Common use of Deployment Models Clause in Contracts

Deployment Models. Three main deployment models can be considered when designing an SDN-based control plane: • A fully centralized model, with a logically single SDN controller with the whole view of the entire DCN • A hierarchical model, with a first layer of “child” SDN controllers responsible for disjoined portion of the DCN and a “parent” SDN controller which handle a more abstracted view of the whole DCN, obtained through the cooperation with the “child” controllers. This model could be adopted to handle very different technology domains through specialized “child” SDN controllers and requires only a north-south interaction between each child controller and its parent controller. Of course, this interaction can be recursive and involve several layers in the SDN controller hierarchy. • A distributed east-west model, with a set of peer SDN controllers, each of them responsible for a portion of the DCN and cooperating together with horizontal communications to achieve the whole control and management of the entire DCN. In general, the third model is very complex and particularly suitable to large scenarios characterized by a variety of trust domains where each network domain is controlled through proprietary protocols and a very limited amount of information can be exchanged outside the domain boundaries. The inter- controller communication can be regulated using protocols like BGP (Border Gateway Protocol) [RFC4271] or PCEP (Path Computation Element communication Protocol) [RFC5440]. However, this model is scarcely applicable to the intra-DC scenario, where a single DC provider is responsible for the whole DCN. The hierarchical model may be of interest due to the heterogeneous nature of the COSIGN DCN. However, the complexity and the time delays required by the inter-controller synchronization and communication (also in this case the PCEP is a reasonable candidate, with the extensions for the stateful and active mode [PCESTAT], [PCEINIT]) can be considered as strong limitation in highly dynamic scenarios like DCN environment. For this reasons, the COSIGN DCN Control Plane solution is based on the centralized deployment model, with a single SDN controller that maintains the overall view and control of the overall DCN. The specific characteristics of the different technologies available at the data plane are handled through dedicated plugins and abstracted with a powerful information model that allows for the application of unified functions and procedures in the SDN controller core. This approach avoids the need to introduce specialized controllers to deals with each optical device type deployed in the COSIGN DCN. It should be noted that the SDN controller is a single entity from a logical point of view. However, from the architectural point of view, the controller can be deployed as a cluster of controllers for high availability or scaling reasons. This option is supported by some SDN controller platforms available today (including OpenDaylight and ONOS, see section 2.4) and relies on mechanisms for distributed databases, avoiding the complexity of inter-controller protocols.

Deployment Models. Three main deployment models can be considered when designing an SDN-based control plane: •  A fully centralized model, with a logically single SDN controller with the whole view of the entire DCN •  A hierarchical model, with a first layer of “child” SDN controllers responsible for disjoined portion of the DCN and a “parent” SDN controller which handle a more abstracted view of the whole DCN, obtained through the cooperation with the “child” controllers. This model could be adopted to handle very different technology domains through specialized “child” SDN controllers and requires only a north-south interaction between each child controller and its parent controller. Of course, this interaction can be recursive and involve several layers in the SDN controller hierarchy. •  A distributed east-west model, with a set of peer SDN controllers, each of them responsible for a portion of the DCN and cooperating together with horizontal communications to achieve the whole control and management of the entire DCN. In general, the third model is very complex and particularly suitable to large scenarios characterized by a variety of trust domains where each network domain is controlled through proprietary protocols and a very limited amount of information can be exchanged outside the domain boundaries. The inter- controller communication can be regulated using protocols like BGP (Border Gateway Protocol) [RFC4271] or PCEP (Path Computation Element communication Protocol) [RFC5440]. However, this model is scarcely applicable to the intra-DC scenario, where a single DC provider is responsible for the whole DCN. The hierarchical model may be of interest due to the heterogeneous nature of the COSIGN DCN. However, the complexity and the time delays required by the inter-controller synchronization and communication (also in this case the PCEP is a reasonable candidate, with the extensions for the stateful and active mode [PCESTAT], [PCEINIT]) can be considered as strong limitation in highly dynamic scenarios like DCN environment. For this reasons, the COSIGN DCN Control Plane solution is based on the centralized deployment model, with a single SDN controller that maintains the overall view and control of the overall DCN. The specific characteristics of the different technologies available at the data plane are handled through dedicated plugins and abstracted with a powerful information model that allows for the application of unified functions and procedures in the SDN controller core. This approach avoids the need to introduce specialized controllers to deals with each optical device type deployed in the COSIGN DCN. It should be noted that the SDN controller is a single entity from a logical point of view. However, from the architectural point of view, the controller can be deployed as a cluster of controllers for high availability or scaling reasons. This option is supported by some SDN controller platforms available today (including OpenDaylight and ONOS, see section Section 2.4) and relies on mechanisms for distributed databases, avoiding the complexity of inter-controller protocols.