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This paper presents the control and data plane architecture design for a 5G transport solution (5G-Crosshaul) with the aim of integrating the fronthaul and backhaul network segments in a common transport stratum. The control plane relies on the Software-defined networking/Network Functions Virtualization concept to control and orchestrate the different elements of the network (the 5G-Crosshaul control infrastructure). The data plane is based on an mixed optical/packetbased forwarding entity (the 5G-Crosshaul forwarding element) that leverages the benefits of optical passthrough with the statistical multiplexing of packet-based transmission, working on top of a common frame format for both, fronthaul, and backhaul traffic (the 5G-Crosshaul common frame). In addition to the main architecture design, this work includes the impact of providing multi-tenancy support into the architecture of the overall system, in order to share the costs of building and operating the infrastructure among different operators.This architecture opens the 5G transport network as a service for innovative network applications on top (such as multitenancy, and resource management ), provisioning the required network and IT resources in a flexible, cost-effective, and abstract manner. The proposed design supports the concept of network slicing pushed by the industry for realizing a truly flexible, sharable, and cost-effective future 5G system.

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Abstract-In the recent years, Software Defined Networking (SDN) has changed the way networks are engineered, making them more flexible, programmable and dynamic. SDN advocates for the centralization of control functionalities in a central node, the so-called controller. This entity has a wide view of the entire network, including the topology, facilitating the management and decreasing the complexity. However, the existence of a single entity running the complete control plane constitutes a single point of failure, thus triggering the need of improving the resiliency and reliability of the controller and the connection between the control and the data plane.This paper presents a solution for the improvement of the resiliency and the reliability on the OpenFlow channel through the use of multipath TCP (MPTCP). The proposed solution is based on the simultaneous use of in-band and out-of-band paths for the OpenFlow control channel, and includes a first experimental evaluation of the performance gains that can be achieved.Index Terms-SDN, OpenFlow, Resiliency, Reliability, MPTCP.A centralized controller is a potential single point of failure and a potential bottleneck. A failure on the controller or a disconnection between the control and data planes may lead to performance degradation and packet loss. OpenFlow uses a TCP connection (secured using SSL/TLS) to control the data plane elements. This connection, the so called OpenFlow channel, may use in-band or out-of-band transport signaling. In-band signaling is characterized by carrying the OpenFlow protocol packets through the same paths as the data transport, and therefore requires the network to be preconfigured to forward the OpenFlow signaling. Out-ofband signaling requires a separate network connecting all data plane elements to the controller, therefore requiring of extra network deployments.There is a need to improve the resiliency and reliability on software defined networks. Some efforts are devoted on the controller side, supporting a control plane distribution, starting with the version 1.2 of the OpenFlow protocol which supports mechanisms to use several simultaneous controllers. This concept was extended by diverse projects to increase the reliability on the control plane increasing the scalability and avoiding the single point of failure of a centralized architecture:• Onix [5] presents a platform for building a control plane on top of it as a distributed system. It provides an API which consists on a data model to abstract the network infrastructure, this API provides control logic, the possibility of read/write the state of the data plane and a notification engine for network state changes.• HyperFlow [6] solution is based on a logically centralized but physically distributed control plane synchronized with a publish/subscription system. All the controllers using HyperFlow have a consistent network-wide view and they run as if they are controlling the whole network.• ElastiCon [7] propose an elastic distributed controller architecture with a control...

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