# Practical Implementation of a Blockchain-Enabled SDN for Large-Scale Infrastructure Networks
## 3 System Proposal  
In the preceding sections of the article, the utilization of ISP federation and virtual ISP were theoretically formulated and conceptualized. This chapter elaborates on their potential interactions and communication methods, presenting a proposed model for the integration of blockchain and SDN technologies. When observed externally, the ISP federation collectively engaging in the integration of blockchain across their SDN infrastructures can be conceptualized as a virtual ISP. Thus, for the external ISPs, the federation is seen as a single, larger ISP. The communication between external ISPs not affiliated with the federation and the ISP federation mirrors that of standard communication between two conventional ISPs (external to the federation). In this way, homogeneity and uniformity can be obtained on both levels of the heterogeneous environment between the service providers. A homogeneous environment can be found within the federation, as all the service providers take part in integrating the blockchain technology over their networks. Also, a homogeneous environment can be found in the exterior too, as the federation is considered a virtual ISP in the way that it behaves as any other conventional ISP toward the rest of the participants. In the proposed model, to preserve privacy, an ISP should not be able to access/read data or information belonging to the other ISPs. Furthermore, the interaction of a service provider with the federation blockchain should not affect, by no means, the interaction of other service providers with the blockchain. Thus, the proposed system leverages blockchain technology to guarantee data integrity while simultaneously preserving data confidentiality. Considering the above aspects, the subsequent section will describe the architectural framework of the ISP federation platform. The proposed solution assumes that each ISP will establish a connection and participate in the creation of a permissioned blockchain within the federation. Any new ISP joining the federation will also connect to this blockchain and expand it further. The permissioned blockchain will be used as the repository for data selected by the service provider for storage within the context of integrating the blockchain into its SDN network. Thus, when the ISP joins the federation, it integrates at least one blockchain node that will provide access to the blockchain in order to store and read the desired information. Figure 2 illustrates how the ISPs interact with the blockchain, showcasing various methods of interaction. The blockchain integration within service providers' SDN networks remains consistent; however, the communication with the blockchain varies depending on the specific integration approach employed by the service provider. Since the service providers implement and run a full node, the interaction with the blockchain is direct. It also depends on where the service provider implements the blockchain node. Usually, the blockchain node and the integration with the blockchain are implemented at the SDN controller level. In this manner, the controller communicates directly with the blockchain, both for storing data on the blockchain and for reading information from the blockchain. Every SDN network within the federation belongs to an organization (ISP). The control authority of the SDN network is administered internally from within the organization; thus, every SDN network is a part of the consortium that has permission to access the permissioned (consortium) blockchain. All the data that correspond to the criteria established by every ISP in part are stored in the blockchain. The SDN network controller manages the communication with the other (external) blockchain nodes and the operation of the local blockchain node. Every ISP is able to store the information marked as being of local importance--information that the ISP does not want to share or that is strictly regarding the details of the internal network--in a manner that ensures that other participants will not be able to read it.