Platform as a service (PaaS) is a category of cloud computing services that provide a computing

platform and a solution stack as a service. Along with software as a service (SaaS) and infrastructure as a

service (IaaS), it is a service model of cloud computing. PaaS offerings facilitate the deployment of

applications without the cost and complexity of buying and managing the underlying hardware and

software and provisioning hosting capabilities.

Technically, a PaaS is an Application Platform comprised of an operating system, middleware and other

software that allows applications to run on the cloud with much of the management, security, scaling

and other stack related headaches abstracted away. This allows you to focus on two things: customers

and developing your application. Let the PaaS deal with system administration details like setting up

servers or VMs, installing libraries or frameworks, configuring testing tools, etc.

Platform as a Service allows users to create software applications using tools supplied by the provider.

PaaS services can consist of preconfigured features that customers can subscribe to; they can choose to

include the features that meet their requirements while discarding those that do not. PaaS works on top

of IaaS and will do all of that work automatically. 

Characteristics of PaaS

Multi-tenant architecture 

A PaaS offering must be multi-tenanted. A multi-tenant platform is one that uses common computing

resources including hardware, operating system, software (i.e. application code), and a single underlying

database with a shared schema to support multiple customers simultaneously. This is in direct contrast to

the traditional client/server architecture, which requires an entire stack of hardware and software to be

dedicated to each tenant (customer). 

Customizable /Programmable User Interface

PaaS offering should provide the ability to construct highly flexible user interfaces via a simple “drag &

drop” methodology that permits the creation and configuration of UI components on the fly. Furthermore,

given the growing set of Web devices, additional flexibility to use other technologies such as CSS, AJAX and

Adobe Flex to specify the appearance of the application’s interface should be available to the UI designer.

Unlimited Database Customizations

Database used by application should have option of customization for more flexibility in application

development. Specifying relationships between objects, a key requirement of any sophisticated business

application, must be possible through the declarative Web-based interface. Other mandatory functions

include the ability to incorporate validation rules and permissions at the object/field level and the ability

to specify auditing behavior.

Automation

PaaS environments automate the process of deploying applications to infrastructure, configuring application components, provisioning and configuring supporting technology like load balancers and databases, and managing system change based on policies set by the user. While IaaS is known for its ability to shift capital costs to operational costs through outsourcing, only PaaS is able to cut down costs across the development, deployment and management aspects of the application lifecycle.

Security

The PaaS offering should provide a flexible access control system that allows detailed control over what

users of the SaaS application can see and the data each user can access. Definition of access from the

application level (including tabs, menus, objects, views, charts, reports and workflow actions) to the

individual field level should be possible. Defining an access control model should be possible through the

creation of groups and roles and the assignment of users to either groups or roles.

Runtime Framework

This is the “software stack” aspect of PaaS, and perhaps the aspect that comes first to mind for most

people. The PaaS runtime framework executes end-user code according to policies set by the application

owner and cloud provider. PaaS runtime frameworks come in many flavors, some based on traditional

application runtimes, others based on 4GL and visual programming concepts, and some with pluggable

support for multiple application runtimes. 

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Software as a Service

Software as a service , sometimes referred to as "on-demand software", is a which software and associated data are centrally hosted on the cloud. SaaS is typically accessed software delivery model in by users using a thin client via a web browser.

In this model, the software is not hosted on the customers' individual computers. Under the a vendor is responsible for the creation, updating, and maintenance of software. Customers buy a subscription to access it, which includes a separate license, or seat, for each person that will use the software.

SaaS has become a common delivery model for many business applications, including accounting, collaboration, customer relationship management (CRM), management information systems(MIS), enterprise resource planning (ERP), invoicing, human resource management (HRM), content management (CM) and service desk management. The emergence of SaaS as an effective software-delivery mechanism creates an opportunity for IT departments to change their focus from deploying and supporting applications to managing the services that those applications provide.

