# On Blockchain-Based Cross-Service Communication and Resource Orchestration on Edge Clouds
## 2 Related Work  
In this section, the most recent and interesting studies and projects relevant to the cross-service, multi-domain and Blockchain-based orchestration are presented. On top of the open-source MANO (OSM) [9], MESON orchestration platform enables the cross-slice communication within an Edge Point of Presence (EPoP) [10]. Aligned with ETSI-NFV [11] and ETSI MEC [12] architecture, MESON platform provides centralized service discovery through a service registry, EPoP selection and establishment of cross-slice communication. Based on functional and non-functional requirements, the EPoP selection is performed by a multi-criteria EC selection methodology that determines the most suitable EC for the slice deployment [13]. Then, through OSM, an automated mechanism establishes the actual cross-slice communication that aims to minimize the generated intra-EC network traffic and allocated resources [14]. Also aligned with ETSI-NFV architecture, FENDE marketplace [15] enables developers to offer their VNF-based services, while users can select Virtual Network Functions (VNFs) from the service and VNF catalogue, compose custom service chains and instantiate them in public or private cloud infrastructures. NECOS marketplace is a broker-based platform that enables the resource discovery, negotiation and selection for deploying network slice over multiple administrative domains [16], while the 5 GEx platform focuses on cross-domain orchestration of network services [17]. With respect to the latter, a hierarchical architecture of multi-domain orchestrators enables the exchange of business-level information with customers, the service discovery and placement and supports the VNF configuration and monitoring. [PERSON] et al.proposed a Blockchain-enabled multi-domain orchestrator at the edge of the network [18]. The objectives of this approach are the automated orchestration of network slices over heterogeneous networks and the Service Level Agreement (SLA) assessment for 5G services using smart contracts. Nubo is a virtual service marketplace created to connect providers and consumers of such services in an edge/cloud computing environment [19]. Nubo is basically a web portal built over and extending Saranyu [20], which is a decentralized application (DApp) built on top of Quorum private Blockchain [21]. Saranyu is used for the management of cloud tenants and services, providing identity management, authentication and charging functionality with the use of smart contracts. The authors in [22] present an experimental prototype for a multi-administrative domain federation of 5G services using distributed ledger technologies. Its objective is to provide a distributed federation solution where different administrative domains and providers participate in a permissioned Blockchain network with a single node. A single generic Federation Smart Contract acts as a distributed authority to enable secure and trusted interactions for functionalities such as registration to the federation, service announcement/discovery and service auctioning. The 5 GZORRO project proposes an architecture focused on cross-domain security and trust resource orchestration mechanisms, by coupling Blockchain with AI-driven operations and service lifecycle automation in multi-tenant and multi-stakeholder environment [23]. Specifically, smart contracts are used to support multilateral agreements among all parties that are involved in the end-to-end service delivery. In [24], a Blockchain-based resource brokering mechanism for end-to-end slice deployment is proposed to secure transactions in the resource auctioning procedure. Upon a slice request, the slice is divided in sub-slices and an auction mechanism facilitates the resource providers to make bids for every sub-slice. The slice owner selects the best offers for each sub-slice. The authors of [25] proposes Bsec-NFVO, a Blockchain-based system, to enable secure orchestration operations in virtualized networks ensuring auditability, non-repudiation and integrity.