can pass though are twisted-pair cooper wire cable,

coaxial cable, optical fiber, power lines, and other different wireless technologies. Different

cables have different exceed different meters; this is the main difference between the cables.

SOFTWARE ENGINEER

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Some known programs that share both networking and communication are Messenger,

Skype, and Pal talk. There are many other types but these are some of the most famous ones that

are released to communicate with individual people or groups.

Nowadays, people who don’t have internet and mobile phones are considered isolated

from the rest of the world. Now it is so easy to reach any part of the world, if it is so, what is the

future of networking? Will it be possible to phone someone on the moon from a mobile phone?

The future remains mystery.

What is Communication Networks?

What are Networks?

Networks are large distributed systems designed to send information from one location to

another. An end point is a place in a network where data transmission either originates or

terminates. A node is a point in the network where data travels through without stopping. Nodes

are connected by channels, paths that data flows down. Channels can be physical linear objects

such as a wire or a fiber optic cable, or it can be less tangible, like a wireless connection at a

particular frequency.

Providers and Consumers

An end point that produces information is known as a "producer" or a "server". An endpoint that

receives information is known as a "consumer" or a "client". In many networks, such as bi-

directional networks, an endpoint can be both a client and a server.

Bi-directional Communications

Bi-directional communications means that data is flowing both to and from an end point. An end

point can be both a client and a server.

Point-to-point communication

Some channels are point-to-point -- they have only a single producer (at one end), and a single

consumer (at the far end).

Many networks have "full duplex" communication between nodes, meaning they have 2 separate

point-to-point channels (one in each direction) between the nodes (on separate wires or allocated

to separate frequencies).

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Some "mesh" networks are built from point-to-point channels. Since wiring every node to every

other node is prohibitively expensive, when one node needs to communicate with a distant node,

the "intermediate" nodes must pass through the information.

Multiple Accesses

Multiple access networks are networks where multiple clients, multiple servers, or both are

attempting to access the network simultaneously. Networks with one server and multiple clients

are called "broadcast networks", "multicast networks", or "SIMO networks". "SIMO" stands for

"Single Input Multiple Output". Networks with multiple clients and servers are known as

"MIMO" or "Multiple Input Multiple Output" networks.

Data Collisions

In a MIMO network, when multiple servers attempt to send data on a single channel at the same

time, a data collision occurs. Because data typically consists of electric or electromagnetic

radiation, a data collision causes both pieces of information to become unreadable. Clients on the

network will either read meaningless data (garbage data) or will read no data at all. MIMO

networks therefore will use some sort of collision avoidance or collision detection mechanisms

to prevent data collision problems from affecting the network.

Networks with only one fixed sender per channel (point-to-point channels and SIMO channels)

never have data collisions on the channel.

What is telecommunication?

Telecommunications is a general term for a vast array of technologies that send information over

distances. Mobile phones, land lines, satellite phones and voice over Internet protocol (VoIP) are

all telephony technologies -- just one field of telecommunications. Radio, television and networks

are a few more examples of telecommunication.

While most people associate telecommunications with modern technologies, the strict definit ion

of the term encompasses primitive and even ancient forms of telecommunication. Among these is

the use of smoke signals as a kind of visual telegraph. Puffs of smoke were time-released by

smothering a fire with a blanket, then quickly removing and replacing the blanket. Widely used by

the American Indians, smoke signals could communicate short messages over long distances,

assuming a clear line of sight.

When armies were spotted in the distance, he would light a bonfire. The fire could be seen from

a good distance away by the next man in the relay, who would in turn light his own bonfire, and

so the fires were lit in succession along the range, creating an effective telecommunications signal

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that traveled back over several miles in a relatively short period of time. Finally, the last man in

the relay would light a beacon to signal his army below that the opponent was en-route.

Throughout the 19th century, telecommunications devices became more sophisticated with the

advent of electricity, leading to the telegraph, Morse code, and signal lamps. A signal lamp, the

optical version of the telegraph, is a powerful lamp with shutters that block the light in long or

short durations to translate to the dots and dashes of Morse code. A heliograph is another optical

telegraph -- a mirror used to reflect light to mimic a signal lamp.