Unlike traditional software which is conventionally sold as a perpetual license with an up-front cost (and

an optional ongoing support fee), SaaS providers generally price applications using a subscription fee,

most commonly a monthly fee or an annual fee. Consequently, the initial setup cost for SaaS is typically

lower than the equivalent enterprise software. SaaS vendors typically price their applications based on

some usage parameters, such as the number of users ("seats") using the application. However, because

in a SaaS environment customers' data reside with the SaaS vendor, opportunities also exist to charge

per transaction, event, or other unit of value.

Benefits of SaaS (Hope now you can explain all):

•   Save money by not having to purchase servers or other software to support use.
  
•   Focus Budgets on competitive advantage rather than infrastructure.
  
•   Monthly obligation rather than up front capital cost.
  
•   Reduced need to predict scale of demand and infrastructure investment up front as available
  capacity matches demand.
  
•   Multi-Tenant efficiency
  
•   Flexibility and scalability
  
•   Security 
  

Characteristics of SaaS

•   Simple and quick system implementation: As Saas sits on top of PaaS and IaaS, deploying any enterprise level software becomes easy and quick as SaaS inherits all the features of underlying infrastructure. Also since SaaS is scalable, any user request can be addressed with required elasticity.
  
•   Transparent and low pricing: With common infrastructure, cloud vendor can leverage their infrastructure with lower cost and transparency. End result of this directly impacts customer cost of software implementation as they gets it cheaper with enhanced security and high availability.
  
•   Multitenant Architecture: A multitenant architecture, in which all users and applications share a single, common infrastructure and code base that is centrally maintained. Because SaaS vendor clients are all on the same infrastructure and code base, vendors can innovate more quickly and save the valuable development time previously spent on maintaining numerous versions of outdated code.
  
•   Easy software maintenance and Customization: The ability for each user to easily customize applications to fit their business processes without affecting the common infrastructure. Because of the way SaaS is architected, these customizations are unique to each company or user and are always preserved through upgrades. That means SaaS providers can make upgrades more often, with less customer risk and much lower adoption cost.
  
•   Better Access: Improved access to data from any networked device while making it easier to manage privileges, monitor data use, and ensure everyone sees the same information at the same time. 
  

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Infrastructure as a Service (IaaS) is one of the three fundamental service models of cloud computing

alongside Platform as a Service (PaaS) and Software as a Service (SaaS).

Infrastructure as a Service is a provision model in which an organization outsources the equipment used

to support operations, including storage, hardware, servers and networking components. The service

provider owns the equipment and is responsible for housing, running and maintaining it. The client

typically pays on a per-use basis. Clients are able to self-provision this infrastructure, using a Web-based

graphical user interface that serves as an IT operations management console for the overall

environment. API access to the infrastructure may also be offered as an option. 

A typical Infrastructure as a Service offering can deliver the following features and benefits:

• Scalability: resource is available as and when the client needs it and, therefore, there are no delays in expanding capacity or the wastage of unused capacity. 
• No investment in hardware: the underlying physical hardware that supports an IaaS service is set up and maintained by the cloud provider, saving the time and cost of doing so on the client side
• Utility style costing; the service can be accessed on demand and the client only pays for the resource that they actually use
•  Location independence; the service can usually be accessed from any location as long as there is an internet connection and the security protocol of the cloud allows it
• Physical security of data center locations; services available through a public cloud, or private clouds hosted externally with the cloud provider, benefit from the physical security afforded to the servers which are hosted within a data center
• No single point of failure; if one server or network switch, for example, were to fail, the broader service would be unaffected due to the remaining multitude of hardware resources and redundancy configurations. For many services if one entire data center were to go offline, never mind one server, the IaaS service could still run successfully. 

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Communications as a Service (CaaS) is an outsourced enterprise communications solution that can be

leased from a single vendor. Such communications can include voice over IP (VoIP or Internet

telephony), instant messaging (IM), collaboration and videoconference applications using fixed and

mobile devices. CaaS has evolved along the same lines as Software as a Service (SaaS).

