Build Your Skills: The three-layer hierarchical model

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Build Your Skills: The three-layer hierarchical model

Anyone involved in networking and/or telecommunications should be somewhat familiar with the use of layers. Many communications systems, computer operating systems,Next-Generation Firewall and software packages are designed in layers or modules. When a network or operating system is designed and built with layers or modules, more importantly, understanding that network all become easier. Additionally, adding a hierarchical structure to the layered approach allows for a scalable design. Here, I will explain how the three-layer hierarchical design can be used to create a modular network.

The common approach to designing enterprise networks involves three layers: the Access layer, the Distribution layer, and the Core layer. The Access layer is the level where host computers are connected to the network. The Distribution layer acts as an aggregation point for all the Access layer devices. The Core layer connects all Distribution layer devices and reliably and quickly switches and routes large amounts of traffic.

Whether you have an Ethernet connection to each end station or a remote access server, if the device allows users to connect to the network, it's considered an Access layer device. Typically, these devices are hubs, multistation access units (MAUs), or switches deployed in wiring closets on each floor of a building. Users' network cables are then terminated into such an Access layer device, where they are connected to each user on the local network. Typically, virtual LANs (VLANs) are implemented to separate broadcast domains on the Access layer.

When choosing Access layer devices, there are many points to consider. For example, when pricing equipment to connect a large number of users, you should consider the cost per port. A 24-port switch that costs approximately $1,200 has a port cost of $50 per port. But a 24-port hub that costs approximately $500 will have a port cost of only $10 per port.