Collapsed Core Architecture is a campus network design wherein we combine the core and distribution layers. The core and distribution functions are implemented by a single device. In this discussion, let's break down three major network architectures—Two-Tier, Three-Tier, and Spine-Leaf—using simple language and real-world examples to help you pick the best fit for your needs. Access Layer – Access switches connect end devices to the network. But this is a. Whether you are studying for the Cisco CCNA or CCNP Enterprise certifications, or designing a production network for a real organization, the three-tier hierarchical model is one of the most foundational architectures you will ever work with. Three-Tier Hierarchical Architecture.