# On Blockchain-Based Cross-Service Communication and Resource Orchestration on Edge Clouds
## 1 Introduction  
With the advent of the Internet of Things (IoT) and 5G era, modern time- and mission-critical applications with stringent requirements have been developed for every section of human activity. These complex end-to-end applications consist of network services that form a structured service chain. However, the abundant cloud resources cannot guarantee the delay requirements, and this motivates the need for the infrastructure operators to provide computing capabilities closer to end users. Thus, presently, the Edge Computing service delivery model is the most promising one to meet the requirements of applications derived from 5G verticals, Industry 4.0 [1] and smart cities [2, 3]. As with cloud computing, the resource orchestration at the edge of the network relies on the Network Function Virtualization (NFV) [4] and Software-Defined Networking (SDN) [5] concepts that facilitate network slicing. A network slice is actually a structured chain of network services that perform specific tasks of the application logic. This allows infrastructure providers to lease customized bundles of computing, storage and network resources, to their tenants allowing the addressing of the service-specific (non-)functional requirements in an isolated fashion. Many standardization initiatives, i.e., ETSI Multi-access Edge Computing (MEC) ([[https://www.etsi.org/technologies/multi-access-edge-computing](https://www.etsi.org/technologies/multi-access-edge-computing)]([https://www.etsi.org/technologies/multi-access-edge-computing](https://www.etsi.org/technologies/multi-access-edge-computing)) (accessed on 31 January 2021)) and ETSI-NFV ([[https://www.etsi.org/technologies/nfv](https://www.etsi.org/technologies/nfv)]([https://www.etsi.org/technologies/nfv](https://www.etsi.org/technologies/nfv)) (accessed on31 January 2021)) aim to describe and standardize the specifications on the automated resource orchestration and support of the entire lifecycle of network services. The evolution of 5G ecosystems and verticals requires the deployment of end-to-end network services over multiple domains or multi-administrative domain. Under this multi-tenant and multi-provider setting, the isolation of network slicing, which is its greatest advantage till now, impedes the cross-service communication (CSC). Thus, next-generation network service marketplaces (NSMs) aspire to overcome this obstacle and enable tenants to create tailor-made service chains using off-the-shelf network services that can consume other services in a secure manner. With this capacity, a multi-tier NSM should provide various functionality elements for both service provider and consumer. At the top layer of the marketplace, functionalities such as easy registration, enriched description and on-boarding of services should be provided to service providers. Furthermore, a service discovery and lease mechanism are essential for the tenants, who search for the network service to be included in their custom service chain. The next downward layer is responsible for handling the high-level information of every service chain and automating the resource orchestration of the network services. At the bottom layer, the service chain is instantiated by the resource orchestrator. At the middle layer of the network service marketplace, various transactions between the evolving entities occur. Although a centralized trusted authority and a trust management mechanism provide the desired level of trust, this is usually performed through non-automated functionality and requires a lot of human intervention. Furthermore, the complexity of trust management significantly increases in the case of multi-domain or multi-administrative resource orchestration. Contrary to centralized solution, Blockchain enables entities in trustless environment to make transactions in a decentralized manner and guarantees the integrity of the outcome of the transactions to all participants of the Blockchain network ([PERSON], 2016).