In the 20th century, telecommunications reached beyond our planet. In June 1969, the world

watched and listened as astronauts walked on the moon. Twenty years later, in August 1989, we

would see pictures of Neptune arrive back from the Voyager 2 spacecraft, riding radio waves that

traveled over roughly three billion miles (4.8 billion km) to reach us in a matter of a few hours.

Strides in telecommunications have changed the world immeasurably. While pockets of

humankind were once isolated from each other, people now have multiple ways to see and hear

what is occurring on the other side of the world in real time. Satellite technology, television, the

Internet and telephony keep the globe connected in a humming buzz of interactive voices and

pictures. In short, telecommunications has come a long way from smoke signals.

What is Network Topology?

The physical topology of a network refers to the configuration of cables, computers, and other

peripherals. Physical topology should not be confused with logical topology which is the method

used to pass information between workstations.

Main Types of Network Topologies In networking, the term "topology" refers to the layout of connected devices on a network. This

article introduces the standard topologies of computer networking.

One can think of a topology as a network's virtual shape or structure. This shape does not

necessarily correspond to the actual physical layout of the devices on the network. For example,

the computers on a home LAN may be arranged in a circle in a family room, but it would be

highly unlikely to find an actual ring topology there.

Network topologies are categorized into the following basic types:

Star Topology

Ring Topology

Bus Topology

Tree Topology

Mesh Topology

Hybrid Topology

More complex networks can be built as hybrids of two or more of the above basic topologies.

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Star Topology Many home networks use the star topology. A star network features a central connection point

called a "hub" that may be a hub, switch or router. Devices typically connect to the hub with

Unshielded Twisted Pair (UTP) Ethernet.

Compared to the bus topology, a star network generally requires more cable, but a failure in any

star network cable will only take down one computer's network access and not the entire LAN.

(If the hub fails, however, the entire network also fails.)

See the illustration of Star Network Topology.

Advantages of a Star Topology Easy to install and wire.

No disruptions to the network then connecting or removing devices.

Easy to detect faults and to remove parts.

Disadvantages of a Star Topology Requires more cable length than a linear topology.

If the hub or concentrator fails, nodes attached are disabled.

More expensive than linear bus topologies because of the cost of the concentrators.

The protocols used with star configurations are usually Ethernet or Local Talk. Token Ring uses

a similar topology, called the star-wired ring.

Star-Wired Ring A star-wired ring topology may appear (externally) to be the same as a star topology. Internally,

the MAU of a star-wired ring contains wiring that allows information to pass from one device to

another in a circle or ring (See fig. 3). The Token Ring protocol uses a star-wired ring topology.

Ring Topology

In a ring network, every device has exactly two neighbors for communication purposes. All

messages travel through a ring in the same direction (either "clockwise" or "counterclockwise").

A failure in any cable or device breaks the loop and can take down the entire network.

To implement a ring network, one typically uses FDDI, SONET, or Token Ring technology.

Ring topologies are found in some office buildings or school campuses.

See the illustration of Ring Topology.

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Bus Topology Bus networks (not to be confused with the system bus of a computer) use a common backbone to

connect all devices. A single cable, the backbone functions as a shared communication medium

that devices attach or tap into with an interface connector. A device wanting to communicate

with another device on the network sends a broadcast message onto the wire that all other

devices see, but only the intended recipient actually accepts and processes the message.

Ethernet bus topologies are relatively easy to install and don't require much cabling compared to

the alternatives. 10Base-2 ("Thin Net") and 10Base-5 ("Thick Net") both were popular Ethernet

cabling options many years ago for bus topologies. However, bus networks work best with a

limited number of devices. If more than a few dozen computers are added to a network bus,

performance problems will likely result. In addition, if the backbone cable fails, the entire

network effectively becomes unusable.

See the illustration of Bus Network Topology.

Advantages of a Linear Bus Topology Easy to connect a computer or peripheral to a linear bus.

Requires less cable length than a star topology.

Disadvantages of a Linear Bus Topology

Entire network shuts down if there is a break in the main cable.

Terminators are required at both ends of the backbone cable.

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Difficult to identify the problem if the entire network shuts down.

