1, the last 20 years the development of programmable network can be divided into several stages? What is the contribution of each stage?
- Active Network (from the mid-1990s to early 2000s)
- It introduces programmable functions in the network in order to achieve more innovation;
- The early 1990s, active network research project explores the traditional Internet via IP stack or ATM fundamental alternative services (ATM) or another major network provides.
- The idea is to provide a unified architecture MiddleBox choreography.
- Control plane and data plane separation (around the year 2001 to 2007)
- Gave birth to two innovations: the open interface between the control plane and the data plane and the centralized control of the network logically
- All routing functionality to control the state on a separate server, this logically centralized controller reduces the standard routing obstacles embodiment, server technology advances mean single commodity servers can be stored, and a large network computing all routing decisions
- Proposed two concepts are logically centralized control and distributed state management using the data plane of the open interface
- OpenFlow API and network operating systems (from about 2007 to 2010)
- It represents the first example of a widely employed open interfaces, open interfaces and widely used method of developing the control plane and data plane separation scalability and practicality.
- Create a global network of innovation environment to meet the needs of network research community.
- It summarizes the network equipment and functions. OpenFlow forwarding behavior rules may be based on any of the 13 different data traffic packet header a set of definitions. OpenFlow generalize ruleinstallation technology that allows pre-installed from the coarse-grained rules (i.e., using the "wildcard" header field for many) according to application rules grained passive installation.
- Concept of network operating system. OpenFlow work led to the concept of network operating systems. Network operating system from the application logic and control network behavior abstracted network switch status of the installation software.
- Distributed state management techniques. Running a plurality of controllers for scalability, reliability, and performance is critical, but the copies should be like a centralized controller as a single logical work. Recently, ONOS system provides open source controllers with similar capabilities, using existing open-source software distributed state to maintain consistency, and the network topology database to the controller applications.
2, network virtualization and SDN's relationship?
Network virtualization abstraction represented isolated from the underlying physical network of devices. Network virtualization allows multiple virtual networks running on a shared infrastructure, and each virtual network may have simpler than the underlying physical network (more abstract) topology. For example, a virtual LAN (VLAN) to provide the illusion of a single LAN across multiple physical subnets, a plurality of VLAN can be run on the same set of routers and switches. Although the network virtualization conceptually independent of the SDN, but in recent years the relationship between these two technologies become closer.
Network Virtualization (from a logical abstraction of a physical network, network) obviously do not need SDN. Similarly, SDN (separated from the underlying data plane logic centralized control plane) does not mean that the network virtualization. However, interestingly, the symbiotic relationship between network virtualization and SDN has emerged, which has begun to catalyze several new areas of research. SDN and network virtualization there are three relationships:
- SDN network virtualization as a technology support
cloud computing highlight the network virtualization, cloud providers need a way as to allow multiple customers (or "tenants") share the same network infrastructure. Nicira's Network Virtualization Platform (Network Virtualization Platform, NVP) provides this abstraction, without any support for the underlying network hardware. Solution is to use overlay network connections to a single switch that provides an abstraction of all its virtual machines for each tenant. However, compared with the previous work on the cover in the network, each node is actually an extension of coverage physical network - a software switch (e.g., Open vSwitch), which encapsulates the traffic is sent to other servers running on virtual machines . Logic centralized controller installed in these virtual switches rules to control how the encapsulated packet, and update the rules to a new location in the virtual machine. - SDN network for evaluation and testing virtualization
before SDN capacity control application and the underlying data in separate planes so that the application is deployed to operate the network, to test and evaluate SDN control applications in a virtual environment. Mininet process based virtualization OpenFlow run multiple virtual switches, terminals and the host controller SDN on the same physical (or virtual) machine, each controller as a single process. The use of process-based virtualization allows Mininet simulate a network, there are hundreds of hosts and switches on a single machine. In such an environment, researchers can develop a network operator or control logic, and easily test it on a full simulation of production data plane; once on the control plane evaluation, testing and debugging, you can deploy to the actual production network. - Virtualization ( "slice") SDN
in traditional networks, virtualized routers or switches are very complicated, because each virtual components need to run their own software control plane instance. In contrast, the virtualization "dumb" SDN switch is much simpler. FlowVisor system allows test stand to support campus networking study carried on the same physical device production flow. The main idea is to divide the space into the traffic flow (the concept of the early work PlanetLab introduced) "sheet", wherein each sheet has a shared network resource, by different management controller SDN. FlowVisor as the hypervisor runs, say to each SDN OpenFlow switch controller and the backsheet. Recent work has suggested a home network hierarchical control to allow different third-party service providers (such as smart grid operators) service deployed on the network without having to install their own infrastructure. Recent work has proposed a method with their own logical topology and address space to represent each "fragment" software-defined network.