What does sd-wan really accomplish?

       According to my own conclusion and understanding, what sd-wan really wants to achieve is to make full use of the communication means available to enterprises (MPLS/SDH, Ethernet, wireless, 4G/LTE, satellite communication, and private networks and the Internet), and to achieve whole-region routing control and business strategy arrangement with the goal of QoS of the whole traffic in the way of "transfer and control separation".

　　Therefore, compared with traditional router WAN transmission scheme, which realize networking SD - WAN proposed the implementation of the new ideas on the following:

　　Turn accused of separation:

　　Have mentioned this in front of SDN is introduced, the SD - WAN just differ in the degree of separation, because SD - WAN is more of a concern for the overlay layer forward control, so the control more underlay layer will put forward the level.

　　The whole domain routing control:

　　SD - WAN largely to replace the traditional router's dynamic routing protocol. We know that the traditional dynamic routing protocol is usually by collecting local link QoS and accessible information, within the domain for routing information exchange between the router and voting, to maintain the local dynamic routing published for actual forward control. Even the BGP protocol but also through the Route Reflector will be distributed for the routing information, a specific routing, forward control is still done in local. And SD - WAN can simply considered directly in the SDN Controller on a unified maintenance "a" global routing table, CPE/Edge devices only need to upload local link information, and receive SDN Controller for its routing table, routing was greatly simplifies the processing and forwarding control.

　　The unity of QoS control:

　　Compared to traditional gateways and routers equipment acted as local QoS policy control, the SD - WAN emphasizes the realization of unification of centralization of QoS analysis and QoS strategy distribution. The CPE/Edge device reports the local link information data in real time (including the current network characteristics of the link, including delay, jitter, packet loss and available bandwidth), and the SDN Controller performs the analysis uniformly. The network administrator translates the SLA target input into the QoS definition of various specific business applications -- bandwidth, delay, jitter, packet loss, etc. The Controller translates these requirements into the "real-time" routing strategy of the corresponding Edge device to select the best route to send this traffic. From another perspective, the unification of QoS control is also a global routing decisions right strategy.

　　Business strategy layout:

　　SD - WAN "software defined" characteristics rely mainly on "strategy layout". Strategy, illustrates the SD - WAN for the business, application, CPE/Edge devices, link, network characteristics, the SLA/QoS guarantee, such as routing control mode. Arrangement, strategy and SD - WAN has resources (e.g., available Overlay link pool, Overlay network characteristics, available underlay link pool, underlay link features) way of mapping, and associated, in short, how is the business need to use SD - WAN corresponding SLA goal mode of automation. Since an automated way, means of SD - WAN SDN Controller can adjust the spontaneous strategy, resource use, automation level and policy control granularity fine degree, decided the business choreography of SD - WAN ability, namely SD - WAN actual implementation level.