Not meant to be used as a stand-alone solution in a large building.

Tree Topology

Tree topologies integrate multiple star topologies together onto a bus. In its simplest form, only

hub devices connect directly to the tree bus, and each hub functions as the "root" of a tree of

devices. This bus/star hybrid approach supports future expandability of the network much better

than a bus (limited in the number of devices due to the broadcast traffic it generates) or a star

(limited by the number of hub connection points) alone.

See the illustration of Tree Network Topology.

Advantages of a Tree Topology

Point-to-point wiring for individual segments.

Supported by several hardware and software venders.

Disadvantages of a Tree Topology

Overall length of each segment is limited by the type of cabling used.

If the backbone line breaks, the entire segment goes down.

More difficult to configure and wire than other topologies.

Mesh Topology

Mesh topologies involve the concept of routes. Unlike each of the previous topologies, messages

sent on a mesh network can take any of several possible paths from source to destination. (Recall

that even in a ring, although two cable paths exist, messages can only travel in one direction.)

Some WANs, most notably the Internet, employ mesh routing.

A mesh network in which every device connects to every other is called a full mesh. As shown in

the illustration below, partial mesh networks also exist in which some devices connect only

indirectly to others.

See the illustration of Mesh Network Topology.

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Hybrid Topology A combination of any two or more network topologies. Note 1: Instances can occur where two

basic network topologies, when connected together, can still retain the basic network character,

and therefore not be a hybrid network. For example, a tree network connected to a tree network

is still a tree network. Therefore, a hybrid network accrues only when two basic networks are

connected and the resulting network topology fails to meet one of the basic topology definitions.

For example, two star networks connected together exhibit hybrid network topologies. Note 2: A

hybrid topology always accrues when two different basic network topologies are connected.

5-4-3 Rule

A consideration in setting up a tree topology using Ethernet protocol is the 5-4-3 rule. One aspect

of the Ethernet protocol requires that a signal sent out on the network cable reach every part of

the network within a specified length of time. Each concentrator or repeater that a signal goes

through adds a small amount of time. This leads to the rule that between any two nodes on the

network there can only be a maximum of 5 segments, connected through 4

repeaters/concentrators. In addition, only 3 of the segments may be populated (trunk) segments if

they are made of coaxial cable. A populated segment is one which has one or more nodes

attached to it . In Figure 4, the 5-4-3 rule is adhered to. The furthest two nodes on the network

have 4 segments and 3 repeaters/concentrators between them.

This rule does not apply to other network protocols or Ethernet networks where all fiber optic

cabling or a combination of a fiber backbone with UTP cabling is used. If there is a combination

of fiber optic backbone and UTP cabling, the rule is simply translated to 7-6-5 rule.

Considerations When Choosing a Topology

Money. A linear bus network may be the least expensive way to install a network; you do not

have to purchase concentrators.

Length of cable needed. The linear bus network uses shorter lengths of cable.

Future growth. With a star topology, expanding a network is easily done by adding another

concentrator.

Cable type. The most common cable in schools is unshielded twisted pair, which is most often

used with star topologies.

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Other definition of Network Topology

A network consists of multiple computers connected using some type of interface, each having

one or more interface devices such as a Network Interface Card (NIC) and/or a serial device for

PPP networking. Each computer is supported by network software that provides the server or

client functionality. The hardware used to transmit data across the network is called the media. It

may include copper cable, fiber optic, or wireless transmission. The standard cabling used for the

purposes of this document is 10Base-T category 5 Ethernet cable. This is twisted copper cabling

which appears at the surface to look similar to TV coaxial cable. It is terminated on each end by

a connector that looks much like a phone connector. Its maximum segment length is 100 meters.

In a server based network, there are computers set up to be primary providers of services such as

file service or mail service. The computers providing the service are called servers and the

computers that request and use the service are called client computers.

In a peer-to-peer network, various computers on the network can act both as clients and servers.

For instance, many Microsoft Windows based computers will allow file and print sharing. These

computers can act both as a client and a server and are also referred to as peers. Many networks

are combination peer-to-peer and server based networks. The network operating system uses a

network data protocol to communicate on the network to other computers. The network

operating system supports the applications on that computer. A Network Operating System

(NOS) includes Windows NT, Novell Netware, Linux, Unix and others.

