WHAT IS CLOUD COMPUTING or CLOUD APPLICATION?
Cloud computing is using internet connectivity to access computing services not present locally. An example of this would be Dropbox, or Google Docs. In a sense, Steam would also be an example of cloud computing, as would Facebook and other social media.
Cloud computing would ordinarily not be installed per se on a personal computer, but a client can be installed on a personal computer to gain access to cloud computing.
Security is an issue, as is data lock-in. There's no layperson explanation available there - it would concern such things as cryptography (both symmetric and asymmetric) and various cryptographic attacks.
If a computer using a cloud based service gets disconnected, there are two ways this can be handled. Either the computer starts buffering data (in order to transfer them once connectivity is restored - Dropbox does this for instance), or the computer shuts down the service (because connectivity is interrupted - Facebook does this).
Cloud computing isn't necessarily _web based_ per se, it is actually based on _internet connectivity_. Two different things, though the difference is usually too subtle for a layperson to discern, so I won't go into detail there.
The 7 Layers of the OSI Model
Application (Layer 7)
This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.Presentation (Layer 6)
This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.Session (Layer 5)
This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.Transport (Layer 4)
This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.Network (Layer 3)
This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.Data Link (Layer 2)
At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.Physical (Layer 1)
This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.Philippine Internet Comparison
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