concept of internet

7/28/2019 Concept of Internet

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Various Network connecting devices

There are six kind of connecting devices used in Networking.

Hub

A central connecting device in a network that joins communications lines together in a star

configuration. Hub allows transfer of data packet.

A hub is the simplest of these devices. Any data packet coming from one port is sent to all other

ports. It is then up to the receiving computer to decide if the packet is for it. Imagine packets

going through a hub as messages going into a mailing list. The mail is sent out to everyone and

it is up to the receiving party to decide if it is of interest.

The biggest problem with hubs is their simplicity. Since every packet is sent out to every

computer on the network, there is a lot of wasted transmission. This means that the network

can easily become bogged down.

Hubs are typically used on small networks where the amount of data going across the networkis never very high.

Hubs can be classified in the following manner:

a. Passive Hub

Passive hubs are just connecting units that add nothing to the data passing through them. A

passive hub is a simple signal splitter. A passive hub routes all traffic to all nodes. This means

that a tremendous load can be created when much communication takes place between

computers. Every computer has an additional burden of reading the address of each piece of

information it receives to determine if the information is intended for that computer.

Information containing other addresses is discarded.b. Active Hub

Active hubs, also sometimes called multiport repeaters, regenerate the data bits in order to

maintain a strong signal, and intelligent hubs provide added functionality.

An active hub performs the same function as a passive hub but contains electronic circuits that

regenerate and retransmit the information. Thus, active hubs can be used to extend the size of

a network.

c. Intelligent Hub

Intelligent hubs perform the same functions as passive and active hubs. However, they can

make informed path selections and perform some network management. Intelligent hubs route

traffic only to the branch of the star on which the receiving node is located. If redundant pathsexist, an intelligent hub can route information around normally used paths when cable

problems occur.


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Bridge

A bridge goes one step up on a hub in that it looks at the destination of the packet before sending. If the

destination address is not on the other side of the bridge it will not transmit the data.

A bridge only has one incoming and one outgoing port.

To build on the email analogy above, the bridge is allowed to decide if the message should continue on.

It reads the address [email protected] and decides if there is a [email protected] on the other side. If there

isnt, the message will not be transmitted.

Bridges are typically used to separate parts of a network that do not need to communicate regularly, but

still need to be connected.

A bridge device filters data traffic at a network boundary. Bridges reduce the amount of traffic on a LAN.

Bridge is a device that connects two LAN segments together, which may be of similar or dissimilar types,

such as Ethernet and Token Ring. A bridge is inserted into a network to segment it and keep traffic

contained within the segments to improve performance.

Bridges learn from experience and build and maintain address tables of the nodes on the network. By

monitoring which station acknowledged receipt of the address, they learn which nodes belong to the

segment.

Bridges work at the data link layer (OSI layer 2), whereas routers work at the network layer (layer 3).

Bridges are protocol independent; routers are protocol dependent. Bridges are faster than routers

because they do not have to read the protocol to glean routing information.

Bridges with more than two ports (multiport bridges) perform a switching function. Todays LAN

switches are really multiport bridges that can switch at full wire speed. Switches are the modern

counterparts of bridges, functionally equivalent but offering a dedicated segment for every node on the

network


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Repeater

Repeater is a communications device that regenerates or amplify the data signal in order to extend the

transmission distance. Available for both analog and digital signals, it is used extensively in long distance

transmission. It is also used to tie two LANs of the same type together.

Signals that carry information within a network can travel a fixed distance .A repeater receive a signal

and before it becomes too weak or corrupted regenerate the original bit pattern. Repeater then sends

the refreshed signal. Repeaters remove unwanted signal noise in an incoming signal.

In a Wireless communication system a repeater consist of Receiver, an amplifier, a transmitter, an

isolator.A repeater is strategically located on top of high building or a mountain can greatly enhance the

performance of a wireless network by allowing communication over distance much greater then would

be possible without it.