Network Cables

Despite advances in wireless technologies, many computer networks in the 21st century continue

utilizing cables as a physical medium for devices to transfer data. Several different types of

network cables exist, each designed for specific purposes.

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Coaxial Cables

First invented in the 1880s, "coax" was best known as the kind of cable that connected television

sets to home antennas. Coaxial cable is also a standard for 10 Mbps Ethernet cables . When 10

Mbps Ethernet was most popular, during the 1980s and early 1990s,

Network typically utilized one of two kinds of coax cable – thin net (10BASE2 standard) or thick

net (10BASE5). These cables consist of an inner copper wire of varying thickness surrounded by

insulation and other shielding. Their stiffness caused network administrators difficulty in

installing and maintaining thin net and thick net.

Twisted Pair Cables

Twisted pair eventually emerged during the 1990s as the leading cabling standard for Ethernet ,

starting with 10 Mbps (10BASE-T, also known as Category 3 or Cat3), later followed by

improved versions for 100 Mbps (100BASE-TX, Cat5 and Cat5e) and successively higher

speeds up to 10 GBPS (10GBASE-T). Ethernet twisted pair cables contain up to 8 wires wound

together in pairs to minimize electromagnetic interference.

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Two primary types of twisted pair cable industry standards are defined – Unshielded Twisted

Pair (UTP) and Shielded Twisted Pair (STP). Modern Ethernet cables use UTP wiring due to its

lower cost, while STP cabling can be found in some other types of networks such as FDDI.

Fiber Optics

Instead of insulated metal wires transmitting electrical signals, fiber optic network cables work

using strands of glass and pulses of light. These network cables are bendable despite being made

of glass. They have proven especially useful in wide area network (WANs) installations where

long distance underground or outdoor cable runs are required and also in office buildings where

a high volume of communication traffic is common.

Two primary types of fiber optic cable industry standards are defined – single-mode

(100BaseBX standard) and multimode (100BaseSX standard). Long-distance

telecommunications networks more commonly use single-mode for its relatively higher

bandwidth capacity, while local networks typically use multimode instead due to its lower cost.

USB Cables

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Most Universal Serial Bus (USB) cables connect a computer with a peripheral device

(keyboard or mouse) rather than to another computer for networking . However, special

adapters (sometimes called dongles ) also allow connecting an Ethernet cable to a USB

port indirectly. USB cables feature twisted-pair wiring.

Serial and Parallel Cables

Because many PCs in the 1980s and early 1990s lacked Ethernet capability, and USB had not

been developed yet, serial and parallel interfaces that are obsolete on modern computers were

sometimes used for PC-to-PC networking. So-called null model cables , for example, connected

the serial ports of two PCs enabling data transfers at speeds between 0.115 and 0.45 Mbps.

Crossover Cables

Null modem cables are one example of the category of crossover cables . A crossover cable joins

two network devices of the same type, such as two PCs or two network switches .

The use of Ethernet crossover cables was especially common on older home networks years ago

when connecting two PCs directly together. Externally, Ethernet crossover cables appear nearly

identical to ordinary (sometimes also called straight-through), the only visible difference being

the order of color-coded wires appearing on the cable's end connector. Manufacturers typically

applied special distinguishing marks to their crossover cables for this reason. Nowadays, though,

most home networks utilize routers that have built-in crossover capability, eliminating the need

for these special cables.

Other Types of Network Cables

Some networking professionals use the term patch cable to refer to any kind of straight-through

network cable being used for a temporary purpose. Coax, twisted pair and fiber optic types of

patch cables all exist. They do not differ in physical characteristics from other types of network

cables except that they tend to be a shorter length.

Power line networking systems utilize a home's standard electrical wiring for data

communication using special adapters plugged into wall outlets.

Ethernet cables

Question: What Is An Ethernet Cable?

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Answer: An Ethernet cable is one of the most popular forms of network cable used on wired

networks. Ethernet cables connect devices on local area networks such as

PCs, routers and switches.

