Abstract—The several open–source as wellas proprietary tools

Abstract—The orchestration of network services is a wellinvestigated problem. Standards and recommendation have beenproduced by ETSI and IETF while a significant body of scientificliterature can be found exploring both the theoretical and practicalaspects of the problem. Likewise several open–source as wellas proprietary tools for network service orchestration are alreadyavailable. Nevertheless, in most of these cases network servicescan only be provisioned across a single administrative domaineffectively preventing end–to–end network service delivery acrossmultiple Infrastructure Providers (InP). In this paper we presentX–MANO, a cross–domain network service orchestration frameworkconsisting in an inter–domain confidentially–presentingfederation interface and in an information model for multi–domain network service life–cycle programmability. X–MANO iseffectively deployment–agnostic and can be used in hierarchical,peer–to–peer and cascading (or recursive) configuration. Wevalidate X–MANO trough a proof–of–concept implementationover a multi–domain testbed. Finally, we release all the codeunder a permissive APACHE 2.0 license making it available toresearchers and practitioners.Index Terms—Network Management, Network Function Virtualization,Multi-domain orchestration, Multi–technology orchestration,Proof–of–concept.I. INTRODUCTIONDriven by the ever increasing demand for new servicesand applications, telecommunication networks are witnessing amajor revolution in both their architecture and service deliverymodel. In particular, the consideration that not all services areborn equal has led to the creation of the term demand–attentivenetworks 1 highlighting the paradigm shift from a supply–push to a demand–pull service delivery model.Network Function Virtualization (NFV) is the key technologicalenabler for demand–attentive networks. NFV is alreadyused by telecommunications operators to deliver services at afraction of the cost it would take to run them using dedicatedappliances. Nevertheless, future network services already callfor a pooling of resources across multiple InPs. Examplesinclude mobile operators leveraging on satellite network operatorsfor back–hauling connectivity 2 or content providersaggregating cloud, network, and mobile resources to deliveran end–to-end user experience 3, 4.One of the biggest challenge in multi–domain networkservice orchestration is to compose resources from differentInPs under a single umbrella framework without imposingrequirements or restrictions on the different InPs. In particulareach InP shall be allowed to orchestrate its part of thenetwork service according to its own internal administrativepolicies without having to disclose confidential information,such as traffic matrices and internal topology, to the other InPsinvolved in the service. As a result, existing NFV Managementand Orchestration frameworks 5, 6 that assume globalnetwork knowledge are not applicable.In a multi–InPs scenario a network service may spanacross different administrative as well as technological domains.Notice how the different domains can leverage onspecific orchestration frameworks addressing the managementrequirements of that particular technology. Moreover, even iftechnological heterogeneities can be abstracted away under asingle network orchestrator, network services deployed acrossdifferent administrative domains will face unique challengesdue to the lack of network service orchestration frameworkscapable of enabling inter–InP communications.In this work we take a step in the direction of enablingcross–domain network service orchestration by introducing theX–MANO framework. X–MANO consists in a confidentially–preserving interface for inter–domain federation and in a setof abstractions (backed by a consistent information model)enabling network service life–cycle programmability. Saidabstractions tackle all the aspect of cross–domain networkservice provisioning including on–boarding, scaling, and termination.We validate the proposed federation interface andinformation model by implementing them in a proof–of–concept X–MANO prototype and by using it to deploy a videotranscoding network services in a multi–domain InP testbed.Finally, we release the proof–of–concept X–MANO implementationunder a permissive APACHE 2.0 license makingit available to researchers and practitioners1.The rest of the paper is organized as follows. In Sec. IIwe present the related work. Section III introduces the cross–domain orchestration challenges and the associated requirements.The X–MANO architecture and interfaces are describedin Sec. IV. Finally, we draw our conclusions in Sec. V.II. RELATED WORKIn the deployment and orchestration of network services,one of the most important problem to take into account is theso–called virtual network embedding (VNE) problem. Whilethe literature on single–domain VNE is already significant 7,works on multi–domain VNE have just started to appear 8,9, 10, 11, 12. Distributed approaches for VNE areprovided in 8, 9. However, they are more focused on