NETWORK TOPOLOGY

Topology refers to the way in which the network of computers is connected. Each topology is suited to specific tasks and has its own advantages and disadvantages.

The choice of topology is dependent upon

• type and number of equipment being used
• planned applications and rate of data transfers
• required response times
• cost

There are FOUR major competing topologies

• Bus
• Ring
• Star
• FDDI

Most networking software support all topologies.

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Bus Topology

• all workstations connect to the same cable segment
• commonly used for implementing Ethernet at 10mbps
• the cable is terminated at each end
• wiring is normally done point to point
• a faulty cable or workstation will take the entire LAN down
• two wire, generally implemented using coaxial cable during the 1980's

The bus cable carries the transmitted message along the cable. As the message arrives at each workstation, the workstation computer checks the destination address contained in the message to see if it matches it's own. If the address does not match, the workstation does nothing more.

If the workstation address matches that contained in the message, the workstation processes the message. The message is transmitted along the cable and is visible to all computers connected to that cable.

There are THREE common wiring implementations for bus networks

• 10Base2 (thin-net, CheaperNet) 50-ohm cable using BNC T connectors, cards provide transceiver
• 10Base5 (ThickNet) 50-ohm cable using 15-pin AUI D-type connectors and external transceivers
• 10BaseT (UTP) UTP cable using RJ45 connectors and a wiring centre

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 Physical Implementation Of A Bus Network

The above diagram shows a number of computers connected to a Bus cable, in this case, implemented as Thin Ethernet. Each computer has a network card installed, which directly attaches to the network bus cable via a T-Connector.

It is becoming common to use 10BaseT (UTP) for implementing Ethernet LANS. Each workstation is wired in star fashion back to a concentrator wiring centre (hub). The hub is a multi-port device supporting up to about 32 ports. One of these ports is connected to a server, or the output of the hub can be connected to other hubs.

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Ethernet 802.3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
This protocol is commonly used in bus (Ethernet) implementations.

Multiple access refers to the fact that in bus systems, each station has access to the common cable.

Carrier sense refers to the fact that each station listens to see if no other station is transmitting before sending data.

Collision detection refers to the principle of listening to see if other stations are transmitting whilst we are transmitting.

In bus systems, all stations have access to the same cable medium. It is therefore possible that a station may already be transmitting when another station wants to transmit. Rule 1 is that a station must listen to determine if another station is transmitting before initiating a transmission. If the network is busy, then the station must back off and wait a random interval before trying again.

Rule 2 is that a station which is transmitting must monitor the network to see if another station has begun transmission. This is a collision, and if this occurs, both stations must back off and retry after a random time interval. As it takes a finite time for signals to travel down the cable, it is possible for more than one station to think that the network is free and both grab it at the same time.

CSMA/CD models what happens in the real world. People involved in group conversation tend to obey much the same behavior.

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Physical Bus Cable Limits

10Base2 THIN ETHERNET NETWORK LAYOUT

Limitations

• maximum number of trunk segments = 5
• maximum trunk segment length = 607 feet (185 meters)
• maximum network trunk cable = 3035 feet (925 meters)
• maximum number of stations on a trunk segment = 30
• minimum distance between T connectors = 1.5 feet (0.5 meters)

Rules

• each end of the trunk segment is terminated in 50-ohms
• one of the terminators is grounded
• connector splices are kept to a minimum

Cabling

• BNC-T type connectors

RG58-AU 50-ohm cable, 0.2

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10Base5 Thick Ethernet Network layout 

Limitations

• maximum number of trunk segments = 5
• maximum trunk segment length = 1640 feet (500 meters)
• maximum network trunk cable = 8200 feet (2500 meters)
• maximum number of stations on a trunk segment = 100
• minimum distance between transceivers = 8 feet (2.5 meters)
• maximum transceiver cable length = 165 feet (50 meters)

Rules

• each end of the trunk segment is terminated in 50-ohm
• one of the terminators is grounded
• connector splices are kept to a minimum

Cabling

• Transceivers 802.3
• 50-ohm cable RG-11

Male DIX connector.

