Northbound Interface
NBI conceptualizes lower level details (e.g. data or functions) used by, or in the component. It interfaces to higher level layers and is normally drawn at the top of an architectural overview.
e.g. REST API, SMMP, CORBA, SNMP
北向接口，用于接口编程开发各app，采集、分析app在运行中产生的各种数据，因网络管理中从上而下分应用层、数据处理层、数据管理层，北向接口即应用层和数据处理层之间的数据交互定义接口（见下图），因为朝上（上北下南）称北向接口。
Southbound Interface
A southbound interface decomposes concepts in the technical details, mostly specific to a single component of the architecture. Southbound interfaces are drawn at the bottom of an architectural overview.
e.g. OpenFlow, NETCONF, XMPP
A Northbound interface goes “up” and a Southbound interface goes “down”.
northbound interfaces go towards the core of the data center or towards the Internet-facing egress of the network. Southbound goes towards the end-users/servers/VMs.
Northbound interfaces normally talk to southbound interfaces of higher level components and vice versa.