Types of Ethernet Cables

Ethernet cables normally support one or more industry standards including Category 5

(CAT5) and Category 6 (CAT6) .

A crossover cable is a special type of Ethernet cable specially designed for connecting two

computers to each other. By contrast, most Ethernet cables are designed to connect one computer

to a router or switch.

Ethernet cables are physically manufactured in two basic forms called solid and stranded. Solid

Ethernet cables tend to offer better performance and protection against electrical interference,

while stranded cables are less prone to physical cracks and breaks making them more suitable for

travelers and portable devices.

Limitations of Ethernet Cables

A single Ethernet cable, like an electric power cord, can extend only limited distances due to

their electrical transmission characteristics.

Alternatives to Ethernet Cables for Computer Networking

Wireless technologies like Wi-Fi and Bluetooth have replaced Ethernet on many home and

business networks.

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Network Devices

Computer networking devices are units that mediate data in a computer network and are also

called network equipment. Units which are the last receiver or generate data are called hosts or

data terminal equipment.

Hub

Hubs connect computers together in a star topology network. Due to their design, they increase

the chances for collisions. Hubs operate in the physical layer of the OSI model and have no

intelligence. Hubs flood incoming packets to all ports all the time. For this reason, if a network is

connected using hubs, the chances of a collision increase linearly with the number of computers

(assuming equal bandwidth use). Hubs pose a security risk since all packets are flooded to all

ports all the time. If a user has packet sniffing software, they can extract data from the network

and potentially decode it and use it. Hubs make it easy to "spy" on users on the same LAN as

you.

Repeater

A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or

higher power, or onto the other side of an obstruction, so that the signal can cover longer

distances without degradation. Because repeaters work with the actual physical signal, and do

not attempt to interpret the data being transmitted, they operate on the physical layer, the first

layer of the OSI model. Repeaters are majorly employed in long distance transmission to reduce

the effect of attenuation. It is important to note that repeaters do not amplify the original signal

but simply regenerate it.

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Modem

Modem (from modulator-demodulator) is a device that turns the digital 1s and 0s of a personal

computer into sounds that can be transmitted over the telephone lines of Plain Old Telephone

Systems (POTS), and once received on the other side, converts those sounds back into a form

used by a USB, Ethernet, serial, or network connection. Modems are generally classified by the

amount of data they can send in a given time, normally measured in bits per second, or "bps".

NIC (Network Interface Card)

A network interface card is a computer hardware component designed to allow computers to

communicate over a computer network. It is both an OSI layer 1 (physical layer) and layer 2

(data link layer) device, as it provides physical access to a networking medium and provides a

low-level addressing system through the use of MAC addresses. It allows users to connect to

each other either by using cables or wirelessly. Most motherboards today come equipped with a

network interface card in the form of a controller, with the hardware built into the board itself,

eliminating the need for a standalone card.

Media converters

Media converters are simple networking devices that make it possible to connect two dissimilar

media types such as twisted pair with fiber optic cabling. They were introduced to the industry

nearly two decades ago, and are important in interconnecting fiber optic cabling-based systems

with existing copper-based, structured cabling systems. Media converters support many different

data communication protocols including Ethernet, T1/E1, T3/E3, as well as multiple cabling

types such as coaxial, twisted pair, multimode and single-mode fiber optics. When expanding the

reach of a Local Area Network to span multiple locations, media converters are useful in

connecting multiple LANs to form one large "campus area network" that spans over a limited

geographic area. As local networks are primarily copper-based, media converters can extend the

reach of the LAN over single-mode fiber up to 130 kilometers with 1550 nm optics.

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Basic switch

Switches are often confused with bridges because they also operate at the data link layer of

the OSI model. Similar to a hub, switches provide a central connection between two or more

computers on a network, but with some intelligence. They provide traffic control for packets;

rather than forwarding data to all the connected ports, a switch forwards data only to the port on

which the destination system is connected. They use a database of MAC addresses to determine

where computers are located and very efficiently send packets only where they need to go. The

database is created dynamically as computers communicate on the network. The switch simply

watches the incoming packets and memorizes the MAC address and port a packet arrives on. If a

packet arrives with a destination computer that the switch does not have an address for in its

MAC address table, it will flood the packet out all connected ports. A switch creates separate

collision domains for each physical connection. A switch will only create separate broadcast

domains if separate VLANs(Virtual Local Area Networks) are assigned to different ports on the

switch. Otherwise, a broadcast received on one port will be flooded out all ports except the one it

came in on.

