N-tier architecture divides an application into logical layers and physical tiers. Layers are a way to separate responsibilities and manage dependencies. Each layer has a specific responsibility. A higher layer can use services in a lower layer, but not the other way around.
The Core Layer is often known as the backbone or the foundation network because all other switches rely on it. Its purpose is to minimize the delay in the delivery of packets and so responsible for fast and reliable transportation of data across a network.
A data access layer (DAL) in computer software is a layer of a computer program which provides simplified access to data stored in persistent storage of some kind, such as an entity-relational database.
This is the middle layer - the heart of the application. It contains all business logic of the application, describes how business objects interact with each other, where the UI layer and Data Access layer can indirectly communicate with each other
It is the first and topmost layer present in the application where users can interact with the application. This layer is mainly used for design purpose and get or set the data back and forth.