LAN Switches / Switched LANs, access layer overview

LAN Switches
Switched LANs, access layer overview 
5.2.1 The construction of a LAN that satisfies the needs of both medium and large-sized organizations is more likely to be successful if a hierarchical design model is used. The use of a hierarchical design model will make it easier to make changes to the network as the organization grows. This page will discuss the three layers of the hierarchical design model:

• The access layer provides users in workgroups access to the network.
• The distribution layer provides policy-based connectivity.
• The core layer provides optimal transport between sites. The core layer is often referred to as the backbone.

This hierarchical model applies to any network design. It is important to realize that these three layers may exist in clear and distinct physical entities. However, this is not a requirement. These layers are defined to aid in successful network design and to represent functionality that must exist in a network.
The access layer is the entry point for user workstations and servers to the network. In a campus LAN the device used at the access layer can be a switch or a hub.
If a hub is used, bandwidth is shared. If a switch is used, then bandwidth is dedicated. If a workstation or server is directly connected to a switch port, then the full bandwidth of the connection to the switch is available to the connected computer. If a hub is connected to a switch port, bandwidth is shared between all devices connected to the hub.
Access layer functions also include MAC layer filtering and microsegmentation. MAC layer filtering allows switches to direct frames only to the switch port that is connected to the destination device. The switch creates small Layer 2 segments called microsegments. The collision domain can be as small as two devices. Layer 2 switches are used in the access layer.
The next page will describe access layer switches.