## 6 Architecture for Cross-Domain End-to-End Network and Service Management
Domain orchestration services enable automatic life-cycle management of the virtual (and physical) functions in the infrastructure managed by the MD. Domain control services are consumed by other functions in the domain intelligence and domain orchestration service groups to control the states (including configuration, lifecycle, etc.) of the managed domain infrastructure. The E2 EMD is responsible for end-to-end management through orchestration of the management services provided by individual MDs. The E2 EMD together with the set of MDs in the ZSM architecture form a two-level hierarchical structure where each individual MD directly manages the infrastructure resources within a single network domain, while the E2 EMD composes the MD management services for managing customer-facing end-to-end network services. The end-to-end management services provided by the E2 EMD support the following functions: E2E service orchestration that coordinates  
Figure 5: ETSI Zero Touch Network and Service Management (ZSM) architecture. lifecycle management of services across management domains, E2E service intelligence that drives intelligent close-loop automation of end-to-end network and service management, E2E service analytics that derives end-to-end service insights for managing end-to-end service performance, and E2E data collection that collects end-to-end service-related data. As a service-based inter-domain management framework, the ZSM architecture must provide a flexible platform for supporting communications and interoperation of the management functions with respect to the offered and consumed management services, not only within each MD, but also across different MDs. The integration fabric is the mechanism defined in the ZSM architecture for achieving this objective. The integration fabric provides functions for supporting registration/deregistration, discovery, selection, and invocation of management services and providing both synchronous and asynchronous communications among management services. The ZSM integration fabric comprises two levels--a domain integration fabric in each individual MD (including the E2 EMD) and a cross-domain integration fabric for supporting service orchestration across different MDs. For achieving flexible data collection and maintenance in multi-domain management environments, the ZSM architecture provides cross-domain data services as well as data services within each MD. The key functions of ZSM data services include maintaining data persistence and supporting data sharing within and between management domains. ZSM Data services also enable abstraction of data process actions from management functions, which may eliminate the need to handle such actions on a per-function basis, thus allowing stateless management functions. The common cross-domain data services allow the separation of data storage and data processing, thus facilitating cross-domain data exposure and access. It is worth mentioning that ETSI ZSM is not the only standard for cross-domain network and service management. Other network SDOs also developed architectures for service management and orchestration across technology and/or administration domains. For example, the Abstraction and Control of Transport Network (ACTN) specification [43] developed by IETF and the Lifecycle Service Orchestration (LSO) standard [44] developed by MEF both offer a framework for cross-domain management within which analytics techniques may be applied for supporting intelligent management. Compared to other standard architectures for cross-domain management such as ACTN and LSO, ZSM is more representative of the cloud-native design principle and is developed particularly for integrating the various ML techniques employed in individual domains for intelligent and autonomous management. Therefore, ETSI ZSM is chosen as the focus of this section for reflecting the state-of-the-art standardization of cross-domain management architecture for cloud-native future networks