通信系统中的：北向接口、南向接口

A northbound interface is an interface that conceptualizes lower level details. It interfaces to higher level layers and is normally drawn at the top of an architectural overview.

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.

Northbound interfaces normally talk to southbound interfaces of higher level components and vice versa.

 

quoted from http://www.mscbsc.com/bbs/thread-59732-1-1.html