CaaS brings social networking, cloud computing, and smartphones together, providing cloud-

technologies that let users communicate via voice, text, and rich media on whatever device they prefer

to use. To compete in this marketplace, software vendors, enterprises, and service providers must

introduce communications-enhanced services that meet a surging need for value, efficiency, cost

reduction, and convenience.

Through the hosted model, the CaaS provider manages everything, from the telecommunications

infrastructure to the software integration platform for delivering communications offered at a

guaranteed Quality of Service (QoS). As a result, businesses can selectively deploy communications

features, applications, and devices on a pay-as-you-go, as-needed basis, reducing risks while eliminating

capital costs associated with new services.

CaaS offers flexibility and expandability that small and medium-sized business might not otherwise

afford, allowing for the addition of devices, modes or coverage on demand. The network capacity and

feature set can be changed from day to day if necessary so that functionality keeps pace with demand

and resources are not wasted. There is no risk of the system becoming obsolete and requiring periodic

major upgrades or replacement.  

Advantages of Communication as a Service (CaaS)

Fully Integrated Enterprise Class Unified Communication: By managing the LAN/WAN, the

vendor can guarantee consistent Quality of Service (QoS) from the desktop across the VoIP

backbone and back again. Advanced Unified Communications features such as Outlook

integration, soft phones, real-time presence, chat, multimedia conferencing, video calling,

unified messaging and mobility are also part of a standard CaaS deployment. And with CaaS, the

feature set can continue to evolve. Development and introduction of new features and

applications are faster, easier and more economical because the service provider is doing the

work for multiple end users across a scalable platform.

No Upfront Capital Expenses: Since cloud services are supposed to lower capital expenditure

and focus more on operating expenditure, by implementing CaaS, consumers can build up their

communication infrastructure without any upfront cost. They just need to pay it as a service.

Flexibility in Features: Since cloud is a multi-tenant architecture, cloud vendors have to manage

multiple customers and look after the features that they want. What this allows cloud vendor is

to add more advanced features and flexibility in their service model. Economies of scale also

mean that the service provider is not tied to a single vendor investment and can leverage best-

of-breed providers like Cisco, Microsoft and Nortel much more economically than an

independent enterprise.

No Risk of Obsolescence: Technology changes rapidly and are obsolete within few years of

introduction. With CaaS, companies are always privileged with new technologies as cloud

vendors keep on updating their equipment’s and technologies to sustain in market.

No Data Center Cost: As a prime advantages of cloud computing, while using CaaS

infrastructure, organization need not invest on expensive servers, cooling system and electric

equipment. With monthly/ yearly recurring cost, organization can dramatically cut down the

management cost of data center as well.

Guaranteed Business Continuity: With CaaS, organization can be hugely benefitted with

guaranteed business continuity as cloud service providers proactively plans for Business

Continuity Planning for their customers. Service uptime is guaranteed even if any catastrophic

disaster strikes. 

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A distributed computing consists of multiple software components that are on multiple computers, but run as a single system. The computers that are in a distributed system can be physically close together and connected by a local network, or they can be geographically distant and connected by a wide area network. A distributed system can consist of any number of possible configurations, such as mainframes, personal computers, workstations, minicomputers, and so on. The goal of distributed computing is to make such a network work as a single computer. 

Distributed computing, as one can imagine, is where the computing elements of a network are spread over a large geographical area. Both cloud and grid computing are prime examples of distributed computing architectures. 

Another type of of normal computers. distributed computing computing is known as grid computing. Grid consists of many computers operating together remotely and often simply using the idle processor power Grid provides the sharing of:

• Computational resources 
• Storage elements 
• Specific applications 
• Equipment
• Other

While there are many similarities between grid and cloud computing, it is the differences that matters the most. Grid computing is better suited for organizations with large amounts of data being requested by a small number of users (or few but large allocation requests), whereas cloud computing is better suited to environments where there are a large number of users requesting small amounts of data (or many but small allocation requests). 