In satellite wireless a repeater more frequently calla Transponder and receives uplink signals and

retransmit them often on different frequencies to destination location.

In a cellular telephone system a repeater is one of a group of transreceivers in a geographic area that

collectively serve a system user.

Switch

Switches allow different nodes (a network connection point, typically a computer) of a network to

communicate directly with one another in a smooth and efficient manner.

A switch steps up on a bridge in that it has multiple ports. When a packet comes through a

switch it is read to determine which computer to send the data to.

This leads to increased efficiency in that packets are not going to computers that do not require them.

Now the email analogy has multiple people able to send email to multiple users. The switch can

decide where to send the mail based on the address.

Most large networks use switches rather than hubs to connect computers within the same

subnet.In networks, Switch is a device that filters and forwards packets between LAN segments.

A switch substantially reduces the amount of broad cast traffic and is currently most popular network

linking device.


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Router

Router is a device that forwards data packets from one local area network (LAN) or wide areanetwork (WAN) to another. Based on routing tables and routing protocols, routers read the network

address in each transmitted frame and make a decision on how to send it based on the most expedient

route (traffic load, line costs, speed, bad lines, etc.). Routers work at layer 3 in the protocol stack,

whereas bridges and switches work at the layer

Routers are used to segment LANs in order to balance traffic within workgroups and to filter

traffic for security purposes and policy management. Routers are also used at the edge of the network

to connect remote offices.

Most routers are specialized computers that are optimized for communications; however,

router functions can also be implemented by adding routing software to a file server. NetWare, for

example, includes routing software. The NetWare operating system can route from one subnetwork to

another if each one is connected to its own network adapter (NIC) in the server.

Routers serve as an internet backbone, interconnecting all networks in the enterprise. This

architecture strings several routers together via a high-speed LAN topology such as Fast Ethernet or

Gigabit Ethernet. Routers are also the backbone of the Internet, which spans the planet.

Another approach within an enterprise is the collapsed backbone, which uses a single router

with a high-speed backplane to connect the subnets, making network management simpler and

improving performance.

Gateway

A network gateway is an internetworking system capable of joining together two networks that use

different base protocols. A network gateway can be implemented completely in software, completely in

hardware, or as a combination of both. Depending on the types of protocols they support, network

gateways can operate at any level of the OSI model.
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Because a network gateway, by definition, appears at the edge of a network, related capabilities like

firewalls tend to be integrated with it. On home networks, a broadband router typically serves as the

network gateway although ordinary computers can also be configured to perform equivalent functions.

Gateway is a computer that performs protocol conversion between different types of networks or

applications. They perform complete conversions from one protocol to another rather than simplysupport one protocol from within another. Sometimes routers can implement gateway functions.

An electronic mail, or messaging, gateway converts messages between two different messaging

protocols.

Network Topologies

Network topology of a network is the layout or actual appearance of the cabling scheme used on a

network. Topology of a network refers to its shape. I.e. how the cables are arranged.

Mainly Five types of Physical Topologies are used in Networking:

[1]Bus Topology

[2] Star Topology

[3] Ring Topology

[4]Mesh Topology

[5]Hybrid Topology

BUS TOPOLOGY

A bus topology consists of a single communications channel. Each connected device is attached

to the medium at an interface point and has its own unique hardware address. In fact, the hardware

address is provided on the network interface card, whether the system is an Ethernet network, or some

other network implementation. Data transfers between the interfaces or nodes take place using these

hardware addresses.

The bus topology connects workstations using a single cable. Each workstation is connected to

the next workstation in a point-to-point fashion. All workstations connect to the same cable.
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Each end of the cable is terminated using a special terminator. The common implementation of

this topology is Ethernet. A message transmitted by one workstation is heard by all the other

workstations.

Advantage:

[1]Cabling costs are minimized because of the common trunk

[2]Well suited for temporary network.