Bridge

Bridges can be identified by the fact that they operate at the data link layer of the OSI model.

Bridges have intelligence and can "bridge" two of their ports together at very high speed. They

use a database of MAC addresses to determine where computers are located and very efficiently

send frames only where they need to go. The database is created dynamically as computers

communicate on the network. A bridge simply watches the incoming frame and memorizes the

MAC address and port a frame arrives on. It uses this information to locate a computer if a

packet comes in that must be forwarded to it. If a frame arrives at the bridge and the bridge does

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not know where to send it, the bridge will flood the frame just like a hub does. Bridging is often

inaccurately called switching.

Wireless access point

A wireless access point (WAP or AP) is a device that allows wireless communication devices to

connect to a wireless network using Wi-Fi, Bluetooth or related standards. The WAP usually

connects to a wired network, and can relay data between the wireless devices (such as computers

or printers) and wired devices on the network.

A typical corporate use involves attaching several WAPs to a wired network and then providing

wireless access to the office Local Area Network. Within the range of the WAPs, the wireless

end user has a full network connection with the benefit of mobility. In this instance, the WAP

functions as a gateway for clients to access the wired network.

A Hot Spot is a common public application of WAPs, where wireless clients can connect to the

Internet without regard for the particular networks to which they have attached for the moment.

The concept has become common in large cities, where a combination of coffeehouses, libraries,

as well as privately owned open access points, allow clients to stay more or less continuously

connected to the Internet, while moving around. A collection of connected Hot Spots can be

referred to as a lily-pad network.

Home networks generally have only one WAP to connect all the computers in a home. Most are

wireless routers, meaning converged devices that include a WAP, router, and often

an Ethernet switch in the same device. Many also converge a broadband modem. In places where

most homes have their own WAP within range of the neighbors' WAP, it's possible for

technically savvy people to turn off their encryption and set up a wireless community network,

creating an intra-city communication network without the need of wired networks.

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Basic router

Routers operate at the network layer of the OSI model and efficiently route information

between Local Area Networks. Since routers operate in the third layer, the network layer, they

must understand layer 3 addressing... such as TCP/IP. A router will divide a broadcast domain by

not forwarding broadcasts on one connected network to another connected network. Routers

operate in two different planes: the control plane, in which the router learns the outgoing

interface that is most appropriate for forwarding specific packets to specific destinations, and the

forwarding plane, which is responsible for the actual process of sending a packet received on a

logical interface to an outbound logical interface.

Basic firewall

A firewall is a part of a computer system or network that is designed to block unauthorized

access while permitting outward communication. It is also a device or set of devices configured

to permit, deny, encrypt, decrypt, or proxy all computer traffic between different security

domains based upon a set of rules and other criteria.

Firewalls can be implemented in both hardware and software, or a combination of both.

Firewalls are frequently used to prevent unauthorized Internet users from accessing private

networks connected to the Internet. All messages entering or leaving the Local Area

Network pass through the firewall, which examines each message and blocks those that do not

meet the specified security criteria. Without proper configuration, a firewall can often become

worthless. Standard security practices dictate a "default-deny" firewall rule set, in which the only

network connections which are allowed are the ones that have been explicitly allowed.

Basic DHCP (Dynamic Host Configuration Protocol) server

When a DHCP-configured client (be it a computer or any other network-aware device) connects

to a network, the DHCP client sends a broadcast query requesting necessary information from a

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DHCP server. The DHCP server manages a pool of IP addresses and information about client

configuration parameters such as the default gateway, the domain name, the DNS (Domain

Name System) servers, other servers such as time servers, and so forth. Upon receipt of a valid

request the server will assign the computer an IP address, a lease (the length of time for which

the allocation is valid), and other IP configuration parameters, such as the subnet mask and the

default gateway. The query is typically initiated immediately after booting and must be

completed before the client can initiate IP-based communication with other hosts.