Cloud computing is basically a sales and distribution model for various types of resources over the Internet, while distributed computing can be identified as a type of computing, which uses a group of machines to work as a single unit to solve a large scale problem. Distributed computing achieves this by breaking the problem up to simpler tasks, and assigning these tasks to individual nodes. 

Compared to other distributed systems such as grids or clusters, cloud computing solutions give enterprises significantly more flexibility. They can dispense with IT infrastructures of their own and only have to pay for the resources and services they actually use (“pay-per-use”/ “pay as you go”). These can be dynamically adapted to changed business requirements and processes with the help of virtualization technologies and service oriented, distributed software systems.

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Following are the challenges of Cloud computing:

• Privacy 
• Data Security 
• Ownership 
• RASP (Reliability, Availability, Scalability and Performance) 
• Data Recovery and Backup 
• Cross Country Data Migration and Portability 
• Multi-platform Support 
• Intellectual Property 
• Misuse 
• Real Time Processing 
• Compliance

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Service Oriented: The defining characteristics of cloud computing is the service oriented feature. All the IT related services are hosted in cloud infrastructure. Companies should not have to buy expensive servers, network equipment’s and invest on expensive manpower. All they need is to subscribe to any cloud service provider and get what they want. In this way, we can decrease our capital expenditure and move to operate via Operating expenditure. 

Broad Network Access: Cloud Capabilities are available over the network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms such as mobile phones, laptops and PDAs. 

On Demand: A consumer can provision computing capabilities, such as server processing and network storage, as needed automatically without requiring human interaction with each service’s provider. computer services such as email, applications, network or server service can be provided without requiring human interaction with each service provider. Cloud service providers providing on demand self-services include Amazon Web Services (AWS), Microsoft, Google, IBM and Salesforce.com. 

Reliability, Elasticity and scalability: The cloud is reliable in the sense that the infrastructure setup for cloud is robust and backed up for high availability. It is some resilient replication and backup strategy that is targeted for huge customer base. The cloud is elastic, meaning that resource allocation can get bigger or smaller depending on demand. Elasticity enables scalability, which means that the cloud can scale upward for peak demand and downward for lighter demand. Scalability also means that an application can scale when adding users and when application requirements change.  

Resource Pooling (Processor, Memory, and Storage): Cloud infrastructure should have features of resource pooling i.e. resources (CPU, Memory, Disk) should be categorized in a hierarchy as per the need of computing. Resource pooling is mainly used for utilizing servers up to its potential. Since most of the times server  resources are unused, we can use the concept of virtualization to pool its resources. 

Measured Service (Pay per Use): Cloud computing resource usage can be measured, controlled, and reported providing transparency for both the provider and consumer of the utilized service. Cloud computing services use a metering capability which enables to control and optimize resource use. This implies that just like air time, electricity or municipality water IT services are charged per usage metrics – pay per use. The more you utilize the higher the bill. Just as utility companies sell power to subscribers, and telephone companies sell voice and data services, IT services such as network security management, data center hosting or even departmental billing can now be easily delivered as a contractual service. 

Multi Tenancy: Multi tenancy refers to a principle in IT infrastructure where a single instance of the software runs on a server, serving multiple client organizations (tenants). With a multi-tenant architecture, a designed to virtually partition its data and configuration, and each client organization works with a customized virtual application instance. Each customer does its own work without interfering other customer even though they are hosted at the same platform.

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Following are some of the legal issues that can arise while running cloud computing services:

Confidentiality: Data in enterprise world is as important as anything. Placing your data in cloud infrastructure is supposed to be vulnerable and insecure. Hence, before and after moving to cloud infrastructure, organizations should carefully judge whether their data is managed confidentially or not.