[3]Typically cheapest technology to implement.

[4]Easy to implement and extend.

Disadvantage:

[1]Difficult to trouble shoot /administrator because no central distribution points exist.[2]Cable breaks can disable the entire segment because they remove the required termination

from Each of the two cable fragments.

[3]Limited cable length and number of stations.

[4]Maintenance cost may be higher in long run.

[5]Performance degrades as additional computers are added or on heavy traffic.

[6]Low security

[7]One virus in the network will affect all of them.

[8]Proper termination is required.

STAR TOPOLOGY

The star topology uses a central hub through which all components are connected. In a

computer network, the central hub is the host computer, and at the end of each connection is aterminal.

A star network uses a significant amount of cable (each terminal is wired back to the central

hub, even if two terminals are side by side several hundred meters away from the host). All routing

decisions are made by the central hub, and all other workstations can be simple.

Advantage:


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[1] An advantage of the star topology is failure in one of the terminals does not affect any other

terminal; however, failure of the central hub affects all terminals.

[2]This type of topology is frequently used to connect terminals to a large time-sharing host

computer.

[3]Well suited for quick setup.

[4]Easy to implement and extended even in large networks.

[5]No problem with collision of data.

[6]Security can be implemented in the hub.

[7]It is easy to modify and add new computers to a star network without disturbing rest of

computer on the networks.

Disadvantage:

[1]Failure of central hub can disable the entire network.

[2]Limited cable length and no of stations.

[3]Point-to-point wiring is utilized for each node, therefore, more cable is required

RING TOPOLOGY

The ring topology is a physical, closed loop consisting of point-to point links. In the diagram, you can see

how each node on the ring acts as a repeater. It receives a transmission from the previous node and

amplifies it before passing it on.

Advantage:[1]Each repeater duplicates the data signals so that very little signal degradation occurs

[2]Data is quickly transmitted without a bottleneck.

Disadvantage:

[1]A break in the ring can disable the entire network.

[2] Because each node must have the capability of functioning as a repeater, the networking

devices tend to be more expensive.

[3]It is difficult to trouble shoot in the network.


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Mesh Topology

The mesh topology connects all computers to each other. The cable requirements are high, but

there are redundant paths built in. Any failure of one computer allows all others to continue, as they

have alternative paths to other computers.

Mesh topologies are used in critical connection of host computers (typically telephone

exchanges). Alternate paths allow each computer to balance the load to other computer systems in the

network by using more than one of the connection paths available

Advantage:

[1]A mesh network is reliable and offer redundancy. If one node can no longer operate all the rest can

still communicate with each other directly through more intermediate nodes.

Disadvantage:

[1]Mesh topology is expensive because of large no of cables and connection required.

Hybrid Topology:

The hybrid topology scheme combines multiple topologies into one large topology. The hybrid network

is common in large wide-area networks. Because each topology has its own strengths and weaknesses,

several different types can be combined for maximum effectiveness.

Advantages:

[1] A company can combine the benefits of several different types of topologies

[2]Workgroup efficiency and traffic can be customized

Disadvantages :

[1]Devices on one topology cannot be placed into another topology without some hardware

changes.


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TYPES OF NETWORK

[1]LANLocal Area Network

[2]MAN- Metropolitan Area Network

[3]WAN- Wide Area Network

[4]PAN- Personal Area Network

[1]LANLocal Area Network

A LAN- Local Area Network is a digital communication system capable of interconnecting a large

no. of computers, terminals and other peripherals devices within a limited geographic area typically

under 1Km across.LAN typically used in limited small area like within Room, Building, campus or cluster

of buildings.A local area network (LAN) uses direct, high-speed cables to share hardware, software and data

resources. With a LAN, a connection spans a short distance and does not use wires owned by a

telephone company. Typically, a LAN connects the computers in a department, a building, or several

buildings situated near each other. Each hardware device on a LAN, such as a computer or printer is

called a node. A LAN integrates anywhere from two or three computers up to several hundred

computers.

