(ii) Separation of data control

1. Data Control Separation
Data control separation is one of the main features of SDN, as shown in the following figure

From a functional standpoint, the control plane is primarily a local data set, the routing information Base (RIB). The control plane is based on rib creation forwarding (also known as forwarding information Base (FIB)), which is used to guide data traffic forwarding between the device's access ports. The data plane is the high-speed forwarding of data based on the fib created by rib, and of course some other service functions. To ensure that the forwarding behavior and routing decisions are consistent, the FIB needs to be mirrored between the control and the data plane, so the fib is actually a link between the two planes.

The control plane can be divided into two layers control plane, three layer control plane and cross two/three layer control plane according to the functional level. Its main focus on the hardware or physical layer address, in the two-tier network forwarding more attention to the accessibility of MAC address, so the control plane mainly realizes the storage and management of MAC address. The three layer control plane focuses on the network layer addressing, mainly focuses on the network address, forwarding the main focus on the accessibility of the network address.

The first task of the data plane is the fast data packet processing. The data look-up table uses the hardware check list and the general processor to look up the table two kinds of technology, depending on the performance demand. The next step in the search is to forward, discard, re-mark, count, and queue actions, which can also be grouped together. Of course, it also has some accessibility features, such as Access control lists, QoS policies, and so on.

2.SDN Data Control separation

Data and control separation is one of the core ideas of Sdn. SDN separates the data control plane with the FIB table for network devices, and the data control plane is connected by the SDN South Interface protocol, which provides data plane programmability.

The Data Control separation feature of SDN is embodied in the following: Logical centralized control, open interface to data plane and the need to solve distributed state management problem.

Benefits of SDN Data separation:
1. Global centralized control and distribution of high-speed forwarding;
2. Flexible programmable and performance balance;
3. Openness and it.

Disadvantages of SDN Data separation:
1. Scalability issues;
2. Consistency issues;
3. Usability issues.
3. Network Programmable

Network programmability is another important attribute of Sdn. Network programmability means that developers can directly control hardware by compiling code to implement their own protocols or functions.

The basic idea of active network is to break the mode that the traditional network can only transmit information passively, and allow the nodes in the network to perform the calculation that the user needs on the user data.

Two data models for active Networks: 1) package model, 2) programmable router/switch model.

The north-facing interface of SDN mainly faces upper application, the South interface is used to establish the conversation between the controller and the forwarding device, and the SDN controller can be compatible with different hardware devices through different South interface protocols, and realizes the upper logic on the device. The SDN interface mainly solves the problems of physical resource sharing, identity authentication, collaboration among authorized databases and maintaining control logic consistency. The various layer interfaces of SDN are shown in the following figure.