Liability and responsibility: Liability and responsibility is another legal issues that has to be addressed by cloud vendor as well as customers. It should be regularly monitored to investigate that whether cloud vendors has performed their duties in accordance to Service Level Agreements (SLA) or not. As is cloud definition, customer has to ensure that cloud vendors has sufficient infrastructure, proper backup policy, business continuity plan and all the prerequisite to host valuable data.

Compliance: Before customers will entrust their IT needs to managed or cloud services, they need two things: first, assurance that cloud infrastructure is secure and compliant, and second, visibility into their own security and compliance stance in cloud or managed infrastructure. Cloud vendors should ensure the security and compliance of their customer with powerful incident management capabilities, immediate alerts about suspicious activities, and access to detailed forensic data. It should give its customer all the components required to deliver the compliance and security reports and dashboards they demand.

Data protection, safety and recovery: Data in cloud as said should be safe enough to be trusted and protected from various attacks. Safety and protection is not only enough for operating in cloud but it should have some standard recovery mechanism to recover data in case of failure of system.

Copyright and Ownership: Even though data may be residing in cloud infrastructure in any part of the world, data should be owned by customer and it should have legal obligation of being owned by customer themselves. Data once migrated to the cloud data centers should be completely owned and should be protected by some copyright. Customers should be aware of intentional duplication of data, data being copied or any leakage of data.

Data portability: What if customers want to shift data/ app to other cloud vendors? Data portability is a major hurdle for any customer to migrate from on cloud vendor to another. Is there any legal obligation of cloud vendor regarding the move or not? What if existing cloud vendor do not allow customer to migrate data to other provider? These questions should be clear enough for both customer and vendor and there should be defining answer for these questions.

Right to Audit: IT audit in cloud infrastructure is a necessity for maintaining compliance of cloud vendor as well as customer. Before moving to the cloud, and ideally during the procurement process, you should know your risk appetite and how it feeds the control environment — and then determine the potential cloud provider’s risk appetite. Security, Risk, Compliance are some of the factors that customers need to check periodically for the risk free operations. And while moving to cloud data centers, customers should be legally enforced to have the right to audit their hardware, software, systems and applications.

Termination or Suspension Contract: Cloud computing agreement can be terminated on the account of various reasons. The contract may expire at the end of its stipulated term or it may be terminated for default or material breach of terms of contract. User may also want to terminate the contract to migrate to a better or more cost effective cloud computing service. The user’s data is most vulnerable after the termination of contract and in most cases service provider has no legal duty or liability to handle the user’s data properly unless stipulated otherwise in the cloud computing contract. Hence a careful steps should be taken whenever for various reason a customer terminates the services from cloud service provider.

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Reduced Spending on Technology Infrastructure: Moving to cloud computing may reduce the cost of managing and maintaining your IT systems. Rather than purchasing expensive systems and equipment for your business, you can reduce your costs by using the resources of your cloud computing service provider. You may be able to reduce your operating costs because

• the cost of system upgrades, new hardware and software may be included in your contract
• you no longer need to pay wages for expert staff 
• your energy consumption costs may be reduced 
• There are fewer time delays.

Globalizing Workspace/ Easy Accessibility: Globalizing your workspace or system may add additional agility and effectiveness to your system. For example, you have the ability to access data from home, on holiday, or via the commute to and from work (providing you have an Internet connection). If you need access to your data while you are off-site, you can connect to your virtual office, quickly and easily.

Improve Flexibility and Scalability: Your business can scale up or scale down your operation and storage needs quickly to suit your situation, allowing flexibility as your needs change. Rather than purchasing and installing expensive upgrades yourself, your cloud computer service provider can handle this for you. Using the cloud frees up your time so you can get on with running your business.

Better Resource Utilization: Using technologies such as virtualization and distributed computing, computing resources can be used fully up to their potentials. In cloud model, you can pay whatever you use for your operational purpose.

