LITERATURE REVIEW
2.1. Introduction
This chapter reviews the different kinds of literature that are related to the objective of the study. Literatures covered in this section are the basic concept of cloud computing: service types, deployment models, cloud challenges and benefits for agriculture sector, different publications about EAS (Ethiopian agricultural sector) existing ICT usages and related works done on cloud-based service frameworks locally and abroad in order to understand how it is used in agriculture sectors.
2.2. Cloud computing
Over the last few years, many IT professionals, business managers, and researchers have started to talk about a new phenomenon called cloud computing. Each of these groups defined cloud computing differently according to their understanding of its offerings. Although there was no agreement about what precisely constituted cloud computing, it still offered a promising paradigm that could enable businesses to face market volatility in an agile and cost-efficient manner 10. According to 11, Cloud computing is a system, where the resources of a data center are shared using virtualization technology, which also provides elastic, on-demand and instant services to its customers and charges customer usage as a utility bill.

The most widely accepted definition NIST 12, defined Cloud computing as” a model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction”. Regarding its relations to other pre-existing computing models, cloud computing can be used in principle to deliver computing services, including grid computing services, high-performance computing services, etc. This does not imply that cloud computing is a replacement for grid computing, high-performance computing, or any other pre-existing computing model. Instead, cloud computing should be thought of as a new business model that aims at service delivery in a highly scalable and highly flexible manner. The difference between cloud computing and other pre-existing computing models can be better demonstrated by ways of using the characteristics, service, deployment models and its key enabling technologies of virtualization.