The hierarchical structure of communications networks organizes the way in which different devices and services on the network connect and communicate. This structure allows for more efficient management, improves performance, and facilitates scalability and security.

It can be divided into several levels or layers, each with specific functions. Here I detail an overview of this structure:

1. Access Level

• Function: This is the lowest level of the hierarchy and is the entry point to the network for end-user devices such as computers, smartphones, and other IoT (Internet of Things) devices.
• Devices and Technologies: Includes wireless switches and access points that connect devices to the local network (LAN). In wireless networks, this level also includes antennas and wireless access controllers.

2. Distribution Level

• Function: Also known as the aggregation layer, it is responsible for routing traffic from the access layer to central services or to the outside (internet). It acts as a mediator between the access and the core network, implementing network policies, traffic filtering, and segmentation.
• Devices and Technologies: Includes layer 3 (L3) switches and routers that can perform routing functions, ACLs (Access Control Lists), and VLANs (Virtual Local Area Networks) to segment the network.

3. Core Level

• Function: The core network is the high-speed backbone that connects different segments of the network, including data centers, branch offices, and Internet access. Its main task is to provide fast and efficient transport of large-scale data.
• Devices and Technologies: Composed of high-performance routers and switches designed to handle large volumes of traffic with the lowest possible latency. Security or filtering is not typically implemented at this layer to maintain traffic speeds.

4. Data Center Level

• Function: Although not a tier in the traditional three-tier structure, the data center is often considered a crucial part of modern networks, especially in enterprise and cloud services environments. It is responsible for storing, processing and serving applications and data.
• Devices and Technologies: Includes servers, storage systems, fabric switches, and specialized security devices. Modern data centers often use virtualization and cloud computing technologies to improve scalability and efficiency.

5. Network Edge or Perimeter Level

• Function: This level includes devices and services designed to connect the internal network with the outside (such as the Internet) and protect the network from external threats.
• Devices and Technologies: Includes firewalls, intrusion prevention systems (IPS), VPN gateways, and intrusion detection systems (IDS).

This hierarchical structure not only applies to large enterprise or service provider networks, but can also be adapted to smaller networks, maintaining the same principles for organizing and managing network connectivity and services.

When designing or managing a network, understanding this hierarchy is critical to optimizing the performance, security, and scalability of your communications infrastructure.