Backup and Disaster Recovery: Since all your data is stored in the cloud, backing it up and restoring the same is relatively much easier than storing the same on a physical device. Furthermore, most cloud service providers are usually competent enough to handle recovery of information. Hence, this makes the entire process of backup and recovery much simpler than other traditional methods of data storage.

Also adding to backup management, cloud infrastructure can be used as a very strong disaster recovery site as they do have enough infrastructure and technology to be a potent DR Site.

Guaranteed Uptime and Strong Service Level Agreements (SLA): Cloud infrastructure by nature is built for robustness and high availability. Uptime is a major attribute for rapid popularity of cloud computing as all the services provided by cloud vendors should be guaranteed to be working all the time. Hence, the service level agreements between the cloud provider and customer are supposed to be very strong in case of availability and security. By achieving strong SLA’s, customer can operate very effectively with zero downtime.

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Figure: Cloud Deployment Models

Public Cloud: 

This is the deployment model that most commonly described as cloud computing. In this model, all of the physical resources are owned and operated by a third party cloud computing provider. The provider services multiple clients that may consist of individuals or corporations utilizing these resources through the public Internet. Services can be dynamically provisioned and are billed based on usage alone. This model provides the highest degree of cost savings while requiring the least amount of overhead. This model is best suited for business requirements wherein it is required to manage load spikes, host SaaS applications, utilize interim infrastructure for developing and testing applications, and manage applications which are consumed by many users that would otherwise require large investment in infrastructure from businesses.

Private Cloud: 

Private cloud computing systems emulate public cloud service offerings within an organization’s boundaries to make services accessible for one designated organization. Private cloud computing systems make use of virtualization solutions and focus on consolidating distributed IT services often within data centers belonging to the company. The chief advantage of these systems is that the enterprise retains full control over corporate data, security guidelines, and system performance. This model doesn’t bring much in terms of cost efficiency: it is comparable to buying, building and managing your own infrastructure. Still, it brings in tremendous value from a security point of view. In addition to security reasons, this model is adopted by organizations in cases where data or applications are required to conform to various regulatory standards, which may require data to be managed for privacy and audits that govern the corporation.

Hybrid Cloud: 

This can be a combination of private and public clouds that support the requirement to retain some data in an organization, and also the need to offer services in the cloud. A company may use internal resources in a private cloud maintain total control over its proprietary data. It can then use a public cloud storage provider for backing up less sensitive information. At the same time, it might share computing resources with other organizations that have similar needs. By combining the advantages of the other models, the hybrid model offers organizations the most flexibility. This model is also used for handling cloud bursting, which refers to a scenario where the existing private cloud infrastructure is not able to handle load spikes and requires a fallback option to support the load. Hence, the cloud migrates workloads between public and private hosting without any inconvenience to the users.

Community Cloud:

 In the community deployment model, the cloud infrastructure is shared by several organizations with the same policy and compliance considerations. This helps to further reduce costs as compared to a private cloud, as it is shared by larger group. A community cloud contains features of the public and private cloud models. Like a public cloud, the community cloud may contain software, data storage, and computing resources that are utilized by multiple organizations. Where this model differs from the public model is that the infrastructure is only utilized by a group of organizations that are known to each other. Similarly to a private cloud, these organizations are responsible for the operation of their own infrastructure. The community cloud model can provide greater cost savings than the private cloud while offering some of its security features. This model is best suited for organizations that share common requirements such as security or legal compliance policies. It can be managed by the member organizations or by a third party provider.

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Components of Cloud Computing

The Client- The End User: Everything ends with the client. The hardware components, the application and everything else developed for cloud computing will be used in the client. Client systems has some application installed which enables them to connect to cloud software or some infrastructure.

The Service (Functions in Cloud Computing): Cloud computing always has a purpose. One of the main reasons cloud computing become popular is due to the adoption of businesses as the easier way to implement business processes. It has some standard service or procedure of interfacing/ connecting client computers with cloud infrastructure. Cloud computing is all about processes and the services launched through cloud computing always has to deal with processes with an expected output.


