Today, wired and wireless technologies are competing for the dominance of next-generation access networks. Due to the huge demand for bandwidth, optical networks will still play a major role in the next development. Among them, PON is a recognized broadband architecture. This technology can promote network convergence, for example, to develop mobile pre-transmission and back-transmission services for telephone networks. Despite this, hybrid solutions will most likely be used in many scenarios. In this paper, business convergence and unified network control and management mechanisms are considered to be key to enabling technologies beyond data plane integration through appropriate system interfaces.
In response to the above-mentioned requirements, SDN has become the key to the separation of the control plane and the data plane, developing open source software for the programming platform of different operating systems. One of the open source protocols is the OpenFlow protocol, which was originally conceived for Layer 2 switches and Layer 3 routers. In particular, in the OpenFlow network node, the separation of the control and forwarding planes is achieved through a well-defined API interface. The API interface can be used to construct a flow table through the OpenFlow protocol for filtering and searching for data paths and switch nodes. Packets forwarded between.
The field of virtualization is a complementary project to SDN. It defines a network function and service that is used to implement network functions and services, also known as network function virtualization. One notable example of NFV in the field of access networks is the CORD program (reconstruction of the end office to the data center). CORD is designed to virtualize existing proprietary hardware devices and develop corresponding software that runs on commercial hardware. The CORD infrastructure will be based on open source architectures such as white-box devices, ONOS, Openstack and XOS. Therefore, the goal of CORD is to use the simplified GPON optical network unit system as the premise of the user. The access point is equipped with G.fast terminal cabinet and optical line termination chip to provide the lowest level of L1/L2 GPON function.
The CORD proposed by HYDRA also has similar targets for SDN/NFV-based converged services, but with a larger scope. HYDRA is developing a versatile network and computing infrastructure to enhance this highly distributed data center architecture, closer to the end user than CORD Advance NFV, and is a model inspired by fog computing. Active Remote Nodes (ARNs) aggregate traffic from multiple heterogeneous access networks and bypass MAN fragmentation with pure transport, integrating access and core segments in this way, resulting in performance enhancements and clear overhead. In HYDRA, traffic from heterogeneous access systems and microdata center (μ-DC) infrastructure traffic is aggregated in the ARN, providing network functions and applications/services to access network, computing and storage resource pool scenarios Compare with alternatives for transferring data back and forth to the remote. Figure 1 shows a schematic of the ARN.
Figure 1: Abstract representation of the SDN control plane as a GPON-based access domain as a hierarchical switch cascade
Current method of using an SDN based access systemThe operation of the GPON access system based on the SDN-based control plane is still in its early stages, and interface standardization has not yet been agreed. An advanced demonstration of the SDN-based control plane in access is given, and the OpenFlow protocol is revised for the metropolitan area network using the OpenFlow protocol and the GPON access network based on the OpenFlow controller using the L2RS router top-level interface. Fusion. The control plane architecture is similar to the architecture shown in the upper portion of Figure 2, where OF terminates at the access hub and the GPON access segment is managed by the OF agent via the southbound interface to the GPON management system. However, the introduction of OF-based integration goes beyond the access concentrator interface to the backhaul network, preventing the GPON access segments from being seamlessly integrated into the common SDN control plane.
Figure 2: SDN control plane integration, representing a GPON-based access domain as a hierarchical switch cascade
Prototype implementation based on commercial GPON access systemAs mentioned above, HYDRA aims to co-ordinate multiple heterogeneous network accesses, so OF does not require custom extensions. To this end, abstraction is required to hide PON specific details while allowing efficient processing of its operations. For example, the Transmission Convergence (TC) layer of GPON (where QoS is managed) uses multiple internal identifiers (such as Port ID and Alloc-ID) to address logical connections and upstream T-CONT (Traffic Container) queues, respectively. Therefore, we propose emulating the access segment as a cascade of hierarchical switches where the OLT and the ONU associated with the same PON segment are represented as a single OF switch (Figure 2).
The representation of GPON using this switch cascading model is as follows: Traffic is identified as Upstream (VS), Downstream (DS) and Multicast (MC). As shown in FIG. 2, each ONU has a plurality of discrete clients that need to be mapped to internal T-CONT queue ports corresponding to virtual output ports having different priorities. Finally, the output from the OLT is connected to the "L2 Switch" forwarding service for data processing or initiating data services towards the core or to the μ-DC. In DS, traffic matching is used to direct traffic to the appropriate ONU port, while automatically assigning a Port-ID, while applying US traffic matching rules on the client port. Each T-CONT supported by the ONU is represented as a queue in a network port in which the US flow is directed, with the associated Alloc-ID being automatically assigned. Similarly, when using this scheme, the Port-ID can be assigned automatically. For MC streams, for each destination ONU, an "action set" of type "All" should be used.
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