Information and Communication Technology (ICT) is being provided to the variety of end-users demands, thereby providing a better and improved management of services is crucial. Therefore, Service Level Agreements (SLAs) are essential and play a key role to manage the provided services among the network entities. This survey identifies the state of the art covering concepts, approaches and open problems of the SLAs establishment, deployment and management. This paper is organised in a way that the reader can access a variety of proposed SLA methods and models addressed and provides an overview of the SLA actors and elements. It also describes SLAs' characteristics and objectives. SLAs' existing methodologies are explained and categorised followed by the Service Quality Categories (SQD) and Quality-Based Service Descriptions (QSD). SLA modelling and architectures are discussed, and open research problems and future research directions are introduced. The establishment of a reliable, safe and QoE-aware computer networking needs a group of services that goes beyond pure networking services. Therefore, within the paper this broader set of services are taken into consideration and for each Service Level Objective (SLO) the related services domains will be indicated. The purpose of this survey is to identify existing research gaps in utilising SLA elements to develop a generic methodology, considering all quality parameters beyond the Quality of Service (QoS) and what must or can be taken into account to define, establish and deploy an SLA. This study is still an active research on how to specify and develop an SLA to achieve the win-win agreements among all actors.

翻译：信息和通信技术（ICT）正被提供给多样化的最终用户需求，因此，提供更好且改进的服务管理至关重要。因此，服务水平协议（SLA）至关重要，并在管理网络实体间提供的服务中扮演关键角色。本综述概述了SLA建立、部署和管理方面的概念、方法和开放问题的最新进展。本文的组织方式使读者能够了解各种已提出的SLA方法和模型，并提供SLA参与者和要素的概览。它还描述了SLA的特征和目标。对现有的SLA方法论进行了解释和分类，随后介绍了服务质量类别（SQD）和基于质量的服务描述（QSD）。讨论了SLA建模和架构，并介绍了开放的研究问题和未来的研究方向。建立可靠、安全且面向体验质量（QoE）的计算机网络需要一组超越纯网络服务的服务。因此，本文考虑了这一更广泛的服务集合，并为每个服务等级目标（SLO）指明了相关的服务领域。本综述的目的是识别利用SLA要素开发通用方法论方面的现有研究空白，考虑除服务质量（QoS）之外的所有质量参数，以及定义、建立和部署SLA时必须或可以考虑的内容。本研究仍然是关于如何制定和开发SLA以实现所有参与者之间双赢协议的活跃研究。