The [[OSI model|Open Systems Interconnection model]] (OSI model) defines and codifies the concept of layered network architecture. [[Abstraction layer]]s are used to subdivide a [[communications system]] further into smaller manageable parts. A layer is a collection of similar functions that provide services to the layer above it and receives services from the layer below it. On each layer, an instance provides services to the instances at the layer above and requests services from the layer below.<ref>{{Cite news|url=https://searchnetworking.techtarget.com/definition/OSI|title=What is OSI model (Open Systems Interconnection)? - Definition from WhatIs.com|work=SearchNetworking|access-date=2018-10-09|language=en-US}}</ref>