The Application: Application is the core of what users are going to use. It is the mainstay of what users are wanting for their daily operations. Application are normally a program that users use to connect cloud infrastructure either with web interface or any application interface. In simple way, we can define application as a software that end user uses to do their operations in which their main data resides in cloud.

The Platform: The platform is where all the applications and services are based upon. The platform usually comes as the programming language such as Ajax (Asynchronous JavaScript and XML) or Ruby on Rails. In simple way, the platform is the cloud infrastructure where it provides application and service the base to operate. It is the environment provided by cloud vendors which enables all the application to operate and services to operate.

The Storage: The last and most critical components in cloud computing is the storage. Everything that the application knows and the functions that could be provided by service are possible through storage. Modern day cloud storage is based on highly virtualized infrastructure and has the same characteristics as cloud computing in terms of agility, scalability, elasticity and multi-tenancy. Some cloud storage systems are small operations, while others are so large that the physical equipment can fill up an entire warehouse.

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Some of the examples of cloud based services are:

1. Hosted Desktops (virtual machines): The hosted virtual desktop is just like normal PC desktop, except that applications, data and user profile are stored in a secure data center. It is designed to replace traditional desktop PC environment, and provides the same level of functionality and performance as normal PC.
2. Hosted Telephony: It is the way of taking all the telephone infrastructure from on premises to some cloud based telephony system.
3. Hosted websites/Emails: Websites and emails are hosted in cloud based servers. Th main advantages of hosted websites and emails is the saving cost used for procuring new servers, managing servers, power system, experts, maximum uptime, scalability and security.
4. Cloud Storage: It is a service model in which data is maintained, managed and backed up remotely and made available to users over a network.

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Some of the advantages of cloud based services are:

Proven Web-services integration. By their very nature, cloud computing technology is much easier and quicker to integrate with your other enterprise applications (both traditional software and cloud computing infrastructure-based), whether third-party or homegrown. 

World-class service delivery: Cloud computing infrastructures offer much greater scalability, complete disaster recovery, and impressive uptime numbers.

No hardware or software to install: a 100% cloud computing infrastructure. The beauty of cloud computing technology is its simplicity... and in the fact that it requires significantly fewer capital expenditures to get up and running.

Faster and lower-risk deployment: You can get up and running in a fraction of the time with a
cloud computing infrastructure. No more waiting months or years and spending millions of dollars
before anyone gets to log into your new solution. Your cloud computing technology applications
are live in a matter of weeks or months, even with extensive customization or integration.

Support for deep customizations: Some IT professionals mistakenly think that cloud computing
technology is difficult or impossible to customize extensively, and therefore is not a good choice
for complex enterprises. The cloud computing infrastructure not only allows deep customization
and application configuration, it preserves all those customizations even during upgrades. And
even better, cloud computing technology is ideal for application development to support your
organization’s evolving needs.

Empowered business users: Cloud computing technology allows on-the-fly, point-and-click customization and report generation for business users, so IT doesn’t spend half its time making minor changes and running reports.

Automatic upgrades that don’t impact IT resources: Cloud computing infrastructures put an end
to a huge IT dilemma: If we upgrade to the latest-and-greatest version of the application, we’ll be
forced to spend time and resources (that we don’t have) to rebuild our customizations and
integrations. Cloud computing technology doesn’t force you to decide between upgrading and
preserving all your hard work, because those customizations and integrations are automatically
preserved during an upgrade.

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Cloud computing is the use of computing resources (hardware and software) that are delivered

as a service over a network (typically the Internet). The “cloud” in cloud computing can be

defined as the set of hardware, networks, storage, services, and interfaces that combine to

deliver aspects of computing as a service.