Wiring of the DIX Connector

Pin	Ethernet	IEEE 802.3
1	Shield	Control-in	Shield
2	Collision presence+	Control-in	A
3	Transmit+	Data-out	A
4	Reserved	Data-in	Shield
5	Receive+	Data-in	A
6	Power return	Voltage	common
7	Reserved	Control-out	A
8	Reserved	Control-out	Shield
9	Collision presence-	Control-in	B
10	Transmit-	Data-out	B
11	Reserved	Data-out	Shield
12	Receive-	Data-in	B
13	Power	Voltage
14	Reserved	Voltage	Shield
15	Reserved	Control-out	B
Shell	---	Protective	Ground

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10Base TUTP Network layout

 Limitations

• maximum segment length of 100 Meters
• Hub to Hub or repeater to repeater links limited to 100 Meters

Rules

• star topology
• 4 repeater/5 segment rule of 10Base5 is retained
• only two nodes per segment are allowed

Cabling

• RJ-45 Connectors
• Category 3 UTP minimum, preferably Category 5

Bus Network Topology Summary

Advantages	Disadvantages
Easy to implement	Limits on cable length and Workstation numbers
Low Cost	Difficult to isolate network faults
	A cable fault affects all workstations
	As the number of workstations increase, the speed of the network slows down

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Ring Topology

• workstations connect to the ring
• faulty workstations can be bypassed
• more cabling required than bus
• the connectors used tend to cause a lot of problems
•  commonly used to implement token ring at 4 and 16mbps
•   four wire, generally STP or UTP

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Physical Implementation of ring network

Each workstation is connected back to a Multiple Access Unit (MAU), which supports up to eight workstations. Additional MAU are cascaded to provide greater workstation numbers.

Wiring is performed in a physical star fashion, with cables wired directly from each workstation back to the MAU.

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IEEE 802.5 TOKEN RING

This protocol is widely used in ring networks for controlling station access to the ring. A short message (called a token) is circulated around the ring, being passed from station to station (it originates from a controller or master station which inserts it onto the ring).A station which wants to transmit waits for the token to arrive. When the token arrives, the station changes it from a token to a connector message, and appends its message. This new message is then placed on the outgoing side of the ring.Each station passes on received tokens if they have nothing to transmit. They monitor connector messages to see if the message is addressed to them. If connector messages are addressed to them, they copy the message, modify it to signify its receipt, then send it on around the ring. Connector messages which are not addressed to them are passed directly on to the next station in the ring.When the connector message travels full circle and arrives at the original sending station, it checks the message to see if it's been received. It then discards the message and replaces it with a token.

                        OR

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PHYSICAL RING CABLE LIMITS

Token Ring Network Layout

Limitations

• maximum number of workstations = 96
• maximum number of 8228 MAU's = 12
• maximum patch cable distance between an 8228 MAU and a station (not including 8' adapter cable) = 150 feet (45 meters)
• maximum patch cable distance between two 8228's = 150 feet (45 meters)
• maximum patch cable connecting all 8228's = 400 feet (120 meters)

Rules

• stations are connected into the jacks of the 8228 units
• patch cables interconnect RO to RI for 8228 units.
• the last RO is connected to the first RI to form a ring.

Cable

• patch cables generally type 6 (26 awg) or 1 (22 awg)
• type 1 for lengths > 66 feet (20 meters)
• IBM 8310574 MIC connectors
• alternatively, UTP with RJ45 connectors.

Ring Topology: Summary

Advantages	Disadvantages
Cable failures affect limited users	Costly Wiring
Equal access for all users	Difficult Connections
Each workstation has full access speed to the ring	Expensive Adaptor Cards
As workstation numbers increase performance diminishes slightly

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 Star Topology

• all wiring is done from a central point (the server or hub)
• has the greatest cable lengths of any topology (and thus uses the most amount of cable)
• generally STP or UTP, four wire

Star Topology: Summary

Advantages	Disadvantages
Easy to add new workstations	Hub failure cripples all workstations connected to that hub
Centralized control	Hubs are slighty more expensive than thin-Ethernet
Centralized network/hub monitoring

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FDDI Topology

• 100mbps
• normally implemented over fiber optic (fast-Ethernet, UTP)
• dual redundancy built in by use of primary and secondary ring
• automatic bypassing and isolation of faulty nodes

Fiber Distributed Data Inferface

FDDI is based on two counter rotating 100-Mbit/sec token-passing rings. The rings consist of point to point wiring between nodes which repeat the data as it is received.The primary ring is used for data transmission; the secondary is used for data transmission or to back up the primary ring in the event of a link or station failure. FDDI supports a sustained transfer rate of about 80Mbps, a maximum of 1000 connections (500 nodes) and a total distance of 200 kilometers end to end. There is a maximum distance of 2 kilometers between active nodes.

