Application Layer (DCN_Ch_02) - PDF

The Application Layer Dr. Ramakrishna Dantu College of Business Application Layer Topics • Application Architectures • World Wide Web • Electronic Email • Other Applications • Implications for Cyber Security Cloud Computing Architectures Application Architectures Cloud Computing Architectures...

The Application Layer Dr. Ramakrishna Dantu College of Business Application Layer Topics • Application Architectures • World Wide Web • Electronic Email • Other Applications • Implications for Cyber Security Cloud Computing Architectures Application Architectures Cloud Computing Architectures • There are three common cloud-based architecture models that an organization can pick from.  Software-as-a-Service (SaaS)  Platform-as-a-Service (PaaS)  Infrastructure-as-a-Service (IaaS) • Table (next slide) summarizes these three models and compares them to the client–server architecture. Application Architectures Cloud Computing Architectures • Table summarizes three models and compares them to the client– server architecture. Application Architectures Cloud Computing Architectures • Figure shows one row of a server farm at Indiana University. • There are seven more rows like this one in this room • Another room contains about the same number. Application Architectures Cloud Computing Architectures • Many companies use separate storage devices instead of the hard disks in the servers themselves. • These storage devices are specialpurpose hard disks designed to be very large and very fast. • The six devices on the left of Figure comprise a special storage device called a storage area network (SAN). Application Architectures Cloud Computing Architectures • Software-as-a-Service (SaaS)  With SaaS, an organization outsources the entire application to the cloud provider.  The organization uses it as any other application that is available via a browser (thin client).  SaaS is based on multitenancy.  One single copy of the application that everyone shares.  Everyone can customize it as per their needs.  Customers don’t have to worry about upgrades, security, or underlying infrastructure because the cloud provider does it all.  Examples:  the most frequently used SaaS application is email. o At Indiana University, all student email is outsourced to Google’s Gmail.  Customer relationship management (CRM) from Salesforce.com  Many SAP or PeopleSoft applications can be SaaS applications Application Architectures Cloud Computing Architectures • Platform-as-a-Service (PaaS)  What if there is an application you need but no cloud provider offers one you like?  Here, the developers in your organization decide what programming language to use to develop the application of choice.  The organization build their own application and manage their data on the cloud infrastructure provided by your cloud supplier.  The platform (hardware and software infrastructure) is rented from the cloud provider  Hardware = (server, storage, and network); software = (Database software, Operating system, Virtualization software). Application Architectures Cloud Computing Architectures • Platform-as-a-Service (PaaS)  PaaS offers:  1) a much faster development and deployment of custom applications at  2) a fraction of the cost required for the traditional client–server architecture.  PaaS providers include  Amazon Elastic Cloud Compute (EC2)  Microsoft Windows Azure, and  Google App Engine. Application Architectures Cloud Computing Architectures • Infrastructure-as-a-Service (IaaS)  The cloud provider manages the hardware, including servers, storage, and networking components.  The organization is responsible for all the software, including operating system (and virtualization software), database software, and its applications and data.  Also called as Hardware-as-a-Service (HaaS) because in this model, only the hardware is provided; everything else is up to the organization.  This model allows a decrease in capital expenditures for hardware and maintaining the proper environment:  E.g., cooling, redundancy, backups for data and applications.  Providers of IaaS are Amazon Web Services, Microsoft Windows Azure, and Akamai. Peer-to-Peer Architectures Application Architectures Peer-to-Peer Architectures Application Architectures Peer-to-Peer Architectures • Peer-to-peer (P2P) architectures are very old • Their modern design became popular in the early 2000s with the rise of P2P file-sharing applications (e.g., Napster). • Here, all computers act as both a client and a server. • All computers perform all four functions:  presentation logic  application logic  data access logic  data storage Application Architectures Peer-to-Peer Architectures • P2P file-sharing application  A user uses the presentation, application, and data access logic installed on his or her computer to access the data stored on another computer in the network. • P2P application-sharing network  E.g., grid computing such as seti.org  Other users in the network can use others’ computers to access application logic as well. Application Architectures Peer-to-Peer Architectures • Advantages  The data can be installed anywhere on the network.  They spread the storage throughout the network, even globally, so they can be very resilient to the failure of any one computer. • Challenges  Finding the data is difficult.  There must be some central server that enables us to find the needed data.  So P2P architectures often are combined with a client–server architecture.  Security is a major concern in most P2P networks  So P2P architectures are not commonly used in organizations, except for specialized computing needs (e.g., grid computing). World Wide Web World Wide Web Brief History • 1990-91:  First web browser was created • End of 1992:  Several browsers were created. There were about 30 Web servers in the entire world. • 1993:  The first graphical web browser called Mosaic was created by a team of students at the University of Illinois. • End of 1993  There were about 200 Web servers in the world. • Today  There are more than 250 million separate websites, but many of these are hosted on the same servers by large hosting companies such as godaddy.com or Google sites. How the Web Works World Wide Web How the Web Works World Wide Web How the Web Works • The Web is a good example of a two-tier client–server architecture. • Client  Each client computer needs an application layer software package called a Web browser.  There are many different web browsers, such as Microsoft Internet Explorer. • Server  Each server on the network acts as a Web server  Server needs an application layer software package called a Web server.  There are many different Web servers, such as those produced by Microsoft and Apache. World Wide Web How the Web Works • To get a page from the Web, the user must type the Internet uniform resource locator (URL) for the page (e.g., www.yahoo.com) or click on a link that provides the URL. • The URL specifies:  1) the Internet address of the Web server  2) the directory and  3) the name of the specific page wanted. • If no directory and page are specified, the Web server will provide whatever page has been defined as the site’s home page. World Wide Web How the Web Works • Web browser and Web server must use the same standard protocol or language. • The standard protocol for communication between a Web browser and a Web server is Hypertext Transfer Protocol (HTTP). • To get a page from a Web server, the Web browser issues a special packet called an HTTP request that contains the URL and other information about the Web page requested. • Once the server receives the HTTP request, it processes it and sends back an HTTP response • HTTP response will be the requested page or an error message. Thank You