Cloud services include the delivery of software, infrastructure, and storage over the Internet. Most of the cloud computing has following features:

1. It's virtual
2. It can be secure
3. It's flexible and scalable
4. It can be affordable
5. It can be secure and affordable

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Alternatively we have Grid Computing, which is well defined by Mary Humphrey and Mary R. Thomson: “A Computational Grid is a collection of heterogeneous computers and resources spread across multiple administrative domains
with the intend of providing users easy access to these resources.”

Ian Foster made a three point checklist to define what a
Grid is. In this list he said:

•“coordinates resources that are not subject to centralized control” : Which means that not only one entity manages all the system but some different system administrators could be managing different parts of the same Grid at the same time.
•“using standards, open, general-purpose protocols and interfaces” :This will allow to all the companies involved in the Grid to use and access these standards.
•“to deliver nontrivial qualities of service” :In Grid computing not a fixed rate of load is going to be managed and this can be given small or big rates. This phenomenon causes the given quality of service to vary and not always stay constant. Grids allow the use of idle resources. Through this, companies create a Grid in order to share those idle resources and, if necessary, they can access more computational resources(shared by other companies) than they usually can, and share their own resources while they are not carrying out any computationally demanding tasks.

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 The differences between Cloud and Grid computing are listed below:

1. Cloud computing normally runs in a set of homogeneous computers, but Grid, on the other hand, runs on heterogeneous computers.

 2. Grid computing is normally focused on an intensive calculus, while Cloud Computing offers two types of calculuses: standard and intensive.

3. Grid computing is open-source while Cloud Computing is not.[7]. This creates interoperatibility problems between today’s Clouds.

4. Most Grids use a batch-scheduled compute model, while in Cloud Computing all users share all the resources at the same time. And this is why latency sensitive applications, which could run in Grids, could no be supported in Cloud Computing.

5. Grids do not rely on virtualization as much as Cloud does.

6. Cloud Computing does not support as much provenance as Grid does[4], which is a “derivation history of a data product, including all the data sources, intermediate data products,and the procedures that were applied to produce the data product”.

7. High Performance computing is better supported in Grid computing than in Cloud Computing.

8. Grid is distributed, has multiple research user communities (including users accessing resources from varied administration domains) and is grouped in Virtual Organisations. Cloud Computing, on the other hand, usually has only one research community and a common group of system administrators that take care of the entire Cloud.

9. Grid is mostly publicly funded at local, national and international levels, while Cloud Computing is funded mainly by its users

10. Grid computing, must share user and resource inter- faces to allow providers to connect their resources, while Cloud Computing attempts to share only the user interface while the resources interfaces are hidden and given in an abstract way.

11. In Grid computing, the trust model is based on identity delegation, where users can access and browse resources,which are not highly abstracted and virtualized at different Grid sites. In Cloud computing resources are abstracted and virtualized and this trust model does not exist since everything is inside the same Cloud.

12. While in Grid computing, storing very small files (e.g.1-byte files) is not economically suitable, in CloudComputin it is.

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FOUR ASPECTS OF SECURITY

Based on the above expectations, we can say that security involves four aspects:

·      Privacy(confidentiality)

·      Message authentication

·      Message integrity

·      Non-repudiation

Privacy

Privacy means that the sender and the receiver expect confidentially. The transmitted message should make sense to only the intended receiver. To all other message should be unintelligible.

Authentication

Authentication means that the receiver is sure of the sender’s identity and that an imposter has not sent the message.

Integrity

Data integrity means that the data must arrive at the receiver exactly as it was sent. There must be no changes during the transmission, either accidental or malicious. As more and more monetary exchanges occur over the Internet, integrity is crucial. For example, it would be disastrous if a request for transferring $100 changes to a request for $10,000 or $100,000. The integrity of the message must be preserved in a secure communication.

Non-Repudiation

Non-repudiation means that a receiver must be able to prove that a received message came from a specific sender. The sender must be able to deny sending a message that he, in fact did send. The burden of proof falls on the receiver. For example, when a customer sends a message to transfer money from one account to another, the bank must have proof that the customer actually requested this transaction.

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