FDDI Station types

There are two main types of stations, class A which attach directly to dual rings; or class B which attach to a station acting as a concentrator.A concentrator is a specialized workstation that attaches to the ring and has multiple ports that allow attachment of other devices in a physical star configuration. These may be cascaded.

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Logical Networks versus Physical Networks

A logical network describes how the network operates. A physical network describes how the network has been cabled. It is thus possible to have a physical star, logical bus network. In other words, the network operates as a bus network, but the cabling has been implemented using star topology.

Source :   http://uva.ulb.ac.be/cit_courseware/networks/pt2_3.htm#start

Defination wireless Web

The wireless Web refers to use of the World Wide Web through a wireless device, such as a  or personal digital assistant (PDA). Wireless Web connection provides anytime/anywhere connection to e-mail, mobile banking, instant messaging, weather and travel information, and other services. In general, sites aiming to accommodate wireless users must provide services in a format displayable on typically small wireless devices. It is estimated that 95% of wireless Internet devices being manufactured today use the Wireless Application Protocol (WAP) developed by Ericsson, Motorola, Nokia, and Unwired Planet (now Phone.com) for presenting content.

The wireless Web is not gaining in popularity as quickly as some have predicted. The low bandwidth of today's wireless service, relatively high usage charges, and small and difficult-to-use input and output devices contribute to impeding growth, a condition that has been referred to as "wapathy" (WAP apathy).

Source    http://searchmobilecomputing.techtarget.com/definition/wireless-Web

Benefits of wireless technology

The widespread reliance on networking in business as well as the growth of the Internet and online services are strong testimonies to the benefits of shared data and resources. Wireless solutions advance these benefits by allowing users to access shared information, e-mail, and applications without the constraints of a wired connection. Further, wireless technology allows network managers to set up or augment networks without installing or moving wires. Almost all computing devices, including desktops, workstations, monitors, keyboards, notebooks, tablets, handhelds, and printers can be equipped to communicate wirelessly. Wireless solutions offer productivity, convenience, and cost advantages over traditional wired networks.  Wireless solutions allow many benefits, including allowing businesses to benefit from the value of their information. Wireless solutions can provide users with access to real-time information from more places in their organization. This mobility supports productivity and service opportunities not possible with wired networks. Organizations are adopting wireless solutions to improve their competitiveness.


source ; http://h20331.www2.hp.com/Hpsub/downloads/Wireless_Technology.

A Career in Information Technology

The products and end results of information technology are a part of our daily lives, whether it's the operating systems on mobile phones, the computer networks that automate everyday financial transactions, or the reams of information sought and found on the Internet.

So it should come as no surprise that careers in the IT field are expected to grow significantly in the next decade—jobs in computer software engineering, for example, are expected to grow by 32% by 2018, according to the Bureau of Labor Statistics.

And every company or organization has a computer-related component that's critical for getting the job done. So you might program or engineer computer software (though the BLS warns that programming jobs will likely shrink due to offshoring and the increasing ability of users to write their own programs), evaluate and implement the proper computer network architecture to fulfill a company's objectives, develop or administer websites, coordinate a company's information security, or design games and apps.

A strong background in the technical fundamentals of computer science and programming languages like Java, Microsoft.NET, and C++ are obviously important for success in the field. But a creative brain and an ambition to stay updated on the newest advances in the field -- whether through books or training -- are also key, according to recruiters and IT employees. That's because there's never one way to solve a problem and technologies are constantly evolving.

"You always have a new challenge and you're always applying a different set of knowledge to solve it," says Jim Schelle, a solution architect for Synchronoss Technologies in Seattle, Wash. "It's constant work to stay on top of it. You don't get to rest on your laurels in the tech industry."

It's also important that you can communicate and work well with others, because you'll likely be working in a group with other programmers, engineers, or architects. And don't expect to arrive at an interview with strong grades as the main proof of your desirability as a candidate — be prepared to show hiring managers your code from a class project or a student competition (read: get involved with activities outside of your core course load) or a program you created in your spare time.

Salaries in information technology are strong—Web developers start out earning an average of $38,800 a year, according to salary data from PayScale.com. With several years of experience, you can earn $94,800 per year as an information technology program manager, or $93,600 per year as a software development manager. And many companies pay much more for skills that are in-demand.

Your IT Career: In order to get hired in IT, you'll need a strong undergraduate background in computer science, math, and physics classes, because while you'll learn plenty on the job, recruiters and employees in the field stress that those technical building blocks are crucial for cementing the kind of analytical thinking that's necessary to succeed.

