Protocol Stack for Wireless Sensor Networks (WSNs)

The protocol stack for WSNs consists of five protocol layers:

1. Physical layer
2. Data link layer
3. Network layer
4. Transport layer
5. Application layer

Cloud Computing VS Grid Computing

While cloud computing and grid computing are both concepts that involve large-scale computer networks, they are certainly not synonymous with each other. This article explains both cloud and grid computing, and exactly how they differ.

Introduction

Cloud computing and grid computing are two relatively new concepts in the field of computing. They are often mistaken for the same thing, however that is not the case at all.

Both grid and cloud computing are networks which abstract processing tasks. Abstraction masks the actual complex processes taking place within a system, and presents a user with a simplified interface with which they can interact easily. The idea is to be able to make the system more user-friendly whilst retaining all the benefits of more complicated processes.

Although there is a difference in the fundamental concepts of grid and cloud computing that does not necessarily mean that they are mutually exclusive; it is quite feasible to have a cloud within a computational grid, as it is possible to have a computational grid as a part of a cloud. They can also be the same network, merely represented in two different ways.

Grid Computing

Grid computing is a term referring to the combination of computer resources from multiple administrative domains to reach common goal.

What distinguishes grid computing from conventional high performance computing systems such as cluster computing is that grids tend to be more loosely coupled, heterogeneous, and geographically dispersed. Although a grid can be dedicated to a specialized application, it is more common that a single grid will be used for a variety of different purposes. Grids are often constructed with the aid of general-purpose grid software libraries known as middleware.

Grid size can vary by a considerable amount. Grids are a form of distributed computing whereby a “super virtual computer” is composed of many networked loosely coupled computers acting together to perform very large tasks. Furthermore, “Distributed” or “grid” computing in general is a special type of parallel computing that relies on complete computers (with onboard CPUs, storage, power supplies, network interfaces, etc.) connected to a network (private, public or the Internet) by a conventional network interface, such as Ethernet. This is in contrast to the traditional notion of a supercomputer, which has many processors connected by a local high-speed computer bus.

Cloud Computing

Cloud computing is Internet-based computing, whereby shared resources, software, and information are provided to computers and other devices on demand, like the electricity grid.

Cloud computing is a paradigm shift following the shift from mainframe to client–server in the early 1980s. Details are abstracted from the users, who no longer have need for expertise in, or control over, the technology infrastructure “in the cloud” that supports them. Cloud computing describes a new supplement, consumption, and delivery model for IT services based on the Internet, and it typically involves over-the-Internet provision of dynamically scalable and often virtualized resources. The term “cloud” is used as a metaphor for the Internet, based on the cloud drawing used in the past to represent the telephone network, and later to depict the Internet in computer network diagrams as an abstraction of the underlying infrastructure it represents. Typical cloud computing providers deliver common business applications online that are accessed from another Web service or software like a Web browser, while the software and data are stored on servers. A key element of cloud computing is customization and the creation of a user-defined experience.

Switching Technique (Data and Computer Communication)

Quote from Data and Computer Communication Book by William Stallings

Two (2) types of switching technique :

1. Datagram Approach

Each packet is treated independently, with no reference to packets that have gone before. Let us consider the implication of this approach. Suppose that station A has a three-packet message to send to E. It transmits the packet, 1-2-3, to node 4. Node 4 could possibly forward this packet to either node 5 or node 7 as the next step in the route. In this case, node 4 determines that is queue for node 7 is now shorter and so queues packet 3 for that node. So the packets, each with the same destination address, do not all follow the same route. As a result, it is possible that packet 3 will beat packet 2 to node 6. Thus, it is also possible that the packet will be delivered to E in a different sequence from the one in which they were sent. It is up to E to figure out how to reorder them. Also it is possible that packets to be destroyed in the network. From example, if a packet switching node crashes momentarilly, all of its queued packets may be lost. If this were to happen to one of the packets in our example, node 6 has no way of knowing that one of the packets in the sequence of packets has been lost. Again, it is up to E to detect the loss of the packet and figure out how to recover it

2. Virtual Circuit Approach

A preplaned route is established before any packets are sent. For example, suppose that A has one or more messages to sent to E. It first sends a special control packet, referred to as a Call-Request packet, to 4, requesting a logical connection to E.