Followings are the characteristics of LAN:

a) All the connected devices in the network share the transmission media.

b) Each device connected in the network can either operate standalone or in the network.

c) Area covered is small.

d) Data transfer rates are high, usually 1 Mbps (Million of bits per second).

e) Each device connected in the network can communicate with any other device in network.

f) Cost of setting the network is usually low.

Advantages of LAN

Resource Sharing

Resource sharing is perhaps the greatest advantage of a local area network. LAN allows a large number

of intelligent devices to share resources, such as storage devices, programs and even data files. On a


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traditional network, each machine is directly wired into a switching device whereas on a LAN, a single

physical medium is usually shared.

The capability of share resources is a major advantage of a LAN. Because the computers in a LAN share

hardware, several people can use the same network printer. Because the computers in a LAN share

software, only one copy of a software package is needed, as long as that package is designed and

licensed to be used on a network. Sharing data means that at LAN, users can access one database and

get the one which is most up-to-date.

Area Covered

Area covered by LANs is normally restricted to moderate size, such as an office building, a factory, or a

campus. The limiting factors are usually the overall length of the cable used and any inter device

restrictions imposed. In practice, the distances involved range from a few meters to a few kilometers.

Low Cost

Low cost per connection is also an important characteristic of LAN. Many applications of LAN involve

low-cost microprocessor systems, so that the connection of these systems to a LAN should also be

inexpensive. Local area networks are becoming more cost effective as technology expands and new

items, like fan-out units and networks interface units, become prevalent.

High Channel Speed

High channel speed is another quality of LAN. Most of the LANs transfer data at rates between 1-10

million bits per second. This is especially beneficial for applications with high resolution, movable color

graphics and for bulk data transfer between mainframe computers.

Other Characteristics

Furthermore, flexibility in growth, low error rates, reliability of operation and simple maintenance are all

distinguishing features of a LAN.

[2]MAN- Metropolitan Area Network

A metropolitan area network is a system of LANs connected throughout a city or metropolitan

area. MANs require telecommunication media such as voice channels or data channels. Branch offices

are connected to head offices through MANs. Universities, colleges, grocery chains and banks are some

of the examples of organizations using MAN. They typically use various infrastructure or fiber

connections to link their sites.

One can also define it as a network that interconnects users with computer resources in a

geographic area or region larger than that covered by even a large Local Area Network (LAN) but smaller

than the area covered by a Wide Area Network (WAN). The term is applied to the interconnection of

networks in a city into a single larger network (which may then also offer efficient connection to a wide

area network). It is also used to mean the interconnection of several local area networks by bridging

them with backbone lines. The latter usage is also sometimes referred to as a campus network.

MAN is basically a bigger version of a LAN and normally uses similar technology. It might

cover a group of nearby corporate offices or a city and might be either private or public. A MAN can

support both data and voice and might even be related to the local cable television network. A MAN just

has one or two cables and does not contain switching elements which shunt packets over one of several

potential output lines. Not having to switch simplifies its design.


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[3]WAN- Wide Area Network

A wide area network is a network system connecting cities, countries, or continents together. WANs are

connected together using one of the telecommunications media like PSTN[Public Switched Telephone

Network] or Satellite Network.

They may link various computers by means of cables, optical fibers, or satellites but their users

commonly access the networks via a modem (a device that allows computers to communicate over

telephone lines). The largest wide area network is the Internet, a collection of networks and gatewayslinking millions of computer users on every continent.

[4]PAN- Personal Area Network

PAN is a network used for communication among computer devices close to one person. The

reach of a PAN is typically a few meters.PAN can be used for communication among personnel devices

themselves or for connecting to a higher level network and Internet.

A wireless Personal Area Network [WPAN] can also be made possible with network technologies

like Bluetooth, Infrared etc.


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