But you don't have to stick just to tech companies for prospective jobs—you can also take your programming skills and apply them in another field. For example, Adam Roberts, a 2007 computer engineering graduate of the University of Florida, spent two years as a teacher in the Teach for America program, and now works as an IT manager for a school district in Washington, D.C.

Getting Started: While there's not a set career trajectory in IT, as a recent college graduate, you might enter the workforce as an entry-level computer programmer or software engineer, where you'd be writing or updating code or engineering computer software. Recruiters say it can be a plus to have a sense of the creative side—the graphic design elements that compliment programming. But be cautious about focusing only on the latest hot tools.

"We don't want students to circumvent their undergraduate degrees," says Karen Morris, the university relations director at gaming company Electronic Arts, who opposes the increase in the number of two-year "gaming universities" that give students a quick dose of typical game design languages like Adobe's Flash but skip the rest. She points out, "Who knows if we will use Flash in a few years?"

Get on the Fast Track: Hot areas of IT where jobs are expected to grow include cybersecurity and cloud computing, and mobile- and Web-based games and apps are exploding. So if you know the mobile programming language HTML5, or are a whiz at using Flash to design cool graphics, you'll have a leg up. The field of Web analytics, used to enhance user experience or business functions, is also poised for huge growth, so if you have a background in both computer science and marketing or business, you'll be an in-demand hire.

Next Up: After a few years, you could advance in the ranks to become a senior level engineer after becoming faster and more skilled at solving increasingly complex software solutions that involve more moving parts. But recruiters emphasize that ambitious and hardworking entry level hires can make an impact and advance quickly if they show the talent and the drive to continue taking on more responsibilities. An engineer with a knack for management might advance to become a project manager, directing groups of engineers and programmers. But if you prefer the technical side of the coin, you'd advance to become a senior developer, and then a team lead, in which you're advising the team of developers.

Phase Three: Within about 10 years, you might become an architect, in which you are mapping out and testing the kinds of technologies that will best accomplish your goal, and which requires a bigger picture view of the business and its objectives.

Write by Marisa Taylor

http://online.wsj.com/article/SB10001424052748704358904575478133397664058.html

What Are the Benefits of Information Technology in Education?

Information technology may assist in the facilitation of learning or serve as the actual educational structure allowing learning to occur. Information technology benefits both traditional brick-and-mortar education institutions and online educational models in fundamental ways. For example, multimedia presentations, knowledge-management software, video conferencing, cloud computing and collaborative document editing are notable information technology services benefiting education.

Multimedia Presentations

o    Multimedia presentation software empowers both educators and learners to organize, present and consume information in novel ways. For example, multimedia software enables educators to create a tailor-made presentation pertaining to any subject matter involving a complete audio-visual narrative experience. In addition, advanced multimedia software can empower educators to design audio-visual narrative themes involving the student's actual participation (learning video games). Adobe Flash offers industry-standard products assisting developers in creating such applications.

Knowledge-Management Software

o    Knowledge-management software involves categorizing information specific to the learning style of the student. For example, knowledge-management software can empower the user to modify, construct and manipulate information in order of relevance and embed information into audio-visual icons for later rapid recall. As a result, knowledge-management software becomes highly personal, content-rich and hyper-specific to the information consumption preferences of the learner.

Video Conferencing

o    Video conferencing represents a major benefit of information technology to education. Video conferencing allows seminars and lectures to occur regardless of proximity. For example, a classroom full of students can participate in a lecture from a remote location while it's actually occurring. Students' resulting greater accessibility to leaders of academia pertaining to their subject matter benefits both education and society as a whole.

Cloud Computing

o    Cloud computing empowers students and educators to store their data on a remote server as opposed to their own computer. This allows educators and students to access their data from any computer and from a variety of commuting devices. For example, students will no longer lose their homework to unpredictable forces or hungry canines. With cloud computing, homework can be stored safely on alternative platforms. Multiple copies are backed up on these remote computers and are easily accessible with an Internet connection.

Collaborative Document Editing

o    The ability to collaboratively edit documents from various locations is another benefit of information technology in education. For example, students and educators utilizing cloud computing to store their homework can also modify the document's access settings to allow multiple editors and contributors to participate in an assignment. This empowers educators to design work assignments for teams of students working together and, in so doing, cultivate a teamwork ethos preparing them for the workplace.

What Are the Benefits of Information Technology in Education? | eHow.com http://www.ehow.com/about_5292299_benefits-information-technology-education.html#ixzz1dOul0uHL