olemus
OSI mudelis:
koht, kus üks OSI kiht saab taotleda teiselt kihilt teenuseid

ISO/IEC 2382:
punkt, kus ühe kihi olem annab selle kihi teenuseid
ülemise naaberkihi olemile
= the point at which the services of a given layer are provided by an entity of that layer to an entity of the next higher layer

ülevaateid
http://images.slideplayer.com/25/7751593/slides/slide_32.jpg

https://en.wikipedia.org/wiki/Service_Access_Point